xylem pressure potentials: Topics by Science.gov

Sample records for xylem pressure potentials

Seasonal variation in xylem pressure of walnut trees: root and stem pressures.

PubMed

Ewers, F W; Améglio, T; Cochard, H; Beaujard, F; Martignac, M; Vandame, M; Bodet, C; Cruiziat, P

2001-09-01

Measurements of air and soil temperatures and xylem pressure were made on 17-year-old orchard trees and on 5-year-old potted trees of walnut (Juglans regia L.). Cooling chambers were used to determine the relationships between temperature and sugar concentration ([glucose] + [fructose] + [sucrose], GFS) and seasonal changes in xylem pressure development. Pressure transducers were attached to twigs of intact plants, root stumps and excised shoots while the potted trees were subjected to various temperature regimes in autumn, winter and spring. Osmolarity and GFS of the xylem sap (apoplast) were measured before and after cooling or warming treatments. In autumn and spring, xylem pressures of up to 160 kPa were closely correlated with soil temperature but were not correlated with GFS in xylem sap. High root pressures were associated with uptake of mineral nutrients from soil, especially nitrate. In autumn and spring, xylem pressures were detected in root stumps as well as in intact plants, but not in excised stems. In contrast, in winter, 83% of the xylem sap osmolarity in both excised stems and intact plants could be accounted for by GFS, and both GFS and osmolarity were inversely proportional to temperature. Plants kept at 1.5 degrees C developed positive xylem pressures up to 35 kPa, xylem sap osmolarities up to 260 mosmol l(-1) and GFS concentrations up to 70 g l(-1). Autumn and spring xylem pressures, which appeared to be of root origin, were about 55% of the theoretical pressures predicted by osmolarity of the xylem sap. In contrast, winter pressures appeared to be of stem origin and were only 7% of the theoretical pressures, perhaps because of a lower stem water content during winter.
Water relations of coastal and estuarine Rhizophora mangle: xylem pressure potential and dynamics of embolism formation and repair.

PubMed

Melcher, P J; Goldstein, G; Meinzer, F C; Yount, D E; Jones, T J; Holbrook, N M; Huang, C X

2001-01-01

Physiological traits related to water transport were studied in Rhizophora mangle (red mangrove) growing in coastal and estuarine sites in Hawaii. The magnitude of xylem pressure potential (P x ), the vulnerability of xylem to cavitation, the frequency of embolized vessels in situ, and the capacity of R. mangle to repair embolized vessels were evaluated with conventional and recently developed techniques. The osmotic potential of the interstitial soil water (π sw ) surrounding the roots of R. mangle was c. -2.6±5.52×10 -3 and -0.4±6.13×10 -3 MPa in the coastal and estuarine sites, respectively. Midday covered (non-transpiring) leaf water potentials (Ψ L ) determined with a pressure chamber were 0.6-0.8 MPa more positive than those of exposed, freely-transpiring leaves, and osmotic potential of the xylem sap (π x ) ranged from -0.1 to -0.3 MPa. Consequently, estimated midday values of P x (calculated by subtracting π x from covered Ψ L ) were about 1 MPa more positive than Ψ L determined on freely transpiring leaves. The differences in Ψ L between covered and transpiring leaves were linearly related to the transpiration rates. The slope of this relationship was steeper for the coastal site, suggesting that the hydraulic resistance was larger in leaves of coastal R. mangle plants. This was confirmed by both hydraulic conductivity measurements on stem segments and high-pressure flowmeter studies made on excised leafy twigs. Based on two independent criteria, loss of hydraulic conductivity and proportions of gas- and liquid-filled vessels in cryo-scanning electron microscope (cryo-SEM) images, the xylem of R. mangle plants growing at the estuarine site was found to be more vulnerable to cavitation than that of plants growing at the coastal site. However, the cryo-SEM analyses suggested that cavitation occurred more readily in intact plants than in excised branches that were air-dried in the laboratory. Cryo-SEM analyses also revealed that, in both sites
Leaf water potentials measured with a pressure chamber.

PubMed

Boyer, J S

1967-01-01

Leaf water potentials were estimated from the sum of the balancing pressure measured with a pressure chamber and the osmotic potential of the xylem sap in leafy shoots or leaves. When leaf water potentials in yew, rhododendron, and sunflower were compared with those measured with a thermocouple psychrometer known to indicate accurate values of leaf water potential, determinations were within +/- 2 bars of the psychrometer measurements with sunflower and yew. In rhododendron. water potentials measured with the pressure chamber plus xylem sap were 2.5 bars less negative to 4 bars more negative than psychrometer measurements.The discrepancies in the rhododendron measurements could be attributed, at least in part, to the filling of tissues other than xylem with xylem sap during measurements with the pressure chamber. It was concluded that, although stem characteristics may affect the measurements, pressure chamber determinations were sufficiently close to psychrometer measurements that the pressure chamber may be used for relative measurements of leaf water potentials, especially in sunflower and yew. For accurate determinations of leaf water potential, however, pressure chamber measurements must be calibrated with a thermocouple psychrometer.
Leaf Water Potentials Measured with a Pressure Chamber

PubMed Central

Boyer, J. S.

1967-01-01

Leaf water potentials were estimated from the sum of the balancing pressure measured with a pressure chamber and the osmotic potential of the xylem sap in leafy shoots or leaves. When leaf water potentials in yew, rhododendron, and sunflower were compared with those measured with a thermocouple psychrometer known to indicate accurate values of leaf water potential, determinations were within ± 2 bars of the psychrometer measurements with sunflower and yew. In rhododendron. water potentials measured with the pressure chamber plus xylem sap were 2.5 bars less negative to 4 bars more negative than psychrometer measurements. The discrepancies in the rhododendron measurements could be attributed, at least in part, to the filling of tissues other than xylem with xylem sap during measurements with the pressure chamber. It was concluded that, although stem characteristics may affect the measurements, pressure chamber determinations were sufficiently close to psychrometer measurements that the pressure chamber may be used for relative measurements of leaf water potentials, especially in sunflower and yew. For accurate determinations of leaf water potential, however, pressure chamber measurements must be calibrated with a thermocouple psychrometer. PMID:16656476
A potential role for xylem-phloem interactions in the hydraulic architecture of trees: effects of phloem girdling on xylem hydraulic conductance.

PubMed

Zwieniecki, Maciej A; Melcher, Peter J; Feild, Taylor S; Holbrook, N Michele

2004-08-01

We investigated phloem-xylem interactions in Acer rubrum L. and Acer saccharum Marsh. Our experimental method allowed us to determine xylem conductance of an intact branch by measuring the flow rate of water supplied at two delivery pressures to the cut end of a small side branch. We found that removal of bark tissue (phloem girdling) upstream of the point at which deionized water was delivered to the branch resulted in a decrease (24% for A. rubrum and 15% for A. saccharum) in branch xylem hydraulic conductance. Declines in hydraulic conductance with girdling were accompanied by a decrease in the osmotic concentration of xylem sap. The decrease in xylem sap concentration following phloem girdling suggests that ion redistribution from the phloem was responsible for the observed decline in hydraulic conductance. When the same measurements were made on branches perfused with KCl solution (approximately 140 mOsm kg(-1)), phloem girdling had no effect on xylem hydraulic conductance. These results suggest a functional link between phloem and xylem hydraulic systems that is mediated by changes in the ionic content of the cell sap.
Root pressure and beyond: energetically uphill water transport into xylem vessels?

PubMed

Wegner, Lars H

2014-02-01

The thermodynamics of root pressure remains an enigma up to the present day. Water is transported radially into xylem vessels, under some conditions even when the xylem sap is more dilute than the ambient medium (soil solution). It is suggested here that water secretion across the plasma membrane of xylem parenchyma cells is driven by a co-transport of water and solutes as previously shown for mammalian epithelia (Zeuthen T. 2010. Water-transporting proteins. Journal of Membrane Biology 234, 57-73.). This process could drive volume flow 'energetically uphill', against the free energy gradient of water. According to the model, solutes released by xylem parenchyma cells are subsequently retrieved from the sap at the expense of metabolic energy to maintain the concentration gradient that drives the water secretion. Transporters of the CCC type known to mediate water secretion in mammalian cells have also been found in Arabidopsis and in rice. The mechanism proposed here for root pressure could also explain refilling of embolized vessels. Moreover, it could contribute to long-distance water transport in trees when the cohesion-tension mechanism of water ascent fails. This is discussed with respect to the old and the more recent literature on these subjects.
Direct Measurement of Xylem Pressure in Leaves of Intact Maize Plants. A Test of the Cohesion-Tension Theory Taking Hydraulic Architecture into Consideration1

PubMed Central

Wei, Chunfang; Tyree, Melvin T.; Steudle, Ernst

1999-01-01

The water relations of maize (Zea mays L. cv Helix) were documented in terms of hydraulic architecture and xylem pressure. A high-pressure flowmeter was used to characterize the hydraulic resistances of the root, stalk, and leaves. Xylem pressure measurements were made with a Scholander-Hammel pressure bomb and with a cell pressure probe. Evaporation rates were measured by gas exchange and by gravimetric measurements. Xylem pressure was altered by changing the light intensity, by controlling irrigation, or by gas pressure applied to the soil mass (using a root pressure bomb). Xylem pressure measured by the cell pressure probe and by the pressure bomb agreed over the entire measured range of 0 to −0.7 MPa. Experiments were consistent with the cohesion-tension theory. Xylem pressure changed rapidly and reversibly with changes in light intensity and root-bomb pressure. Increasing the root-bomb pressure increased the evaporation rate slightly when xylem pressure was negative and increased water flow rate through the shoots dramatically when xylem pressure was positive and guttation was observed. The hydraulic architecture model could predict all observed changes in water flow rate and xylem. We measured the cavitation threshold for oil- and water-filled pressure probes and provide some suggestions for improvement. PMID:10594106
Water filtration using plant xylem.

PubMed

Boutilier, Michael S H; Lee, Jongho; Chambers, Valerie; Venkatesh, Varsha; Karnik, Rohit

2014-01-01

Effective point-of-use devices for providing safe drinking water are urgently needed to reduce the global burden of waterborne disease. Here we show that plant xylem from the sapwood of coniferous trees--a readily available, inexpensive, biodegradable, and disposable material--can remove bacteria from water by simple pressure-driven filtration. Approximately 3 cm(3) of sapwood can filter water at the rate of several liters per day, sufficient to meet the clean drinking water needs of one person. The results demonstrate the potential of plant xylem to address the need for pathogen-free drinking water in developing countries and resource-limited settings.
Water Filtration Using Plant Xylem

PubMed Central

Chambers, Valerie; Venkatesh, Varsha; Karnik, Rohit

2014-01-01

Effective point-of-use devices for providing safe drinking water are urgently needed to reduce the global burden of waterborne disease. Here we show that plant xylem from the sapwood of coniferous trees – a readily available, inexpensive, biodegradable, and disposable material – can remove bacteria from water by simple pressure-driven filtration. Approximately 3 cm3 of sapwood can filter water at the rate of several liters per day, sufficient to meet the clean drinking water needs of one person. The results demonstrate the potential of plant xylem to address the need for pathogen-free drinking water in developing countries and resource-limited settings. PMID:24587134
Xylem hydraulic safety margins in woody plants: coordination of stomatal control of xylem tension with hydraulic capacitance

Treesearch

Frederick C. Meinzer; Daniel M. Johnson; Barbara Lachenbruch; Katherine A. McCulloh; David R. Woodruff

2009-01-01

The xylem pressure inducing 50% loss of hydraulic conductivity due to embolism (P50) is widely used for comparisons of xylem vulnerability among species and across aridity gradients. However, despite its utility as an index of resistance to catastrophic xylem failure under extreme drought, P50 may have no special...
What are the driving forces for water lifting in the xylem conduit?

PubMed

Zimmermann, Ulrich; Schneider, Heike; Wegner, Lars H; Wagner, Hans-Jürgen; Szimtenings, Michael; Haase, Axel; Bentrup, Friedrich-Wilhelm

2002-03-01

After Renner had shown convincingly in 1925 that the transpirational water loss generates tensions larger than 0.1 MPa (i.e. negative pressures) in the xylem of cut leafy twigs the Cohesion Theory proposed by Böhm, Askenasy, Dixon and Joly at the end of the 19th century was immediately accepted by plant physiologists. Introduction of the pressure chamber technique by Scholander et al. in 1965 enforced the general belief that tension is the only driving force for water lifting although substantial criticism regarding the technique and/or the Cohesion Theory was published by several authors. As typical for scientific disciplines, the advent of minimal- and non-invasive techniques in the last decade as well as the development of a new, reliable method for xylem sap sampling have challenged this view. Today, xylem pressure gradients, potentials, ion concentrations and volume flows as well as cell turgor pressure gradients can be monitored online in intact transpiring higher plants, and within a given physiological context by using the pressure probe technique and high-resolution NMR imaging techniques, respectively. Application of the pressure probe technique to transpiring plants has shown that negative absolute pressures (down to - 0.6 MPa) and pressure gradients can exist temporarily in the xylem conduit, but that the magnitude and (occasionally) direction of gradients contrasts frequently the belief that tension is the only driving force. This seems to be particularly the case for plants faced with problems of height, drought, freezing and salinity as well as with cavitation of the tensile water. Reviewing the current data base shows that other forces come into operation when exclusively tension fails to lift water against gravity due to environmental conditions. Possible candidates are longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels as well as gel- and gas bubble-supported interfacial gradients. The multiforce
Root xylem embolisms and refilling. Relation To water potentials of soil, roots, and leaves, and osmotic potentials of root xylem Sap

PubMed

McCully

1999-03-01

Embolism and refilling of vessels was monitored directly by cryomicroscopy of field-grown corn (Zea mays L.) roots. To test the reliability of an earlier study showing embolism refilling in roots at negative leaf water potentials, embolisms were counted, and root water potentials (Psiroot) and osmotic potentials of exuded xylem sap from the same roots were measured by isopiestic psychrometry. All vessels were full at dawn (Psiroot -0.1 MPa). Embolisms were first seen in late metaxylem vessels at 8 AM. Embolized late metaxylem vessels peaked at 50% at 10 AM (Psiroot -0.1 MPa), fell to 44% by 12 PM (Psiroot -0.23 MPa), then dropped steadily to zero by early evening (Psiroot -0.28 MPa). Transpiration was highest (8.5 μg cm-2 s-1) between 12 and 2 PM when the percentage of vessels embolized was falling. Embolized vessels were refilled by liquid moving through their lateral walls. Xylem sap was very low in solutes. The mechanism of vessel refilling, when Psiroot is negative, requires further investigation. Daily embolism and refilling in roots of well-watered plants is a normal occurrence and may be a component of an important hydraulic signaling mechanism between roots and shoots.
Refilling of a Hydraulically Isolated Embolized Xylem Vessel: Model Calculations

PubMed Central

VESALA, TIMO; HÖLTTÄ, TEEMU; PERÄMÄKI, MARTTI; NIKINMAA, EERO

2003-01-01

When they are hydraulically isolated, embolized xylem vessels can be refilled, while adjacent vessels remain under tension. This implies that the pressure of water in the refilling vessel must be equal to the bubble gas pressure, which sets physical constraints for recovery. A model of water exudation into the cylindrical vessel and of bubble dissolution based on the assumption of hydraulic isolation is developed. Refilling is made possible by the turgor of the living cells adjacent to the refilling vessel, and by a reflection coefficient below 1 for the exchange of solutes across the interface between the vessel and the adjacent cells. No active transport of solutes is assumed. Living cells are also capable of importing water from the water‐conducting vessels. The most limiting factors were found to be the osmotic potential of living cells and the ratio of the volume of the adjacent living cells to that of the embolized vessel. With values for these of 1·5 MPa and 1, respectively, refilling times were in the order of hours for a broad range of possible values of water conductivity coefficients and effective diffusion distances for dissolved air, when the xylem water tension was below 0·6 MPa and constant. Inclusion of the daily pattern for xylem tension improved the simulations. The simulated gas pressure within the refilling vessel was in accordance with recent experimental results. The study shows that the refilling process is physically possible under hydraulic isolation, while water in surrounding vessels is under negative pressure. However, the osmotic potentials in the refilling vessel tend to be large (in the order of 1 MPa). Only if the xylem water tension is, at most, twice atmospheric pressure, the reflection coefficient remains close to 1 (0·95) and the ratio of the volume of the adjacent living cells to that of the embolized vessel is about 2, does the osmotic potential stay below 0·4 MPa. PMID:12588721
Do xylem fibers affect vessel cavitation resistance?

PubMed

Jacobsen, Anna L; Ewers, Frank W; Pratt, R Brandon; Paddock, William A; Davis, Stephen D

2005-09-01

Possible mechanical and hydraulic costs to increased cavitation resistance were examined among six co-occurring species of chaparral shrubs in southern California. We measured cavitation resistance (xylem pressure at 50% loss of hydraulic conductivity), seasonal low pressure potential (P(min)), xylem conductive efficiency (specific conductivity), mechanical strength of stems (modulus of elasticity and modulus of rupture), and xylem density. At the cellular level, we measured vessel and fiber wall thickness and lumen diameter, transverse fiber wall and total lumen area, and estimated vessel implosion resistance using (t/b)(h)(2), where t is the thickness of adjoining vessel walls and b is the vessel lumen diameter. Increased cavitation resistance was correlated with increased mechanical strength (r(2) = 0.74 and 0.76 for modulus of elasticity and modulus of rupture, respectively), xylem density (r(2) = 0.88), and P(min) (r(2) = 0.96). In contrast, cavitation resistance and P(min) were not correlated with decreased specific conductivity, suggesting no tradeoff between these traits. At the cellular level, increased cavitation resistance was correlated with increased (t/b)(h)(2) (r(2) = 0.95), increased transverse fiber wall area (r(2) = 0.89), and decreased fiber lumen area (r(2) = 0.76). To our knowledge, the correlation between cavitation resistance and fiber wall area has not been shown previously and suggests a mechanical role for fibers in cavitation resistance. Fiber efficacy in prevention of vessel implosion, defined as inward bending or collapse of vessels, is discussed.
Comparison of electric and growth responses to excision in cucumber and pea seedlings. II. Long-distance effects are caused by the release of xylem pressure

NASA Technical Reports Server (NTRS)

Stahlberg, R.; Cosgrove, D. J.

1995-01-01

Excision of a growing stem causes local wound responses, such as membrane depolarization and growth inhibition, as well as effects at larger distances from the cut. In this study, cucumber hypocotyls were excised 100 mm below the hook, so that the growing region was beyond the reach of the wound-induced depolarization (up to 40 mm). Even at such a distance, the cut still caused a considerable and rapid drop in the hypocotyl growth rate. This growth response is not a direct wound response because it does not result from the cut-induced depolarization and because it can be simulated by root pressure manipulation (using a pressure chamber). The results indicate that the growth response resulted from the rapid release of the xylem pressure upon excision. To test this conclusion we measured the xylem pressure by connecting a pressure probe to the cut surface of the stem. Xylem pressure (Px) was found to be +10 to +40 kPa in cucumber hypocotyls and -5 to -10 kPa or lower in pea epicotyls. Excision of the cucumber hypocotyl base led to a rapid drop in Px to negative values, whereas excision in pea led to a rapid rise in Px to ambient (zero) pressure. These fast and opposite Px changes parallel the excision-induced changes in growth rate (GR): a decrease in cucumber and a rise in pea. The sign of the endogenous xylem pressure also determined whether excision induced a propagating depolarization in the form of a slow wave potential (SWP). Under normal circumstances pea seedlings generated an SWP upon excision whereas cucumber seedlings failed to do so. When the Px in cucumber hypocotyls was experimentally inverted to negative values by incubating the cumber roots in solutions of NaCN or n-ethylmaleimide, excision caused a propagating depolarization (SWP). The experiment shows that only hydraulic signals in the form of positive Px steps are converted into propagating electric SWP signals. These propagating depolarizations might be causally linked to systemic 'wound
Cell water potential, osmotic potential, and turgor in the epidermis and mesophyll of transpiring leaves : Combined measurements with the cell pressure probe and nanoliter osmometer.

PubMed

Nonami, H; Schulze, E D

1989-01-01

Water potential, osmotic potential and turgor measurements obtained by using a cell pressure probe together with a nanoliter osmometer were compared with measurements obtained with an isopiestic psychrometer. Both types of measurements were conducted in the mature region of Tradescantia virginiana L. leaves under non-transpiring conditions in the dark, and gave similar values of all potentials. This finding indicates that the pressure probe and the osmometer provide accurate measurements of turgor, osmotic potentials and water potentials. Because the pressure probe does not require long equilibration times and can measure turgor of single cells in intact plants, the pressure probe together with the osmometer was used to determine in-situ cell water potentials, osmotic potentials and turgor of epidermal and mesophyll cells of transpiring leaves as functions of stomatal aperture and xylem water potential. When the xylem water potential was-0.1 MPa, the stomatal aperture was at its maximum, but turgor of both epidermal and mesophyll cells was relatively low. As the xylem water potential decreased, the stomatal aperture became gradually smaller, whereas turgor of both epidermal and mesophyll cells first increased and afterward decreased. Water potentials of the mesophyll cells were always lower than those of the epidermal cells. These findings indicate that evaporation of water is mainly occurring from mesophyll cells and that peristomatal transpiration could be less important than it has been proposed previously, although peristomatal transpiration may be directly related to regulation of turgor in the guard cells.
The impact of xylem cavitation on water potential isotherms measured by the pressure chamber technique in Metasequoia glyptostroboides Hu & W.C. Cheng.

PubMed

Yang, Dongmei; Pan, Shaoan; Tyree, Melvin T

2016-08-01

Pressure-volume (PV) curve analysis is the most common and accurate way of estimating all components of the water relationships in leaves (water potential isotherms) as summarized in the Höfler diagram. PV curve analysis yields values of osmotic pressure, turgor pressure, and elastic modulus of cell walls as a function of relative water content. It allows the computation of symplasmic/apoplastic water content partitioning. For about 20 years, cavitation in xylem has been postulated as a possible source of error when estimating the above parameters, but, to the best of the authors' knowledge, no one has ever previously quantified its influence. Results in this paper provide independent estimates of osmotic pressure by PV curve analysis and by thermocouple psychrometer measurement. An anatomical evaluation was also used for the first time to compare apoplastic water fraction estimates from PV analysis with anatomical values. Conclusions include: (i) PV curve values of osmotic pressure are underestimated prior to correcting osmotic pressure for water loss by cavitation in Metasequoia glyptostroboides; (ii) psychrometer estimates of osmotic pressure obtained in tissues killed by freezing or heating agreed with PV values before correction for apoplastic water dilution; (iii) after correction for dilution effects, a solute concentration enhancement (0.27MPa or 0.11 osmolal) was revealed. The possible sources of solute enhancement were starch hydrolysis and release of ions from the Donnan free space of needle cell walls. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.
Xylem sap proteins.

PubMed

Biles, C L; Abeles, F B

1991-06-01

Xylem sap from apple (Malus domestica Borkh), peach (Prunus persica Batsch), and pear (Pyrus communis L.) twigs was collected by means of pressure extrusion. This sap contained a number of acidic peroxidases and other proteins. Two other sources of xylem sap used in this study were stem exudates and guttation fluid. Similar peroxidases were also found in stem exudates and guttation fluids of strawberry (Fragaria x ananassa Duch.), tomato (Lycopersicum esculentum L.), and cucumber (Cucumis sativus L.). Isoelectric focusing activity gels showed that two peroxidases (isoelectric point [pl] 9 and pl 4.6) were present in initial stem exudates collected in the first 30 minutes after excision. Subsequent samples of stem exudate collected contained only the pl 4.6 isozyme. The pl 4.6 peroxidase isozyme was also found in root tissue and guttation fluid. These observations suggest that roots produce and secrete the pl 4.6 peroxidase into xylem sap. Cucumber seedlings were treated with 100 microliters per liter ethylene for 16 hours and the exudate from decapitated hypocotyl stumps was collected over a 3 hour period. Ethylene increased the peroxidase activity of stem exudates and inhibited the amount of exudate released. These observations suggest that xylem sap peroxidase may play a role in plugging damaged vascular tissue.
Physical analysis of the process of cavitation in xylem sap.

PubMed

Shen, Fanyi; Gao, Rongfu; Liu, Wenji; Zhang, Wenjie

2002-06-01

Recent studies have confirmed that cavitation in xylem is caused by air bubbles. We analyzed expansion of a preexistent bubble adhering to a crack in a conduit wall and a bubble formed by the passage of air through a pore of a pit membrane, a process known as air seeding. We consider that there are two equilibrium states for a very small air bubble in the xylem: one is temporarily stable with a bubble radius r1 at point s1 on the curve P(r) relating pressure within the bubble (P) with bubble radius (r); the other is unstable with a bubble radius r2 at point s2 on Pr (where r1 < r2). In each equilibrium state, the bubble collapse pressure (2sigma/r, where sigma is surface tension of water) is balanced by the pressure difference across its surface. In the case of a bubble from a crack in a conduit wall, which is initially at point s1, expansion will occur steadily as water potential decreases. The bubble will burst only if the xylem pressure drops below a threshold value. A formula giving the threshold pressure for bubble bursting is proposed. In the case of an air seed entering a xylem conduit through a pore in a pit membrane, its initial radius may be r2 (i.e., the radius of the pore by which the air seed entered the vessel) at point s2 on Pr. Because the bubble is in an unstable equilibrium when entering the conduit, it can either expand or contract to point s1. As water vaporizes into the air bubble at s2, P rises until it exceeds the gas pressure that keeps the bubble in equilibrium, at which point the bubble will burst and induce a cavitation event in accordance with the air-seeding hypothesis. However, other possible perturbations could make the air-seeded bubble contract to s1, in which case the bubble will burst at a threshold pressure proposed for a bubble expanding from a crack in a conduit wall. For this reason some cavitation events may take place at a xylem threshold pressure (Pl'*) other than that determined by the formula, Plp'* = -2sigma/rp, proposed
Reversible Leaf Xylem Collapse: A Potential “Circuit Breaker” against Cavitation1[OPEN

PubMed Central

Zhang, Yong-Jiang; Rockwell, Fulton E.; Graham, Adam C.; Alexander, Teressa; Holbrook, N. Michele

2016-01-01

We report a novel form of xylem dysfunction in angiosperms: reversible collapse of the xylem conduits of the smallest vein orders that demarcate and intrusively irrigate the areoles of red oak (Quercus rubra) leaves. Cryo-scanning electron microscopy revealed gradual increases in collapse from approximately −2 MPa down to −3 MPa, saturating thereafter (to −4 MPa). Over this range, cavitation remained negligible in these veins. Imaging of rehydration experiments showed spatially variable recovery from collapse within 20 s and complete recovery after 2 min. More broadly, the patterns of deformation induced by desiccation in both mesophyll and xylem suggest that cell wall collapse is unlikely to depend solely on individual wall properties, as mechanical constraints imposed by neighbors appear to be important. From the perspective of equilibrium leaf water potentials, petioles, whose vessels extend into the major veins, showed a vulnerability to cavitation that overlapped in the water potential domain with both minor vein collapse and buckling (turgor loss) of the living cells. However, models of transpiration transients showed that minor vein collapse and mesophyll capacitance could effectively buffer major veins from cavitation over time scales relevant to the rectification of stomatal wrong-way responses. We suggest that, for angiosperms, whose subsidiary cells give up large volumes to allow large stomatal apertures at the cost of potentially large wrong-way responses, vein collapse could make an important contribution to these plants’ ability to transpire near the brink of cavitation-inducing water potentials. PMID:27733514

Evidence for Hydraulic Vulnerability Segmentation and Lack of Xylem Refilling under Tension.

PubMed

Charrier, Guillaume; Torres-Ruiz, José M; Badel, Eric; Burlett, Regis; Choat, Brendan; Cochard, Herve; Delmas, Chloe E L; Domec, Jean-Christophe; Jansen, Steven; King, Andrew; Lenoir, Nicolas; Martin-StPaul, Nicolas; Gambetta, Gregory Alan; Delzon, Sylvain

2016-11-01

The vascular system of grapevine (Vitis spp.) has been reported as being highly vulnerable, even though grapevine regularly experiences seasonal drought. Consequently, stomata would remain open below water potentials that would generate a high loss of stem hydraulic conductivity via xylem embolism. This situation would necessitate daily cycles of embolism repair to restore hydraulic function. However, a more parsimonious explanation is that some hydraulic techniques are prone to artifacts in species with long vessels, leading to the overestimation of vulnerability. The aim of this study was to provide an unbiased assessment of (1) the vulnerability to drought-induced embolism in perennial and annual organs and (2) the ability to refill embolized vessels in two Vitis species X-ray micro-computed tomography observations of intact plants indicated that both Vitis vinifera and Vitis riparia were relatively vulnerable, with the pressure inducing 50% loss of stem hydraulic conductivity = -1.7 and -1.3 MPa, respectively. In V. vinifera, both the stem and petiole had similar sigmoidal vulnerability curves but differed in pressure inducing 50% loss of hydraulic conductivity (-1.7 and -1 MPa for stem and petiole, respectively). Refilling was not observed as long as bulk xylem pressure remained negative (e.g. at the apical part of the plants; -0.11 ± 0.02 MPa) and change in percentage loss of conductivity was 0.02% ± 0.01%. However, positive xylem pressure was observed at the basal part of the plant (0.04 ± 0.01 MPa), leading to a recovery of conductance (change in percentage loss of conductivity = -0.24% ± 0.12%). Our findings provide evidence that grapevine is unable to repair embolized xylem vessels under negative pressure, but its hydraulic vulnerability segmentation provides significant protection of the perennial stem. © 2016 American Society of Plant Biologists. All Rights Reserved.
Identification and expression analyses of new potential regulators of xylem development and cambium activity in cassava (Manihot esculenta).

PubMed

Siebers, Tyche; Catarino, Bruno; Agusti, Javier

2017-03-01

We have identified new potential regulators of xylem cell-type determination and cellular proliferation in cassava and studied their expression in roots. Results are highly relevant for cassava biotechnology. Cassava's root system is composed of two types of root that coexist in every individual: the fibrous and the storage roots. Whether a root becomes fibrous or storage depends on the xylem cell types that it develops: fibrous roots develop xylem fibres and vessels while storage roots develop parenchyma xylem, the starch-storing tissue. A crucial question in cassava root development is how the specific xylem cell types differentiate and proliferate in the fibrous and storage roots. Using phylogenetic, protein sequence and synteny analyses we identified (1) MeVND6, MeVND7.1, MeVND7.2, MeNST3.1 and MeNST3.2 as the potential cassava orthologues of the Arabidopsis regulators of xylem cell type determination AtVND6, AtVND7 and AtNST3; and (2) MeWOX4.1 and MeWOX4.2 as the potential cassava orthologues of the Arabidopsis cambium regulator AtWOX4. Fibrous and storage roots were anatomically characterised and tested for the expression of the identified genes. Results revealed that (1) MeVND7.1 and MeVND7.2 are expressed in the fibrous but not in the storage roots; (2) MeVND6 shows low expression in both root types; (3) MeNST3.1 is not expressed in the fibrous or storage roots, while MeNST3.2 is highly expressed in both root-types and (4) MeWOX4.1 and, to a higher level, MeWOX4.2 are expressed in both the fibrous and storage roots. Results open new avenues for research in cassava root development and for food security-oriented biotechnology programmes.
Glassy-winged sharpshooter feeding does not cause air embolisms in xylem of well-watered plants.

USDA-ARS?s Scientific Manuscript database

Plant xylem vessels are under negative hydrostatic pressure (tension) as evapotranspiration of water from the leaf surface pulls the column of water in xylem upwards. When xylem fluid flux is under extreme tension, any puncture or breakage of the xylem vessel wall can cause formation of air embolis...
Xylem Surfactants Introduce a New Element to the Cohesion-Tension Theory.

PubMed

Schenk, H Jochen; Espino, Susana; Romo, David M; Nima, Neda; Do, Aissa Y T; Michaud, Joseph M; Papahadjopoulos-Sternberg, Brigitte; Yang, Jinlong; Zuo, Yi Y; Steppe, Kathy; Jansen, Steven

2017-02-01

Vascular plants transport water under negative pressure without constantly creating gas bubbles that would disable their hydraulic systems. Attempts to replicate this feat in artificial systems almost invariably result in bubble formation, except under highly controlled conditions with pure water and only hydrophilic surfaces present. In theory, conditions in the xylem should favor bubble nucleation even more: there are millions of conduits with at least some hydrophobic surfaces, and xylem sap is saturated or sometimes supersaturated with atmospheric gas and may contain surface-active molecules that can lower surface tension. So how do plants transport water under negative pressure? Here, we show that angiosperm xylem contains abundant hydrophobic surfaces as well as insoluble lipid surfactants, including phospholipids, and proteins, a composition similar to pulmonary surfactants. Lipid surfactants were found in xylem sap and as nanoparticles under transmission electron microscopy in pores of intervessel pit membranes and deposited on vessel wall surfaces. Nanoparticles observed in xylem sap via nanoparticle-tracking analysis included surfactant-coated nanobubbles when examined by freeze-fracture electron microscopy. Based on their fracture behavior, this technique is able to distinguish between dense-core particles, liquid-filled, bilayer-coated vesicles/liposomes, and gas-filled bubbles. Xylem surfactants showed strong surface activity that reduces surface tension to low values when concentrated as they are in pit membrane pores. We hypothesize that xylem surfactants support water transport under negative pressure as explained by the cohesion-tension theory by coating hydrophobic surfaces and nanobubbles, thereby keeping the latter below the critical size at which bubbles would expand to form embolisms. © 2017 American Society of Plant Biologists. All Rights Reserved.
Xylem sap proteomics.

PubMed

de Bernonville, Thomas Dugé; Albenne, Cécile; Arlat, Matthieu; Hoffmann, Laurent; Lauber, Emmanuelle; Jamet, Elisabeth

2014-01-01

Proteomic analysis of xylem sap has recently become a major field of interest to understand several biological questions related to plant development and responses to environmental clues. The xylem sap appears as a dynamic fluid undergoing changes in its proteome upon abiotic and biotic stresses. Unlike cell compartments which are amenable to purification in sufficient amount prior to proteomic analysis, the xylem sap has to be collected in particular conditions to avoid contamination by intracellular proteins and to obtain enough material. A model plant like Arabidopsis thaliana is not suitable for such an analysis because efficient harvesting of xylem sap is difficult. The analysis of the xylem sap proteome also requires specific procedures to concentrate proteins and to focus on proteins predicted to be secreted. Indeed, xylem sap proteins appear to be synthesized and secreted in the root stele or to originate from dying differentiated xylem cells. This chapter describes protocols to collect xylem sap from Brassica species and to prepare total and N-glycoprotein extracts for identification of proteins by mass spectrometry analyses and bioinformatics.
Weak tradeoff between xylem safety and xylem-specific hydraulic efficiency across the world's woody plant species.

PubMed

Gleason, Sean M; Westoby, Mark; Jansen, Steven; Choat, Brendan; Hacke, Uwe G; Pratt, Robert B; Bhaskar, Radika; Brodribb, Tim J; Bucci, Sandra J; Cao, Kun-Fang; Cochard, Hervé; Delzon, Sylvain; Domec, Jean-Christophe; Fan, Ze-Xin; Feild, Taylor S; Jacobsen, Anna L; Johnson, Daniel M; Lens, Frederic; Maherali, Hafiz; Martínez-Vilalta, Jordi; Mayr, Stefan; McCulloh, Katherine A; Mencuccini, Maurizio; Mitchell, Patrick J; Morris, Hugh; Nardini, Andrea; Pittermann, Jarmila; Plavcová, Lenka; Schreiber, Stefan G; Sperry, John S; Wright, Ian J; Zanne, Amy E

2016-01-01

The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves. A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water). We tested this safety-efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species. Safety was considered at three levels: the xylem water potentials where 12%, 50% and 88% of maximal conductivity are lost. Although correlations between safety and efficiency were weak (r(2) < 0.086), no species had high efficiency and high safety, supporting the idea for a safety-efficiency tradeoff. However, many species had low efficiency and low safety. Species with low efficiency and low safety were weakly associated (r(2) < 0.02 in most cases) with higher wood density, lower leaf- to sapwood-area and shorter stature. There appears to be no persuasive explanation for the considerable number of species with both low efficiency and low safety. These species represent a real challenge for understanding the evolution of xylem. No claim to US government works. New Phytologist © 2015 New Phytologist Trust.
Evidence for Hydraulic Vulnerability Segmentation and Lack of Xylem Refilling under Tension1[OPEN

PubMed Central

Charrier, Guillaume; Choat, Brendan; Delmas, Chloe E. L.; Domec, Jean-Christophe; King, Andrew; Lenoir, Nicolas

2016-01-01

The vascular system of grapevine (Vitis spp.) has been reported as being highly vulnerable, even though grapevine regularly experiences seasonal drought. Consequently, stomata would remain open below water potentials that would generate a high loss of stem hydraulic conductivity via xylem embolism. This situation would necessitate daily cycles of embolism repair to restore hydraulic function. However, a more parsimonious explanation is that some hydraulic techniques are prone to artifacts in species with long vessels, leading to the overestimation of vulnerability. The aim of this study was to provide an unbiased assessment of (1) the vulnerability to drought-induced embolism in perennial and annual organs and (2) the ability to refill embolized vessels in two Vitis species X-ray micro-computed tomography observations of intact plants indicated that both Vitis vinifera and Vitis riparia were relatively vulnerable, with the pressure inducing 50% loss of stem hydraulic conductivity = −1.7 and −1.3 MPa, respectively. In V. vinifera, both the stem and petiole had similar sigmoidal vulnerability curves but differed in pressure inducing 50% loss of hydraulic conductivity (−1.7 and −1 MPa for stem and petiole, respectively). Refilling was not observed as long as bulk xylem pressure remained negative (e.g. at the apical part of the plants; −0.11 ± 0.02 MPa) and change in percentage loss of conductivity was 0.02% ± 0.01%. However, positive xylem pressure was observed at the basal part of the plant (0.04 ± 0.01 MPa), leading to a recovery of conductance (change in percentage loss of conductivity = −0.24% ± 0.12%). Our findings provide evidence that grapevine is unable to repair embolized xylem vessels under negative pressure, but its hydraulic vulnerability segmentation provides significant protection of the perennial stem. PMID:27613852
Xylem Surfactants Introduce a New Element to the Cohesion-Tension Theory1[OPEN

PubMed Central

Espino, Susana; Nima, Neda; Do, Aissa Y.T.; Michaud, Joseph M.; Papahadjopoulos-Sternberg, Brigitte; Yang, Jinlong; Steppe, Kathy

2017-01-01

Vascular plants transport water under negative pressure without constantly creating gas bubbles that would disable their hydraulic systems. Attempts to replicate this feat in artificial systems almost invariably result in bubble formation, except under highly controlled conditions with pure water and only hydrophilic surfaces present. In theory, conditions in the xylem should favor bubble nucleation even more: there are millions of conduits with at least some hydrophobic surfaces, and xylem sap is saturated or sometimes supersaturated with atmospheric gas and may contain surface-active molecules that can lower surface tension. So how do plants transport water under negative pressure? Here, we show that angiosperm xylem contains abundant hydrophobic surfaces as well as insoluble lipid surfactants, including phospholipids, and proteins, a composition similar to pulmonary surfactants. Lipid surfactants were found in xylem sap and as nanoparticles under transmission electron microscopy in pores of intervessel pit membranes and deposited on vessel wall surfaces. Nanoparticles observed in xylem sap via nanoparticle-tracking analysis included surfactant-coated nanobubbles when examined by freeze-fracture electron microscopy. Based on their fracture behavior, this technique is able to distinguish between dense-core particles, liquid-filled, bilayer-coated vesicles/liposomes, and gas-filled bubbles. Xylem surfactants showed strong surface activity that reduces surface tension to low values when concentrated as they are in pit membrane pores. We hypothesize that xylem surfactants support water transport under negative pressure as explained by the cohesion-tension theory by coating hydrophobic surfaces and nanobubbles, thereby keeping the latter below the critical size at which bubbles would expand to form embolisms. PMID:27927981
Xylem resistance to embolism: presenting a simple diagnostic test for the open vessel artefact.

PubMed

Torres-Ruiz, José M; Cochard, Hervé; Choat, Brendan; Jansen, Steven; López, Rosana; Tomášková, Ivana; Padilla-Díaz, Carmen M; Badel, Eric; Burlett, Regis; King, Andrew; Lenoir, Nicolas; Martin-StPaul, Nicolas K; Delzon, Sylvain

2017-07-01

Xylem vulnerability to embolism represents an essential trait for the evaluation of the impact of hydraulics in plant function and ecology. The standard centrifuge technique is widely used for the construction of vulnerability curves, although its accuracy when applied to species with long vessels remains under debate. We developed a simple diagnostic test to determine whether the open-vessel artefact influences centrifuge estimates of embolism resistance. Xylem samples from three species with differing vessel lengths were exposed to less negative xylem pressures via centrifugation than the minimum pressure the sample had previously experienced. Additional calibration was obtained from non-invasive measurement of embolism on intact olive plants by X-ray microtomography. Results showed artefactual decreases in hydraulic conductance (k) for samples with open vessels when exposed to a less negative xylem pressure than the minimum pressure they had previously experienced. X-Ray microtomography indicated that most of the embolism formation in olive occurs at xylem pressures below -4.0 MPa, reaching 50% loss of hydraulic conductivity at -5.3 MPa. The artefactual reductions in k induced by centrifugation underestimate embolism resistance data of species with long vessels. A simple test is suggested to avoid this open vessel artefact and to ensure the reliability of this technique in future studies. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.
Arabidopsis thaliana as a model species for xylem hydraulics: does size matter?

PubMed Central

Tixier, Aude; Cochard, Hervé; Badel, Eric; Dusotoit-Coucaud, Anaïs; Jansen, Steven; Herbette, Stéphane

2013-01-01

While Arabidopsis thaliana has been proposed as a model species for wood development, the potential of this tiny herb for studying xylem hydraulics remains unexplored and anticipated by scepticism. Inflorescence stems of A. thaliana were used to measure hydraulic conductivity and cavitation resistance, whereas light and electron microscopy allowed observations of vessels. In wild-type plants, measured and theoretical conductivity showed a significant correlation (R 2 = 0.80, P < 0.01). Moreover, scaling of vessel dimensions and intervessel pit structure of A. thaliana were consistent with structure–function relationships of woody plants. The reliability and resolution of the hydraulic methods applied to measure vulnerability to cavitation were addressed by comparing plants grown under different photoperiods or different mutant lines. Sigmoid vulnerability curves of A. thaliana indicated a pressure corresponding to 50% loss of hydraulic conductance (P 50) between –3 and –2.5MPa for short-day and long-day plants, respectively. Polygalacturonase mutants showed a higher P 50 value (–2.25MPa), suggesting a role for pectins in vulnerability to cavitation. The application of A. thaliana as a model species for xylem hydraulics provides exciting possibilities for (1) exploring the molecular basis of xylem anatomical features and (2) understanding genetic mechanisms behind xylem functional traits such as cavitation resistance. Compared to perennial woody species, however, the lesser amount of xylem in A. thaliana has its limitations. PMID:23547109
Arabidopsis thaliana as a model species for xylem hydraulics: does size matter?

PubMed

Tixier, Aude; Cochard, Hervé; Badel, Eric; Dusotoit-Coucaud, Anaïs; Jansen, Steven; Herbette, Stéphane

2013-05-01

While Arabidopsis thaliana has been proposed as a model species for wood development, the potential of this tiny herb for studying xylem hydraulics remains unexplored and anticipated by scepticism. Inflorescence stems of A. thaliana were used to measure hydraulic conductivity and cavitation resistance, whereas light and electron microscopy allowed observations of vessels. In wild-type plants, measured and theoretical conductivity showed a significant correlation (R (2) = 0.80, P < 0.01). Moreover, scaling of vessel dimensions and intervessel pit structure of A. thaliana were consistent with structure-function relationships of woody plants. The reliability and resolution of the hydraulic methods applied to measure vulnerability to cavitation were addressed by comparing plants grown under different photoperiods or different mutant lines. Sigmoid vulnerability curves of A. thaliana indicated a pressure corresponding to 50% loss of hydraulic conductance (P 50) between -3 and -2.5MPa for short-day and long-day plants, respectively. Polygalacturonase mutants showed a higher P 50 value (-2.25MPa), suggesting a role for pectins in vulnerability to cavitation. The application of A. thaliana as a model species for xylem hydraulics provides exciting possibilities for (1) exploring the molecular basis of xylem anatomical features and (2) understanding genetic mechanisms behind xylem functional traits such as cavitation resistance. Compared to perennial woody species, however, the lesser amount of xylem in A. thaliana has its limitations.
Dynamic control of osmolality and ionic composition of the xylem sap in two mangrove species.

PubMed

López-Portillo, Jorge; Ewers, Frank W; Méndez-Alonzo, Rodrigo; Paredes López, Claudia L; Angeles, Guillermo; Alarcón Jiménez, Ana Luisa; Lara-Domínguez, Ana Laura; Torres Barrera, María Del Carmen

2014-06-01

• Premise of the study: Xylem sap osmolality and salinity is a critical unresolved issue in plant function with impacts on transport efficiency, pressure gradients, and living cell turgor pressure, especially for halophytes such as mangrove trees.• Methods: We collected successive xylem vessel sap samples from stems and shoots of Avicennia germinans and Laguncularia racemosa using vacuum and pressure extraction and measured their osmolality. Following a series of extractions with the pressure chamber, we depressurized the shoot and pressurized again after various equilibration periods (minutes to hours) to test for dynamic control of osmolality. Transpiration and final sap osmolality were measured in shoots perfused with deionized water or different seawater dilutions.• Key results: For both species, the sap osmolality values of consecutive samples collected by vacuum extraction were stable and matched those of the initial samples extracted with the pressure chamber. Further extraction of samples with the pressure chamber decreased sap osmolality, suggesting reverse osmosis occurred. However, sap osmolalities increased when longer equilibration periods after sap extraction were allowed. Analysis of expressed sap with HPLC indicated a 1:1 relation between measured osmolality and the osmolality of the inorganic ions in the sap (mainly Na + , K + , and Cl - ), suggesting no contamination by organic compounds. In stems perfused with deionized water, the sap osmolality increased to mimic the native sap osmolality.• Conclusions: Xylem sap osmolality and ionic contents are dynamically adjusted by mangroves and may help modulate turgor pressure, hydraulic conductivity, and water potential, thus being important for mangrove physiology, survival, and distribution. © 2014 Botanical Society of America, Inc.
Conservation of element concentration in xylem sap of red spruce

Treesearch

Kevin T. Smith; Walter C. Shortle

2001-01-01

We investigated the chemistry of xylem sap as a marker of red spruce metabolism and soil chemistry at three locations in northern New England. A Scholander pressure chamber was used to extract xylem sap from roots and branches cut from mature trees in early June and September. Root sap contained significantly greater concentrations of K, Ca, Mg, Mn, and A1 than branch...
Use of Positive Pressures to Establish Vulnerability Curves 1

PubMed Central

Cochard, Hervé; Cruiziat, Pierre; Tyree, Melvin T.

1992-01-01

Loss of hydraulic conductivity occurs in stems when the water in xylem conduits is subjected to sufficiently negative pressure. According to the air-seeding hypothesis, this loss of conductivity occurs when air bubbles are sucked into water-filled conduits through micropores adjacent to air spaces in the stem. Results in this study showed that loss of hydraulic conductivity occurred in stem segments pressurized in a pressure chamber while the xylem water was under positive pressure. Vulnerability curves can be defined as a plot of percentage loss of hydraulic conductivity versus the pressure difference between xylem water and the outside air inducing the loss of conductivity. Vulnerability curves were similar whether loss of conductivity was induced by lowering the xylem water pressure or by raising the external air pressure. These results are consistent with the air-seeding hypothesis of how embolisms are nucleated, but not with the nucleation of embolisms at hydrophobic cracks because the latter requires negative xylem water pressure. The results also call into question some basic underlying assumptions used in the determination of components of tissue water potential using “pressure-volume” analysis. PMID:16652947
Outside-Xylem Vulnerability, Not Xylem Embolism, Controls Leaf Hydraulic Decline during Dehydration.

PubMed

Scoffoni, Christine; Albuquerque, Caetano; Brodersen, Craig R; Townes, Shatara V; John, Grace P; Bartlett, Megan K; Buckley, Thomas N; McElrone, Andrew J; Sack, Lawren

2017-02-01

Leaf hydraulic supply is crucial to maintaining open stomata for CO 2 capture and plant growth. During drought-induced dehydration, the leaf hydraulic conductance (K leaf ) declines, which contributes to stomatal closure and, eventually, to leaf death. Previous studies have tended to attribute the decline of K leaf to embolism in the leaf vein xylem. We visualized at high resolution and quantified experimentally the hydraulic vulnerability of xylem and outside-xylem pathways and modeled their respective influences on plant water transport. Evidence from all approaches indicated that the decline of K leaf during dehydration arose first and foremost due to the vulnerability of outside-xylem tissues. In vivo x-ray microcomputed tomography of dehydrating leaves of four diverse angiosperm species showed that, at the turgor loss point, only small fractions of leaf vein xylem conduits were embolized, and substantial xylem embolism arose only under severe dehydration. Experiments on an expanded set of eight angiosperm species showed that outside-xylem hydraulic vulnerability explained 75% to 100% of K leaf decline across the range of dehydration from mild water stress to beyond turgor loss point. Spatially explicit modeling of leaf water transport pointed to a role for reduced membrane conductivity consistent with published data for cells and tissues. Plant-scale modeling suggested that outside-xylem hydraulic vulnerability can protect the xylem from tensions that would induce embolism and disruption of water transport under mild to moderate soil and atmospheric droughts. These findings pinpoint outside-xylem tissues as a central locus for the control of leaf and plant water transport during progressive drought. © 2017 The author(s). All Rights Reserved.
Vulnerability of Xylem Vessels to Cavitation in Sugar Maple. Scaling from Individual Vessels to Whole Branches1

PubMed Central

Melcher, Peter J.; Zwieniecki, Maciej A.; Holbrook, N. Michele

2003-01-01

The relation between xylem vessel age and vulnerability to cavitation of sugar maple (Acer saccharum Marsh.) was quantified by measuring the pressure required to force air across bordered pit membranes separating individual xylem vessels. We found that the bordered pit membranes of vessels located in current year xylem could withstand greater applied gas pressures (3.8 MPa) compared with bordered pit membranes in vessels located in older annular rings (2.0 MPa). A longitudinal transect along 6-year-old branches indicated that the pressure required to push gas across bordered pit membranes of current year xylem did not vary with distance from the growing tip. To understand the contribution of age-related changes in vulnerability to the overall resistance to cavitation, we combined data on the pressure thresholds of individual xylem vessels with measurements of the relative flow rate through each annual ring. The annual ring of the current year contributed only 16% of the total flow measured on 10-cm-long segments cut from 6-year-old branches, but it contributed more than 70% of the total flow when measured through 6-year-old branches to the point of leaf attachment. The vulnerability curve calculated using relative flow rates measured on branch segments were similar to vulnerability curves measured on 6-year-old branches (pressure that reduces hydraulic conductance by 50% = 1.6–2.4 MPa), whereas the vulnerability curve calculated using relative flow rates measured on 6-year-old branches were similar to ones measured on the extension growth of the current year (pressure that reduces hydraulic conductance by 50% = 3.8 MPa). These data suggest that, in sugar maple, the xylem of the current year can withstand larger xylem tensions than older wood and dominates water delivery to leaves. PMID:12692336
Applications of the compensating pressure theory of water transport.

PubMed

Canny, M

1998-07-01

Some predictions of the recently proposed theory of long-distance water transport in plants (the Compensating Pressure Theory) have been verified experimentally in sunflower leaves. The xylem sap cavitates early in the day under quite small water stress, and the compensating pressure P (applied as the tissue pressure of turgid cells) pushes water into embolized vessels, refilling them during active transpiration. The water potential, as measured by the pressure chamber or psychrometer, is not a measure of the pressure in the xylem, but (as predicted by the theory) a measure of the compensating pressure P. As transpiration increases, P is increased to provide more rapid embolism repair. In many leaf petioles this increase in P is achieved by the hydrolysis of starch in the starch sheath to soluble sugars. At night P falls as starch is reformed. A hypothesis is proposed to explain these observations by pressure-driven reverse osmosis of water from the ground parenchyma of the petiole. Similar processes occur in roots and are manifested as root pressure. The theory requires a pump to transfer water from the soil into the root xylem. A mechanism is proposed by which this pump may function, in which the endodermis acts as a one-way valve and a pressure-confining barrier. Rays and xylem parenchyma of wood act like the xylem parenchyma of petioles and roots to repair embolisms in trees. The postulated root pump permits a re-appraisal of the work done by evaporation during transpiration, leading to the proposal that in tall trees there is no hydrostatic gradient to be overcome in lifting water. Some published observations are re-interpreted in terms of the theory: doubt is cast on the validity of measurements of hydraulic conductance of wood; vulnerability curves are found not to measure the cavitation threshold of water in the xylem, but the osmotic pressure of the xylem parenchyma; if measures of xylem pressure and of hydraulic conductance are both suspect, the accepted
Investigating differences in the root to shoot transfer and xylem sap solubility of organic compounds between zucchini, squash and soybean using a pressure chamber method.

PubMed

Garvin, Naho; Doucette, William J; White, Jason C

2015-07-01

A pressure chamber method was used to examine differences in the root to shoot transfer and xylem sap solubility of caffeine (log Kow=-0.07), triclocarban (log Kow=3.5-4.2) and endosulfan (log Kow=3.8-4.8) for zucchini (cucurbita pepo ssp pepo), squash (cucurbita pepo ssp ovifera), and soybean (glycine max L.). Transpiration stream concentration factors (TSCF) for caffeine (TSCF=0.8) were statistically equivalent for all plant species. However, for the more hydrophobic endosulfan and triclocarban, the TSCF values for zucchini (TSCF=0.6 and 0.4, respectively) were 3 and 10 times greater than the soybean and squash (TSCF=0.2 and 0.05, respectively). The difference in TSCF values was examined by comparing the measured solubilities of caffeine, endosulfan and triclocarban in deionized water to those in soybean and zucchini xylem saps using a modified shake flask method. The measured solubility of organic contaminants in xylem sap has not previously been reported. Caffeine solubilities in the xylem saps of soybean and zucchini were statistically equal to deionized water (21500mgL(-1)) while endosulfan and triclocarban solubilities in the zucchini xylem sap were significantly greater (0.43 and 0.21mgL(-1), respectively) than that of the soybean xylem sap (0.31 and 0.11mgL(-1), respectively) and deionized water (0.34 and 0.11mgL(-1), respectively). This suggests that the enhanced root to shoot transfer of hydrophobic organics reported for zucchini is partly due to increased solubility in the xylem sap. Further xylem sap characterization is needed to determine the mechanism of solubility enhancement. Copyright © 2014 Elsevier Ltd. All rights reserved.
Dissolved atmospheric gas in xylem sap measured with membrane inlet mass spectrometry.

PubMed

Schenk, H Jochen; Espino, Susana; Visser, Ate; Esser, Bradley K

2016-04-01

A new method is described for measuring dissolved gas concentrations in small volumes of xylem sap using membrane inlet mass spectrometry. The technique can be used to determine concentrations of atmospheric gases, such as argon, as reported here, or for any dissolved gases and their isotopes for a variety of applications, such as rapid detection of trace gases from groundwater only hours after they were taken up by trees and rooting depth estimation. Atmospheric gas content in xylem sap directly affects the conditions and mechanisms that allow for gas removal from xylem embolisms, because gas can dissolve into saturated or supersaturated sap only under gas pressure that is above atmospheric pressure. The method was tested for red trumpet vine, Distictis buccinatoria (Bignoniaceae), by measuring atmospheric gas concentrations in sap collected at times of minimum and maximum daily temperature and during temperature increase and decline. Mean argon concentration in xylem sap did not differ significantly from saturation levels for the temperature and pressure conditions at any time of collection, but more than 40% of all samples were supersaturated, especially during the warm parts of day. There was no significant diurnal pattern, due to high variability between samples. © 2015 John Wiley & Sons Ltd.
Outside-Xylem Vulnerability, Not Xylem Embolism, Controls Leaf Hydraulic Decline during Dehydration1[CC-BY

PubMed Central

Townes, Shatara V.; Bartlett, Megan K.; Buckley, Thomas N.; McElrone, Andrew J.; Sack, Lawren

2017-01-01

Leaf hydraulic supply is crucial to maintaining open stomata for CO2 capture and plant growth. During drought-induced dehydration, the leaf hydraulic conductance (Kleaf) declines, which contributes to stomatal closure and, eventually, to leaf death. Previous studies have tended to attribute the decline of Kleaf to embolism in the leaf vein xylem. We visualized at high resolution and quantified experimentally the hydraulic vulnerability of xylem and outside-xylem pathways and modeled their respective influences on plant water transport. Evidence from all approaches indicated that the decline of Kleaf during dehydration arose first and foremost due to the vulnerability of outside-xylem tissues. In vivo x-ray microcomputed tomography of dehydrating leaves of four diverse angiosperm species showed that, at the turgor loss point, only small fractions of leaf vein xylem conduits were embolized, and substantial xylem embolism arose only under severe dehydration. Experiments on an expanded set of eight angiosperm species showed that outside-xylem hydraulic vulnerability explained 75% to 100% of Kleaf decline across the range of dehydration from mild water stress to beyond turgor loss point. Spatially explicit modeling of leaf water transport pointed to a role for reduced membrane conductivity consistent with published data for cells and tissues. Plant-scale modeling suggested that outside-xylem hydraulic vulnerability can protect the xylem from tensions that would induce embolism and disruption of water transport under mild to moderate soil and atmospheric droughts. These findings pinpoint outside-xylem tissues as a central locus for the control of leaf and plant water transport during progressive drought. PMID:28049739

Structures of Bordered Pits Potentially Contributing to Isolation of a Refilled Vessel from Negative Xylem Pressure in Stems of Morus australis Poir.: Testing of the Pit Membrane Osmosis and Pit Valve Hypotheses.

PubMed

Ooeda, Hiroki; Terashima, Ichiro; Taneda, Haruhiko

2017-02-01

Two hypotheses have been proposed to explain the mechanism preventing the refilling vessel water from being drained to the neighboring functional vessels under negative pressure. The pit membrane osmosis hypothesis proposes that the xylem parenchyma cells release polysaccharides that are impermeable to the intervessel pit membranes into the refilling vessel; this osmotically counteracts the negative pressure, thereby allowing the vessel to refill. The pit valve hypothesis proposes that gas trapped within intervessel bordered pits isolates the refilling vessel water from the surrounding functional vessels. Here, using the single-vessel method, we assessed these hypotheses in shoots of mulberry (Morus australis Poir.). First, we confirmed the occurrence of xylem refilling under negative pressure in the potted mulberry saplings. To examine the pit membrane osmosis hypothesis, we estimated the semi-permeability of pit membranes for molecules of various sizes and found that the pit membranes were not semi-permeable to polyethylene glycol of molecular mass <20,000. For the pit valve hypothesis, we formed pit valves in the intervessel pits in the short stem segments and measured the maximum liquid pressure up to which gases in bordered pits were retained. The threshold pressure ranged from 0.025 to 0.10 MPa. These values matched the theoretical value calculated from the geometry of the pit chamber (0.0692-0.101 MPa). Our results suggest that gas in the pits is retained by surface tension, even under substantial positive pressure to resolve gases in the refilling vessel, whereas the molecule size required for the pit membrane osmosis mechanism in mulberry would be unrealistically large. © The Author 2016. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.
Water Transport Properties of the Grape Pedicel during Fruit Development: Insights into Xylem Anatomy and Function Using Microtomography.

PubMed

Knipfer, Thorsten; Fei, Jiong; Gambetta, Gregory A; McElrone, Andrew J; Shackel, Kenneth A; Matthews, Mark A

2015-08-01

Xylem flow of water into fruits declines during fruit development, and the literature indicates a corresponding increase in hydraulic resistance in the pedicel. However, it is unknown how pedicel hydraulics change developmentally in relation to xylem anatomy and function. In this study on grape (Vitis vinifera), we determined pedicel hydraulic conductivity (kh) from pressure-flow relationships using hydrostatic and osmotic forces and investigated xylem anatomy and function using fluorescent light microscopy and x-ray computed microtomography. Hydrostatic kh (xylem pathway) was consistently 4 orders of magnitude greater than osmotic kh (intracellular pathway), but both declined before veraison by approximately 40% and substantially over fruit development. Hydrostatic kh declined most gradually for low (less than 0.08 MPa) pressures and for water inflow and outflow conditions. Specific kh (per xylem area) decreased in a similar fashion to kh despite substantial increases in xylem area. X-ray computed microtomography images provided direct evidence that losses in pedicel kh were associated with blockages in vessel elements, whereas air embolisms were negligible. However, vessel elements were interconnected and some remained continuous postveraison, suggesting that across the grape pedicel, a xylem pathway of reduced kh remains functional late into berry ripening. © 2015 American Society of Plant Biologists. All Rights Reserved.
Dynamics of leaf gas exchange, xylem and phloem transport, water potential and carbohydrate concentration in a realistic 3-D model tree crown.

PubMed

Nikinmaa, Eero; Sievänen, Risto; Hölttä, Teemu

2014-09-01

Tree models simulate productivity using general gas exchange responses and structural relationships, but they rarely check whether leaf gas exchange and resulting water and assimilate transport and driving pressure gradients remain within acceptable physical boundaries. This study presents an implementation of the cohesion-tension theory of xylem transport and the Münch hypothesis of phloem transport in a realistic 3-D tree structure and assesses the gas exchange and transport dynamics. A mechanistic model of xylem and phloem transport was used, together with a tested leaf assimilation and transpiration model in a realistic tree architecture to simulate leaf gas exchange and water and carbohydrate transport within an 8-year-old Scots pine tree. The model solved the dynamics of the amounts of water and sucrose solute in the xylem, cambium and phloem using a fine-grained mesh with a system of coupled ordinary differential equations. The simulations predicted the observed patterns of pressure gradients and sugar concentration. Diurnal variation of environmental conditions influenced tree-level gradients in turgor pressure and sugar concentration, which are important drivers of carbon allocation. The results and between-shoot variation were sensitive to structural and functional parameters such as tree-level scaling of conduit size and phloem unloading. Linking whole-tree-level water and assimilate transport, gas exchange and sink activity opens a new avenue for plant studies, as features that are difficult to measure can be studied dynamically with the model. Tree-level responses to local and external conditions can be tested, thus making the approach described here a good test-bench for studies of whole-tree physiology.
Accumulation of sugars in the xylem apoplast observed under water stress conditions is controlled by xylem pH.

PubMed

Secchi, Francesca; Zwieniecki, Maciej A

2016-11-01

Severe water stress constrains, or even stops, water transport in the xylem due to embolism formation. Previously, the xylem of poplar trees was shown to respond to embolism formation by accumulating carbohydrates in the xylem apoplast and dropping xylem sap pH. We hypothesize that these two processes may be functionally linked as lower pH activates acidic invertases degrading sucrose and inducing accumulation of monosaccharides in xylem apoplast. Using a novel in vivo method to measure xylem apoplast pH, we show that pH drops from ~6.2 to ~5.6 in stems of severely stressed plants and rises following recovery of stem water status. We also show that in a lower pH environment, sugars are continuously accumulating in the xylem apoplast. Apoplastic carbohydrate accumulation was reduced significantly in the presence of a proton pump blocker (orthovanadate). These observations suggest that a balance in sugar concentrations exists between the xylem apoplast and symplast that can be controlled by xylem pH and sugar concentration. We conclude that lower pH is related to loss of xylem transport function, eventually resulting in accumulation of sugars that primes stems for recovery from embolism when water stress is relieved. © 2016 John Wiley & Sons Ltd.
Water Transport Properties of the Grape Pedicel during Fruit Development: Insights into Xylem Anatomy and Function Using Microtomography1[OPEN

PubMed Central

Fei, Jiong; McElrone, Andrew J.; Shackel, Kenneth A.; Matthews, Mark A.

2015-01-01

Xylem flow of water into fruits declines during fruit development, and the literature indicates a corresponding increase in hydraulic resistance in the pedicel. However, it is unknown how pedicel hydraulics change developmentally in relation to xylem anatomy and function. In this study on grape (Vitis vinifera), we determined pedicel hydraulic conductivity (kh) from pressure-flow relationships using hydrostatic and osmotic forces and investigated xylem anatomy and function using fluorescent light microscopy and x-ray computed microtomography. Hydrostatic kh (xylem pathway) was consistently 4 orders of magnitude greater than osmotic kh (intracellular pathway), but both declined before veraison by approximately 40% and substantially over fruit development. Hydrostatic kh declined most gradually for low (less than 0.08 MPa) pressures and for water inflow and outflow conditions. Specific kh (per xylem area) decreased in a similar fashion to kh despite substantial increases in xylem area. X-ray computed microtomography images provided direct evidence that losses in pedicel kh were associated with blockages in vessel elements, whereas air embolisms were negligible. However, vessel elements were interconnected and some remained continuous postveraison, suggesting that across the grape pedicel, a xylem pathway of reduced kh remains functional late into berry ripening. PMID:26077763
Diurnal patterns in Scots pine stem oleoresin pressure in a boreal forest.

PubMed

Rissanen, K; Hölttä, T; Vanhatalo, A; Aalto, J; Nikinmaa, E; Rita, H; Bäck, J

2016-03-01

Coniferous tree stems contain large amounts of oleoresin under positive pressure in the resin ducts. Studies in North-American pines indicated that the stem oleoresin exudation pressure (OEP) correlates negatively with transpiration rate and soil water content. However, it is not known how the OEP changes affect the emissions of volatile vapours from the trees. We measured the OEP, xylem diameter changes indicating changes in xylem water potential and monoterpene emissions under field conditions in mature Scots pine (Pinus sylvestris L.) trees in southern Finland. Contrary to earlier reports, the diurnal OEP changes were positively correlated with temperature and transpiration rate. OEP was lowest at the top part of the stem, where water potentials were also more negative, and often closely linked to ambient temperature and stem monoterpene emissions. However, occasionally OEP was affected by sudden changes in vapour pressure deficit (VPD), indicating the importance of xylem water potential on OEP as well. We conclude that the oleoresin storage pools in tree stems are in a dynamic relationship with ambient temperature and xylem water potential, and that the canopy monoterpene emission rates may therefore be also regulated by whole tree processes and not only by the conditions prevailing in the upper canopy. © 2015 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.
Linking Xylem Hydraulic Conductivity and Vulnerability to the Leaf Economics Spectrum—A Cross-Species Study of 39 Evergreen and Deciduous Broadleaved Subtropical Tree Species

PubMed Central

Kröber, Wenzel; Zhang, Shouren; Ehmig, Merten; Bruelheide, Helge

2014-01-01

While the fundamental trade-off in leaf traits related to carbon capture as described by the leaf economics spectrum is well-established among plant species, the relationship of the leaf economics spectrum to stem hydraulics is much less known. Since carbon capture and transpiration are coupled, a close connection between leaf traits and stem hydraulics should be expected. We thus asked whether xylem traits that describe drought tolerance and vulnerability to cavitation are linked to particular leaf traits. We assessed xylem vulnerability, using the pressure sleeve technique, and anatomical xylem characteristics in 39 subtropical tree species grown under common garden conditions in the BEF-China experiment and tested for correlations with traits related to the leaf economics spectrum as well as to stomatal control, including maximum stomatal conductance, vapor pressure deficit at maximum stomatal conductance and vapor pressure deficit at which stomatal conductance is down-regulated. Our results revealed that specific xylem hydraulic conductivity and cavitation resistance were closely linked to traits represented in the leaf economic spectrum, in particular to leaf nitrogen concentration, as well as to log leaf area and leaf carbon to nitrogen ratio but not to any parameter of stomatal conductance. The study highlights the potential use of well-known leaf traits from the leaf economics spectrum to predict plant species' drought resistance. PMID:25423316
Linking xylem hydraulic conductivity and vulnerability to the leaf economics spectrum--a cross-species study of 39 evergreen and deciduous broadleaved subtropical tree species.

PubMed

Kröber, Wenzel; Zhang, Shouren; Ehmig, Merten; Bruelheide, Helge

2014-01-01

While the fundamental trade-off in leaf traits related to carbon capture as described by the leaf economics spectrum is well-established among plant species, the relationship of the leaf economics spectrum to stem hydraulics is much less known. Since carbon capture and transpiration are coupled, a close connection between leaf traits and stem hydraulics should be expected. We thus asked whether xylem traits that describe drought tolerance and vulnerability to cavitation are linked to particular leaf traits. We assessed xylem vulnerability, using the pressure sleeve technique, and anatomical xylem characteristics in 39 subtropical tree species grown under common garden conditions in the BEF-China experiment and tested for correlations with traits related to the leaf economics spectrum as well as to stomatal control, including maximum stomatal conductance, vapor pressure deficit at maximum stomatal conductance and vapor pressure deficit at which stomatal conductance is down-regulated. Our results revealed that specific xylem hydraulic conductivity and cavitation resistance were closely linked to traits represented in the leaf economic spectrum, in particular to leaf nitrogen concentration, as well as to log leaf area and leaf carbon to nitrogen ratio but not to any parameter of stomatal conductance. The study highlights the potential use of well-known leaf traits from the leaf economics spectrum to predict plant species' drought resistance.
Sugar demand of ripening grape berries leads to recycling of surplus phloem water via the xylem.

PubMed

Keller, Markus; Zhang, Yun; Shrestha, Pradeep M; Biondi, Marco; Bondada, Bhaskar R

2015-06-01

We tested the common assumption that fleshy fruits become dependent on phloem water supply because xylem inflow declines at the onset of ripening. Using two distinct grape genotypes exposed to drought stress, we found that a sink-driven rise in phloem inflow at the beginning of ripening was sufficient to reverse drought-induced berry shrinkage. Rewatering accelerated berry growth and sugar accumulation concurrently with leaf photosynthetic recovery. Interrupting phloem flow through the peduncle prevented the increase in berry growth after rewatering, but interrupting xylem flow did not. Nevertheless, xylem flow in ripening berries, but not berry size, remained responsive to root or shoot pressurization. A mass balance analysis on ripening berries sampled in the field suggested that phloem water inflow may exceed growth and transpiration water demands. Collecting apoplastic sap from ripening berries showed that osmotic pressure increased at distinct rates in berry vacuoles and apoplast. Our results indicate that the decrease in xylem inflow at the onset of ripening may be a consequence of the sink-driven increase in phloem inflow. We propose a conceptual model in which surplus phloem water bypasses the fruit cells and partly evaporates from the berry surface and partly moves apoplastically to the xylem for outflow. © 2014 John Wiley & Sons Ltd.
How reliable are methods to assess xylem vulnerability to cavitation? The issue of 'open vessel' artifact in oaks.

PubMed

Martin-StPaul, N K; Longepierre, D; Huc, R; Delzon, S; Burlett, R; Joffre, R; Rambal, S; Cochard, H

2014-08-01

Three methods are in widespread use to build vulnerability curves (VCs) to cavitation. The bench drying (BD) method is considered as a reference because embolism and xylem pressure are measured on large branches dehydrating in the air, in conditions similar to what happens in nature. Two other methods of embolism induction have been increasingly used. While the Cavitron (CA) uses centrifugal force to induce embolism, in the air injection (AI) method embolism is induced by forcing pressurized air to enter a stem segment. Recent studies have suggested that the AI and CA methods are inappropriate in long-vesselled species because they produce a very high-threshold xylem pressure for embolism (e.g., P50) compared with what is expected from (i) their ecophysiology in the field (native embolism, water potential and stomatal response to xylem pressure) and (ii) the P50 obtained with the BD method. However, other authors have argued that the CA and AI methods may be valid because they produce VCs similar to the BD method. In order to clarify this issue, we assessed VCs with the three above-mentioned methods on the long-vesselled Quercus ilex L. We showed that the BD VC yielded threshold xylem pressure for embolism consistent with in situ measurements of native embolism, minimal water potential and stomatal conductance. We therefore concluded that the BD method provides a reliable estimate of the VC for this species. The CA method produced a very high P50 (i.e., less negative) compared with the BD method, which is consistent with an artifact related to the vessel length. The VCs obtained with the AI method were highly variable, producing P50 ranging from -2 to -8.2 MPa. This wide variability was more related to differences in base diameter among samples than to differences in the length of samples. We concluded that this method is probably subject to an artifact linked to the distribution of vessel lengths within the sample. Overall, our results indicate that the CA
Recovery performance in xylem hydraulic conductivity is correlated with cavitation resistance for temperate deciduous tree species.

PubMed

Ogasa, Mayumi; Miki, Naoko H; Murakami, Yuki; Yoshikawa, Ken

2013-04-01

Woody species hydraulically vulnerable to xylem cavitation may experience daily xylem embolism. How such species cope with the possibility of accumulated embolism is unclear. In this study, we examined seven temperate woody species to assess the hypothesis that low cavitation resistance (high vulnerability to cavitation) is compensated by high recovery performance via vessel refilling. We also evaluated leaf functional and xylem structural traits. The xylem recovery index (XRI), defined as the ratio of xylem hydraulic conductivity in plants rewatered after soil drought to that in plants under moist conditions, varied among species. The xylem water potential causing 50% loss of hydraulic conductivity (Ψ50) varied among the species studied, whereas only a slight difference was detected with respect to midday xylem water potential (Ψmin), indicating smaller hydraulic safety margins (Ψmin - Ψ50) for species more vulnerable to cavitation. Cavitation resistance (|Ψ50|) was negatively correlated with XRI across species, with cavitation-vulnerable species showing a higher performance in xylem recovery. Wood density was positively correlated with cavitation resistance and was negatively correlated with XRI. These novel results reveal that coordination exists between cavitation resistance and xylem recovery performance, in association with wood functional traits such as denser wood for cavitation-resistant xylem and less-dense but water-storable wood for refillable xylem. These findings provide insights into long-term maintenance of water transport in tree species growing under variable environmental conditions.
Circadian patterns of xylem sap properties and their covariation with plant hydraulic traits in hybrid aspen.

PubMed

Meitern, Annika; Õunapuu-Pikas, Eele; Sellin, Arne

2017-06-01

Physiological processes taking place in plants are subject to diverse circadian patterns but some of them are poorly documented in natural conditions. The daily dynamics of physico-chemical properties of xylem sap and their covariation with tree hydraulic traits were investigated in hybrid aspen (Populus tremula L.×P. tremuloides Michx) in field conditions in order to clarify which environmental drivers govern the daily variation in these parameters. K + concentration ([K + ]), electrical conductivity (σ sap ), osmolality (Osm) and pH of the xylem sap, as well as branch hydraulic traits, were measured in the field over 24-h cycles. All studied xylem sap properties and hydraulic characteristics including whole-branch (K wb ), leaf blade (K lb ) and petiole hydraulic conductances (K P ) showed clear daily dynamics. Air temperature (T A ) and photosynthetic photon flux density (PPFD), but also water vapour pressure deficit (VPD) and relative humidity (RH), had significant impacts on K wb K lb , K P , [K + ] and σ sap . Osm varied only with light intensity, while K B varied depending on atmospheric evaporative demand expressed as T A , VPD or RH. Xylem sap pH depended inversely on soil water potential (Ψ S ) and during daylight also on VPD. Although soil water content was close to saturation during the study period, Ψ S influenced also [K + ] and σ sap . The present study presents evidence of coupling between circadian patterns of xylem sap properties and plant hydraulic conductance providing adequate water supply to foliage under environmental conditions characterised by diurnal variation. Copyright © 2017 Elsevier GmbH. All rights reserved.
Direct Demonstration of a Growth-Induced Water Potential Gradient.

PubMed

Nonami, H.; Boyer, J. S.

1993-05-01

When transpiration is negligible, water potentials in growing tissues are less than those in mature tissues and have been predicted to form gradients that move water into the enlarging cells. To determine directly whether the gradients exist, we measured water potentials along the radius of stems of intact soybean (Glycine max [L.] Merr.) seedlings growing in vermiculite in a water-saturated atmosphere. The measurements were made in individual cells by first determining the turgor with a miniature pressure probe, then determining the osmotic potential of solution from the same cell, and finally summing the two potentials. The osmotic potentials were corrected for sample mixing in the probe. The measurements were checked with a thermocouple psychrometer that gave average tissue water potentials. In the elongating region, the water potential was highest near the xylem and lowest near the epidermis and in the center of the pith. In the basal, more mature region of the same stems, water potentials were near zero next to the xylem and throughout the tissue. These basal potentials reflected mostly the potential of the xylem, which extended into the elongating tissues. Thus, the high basal potential confirmed the high potential near the xylem in the elongating tissues. The psychrometer measurements for each tissue gave average potentials that agreed with the average of the cell potentials from the pressure probe. We conclude that a radial gradient was present in the elongating region that formed a water potential field in three dimensions around the xylem and that confirmed the predictions of Molz and Boyer (F.J. Molz and J.S. Boyer [1978] Plant Physiol 62: 423-429).
Direct Demonstration of a Growth-Induced Water Potential Gradient.

PubMed Central

Nonami, H.; Boyer, J. S.

1993-01-01

When transpiration is negligible, water potentials in growing tissues are less than those in mature tissues and have been predicted to form gradients that move water into the enlarging cells. To determine directly whether the gradients exist, we measured water potentials along the radius of stems of intact soybean (Glycine max [L.] Merr.) seedlings growing in vermiculite in a water-saturated atmosphere. The measurements were made in individual cells by first determining the turgor with a miniature pressure probe, then determining the osmotic potential of solution from the same cell, and finally summing the two potentials. The osmotic potentials were corrected for sample mixing in the probe. The measurements were checked with a thermocouple psychrometer that gave average tissue water potentials. In the elongating region, the water potential was highest near the xylem and lowest near the epidermis and in the center of the pith. In the basal, more mature region of the same stems, water potentials were near zero next to the xylem and throughout the tissue. These basal potentials reflected mostly the potential of the xylem, which extended into the elongating tissues. Thus, the high basal potential confirmed the high potential near the xylem in the elongating tissues. The psychrometer measurements for each tissue gave average potentials that agreed with the average of the cell potentials from the pressure probe. We conclude that a radial gradient was present in the elongating region that formed a water potential field in three dimensions around the xylem and that confirmed the predictions of Molz and Boyer (F.J. Molz and J.S. Boyer [1978] Plant Physiol 62: 423-429). PMID:12231794
Sugars from woody tissue photosynthesis reduce xylem vulnerability to cavitation.

PubMed

De Baerdemaeker, Niels J F; Salomón, Roberto Luis; De Roo, Linus; Steppe, Kathy

2017-11-01

Reassimilation of internal CO 2 via woody tissue photosynthesis has a substantial effect on tree carbon income and wood production. However, little is known about its role in xylem vulnerability to cavitation and its implications in drought-driven tree mortality. Young trees of Populus nigra were subjected to light exclusion at the branch and stem levels. After 40 d, measurements of xylem water potential, diameter variation and acoustic emission (AE) were performed in detached branches to obtain acoustic vulnerability curves to cavitation following bench-top dehydration. Acoustic vulnerability curves and derived AE 50 values (i.e. water potential at which 50% of cavitation-related acoustic emissions occur) differed significantly between light-excluded and control branches (AE 50,light-excluded = -1.00 ± 0.13 MPa; AE 50,control = -1.45 ± 0.09 MPa; P = 0.007) denoting higher vulnerability to cavitation in light-excluded trees. Woody tissue photosynthesis represents an alternative and immediate source of nonstructural carbohydrates (NSC) that confers lower xylem vulnerability to cavitation via sugar-mediated mechanisms. Embolism repair and xylem structural changes could not explain this observation as the amount of cumulative AE and basic wood density did not differ between treatments. We suggest that woody tissue assimilates might play a role in the synthesis of xylem surfactants for nanobubble stabilization under tension. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.
Embolism spread in the primary xylem of Polystichum munitum: implications for water transport during seasonal drought.

PubMed

Brodersen, Craig R; Rico, Christopher; Guenni, Orlando; Pittermann, Jarmila

2016-02-01

Xylem network structure and function have been characterized for many woody plants, but less is known about fern xylem, particularly in species endemic to climates where water is a limiting resource for months at a time. We characterized seasonal variability in soil moisture and frond water status in a common perennial fern in the redwood understory of a costal California, and then investigated the consequences of drought-induced embolism on vascular function. Seasonal variability in air temperature and soil water content was minimal, and frond water potential declined slowly over the observational period. Our data show that Polystichum munitum was protected from significant drought-induced hydraulic dysfunction during this growing season because of a combination of cavitation resistant conduits (Air-seeding threshold (ASP) = -1.53 MPa; xylem pressure inducing 50% loss of hydraulic conductivity (P50 ) = -3.02 MPa) and a soil with low moisture variability. High resolution micro-computed tomography (MicroCT) imaging revealed patterns of embolism formation in vivo for the first time in ferns providing insight into the functional status of the xylem network under drought conditions. Together with stomatal conductance measurements, these data suggest that P. munitum is adapted to tolerate drier conditions than what was observed during the growing season. © 2015 John Wiley & Sons Ltd.
Scaling of xylem and phloem transport capacity and resource usage with tree size

PubMed Central

Hölttä, Teemu; Kurppa, Miika; Nikinmaa, Eero

2013-01-01

Xylem and phloem need to maintain steady transport rates of water and carbohydrates to match the exchange rates of these compounds at the leaves. A major proportion of the carbon and nitrogen assimilated by a tree is allocated to the construction and maintenance of the xylem and phloem long distance transport tissues. This proportion can be expected to increase with increasing tree size due to the growing transport distances between the assimilating tissues, i.e., leaves and fine roots, at the expense of their growth. We formulated whole tree level scaling relations to estimate how xylem and phloem volume, nitrogen content and hydraulic conductance scale with tree size, and how these properties are distributed along a tree height. Xylem and phloem thicknesses and nitrogen contents were measured within varying positions in four tree species from Southern Finland. Phloem volume, nitrogen amount and hydraulic conductance were found to be concentrated toward the branch and stem apices, in contrast to the xylem where these properties were more concentrated toward the tree base. All of the species under study demonstrated very similar trends. Total nitrogen amount allocated to xylem and phloem was predicted to be comparable to the nitrogen amount allocated to the leaves in small and medium size trees, and to increase significantly above the nitrogen content of the leaves in larger trees. Total volume, hydraulic conductance and nitrogen content of the xylem were predicted to increase faster than that of the phloem with increasing tree height in small trees (<~10 m in height). In larger trees, xylem sapwood turnover to heartwood, if present, would maintain phloem conductance at the same level with xylem conductance with further increases in tree height. Further simulations with a previously published xylem-phloem transport model demonstrated that the Münch pressure flow hypothesis could explain phloem transport with increasing tree height even for the tallest trees. PMID
Water potential gradient in a tall sequoiadendron.

PubMed

Tobiessen, P

1971-09-01

With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about -0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees.
Water Potential Gradient in a Tall Sequoiadendron

PubMed Central

Tobiessen, Peter; Rundel, Philip W.; Stecker, R. E.

1971-01-01

With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about −0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees. PMID:16657786
Xylem vulnerability to cavitation can be accurately characterised in species with long vessels using a centrifuge method.

PubMed

Tobin, M F; Pratt, R B; Jacobsen, A L; De Guzman, M E

2013-05-01

Vulnerability to cavitation curves describe the decrease in xylem hydraulic conductivity as xylem pressure declines. Several techniques for constructing vulnerability curves use centrifugal force to induce negative xylem pressure in stem or root segments. Centrifuge vulnerability curves constructed for long-vesselled species have been hypothesised to overestimate xylem vulnerability to cavitation due to increased vulnerability of vessels cut open at stem ends that extend to the middle or entirely through segments. We tested two key predictions of this hypothesis: (i) centrifugation induces greater embolism than dehydration in long-vesselled species, and (ii) the proportion of open vessels changes centrifuge vulnerability curves. Centrifuge and dehydration vulnerability curves were compared for a long- and short-vesselled species. The effect of open vessels was tested in four species by comparing centrifuge vulnerability curves for stems of two lengths. Centrifuge and dehydration vulnerability curves agreed well for the long- and short-vesselled species. Centrifuge vulnerability curves constructed using two stem lengths were similar. Also, the distribution of embolism along the length of centrifuged stems matched the theoretical pressure profile induced by centrifugation. We conclude that vulnerability to cavitation can be accurately characterised with vulnerability curves constructed using a centrifuge technique, even in long-vesselled species. © 2012 German Botanical Society and The Royal Botanical Society of the Netherlands.

Vascular defense responses in rice: peroxidase accumulation in xylem parenchyma cells and xylem wall thickening

NASA Technical Reports Server (NTRS)

Hilaire, E.; Young, S. A.; Willard, L. H.; McGee, J. D.; Sweat, T.; Chittoor, J. M.; Guikema, J. A.; Leach, J. E.

2001-01-01

The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae is a vascular pathogen that elicits a defensive response through interaction with metabolically active rice cells. In leaves of 12-day-old rice seedlings, the exposed pit membrane separating the xylem lumen from the associated parenchyma cells allows contact with bacterial cells. During resistant responses, the xylem secondary walls thicken within 48 h and the pit diameter decreases, effectively reducing the area of pit membrane exposed for access by bacteria. In susceptible interactions and mock-inoculated controls, the xylem walls do not thicken within 48 h. Xylem secondary wall thickening is developmental and, in untreated 65-day-old rice plants, the size of the pit also is reduced. Activity and accumulation of a secreted cationic peroxidase, PO-C1, were previously shown to increase in xylem vessel walls and lumen. Peptide-specific antibodies and immunogold-labeling were used to demonstrate that PO-C1 is produced in the xylem parenchyma and secreted to the xylem lumen and walls. The timing of the accumulation is consistent with vessel secondary wall thickening. The PO-C1 gene is distinct but shares a high level of similarity with previously cloned pathogen-induced peroxidases in rice. PO-C1 gene expression was induced as early as 12 h during resistant interactions and peaked between 18 and 24 h after inoculation. Expression during susceptible interactions was lower than that observed in resistant interactions and was undetectable after infiltration with water, after mechanical wounding, or in mature leaves. These data are consistent with a role for vessel secondary wall thickening and peroxidase PO-C1 accumulation in the defense response in rice to X. oryzae pv. oryzae.
Sequential depolarization of root cortical and stelar cells induced by an acute salt shock - implications for Na(+) and K(+) transport into xylem vessels.

PubMed

Wegner, Lars H; Stefano, Giovanni; Shabala, Lana; Rossi, Marika; Mancuso, Stefano; Shabala, Sergey

2011-05-01

Early events in NaCl-induced root ion and water transport were investigated in maize (Zea mays L) roots using a range of microelectrode and imaging techniques. Addition of 100 mm NaCl to the bath resulted in an exponential drop in root xylem pressure, rapid depolarization of trans-root potential and a transient drop in xylem K(+) activity (A(K+) ) within ∼1 min after stress onset. At this time, no detectable amounts of Na(+) were released into the xylem vessels. The observed drop in A(K+) was unexpected, given the fact that application of the physiologically relevant concentrations of Na(+) to isolated stele has caused rapid plasma membrane depolarization and a subsequent K(+) efflux from the stelar tissues. This controversy was explained by the difference in kinetics of NaCl-induced depolarization between cortical and stelar cells. As root cortical cells are first to be depolarized and lose K(+) to the environment, this is associated with some K(+) shift from the stelar symplast to the cortex, resulting in K(+) being transiently removed from the xylem. Once Na(+) is loaded into the xylem (between 1 and 5 min of root exposure to NaCl), stelar cells become more depolarized, and a gradual recovery in A(K+) occurs. © 2011 Blackwell Publishing Ltd.
Scaling of angiosperm xylem structure with safety and efficiency.

PubMed

Hacke, Uwe G; Sperry, John S; Wheeler, James K; Castro, Laura

2006-06-01

We tested the hypothesis that greater cavitation resistance correlates with less total inter-vessel pit area per vessel (the pit area hypothesis) and evaluated a trade-off between cavitation safety and transport efficiency. Fourteen species of diverse growth form (vine, ring- and diffuse-porous tree, shrub) and family affinity were added to published data predominately from the Rosaceae (29 species total). Two types of vulnerability-to-cavitation curves were found. Ring-porous trees and vines showed an abrupt drop in hydraulic conductivity with increasing negative pressure, whereas hydraulic conductivity in diffuse-porous species generally decreased gradually. The ring-porous type curve was not an artifact of the centrifuge method because it was obtained also with the air-injection technique. A safety versus efficiency trade-off was evident when curves were compared across species: for a given pressure, there was a limited range of optimal vulnerability curves. The pit area hypothesis was supported by a strong relationship (r2 = 0.77) between increasing cavitation resistance and diminishing pit membrane area per vessel (A(P)). Small A(P) was associated with small vessel surface area and hence narrow vessel diameter (D) and short vessel length (L)--consistent with an increase in vessel flow resistance with cavitation resistance. This trade-off was amplified at the tissue level by an increase in xylem/vessel area ratio with cavitation resistance. Ring-porous species were more efficient than diffuse-porous species on a vessel basis but not on a xylem basis owing to higher xylem/vessel area ratios in ring-porous anatomy. Across four orders of magnitude, lumen and end-wall resistivities maintained a relatively tight proportionality with a near-optimal mean of 56% of the total vessel resistivity residing in the end-wall. This was consistent with an underlying scaling of L to D(3/2) across species. Pit flow resistance did not increase with cavitation safety, suggesting
Tolerance to oxidative stress is required for maximal xylem colonization by the xylem-limited bacterial phytopathogen, Xylella fastidiosa.

PubMed

Wang, Peng; Lee, Yunho; Igo, Michele M; Roper, M Caroline

2017-09-01

Bacterial plant pathogens often encounter reactive oxygen species (ROS) during host invasion. In foliar bacterial pathogens, multiple regulatory proteins are involved in the sensing of oxidative stress and the activation of the expression of antioxidant genes. However, it is unclear whether xylem-limited bacteria, such as Xylella fastidiosa, experience oxidative stress during the colonization of plants. Examination of the X. fastidiosa genome uncovered only one homologue of oxidative stress regulatory proteins, OxyR. Here, a knockout mutation in the X. fastidiosa oxyR gene was constructed; the resulting strain was significantly more sensitive to hydrogen peroxide (H 2 O 2 ) relative to the wild-type. In addition, during early stages of grapevine infection, the survival rate was 1000-fold lower for the oxyR mutant than for the wild-type. This supports the hypothesis that grapevine xylem represents an oxidative environment and that X. fastidiosa must overcome this challenge to achieve maximal xylem colonization. Finally, the oxyR mutant exhibited reduced surface attachment and cell-cell aggregation and was defective in biofilm maturation, suggesting that ROS could be a potential environmental cue stimulating biofilm development during the early stages of host colonization. © 2016 BSPP AND JOHN WILEY & SONS LTD.
Is desiccation tolerance and avoidance reflected in xylem and phloem anatomy of two co-existing arid-zone coniferous trees?: Xylem and Phloem Anatomy

DOE PAGES

Sevanto, Sanna Annika; Ryan, Max; Turin Dickman, L.; ...

2018-03-22

Plants close their stomata during drought to avoid excessive water loss, but species differ in respect to the drought severity at which stomata close. The stomatal closure point is related to xylem anatomy and vulnerability to embolism, but it also has implications for phloem transport, and possibly phloem anatomy to allow sugar transport at low water potentials. Desiccation tolerant plants that close their stomata at severe drought should have smaller xylem conduits and/or fewer and smaller inter-conduit pits to reduce vulnerability to embolism, but more phloem tissue and larger phloem conduits compared to plants that avoid desiccation. These anatomical differencesmore » could be expected to increase in response to long-term reduction in precipitation. To test these hypotheses we used tridimensional synchroton X-ray microtomograph and light microscope imaging of combined xylem and phloem tissues of two coniferous species: one-seed juniper (Juniperus monosperma) and piñon pine (Pinus edulis) subjected to precipitation manipulation treatments. These species show different xylem vulnerability to embolism, contrasting desiccation tolerance, and stomatal closure points. Our results support the hypothesis that desiccation tolerant plants require higher phloem transport capacity than desiccation avoiding plants, but this can be gained through various anatomical adaptations in addition to changing conduit or tissue size.« less
Is desiccation tolerance and avoidance reflected in xylem and phloem anatomy of two co-existing arid-zone coniferous trees?: Xylem and Phloem Anatomy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sevanto, Sanna Annika; Ryan, Max; Turin Dickman, L.

Plants close their stomata during drought to avoid excessive water loss, but species differ in respect to the drought severity at which stomata close. The stomatal closure point is related to xylem anatomy and vulnerability to embolism, but it also has implications for phloem transport, and possibly phloem anatomy to allow sugar transport at low water potentials. Desiccation tolerant plants that close their stomata at severe drought should have smaller xylem conduits and/or fewer and smaller inter-conduit pits to reduce vulnerability to embolism, but more phloem tissue and larger phloem conduits compared to plants that avoid desiccation. These anatomical differencesmore » could be expected to increase in response to long-term reduction in precipitation. To test these hypotheses we used tridimensional synchroton X-ray microtomograph and light microscope imaging of combined xylem and phloem tissues of two coniferous species: one-seed juniper (Juniperus monosperma) and piñon pine (Pinus edulis) subjected to precipitation manipulation treatments. These species show different xylem vulnerability to embolism, contrasting desiccation tolerance, and stomatal closure points. Our results support the hypothesis that desiccation tolerant plants require higher phloem transport capacity than desiccation avoiding plants, but this can be gained through various anatomical adaptations in addition to changing conduit or tissue size.« less
Comparative genomics reveals conservative evolution of the xylem transcriptome in vascular plants.

PubMed

Li, Xinguo; Wu, Harry X; Southerton, Simon G

2010-06-21

Wood is a valuable natural resource and a major carbon sink. Wood formation is an important developmental process in vascular plants which played a crucial role in plant evolution. Although genes involved in xylem formation have been investigated, the molecular mechanisms of xylem evolution are not well understood. We use comparative genomics to examine evolution of the xylem transcriptome to gain insights into xylem evolution. The xylem transcriptome is highly conserved in conifers, but considerably divergent in angiosperms. The functional domains of genes in the xylem transcriptome are moderately to highly conserved in vascular plants, suggesting the existence of a common ancestral xylem transcriptome. Compared to the total transcriptome derived from a range of tissues, the xylem transcriptome is relatively conserved in vascular plants. Of the xylem transcriptome, cell wall genes, ancestral xylem genes, known proteins and transcription factors are relatively more conserved in vascular plants. A total of 527 putative xylem orthologs were identified, which are unevenly distributed across the Arabidopsis chromosomes with eight hot spots observed. Phylogenetic analysis revealed that evolution of the xylem transcriptome has paralleled plant evolution. We also identified 274 conifer-specific xylem unigenes, all of which are of unknown function. These xylem orthologs and conifer-specific unigenes are likely to have played a crucial role in xylem evolution. Conifers have highly conserved xylem transcriptomes, while angiosperm xylem transcriptomes are relatively diversified. Vascular plants share a common ancestral xylem transcriptome. The xylem transcriptomes of vascular plants are more conserved than the total transcriptomes. Evolution of the xylem transcriptome has largely followed the trend of plant evolution.
A closed-form solution for steady-state coupled phloem/xylem flow using the Lambert-W function.

PubMed

Hall, A J; Minchin, P E H

2013-12-01

A closed-form solution for steady-state coupled phloem/xylem flow is presented. This incorporates the basic Münch flow model of phloem transport, the cohesion model of xylem flow, and local variation in the xylem water potential and lateral water flow along the transport pathway. Use of the Lambert-W function allows this solution to be obtained under much more general and realistic conditions than has previously been possible. Variation in phloem resistance (i.e. viscosity) with solute concentration, and deviations from the Van't Hoff expression for osmotic potential are included. It is shown that the model predictions match those of the equilibrium solution of a numerical time-dependent model based upon the same mechanistic assumptions. The effect of xylem flow upon phloem flow can readily be calculated, which has not been possible in any previous analytical model. It is also shown how this new analytical solution can handle multiple sources and sinks within a complex architecture, and can describe competition between sinks. The model provides new insights into Münch flow by explicitly including interactions with xylem flow and water potential in the closed-form solution, and is expected to be useful as a component part of larger numerical models of entire plants. © 2013 John Wiley & Sons Ltd.
Phloem as Capacitor: Radial Transfer of Water into Xylem of Tree Stems Occurs via Symplastic Transport in Ray Parenchyma[OPEN

PubMed Central

Renard, Justine; Tjoelker, Mark G.; Salih, Anya

2015-01-01

The transfer of water from phloem into xylem is thought to mitigate increasing hydraulic tension in the vascular system of trees during the diel cycle of transpiration. Although a putative plant function, to date there is no direct evidence of such water transfer or the contributing pathways. Here, we trace the radial flow of water from the phloem into the xylem and investigate its diel variation. Introducing a fluorescent dye (0.1% [w/w] fluorescein) into the phloem water of the tree species Eucalyptus saligna allowed localization of the dye in phloem and xylem tissues using confocal laser scanning microscopy. Our results show that the majority of water transferred between the two tissues is facilitated via the symplast of horizontal ray parenchyma cells. The method also permitted assessment of the radial transfer of water during the diel cycle, where changes in water potential gradients between phloem and xylem determine the extent and direction of radial transfer. When injected during the morning, when xylem water potential rapidly declined, fluorescein was translocated, on average, farther into mature xylem (447 ± 188 µm) compared with nighttime, when xylem water potential was close to zero (155 ± 42 µm). These findings provide empirical evidence to support theoretical predictions of the role of phloem-xylem water transfer in the hydraulic functioning of plants. This method enables investigation of the role of phloem tissue as a dynamic capacitor for water storage and transfer and its contribution toward the maintenance of the functional integrity of xylem in trees. PMID:25588734
Comparative genomics reveals conservative evolution of the xylem transcriptome in vascular plants

PubMed Central

2010-01-01

Background Wood is a valuable natural resource and a major carbon sink. Wood formation is an important developmental process in vascular plants which played a crucial role in plant evolution. Although genes involved in xylem formation have been investigated, the molecular mechanisms of xylem evolution are not well understood. We use comparative genomics to examine evolution of the xylem transcriptome to gain insights into xylem evolution. Results The xylem transcriptome is highly conserved in conifers, but considerably divergent in angiosperms. The functional domains of genes in the xylem transcriptome are moderately to highly conserved in vascular plants, suggesting the existence of a common ancestral xylem transcriptome. Compared to the total transcriptome derived from a range of tissues, the xylem transcriptome is relatively conserved in vascular plants. Of the xylem transcriptome, cell wall genes, ancestral xylem genes, known proteins and transcription factors are relatively more conserved in vascular plants. A total of 527 putative xylem orthologs were identified, which are unevenly distributed across the Arabidopsis chromosomes with eight hot spots observed. Phylogenetic analysis revealed that evolution of the xylem transcriptome has paralleled plant evolution. We also identified 274 conifer-specific xylem unigenes, all of which are of unknown function. These xylem orthologs and conifer-specific unigenes are likely to have played a crucial role in xylem evolution. Conclusions Conifers have highly conserved xylem transcriptomes, while angiosperm xylem transcriptomes are relatively diversified. Vascular plants share a common ancestral xylem transcriptome. The xylem transcriptomes of vascular plants are more conserved than the total transcriptomes. Evolution of the xylem transcriptome has largely followed the trend of plant evolution. PMID:20565927
Nitrogen recycling from the xylem in rice leaves: dependence upon metabolism and associated changes in xylem hydraulics

PubMed Central

Bailey, Karen J.

2016-01-01

Measurements of amino acids in the guttation fluid and in the xylem exudates of cut leaves from intact plants provide evidence of the remarkable efficiency with which these nitrogenous compounds are reabsorbed from the xylem sap. This could be achieved by mechanisms involving intercellular transport and/or metabolism. Developmental changes in transcripts and protein showed that transcripts for phosphoenolpyruvate carboxykinase (PEPCK) increased from the base to the leaf tip, and were markedly increased by supplying asparagine. Supplying amino acids also increased the amounts of protein of PEPCK and, to a lesser extent, of pyruvate, Pi dikinase. PEPCK is present in the hydathodes, stomata and vascular parenchyma of rice leaves. Evidence for the role of PEPCK was obtained by using 3-mercaptopicolinic acid (MPA), a specific inhibitor of PEPCK, and by using an activation-tagged rice line that had an increase in PEPCK activity, to show that activation of PEPCK resulted in a decrease in N in the guttation fluid and that treatment by MPA resulted in an increase in amino acids in the guttation fluid and xylem sap towards the leaf tip. Furthermore, increasing PEPCK activity decreased the amount of guttation fluid, whereas decreasing PEPCK activity increased the amount of xylem sap or guttation fluid towards the leaf tip. The findings suggest the following hypotheses: (i) both metabolism and transport are involved in xylem recycling and (ii) excess N is the signal involved in modulating xylem hydraulics, perhaps via nutrient regulation of water-transporting aquaporins. Water relations and vascular metabolism and transport are thus intimately linked. PMID:27053722
Water transport through tall trees: A vertically-explicit, analytical model of xylem hydraulic conductance in stems.

PubMed

Couvreur, Valentin; Ledder, Glenn; Manzoni, Stefano; Way, Danielle A; Muller, Erik B; Russo, Sabrina E

2018-05-08

Trees grow by vertically extending their stems, so accurate stem hydraulic models are fundamental to understanding the hydraulic challenges faced by tall trees. Using a literature survey, we showed that many tree species exhibit continuous vertical variation in hydraulic traits. To examine the effects of this variation on hydraulic function, we developed a spatially-explicit, analytical water transport model for stems. Our model allows Huber ratio, stem-saturated conductivity, pressure at 50% loss of conductivity, leaf area, and transpiration rate to vary continuously along the hydraulic path. Predictions from our model differ from a matric flux potential model parameterized with uniform traits. Analyses show that cavitation is a whole-stem emergent property resulting from nonlinear pressure-conductivity feedbacks that, with gravity, cause impaired water transport to accumulate along the path. Because of the compounding effects of vertical trait variation on hydraulic function, growing proportionally more sapwood and building tapered xylem with height, as well as reducing xylem vulnerability only at branch tips while maintaining transport capacity at the stem base, can compensate for these effects. We therefore conclude that the adaptive significance of vertical variation in stem hydraulic traits is to allow trees to grow tall and tolerate operating near their hydraulic limits. This article is protected by copyright. All rights reserved.
Nitrogen recycling from the xylem in rice leaves: dependence upon metabolism and associated changes in xylem hydraulics.

PubMed

Bailey, Karen J; Leegood, Richard C

2016-04-01

Measurements of amino acids in the guttation fluid and in the xylem exudates of cut leaves from intact plants provide evidence of the remarkable efficiency with which these nitrogenous compounds are reabsorbed from the xylem sap. This could be achieved by mechanisms involving intercellular transport and/or metabolism. Developmental changes in transcripts and protein showed that transcripts for phosphoenolpyruvate carboxykinase (PEPCK) increased from the base to the leaf tip, and were markedly increased by supplying asparagine. Supplying amino acids also increased the amounts of protein of PEPCK and, to a lesser extent, of pyruvate, Pi dikinase. PEPCK is present in the hydathodes, stomata and vascular parenchyma of rice leaves. Evidence for the role of PEPCK was obtained by using 3-mercaptopicolinic acid (MPA), a specific inhibitor of PEPCK, and by using an activation-tagged rice line that had an increase in PEPCK activity, to show that activation of PEPCK resulted in a decrease in N in the guttation fluid and that treatment by MPA resulted in an increase in amino acids in the guttation fluid and xylem sap towards the leaf tip. Furthermore, increasing PEPCK activity decreased the amount of guttation fluid, whereas decreasing PEPCK activity increased the amount of xylem sap or guttation fluid towards the leaf tip. The findings suggest the following hypotheses: (i) both metabolism and transport are involved in xylem recycling and (ii) excess N is the signal involved in modulating xylem hydraulics, perhaps via nutrient regulation of water-transporting aquaporins. Water relations and vascular metabolism and transport are thus intimately linked. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.
Xylem vulnerability curves of canopy branches of mature trees from Caxiuana and Tapajos National Forests, Para, Brazil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powell, Thomas; Moorcroft, Paul

Raw data for xylem vulnerability curves measured on upper canopy branches of mature trees from the Caxiuana and Tapajos National Forests, Para, Brazil. Tapajos samples were harvested from km67 transects, which is nearby the decommissioned throughfall-exclusion, drought-experiment plots. Caxiuana samples were harvested from trees growing in the throughfall-exclusion, drought-experiment plots. Data were collected in 2011 and 2012. Dataset includes: date of measurement, site ID, plot ID, tree ID (species, tree tag #), xylem pressure, percent loss of conductivity. Air injection method was used. Data reference: Powell et al. (2017) Differences in xylem cavitation resistance and leaf hydraulic traits explain differencesmore » in drought tolerance among mature Amazon rainforest trees. Global Change Biology.« less
Loss of water transport capacity due to xylem cavitation in roots of two CAM succulents.

PubMed

Linton, M J; Nobel, P S

1999-11-01

Loss of axial hydraulic conductance as a result of xylem cavitation was examined for roots of the Crassulacean acid metabolism (CAM) succulents Agave deserti and Opuntia ficus-indica. Vulnerability to cavitation was not correlated with either root size or vessel diameter. Agave deserti had a mean cavitation pressure of -0.93 ± 0.08 MPa by both an air-injection and a centrifugal method compared to -0.70 ± 0.02 MPa by the centrifugal method for O. ficus-indica, reflecting the greater tolerance of the former species to low water potentials in its native habitat. Substantial xylem cavitation would occur at a soil water potential of -0.25 MPa, resulting in a predicted 22% loss of conductance for A. deserti and 32% for O. ficus-indica. For an extended drought of 3 mo, further cavitation could cause a 69% loss of conductance for A. deserti and 62% for O. ficus-indica. A model of axial hydraulic flow based upon the cavitation response of these species predicted that water uptake rates are far below the maximum possible, owing to the high root water potentials of these desert succulents. Despite various shoot adaptations to aridity, roots of A. deserti and O. ficus-indica are highly vulnerable to cavitation, which partially limits water uptake in a wet soil but helps reduce water loss to a drying soil.
Modified water regimes affect photosynthesis, xylem water potential, cambial growth and resistance of juvenile Pinus taeda L. to Dendroctonus frontalis (Coleoptera: Scolytidae)

Treesearch

James P. Dunn; Peter L. Jr. Lorio

1993-01-01

We modified soil water supply to two groups of juvenile loblolly pines, Pinus taeda L., by sheltering or irrigating root systems in early summer or in later summer and measured oleoresin flow (primary defense), net photosynthesis, xylem water potential, and cambial growth throughout the growing season. When consistent significant differences in...
Maximum sustainable xylem sap tensions in Rhododendron and other species.

PubMed

Crombie, D S; Milburn, J A; Hipkins, M F

1985-01-01

The acoustic technique was used in conjunction with the pressure chamber to determine the tensions causing cavitation of xylem sap in leaves of five woody angiosperms (Acer pseudoplatanus L., Alnus glutinosa L. Gaertn., Eucalyptus globulus Labill., Fraxinus excelsior L. and Rhododendron ponticum L.) and three species of herbs (Lycopersicum esculentum Mill., Plantago major L. and Ricinus communis L.). The results showed leaves of most species to suffer considerably from cavitation at sap tensions of 1.6-3 MPa. Two of the herbs, Lycopersicum and Ricinus, cavitated extensively at sap tensions below 1 MPa. Additional evidence is presented that clicks, detected by acoustic amplification, are caused by cavitation of sap in the xylem conduits. A rapid method is suggested for the determination of sap tensions in cavitating leaves and which is suitable for surveys of the critical sap tension in a large number of species.
Identity and Behavior of Xylem-Residing Bacteria in Rough Lemon Roots of Florida Citrus Trees †

PubMed Central

Gardner, John M.; Feldman, Albert W.; Zablotowicz, Robert M.

1982-01-01

An aseptic vacuum extraction technique was used to obtain xylem fluid from the roots of rough lemon (Citrus jambhiri Lush.) rootstock of Florida citrus trees. Bacteria were consistently isolated from vascular fluid of both healthy and young tree decline-affected trees. Thirteen genera of bacteria were found, the most frequently occurring genera being Pseudomonas (40%), Enterobacter (18%), Bacillus, Corynebacterium, and other gram-positive bacteria (16%), and Serratia (6%). Xylem bacterial counts fluctuated seasonally. Bacterial populations ranged from 0.1 to 22 per mm3 of root tissue (about 102 to 2 × 104 bacteria per g of xylem) when bacterial counts were made on vascular fluid, but these numbers were 10- to 1,000-fold greater when aseptically homogenized xylem tissue was examined similarly. Some of the resident bacteria (4%) are potentially phytopathogenic. It is proposed that xylem bacteria have an important role in the physiology of citrus. PMID:16346030
Xylem structure of four grape varieties and 12 alternative hosts to the xylem-limited bacterium Xylella fastidious

PubMed Central

Chatelet, David S.; Wistrom, Christina M.; Purcell, Alexander H.; Rost, Thomas L.; Matthews, Mark A.

2011-01-01

Background and Aims The bacterium Xylella fastidiosa (Xf), responsible for Pierce's disease (PD) of grapevine, colonizes the xylem conduits of vines, ultimately killing the plant. However, Vitis vinifera grapevine varieties differ in their susceptibility to Xf and numerous other plant species tolerate Xf populations without showing symptoms. The aim of this study was to examine the xylem structure of grapevines with different susceptibilities to Xf infection, as well as the xylem structure of non-grape plant species that support or limit movement of Xf to determine if anatomical differences might explain some of the differences in susceptibility to Xf. Methods Air and paint were introduced into leaves and stems to examine the connectivity between stem and leaves and the length distribution of their vessels. Leaf petiole and stem anatomies were studied to determine the basis for the free or restricted movement of Xf into the plant. Key Results There were no obvious differences in stem or petiole vascular anatomy among the grape varieties examined, nor among the other plant species that would explain differences in resistance to Xf. Among grape varieties, the more tolerant ‘Sylvaner’ had smaller stem vessel diameters and 20 % more parenchyma rays than the other three varieties. Alternative hosts supporting Xf movement had slightly longer open xylem conduits within leaves, and more connection between stem and leaves, when compared with alternative hosts that limit Xf movement. Conclusions Stem–leaf connectivity via open xylem conduits and vessel length is not responsible for differences in PD tolerance among grape varieties, or for limiting bacterial movement in the tolerant plant species. However, it was found that tolerant host plants had narrower vessels and more parenchyma rays, possibly restricting bacterial movement at the level of the vessels. The implications of xylem structure and connectivity for the means and regulation of bacterial movement are
Differences in xylem and leaf hydraulic traits explain differences in drought tolerance among mature Amazon rainforest trees.

PubMed

Powell, Thomas L; Wheeler, James K; de Oliveira, Alex A R; da Costa, Antonio Carlos Lola; Saleska, Scott R; Meir, Patrick; Moorcroft, Paul R

2017-10-01

Considerable uncertainty surrounds the impacts of anthropogenic climate change on the composition and structure of Amazon forests. Building upon results from two large-scale ecosystem drought experiments in the eastern Brazilian Amazon that observed increases in mortality rates among some tree species but not others, in this study we investigate the physiological traits underpinning these differential demographic responses. Xylem pressure at 50% conductivity (xylem-P 50 ), leaf turgor loss point (TLP), cellular osmotic potential (π o ), and cellular bulk modulus of elasticity (ε), all traits mechanistically linked to drought tolerance, were measured on upper canopy branches and leaves of mature trees from selected species growing at the two drought experiment sites. Each species was placed a priori into one of four plant functional type (PFT) categories: drought-tolerant versus drought-intolerant based on observed mortality rates, and subdivided into early- versus late-successional based on wood density. We tested the hypotheses that the measured traits would be significantly different between the four PFTs and that they would be spatially conserved across the two experimental sites. Xylem-P 50 , TLP, and π o , but not ε, occurred at significantly higher water potentials for the drought-intolerant PFT compared to the drought-tolerant PFT; however, there were no significant differences between the early- and late-successional PFTs. These results suggest that these three traits are important for determining drought tolerance, and are largely independent of wood density-a trait commonly associated with successional status. Differences in these physiological traits that occurred between the drought-tolerant and drought-intolerant PFTs were conserved between the two research sites, even though they had different soil types and dry-season lengths. This more detailed understanding of how xylem and leaf hydraulic traits vary between co-occuring drought-tolerant and

Drought tolerance, xylem sap abscisic acid and stomatal conductance during soil drying: a comparison of canopy trees of three temperate deciduous angiosperms.

PubMed

Loewenstein, Nancy J.; Pallardy, Stephen G.

1998-07-01

Patterns of water relations, xylem sap abscisic acid concentration ([ABA]) and stomatal aperture were characterized and compared in drought-sensitive black walnut (Juglans nigra L.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.) trees co-occurring in a second-growth forest in Missouri, USA. There were strong correlations among reduction in predawn leaf water potential, increased xylem sap [ABA] and stomatal closure in all species. Stomatal conductance was more closely correlated with xylem sap ABA concentration than with ABA flux or xylem sap pH and cation concentrations. In isohydric black walnut, increased concentrations of ABA in the xylem sap appeared to be primarily of root origin, causing stomatal closure in response to soil drying. In anisohydric sugar maple and white oak, however, there were reductions in midday leaf water potential associated with stomatal closure, making it uncertain whether drought-induced xylem sap ABA was of leaf or root origin. The role of root-originated xylem sap ABA in these species as a signal to the shoot of the water status of the roots is, therefore, less certain.
Investigating xylem embolism formation, refilling and water storage in tree trunks using frequency domain reflectometry.

PubMed

Hao, Guang-You; Wheeler, James K; Holbrook, N Michele; Goldstein, Guillermo

2013-05-01

Trunks of large trees play an important role in whole-plant water balance but technical difficulties have limited most hydraulic research to small stems, leaves, and roots. To investigate the dynamics of water-related processes in tree trunks, such as winter embolism refilling, xylem hydraulic vulnerability, and water storage, volumetric water content (VWC) in the main stem was monitored continuously using frequency domain moisture sensors in adult Betula papyrifera trees from early spring through the beginning of winter. An air injection technique was developed to estimate hydraulic vulnerability of the trunk xylem. Trunk VWC increased in early spring and again in autumn, concurrently with root pressure during both seasons. Diurnal fluctuations and a gradual decrease in trunk VWC through the growing season were observed, which, in combination with VWC increase after significant rainfall events and depletion during periods of high water demand, indicate the importance of stem water storage in both short- and long-term water balance. Comparisons between the trunk air injection results and conventional branch hydraulic vulnerability curves showed no evidence of 'vulnerability segmentation' between the main stem and small branches in B. papyrifera. Measurements of VWC following air injection, together with evidence from air injection and xylem dye perfusion, indicate that embolized vessels can be refilled by active root pressure but not in the absence of root pressure. The precise, continuous, and non-destructive measurement of wood water content using frequency domain sensors provides an ideal way to probe many hydraulic processes in large tree trunks that are otherwise difficult to investigate.
Investigating xylem embolism formation, refilling and water storage in tree trunks using frequency domain reflectometry

PubMed Central

Hao, Guang-You; Wheeler, James K.; Holbrook, N. Michele; Goldstein, Guillermo

2013-01-01

Trunks of large trees play an important role in whole-plant water balance but technical difficulties have limited most hydraulic research to small stems, leaves, and roots. To investigate the dynamics of water-related processes in tree trunks, such as winter embolism refilling, xylem hydraulic vulnerability, and water storage, volumetric water content (VWC) in the main stem was monitored continuously using frequency domain moisture sensors in adult Betula papyrifera trees from early spring through the beginning of winter. An air injection technique was developed to estimate hydraulic vulnerability of the trunk xylem. Trunk VWC increased in early spring and again in autumn, concurrently with root pressure during both seasons. Diurnal fluctuations and a gradual decrease in trunk VWC through the growing season were observed, which, in combination with VWC increase after significant rainfall events and depletion during periods of high water demand, indicate the importance of stem water storage in both short- and long-term water balance. Comparisons between the trunk air injection results and conventional branch hydraulic vulnerability curves showed no evidence of ‘vulnerability segmentation’ between the main stem and small branches in B. papyrifera. Measurements of VWC following air injection, together with evidence from air injection and xylem dye perfusion, indicate that embolized vessels can be refilled by active root pressure but not in the absence of root pressure. The precise, continuous, and non-destructive measurement of wood water content using frequency domain sensors provides an ideal way to probe many hydraulic processes in large tree trunks that are otherwise difficult to investigate. PMID:23585669
Cu2+ inhibition of gel secretion in the xylem and its potential implications for water uptake of cut Acacia holosericea stems.

PubMed

Ratnayake, Kamani; Joyce, Daryl C; Webb, Richard I

2013-08-01

Maintaining a high rate of water uptake is crucial for maximum longevity of cut stems. Physiological gel/tylosis formation decreases water transport efficiency in the xylem. The primary mechanism of action for post-harvest Cu(2+) treatments in improving cut flower and foliage longevity has been elusive. The effect of Cu(2+) on wound-induced xylem vessel occlusion was investigated for Acacia holosericea A. Cunn. ex G. Don. Experiments were conducted using a Cu(2+) pulse (5 h, 2.2 mM) and a Cu(2+) vase solution (0.5 mM) vs a deionized water (DIW) control. Development of xylem blockage in the stem-end region 10 mm proximal to the wounded stem surface was examined over 21 days by light and transmission electron microscopy. Xylem vessels of stems stood into DIW were occluded with gels secreted into vessel lumens via pits from surrounding axial parenchyma cells. Gel secretion was initiated within 1-2 days post-wounding and gels were detected in the xylem from day 3. In contrast, Cu(2+) treatments disrupted the surrounding parenchyma cells, thereby inhibiting gel secretion and maintaining the vessel lumens devoid of occlusions. The Cu(2+) treatments significantly improved water uptake by the cut stems as compared to the control. © 2013 Scandinavian Plant Physiology Society.
Are needles of Pinus pinaster more vulnerable to xylem embolism than branches? New insights from X-ray computed tomography.

PubMed

Bouche, Pauline S; Delzon, Sylvain; Choat, Brendan; Badel, Eric; Brodribb, Timothy J; Burlett, Regis; Cochard, Hervé; Charra-Vaskou, Katline; Lavigne, Bruno; Li, Shan; Mayr, Stefan; Morris, Hugh; Torres-Ruiz, José M; Zufferey, Vivian; Jansen, Steven

2016-04-01

Plants can be highly segmented organisms with an independently redundant design of organs. In the context of plant hydraulics, leaves may be less embolism resistant than stems, allowing hydraulic failure to be restricted to distal organs that can be readily replaced. We quantified drought-induced embolism in needles and stems of Pinus pinaster using high-resolution computed tomography (HRCT). HRCT observations of needles were compared with the rehydration kinetics method to estimate the contribution of extra-xylary pathways to declining hydraulic conductance. High-resolution computed tomography images indicated that the pressure inducing 50% of embolized tracheids was similar between needle and stem xylem (P50 needle xylem = -3.62 MPa, P50 stem xylem = -3.88 MPa). Tracheids in both organs showed no difference in torus overlap of bordered pits. However, estimations of the pressure inducing 50% loss of hydraulic conductance at the whole needle level by the rehydration kinetics method were significantly higher (P50 needle = -1.71 MPa) than P50 needle xylem derived from HRCT. The vulnerability segmentation hypothesis appears to be valid only when considering hydraulic failure at the entire needle level, including extra-xylary pathways. Our findings suggest that native embolism in needles is limited and highlight the importance of imaging techniques for vulnerability curves. © 2015 John Wiley & Sons Ltd.
Ion-mediated changes of xylem hydraulic resistance in planta: fact or fiction?

PubMed

van Ieperen, Wim

2007-04-01

Although xylem provides an efficient transport pathway for water in plants, the hydraulic conductivity of xylem (K(h)) can still influence plant water status. For decades, the K(h) of functional xylem has been assumed to be constant in the short term because xylem consists of a network of dead interconnected capillary elements (conduits). Recent research has shown that K(h) can change in response to the cation content of the xylem fluid. Volume changes of pectin gel in nanometer-sized pores at inter-conduit connections are hypothesized to be the cause, and implications for xylem transport in planta are suggested. However, it seems too early to be conclusive about this phenomenon because the phenomenon has not been measured in planta with xylem fluids that realistically mimic natural xylem sap and the applied methods used to measure ion-mediated changes in K(h) have drawbacks.
Mobile Gibberellin Directly Stimulates Arabidopsis Hypocotyl Xylem Expansion[W][OA

PubMed Central

Ragni, Laura; Nieminen, Kaisa; Pacheco-Villalobos, David; Sibout, Richard; Schwechheimer, Claus; Hardtke, Christian S.

2011-01-01

Secondary growth of the vasculature results in the thickening of plant structures and continuously produces xylem tissue, the major biological carbon sink. Little is known about the developmental control of this quantitative trait, which displays two distinct phases in Arabidopsis thaliana hypocotyls. The later phase of accelerated xylem expansion resembles the secondary growth of trees and is triggered upon flowering by an unknown, shoot-derived signal. We found that flowering-dependent hypocotyl xylem expansion is a general feature of herbaceous plants with a rosette growth habit. Flowering induction is sufficient to trigger xylem expansion in Arabidopsis. By contrast, neither flower formation nor elongation of the main inflorescence is required. Xylem expansion also does not depend on any particular flowering time pathway or absolute age. Through analyses of natural genetic variation, we found that ERECTA acts locally to restrict xylem expansion downstream of the gibberellin (GA) pathway. Investigations of mutant and transgenic plants indicate that GA and its signaling pathway are both necessary and sufficient to directly trigger enhanced xylogenesis. Impaired GA signaling did not affect xylem expansion systemically, suggesting that it acts downstream of the mobile cue. By contrast, the GA effect was graft transmissible, suggesting that GA itself is the mobile shoot-derived signal. PMID:21498678
Limitations in the hydraulic pathway: Effects of xylem embolisms on sap velocity and flow

USDA-ARS?s Scientific Manuscript database

Sap flow in plants takes place in the xylem, a hydraulic system that is usually under negative pressure and in which gas and liquid phases are separated by nanoporous, fibrous pit membranes. It has long been known that this system is at risk of drawing gas nanobubbles through these membranes into th...
Divergence in strategies for coping with winter embolism among co-occurring temperate tree species: the role of positive xylem pressure, wood type and tree stature

Treesearch

Cun-Yang Niu; Frederick C. Meinzer; Guang-You Hao

2017-01-01

1. In temperate ecosystems, freeze-thaw events are an important environmental stress that can induce severe xylem embolism (i.e. clogging of conduits by air bubbles) in overwintering organs of trees. However, no comparative studies of different adaptive strategies among sympatric tree species for coping with winter embolism have examined the potential role of the...
Xylem and phloem phenology in co-occurring conifers exposed to drought.

PubMed

Swidrak, Irene; Gruber, Andreas; Oberhuber, Walter

2014-01-01

Variability in xylem and phloem phenology among years and species is caused by contrasting temperatures prevailing at the start of the growing season and species-specific sensitivity to drought. The focus of this study was to determine temporal dynamics of xylem and phloem formation in co-occurring deciduous and evergreen coniferous species in a dry inner Alpine environment (750 m a.s.l., Tyrol, Austria). By repeated micro-sampling of the stem, timing of key phenological dates of xylem and phloem formation was compared among mature Pinus sylvestris , Larix decidua and Picea abies during two consecutive years. Xylem formation in P. sylvestris started in mid and late April 2011 and 2012, respectively, and in both years about 2 week later in P. abies and L. decidua . Phloem formation preceded xylem formation on average by 3 week in P. sylvestris , and c . 5 week in P. abies and L. decidua . Based on modeled cell number increase, tracheid production peaked between early through late May 2011 and late May through mid-June 2012. Phloem formation culminated between late April and mid-May in 2011 and in late May 2012. Production of xylem and phloem cells continued for about 4 and 5-6 months, respectively. High variability in xylem increment among years and species is related to exogenous control by climatic factors and species-specific sensitivity to drought, respectively. On the other hand, production of phloem cells was quite homogenous and showed asymptotic decrease with respect to xylem cells indicating endogenous control. Results indicate that onset and culmination of xylem and phloem formation are controlled by early spring temperature, whereby strikingly advanced production of phloem compared to xylem cells suggests lower temperature requirement for initiation of the former.
Hydraulic efficiency and coordination with xylem resistance to cavitation, leaf function, and growth performance among eight unrelated Populus deltoidesxPopulus nigra hybrids.

PubMed

Fichot, Régis; Chamaillard, Sylvain; Depardieu, Claire; Le Thiec, Didier; Cochard, Hervé; Barigah, Têtè S; Brignolas, Franck

2011-03-01

Tests were carried out to determine whether variations in the hydraulic architecture of eight Populus deltoides×Populus nigra genotypes could be related to variations in leaf function and growth performance. Measurements were performed in a coppice plantation on 1-year-old shoots under optimal irrigation. Hydraulic architecture was characterized through estimates of hydraulic efficiency (the ratio of conducting sapwood area to leaf area, A(X):A(L); leaf- and xylem-specific hydraulic conductance of defoliated shoots, k(SL) and k(SS), respectively; apparent whole-plant leaf-specific hydraulic conductance, k(plant)) and xylem safety (water potential inducing 50% loss in hydraulic conductance). The eight genotypes spanned a significant range of k(SL) from 2.63 kg s(-1) m(-2) MPa(-1) to 4.18 kg s(-1) m(-2) MPa(-1), variations being mostly driven by k(SS) rather than A(X):A(L). There was a strong trade-off between hydraulic efficiency and xylem safety. Values of k(SL) correlated positively with k(plant), indicating that high-pressure flowmeter (HPFM) measurements of stem hydraulic efficiency accurately reflected whole-plant water transport efficiency of field-grown plants at maximum transpiration rate. No clear relationship could be found between hydraulic efficiency and either net CO(2) assimilation rates, water-use efficiency estimates (intrinsic water-use efficiency and carbon isotope discrimination against (13)C), or stomatal characteristics (stomatal density and stomatal pore area index). Estimates of hydraulic efficiency were negatively associated with relative growth rate. This unusual pattern, combined with the trade-off observed between hydraulic efficiency and xylem safety, provides the rationale for the positive link already reported between relative growth rate and xylem safety among the same eight P. deltoides×P. nigra genotypes.
Branch xylem density variations across the Amazon Basin

NASA Astrophysics Data System (ADS)

Patiño, S.; Lloyd, J.; Paiva, R.; Baker, T. R.; Quesada, C. A.; Mercado, L. M.; Schmerler, J.; Schwarz, M.; Santos, A. J. B.; Aguilar, A.; Czimczik, C. I.; Gallo, J.; Horna, V.; Hoyos, E. J.; Jimenez, E. M.; Palomino, W.; Peacock, J.; Peña-Cruz, A.; Sarmiento, C.; Sota, A.; Turriago, J. D.; Villanueva, B.; Vitzthum, P.; Alvarez, E.; Arroyo, L.; Baraloto, C.; Bonal, D.; Chave, J.; Costa, A. C. L.; Herrera, R.; Higuchi, N.; Killeen, T.; Leal, E.; Luizão, F.; Meir, P.; Monteagudo, A.; Neil, D.; Núñez-Vargas, P.; Peñuela, M. C.; Pitman, N.; Priante Filho, N.; Prieto, A.; Panfil, S. N.; Rudas, A.; Salomão, R.; Silva, N.; Silveira, M.; Soares Dealmeida, S.; Torres-Lezama, A.; Vásquez-Martínez, R.; Vieira, I.; Malhi, Y.; Phillips, O. L.

2009-04-01

Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, ρx, were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin. Measured values ranged from 218 kg m-3 for a Cordia sagotii (Boraginaceae) from Mountagne de Tortue, French Guiana to 1130 kg m-3 for an Aiouea sp. (Lauraceae) from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average ρx across regions and sampled plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that species identity (family, genera and species) accounted for 33% with environment (geographic location and plot) accounting for an additional 26%; the remaining "residual" variance accounted for 41% of the total variance. Variations in plot means, were, however, not only accountable by differences in species composition because xylem density of the most widely distributed species in our dataset varied systematically from plot to plot. Thus, as well as having a genetic component, branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing in a predictable manner. Within the analysed taxa, exceptions to this general rule seem to be pioneer species belonging for example to the Urticaceae whose branch xylem density is more constrained than most species sampled in this study. These patterns of variation of branch xylem density across Amazonia suggest a large functional diversity amongst Amazonian trees which is not well understood.
Drought tolerance, xylem sap abscisic acid and stomatal conductance during soil drying: a comparison of young plants of four temperate deciduous angiosperms.

PubMed

Loewenstein, Nancy J.; Pallardy, Stephen G.

1998-07-01

Patterns of water relations, xylem sap abscisic acid (ABA) concentration ([ABA]) and stomatal aperture were compared in drought-sensitive black walnut (Juglans nigra L.) and black willow (Salix nigra Marsh.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.). Strong correlations among reduction in predawn water potential, increase in xylem sap [ABA] and stomatal closure were observed in all species. Stomatal response was more highly correlated with xylem [ABA] than with ABA flux. Xylem sap pH and ion concentrations appeared not to play a major role in the stomatal response of these species. Stomata were more sensitive to relative changes in [ABA] in drought-sensitive black walnut and black willow than in sugar maple and white oak. In the early stages of drought, increased [ABA] in the xylem sap of black walnut and black willow was probably of root origin and provided a signal to the shoot of the water status of the roots. In sugar maple and white oak, leaf water potential declined with the onset of stomatal closure, so that stomatal closure also may have occurred in response to the change in leaf water potential.
Lateral Movement of Water and Sugar Across Xylem in Sugarcane Stalks

PubMed Central

Bull, T. A.; Gayler, K. R.; Glasziou, K. T.

1972-01-01

Laterally connected vascular bundles in the nodes of sugarcane (Saccharum species cv. Pindar) stalks allow a rapid redistribution of water across the stalk should the vascular continuity be partly disrupted. Tritiated water supplied to the roots exchanged rapidly between the xylem and storage tissue so that net movement up the stalk was slow. The half-time for exchange in a labeled stalk was about 4 hours so that the entire water content of a sugarcane stalk can turn over at least once in a single day. No rapid flux of sugar between xylem and phloem or xylem and storage tissue was detected. Functional xylem contained only low sugar concentrations: less than 0.3% w/v in the stalk and less than 0.02% w/v in the leaf. Previous reports of high sugar levels (9% w/v) in sugarcane stalk xylem reflect some degree of xylem blockage followed by a slow equilibration with free space sugars in the storage tissue. PMID:16658067
Improving xylem hydraulic conductivity measurements by correcting the error caused by passive water uptake.

PubMed

Torres-Ruiz, José M; Sperry, John S; Fernández, José E

2012-10-01

Xylem hydraulic conductivity (K) is typically defined as K = F/(P/L), where F is the flow rate through a xylem segment associated with an applied pressure gradient (P/L) along the segment. This definition assumes a linear flow-pressure relationship with a flow intercept (F(0)) of zero. While linearity is typically the case, there is often a non-zero F(0) that persists in the absence of leaks or evaporation and is caused by passive uptake of water by the sample. In this study, we determined the consequences of failing to account for non-zero F(0) for both K measurements and the use of K to estimate the vulnerability to xylem cavitation. We generated vulnerability curves for olive root samples (Olea europaea) by the centrifuge technique, measuring a maximally accurate reference K(ref) as the slope of a four-point F vs P/L relationship. The K(ref) was compared with three more rapid ways of estimating K. When F(0) was assumed to be zero, K was significantly under-estimated (average of -81.4 ± 4.7%), especially when K(ref) was low. Vulnerability curves derived from these under-estimated K values overestimated the vulnerability to cavitation. When non-zero F(0) was taken into account, whether it was measured or estimated, more accurate K values (relative to K(ref)) were obtained, and vulnerability curves indicated greater resistance to cavitation. We recommend accounting for non-zero F(0) for obtaining accurate estimates of K and cavitation resistance in hydraulic studies. Copyright © Physiologia Plantarum 2012.
Lengthening of the duration of xylogenesis engenders disproportionate increases in xylem production.

PubMed

Rossi, Sergio; Girard, Marie-Josée; Morin, Hubert

2014-07-01

In cold climates, the expected global warming will lead to earlier cambial resumptions in spring, with a resultant lengthening of the growing season but unknown consequences on forest productivity. The phenological traits of cambium activity and xylem formation were analyzed at a short time scale along a thermal gradient represented by an alti-latitudinal range from the 48th to 53rd parallels and covering the whole closed black-spruce [Picea mariana (Mill.) BSP] forest in Quebec, Canada. A hypothesis was tested that warmer temperatures influence cambium phenology, allowing longer duration and higher intensity of growth, and resulting in proportionally increased xylem production. From April to October 2012, cell division in cambium and post-cambial differentiation of xylem were observed on anatomical sections obtained from microcores collected weekly from the stem of fifty trees. The southern and warmer site was characterized by the highest radial growth, which corresponded to both the highest rates and longest durations of cell production. The differences in terms of xylem phenology and growth were marginal between the other sites. Xylem growth was positively correlated with rate and duration of cell production, with the latter explaining most variability in growth. Within the range analyzed, the relationship between temperature and most phenological phases of xylogenesis was linear. On the contrary, temperature was related with cell production according to an exponential pattern. Periods of xylogenesis of 14 days longer (+13.1%) corresponded to a massive increase in cell production (33 cells, +109%). This disproportionate change occurred at a May-September average temperature of ca. 14 °C and a snow-free period of 210-235 days. At the lower boundary of the distribution of black spruce, small environmental changes allowing marginal lengthening of the period of cell division could potentially lead to disproportionate increases in xylem cell production, with
Hierarchical statistical modeling of xylem vulnerability to cavitation.

PubMed

Ogle, Kiona; Barber, Jarrett J; Willson, Cynthia; Thompson, Brenda

2009-01-01

Cavitation of xylem elements diminishes the water transport capacity of plants, and quantifying xylem vulnerability to cavitation is important to understanding plant function. Current approaches to analyzing hydraulic conductivity (K) data to infer vulnerability to cavitation suffer from problems such as the use of potentially unrealistic vulnerability curves, difficulty interpreting parameters in these curves, a statistical framework that ignores sampling design, and an overly simplistic view of uncertainty. This study illustrates how two common curves (exponential-sigmoid and Weibull) can be reparameterized in terms of meaningful parameters: maximum conductivity (k(sat)), water potential (-P) at which percentage loss of conductivity (PLC) =X% (P(X)), and the slope of the PLC curve at P(X) (S(X)), a 'sensitivity' index. We provide a hierarchical Bayesian method for fitting the reparameterized curves to K(H) data. We illustrate the method using data for roots and stems of two populations of Juniperus scopulorum and test for differences in k(sat), P(X), and S(X) between different groups. Two important results emerge from this study. First, the Weibull model is preferred because it produces biologically realistic estimates of PLC near P = 0 MPa. Second, stochastic embolisms contribute an important source of uncertainty that should be included in such analyses.
Tree shoot bending generates hydraulic pressure pulses: a new long-distance signal?

PubMed Central

Lopez, Rosana; Badel, Eric

2014-01-01

When tree stems are mechanically stimulated, a rapid long-distance signal is induced that slows down primary growth. An investigation was carried out to determine whether the signal might be borne by a mechanically induced pressure pulse in the xylem. Coupling xylem flow meters and pressure sensors with a mechanical testing device, the hydraulic effects of mechanical deformation of tree stem and branches were measured. Organs of several tree species were studied, including gymnosperms and angiosperms with different wood densities and anatomies. Bending had a negligible effect on xylem conductivity, even when deformations were sustained or were larger than would be encountered in nature. It was found that bending caused transient variation in the hydraulic pressure within the xylem of branch segments. This local transient increase in pressure in the xylem was rapidly propagated along the vascular system in planta to the upper and lower regions of the stem. It was shown that this hydraulic pulse originates from the apoplast. Water that was mobilized in the hydraulic pulses came from the saturated porous material of the conduits and their walls, suggesting that the poroelastic behaviour of xylem might be a key factor. Although likely to be a generic mechanical response, quantitative differences in the hydraulic pulse were found in different species, possibly related to differences in xylem anatomy. Importantly the hydraulic pulse was proportional to the strained volume, similar to known thigmomorphogenetic responses. It is hypothesized that the hydraulic pulse may be the signal that rapidly transmits mechanobiological information to leaves, roots, and apices. PMID:24558073
Tree shoot bending generates hydraulic pressure pulses: a new long-distance signal?

PubMed

Lopez, Rosana; Badel, Eric; Peraudeau, Sebastien; Leblanc-Fournier, Nathalie; Beaujard, François; Julien, Jean-Louis; Cochard, Hervé; Moulia, Bruno

2014-05-01

When tree stems are mechanically stimulated, a rapid long-distance signal is induced that slows down primary growth. An investigation was carried out to determine whether the signal might be borne by a mechanically induced pressure pulse in the xylem. Coupling xylem flow meters and pressure sensors with a mechanical testing device, the hydraulic effects of mechanical deformation of tree stem and branches were measured. Organs of several tree species were studied, including gymnosperms and angiosperms with different wood densities and anatomies. Bending had a negligible effect on xylem conductivity, even when deformations were sustained or were larger than would be encountered in nature. It was found that bending caused transient variation in the hydraulic pressure within the xylem of branch segments. This local transient increase in pressure in the xylem was rapidly propagated along the vascular system in planta to the upper and lower regions of the stem. It was shown that this hydraulic pulse originates from the apoplast. Water that was mobilized in the hydraulic pulses came from the saturated porous material of the conduits and their walls, suggesting that the poroelastic behaviour of xylem might be a key factor. Although likely to be a generic mechanical response, quantitative differences in the hydraulic pulse were found in different species, possibly related to differences in xylem anatomy. Importantly the hydraulic pulse was proportional to the strained volume, similar to known thigmomorphogenetic responses. It is hypothesized that the hydraulic pulse may be the signal that rapidly transmits mechanobiological information to leaves, roots, and apices.
Trade-offs between xylem hydraulic properties, wood anatomy and yield in Populus.

PubMed

Hajek, Peter; Leuschner, Christoph; Hertel, Dietrich; Delzon, Sylvain; Schuldt, Bernhard

2014-07-01

Trees face the dilemma that achieving high plant productivity is accompanied by a risk of drought-induced hydraulic failure due to a trade-off in the trees' vascular system between hydraulic efficiency and safety. By investigating the xylem anatomy of branches and coarse roots, and measuring branch axial hydraulic conductivity and vulnerability to cavitation in 4-year-old field-grown aspen plants of five demes (Populus tremula L. and Populus tremuloides Michx.) differing in growth rate, we tested the hypotheses that (i) demes differ in wood anatomical and hydraulic properties, (ii) hydraulic efficiency and safety are related to xylem anatomical traits, and (iii) aboveground productivity and hydraulic efficiency are negatively correlated to cavitation resistance. Significant deme differences existed in seven of the nine investigated branch-related anatomical and hydraulic traits but only in one of the four coarse-root-related anatomical traits; this likely is a consequence of high intra-plant variation in root morphology and the occurrence of a few 'high-conductivity roots'. Growth rate was positively related to branch hydraulic efficiency (xylem-specific conductivity) but not to cavitation resistance; this indicates that no marked trade-off exists between cavitation resistance and growth. Both branch hydraulic safety and hydraulic efficiency significantly depended on vessel size and were related to the genetic distance between the demes, while the xylem pressure causing 88% loss of hydraulic conductivity (P88 value) was more closely related to hydraulic efficiency than the commonly used P50 value. Deme-specific variation in the pit membrane structure may explain why vessel size was not directly linked to growth rate. We conclude that branch hydraulic efficiency is an important growth-influencing trait in aspen, while the assumed trade-off between productivity and hydraulic safety is weak. © The Author 2014. Published by Oxford University Press. All rights reserved

Structure-function constraints of tracheid-based xylem: a comparison of conifers and ferns.

PubMed

Pittermann, Jarmila; Limm, Emily; Rico, Christopher; Christman, Mairgareth A

2011-10-01

The ferns comprise one of the most ancient tracheophytic plant lineages, and occupy habitats ranging from tundra to deserts and the equatorial tropics. Like their nearest relatives the conifers, modern ferns possess tracheid-based xylem but the structure-function relationships of fern xylem are poorly understood. Here, we sampled the fronds (megaphylls) of 16 species across the fern phylogeny, and examined the relationships among hydraulic transport, drought-induced cavitation resistance, the xylem anatomy of the stipe, and the gas-exchange response of the pinnae. For comparison, the results are presented alongside a similar suite of conifer data. Fern xylem is as resistant to cavitation as conifer xylem, but exhibits none of the hydraulic or structural trade-offs associated with resistance to cavitation. On a conduit diameter basis, fern xylem can exhibit greater hydraulic efficiency than conifer and angiosperm xylem. In ferns, wide and long tracheids compensate in part for the lack of secondary xylem and allow ferns to exhibit transport rates on a par with those of conifers. We suspect that it is the arrangement of the primary xylem, in addition to the intrinsic traits of the conduits themselves, that may help explain the broad range of cavitation resistance in ferns. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.
Uptake of water via branches helps timberline conifers refill embolized xylem in late winter.

PubMed

Mayr, Stefan; Schmid, Peter; Laur, Joan; Rosner, Sabine; Charra-Vaskou, Katline; Dämon, Birgit; Hacke, Uwe G

2014-04-01

Xylem embolism is a limiting factor for woody species worldwide. Conifers at the alpine timberline are exposed to drought and freeze-thaw stress during winter, which induce potentially lethal embolism. Previous studies indicated that timberline trees survive by xylem refilling. In this study on Picea abies, refilling was monitored during winter and spring seasons and analyzed in the laboratory and in situ experiments, based on hydraulic, anatomical, and histochemical methods. Refilling started in late winter, when the soil was frozen and soil water not available for the trees. Xylem embolism caused up to 86.2% ± 3.1% loss of conductivity and was correlated with the ratio of closed pits. Refilling of xylem as well as recovery in shoot conductance started in February and corresponded with starch accumulation in secondary phloem and in the mesophyll of needles, where we also observed increasing aquaporin densities in the phloem and endodermis. This indicates that active, cellular processes play a role for refilling even under winter conditions. As demonstrated by our experiments, water for refilling was thereby taken up via the branches, likely by foliar water uptake. Our results suggest that refilling is based on water shifts to embolized tracheids via intact xylem, phloem, and parenchyma, whereby aquaporins reduce resistances along the symplastic pathway and aspirated pits facilitate isolation of refilling tracheids. Refilling must be taken into account as a key process in plant hydraulics and in estimating future effects of climate change on forests and alpine tree ecosystems.
Growth of Verticillium longisporum in Xylem Sap of Brassica napus is Independent from Cultivar Resistance but Promoted by Plant Aging.

PubMed

Lopisso, Daniel Teshome; Knüfer, Jessica; Koopmann, Birger; von Tiedemann, Andreas

2017-09-01

As Verticillium stem striping of oilseed rape (OSR), a vascular disease caused by Verticillium longisporum, is extending into new geographic regions and no control with fungicides exists, the demand for understanding mechanisms of quantitative resistance increases. Because V. longisporum is strictly limited to the xylem and resistance is expressed in the systemic stage post root invasion, we investigated a potential antifungal role of soluble constituents and nutritional conditions in xylem sap as determinants of cultivar resistance of OSR to V. longisporum. Assessment of biometric and molecular genetic parameters applied to describe V. longisporum resistance (net area under disease progress curve, stunting, stem thickness, plant biomass, and V. longisporum DNA content) showed consistent susceptibility of cultivar 'Falcon' in contrast to two resistant genotypes, 'SEM' and 'Aviso'. Spectrophotometric analysis revealed a consistently stronger in vitro growth of V. longisporum in xylem sap extracted from OSR compared with the water control. Further comparisons of fungal growth in xylem sap of different cultivars revealed the absence of constitutive or V. longisporum induced antifungal activity in the xylem sap of resistant versus susceptible genotypes. The similar growth of V. longisporum in xylem sap, irrespective of cultivar, infection with V. longisporum and xylem sap filtration, was correlated with about equal amounts of total soluble proteins in xylem sap from these treatments. Interestingly, compared with younger plants, xylem sap from older plants induced significantly stronger fungal growth. Growth enhancement of V. longisporum in xylem sap of aging plants was reflected by increased contents of carbohydrates, which was consistent in mock or V. longisporum-infected plants and independent from cultivar resistance. The improved nutritional conditions in the xylem of more mature plants may explain the late appearance of disease symptoms, which are observed only in
Differential expression of genes of Xylella fastidiosa in xylem fluid of citrus and grapevine.

PubMed

Shi, Xiangyang; Bi, Jianlong; Morse, Joseph G; Toscano, Nick C; Cooksey, Donald A

2010-03-01

Xylella fastidiosa causes a serious Pierce's disease (PD) in grapevine. Xylella fastidiosa cells from a PD strain were grown in a pure xylem fluid of a susceptible grapevine cultivar vs. xylem fluid from citrus, which is not a host for this strain of X. fastidiosa. When grown in grapevine xylem fluid, cells of the PD strain formed clumps and biofilm formed to a greater extent than in citrus xylem fluid, although the PD strain did grow in xylem fluid of three citrus varieties. The differential expression of selected genes of a PD X. fastidiosa strain cultured in the two xylem fluids was analyzed using a DNA macroarray. Compared with citrus xylem fluid, grapevine xylem fluid stimulated the expression of X. fastidiosa genes involved in virulence regulation, such as gacA, algU, xrvA, and hsq, and also genes involved in the biogenesis of pili and twitching motility, such as fimT, pilI, pilU, and pilY1. Increased gene expression likely contributes to PD expression in grapevine, whereas citrus xylem fluid did not support or possibly suppressed the expression of these virulence genes.
Causes and Effects of Changes in Xylem Functionality in Apple Fruit

PubMed Central

DRAŽETA, LAZAR; LANG, ALEXANDER; HALL, ALISTAIR J.; VOLZ, RICHARD K.; JAMESON, PAULA E.

2004-01-01

• Background and Aims The xylem in fruit of a number of species becomes dysfunctional as the fruit develops, resulting in a reduction of xylem inflow to the fruit. Such a reduction may have consequential effects on the mineral balance of the fruit. The aim of this study was to elucidate the dynamics and nature of xylem failure in developing apples (Malus domestica) showing differing susceptibilities to bitter pit, a calcium‐related disorder. • Methods Developmental changes in xylem functionality of the fruit were investigated in ‘Braeburn’ and ‘Granny Smith’ apples by using a dye infusion technique, to stain the vasculature along the path of dye movement. The vascular bundles were clearly visible in transverse section when fruit were sectioned equatorially. The intensity of staining of the vascular bundles in the fruit was recorded at regular intervals throughout the season. Tissue containing dysfunctional bundles was fixed and embedded in wax for subsequent sectioning and examination. • Key Results As the season progressed, an increasing proportion of vascular bundles failed to show any staining, with the most marked change occurring in the primary bundles, and in nearly all bundles with increasing distance from the stalk end of the fruit. Decreased conductance in the primary bundles of ‘Braeburn’ occurred earlier than in ‘Granny Smith’. Microscopy revealed that the xylem in vascular bundles of the fruit suffered substantial damage, indicating that the mode of dysfunction was via the physical disruption of the xylem caused by expansion of the flesh. • Conclusions Results support the view that the relative calcium deficiency of apple fruit is due to a progressive breakdown of xylem conductance caused by growth‐induced damage to the xylem strand in the bundle. The earlier onset of xylem dysfunction in the cultivar more susceptible to bitter pit suggests that the relative growth dynamics of the fruit may control the occurrence of calcium�
Spatial and temporal patterns of xylem sap pH derived from stems and twigs of Populus deltoides L.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aubrey, Doug P.; Boyles, Justin G.; Krysinsky, Laura S.

2011-02-12

Xylem sap pH (pHX) is critical in determining the quantity of inorganic carbon dissolved in xylem solution from gaseous [CO2] measurements. Studies of internal carbon transport have generally assumed that pHX derived from stems and twigs is similar and that pHX remains constant through time; however, no empirical studies have investigated these assumptions. If any of these assumptions are violated, potentially large errors can be introduced into calculations of dissolved CO 2 in xylem and resulting estimates of internal carbon transport.Wetested the validity of assumptions related to pHX in Populus deltoides L. with a series of non-manipulative experiments. The pHXmore » derived from stems and twigs was generally similar and remained relatively constant through a diel period. The only exception was that pHX derived from lower stem sections at night was higher than that derived from twigs. The pHX derived from stems was similar on clear days when solar radiation and vapor pressure deficit (VPD) were similar, but higher on an overcast day when solar radiation and VPD were lower. Similarly, cloudy conditions immediately before an afternoon thunderstorm increased pHX derived from twigs. The pHX derived from twigs remained similar when measured on sunny afternoons between July and October. Our results suggest that common assumptions of pHX used in studies of internal carbon transport appear valid for P. deltoides and further suggest pHX is influenced by environmental factors, such as solar radiation and VPD that affect transpiration rates.« less
Metal Complexation in Xylem Fluid 1

PubMed Central

White, Michael C.; Decker, A. Morris; Chaney, Rufus L.

1981-01-01

Xylem fluid was analyzed for numerous solutes to characterize chemically the sap as a medium for forming and transporting metal complexes. The stem exudate was collected hourly for 8 hours from topped 31-day-old soybean (Glycine max L. Merr.) and 46-day-old tomato (Lycopersicon esculentum Mill.) plants grown in normal (0.5 micromolar) and Za-phytotoxic nutrient solutions. Soybean plants were grown in the normal and high-Zn solutions for 24 days; tomato plants were grown for 32 days. The exudate was analyzed for seven organic acids, 22 amino acids, eight inorganic solutes, apparent ionic strength, and pH. Significant changes in many solutes occurred over the 8-hour sampling period. These fluctuations depended on plant species, individual solute, and Zn treatment, and demonstrated that extrapolation of xylem-fluid analyses to whole-plant xylem sap is valid only for sap samples collected shortly after topping a plant. Exudate pH decreased over the 8-hour period for both species; exudate ionic strength increased for tomato and decreased for soybean. At the normal-Zn treatment (0 to 1 hour), the highest acid micromolar concentrations in soybean exudate were: asparagine, 2,583; citric, 1,706; malic, 890; and malonic, 264. Under the same conditions, the highest acid micromolar concentrations in tomato exudate were: maleic, 1,206; malic, 628; glutamine, 522; citric, 301; and asparagine, 242. Cysteine and methionine were above detection limits only in soybean exudate. Zinc phytotoxicity caused significant changes in many solutes. The analyses reported here provide a comprehensive data base for further studies on metal-complex equilibria in xylem fluid. PMID:16661664
Xylem development in prunus flower buds and the relationship to deep supercooling.

PubMed

Ashworth, E N

1984-04-01

Xylem development in eight Prunus species was examined and the relationship to deep supercooling assessed. Dormant buds of six species, P. armeniaca, P. avium, P. cerasus, P. persica, P. salicina, and P. sargentii deep supercooled. Xylem vessel elements were not observed within the dormant floral primordia of these species. Instead, discrete bundles containing procambial cells were observed. Vascular differentiation resumed and xylem continuity was established during the time that the capacity to deep supercool was lost. In P. serotina and P. virginiana, two species which do not supercool, xylem vessels ran the length of the inflorescence and presumably provided a conduit for the spread of ice into the bud. The results support the hypothesis that the lack of xylem continuity is an important feature of buds which deep supercool.
Ear Rachis Xylem Occlusion and Associated Loss in Hydraulic Conductance Coincide with the End of Grain Filling for Wheat

PubMed Central

Neghliz, Hayet; Cochard, Hervé; Brunel, Nicole; Martre, Pierre

2016-01-01

Seed dehydration is the normal terminal event in the development of orthodox seeds and is physiologically related to the cessation of grain dry mass accumulation and crop grain yield. For a better understanding of grain dehydration, we evaluated the hypothesis that hydraulic conductance of the ear decreases during the latter stages of development and that this decrease results from disruption or occlusion of xylem conduits. Whole ear, rachis, and stem nodes hydraulic conductance and percentage loss of xylem conductivity were measured from flowering to harvest-ripeness on bread wheat (Triticum aestivum L.) cv. Récital grown under controlled environments. Flag leaf transpiration, stomatal conductance, chlorophyll content and grain and ear water potentials were also measured during grain development. We show that grain dehydration was not related with whole plant physiology and leaf senescence, but closely correlated with the hydraulic properties of the xylem conduits irrigating the grains. Indeed, there was a substantial decrease in rachis hydraulic conductance at the onset of the grain dehydration phase. This hydraulic impairment was not caused by the presence of air embolism in xylem conduits of the stem internodes or rachis but by the occlusion of the xylem lumens by polysaccharides (pectins and callose). Our results demonstrate that xylem hydraulics plays a key role during grain maturation. PMID:27446150
Increasing atmospheric [CO2] from glacial through future levels affects drought tolerance via impacts on leaves, xylem and their integrated function

PubMed Central

Medeiros, Juliana S.; Ward, Joy K.

2013-01-01

Summary Changes in atmospheric carbon dioxide concentration ([CO2]) affect plant carbon/water trade-offs, with implications for drought tolerance. Leaf-level studies often indicate that drought tolerance may increase with rising [CO2], but integrated leaf and xylem responses are not well understood in this respect. In addition, the influence of low [CO2] of the last glacial period on drought tolerance and xylem properties is not well understood.We investigated the interactive effects of a broad range of [CO2] and plant water potentials on leaf function, xylem structure and function and the integration of leaf and xylem function in Phaseolus vulgaris.Elevated [CO2] decreased vessel implosion strength, reduced conduit specific hydraulic conductance, and compromised leaf specific xylem hydraulic conductance under moderate drought. By contrast, at glacial [CO2], transpiration was maintained under moderate drought via greater conduit specific and leaf specific hydraulic conductance in association with increased vessel implosion strength.Our study involving the integration of leaf and xylem responses suggests that increasing [CO2] does not improve drought tolerance. We show that under glacial conditions changes in leaf and xylem properties could increase drought tolerance, while under future conditions greater productivity may only occur when higher water use can be accommodated. PMID:23668237
Analysis of xylem formation in pine by cDNA sequencing

NASA Technical Reports Server (NTRS)

Allona, I.; Quinn, M.; Shoop, E.; Swope, K.; St Cyr, S.; Carlis, J.; Riedl, J.; Retzel, E.; Campbell, M. M.; Sederoff, R.;

1998-01-01

Secondary xylem (wood) formation is likely to involve some genes expressed rarely or not at all in herbaceous plants. Moreover, environmental and developmental stimuli influence secondary xylem differentiation, producing morphological and chemical changes in wood. To increase our understanding of xylem formation, and to provide material for comparative analysis of gymnosperm and angiosperm sequences, ESTs were obtained from immature xylem of loblolly pine (Pinus taeda L.). A total of 1,097 single-pass sequences were obtained from 5' ends of cDNAs made from gravistimulated tissue from bent trees. Cluster analysis detected 107 groups of similar sequences, ranging in size from 2 to 20 sequences. A total of 361 sequences fell into these groups, whereas 736 sequences were unique. About 55% of the pine EST sequences show similarity to previously described sequences in public databases. About 10% of the recognized genes encode factors involved in cell wall formation. Sequences similar to cell wall proteins, most known lignin biosynthetic enzymes, and several enzymes of carbohydrate metabolism were found. A number of putative regulatory proteins also are represented. Expression patterns of several of these genes were studied in various tissues and organs of pine. Sequencing novel genes expressed during xylem formation will provide a powerful means of identifying mechanisms controlling this important differentiation pathway.

Xylem phenology and wood production: resolving the chicken-or-egg dilemma.

PubMed

Lupi, Carlo; Morin, Hubert; Deslauriers, Annie; Rossi, Sergio

2010-10-01

Delays in the start of the growing season reduce the period available for growth and the amount of xylem production. However, a higher number of developing tracheids could prolong cell differentiation and, consequently, lengthen the growing season. The relationship between the amount and duration of cell production in the xylem remains an unresolved issue. The aim of this study was to resolve the chicken-or-egg causality dilemma about duration of growth and cell production through simple- and double-cause models. This was achieved by (1) analysing the intra-annual growth dynamics of the xylem in Picea mariana (Mill.) BSP during 2006-2009 in two contrasting sites of the boreal forest of Quebec, Canada, and (2) extracting the dates of onset and ending of xylem formation and the number of radial cells along the tree ring. A higher number of cells was linked to an earlier onset (r=0.74) and later ending (r=0.61) of cell differentiation. The absence of a relationship between the residuals of the onset and ending of xylogenesis (r(p)=-0.06) indicated that cell production influenced the correlation between the two phenophases of the xylem. These results demonstrated that a higher number of cells produced delay the ending of xylem maturation, so extending the duration of wood formation. © 2010 Blackwell Publishing Ltd.
Xylem Development in Prunus Flower Buds and the Relationship to Deep Supercooling

PubMed Central

Ashworth, Edward N.

1984-01-01

Xylem development in eight Prunus species was examined and the relationship to deep supercooling assessed. Dormant buds of six species, P. armeniaca, P. avium, P. cerasus, P. persica, P. salicina, and P. sargentii deep supercooled. Xylem vessel elements were not observed within the dormant floral primordia of these species. Instead, discrete bundles containing procambial cells were observed. Vascular differentiation resumed and xylem continuity was established during the time that the capacity to deep supercool was lost. In P. serotina and P. virginiana, two species which do not supercool, xylem vessels ran the length of the inflorescence and presumably provided a conduit for the spread of ice into the bud. The results support the hypothesis that the lack of xylem continuity is an important feature of buds which deep supercool. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 PMID:16663523
Protein and metabolite composition of xylem sap from field-grown soybeans (Glycine max).

PubMed

Krishnan, Hari B; Natarajan, Savithiry S; Bennett, John O; Sicher, Richard C

2011-05-01

The xylem, in addition to transporting water, nutrients and metabolites, is also involved in long-distance signaling in response to pathogens, symbionts and environmental stresses. Xylem sap has been shown to contain a number of proteins including metabolic enzymes, stress-related proteins, signal transduction proteins and putative transcription factors. Previous studies on xylem sap have mostly utilized plants grown in controlled environmental chambers. However, plants in the field are subjected to high light and to environmental stress that is not normally found in growth chambers. In this study, we have examined the protein and metabolite composition of xylem sap from field-grown cultivated soybean plants. One-dimensional gel electrophoresis of xylem sap from determinate, indeterminate, nodulating and non-nodulating soybean cultivars revealed similar protein profiles consisting of about 8-10 prominent polypeptides. Two-dimensional gel electrophoresis of soybean xylem sap resulted in the visualization of about 60 distinct protein spots. A total of 38 protein spots were identified using MALDI-TOF MS and LC-MS/MS. The most abundant proteins present in the xylem sap were identified as 31 and 28 kDa vegetative storage proteins. In addition, several proteins that are conserved among different plant species were also identified. Diurnal changes in the metabolite profile of xylem sap collected during a 24-h cycle revealed that asparagine and aspartate were the two predominant amino acids irrespective of the time collected. Pinitol (D-3-O-methyl-chiro-inositol) was the most abundant carbohydrate present. The possible roles of xylem sap proteins and metabolites as nutrient reserves for sink tissue and as an indicator of biotic stress are also discussed.
Functional adjustments of xylem anatomy to climatic variability: insights from long-term Ilex aquifolium tree-ring series.

PubMed

Rita, Angelo; Cherubini, Paolo; Leonardi, Stefano; Todaro, Luigi; Borghetti, Marco

2015-08-01

The present study assessed the effects of climatic conditions on radial growth and functional anatomical traits, including ring width, vessel size, vessel frequency and derived variables, i.e., potential hydraulic conductivity and xylem vulnerability to cavitation in Ilex aquifolium L. trees using long-term tree-ring time series obtained at two climatically contrasting sites, one mesic site in Switzerland (CH) and one drought-prone site in Italy (ITA). Relationships were explored by examining different xylem traits, and point pattern analysis was applied to investigate vessel clustering. We also used generalized additive models and bootstrap correlation functions to describe temperature and precipitation effects. Results indicated modified radial growth and xylem anatomy in trees over the last century; in particular, vessel frequency increased markedly at both sites in recent years, and all xylem traits examined, with the exception of xylem cavitation vulnerability, were higher at the CH mesic compared with the ITA drought site. A significant vessel clustering was observed at the ITA site, which could contribute to an enhanced tolerance to drought-induced embolism. Flat and negative relationships between vessel size and ring width were observed, suggesting carbon was not allocated to radial growth under conditions which favored stem water conduction. Finally, in most cases results indicated that climatic conditions influenced functional anatomical traits more substantially than tree radial growth, suggesting a crucial role of functional xylem anatomy in plant acclimation to future climatic conditions. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Source of Sustained Voltage Difference between the Xylem of a Potted Ficus benjamina Tree and Its Soil

PubMed Central

Love, Christopher J.; Zhang, Shuguang; Mershin, Andreas

2008-01-01

It has long been known that there is a sustained electrical potential (voltage) difference between the xylem of many plants and their surrounding soil, but the mechanism behind this voltage has remained controversial. After eliminating any extraneous capacitive or inductive couplings and ground-mediated electric current flows, we have measured sustained differences of 50–200 mV between the xylem region of a Faraday-caged, intact, potted Ficus benjamina tree and its soil, as well as between its cut branches and soils and ionic solutions standardized to various pH values. Using identical platinum electrodes, no correlation between the voltage and time of day, illumination, sap flow, electrode elevation, or ionic composition of soil was found, suggesting no direct connection to simple dissimilar-metal redox reactions or transpirational activity. Instead, a clear relationship between the voltage polarity and magnitude and the pH difference between xylem and soil was observed. We attribute these sustained voltages to a biological concentration cell likely set up by the homeostatic mechanisms of the tree. Potential applications of this finding are briefly explored. PMID:18698415
Transport and coordination in the coupled soil-root-xylem-phloem leaf system

NASA Astrophysics Data System (ADS)

Huang, C. W.; Katul, G. G.; Pockman, W.; Litvak, M. E.; Domec, J. C.; Palmroth, S.

2016-12-01

In response to varying environmental conditions, stomatal pores act as biological valves that dynamically adjust their size thereby determining the rate of CO2 assimilation and water loss (i.e., transpiration) to the dry atmosphere. Although the significance of this biotic control on gas exchange is rarely disputed, representing parsimoniously all the underlying mechanisms responsible for stomatal kinetics remain a subject of some debate. It has been conjectured that stomatal control in seed plants (i.e., angiosperm and gymnosperm) represents a compromise between biochemical demand for CO2 and prevention of excessive water loss. This view has been amended at the whole-plant level, where xylem hydraulics and sucrose transport efficiency in phloem appear to impose additional constraints on gas exchange. If such additional constraints impact stomatal opening and closure, then seed plants may have evolved coordinated photosynthetic-hydraulic-sugar transporting machinery that confers some competitive advantages in fluctuating environmental conditions. Thus, a stomatal optimization model that explicitly considers xylem hydraulics and maximum sucrose transport is developed to explore this coordination in the leaf-xylem-phloem system. The model is then applied to progressive drought conditions. The main findings from the model calculations are that (1) the predicted stomatal conductance from the conventional stomatal optimization theory at the leaf and the newly proposed models converge, suggesting a tight coordination in the leaf-xylem-phloem system; (2) stomatal control is mainly limited by the water supply function of the soil-xylem hydraulic system especially when the water flux through the transpiration stream is significantly larger than water exchange between xylem and phloem; (3) thus, xylem limitation imposed on the supply function can be used to differentiate species with different water use strategy across the spectrum of isohydric to anisohydric behavior
A broad survey of hydraulic and mechanical safety in the xylem of conifers

Treesearch

Pauline S. Bouche; Maximilien Larter; Jean-Christophe Domec; Regis Burlett; Peter Gasson; Steven Jansen; Sylvain Delzon

2014-01-01

Drought-induced forest dieback has been widely reported over the last decades, and the evidence for a direct causal link between survival and hydraulic failure (xylem cavitation) is now well known. Because vulnerability to cavitation is intimately linked to the anatomy of the xylem, the main objective of this study was to better understand the xylem anatomical...
18O Spatial Patterns of Vein Xylem Water, Leaf Water, and Dry Matter in Cotton Leaves

PubMed Central

Gan, Kim Suan; Wong, Suan Chin; Yong, Jean Wan Hong; Farquhar, Graham Douglas

2002-01-01

Three leaf water models (two-pool model, Péclet effect, and string-of-lakes) were assessed for their robustness in predicting leaf water enrichment and its spatial heterogeneity. This was achieved by studying the 18O spatial patterns of vein xylem water, leaf water, and dry matter in cotton (Gossypium hirsutum) leaves grown at different humidities using new experimental approaches. Vein xylem water was collected from intact transpiring cotton leaves by pressurizing the roots in a pressure chamber, whereas the isotopic content of leaf water was determined without extracting it from fresh leaves with the aid of a purpose-designed leaf punch. Our results indicate that veins have a significant degree of lateral exchange with highly enriched leaf water. Vein xylem water is thus slightly, but progressively enriched in the direction of water flow. Leaf water enrichment is dependent on the relative distances from major veins, with water from the marginal and intercostal regions more enriched and that next to veins and near the leaf base more depleted than the Craig-Gordon modeled enrichment of water at the sites of evaporation. The spatial pattern of leaf water enrichment varies with humidity, as expected from the string-of-lakes model. This pattern is also reflected in leaf dry matter. All three models are realistic, but none could fully account for all of the facets of leaf water enrichment. Our findings acknowledge the presence of capacitance in the ground tissues of vein ribs and highlight the essential need to incorporate Péclet effects into the string-of-lakes model when applying it to leaves. PMID:12376664
Plant xylem hydraulics: What we understand, current research, and future challenges.

PubMed

Venturas, Martin D; Sperry, John S; Hacke, Uwe G

2017-06-01

Herein we review the current state-of-the-art of plant hydraulics in the context of plant physiology, ecology, and evolution, focusing on current and future research opportunities. We explain the physics of water transport in plants and the limits of this transport system, highlighting the relationships between xylem structure and function. We describe the great variety of techniques existing for evaluating xylem resistance to cavitation. We address several methodological issues and their connection with current debates on conduit refilling and exponentially shaped vulnerability curves. We analyze the trade-offs existing between water transport safety and efficiency. We also stress how little information is available on molecular biology of cavitation and the potential role of aquaporins in conduit refilling. Finally, we draw attention to how plant hydraulic traits can be used for modeling stomatal responses to environmental variables and climate change, including drought mortality. © 2017 Institute of Botany, Chinese Academy of Sciences.

Compositions and methods for xylem-specific expression in plant cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Kyung-Hwan; Ko, Jae-Heung

The invention provides promoter sequences that regulate specific expression of operably linked sequences in developing xylem cells and/or in developing xylem tissue. The developing xylem-specific sequences are exemplified by the DX5, DX8, DX11, and DX15 promoters, portions thereof, and homologs thereof. The invention further provides expression vectors, cells, tissues and plants that contain the invention's sequences. The compositions of the invention and methods of using them are useful in, for example, improving the quantity (biomass) and/or the quality (wood density, lignin content, sugar content etc.) of expressed biomass feedstock products that may be used for bioenergy, biorefinary, and generating woodmore » products such as pulp, paper, and solid wood.« less
Relationships between xylem vessel characteristics, calculated axial hydraulic conductance and size-controlling capacity of peach rootstocks

PubMed Central

Tombesi, Sergio; Johnson, R. Scott; Day, Kevin R.; DeJong, Theodore M.

2010-01-01

Background and Aims Previous studies indicate that the size-controlling capacity of peach rootstocks is associated with reductions of scion water potential during mid-day that are caused by the reduced hydraulic conductance of the rootstock. Thus, shoot growth appears to be reduced by decreases in stem water potential. The aim of this study was to investigate the mechanism of reduced hydraulic conductance in size-controlling peach rootstocks. Methods Anatomical measurements (diameter and frequency) of xylem vessels were determined in shoots, trunks and roots of three contrasting peach rootstocks grown as trees, each with different size-controlling characteristics: ‘Nemaguard’ (vigorous), ‘P30-135’ (intermediate vigour) and ‘K146-43’ (substantially dwarfing). Based on anatomical measurements, the theoretical axial xylem conductance of each tissue type and rootstock genotype was calculated via the Poiseuille–Hagen law. Key Results Larger vessel dimensions were found in the vigorous rootstock (‘Nemaguard’) than in the most dwarfing one (‘K146-43’) whereas vessels of ‘P30-135’ had intermediate dimensions. The density of vessels per xylem area in ‘Nemaguard’ was also less than in ‘P30-135’and ‘K146-43’. These characteristics resulted in different estimated hydraulic conductance among rootstocks: ‘Nemaguard’ had higher theoretical values followed by ‘P30-135’ and ‘K146-43’. Conclusions These data indicate that phenotypic differences in xylem anatomical characteristics of rootstock genotypes appear to influence hydraulic conductance capacity directly, and therefore may be the main determinant of dwarfing in these peach rootstocks. PMID:19939979
De novo transcriptome assemblies of four xylem sap-feeding insects

PubMed Central

Tassone, Erica E.; Cowden, Charles C.

2017-01-01

Abstract Background: Spittle bugs and sharpshooters are well-known xylem sap-feeding insects and vectors of the phytopathogenic bacterium Xylella fastidiosa (Wells), a causal agent of Pierce's disease of grapevines and other crop diseases. Specialized feeding on nutrient-deficient xylem sap is relatively rare among insect herbivores, and only limited genomic and transcriptomic information has been generated for xylem-sap feeders. To develop a more comprehensive understanding of biochemical adaptations and symbiotic relationships that support survival on a nutritionally austere dietary source, transcriptome assemblies for three sharpshooter species and one spittlebug species were produced. Findings: Trinity-based de novo transcriptome assemblies were generated for all four xylem-sap feeders using raw sequencing data originating from whole-insect preps. Total transcripts for each species ranged from 91 384 for Cuerna arida to 106 998 for Homalodisca liturata with transcript totals for Graphocephala atropunctata and the spittlebug Clastoptera arizonana falling in between. The percentage of transcripts comprising complete open reading frames ranged from 60% for H. liturata to 82% for C. arizonana. Bench-marking universal single-copy orthologs analyses for each dataset indicated quality assemblies and a high degree of completeness for all four species. Conclusions: These four transcriptomes represent a significant expansion of data for insect herbivores that feed exclusively on xylem sap, a nutritionally deficient dietary source relative to other plant tissues and fluids. Comparison of transcriptome data with insect herbivores that utilize other dietary sources may illuminate fundamental differences in the biochemistry of dietary specialization. PMID:28327966
Effects of environmental conditions on onset of xylem growth in Pinus sylvestris under drought

PubMed Central

Swidrak, Irene; Gruber, Andreas; Kofler, Werner; Oberhuber, Walter

2012-01-01

Summary We determined influence of environmental factors (air and soil temperature, precipitation, photoperiod) on onset of xylem growth in Scots pine (Pinus sylvestris L.) within a dry inner Alpine valley (750 m a.s.l., Tyrol, Austria) by repeatedly sampling micro-cores throughout 2007-2010 at two sites (xeric and dry-mesic) at the start of the growing season. Temperature sums were calculated in degree-days (DD) ≥ 5 °C from 1 January and 20 March, i.e. spring equinox, to account for photoperiodic control of release from winter dormancy. Threshold temperatures at which xylogenesis had a 0.5 probability of being active were calculated by logistic regression. Onset of xylem growth, which was not significantly different between the xeric and dry-mesic site, ranged from mid-April in 2007 to early May in 2008. Among most study years statistically significant differences (P < 0.05) in onset of xylem growth were detected. Mean air temperature sums calculated from 1 January until onset of xylem growth were 230 ± 44 DD (mean ± standard deviation) at the xeric and 205 ± 36 DD at the dry-mesic site. Temperature sums calculated from spring equinox until onset of xylem growth showed quite less variability during the four year study period amounting to 144 ± 10 and 137 ± 12 DD at the xeric and dry-mesic site, respectively. At both sites xylem growth was active when daily minimum, mean and maximum air temperatures were 5.3, 10.1 and 16.2 °C, respectively. Soil temperature thresholds and DD until onset of xylem growth differed significantly between sites indicating minor importance of root-zone temperature for onset of xylem growth. Although spring precipitation is known to limit radial growth in P. sylvestris exposed to dry inner Alpine climate, results of this study revealed that (i) a daily minimum air temperature threshold for onset of xylem growth in the range of 5-6 °C exists and (ii) air temperature sum rather than precipitation or soil temperature triggers start
Comparative interrogation of the developing xylem transcriptomes of two wood-forming species: Populus trichocarpa and Eucalyptus grandis.

PubMed

Hefer, Charles A; Mizrachi, Eshchar; Myburg, Alexander A; Douglas, Carl J; Mansfield, Shawn D

2015-06-01

Wood formation is a complex developmental process governed by genetic and environmental stimuli. Populus and Eucalyptus are fast-growing, high-yielding tree genera that represent ecologically and economically important species suitable for generating significant lignocellulosic biomass. Comparative analysis of the developing xylem and leaf transcriptomes of Populus trichocarpa and Eucalyptus grandis together with phylogenetic analyses identified clusters of homologous genes preferentially expressed during xylem formation in both species. A conserved set of 336 single gene pairs showed highly similar xylem preferential expression patterns, as well as evidence of high functional constraint. Individual members of multi-gene orthologous clusters known to be involved in secondary cell wall biosynthesis also showed conserved xylem expression profiles. However, species-specific expression as well as opposite (xylem versus leaf) expression patterns observed for a subset of genes suggest subtle differences in the transcriptional regulation important for xylem development in each species. Using sequence similarity and gene expression status, we identified functional homologs likely to be involved in xylem developmental and biosynthetic processes in Populus and Eucalyptus. Our study suggests that, while genes involved in secondary cell wall biosynthesis show high levels of gene expression conservation, differential regulation of some xylem development genes may give rise to unique xylem properties. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.
Fluctuations of cambial activity in relation to precipitation result in annual rings and intra-annual growth zones of xylem and phloem in teak (Tectona grandis) in Ivory Coast

PubMed Central

Dié, Agathe; Kitin, Peter; Kouamé, François N'Guessan; Van den Bulcke, Jan; Van Acker, Joris; Beeckman, Hans

2012-01-01

Background and Aims Teak forms xylem rings that potentially carry records of carbon sequestration and climate in the tropics. These records are only useful when the structural variations of tree rings and their periodicity of formation are known. Methods The seasonality of ring formation in mature teak trees was examined via correlative analysis of cambial activity, xylem and phloem formation, and climate throughout 1·5 years. Xylem and phloem differentiation were visualized by light microscopy and scanning electron microscopy. Key Results A 3 month dry season resulted in semi-deciduousness, cambial dormancy and formation of annual xylem growth rings (AXGRs). Intra-annual xylem and phloem growth was characterized by variable intensity. Morphometric features of cambium such as cambium thickness and differentiating xylem layers were positively correlated. Cambium thickness was strongly correlated with monthly rainfall (R2 = 0·7535). In all sampled trees, xylem growth zones (XGZs) were formed within the AXGRs during the seasonal development of new foliage. When trees achieved full leaf, the xylem in the new XGZs appeared completely differentiated and functional for water transport. Two phloem growth rings were formed in one growing season. Conclusions The seasonal formation pattern and microstructure of teak xylem suggest that AXGRs and XGZs can be used as proxies for analyses of the tree history and climate at annual and intra-annual resolution. PMID:22805529
Are phloem-derived amino acids the origin of the elevated malate concentration in the xylem sap following mineral N starvation in soybean?

PubMed

Vitor, Simone C; do Amarante, Luciano; Sodek, Ladaslav

2018-05-16

A substantial increase in malate in the xylem sap of soybean subjected to mineral N starvation originates mainly from aspartate, a prominent amino acid of the phloem. A substantial increase in xylem malate was found when non-nodulated soybean plants were transferred to a N-free medium. Nodulated plants growing in the absence of mineral N and, therefore, dependent on symbiotic N 2 fixation also contained elevated concentrations of malate in the xylem sap. When either nitrate or ammonium was supplied, malate concentrations in the xylem sap were low, both for nodulated and non-nodulated plants. Evidence was obtained that the elevated malate concentration of the xylem was derived from amino acids supplied by the phloem. Aspartate was a prominent component of the phloem sap amino acids and, therefore, a potential source of malate. Supplying the roots of intact plants with 13 C-aspartate revealed that malate of the xylem sap was readily labelled under N starvation. A hypothetical scheme is proposed whereby aspartate supplied by the phloem is metabolised in the roots and the products of this metabolism cycled back to the shoot. Under N starvation, aspartate metabolism is diverted from asparagine synthesis to supply N for the synthesis of other amino acids via transaminase activity. The by-product of aspartate transaminase activity, oxaloacetate, is transformed to malate and its export accounts for much of the elevated concentration of malate found in the xylem sap. This mechanism represents a new additional role for malate during mineral N starvation of soybean, beyond that of charge balance.
De novo transcriptome assemblies of four xylem sap-feeding insects.

PubMed

Tassone, Erica E; Cowden, Charles C; Castle, S J

2017-03-01

Spittle bugs and sharpshooters are well-known xylem sap-feeding insects and vectors of the phytopathogenic bacterium Xylella fastidiosa (Wells), a causal agent of Pierce's disease of grapevines and other crop diseases. Specialized feeding on nutrient-deficient xylem sap is relatively rare among insect herbivores, and only limited genomic and transcriptomic information has been generated for xylem-sap feeders. To develop a more comprehensive understanding of biochemical adaptations and symbiotic relationships that support survival on a nutritionally austere dietary source, transcriptome assemblies for three sharpshooter species and one spittlebug species were produced. Trinity-based de novo transcriptome assemblies were generated for all four xylem-sap feeders using raw sequencing data originating from whole-insect preps. Total transcripts for each species ranged from 91 384 for Cuerna arida to 106 998 for Homalodisca liturata with transcript totals for Graphocephala atropunctata and the spittlebug Clastoptera arizonana falling in between. The percentage of transcripts comprising complete open reading frames ranged from 60% for H. liturata to 82% for C. arizonana. Bench-marking universal single-copy orthologs analyses for each dataset indicated quality assemblies and a high degree of completeness for all four species. These four transcriptomes represent a significant expansion of data for insect herbivores that feed exclusively on xylem sap, a nutritionally deficient dietary source relative to other plant tissues and fluids. Comparison of transcriptome data with insect herbivores that utilize other dietary sources may illuminate fundamental differences in the biochemistry of dietary specialization. Published by Oxford University Press on behalf of GIGSCI 2017. This work is written by (a) US Government employee(s) and is in the public domain in the US.
Separation and characterization of needle and xylem maritime pine proteins.

PubMed

Costa, P; Pionneau, C; Bauw, G; Dubos, C; Bahrmann, N; Kremer, A; Frigerio, J M; Plomion, C

1999-01-01

Two-dimensional gel electrophoresis (2-DE) and image analysis are currently used for proteome analysis in maritime pine (Pinus pinaster Ait.). This study presents a database of expressed proteins extracted from needles and xylem, two important tissues for growth and wood formation. Electrophoresis was carried out by isoelectric focusing (IEF) in the first dimension and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in the second. Silver staining made it possible to detect an average of 900 and 600 spots on 2-DE gels from needles and xylem, respectively. A total of 28 xylem and 35 needle proteins were characterized by internal peptide microsequencing. Out of these 63 proteins, 57 (90%) could be identified based on amino acid similarity with known proteins, of which 24 (42%) have already been described in conifers. Overall comparison of both tissues indicated that 29% and 36% of the spots were specific to xylem and needles, respectively, while the other spots were of identical molecular weight and isoelectric point. The homology of spot location in 2-DE patterns was further validated by sequence analysis of proteins present in both tissues. A proteomic database of maritime pine is accessible on the internet (http://www.pierroton.inra.fr/genetics/2D/).
Resistance to Dutch Elm Disease Reduces Presence of Xylem Endophytic Fungi in Elms (Ulmus spp.)

PubMed Central

Martín, Juan A.; Witzell, Johanna; Blumenstein, Kathrin; Rozpedowska, Elzbieta; Helander, Marjo; Sieber, Thomas N.; Gil, Luis

2013-01-01

Efforts to introduce pathogen resistance into landscape tree species by breeding may have unintended consequences for fungal diversity. To address this issue, we compared the frequency and diversity of endophytic fungi and defensive phenolic metabolites in elm (Ulmus spp.) trees with genotypes known to differ in resistance to Dutch elm disease. Our results indicate that resistant U. minor and U. pumila genotypes exhibit a lower frequency and diversity of fungal endophytes in the xylem than susceptible U. minor genotypes. However, resistant and susceptible genotypes showed a similar frequency and diversity of endophytes in the leaves and bark. The resistant and susceptible genotypes could be discriminated on the basis of the phenolic profile of the xylem, but not on basis of phenolics in the leaves or bark. As the Dutch elm disease pathogen develops within xylem tissues, the defensive chemistry of resistant elm genotypes thus appears to be one of the factors that may limit colonization by both the pathogen and endophytes. We discuss a potential trade-off between the benefits of breeding resistance into tree species, versus concomitant losses of fungal endophytes and the ecosystem services they provide. PMID:23468900
Analysis of spatial and temporal dynamics of xylem refilling in Acer rubrum L. using magnetic resonance imaging.

PubMed

Zwieniecki, Maciej A; Melcher, Peter J; Ahrens, Eric T

2013-01-01

We report results of an analysis of embolism formation and subsequent refilling observed in stems of Acer rubrum L. using magnetic resonance imaging (MRI). MRI is one of the very few techniques that can provide direct non-destructive observations of the water content within opaque biological materials at a micrometer resolution. Thus, it has been used to determine temporal dynamics and water distributions within xylem tissue. In this study, we found good agreement between MRI measures of pixel brightness to assess xylem liquid water content and the percent loss in hydraulic conductivity (PLC) in response to water stress (P50 values of 2.51 and 2.70 for MRI and PLC, respectively). These data provide strong support that pixel brightness is well correlated to PLC and can be used as a proxy of PLC even when single vessels cannot be resolved on the image. Pressure induced embolism in moderately stressed plants resulted in initial drop of pixel brightness. This drop was followed by brightness gain over 100 min following pressure application suggesting that plants can restore water content in stem after induced embolism. This recovery was limited only to current-year wood ring; older wood did not show signs of recovery within the length of experiment (16 h). In vivo MRI observations of the xylem of moderately stressed (~-0.5 MPa) A. rubrum stems revealed evidence of a spontaneous embolism formation followed by rapid refilling (~30 min). Spontaneous (not induced) embolism formation was observed only once, despite over 60 h of continuous MRI observations made on several plants. Thus this observation provide evidence for the presence of naturally occurring embolism-refilling cycle in A. rubrum, but it is impossible to infer any conclusions in relation to its frequency in nature.
Analysis of spatial and temporal dynamics of xylem refilling in Acer rubrum L. using magnetic resonance imaging

PubMed Central

Zwieniecki, Maciej A.; Melcher, Peter J.; Ahrens, Eric T.

2013-01-01

We report results of an analysis of embolism formation and subsequent refilling observed in stems of Acer rubrum L. using magnetic resonance imaging (MRI). MRI is one of the very few techniques that can provide direct non-destructive observations of the water content within opaque biological materials at a micrometer resolution. Thus, it has been used to determine temporal dynamics and water distributions within xylem tissue. In this study, we found good agreement between MRI measures of pixel brightness to assess xylem liquid water content and the percent loss in hydraulic conductivity (PLC) in response to water stress (P50 values of 2.51 and 2.70 for MRI and PLC, respectively). These data provide strong support that pixel brightness is well correlated to PLC and can be used as a proxy of PLC even when single vessels cannot be resolved on the image. Pressure induced embolism in moderately stressed plants resulted in initial drop of pixel brightness. This drop was followed by brightness gain over 100 min following pressure application suggesting that plants can restore water content in stem after induced embolism. This recovery was limited only to current-year wood ring; older wood did not show signs of recovery within the length of experiment (16 h). In vivo MRI observations of the xylem of moderately stressed (~-0.5 MPa) A. rubrum stems revealed evidence of a spontaneous embolism formation followed by rapid refilling (~30 min). Spontaneous (not induced) embolism formation was observed only once, despite over 60 h of continuous MRI observations made on several plants. Thus this observation provide evidence for the presence of naturally occurring embolism-refilling cycle in A. rubrum, but it is impossible to infer any conclusions in relation to its frequency in nature. PMID:23885258
Analysis of HRCT-derived xylem network reveals reverse flow in some vessels

USDA-ARS?s Scientific Manuscript database

Flow in xylem vessels is modeled based on constructions of three dimensional xylem networks derived from High Resolution Computed Tomography (HRCT) images of grapevine (Vitis vinifera) stems. Flow in 6-14% of the vessels was found to be oriented in the opposite direction to the bulk flow under norma...
Effects of environmental conditions on onset of xylem growth in Pinus sylvestris under drought.

PubMed

Swidrak, Irene; Gruber, Andreas; Kofler, Werner; Oberhuber, Walter

2011-05-01

We determined the influence of environmental factors (air and soil temperature, precipitation, photoperiod) on onset of xylem growth in Scots pine (Pinus sylvestris L.) within a dry inner Alpine valley (750 m a.s.l., Tyrol, Austria) by repeatedly sampling micro-cores throughout 2007-10 at two sites (xeric and dry-mesic) at the start of the growing season. Temperature sums were calculated in degree-days (DD) ≥5 °C from 1 January and 20 March, i.e., spring equinox, to account for photoperiodic control of release from winter dormancy. Threshold temperatures at which xylogenesis had a 0.5 probability of being active were calculated by logistic regression. Onset of xylem growth, which was not significantly different between the xeric and dry-mesic sites, ranged from mid-April in 2007 to early May in 2008. Among most study years, statistically significant differences (P<0.05) in onset of xylem growth were detected. Mean air temperature sums calculated from 1 January until onset of xylem growth were 230 ± 44 DD (mean ± standard deviation) at the xeric site and 205 ± 36 DD at the dry-mesic site. Temperature sums calculated from spring equinox until onset of xylem growth showed somewhat less variability during the 4-year study period, amounting to 144 ± 10 and 137 ± 12 DD at the xeric and dry-mesic sites, respectively. At both sites, xylem growth was active when daily minimum, mean and maximum air temperatures were 5.3, 10.1 and 16.2 °C, respectively. Soil temperature thresholds and DD until onset of xylem growth differed significantly between sites, indicating minor importance of root-zone temperature for onset of xylem growth. Although spring precipitation is known to limit radial growth in P. sylvestris exposed to a dry inner Alpine climate, the results of this study revealed that (i) a daily minimum air temperature threshold for onset of xylem growth in the range 5-6 °C exists and (ii) air temperature sum rather than precipitation or soil temperature triggers
Turnip mosaic virus Moves Systemically through Both Phloem and Xylem as Membrane-Associated Complexes1

PubMed Central

Zheng, Huanquan

2015-01-01

Plant viruses move systemically in plants through the phloem. They move as virions or as ribonucleic protein complexes, although it is not clear what these complexes are made of. The approximately 10-kb RNA genome of Turnip mosaic virus (TuMV) encodes a membrane protein, known as 6K2, that induces endomembrane rearrangements for the formation of viral replication factories. These factories take the form of vesicles that contain viral RNA (vRNA) and viral replication proteins. In this study, we report the presence of 6K2-tagged vesicles containing vRNA and the vRNA-dependent RNA polymerase in phloem sieve elements and in xylem vessels. Transmission electron microscopy observations showed the presence in the xylem vessels of vRNA-containing vesicles that were associated with viral particles. Stem-girdling experiments, which leave xylem vessels intact but destroy the surrounding tissues, confirmed that TuMV could establish a systemic infection of the plant by going through xylem vessels. Phloem sieve elements and xylem vessels from Potato virus X-infected plants also contained lipid-associated nonencapsidated vRNA, indicating that the presence of membrane-associated ribonucleic protein complexes in the phloem and xylem may not be limited to TuMV. Collectively, these studies indicate that viral replication factories could end up in the phloem and the xylem. PMID:25717035
Organic geochemical studies of the transformation of gymnospermous xylem during peatification and coalification to subbituminous coal

USGS Publications Warehouse

Hatcher, P.G.; Lerch, H. E.; Verheyen, T.V.

1990-01-01

It is generally recognized that xylem from trees that are buried in peat swamps is transformed first to huminite macerals in brown coal and then to vitrinite macerals in bituminous coal by processes collectively known as coalification. In order to understand the chemical nature of coalification of xylem and the chemical structures that eventually evolve in coal, we examined a series of gymnospermous xylem samples coalified to varying degrees. The samples included modern fresh xylem, modern degraded xylem in peat, and xylem coalified to ranks of brown coal (lignite B), lignite A, and subbituminous coal. The organic geochemical methods used in this study included solid-state 13C nuclear magnetic resonance (NMR) and pyrolysis/gas chromatography/mass spectrometry. The NMR method provided average compositional information, and the pyrolysis provided detailed molecular information. Although the samples examined include different plants of different geologic ages, they all share a common feature in that they are gymnospermous and presumably have or had a similar kind of lignin. The data obtained in this study provide enough details to allow delineation of specific coalification pathway for the xylem is microbial degradation in peat (peatification), leading to selective removal of cellulosic components. These components constitute a large fraction of the total mass of xylem, usually greater than 50%. Although cellulosic components can survive degradation under certain conditions, their loss during microbial degradation is the rule rather than exception during peatification. As these components of xylem are degraded and lost, lignin, another major component of xylem, is selectively enriched because it is more resistant to microbial degradation than the cellulosic components. Thus, lignin survives peatification in a practically unaltered state and becomes the major precursor of coalified xylem. During its transformation to brown coal and lignite A, lignin in xylem is altered
Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter1[C][W][OPEN

PubMed Central

Mayr, Stefan; Schmid, Peter; Laur, Joan; Rosner, Sabine; Charra-Vaskou, Katline; Dämon, Birgit; Hacke, Uwe G.

2014-01-01

Xylem embolism is a limiting factor for woody species worldwide. Conifers at the alpine timberline are exposed to drought and freeze-thaw stress during winter, which induce potentially lethal embolism. Previous studies indicated that timberline trees survive by xylem refilling. In this study on Picea abies, refilling was monitored during winter and spring seasons and analyzed in the laboratory and in situ experiments, based on hydraulic, anatomical, and histochemical methods. Refilling started in late winter, when the soil was frozen and soil water not available for the trees. Xylem embolism caused up to 86.2% ± 3.1% loss of conductivity and was correlated with the ratio of closed pits. Refilling of xylem as well as recovery in shoot conductance started in February and corresponded with starch accumulation in secondary phloem and in the mesophyll of needles, where we also observed increasing aquaporin densities in the phloem and endodermis. This indicates that active, cellular processes play a role for refilling even under winter conditions. As demonstrated by our experiments, water for refilling was thereby taken up via the branches, likely by foliar water uptake. Our results suggest that refilling is based on water shifts to embolized tracheids via intact xylem, phloem, and parenchyma, whereby aquaporins reduce resistances along the symplastic pathway and aspirated pits facilitate isolation of refilling tracheids. Refilling must be taken into account as a key process in plant hydraulics and in estimating future effects of climate change on forests and alpine tree ecosystems. PMID:24521876
78 FR 77649 - Notification of Proposed Production Activity, Xylem Water Systems USA LLC, Subzone 37D...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-24

... DEPARTMENT OF COMMERCE Foreign-Trade Zones Board [B-106-2013] Notification of Proposed Production Activity, Xylem Water Systems USA LLC, Subzone 37D, (Centrifugal, Submersible Pumps and Related Components), Auburn, New York Xylem Water Systems USA LLC (Xylem), operator of Subzone 37D, submitted a notification of proposed production activity to...
Seasonal dynamics of mobile carbohydrate pools in phloem and xylem of two alpine timberline conifers.

PubMed

Gruber, A; Pirkebner, D; Oberhuber, W

2013-10-01

Recent studies on non-structural carbohydrate (NSC) reserves in trees focused on xylem NSC reserves, while still little is known about changes in phloem carbohydrate pools, where NSC charging might be significantly different. To gain insight on NSC dynamics in xylem and phloem, we monitored NSC concentrations in stems and roots of Pinus cembra (L.) and Larix decidua (Mill.) growing at the alpine timberline throughout 2011. Species-specific differences affected tree phenology and carbon allocation during the course of the year. After a delayed start in spring, NSC concentrations in L. decidua were significantly higher in all sampled tissues from August until the end of growing season. In both species, NSC concentrations were five to seven times higher in phloem than that in xylem. However, significant correlations between xylem and phloem starch content found for both species indicate a close linkage between long-term carbon reserves in both tissues. In L. decidua also, free sugar concentrations in xylem and phloem were significantly correlated throughout the year, while a lack of correlation between xylem and phloem free sugar pools in P. cembra indicate a decline of phloem soluble carbohydrate pools during periods of high sink demand.
Seasonal dynamics of mobile carbohydrate pools in phloem and xylem of two alpine timberline conifers

PubMed Central

GRUBER, A.; PIRKEBNER, D.; OBERHUBER, W.

2016-01-01

Recent studies on non-structural carbohydrate (NSC) reserves in trees focused on xylem NSC reserves, while still little is known about changes in phloem carbohydrate pools, where NSC charging might be significantly different. To gain insight on NSC dynamics in xylem and phloem, we monitored NSC concentrations in stems and roots of Pinus cembra and Larix decidua growing at the alpine timberline throughout 2011. Species-specific differences affected tree phenology and carbon allocation in the course of the year. After a delayed start in spring, NSC concentrations in Larix decidua were significantly higher in all sampled tissues from August until end of growing season. In both species NSC concentrations were five to seven times higher in phloem than in xylem. However, significant correlations between xylem and phloem starch content found for both species indicate a close linkage between long term carbon reserves in both tissues. In Larix decidua also free sugar concentrations in xylem and phloem were significantly correlated throughout the year, while missing correlations between xylem and phloem free sugar pools in Pinus cembra indicate a decline of phloem soluble carbohydrate pools during periods of high sink demand. PMID:24186941

Metal Complexation in Xylem Fluid 1

PubMed Central

White, Michael C.; Chaney, Rufus L.; Decker, A. Morris

1981-01-01

The capacity of ligands in xylem fluid to form metal complexes was tested with a series of in vitro experiments using paper electrophoresis and radiographs. The xylem fluid was collected hourly for 8 hours from soybean (Glycine max L. Merr.) and tomato (Lycopersicon esculentum Mill.) plants grown in normal and Zn-phytotoxic nutrient solutions. Metal complexation was assayed by anodic or reduced cathodic movement of radionuclides (63Ni, 65Zn, 109Cd, 54Mn) that were presumed to have formed negatively charged complexes. Electrophoretic migration of Ni, Zn, Cd, and Mn added to xylem exudate and spotted on KCl- or KNO3-wetted paper showed that stable Ni, Zn, and Cd metal complexes were formed by exudate ligands. No anodic Mn complexes were observed in this test system. Solution pH, plant species, exudate collection time, and Zn phytotoxicity all affected the amount of metal complex formed in exudate. As the pH increased, there was increased anodic metal movement. Soybean exudate generally bound more of each metal than did tomato exudate. Metal binding usually decreased with increasing exudate collection time, and less metal was bound by the high-Zn exudate. Ni, Zn, Cd, and Mn in exudate added to exudate-wetted paper demonstrated the effect of ligand concentration on stable metal complex formation. Complexes for each metal were demonstratable with this method. Cathodic metal movement increased with time of exudate collection, and it was greater in the high-Zn exudate than in the normal-Zn exudate. A model study illustrated the effect of ligand concentration on metal complex stability in the electrophoretic field. Higher ligand (citric acid) concentrations increased the stability for all metals tested. Images PMID:16661666
Effects of Age and Size on Xylem Phenology in Two Conifers of Northwestern China.

PubMed

Zeng, Qiao; Rossi, Sergio; Yang, Bao

2017-01-01

The climatic signals that directly affect the trees can be registered by xylem during its growth. If the timings and duration of xylem formation change, xylogenesis can occur under different environmental conditions and subsequently be subject to different climatic signals. An experimental design was applied in the field to disentangle the effects of age and size on xylem phenology, and it challenges the hypothesis that the timings and dynamics of xylem growth are size-dependent. Intra-annual dynamics of xylem formation were monitored weekly during the growing seasons 2013 and 2014 in Chinese pine ( Pinus tabulaeformis ) and Qilian juniper ( Juniperus przewalskii ) with different sizes and ages in a semi-arid region of northwestern China. Cell differentiation started 3 weeks earlier in 2013 and terminated 1 week later in 2014 in small-young pines than in big-old pines. However, differences in the timings of growth reactivation disappeared when comparing the junipers with different sizes but similar age. Overall, 77 days were required for xylem differentiation to take place, but timings were shorter for older trees, which also exhibited smaller cell production. Results from this study suggest that tree age does play an important role in timings and duration of growth. The effect of age should also be considered to perform reliable responses of trees to climate.
Effects of Age and Size on Xylem Phenology in Two Conifers of Northwestern China

PubMed Central

Zeng, Qiao; Rossi, Sergio; Yang, Bao

2018-01-01

The climatic signals that directly affect the trees can be registered by xylem during its growth. If the timings and duration of xylem formation change, xylogenesis can occur under different environmental conditions and subsequently be subject to different climatic signals. An experimental design was applied in the field to disentangle the effects of age and size on xylem phenology, and it challenges the hypothesis that the timings and dynamics of xylem growth are size-dependent. Intra-annual dynamics of xylem formation were monitored weekly during the growing seasons 2013 and 2014 in Chinese pine (Pinus tabulaeformis) and Qilian juniper (Juniperus przewalskii) with different sizes and ages in a semi-arid region of northwestern China. Cell differentiation started 3 weeks earlier in 2013 and terminated 1 week later in 2014 in small-young pines than in big-old pines. However, differences in the timings of growth reactivation disappeared when comparing the junipers with different sizes but similar age. Overall, 77 days were required for xylem differentiation to take place, but timings were shorter for older trees, which also exhibited smaller cell production. Results from this study suggest that tree age does play an important role in timings and duration of growth. The effect of age should also be considered to perform reliable responses of trees to climate. PMID:29379517
Static and dynamic bending has minor effects on xylem hydraulics of conifer branches (Picea abies, Pinus sylvestris)

PubMed Central

Mayr, Stefan; Bertel, Clara; Dämon, Birgit; Beikircher, Barbara

2014-01-01

The xylem hydraulic efficiency and safety is usually measured on mechanically unstressed samples, although trees may be exposed to combined hydraulic and mechanical stress in the field. We analysed changes in hydraulic conductivity and vulnerability to drought-induced embolism during static bending of Picea abies and Pinus sylvestris branches as well as the effect of dynamic bending on the vulnerability. We hypothesized this mechanical stress to substantially impair xylem hydraulics. Intense static bending caused an only small decrease in hydraulic conductance (−19.5 ± 2.4% in P. abies) but no shift in vulnerability thresholds. Dynamic bending caused a 0.4 and 0.8 MPa decrease of the water potential at 50 and 88% loss of conductivity in P. sylvestris, but did not affect vulnerability thresholds in P. abies. With respect to applied extreme bending radii, effects on plant hydraulics were surprisingly small and are thus probably of minor eco-physiological importance. More importantly, results indicate that available xylem hydraulic analyses (of conifers) sufficiently reflect plant hydraulics under field conditions. PMID:24697679
The tomato plastidic fructokinase SlFRK3 plays a role in xylem development.

PubMed

Stein, Ofer; Damari-Weissler, Hila; Secchi, Francesca; Rachmilevitch, Shimon; German, Marcelo A; Yeselson, Yelena; Amir, Rachel; Schaffer, Arthur; Holbrook, N Michele; Aloni, Roni; Zwieniecki, Maciej A; Granot, David

2016-03-01

Plants have two kinds of fructokinases (FRKs) that catalyze the key step of fructose phosphorylation, cytosolic and plastidic. The major cytosolic tomato FRK, SlFRK2, is essential for the development of xylem vessels. In order to study the role of SlFRK3, which encodes the only plastidic FRK, we generated transgenic tomato (Solanum lycopersicon) plants with RNAi suppression of SlFRK3 as well as plants expressing beta-glucoronidase (GUS) under the SlFRK3 promoter. GUS staining indicated SlFRK3 expression in vascular tissues of the leaves and stems, including cambium, differentiating xylem, young xylem fibers and phloem companion cells. Suppression of SlFRK3 reduced the stem xylem area, stem and root water conductance, and whole-plant transpiration, with minor effects on plant development. However, suppression of SlFRK3 accompanied by partial suppression of SlFRK2 induced significant growth-inhibition effects, including the wilting of mature leaves. Grafting experiments revealed that these growth effects are imposed primarily by the leaves, whose petioles had unlignified, thin-walled xylem fibers with collapsed parenchyma cells around the vessels. A cross between the SlFRK2-antisense and SlFRK3-RNAi lines exhibited similar wilting and anatomical effects, confirming that these effects are the result of the combined suppression of SlFRK3 and SlFRK2. These results demonstrate a role of the plastidic SlFRK3 in xylem development and hydraulic conductance. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.
Are flowers vulnerable to xylem cavitation during drought?

PubMed

Zhang, Feng-Ping; Brodribb, Timothy J

2017-05-17

Water stress is known to cause xylem cavitation in the leaves, roots and stems of plants, but little is known about the vulnerability of flowers to xylem damage during drought. This is an important gap in our understanding of how and when plants become damaged by water stress. Here we address fundamental questions about if and when flowers suffer cavitation damage, using a new technique of cavitation imaging to resolve the timing of cavitation in water-stressed flower petals compared with neighbouring leaves. Leaves and flowers from a sample of two herbaceous and two woody eudicots were exposed to a severe water stress while the spatial and temporal propagation of embolism through veins was recorded. Although in most cases water potentials inducing 50% embolism of herbaceous flower veins were more negative than neighbouring leaves, there was no significant difference between the average vulnerability of leaves and petals of herbaceous species. In both woody species, petals were more vulnerable to cavitation than leaves, in one case by more than 3 MPa. Early cavitation and subsequent damage of flowers in the two woody species would thus be expected to precede leaf damage during drought. Similar cavitation thresholds of flowers and leaves in the herb sample suggest that cavitation during water shortage in these species will occur simultaneously among aerial tissues. Species-specific differences in the cavitation thresholds of petals provide a new axis of variation that may explain contrasting flowering ecology among plant species. © 2017 The Author(s).
The functional role of xylem parenchyma cells and aquaporins during recovery from severe water stress.

PubMed

Secchi, Francesca; Pagliarani, Chiara; Zwieniecki, Maciej A

2017-06-01

Xylem parenchyma cells [vessel associated cells (VACs)] constitute a significant fraction of the xylem in woody plants. These cells are often closely connected with xylem vessels or tracheids via simple pores (remnants of plasmodesmata fields). The close contact and biological activity of VACs during times of severe water stress and recovery from stress suggest that they are involved in the maintenance of xylem transport capacity and responsible for the restoration of vessel/tracheid functionality following embolism events. As recovery from embolism requires the transport of water across xylem parenchyma cell membranes, an understanding of stem-specific aquaporin expression patterns, localization and activity is a crucial part of any biological model dealing with embolism recovery processes in woody plants. In this review, we provide a short overview of xylem parenchyma cell biology with a special focus on aquaporins. In particular we address their distributions and activity during the development of drought stress, during the formation of embolism and the subsequent recovery from stress that may result in refilling. Complemented by the current biological model of parenchyma cell function during recovery from stress, this overview highlights recent breakthroughs on the unique ability of long-lived perennial plants to undergo cycles of embolism-recovery related to drought/rewetting or freeze/thaw events. © 2016 John Wiley & Sons Ltd.
Phototropic bending of non-elongating and radially growing woody stems results from asymmetrical xylem formation.

PubMed

Matsuzaki, Jun; Masumori, Masaya; Tange, Takeshi

2007-05-01

Active phototropic bending of non-elongating and radially growing portion of stems (woody stems) has not been previously documented, whereas negative gravitropic bending is well known. We found phototropic bending in woody stems and searched for the underlying mechanism. We inclined 1-year-old Quercus crispula Blume seedlings and unilaterally illuminated them from a horizontal direction perpendicular to ('normal' illumination) or parallel to ('parallel' illumination) the inclination azimuth. With normal illumination, active phototropic bending and xylem formation could be evaluated separately from the negative gravitropic response and vertical deflection resulting from the weight of the seedlings. One-year-old stems with normal illumination bent significantly, with asymmetrical xylem formation towards the illuminated upper surface and side of the stem, whereas those with parallel illumination showed non-significant lateral bending, with asymmetrical xylem formation only on the upper side. A mechanical model was built on the assumption that a bending moment resulted from the asymmetrical xylem formation during phototropic bending of the woody stems. The model fitted the relationship between the observed spatial distributions of the xylem and the observed lateral bending, and thus supported the hypothesis that phototropic bending of woody stems results from asymmetrical xylem formation, as such occurs during gravitropism.
Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status.

PubMed

Domec, J C; Scholz, F G; Bucci, S J; Meinzer, F C; Goldstein, G; Villalobos-Vega, R

2006-01-01

Vulnerability to water-stress-induced embolism and variation in the degree of native embolism were measured in lateral roots of four co-occurring neotropical savanna tree species. Root embolism varied diurnally and seasonally. Late in the dry season, loss of root xylem conductivity reached 80% in the afternoon when root water potential (psi root) was about -2.6 MPa, and recovered to 25-40% loss of conductivity in the morning when psi root was about -1.0 MPa. Daily variation in psi root decreased, and root xylem vulnerability and capacitance increased with rooting depth. However, all species experienced seasonal minimum psi root close to complete hydraulic failure independent of their rooting depth or resistance to embolism. Predawn psi root was lower than psi soil when psi soil was relatively high (> -0.7 MPa) but became less negative than psi soil, later in the dry season, consistent with a transition from a disequilibrium between plant and soil psi induced by nocturnal transpiration to one induced by hydraulic redistribution of water from deeper soil layers. Shallow longitudinal root incisions external to the xylem prevented reversal of embolism overnight, suggesting that root mechanical integrity was necessary for recovery, consistent with the hypothesis that if embolism is a function of tension, refilling may be a function of internal pressure imbalances. All species shared a common relationship in which maximum daily stomatal conductance declined linearly with increasing afternoon loss of root conductivity over the course of the dry season. Daily embolism and refilling in roots is a common occurrence and thus may be an inherent component of a hydraulic signaling mechanism enabling stomata to maintain the integrity of the hydraulic pipeline in long-lived structures such as stems.
Uncoupling between soil and xylem water isotopic composition: how to discriminate mobile and tightly-bound water?

NASA Astrophysics Data System (ADS)

Martín Gómez, Paula; Aguilera, Mònica; Pemán, Jesús; Gil Pelegrín, Eustaquio; Ferrio, Juan Pedro

2014-05-01

As a general rule, no isotopic fractionation occurs during water uptake and water transport, thus, xylem water reflects source water. However, this correspondence does not always happen. Isotopic enrichment of xylem water has been found in several cases and has been either associated to 'stem processes' like cuticular evaporation 1 and xylem-phloem communication under water stress 2,3 or to 'soil processes' such as species-specific use of contrasting water sources retained at different water potential forces in soil. In this regard, it has been demonstrated that mobile and tightly-bound water may show different isotopic signature 4,5. However, standard cryogenic distillation does not allow to separate different water pools within soil samples. Here, we carried out a study in a mixed adult forest (Pinus sylvestris, Quercus subpyrenaica and Buxus sempervirens) growing in a relatively deep loamy soil in the Pre-Pyrenees. During one year, we sampled xylem from twigs and soil at different depths (10, 30 and 50 cm). We also sampled xylem from trunk and bigger branches to assess whether xylem water was enriched in the distal parts of the tree. We found average deviations in the isotopic signature from xylem to soil of 4o 2o and 2.4o in δ18O and 18.3o 7.3o and 8.9o in δ2H, for P.sylvestris, Q.subpyrenaica and B.sempervirens respectively. Xylem water was always enriched compared to soil. In contrast, we did not find clear differences in isotopic composition between xylem samples along the tree. Declining the hypothesis that 'stem processes' would cause these uncoupling between soil and xylem isotopic values, we tested the possibility to separate mobile and tightly-bound water by centrifugation. Even though we could separate two water fractions in soils close to saturation, we could not recover a mobile fraction in drier soils. In this regard, we welcome suggestions on alternatives to separate different soil fractions in order to find the correspondence between soil and
Hydraulic efficiency and safety of branch xylem increases with height in Sequoia sempervirens (D. Don) crowns.

PubMed

Burgess, Stephen S O; Pittermann, Jarmila; Dawson, Todd E

2006-02-01

The hydraulic limitation hypothesis of Ryan & Yoder (1997, Bioscience 47, 235-242) suggests that water supply to leaves becomes increasingly difficult with increasing tree height. Within the bounds of this hypothesis, we conjectured that the vertical hydrostatic gradient which gravity generates on the water column in tall trees would cause a progressive increase in xylem 'safety' (increased resistance to embolism and implosion) and a concomitant decrease in xylem 'efficiency' (decreased hydraulic conductivity). We based this idea on the historically recognized concept of a safety-efficiency trade-off in xylem function, and tested it by measuring xylem conductivity and vulnerability to embolism of Sequoia sempervirens branches collected at a range of heights. Measurements of resistance of branch xylem to embolism did indeed show an increase in 'safety' with height. However, the expected decrease in xylem 'efficiency' was not observed. Instead, sapwood-specific hydraulic conductivities (Ks) of branches increased slightly, while leaf-specific hydraulic conductivities increased dramatically, with height. The latter could be largely explained by strong vertical gradients in specific leaf area. The increase in Ks with height corresponded to a decrease in xylem wall fraction (a measure of wall thickness), an increase in percentage of earlywood and slight increases in conduit diameter. These changes are probably adaptive responses to the increased transport requirements of leaves growing in the upper canopy where evaporative demand is greater. The lack of a safety-efficiency tradeoff may be explained by opposing height trends in the pit aperture and conduit diameter of tracheids and the major and semi-independent roles these play in determining xylem safety and efficiency, respectively.
Ultrasonic emissions during ice nucleation and propagation in plant xylem.

PubMed

Charrier, Guillaume; Pramsohler, Manuel; Charra-Vaskou, Katline; Saudreau, Marc; Améglio, Thierry; Neuner, Gilbert; Mayr, Stefan

2015-08-01

Ultrasonic acoustic emission analysis enables nondestructive monitoring of damage in dehydrating or freezing plant xylem. We studied acoustic emissions (AE) in freezing stems during ice nucleation and propagation, by combining acoustic and infrared thermography techniques and controlling the ice nucleation point. Ultrasonic activity in freezing samples of Picea abies showed two distinct phases: the first on ice nucleation and propagation (up to 50 AE s(-1) ; reversely proportional to the distance to ice nucleation point), and the second (up to 2.5 AE s(-1) ) after dissipation of the exothermal heat. Identical patterns were observed in other conifer and angiosperm species. The complex AE patterns are explained by the low water potential of ice at the ice-liquid interface, which induced numerous and strong signals. Ice propagation velocities were estimated via AE (during the first phase) and infrared thermography. Acoustic activity ceased before the second phase probably because the exothermal heating and the volume expansion of ice caused decreasing tensions. Results indicate cavitation events at the ice front leading to AE. Ultrasonic emission analysis enabled new insights into the complex process of xylem freezing and might be used to monitor ice propagation in natura. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.
Protein S-Nitrosylation Regulates Xylem Vessel Cell Differentiation in Arabidopsis.

PubMed

Kawabe, Harunori; Ohtani, Misato; Kurata, Tetsuya; Sakamoto, Tomoaki; Demura, Taku

2018-01-01

Post-translational modifications of proteins have important roles in the regulation of protein activity. One such modification, S-nitrosylation, involves the covalent binding of nitric oxide (NO)-related species to a cysteine residue. Recent work showed that protein S-nitrosylation has crucial functions in plant development and environmental responses. In the present study, we investigated the importance of protein S-nitrosylation for xylem vessel cell differentiation using a forward genetics approach. We performed ethyl methanesulfonate mutagenesis of a transgenic Arabidopsis 35S::VND7-VP16-GR line in which the activity of VASCULAR-RELATED NAC-DOMAIN7 (VND7), a key transcription factor involved in xylem vessel cell differentiation, can be induced post-translationally by glucocorticoid treatment, with the goal of obtaining suppressor mutants that failed to differentiate ectopic xylem vessel cells; we named these mutants suppressor of ectopic vessel cell differentiation induced by VND7 (seiv) mutants. We found the seiv1 mutant to be a recessive mutant in which ectopic xylem cell differentiation was inhibited, especially in aboveground organs. In seiv1 mutants, a single nucleic acid substitution (G to A) leading to an amino acid substitution (E36K) was present in the gene encoding S-NITROSOGLUTATHIONE REDUCTASE 1 (GSNOR1), which regulates the turnover of the natural NO donor, S-nitrosoglutathione. An in vitro S-nitrosylation assay revealed that VND7 can be S-nitrosylated at Cys264 and Cys320 located near the transactivation activity-related domains, which were shown to be important for transactivation activity of VND7 by transient reporter assay. Our results suggest crucial roles for GSNOR1-regulated protein S-nitrosylation in xylem vessel cell differentiation, partly through the post-translational modification of VND7. © The Author 2017. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions
A broad survey of hydraulic and mechanical safety in the xylem of conifers

PubMed Central

Bouche, Pauline S.; Larter, Maximilien; Domec, Jean-Christophe; Burlett, Régis; Gasson, Peter; Jansen, Steven; Delzon, Sylvain

2014-01-01

Drought-induced forest dieback has been widely reported over the last decades, and the evidence for a direct causal link between survival and hydraulic failure (xylem cavitation) is now well known. Because vulnerability to cavitation is intimately linked to the anatomy of the xylem, the main objective of this study was to better understand the xylem anatomical properties associated with cavitation resistance. An extensive data set of cavitation resistance traits and xylem anatomical properties was developed for 115 conifer species, with special attention given to the micro-morphology of bordered pits. The ratio of torus to pit aperture diameter, so-called torus overlap, increased with increasing cavitation resistance, while the flexibility of the margo does not seem to play a role, suggesting that air-seeding is located at the seal between the aspirated torus and pit aperture. Moreover, punctured tori were reported in various Pinaceae species. Species resistant to cavitation had thicker tracheid walls, while their lumen diameter (conduit size) was only slightly reduced, minimizing the impact on hydraulic conductance. The results also demonstrated (i) the existence of an indirect trade-off between hydraulic safety and mechanical strength; and (ii) a consistency between species distribution and xylem anatomy: species with a wide torus overlap and high valve effects are found in arid environments such as the Mediterranean region. PMID:24916072
Factors Which Affect the Amount of Inorganic Phosphate, Phosphorylcholine, and Phosphorylethanolamine in Xylem Exudate of Tomato Plants 1

PubMed Central

Martin, Barry A.; Tolbert, N. E.

1983-01-01

Phosphate in the xylem exudate of tomato (Lycopersicon esculentum) plants was 70 to 98% inorganic phosphate (Pi), 2 to 30% P-choline, and less than 1% P-ethanolamine. Upon adding 32Pi to the nutrient, Pi in xylem exudate had the same specific activity within 4 hours. P-choline and P-ethanolamine reached the same specific activity only after 96 hours. The amount of Pi in xylem exudate was dependent on Pi concentration in the nutrient and decreased from 1700 to 170 micromolar when Pi in the nutrient decreased from 50 to 2 micromolar. The flux of 0.4 nmoles organic phosphate per minute per gram fresh weight root into the xylem exudate was not affected by the Pi concentration in the nutrient solution unless it was below 1 micromolar. During 7 days of Pi starvation, Pi in the xylem exudate decreased from 1400 to 130 micromolar while concentrations of the two phosphate esters remained unchanged. The concentration of phosphate esters in the xylem exudate was increased by addition of choline or ethanolamine to the nutrient solution, but Pi remained unchanged. Upon adding [14C]choline to the nutrient, 10 times more [14C]P-choline than [14C]choline was in the xylem exudate and 85 to 90% of the ester phosphate was P-choline. When [14C]ethanolamine was added, [14C]P-ethanolamine and [14C]ethanolamine in the xylem sap were equal in amount. P-choline and P-ethanolamine accumulated in leaves of whole plants at the same time and the same proportion as observed for their flux into the xylem exudate. No relationship between the transport of P-choline and Pi in the xylem was established. Rather, the amount of choline in xylem exudate and its incorporation into phosphatidylcholine in the leaf suggest that the root is a site of synthesis of P-choline and P-ethanolamine for phospholipid synthesis in tomato leaves. PMID:16663240
Relating xylem cavitation to transpiration in cotton

USDA-ARS?s Scientific Manuscript database

Acoustic emmisions (AEs) from xylem cavitation events are characteristic of transpiration processes. Even though a body of work employing AE exists with a large number of species, cotton and other agronomically important crops have either not been investigated, or limited information exists. A few s...
Foliar water supply of tall trees: evidence for mucilage-facilitated moisture uptake from the atmosphere and the impact on pressure bomb measurements.

PubMed

Zimmermann, D; Westhoff, M; Zimmermann, G; Gessner, P; Gessner, A; Wegner, L H; Rokitta, M; Ache, P; Schneider, H; Vásquez, J A; Kruck, W; Shirley, S; Jakob, P; Hedrich, R; Bentrup, F-W; Bamberg, E; Zimmermann, U

2007-01-01

The water supply to leaves of 25 to 60 m tall trees (including high-salinity-tolerant ones) was studied. The filling status of the xylem vessels was determined by xylem sap extraction (using jet-discharge, gravity-discharge, and centrifugation) and by (1)H nuclear magnetic resonance imaging of wood pieces. Simultaneously, pressure bomb experiments were performed along the entire trunk of the trees up to a height of 57 m. Clear-cut evidence was found that the balancing pressure (P(b)) values of leafy twigs were dictated by the ambient relative humidity rather than by height. Refilling of xylem vessels of apical leaves (branches) obviously mainly occurred via moisture uptake from the atmosphere. These findings could be traced back to the hydration and rehydration of mucilage layers on the leaf surfaces and/or of epistomatal mucilage plugs. Xylem vessels also contained mucilage. Mucilage formation was apparently enforced by water stress. The observed mucilage-based foliar water uptake and humidity dependency of the P(b) values are at variance with the cohesion-tension theory and with the hypothesis that P(b) measurements yield information about the relationships between xylem pressure gradients and height.
Arsenate Impact on the Metabolite Profile, Production, and Arsenic Loading of Xylem Sap in Cucumbers (Cucumis sativus L.)

PubMed Central

Uroic, M. Kalle; Salaün, Pascal; Raab, Andrea; Feldmann, Jörg

2012-01-01

Arsenic uptake and translocation studies on xylem sap focus generally on the concentration and speciation of arsenic in the xylem. Arsenic impact on the xylem sap metabolite profile and its production during short term exposure has not been reported in detail. To investigate this, cucumbers were grown hydroponically and arsenate (AsV) and DMA were used for plant treatment for 24 h. Total arsenic and arsenic speciation in xylem sap was analyzed including a metabolite profiling under AsV stress. Produced xylem sap was quantified and absolute arsenic transported was determined. AsV exposure had a significant impact on the metabolite profile of xylem sap. Four m/z values corresponding to four compounds were up-regulated, one compound down-regulated by AsV exposure. The compound down-regulated was identified to be isoleucine. Furthermore, AsV exposure had a significant influence on sap production, leading to a reduction of up to 96% sap production when plants were exposed to 1000 μg kg−1 AsV. No difference to control plants was observed when plants were exposed to 1000 μg kg−1 DMA. Absolute arsenic amount in xylem sap was the lowest at high AsV exposure. These results show that AsV has a significant impact on the production and metabolite profile of xylem sap. The physiological importance of isoleucine needs further attention. PMID:22536187
Organic geochemical studies of the transformation of gymnospermous xylem during peatification and coalification to subbituminous coal

USGS Publications Warehouse

Hatcher, P.G.; Lerch, H. E.; Verheyen, Vincent T.

1989-01-01

Organic geochemical investigations of peatified and coalified xylem from gymnosperms have provided useful information on the organic transformational processes collectively known as coalification. The combined use of solid-state 13C nuclear magnetic resonance (NMR) and pyrolysis/gas chromatography/mass spectrometry (py/gc/ms) has allowed us to examine the organic composition of peatified and coalified xylem on both a bulk (average) compositional basis and on a detailed molecular basis. We conclude from our studies that coalification of gymnospermous xylem involves the following processes: 1. (1) early selective removal of cellulosic materials so that lignin, a primary constituent of xylem, is transformed to macromolecular aromatic components in coal; 2. (2) modification of gymnospermous lignin by demethylation to form catechol-like structures, and by condensation reactions to induce a high level of cross-linking at an early stage of coalification; and 3. (3) dehydroxylation during increasing coalification to subbituminous coal, the resultant xylem becomes more phenolic in character as the catechol-like structures decrease. ?? 1989.
Changes in the Proteome of Xylem Sap in Brassica oleracea in Response to Fusarium oxysporum Stress

PubMed Central

Pu, Zijing; Ino, Yoko; Kimura, Yayoi; Tago, Asumi; Shimizu, Motoki; Natsume, Satoshi; Sano, Yoshitaka; Fujimoto, Ryo; Kaneko, Kentaro; Shea, Daniel J.; Fukai, Eigo; Fuji, Shin-Ichi; Hirano, Hisashi; Okazaki, Keiichi

2016-01-01

Fusarium oxysporum f.sp. conlutinans (Foc) is a serious root-invading and xylem-colonizing fungus that causes yellowing in Brassica oleracea. To comprehensively understand the interaction between F. oxysporum and B. oleracea, composition of the xylem sap proteome of the non-infected and Foc-infected plants was investigated in both resistant and susceptible cultivars using liquid chromatography-tandem mass spectrometry (LC-MS/MS) after in-solution digestion of xylem sap proteins. Whole genome sequencing of Foc was carried out and generated a predicted Foc protein database. The predicted Foc protein database was then combined with the public B. oleracea and B. rapa protein databases downloaded from Uniprot and used for protein identification. About 200 plant proteins were identified in the xylem sap of susceptible and resistant plants. Comparison between the non-infected and Foc-infected samples revealed that Foc infection causes changes to the protein composition in B. oleracea xylem sap where repressed proteins accounted for a greater proportion than those of induced in both the susceptible and resistant reactions. The analysis on the proteins with concentration change > = 2-fold indicated a large portion of up- and down-regulated proteins were those acting on carbohydrates. Proteins with leucine-rich repeats and legume lectin domains were mainly induced in both resistant and susceptible system, so was the case of thaumatins. Twenty-five Foc proteins were identified in the infected xylem sap and 10 of them were cysteine-containing secreted small proteins that are good candidates for virulence and/or avirulence effectors. The findings of differential response of protein contents in the xylem sap between the non-infected and Foc-infected samples as well as the Foc candidate effectors secreted in xylem provide valuable insights into B. oleracea-Foc interactions. PMID:26870056

Changes in the Proteome of Xylem Sap in Brassica oleracea in Response to Fusarium oxysporum Stress.

PubMed

Pu, Zijing; Ino, Yoko; Kimura, Yayoi; Tago, Asumi; Shimizu, Motoki; Natsume, Satoshi; Sano, Yoshitaka; Fujimoto, Ryo; Kaneko, Kentaro; Shea, Daniel J; Fukai, Eigo; Fuji, Shin-Ichi; Hirano, Hisashi; Okazaki, Keiichi

2016-01-01

Fusarium oxysporum f.sp. conlutinans (Foc) is a serious root-invading and xylem-colonizing fungus that causes yellowing in Brassica oleracea. To comprehensively understand the interaction between F. oxysporum and B. oleracea, composition of the xylem sap proteome of the non-infected and Foc-infected plants was investigated in both resistant and susceptible cultivars using liquid chromatography-tandem mass spectrometry (LC-MS/MS) after in-solution digestion of xylem sap proteins. Whole genome sequencing of Foc was carried out and generated a predicted Foc protein database. The predicted Foc protein database was then combined with the public B. oleracea and B. rapa protein databases downloaded from Uniprot and used for protein identification. About 200 plant proteins were identified in the xylem sap of susceptible and resistant plants. Comparison between the non-infected and Foc-infected samples revealed that Foc infection causes changes to the protein composition in B. oleracea xylem sap where repressed proteins accounted for a greater proportion than those of induced in both the susceptible and resistant reactions. The analysis on the proteins with concentration change > = 2-fold indicated a large portion of up- and down-regulated proteins were those acting on carbohydrates. Proteins with leucine-rich repeats and legume lectin domains were mainly induced in both resistant and susceptible system, so was the case of thaumatins. Twenty-five Foc proteins were identified in the infected xylem sap and 10 of them were cysteine-containing secreted small proteins that are good candidates for virulence and/or avirulence effectors. The findings of differential response of protein contents in the xylem sap between the non-infected and Foc-infected samples as well as the Foc candidate effectors secreted in xylem provide valuable insights into B. oleracea-Foc interactions.
Static and dynamic bending has minor effects on xylem hydraulics of conifer branches (Picea abies, Pinus sylvestris).

PubMed

Mayr, Stefan; Bertel, Clara; Dämon, Birgit; Beikircher, Barbara

2014-09-01

The xylem hydraulic efficiency and safety is usually measured on mechanically unstressed samples, although trees may be exposed to combined hydraulic and mechanical stress in the field. We analysed changes in hydraulic conductivity and vulnerability to drought-induced embolism during static bending of Picea abies and Pinus sylvestris branches as well as the effect of dynamic bending on the vulnerability. We hypothesized this mechanical stress to substantially impair xylem hydraulics. Intense static bending caused an only small decrease in hydraulic conductance (-19.5 ± 2.4% in P. abies) but no shift in vulnerability thresholds. Dynamic bending caused a 0.4 and 0.8 MPa decrease of the water potential at 50 and 88% loss of conductivity in P. sylvestris, but did not affect vulnerability thresholds in P. abies. With respect to applied extreme bending radii, effects on plant hydraulics were surprisingly small and are thus probably of minor eco-physiological importance. More importantly, results indicate that available xylem hydraulic analyses (of conifers) sufficiently reflect plant hydraulics under field conditions. © 2014 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.
Altitudinal variations of ground tissue and xylem tissue in terminal shoot of woody species: implications for treeline formation.

PubMed

Chen, Hong; Wang, Haiyang; Liu, Yanfang; Dong, Li

2013-01-01

1. The terminal shoot (or current-year shoot), as one of the most active parts on a woody plant, is a basic unit determining plant height and is potentially influenced by a variety of environmental factors. It has been predicted that tissues amount and their allocation in plant stems may play a critical role in determining plant size in alpine regions. The primary structure in terminal shoots is a key to our understanding treeline formation. The existing theories on treeline formation, however, are still largely lacking of evidence at the species level, much less from anatomy for the terminal shoot. 2. The primary structures within terminal shoot were measured quantitatively for 100 species from four elevation zones along the eastern slope of Gongga Mountain, southwestern China; one group was sampled from above the treeline. An allometric approach was employed to examine scaling relationships interspecifically, and a principal components analysis (PCA) was performed to test the relation among primary xylem, ground tissue, species growth form and altitude. 3. The results showed that xylem tissue size was closely correlated with ground tissue size isometrically across species, while undergoing significant y- or/and x-intercept shift in response to altitudinal belts. Further, a conspicuous characteristic of terminal shoot was its allocation of contrasting tissues between primary xylem and ground tissues with increasing elevation. The result of the PCA showed correlations between anatomical variation, species growth form/height classes and environment. 4. The current study presents a comparative assessment of the allocation of tissue in terminal shoot across phylogenically and ecologically diverse species, and analyzes tissue, function and climate associations with plant growth forms and height classes among species. The interspecific connection between primary xylem ratio and plant size along an elevation gradient suggests the importance of primary xylem in explaining
Altitudinal Variations of Ground Tissue and Xylem Tissue in Terminal Shoot of Woody Species: Implications for Treeline Formation

PubMed Central

Chen, Hong; Wang, Haiyang; Liu, Yanfang; Dong, Li

2013-01-01

1. The terminal shoot (or current-year shoot), as one of the most active parts on a woody plant, is a basic unit determining plant height and is potentially influenced by a variety of environmental factors. It has been predicted that tissues amount and their allocation in plant stems may play a critical role in determining plant size in alpine regions. The primary structure in terminal shoots is a key to our understanding treeline formation. The existing theories on treeline formation, however, are still largely lacking of evidence at the species level, much less from anatomy for the terminal shoot. 2. The primary structures within terminal shoot were measured quantitatively for 100 species from four elevation zones along the eastern slope of Gongga Mountain, southwestern China; one group was sampled from above the treeline. An allometric approach was employed to examine scaling relationships interspecifically, and a principal components analysis (PCA) was performed to test the relation among primary xylem, ground tissue, species growth form and altitude. 3. The results showed that xylem tissue size was closely correlated with ground tissue size isometrically across species, while undergoing significant y- or/and x-intercept shift in response to altitudinal belts. Further, a conspicuous characteristic of terminal shoot was its allocation of contrasting tissues between primary xylem and ground tissues with increasing elevation. The result of the PCA showed correlations between anatomical variation, species growth form/height classes and environment. 4. The current study presents a comparative assessment of the allocation of tissue in terminal shoot across phylogenically and ecologically diverse species, and analyzes tissue, function and climate associations with plant growth forms and height classes among species. The interspecific connection between primary xylem ratio and plant size along an elevation gradient suggests the importance of primary xylem in explaining
Palaeo‐adaptive Properties of the Xylem of Metasequoia: Mechanical/Hydraulic Compromises

PubMed Central

JAGELS, RICHARD; VISSCHER, GEORGE E.; LUCAS, JOHN; GOODELL, BARRY

2003-01-01

The xylem of Metasequoia glyptostroboides Hu et Cheng is characterized by very low density (average specific gravity = 0·27) and tracheids with relatively large dimensions (length and diameter). The microfibril angle in the S2 layer of tracheid walls is large, even in outer rings, suggesting a cambial response to compressive rather than tensile stresses. In some cases, this compressive stress is converted to irreversible strain (plastic deformation), as evidenced by cell wall corrugations. The heartwood is moderately decay resistant, helping to prevent Brazier buckling. These xylem properties are referenced to the measured bending properties of modulus of rupture and modulus of elasticity, and compared with other low‐to‐moderate density conifers. The design strategy for Metasequoia is to produce a mechanically weak but hydraulically efficient xylem that permits rapid height growth and crown development to capture and dominate a wet site environment. The adaptability of these features to a high‐latitude Eocene palaeoenvironment is discussed. PMID:12763758
Palaeo-adaptive properties of the xylem of Metasequoia: mechanical/hydraulic compromises.

PubMed

Jagels, Richard; Visscher, George E; Lucas, John; Goodell, Barry

2003-07-01

The xylem of Metasequoia glyptostroboides Hu et Cheng is characterized by very low density (average specific gravity = 0.27) and tracheids with relatively large dimensions (length and diameter). The microfibril angle in the S2 layer of tracheid walls is large, even in outer rings, suggesting a cambial response to compressive rather than tensile stresses. In some cases, this compressive stress is converted to irreversible strain (plastic deformation), as evidenced by cell wall corrugations. The heartwood is moderately decay resistant, helping to prevent Brazier buckling. These xylem properties are referenced to the measured bending properties of modulus of rupture and modulus of elasticity, and compared with other low-to-moderate density conifers. The design strategy for Metasequoia is to produce a mechanically weak but hydraulically efficient xylem that permits rapid height growth and crown development to capture and dominate a wet site environment. The adaptability of these features to a high-latitude Eocene palaeoenvironment is discussed.
A broad survey of hydraulic and mechanical safety in the xylem of conifers.

PubMed

Bouche, Pauline S; Larter, Maximilien; Domec, Jean-Christophe; Burlett, Régis; Gasson, Peter; Jansen, Steven; Delzon, Sylvain

2014-08-01

Drought-induced forest dieback has been widely reported over the last decades, and the evidence for a direct causal link between survival and hydraulic failure (xylem cavitation) is now well known. Because vulnerability to cavitation is intimately linked to the anatomy of the xylem, the main objective of this study was to better understand the xylem anatomical properties associated with cavitation resistance. An extensive data set of cavitation resistance traits and xylem anatomical properties was developed for 115 conifer species, with special attention given to the micro-morphology of bordered pits. The ratio of torus to pit aperture diameter, so-called torus overlap, increased with increasing cavitation resistance, while the flexibility of the margo does not seem to play a role, suggesting that air-seeding is located at the seal between the aspirated torus and pit aperture. Moreover, punctured tori were reported in various Pinaceae species. Species resistant to cavitation had thicker tracheid walls, while their lumen diameter (conduit size) was only slightly reduced, minimizing the impact on hydraulic conductance. The results also demonstrated (i) the existence of an indirect trade-off between hydraulic safety and mechanical strength; and (ii) a consistency between species distribution and xylem anatomy: species with a wide torus overlap and high valve effects are found in arid environments such as the Mediterranean region. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.
In vivo dynamic analysis of water refilling in embolized xylem vessels of intact Zea mays leaves

PubMed Central

Ryu, Jeongeun; Hwang, Bae Geun; Lee, Sang Joon

2016-01-01

Background and Aims The refilling of embolized xylem vessels under tension is a major issue in water transport among vascular plants. However, xylem embolism and refilling remain poorly understood because of technical limitations. Direct observation of embolism repair in intact plants is essential to understand the biophysical aspects of water refilling in embolized xylem vessels. This paper reports on details of the water refilling process in leaves of the intact herbaceous monocot plant Zea mays and its refilling kinetics obtained by a direct visualization technique. Methods A synchrotron X-ray micro-imaging technique was used to monitor water refilling in embolized xylem vessels of intact maize leaves. Xylem embolism was artificially induced by using a glass capillary; real-time images of water refilling dynamics were consecutively captured at a frame rate of 50 f.p.s. Key Results Water supply in the radial direction initiates droplet formation on the wall of embolized xylem vessels. Each droplet grows into a water column; this phenomenon shows translation motion or continuous increase in water column volume. In some instances, water columns merge and form one large water column. Water refilling in the radial direction causes rapid recovery from embolism in several minutes. The average water refilling velocity is approx. 1 μm s−1. Conclusions Non-destructive visualization of embolized xylem vessels demonstrates rapid water refilling and gas bubble removal as key elements of embolism repair in a herbaceous monocot species. The refilling kinetics provides new insights into the dynamic mechanism of water refilling phenomena. PMID:27539601
Accounting for sap flow from different parts of the root system improves the prediction of xylem ABA concentration in plants grown with heterogeneous soil moisture.

PubMed

Dodd, Ian C; Egea, Gregorio; Davies, William J

2008-01-01

When soil moisture is heterogeneous, sap flow from, and ABA status of, different parts of the root system impact on leaf xylem ABA concentration ([X-ABA]leaf). The robustness of a model for predicting [X-ABA]leaf was assessed. 'Two root-one shoot' grafted sunflower (Helianthus annuus L.) plants received either deficit irrigation (DI, each root system received the same irrigation volumes) or partial rootzone drying (PRD, only one root system was watered and the other dried the soil). Irrespective of whether relative sap flow was assessed using sap flow sensors in vivo or by pressurization of de-topped roots, each root system contributed similarly to total sap flow during DI, while sap flow from roots in drying soil declined linearly with soil water potential (Psisoil) during PRD. Although Psisoil of the irrigated pot determined the threshold Psisoil at which sap flow from roots in drying soil decreased, the slope of this decrease was independent of the wet pot Psisoil. Irrespective of whether sap was collected from the wet or dry root system of PRD plants, or a DI plant, root xylem ABA concentration increased as Psisoil declined. The model, which weighted ABA contributions of each root system according to the sap flow from each, almost perfectly explained [X-ABA] immediately above the graft union. That the model overestimated measured [X-ABA]leaf may result from changes in [X-ABA] along the transport pathway or an artefact of collecting xylem sap from detached leaves. The implications of declining sap flow through partially dry roots during PRD for the control of stomatal behaviour and irrigation scheduling are discussed.
Proteomics approach to identify unique xylem sap proteins in Pierce's disease-tolerant Vitis species.

PubMed

Basha, Sheikh M; Mazhar, Hifza; Vasanthaiah, Hemanth K N

2010-03-01

Pierce's disease (PD) is a destructive bacterial disease of grapes caused by Xylella fastidiosa which is xylem-confined. The tolerance level to this disease varies among Vitis species. Our research was aimed at identifying unique xylem sap proteins present in PD-tolerant Vitis species. The results showed wide variation in the xylem sap protein composition, where a set of polypeptides with pI between 4.5 and 4.7 and M(r) of 31 kDa were present in abundant amount in muscadine (Vitis rotundifolia, PD-tolerant), in reduced levels in Florida hybrid bunch (Vitis spp., PD-tolerant) and absent in bunch grapes (Vitis vinifera, PD-susceptible). Liquid chromatography/mass spectrometry/mass spectrometry analysis of these proteins revealed their similarity to beta-1, 3-glucanase, peroxidase, and a subunit of oxygen-evolving enhancer protein 1, which are known to play role in defense and oxygen generation. In addition, the amount of free amino acids and soluble sugars was found to be significantly lower in xylem sap of muscadine genotypes compared to V. vinifera genotypes, indicating that the higher nutritional value of bunch grape sap may be more suitable for Xylella growth. These data suggest that the presence of these unique proteins in xylem sap is vital for PD tolerance in muscadine and Florida hybrid bunch grapes.
Surface tension phenomena in the xylem sap of three diffuse porous temperate tree species

Treesearch

K. K. Christensen-Dalsgaard; M. T. Tyree; P. G. Mussone

2011-01-01

In plant physiology models involving bubble nucleation, expansion or elimination, it is typically assumed that the surface tension of xylem sap is equal to that of pure water, though this has never been tested. In this study we collected xylem sap from branches of the tree species Populus tremuloides, Betula papyrifera and Sorbus...
Lignin Composition and Structure Differs between Xylem, Phloem and Phellem in Quercus suber L.

PubMed Central

Lourenço, Ana; Rencoret, Jorge; Chemetova, Catarina; Gominho, Jorge; Gutiérrez, Ana; del Río, José C.; Pereira, Helena

2016-01-01

The composition and structure of lignin in different tissues—phellem (cork), phloem and xylem (wood)—of Quercus suber was studied. Whole cell walls and their respective isolated milled lignins were analyzed by pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) and derivatization followed by reductive cleavage (DFRC). Different tissues presented varied p-hydroxyphenyl:guaiacyl:syringyl (H:G:S) lignin compositions. Whereas lignin from cork has a G-rich lignin (H:G:S molar ratio 2:85:13), lignin from phloem presents more S-units (H:G:S molar ratio of 1:58:41) and lignin from xylem is slightly enriched in S-lignin (H:G:S molar ratio 1:45:55). These differences were reflected in the relative abundances of the different interunit linkages. Alkyl-aryl ethers (β–O–4′) were predominant, increasing from 68% in cork, to 71% in phloem and 77% in xylem, as consequence of the enrichment in S-lignin units. Cork lignin was enriched in condensed structures such as phenylcoumarans (β-5′, 20%), dibenzodioxocins (5–5′, 5%), as corresponds to a lignin enriched in G-units. In comparison, lignin from phloem and xylem presented lower levels of condensed linkages. The lignin from cork was highly acetylated at the γ-OH of the side-chain (48% lignin acetylation), predominantly over G-units; while the lignins from phloem and xylem were barely acetylated and this occurred mainly over S-units. These results are a first time overview of the lignin structure in xylem, phloem (generated by cambium), and in cork (generated by phellogen), in agreement with literature that reports that lignin biosynthesis is flexible and cell specific. PMID:27833631
Two Complementary Mechanisms Underpin Cell Wall Patterning during Xylem Vessel Development.

PubMed

Schneider, Rene; Tang, Lu; Lampugnani, Edwin R; Barkwill, Sarah; Lathe, Rahul; Zhang, Yi; McFarlane, Heather E; Pesquet, Edouard; Niittyla, Totte; Mansfield, Shawn D; Zhou, Yihua; Persson, Staffan

2017-10-01

The evolution of the plant vasculature was essential for the emergence of terrestrial life. Xylem vessels are solute-transporting elements in the vasculature that possess secondary wall thickenings deposited in intricate patterns. Evenly dispersed microtubule (MT) bands support the formation of these wall thickenings, but how the MTs direct cell wall synthesis during this process remains largely unknown. Cellulose is the major secondary wall constituent and is synthesized by plasma membrane-localized cellulose synthases (CesAs) whose catalytic activity propels them through the membrane. We show that the protein CELLULOSE SYNTHASE INTERACTING1 (CSI1)/POM2 is necessary to align the secondary wall CesAs and MTs during the initial phase of xylem vessel development in Arabidopsis thaliana and rice ( Oryza sativa ). Surprisingly, these MT-driven patterns successively become imprinted and sufficient to sustain the continued progression of wall thickening in the absence of MTs and CSI1/POM2 function. Hence, two complementary principles underpin wall patterning during xylem vessel development. © 2017 American Society of Plant Biologists. All rights reserved.
Synchrotron X-ray microtomography of xylem embolism in Sequoia sempervirens saplings during cycles of drought and recovery.

PubMed

Choat, Brendan; Brodersen, Craig R; McElrone, Andrew J

2015-02-01

The formation of emboli in xylem conduits can dramatically reduce hydraulic capacity and represents one of the principal mechanisms of drought-induced mortality in woody plants. However, our understanding of embolism formation and repair is constrained by a lack of tools to directly and nondestructively measure these processes at high spatial resolution. Using synchrotron-based microcomputed tomography (microCT), we examined embolism in the xylem of coast redwood (Sequoia sempervirens) saplings that were subjected to cycles of drought and rewatering. Embolism formation was observed occurring by three different mechanisms: as tracheids embolizing in wide tangential bands; as isolated tracheids in seemingly random events; and as functional groups connected to photosynthetic organs. Upon rewatering, stem water potential recovered to predrought stress levels within 24 h; however, no evidence of embolism repair was observed even after a further 2 wk under well-watered conditions. The results indicate that intertracheid air seeding is the primary mechanism by which embolism spreads in the xylem of S. sempervirens, but also show that a small number of tracheids initially become gas-filled via another mechanism. The inability of S. sempervirens saplings to reverse drought-induced embolism is likely to have important ecological impacts on this species. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.
Effect of long-term forest fertilization on Scots pine xylem quality and wood borer performance.

PubMed

Heijari, Juha; Nerg, Anne-Marja; Kainulainen, Pirjo; Noldt, Uwe; Levula, Teuvo; Raitio, Hannu; Holopainen, Jarmo K

2008-01-01

We tested whether changes in long-term nutrient availability would affect the xylem quality and characteristics of Scots pine trees as a food source for the larvae of the xylophagous wood borer Hylotrupes bajulus L. (Cerambycidae). We looked for an effect of host plant growth and xylem structural traits on H. bajulus larval performance, and looked for delayed effects of long-term forest fertilization on xylem chemical quality. In general, larval performance was dependent on larval developmental stage. However, the growth of larvae also varied with host plant quality (increases in the concentration of nitrogen and carbon-based secondary compounds of xylem were correlated with a decrease in the larval growth rate). The greater annual growth of trees reduced tracheid length and correlated positively with second-instar H. bajulus growth rate. This is consistent with the hypothesis that intrinsic growth patterns of host plants influence the development of the xylophagous wood borer H. bajulus.
Coordination and transport of water and carbohydrates in the coupled soil-root-xylem-phloem leaf system

NASA Astrophysics Data System (ADS)

Katul, Gabriel; Huang, Cheng-Wei

2017-04-01

In response to varying environmental conditions, stomatal pores act as biological valves that dynamically adjust their size thereby determining the rate of CO2 assimilation and water loss (i.e., transpiration) to the atmosphere. Although the significance of this biotic control on gas exchange is rarely disputed, representing parsimoniously all the underlying mechanisms responsible for stomatal kinetics remain a subject of some debate. It has been conjectured that stomatal control in seed plants (i.e., angiosperm and gymnosperm) represents a compromise between biochemical demand for CO2 and prevention of excessive water loss. This view has been amended at the whole-plant level, where xylem hydraulics and sucrose transport efficiency in phloem appear to impose additional constraints on gas exchange. If such additional constraints impact stomatal opening and closure, then seed plants may have evolved coordinated photosynthetic-hydraulic-sugar transporting machinery that confers some competitive advantages in fluctuating environmental conditions. Thus, a stomatal optimization model that explicitly considers xylem hydraulics and maximum sucrose transport is developed to explore this coordination in the leaf-xylem-phloem system. The model is then applied to progressive drought conditions. The main findings from the model calculations are that (1) the predicted stomatal conductance from the conventional stomatal optimization theory at the leaf and the newly proposed models converge, suggesting a tight coordination in the leaf-xylem-phloem system; (2) stomatal control is mainly limited by the water supply function of the soil-xylem hydraulic system especially when the water flux through the transpiration stream is significantly larger than water exchange between xylem and phloem; (3) thus, xylem limitation imposed on the supply function can be used to differentiate species with different water use strategy across the spectrum of isohydric to anisohydric behavior.
Relating xylem cavitation to gas exchange in cotton

USDA-ARS?s Scientific Manuscript database

Acoustic emissions (AEs) from xylem cavitation events are characteristic of transpiration processes. Though a body of work using AE exists with a large number of species, cotton and other agronomically important crops have either not been investigated, or limited information exists. The objective of...
Xylella fastidiosa infection of grapevines affects xylem levels of phenolic compounds and pathogenesis-related proteins

USDA-ARS?s Scientific Manuscript database

Pierce’s disease (PD), caused by the xylem-dwelling pathogen Xylella fastidiosa (X.f.), is a serious threat to grape production. The effects of X.f. infection six months post-inoculation on defense-associated proteins and phenolic compounds found in xylem sap and tissue were evaluated. Defense-assoc...
Two Complementary Mechanisms Underpin Cell Wall Patterning during Xylem Vessel Development[OPEN

PubMed Central

Tang, Lu; Barkwill, Sarah; Lathe, Rahul; McFarlane, Heather E.

2017-01-01

The evolution of the plant vasculature was essential for the emergence of terrestrial life. Xylem vessels are solute-transporting elements in the vasculature that possess secondary wall thickenings deposited in intricate patterns. Evenly dispersed microtubule (MT) bands support the formation of these wall thickenings, but how the MTs direct cell wall synthesis during this process remains largely unknown. Cellulose is the major secondary wall constituent and is synthesized by plasma membrane-localized cellulose synthases (CesAs) whose catalytic activity propels them through the membrane. We show that the protein CELLULOSE SYNTHASE INTERACTING1 (CSI1)/POM2 is necessary to align the secondary wall CesAs and MTs during the initial phase of xylem vessel development in Arabidopsis thaliana and rice (Oryza sativa). Surprisingly, these MT-driven patterns successively become imprinted and sufficient to sustain the continued progression of wall thickening in the absence of MTs and CSI1/POM2 function. Hence, two complementary principles underpin wall patterning during xylem vessel development. PMID:28947492
Variations in xylem embolism susceptibility under drought between intact saplings of three walnut species.

PubMed

Knipfer, Thorsten; Barrios-Masias, Felipe H; Cuneo, Italo F; Bouda, Martin; Albuquerque, Caetano P; Brodersen, Craig R; Kluepfel, Daniel A; McElrone, Andrew J

2018-05-30

A germplasm collection containing varied Juglans genotypes holds potential to improve drought resistance of plant materials for commercial production. We used X-ray computed microtomography to evaluate stem xylem embolism susceptibility/repair in relation to vessel anatomical features (size, arrangement, connectivity and pit characteristics) in 2-year-old saplings of three Juglans species. In vivo analysis revealed interspecific variations in embolism susceptibility among Juglans microcarpa, J. hindsii (both native to arid habitats) and J. ailantifolia (native to mesic habitats). Stem xylem of J. microcarpa was more resistant to drought-induced embolism as compared with J. hindsii and J. ailantifolia (differences in embolism susceptibility among older and current year xylem were not detected in any species). Variations in most vessel anatomical traits were negligible among the three species; however, we detected substantial interspecific differences in intervessel pit characteristics. As compared with J. hindsii and J. ailantifolia, low embolism susceptibility in J. microcarpa was associated with smaller pit size in larger diameter vessels, a smaller area of the shared vessel wall occupied by pits, lower pit frequency and no changes in pit characteristics as vessel diameters increased. Changes in amount of embolized vessels following 40 days of re-watering were minor in intact saplings of all three species highlighting that an embolism repair mechanism did not contribute to drought recovery. In conclusion, our data indicate that interspecific variations in drought-induced embolism susceptibility are associated with species-specific pit characteristics, and these traits may provide a future target for breeding efforts aimed at selecting walnut germplasm with improved drought resistance.

Frost drought in conifers at the alpine timberline: xylem dysfunction and adaptations.

PubMed

Mayr, Stefan; Hacke, Uwe; Schmid, Peter; Schwienbacher, Franziska; Gruber, Andreas

2006-12-01

Drought stress can cause xylem embolism in trees when the water potential (psi) in the xylem falls below specific vulnerability thresholds. At the alpine timberline, frost drought is known to cause excessive winter embolism unless xylem vulnerability or transpiration is sufficiently reduced to avoid critical psi. We compared annual courses of psi and embolism in Picea abies, Pinus cembra, Pinus mugo, Larix decidua, and Juniperus communis growing at the timberline vs. low altitude. In addition, vulnerability properties and related anatomical parameters as well as wood density (D(t)) and wall reinforcement (wall thickness related to conduit diameter) were studied. This allowed an estimate of stress intensities as well as a detection of adaptations that reduce embolism formation. At the alpine timberline, psi was lowest during winter with corresponding embolism rates of up to 100% in three of the conifers studied. Only Pinus cembra and Larix decidua avoided winter embolism due to moderate psi. Minor embolism was observed at low altitude where the water potentials of all species remained within a narrow range throughout the year. Within species, differences in psi50 (psi at 50% loss of conductivity) at high vs. low altitude were less than 1 MPa. In Picea abies and Pinus cembra, psi50 was more negative at the timberline while, in the other conifer species, psi50 was more negative at low altitude. Juniperus communis exhibited the lowest (-6.4 +/- 0.04 MPa; mean +/- SE) and Pinus mugo the highest psi50 (-3.34 +/- 0.03 MPa). In some cases, D(t) and tracheid wall reinforcement were higher than in previously established relationships of these parameters with psi50, possibly because of mechanical demands associated with the specific growing conditions. Conifers growing at the alpine timberline were exposed to higher drought stress intensities than individuals at low altitude. Frost drought during winter caused high embolism rates which were probably amplified by freeze
Expression profile of small RNAs in Acacia mangium secondary xylem tissue with contrasting lignin content - potential regulatory sequences in monolignol biosynthetic pathway

PubMed Central

2011-01-01

Background Lignin, after cellulose, is the second most abundant biopolymer accounting for approximately 15-35% of the dry weight of wood. As an important component during wood formation, lignin is indispensable for plant structure and defense. However, it is an undesirable component in the pulp and paper industry. Removal of lignin from cellulose is costly and environmentally hazardous process. Tremendous efforts have been devoted to understand the role of enzymes and genes in controlling the amount and composition of lignin to be deposited in the cell wall. However, studies on the impact of downregulation and overexpression of monolignol biosynthesis genes in model species on lignin content, plant fitness and viability have been inconsistent. Recently, non-coding RNAs have been discovered to play an important role in regulating the entire monolignol biosynthesis pathway. As small RNAs have critical functions in various biological process during wood formation, small RNA profiling is an important tool for the identification of complete set of differentially expressed small RNAs between low lignin and high lignin secondary xylem. Results In line with this, we have generated two small RNAs libraries from samples with contrasting lignin content using Illumina GAII sequencer. About 10 million sequence reads were obtained in secondary xylem of Am48 with high lignin content (41%) and a corresponding 14 million sequence reads were obtained in secondary xylem of Am54 with low lignin content (21%). Our results suggested that A. mangium small RNAs are composed of a set of 12 highly conserved miRNAs families found in plant miRNAs database, 82 novel miRNAs and a large proportion of non-conserved small RNAs with low expression levels. The predicted target genes of those differentially expressed conserved and non-conserved miRNAs include transcription factors associated with regulation of the lignin biosynthetic pathway genes. Some of these small RNAs play an important role in
Expression profile of small RNAs in Acacia mangium secondary xylem tissue with contrasting lignin content - potential regulatory sequences in monolignol biosynthetic pathway.

PubMed

Ong, Seong Siang; Wickneswari, Ratnam

2011-11-30

Lignin, after cellulose, is the second most abundant biopolymer accounting for approximately 15-35% of the dry weight of wood. As an important component during wood formation, lignin is indispensable for plant structure and defense. However, it is an undesirable component in the pulp and paper industry. Removal of lignin from cellulose is costly and environmentally hazardous process. Tremendous efforts have been devoted to understand the role of enzymes and genes in controlling the amount and composition of lignin to be deposited in the cell wall. However, studies on the impact of downregulation and overexpression of monolignol biosynthesis genes in model species on lignin content, plant fitness and viability have been inconsistent. Recently, non-coding RNAs have been discovered to play an important role in regulating the entire monolignol biosynthesis pathway. As small RNAs have critical functions in various biological process during wood formation, small RNA profiling is an important tool for the identification of complete set of differentially expressed small RNAs between low lignin and high lignin secondary xylem. In line with this, we have generated two small RNAs libraries from samples with contrasting lignin content using Illumina GAII sequencer. About 10 million sequence reads were obtained in secondary xylem of Am48 with high lignin content (41%) and a corresponding 14 million sequence reads were obtained in secondary xylem of Am54 with low lignin content (21%). Our results suggested that A. mangium small RNAs are composed of a set of 12 highly conserved miRNAs families found in plant miRNAs database, 82 novel miRNAs and a large proportion of non-conserved small RNAs with low expression levels. The predicted target genes of those differentially expressed conserved and non-conserved miRNAs include transcription factors associated with regulation of the lignin biosynthetic pathway genes. Some of these small RNAs play an important role in epigenetic silencing
Xylella fastidiosa infection of grapevines affects host secondary metabolite and defense-related protein levels within xylem

USDA-ARS?s Scientific Manuscript database

Pierce’s disease of grapevine is a serious threat to grape production and is caused by the xylem-dwelling bacterial pathogen Xylella fastidiosa. Microscopy studies have documented morphological changes to grapevine xylem due to infection by X. fastidiosa. Comparatively, less is known about the bi...
Salivary enzymes are injected into xylem by the glassy-winged sharpshooter, a vector of Xylella fastidiosa

USDA-ARS?s Scientific Manuscript database

Certain hemipteran insects such as the glassy-winged sharpshooter, Homalodisca vitripennis, subsist entirely on xylem fluid, notwithstanding the poor nutrition of such food. Among many adaptations enabling xylem-feeding are aspects of the insect’s salivation that may also allow these insects to tra...
In Situ Visualization of the Dynamics in Xylem Embolism Formation and Removal in the Absence of Root Pressure: A Study on Excised Grapevine Stems.

PubMed

Knipfer, Thorsten; Cuneo, Italo F; Brodersen, Craig R; McElrone, Andrew J

2016-06-01

Gas embolisms formed during drought can disrupt long-distance water transport through plant xylem vessels, but some species have the ability to remove these blockages. Despite evidence suggesting that embolism removal is linked to the presence of vessel-associated parenchyma, the underlying mechanism remains controversial and is thought to involve positive pressure generated by roots. Here, we used in situ x-ray microtomography on excised grapevine stems to determine if embolism removal is possible without root pressure, and if the embolism formation/removal affects vessel functional status after sample excision. Our data show that embolism removal in excised stems was driven by water droplet growth and was qualitatively identical to refilling in intact plants. When stem segments were rehydrated with H2O after excision, vessel refilling occurred rapidly (<1 h). The refilling process was substantially slower when polyethylene glycol was added to the H2O source, thereby providing new support for an osmotically driven refilling mechanism. In contrast, segments not supplied with H2O showed no refilling and increased embolism formation. Dynamic changes in liquid/wall contact angles indicated that the processes of embolism removal (i.e. vessel refilling) by water influx and embolism formation by water efflux were directly linked to the activity of vessel-associated living tissue. Overall, our results emphasize that root pressure is not required as a driving force for vessel refilling, and care should be taken when performing hydraulics measurements on excised plant organs containing living vessel-associated tissue, because the vessel behavior may not be static. © 2016 American Society of Plant Biologists. All Rights Reserved.
Plant GSK3 proteins regulate xylem cell differentiation downstream of TDIF-TDR signalling

NASA Astrophysics Data System (ADS)

Kondo, Yuki; Ito, Tasuku; Nakagami, Hirofumi; Hirakawa, Yuki; Saito, Masato; Tamaki, Takayuki; Shirasu, Ken; Fukuda, Hiroo

2014-03-01

During plant radial growth typically seen in trees, procambial and cambial cells act as meristematic cells in the vascular system to self-proliferate and differentiate into xylem cells. These two processes are regulated by a signalling pathway composed of a peptide ligand and its receptor; tracheary element differentiation inhibitory factor (TDIF) and TDIF RECEPTOR (TDR). Here we show that glycogen synthase kinase 3 proteins (GSK3s) are crucial downstream components of the TDIF signalling pathway suppressing xylem differentiation from procambial cells. TDR interacts with GSK3s at the plasma membrane and activates GSK3s in a TDIF-dependent fashion. Consistently, a specific inhibitor of plant GSK3s strongly induces xylem cell differentiation through BRI1-EMS SUPPRESSOR 1 (BES1), a well-known target transcription factor of GSK3s. Our findings provide insight into the regulation of cell fate determination in meristem maintenance.
A comprehensive strategy for identifying long-distance mobile peptides in xylem sap.

PubMed

Okamoto, Satoru; Suzuki, Takamasa; Kawaguchi, Masayoshi; Higashiyama, Tetsuya; Matsubayashi, Yoshikatsu

2015-11-01

There is a growing awareness that secreted pemediate organ-to-organ communication in higher plants. Xylem sap peptidomics is an effective but challenging approach for identifying long-distance mobile peptides. In this study we developed a simple, gel-free purification system that combines o-chlorophenol extraction with HPLC separation. Using this system, we successfully identified seven oligopeptides from soybean xylem sap exudate that had one or more post-transcriptional modifications: glycosylation, sulfation and/or hydroxylation. RNA sequencing and quantitative PCR analyses showed that the peptide-encoding genes are expressed in multiple tissues. We further analyzed the long-distance translocation of four of the seven peptides using gene-encoding peptides with single amino acid substitutions, and identified these four peptides as potential root-to-shoot mobile oligopeptides. Promoter-GUS analysis showed that all four peptide-encoding genes were expressed in the inner tissues of the root endodermis. Moreover, we found that some of these peptide-encoding genes responded to biotic and/or abiotic factors. These results indicate that our purification system provides a comprehensive approach for effectively identifying endogenous small peptides and reinforce the concept that higher plants employ various peptides in root-to-shoot signaling. © 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.
Xylem formation can be modeled statistically as a function of primary growth and cambium activity.

PubMed

Huang, Jian-Guo; Deslauriers, Annie; Rossi, Sergio

2014-08-01

Primary (budburst, foliage and shoot) growth and secondary (cambium and xylem) growth of plants play a vital role in sequestering atmospheric carbon. However, their potential relationships have never been mathematically quantified and the underlying physiological mechanisms are unclear. We monitored primary and secondary growth in Picea mariana and Abies balsamea on a weekly basis from 2010 to 2013 at four sites over an altitudinal gradient (25-900 m) in the eastern Canadian boreal forest. We determined the timings of onset and termination through the fitted functions and their first derivative. We quantified the potential relationships between primary growth and secondary growth using the mixed-effects model. We found that xylem formation of boreal conifers can be modeled as a function of cambium activity, bud phenology, and shoot and needle growth, as well as species- and site-specific factors. Our model reveals that there may be an optimal mechanism to simultaneously allocate the photosynthetic products and stored nonstructural carbon to growth of different organs at different times in the growing season. This mathematical link can bridge phenological modeling, forest ecosystem productivity and carbon cycle modeling, which will certainly contribute to an improved prediction of ecosystem productivity and carbon equilibrium. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.
Effects of Xylem-Sap Composition on Glassy-Winged Sharpshooter (Hemiptera: Cicadellidae) Egg Maturation on High- and Low-Quality Host Plants.

PubMed

Sisterson, Mark S; Wallis, Christopher M; Stenger, Drake C

2017-04-01

Glassy-winged sharpshooters must feed as adults to produce mature eggs. Cowpea and sunflower are both readily accepted by the glassy-winged sharpshooter for feeding, but egg production on sunflower was reported to be lower than egg production on cowpea. To better understand the role of adult diet in egg production, effects of xylem-sap chemistry on glassy-winged sharpshooter egg maturation was compared for females confined to cowpea and sunflower. Females confined to cowpea consumed more xylem-sap than females held on sunflower. In response, females held on cowpea produced more eggs, had heavier bodies, and greater lipid content than females held on sunflower. Analysis of cowpea and sunflower xylem-sap found that 17 of 19 amino acids were more concentrated in cowpea xylem-sap than in sunflower xylem-sap. Thus, decreased consumption of sunflower xylem-sap was likely owing to perceived lower quality, with decreased egg production owing to a combination of decreased feeding and lower return per unit volume of xylem-sap consumed. Examination of pairwise correlation coefficients among amino acids indicated that concentrations of several amino acids within a plant species were correlated. Principal component analyses identified latent variables describing amino acid composition of xylem-sap. For females held on cowpea, egg maturation was affected by test date, volume of excreta produced, and principal components describing amino acid composition of xylem-sap. Principal component analyses aided in identifying amino acids that were positively or negatively associated with egg production, although determining causality with respect to key nutritional requirements for glassy-winged sharpshooter egg production will require additional testing. Published by Oxford University Press on behalf of Entomological Society of America 2017. This work is written by US Government employees and is in the public domain in the US.
Seasonal development of cambial activity in relation to xylem formation in Chinese fir.

PubMed

Wu, Hongyang; Xu, Huimin; Li, Hanyin; Wei, Dongmei; Lin, Jinxing; Li, Xiaojuan

2016-05-20

The vascular cambium is a lateral meristem which can differentiate into secondary phloem and xylem. The secondary growth of woody plants resulting from vascular cambium activity has been a focus of considerable attention, but the quantitative relationships between cambial activity and secondary xylem formation have been little studied. Our analysis of cytological changes in the cambium of Chinese fir (Cunninghamia lanceolata), revealed a significant positive correlation between vascular cambium cell numbers and cambium zone width through the seasonal cycle. Cambium cell numbers and the cambium cell radial diameter were closely related to xylem formation. Immuno-labeling showed that de-esterified homogalacturonan and (1-4)-β-d-galactan epitopes were highly abundant in cell walls of dormant-stage cambium, whereas high methylesterified homogalacturonan was strongly labeled in the active stage. Raman spectroscopy detected significant changes in the chemical composition of cell walls during the active-dormant stage transition. More pectin and less monolignols occurred in radial cell walls than in tangential walls during the dormant stage, but no significant changes were found in other stages, indicating that pectin accumulation facilitates cell wall expansion, with cambium activity transition. Our quantitative analysis of the relationship between cambial activity and xylem formation, as well as the cell wall modification during the active stage provides useful information about cambial characteristics and xylogenesis. Copyright © 2016. Published by Elsevier GmbH.
Anti-transpirant activity in xylem sap from flooded tomato (Lycopersicon esculentum Mill.) plants is not due to pH-mediated redistributions of root- or shoot-sourced ABA.

PubMed

Else, Mark A; Taylor, June M; Atkinson, Christopher J

2006-01-01

In flooded soils, the rapid effects of decreasing oxygen availability on root metabolic activity are likely to generate many potential chemical signals that may impact on stomatal apertures. Detached leaf transpiration tests showed that filtered xylem sap, collected at realistic flow rates from plants flooded for 2 h and 4 h, contained one or more factors that reduced stomatal apertures. The closure could not be attributed to increased root output of the glucose ester of abscisic acid (ABA-GE), since concentrations and deliveries of ABA conjugates were unaffected by soil flooding. Although xylem sap collected from the shoot base of detopped flooded plants became more alkaline within 2 h of flooding, this rapid pH change of 0.5 units did not alter partitioning of root-sourced ABA sufficiently to prompt a transient increase in xylem ABA delivery. More shoot-sourced ABA was detected in the xylem when excised petiole sections were perfused with pH 7 buffer, compared with pH 6 buffer. Sap collected from the fifth oldest leaf of "intact" well-drained plants and plants flooded for 3 h was more alkaline, by approximately 0.4 pH units, than sap collected from the shoot base. Accordingly, xylem [ABA] was increased 2-fold in sap collected from the fifth oldest petiole compared with the shoot base of flooded plants. However, water loss from transpiring, detached leaves was not reduced when the pH of the feeding solution containing 3-h-flooded [ABA] was increased from 6.7 to 7.1 Thus, the extent of the pH-mediated, shoot-sourced ABA redistribution was not sufficient to raise xylem [ABA] to physiologically active levels. Using a detached epidermis bioassay, significant non-ABA anti-transpirant activity was also detected in xylem sap collected at intervals during the first 24 h of soil flooding.
Hydrolase treatments help unravel the function of intervessel pits in xylem hydraulics.

PubMed

Dusotoit-Coucaud, Anaïs; Brunel, Nicole; Tixier, Aude; Cochard, Hervé; Herbette, Stéphane

2014-03-01

Intervessel pits are structures that play a key role in the efficiency and safety functions of xylem hydraulics. However, little is known about the components of the pit membrane (PM) and their role in hydraulic functions, especially in resistance to cavitation. We tested the effect of commercial chemicals including a cellulase, a hemicellulase, a pectolyase, a proteinase and DTT on xylem hydraulic properties: vulnerability to cavitation (VC) and conductance. The effects were tested on branch segments from Fagus sylvatica (where the effects on pit structure were analyzed using TEM) and Populus tremula. Cellulose hydrolysis resulted in a sharp increase in VC and a significant increase in conductance, related to complete breakdown of the PM. Pectin hydrolysis also induced a sharp increase in VC but with no effect on conductance or pit structure observable by TEM. The other treatments with hemicellulase, proteinase or DTT showed no effect. This study brings evidence that cellulose and pectins are critical components underpinning VC, and that PM components may play distinct roles in the xylem hydraulic safety and efficiency. © 2013 Scandinavian Plant Physiology Society.
N. plumbaginifolia zeaxanthin epoxidase transgenic lines have unaltered baseline ABA accumulations in roots and xylem sap, but contrasting sensitivities of ABA accumulation to water deficit.

PubMed

Borel, C; Audran, C; Frey, A; Marion-Poll, A; Tardieu, F; Simonneau, T

2001-03-01

A series of transgenic lines of Nicotiana plumbaginifolia with modified expression of zeaxanthin epoxidase gene (ZEP) provided contrasting ABA accumulation in roots and xylem sap. For mild water stress, concentration of ABA in the xylem sap ([ABA](xylem)) was clearly lower in plants underexpressing ZEP mRNA (complemented mutants and antisense transgenic lines) than in wild-type. In well-watered conditions, all lines presented similar [ABA](xylem) and similar ABA accumulation rates in detached roots. Plants could, therefore, be grown under normal light intensities and evaporative demand. Both ZEP mRNA abundance and ABA accumulation rate in roots increased with water deficit in all transgenic lines, except in complemented aba2-s1 mutants in which the ZEP gene was controlled by a constitutive promoter which does not respond to water deficit. These lines presented no change in root ABA content either with time or dehydration. The increase in ZEP mRNA abundance in roots with decreasing RWC was more pronounced in detached roots than in whole plants, suggesting a difference in mechanism. In all transgenic lines, a linear relationship was observed between predawn leaf water potential and [ABA](xylem), which could be reproduced in several experiments in the greenhouse and in the growth chamber. It is therefore possible to represent the effect of the transformation by a single parameter, thereby allowing the use of a quantitative approach to assist understanding of the behaviour of transgenic lines.
X-ray CT and histological imaging of xylem vessels organization in Mimosa pudica.

PubMed

Lee, Sang Joon; Song, Kahye; Kim, Hae Koo; Park, Joonghyuk

2013-11-01

Mimosa pudica has three distinct specialized organs, namely, pulvinus, secondary pulvinus, and pulvinule, which are respectively controlling the movements of petioles, leaflets, and pinna in response to external stimuli. Water flow is a key factor for such movements, but detailed studies on the organization of the vascular system for water transport in these organs have not been published yet. In this study, organizations of the xylem vessels and morphological features of the pulvinus, the secondary pulvinus, and the pulvinule were experimentally investigated by X-ray computed tomography and histological technique. Results showed that the xylem vessels were circularly distributed in the specialized motile organs and reorganized into distinct vascular bundles at the extremities. The number and the total cross-sectional area of the xylem vessels were increased inside the specialized motile organs. Morphological characteristics obtained in this study provided new insight to understand the functions of the vascular networks in the dynamic movements of M. pudica. Copyright © 2013 Wiley Periodicals, Inc.
Transcriptome Analysis of the Phytobacterium Xylella fastidiosa Growing under Xylem-Based Chemical Conditions

PubMed Central

Ciraulo, Maristela Boaceff; Santos, Daiene Souza; Rodrigues, Ana Claudia de Freitas Oliveira; de Oliveira, Marcus Vinícius; Rodrigues, Tiago; de Oliveira, Regina Costa; Nunes, Luiz R.

2010-01-01

Xylella fastidiosa is a xylem-limited bacterium responsible for important plant diseases, like citrus-variegated chlorosis (CVC) and grapevine Pierce's disease (PD). Interestingly, in vitro growth of X. fastidiosa in chemically defined media that resemble xylem fluid has been achieved, allowing studies of metabolic processes used by xylem-dwelling bacteria to thrive in such nutrient-poor conditions. Thus, we performed microarray hybridizations to compare transcriptomes of X. fastidiosa cells grown in 3G10-R, a medium that resembles grape sap, and in Periwinkle Wilt (PW), the complex medium traditionally used to cultivate X. fastidiosa. We identified 299 transcripts modulated in response to growth in these media. Some 3G10R-overexpressed genes have been shown to be upregulated in cells directly isolated from infected plants and may be involved in plant colonization, virulence and environmental competition. In contrast, cells cultivated in PW show a metabolic switch associated with increased aerobic respiration and enhanced bacterial growth rates. PMID:20625415
Transcriptome analysis of the phytobacterium Xylella fastidiosa growing under xylem-based chemical conditions.

PubMed

Ciraulo, Maristela Boaceff; Santos, Daiene Souza; Rodrigues, Ana Claudia de Freitas Oliveira; de Oliveira, Marcus Vinícius; Rodrigues, Tiago; de Oliveira, Regina Costa; Nunes, Luiz R

2010-01-01

Xylella fastidiosa is a xylem-limited bacterium responsible for important plant diseases, like citrus-variegated chlorosis (CVC) and grapevine Pierce's disease (PD). Interestingly, in vitro growth of X. fastidiosa in chemically defined media that resemble xylem fluid has been achieved, allowing studies of metabolic processes used by xylem-dwelling bacteria to thrive in such nutrient-poor conditions. Thus, we performed microarray hybridizations to compare transcriptomes of X. fastidiosa cells grown in 3G10-R, a medium that resembles grape sap, and in Periwinkle Wilt (PW), the complex medium traditionally used to cultivate X. fastidiosa. We identified 299 transcripts modulated in response to growth in these media. Some 3G10R-overexpressed genes have been shown to be upregulated in cells directly isolated from infected plants and may be involved in plant colonization, virulence and environmental competition. In contrast, cells cultivated in PW show a metabolic switch associated with increased aerobic respiration and enhanced bacterial growth rates.
Linking xylem water storage with anatomical parameters in five temperate tree species.

PubMed

Jupa, Radek; Plavcová, Lenka; Gloser, Vít; Jansen, Steven

2016-06-01

The release of water from storage compartments to the transpiration stream is an important functional mechanism that provides the buffering of sudden fluctuations in water potential. The ability of tissues to release water per change in water potential, referred to as hydraulic capacitance, is assumed to be associated with the anatomy of storage tissues. However, information about how specific anatomical parameters determine capacitance is limited. In this study, we measured sapwood capacitance (C) in terminal branches and roots of five temperate tree species (Fagus sylvatica L., Picea abies L., Quercus robur L., Robinia pseudoacacia L., Tilia cordata Mill.). Capacitance was calculated separately for water released mainly from capillary (CI; open vessels, tracheids, fibres, intercellular spaces and cracks) and elastic storage compartments (CII; living parenchyma cells), corresponding to two distinct phases of the moisture release curve. We found that C was generally higher in roots than branches, with CI being 3-11 times higher than CII Sapwood density and the ratio of dead to living xylem cells were most closely correlated with C In addition, the magnitude of CI was strongly correlated with fibre/tracheid lumen area, whereas CII was highly dependent on the thickness of axial parenchyma cell walls. Our results indicate that water released from capillary compartments predominates over water released from elastic storage in both branches and roots, suggesting the limited importance of parenchyma cells for water storage in juvenile xylem of temperate tree species. Contrary to intact organs, water released from open conduits in our small wood samples significantly increased CI at relatively high water potentials. Linking anatomical parameters with the hydraulic capacitance of a tissue contributes to a better understanding of water release mechanisms and their implications for plant hydraulics. © The Author 2016. Published by Oxford University Press. All rights
Native root xylem embolism and stomatal closure in stands of Douglas-fir and ponderosa pine: mitigation by hydraulic redistribution.

PubMed

Domec, J-C; Warren, J M; Meinzer, F C; Brooks, J R; Coulombe, R

2004-09-01

Hydraulic redistribution (HR), the passive movement of water via roots from moist to drier portions of the soil, occurs in many ecosystems, influencing both plant and ecosystem-water use. We examined the effects of HR on root hydraulic functioning during drought in young and old-growth Douglas-fir [ Pseudotsuga menziesii (Mirb.) Franco] and ponderosa pine ( Pinus ponderosa Dougl. Ex Laws) trees growing in four sites. During the 2002 growing season, in situ xylem embolism, water deficit and xylem vulnerability to embolism were measured on medium roots (2-4-mm diameter) collected at 20-30 cm depth. Soil water content and water potentials were monitored concurrently to determine the extent of HR. Additionally, the water potential and stomatal conductance ( g(s)) of upper canopy leaves were measured throughout the growing season. In the site with young Douglas-fir trees, root embolism increased from 20 to 55 percent loss of conductivity (PLC) as the dry season progressed. In young ponderosa pine, root embolism increased from 45 to 75 PLC. In contrast, roots of old-growth Douglas-fir and ponderosa pine trees never experienced more than 30 and 40 PLC, respectively. HR kept soil water potential at 20-30 cm depth above -0.5 MPa in the old-growth Douglas-fir site and -1.8 MPa in the old-growth ponderosa pine site, which significantly reduced loss of shallow root function. In the young ponderosa pine stand, where little HR occurred, the water potential in the upper soil layers fell to about -2.8 MPa, which severely impaired root functioning and limited recovery when the fall rains returned. In both species, daily maximum g(s) decreased linearly with increasing root PLC, suggesting that root xylem embolism acted in concert with stomata to limit water loss, thereby maintaining minimum leaf water potential above critical values. HR appears to be an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure.
In Situ Visualization of the Dynamics in Xylem Embolism Formation and Removal in the Absence of Root Pressure: A Study on Excised Grapevine Stems1[OPEN

PubMed Central

Knipfer, Thorsten; Cuneo, Italo F.; Brodersen, Craig R.; McElrone, Andrew J.

2016-01-01

Gas embolisms formed during drought can disrupt long-distance water transport through plant xylem vessels, but some species have the ability to remove these blockages. Despite evidence suggesting that embolism removal is linked to the presence of vessel-associated parenchyma, the underlying mechanism remains controversial and is thought to involve positive pressure generated by roots. Here, we used in situ x-ray microtomography on excised grapevine stems to determine if embolism removal is possible without root pressure, and if the embolism formation/removal affects vessel functional status after sample excision. Our data show that embolism removal in excised stems was driven by water droplet growth and was qualitatively identical to refilling in intact plants. When stem segments were rehydrated with H2O after excision, vessel refilling occurred rapidly (<1 h). The refilling process was substantially slower when polyethylene glycol was added to the H2O source, thereby providing new support for an osmotically driven refilling mechanism. In contrast, segments not supplied with H2O showed no refilling and increased embolism formation. Dynamic changes in liquid/wall contact angles indicated that the processes of embolism removal (i.e. vessel refilling) by water influx and embolism formation by water efflux were directly linked to the activity of vessel-associated living tissue. Overall, our results emphasize that root pressure is not required as a driving force for vessel refilling, and care should be taken when performing hydraulics measurements on excised plant organs containing living vessel-associated tissue, because the vessel behavior may not be static. PMID:27208267

Salivary enzymes are injected into xylem by the glassy-winged sharpshooter, a vector of Xylella fastidiosa.

PubMed

Backus, Elaine A; Andrews, Kim B; Shugart, Holly J; Carl Greve, L; Labavitch, John M; Alhaddad, Hasan

2012-07-01

A few phytophagous hemipteran species such as the glassy-winged sharpshooter, Homalodisca vitripennis, (Germar), subsist entirely on xylem fluid. Although poorly understood, aspects of the insect's salivary physiology may facilitate both xylem-feeding and transmission of plant pathogens. Xylella fastidiosa is a xylem-limited bacterium that causes Pierce's disease of grape and other scorch diseases in many important crops. X. fastidiosa colonizes the anterior foregut (precibarium and cibarium) of H. vitripennis and other xylem-feeding vectors. Bacteria form a dense biofilm anchored in part by an exopolysaccharide (EPS) matrix that is reported to have a β-1,4-glucan backbone. Recently published evidence supports the following, salivation-egestion hypothesis for the inoculation of X. fastidiosa during vector feeding. The insect secretes saliva into the plant and then rapidly takes up a mixture of saliva and plant constituents. During turbulent fluid movements in the precibarium, the bacteria may become mechanically and enzymatically dislodged; the mixture is then egested back out through the stylets into plant cells, possibly including xylem vessels. The present study found that proteins extracted from dissected H. vitripennis salivary glands contain several enzyme activities capable of hydrolyzing glycosidic linkages in polysaccharides such as those found in EPS and plant cell walls, based on current information about the structures of those polysaccharides. One of these enzymes, a β-1,4-endoglucanase (EGase) was enriched in the salivary gland protein extract by subjecting the extract to a few, simple purification steps. The EGase-enriched extract was then used to generate a polyclonal antiserum that was used for immunohistochemical imaging of enzymes in sharpshooter salivary sheaths in grape. Results showed that enzyme-containing gelling saliva is injected into xylem vessels during sharpshooter feeding, in one case being carried by the transpiration stream away
The effect of xylem age on volume yield and sugar content of sugar maple sap

Treesearch

Carter B. Gibbs; Carter B. Gibbs

1969-01-01

At the Burlington, Vermont, research unit of the Northeastern Forest Experiment Station, a study was begun in 1966 in an effort to identify the portions of the xylem that produce the most sap and the sap with the highest sugar content. The study revealed that the greatest volume of sap comes from xylem that is about 35 years old, and that the sweetest sap comes from...
Xylem- and phloem-based transport of CuO nanoparticles in maize (Zea mays L.).

PubMed

Wang, Zhenyu; Xie, Xiaoyan; Zhao, Jian; Liu, Xiaoyun; Feng, Wenqiang; White, Jason C; Xing, Baoshan

2012-04-17

This work reports on the toxicity of CuO nanoparticles (NPs) to maize (Zea mays L.) and their transport and redistribution in the plant. CuO NPs (100 mg L(-1)) had no effect on germination, but inhibited the growth of maize seedlings; in comparison the dissolved Cu(2+) ions and CuO bulk particles had no obvious effect on maize growth. CuO NPs were present in xylem sap as examined by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), showing that CuO NPs were transported from roots to shoots via xylem. Split-root experiments and high-resolution TEM observation further showed that CuO NPs could translocate from shoots back to roots via phloem. During this translocation, CuO NPs could be reduced from Cu (II) to Cu (I). To our knowledge, this is the first report of root-shoot-root redistribution of CuO NPs within maize. The current study provides direct evidence for the bioaccumulation and biotransformation of CuO NPs (20-40 nm) in maize, which has significant implications on the potential risk of NPs and food safety.
Lead mobility within the xylem of red spruce seedlings: Implications for the development of pollution histories

Treesearch

John R. Donnelly; John B. Shane; Paul G. Schaberg

1990-01-01

Development of Pb pollution histories using tree ring analyses has been troubled by possible mobility of Pb within stem xylem. In a 2-yr study, we exposed red spruce (Picea rubens Sarg.) seedlings to Pb during one growing season, with Pb excluded in either the previous or following growing season. Lead levels within xylem rings and bark were...
Plasticity in variation of xylem and phloem cell characteristics of Norway spruce under different local conditions

PubMed Central

Gričar, Jožica; Prislan, Peter; de Luis, Martin; Gryc, Vladimír; Hacurová, Jana; Vavrčík, Hanuš; Čufar, Katarina

2015-01-01

There is limited information on intra-annual plasticity of secondary tissues of tree species growing under different environmental conditions. To increase the knowledge about the plasticity of secondary growth, which allows trees to adapt to specific local climatic regimes, we examined climate–radial growth relationships of Norway spruce [Picea abies (L.) H. Karst.] from three contrasting locations in the temperate climatic zone by analyzing tree-ring widths for the period 1932–2010, and cell characteristics in xylem and phloem increments formed in the years 2009–2011. Variation in the structure of xylem and phloem increments clearly shows that plasticity in seasonal dynamics of cambial cell production and cell differentiation exists on xylem and phloem sides. Anatomical characteristics of xylem and phloem cells are predominantly site-specific characteristics, because they varied among sites but were fairly uniform among years in trees from the same site. Xylem and phloem tissues formed in the first part of the growing season seemed to be more stable in structure, indicating their priority over latewood and late phloem for tree performance. Long-term climate and radial growth analyses revealed that growth was in general less dependent on precipitation than on temperature; however, growth sensitivity to local conditions differed among the sites. Only partial dependence of radial growth of spruce on climatic factors on the selected sites confirms its strategy to adapt the structure of wood and phloem increments to function optimally in local conditions. PMID:26442044
Synchronisms between bud and cambium phenology in black spruce: early-flushing provenances exhibit early xylem formation.

PubMed

Perrin, Magali; Rossi, Sergio; Isabel, Nathalie

2017-05-01

Bud and cambial phenology represent the adaptation of species to the local environment that allows the growing season to be maximized while minimizing the risk of frost for the developing tissues. The temporal relationship between the apical and radial meristems can help in the understanding of tree growth as a whole process. The aim of this study was to compare cambial phenology in black spruce (Picea mariana (Mill.) B.S.P.) provenances classified as early and late bud flushing. The different phases of cambial phenology were assessed on wood microcores sampled weekly from April to October in 2014 and 2015 from 61 trees growing in a provenance trial in Quebec, Canada. Trees showing an early bud flush also exhibited early reactivation of xylem differentiation, although an average difference of 12 days for buds corresponded to small although significant differences of 4 days for xylem. Provenances with early bud flush had an early bud set and completed xylem formation earlier than late bud flush provenances. No significant difference in the period of xylem formation and total growth was observed between the flushing classes. Our results demonstrate that the ecotype differentiation of black spruce provenances represented by the phenological adaptation of buds to the local climate corresponds to specific growth dynamics of the xylem. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Xylella fastidiosa infection and ethylene exposure result in xylem and water movement disruption in grapevine shoots.

PubMed

Pérez-Donoso, Alonso G; Greve, L Carl; Walton, Jeffrey H; Shackel, Ken A; Labavitch, John M

2007-02-01

It is conventionally thought that multiplication of the xylem-limited bacterium Xylella fastidiosa (Xf) within xylem vessels is the sole factor responsible for the blockage of water movement in grapevines (Vitis vinifera) affected by Pierce's disease. However, results from our studies have provided substantial support for the idea that vessel obstructions, and likely other aspects of the Pierce's disease syndrome, result from the grapevine's active responses to the presence of Xf, rather than to the direct action of the bacterium. The use of magnetic resonance imaging (MRI) to observe the distribution of water within the xylem has allowed us to follow nondestructively the development of vascular system obstructions subsequent to inoculation of grapevines with Xf. Because we have hypothesized a role for ethylene produced in vines following infection, the impact of vine ethylene exposure on obstruction development was also followed using MRI. In both infected and ethylene-exposed plants, MRI shows that an important proportion of the xylem vessels become progressively air embolized after the treatments. The loss of xylem water-transporting function, assessed by MRI, has been also correlated with a decrease in stem-specific hydraulic conductivity (K(S)) and the presence of tyloses in the lumens of obstructed water conduits. We have observed that the ethylene production of leaves from infected grapevines is greater than that from healthy vines and, therefore, propose that ethylene may be involved in a series of cellular events that coordinates the vine's response to the pathogen.
The amino acid distribution in rachis xylem sap and phloem exudate of Vitis vinifera 'Cabernet Sauvignon' bunches.

PubMed

Gourieroux, Aude M; Holzapfel, Bruno P; Scollary, Geoffrey R; McCully, Margaret E; Canny, Martin J; Rogiers, Suzy Y

2016-08-01

Amino acids are essential to grape berry and seed development and they are transferred to the reproductive structures through the phloem and xylem from various locations within the plant. The diurnal and seasonal dynamics of xylem and phloem amino acid composition in the leaf petiole and bunch rachis of field-grown Cabernet Sauvignon are described to better understand the critical periods for amino acid import into the berry. Xylem sap was extracted by the centrifugation of excised leaf petioles and rachises, while phloem exudate was collected by immersing these structures in an ethylenediaminetetraacetic acid (EDTA) buffer. Glutamine and glutamic acid were the predominant amino acids in the xylem sap of both grapevine rachises and petioles, while arginine and glycine were the principal amino acids of the phloem exudate. The amino acid concentrations within the xylem sap and phloem exudate derived from these structures were greatest during anthesis and fruit set, and a second peak occurred within the rachis phloem at the onset of ripening. The concentrations of the amino acids within the phloem and xylem sap of the rachis were highest just prior to or after midnight while the flow of sugar through the rachis phloem was greatest during the early afternoon. Sugar exudation rates from the rachis was greater than that of the petiole phloem between anthesis and berry maturity. In summary, amino acid and sugar delivery through the vasculature to grape berries fluctuates over the course of the day as well as through the season and is not necessarily related to levels near the source. Copyright © 2016 Elsevier Masson SAS. All rights reserved.
Vulnerability to xylem embolism as a major correlate of the environmental distribution of rain forest species on a tropical island.

PubMed

Trueba, Santiago; Pouteau, Robin; Lens, Frederic; Feild, Taylor S; Isnard, Sandrine; Olson, Mark E; Delzon, Sylvain

2017-02-01

Increases in drought-induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P 50 ) of 13 woody species endemic to New Caledonia and with different xylem conduit morphologies. We examined the relation between P 50 , along with other leaf and xylem functional traits, and a range of habitat variables. Selected species had P 50 values ranging between -4.03 and -2.00 MPa with most species falling in a narrow range of resistance to embolism above -2.7 MPa. Embolism vulnerability was significantly correlated with elevation, mean annual temperature and percentage of species occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P 50 . Commonly used functional traits such as wood density and leaf traits were not related to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as a major driver of species environmental distribution. Drought-induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rain forest woody species. © 2016 John Wiley & Sons Ltd.
Secondary metabolite concentrations and terpene emissions of Scots pine xylem after long-term forest fertilization.

PubMed

Turtola, S; Manninen, A M; Holopainen, J K; Levula, T; Raitio, H; Kainulainen, P

2002-01-01

Secondary compounds are known to be associated with the resistance of conifer xylem against insects and fungi. The effects of long-term forest fertilization with nitrogen (N) or with N, calcium (Ca), and phosphorus (P) on secondary compounds in the xylem of 50-yr-old Scots pine (Pinus sylvestris L.) trees were examined. Xylem samples were collected from trees growing in three locations in southern Finland: Vilppula, Padasjoki, and Punkaharju. Forests were fertilized every fifth (Vilppula and Padasjoki) or tenth (Punkaharju) year since the 1950s. We compared concentrations of individual and total monoterpenes and resin acids in the heartwood and sapwood of Scots pine. Terpene emissions were analyzed from the sapwood and total phenolics from the heartwood. Fertilization did not have any significant effect on the concentrations and emissions of xylem monoterpenes. Concentrations of several individual terpenes in sapwood were positively correlated with the corresponding terpene emission. The concentrations of individual resin acids (i.e., abietic and dehydroabietic) decreased significantly in Punkaharju, but increased in the sapwood of N-fertilized trees compared with control ones at Padasjoki and Vilppula. The concentrations of resin acids in the heartwood were not significantly affected by fertilization. Both fertilization treatments decreased the total phenolic concentrations in the heartwood of trees growing in Padasjoki. There was a significant positive correlation between the total phenolics and total resin acid concentration. Overall, resin acids and phenolics seemed be more responsive than monoterpenes to N treatment. These results suggest that forest fertilization might cause slight changes in secondary compound concentrations of xylem, and thus might have significance in the decay resistance of wood.
A noninvasive optical system for the measurement of xylem and phloem sap flow in woody plants of small stem size.

PubMed

Helfter, Carole; Shephard, Jonathon D; Martinez-Vilalta, Jordi; Mencuccini, Maurizio; Hand, Duncan P

2007-02-01

Over the past 70 years, heat has been widely used as a tracer for estimating the flow of water in woody and herbaceous plants. However, most commercially available techniques for monitoring whole plant water use are invasive and the measurements are potentially flawed because of wounding of the xylem tissue. The study of photosynthate transport in the phloem remains in its infancy, and little information about phloem transport rates is available owing to the fragility of the vascular tissue. The aim of our study was to develop a compact, stand-alone non-invasive system allowing for direct detection of phloem and xylem sap movement. The proposed method uses a heat pulse as a tracer for sap flow. Heat is applied to the surface of the stem with a near-infrared laser source, and heat propagation is monitored externally by means of an infrared camera. Heat pulse velocities are determined from the thermometric data and related to the more useful quantity, mass flow rate. Simulation experiments on the xylem tissue of severed silver birch (Betula pendula Roth.) branch segments were performed to assess the feasibility of the proposed approach, highlight the characteristics of the technique and outline calibration strategies. Good agreement between imposed and measured flow rates was achieved leading to experimentation with live silver birch and oak (Quercus robur L.) saplings. It was demonstrated that water flow through xylem vessels can be monitored non-invasively on an intact stem with satisfactory accuracy despite simultaneous sugar transport in the phloem. In addition, it was demonstrated that the technique allows for unequivocal detection of phloem flow velocities.
Curios relationship revealed by looking at long term data sets-The geometry and allometric scaling of diel xylem sap flux in tropical trees.

PubMed

Kunert, Norbert

2016-10-20

Daily xylem sap flux values (daily J s ) and maximum xylem sap flux values (max J s ) from 125 tropical trees from different study sites in the Neotropics were compared. A cross species and study site relationship was found between daily and maximum values. The relationship can be expressed as daily J s =6.5x max J s . The geometrical relationship between the maximum xylem sap flux of a given day is thus defining the daily xylem sap flux rates. Assuming a bell-shaped diurnal sap flux course and a relatively constant day length the maximum xylem sap flux is the only possible changing variable to define daily fluxes. Further, this relationship is showing the inertia of the xylem sap flux as a physical object and highlights the delayed response to environmental changes and its subsequent inevitable susceptibility under environmental stress to hydraulic failure. Copyright © 2016 Elsevier GmbH. All rights reserved.
Interplay of growth rate and xylem plasticity for optimal coordination of carbon and hydraulic economies in Fraxinus ornus trees.

PubMed

Petit, Giai; Savi, Tadeja; Consolini, Martina; Anfodillo, Tommaso; Nardini, Andrea

2016-11-01

Efficient leaf water supply is fundamental for assimilation processes and tree growth. Renovating the architecture of the xylem transport system requires an increasing carbon investment while growing taller, and any deficiency of carbon availability may result in increasing hydraulic constraints to water flow. Therefore, plants need to coordinate carbon assimilation and biomass allocation to guarantee an efficient and safe long-distance transport system. We tested the hypothesis that reduced branch elongation rates together with carbon-saving adjustments of xylem anatomy hydraulically compensate for the reduction in biomass allocation to xylem. We measured leaf biomass, hydraulic and anatomical properties of wood segments along the main axis of branches in 10 slow growing (SG) and 10 fast growing (FG) Fraxinus ornus L. trees. Branches of SG trees had five times slower branch elongation rate (7 vs 35 cm year -1 ), and produced a higher leaf biomass (P < 0.0001) and thinner xylem rings with fewer but larger vessels (P < 0.0001). On the contrary, we found no differences between SG and FG trees in terms of leaf-specific conductivity (P > 0.05) and xylem safety (Ψ 50 ≈ -3.2 MPa). Slower elongation rate coupled with thinner annual rings and larger vessels allows the reduction of carbon costs associated with growth, while maintaining similar leaf-specific conductivity and xylem safety. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.
Up-regulation of abscisic acid signaling pathway facilitates aphid xylem absorption and osmoregulation under drought stress.

PubMed

Guo, Huijuan; Sun, Yucheng; Peng, Xinhong; Wang, Qinyang; Harris, Marvin; Ge, Feng

2016-02-01

The activation of the abscisic acid (ABA) signaling pathway reduces water loss from plants challenged by drought stress. The effect of drought-induced ABA signaling on the defense and nutrition allocation of plants is largely unknown. We postulated that these changes can affect herbivorous insects. We studied the effects of drought on different feeding stages of pea aphids in the wild-type A17 of Medicago truncatula and ABA signaling pathway mutant sta-1. We examined the impact of drought on plant water status, induced plant defense signaling via the abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA) pathways, and on the host nutritional quality in terms of leaf free amino acid content. During the penetration phase of aphid feeding, drought decreased epidermis/mesophyll resistance but increased mesophyll/phloem resistance of A17 but not sta-1 plants. Quantification of transcripts associated with ABA, JA and SA signaling indicated that the drought-induced up-regulation of ABA signaling decreased the SA-dependent defense but increased the JA-dependent defense in A17 plants. During the phloem-feeding phase, drought had little effect on the amino acid concentrations and the associated aphid phloem-feeding parameters in both plant genotypes. In the xylem absorption stage, drought decreased xylem absorption time of aphids in both genotypes because of decreased water potential. Nevertheless, the activation of the ABA signaling pathway increased water-use efficiency of A17 plants by decreasing the stomatal aperture and transpiration rate. In contrast, the water potential of sta-1 plants (unable to close stomata) was too low to support xylem absorption activity of aphids; the aphids on sta-1 plants had the highest hemolymph osmolarity and lowest abundance under drought conditions. Taken together this study illustrates the significance of cross-talk between biotic-abiotic signaling pathways in plant-aphid interaction, and reveals the mechanisms leading to alter
Up-regulation of abscisic acid signaling pathway facilitates aphid xylem absorption and osmoregulation under drought stress

PubMed Central

Guo, Huijuan; Sun, Yucheng; Peng, Xinhong; Wang, Qinyang; Harris, Marvin; Ge, Feng

2016-01-01

The activation of the abscisic acid (ABA) signaling pathway reduces water loss from plants challenged by drought stress. The effect of drought-induced ABA signaling on the defense and nutrition allocation of plants is largely unknown. We postulated that these changes can affect herbivorous insects. We studied the effects of drought on different feeding stages of pea aphids in the wild-type A17 of Medicago truncatula and ABA signaling pathway mutant sta-1. We examined the impact of drought on plant water status, induced plant defense signaling via the abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA) pathways, and on the host nutritional quality in terms of leaf free amino acid content. During the penetration phase of aphid feeding, drought decreased epidermis/mesophyll resistance but increased mesophyll/phloem resistance of A17 but not sta-1 plants. Quantification of transcripts associated with ABA, JA and SA signaling indicated that the drought-induced up-regulation of ABA signaling decreased the SA-dependent defense but increased the JA-dependent defense in A17 plants. During the phloem-feeding phase, drought had little effect on the amino acid concentrations and the associated aphid phloem-feeding parameters in both plant genotypes. In the xylem absorption stage, drought decreased xylem absorption time of aphids in both genotypes because of decreased water potential. Nevertheless, the activation of the ABA signaling pathway increased water-use efficiency of A17 plants by decreasing the stomatal aperture and transpiration rate. In contrast, the water potential of sta-1 plants (unable to close stomata) was too low to support xylem absorption activity of aphids; the aphids on sta-1 plants had the highest hemolymph osmolarity and lowest abundance under drought conditions. Taken together this study illustrates the significance of cross-talk between biotic-abiotic signaling pathways in plant-aphid interaction, and reveals the mechanisms leading to alter
Xylem monoterpenes of pines: distribution, variation, genetics, function

Treesearch

Richard Smith

2000-01-01

The monoterpenes of about 16,000 xylem resin samples of pine (Pinus) speciesand hybridsâlargely from the western United Statesâwere analyzed in this long-term study of the resistance of pines to attack by bark beetles (Coleoptera:Scolytidae), with special emphasis on resistance to the western pine beetle(Dendroctonus brevicomis). The samples were analyzed by gas liquid...
Metabolomics of tomato xylem sap during bacterial wilt reveals Ralstonia solanacearum produces abundant putrescine, a metabolite that accelerates wilt disease.

PubMed

Lowe-Power, Tiffany M; Hendrich, Connor G; von Roepenack-Lahaye, Edda; Li, Bin; Wu, Dousheng; Mitra, Raka; Dalsing, Beth L; Ricca, Patrizia; Naidoo, Jacinth; Cook, David; Jancewicz, Amy; Masson, Patrick; Thomma, Bart; Lahaye, Thomas; Michael, Anthony J; Allen, Caitilyn

2018-04-01

Ralstonia solanacearum thrives in plant xylem vessels and causes bacterial wilt disease despite the low nutrient content of xylem sap. We found that R. solanacearum manipulates its host to increase nutrients in tomato xylem sap, enabling it to grow better in sap from infected plants than in sap from healthy plants. Untargeted GC/MS metabolomics identified 22 metabolites enriched in R. solanacearum-infected sap. Eight of these could serve as sole carbon or nitrogen sources for R. solanacearum. Putrescine, a polyamine that is not a sole carbon or nitrogen source for R. solanacearum, was enriched 76-fold to 37 µM in R. solanacearum-infected sap. R. solanacearum synthesized putrescine via a SpeC ornithine decarboxylase. A ΔspeC mutant required ≥ 15 µM exogenous putrescine to grow and could not grow alone in xylem even when plants were treated with putrescine. However, co-inoculation with wildtype rescued ΔspeC growth, indicating R. solanacearum produced and exported putrescine to xylem sap. Intriguingly, treating plants with putrescine before inoculation accelerated wilt symptom development and R. solanacearum growth and systemic spread. Xylem putrescine concentration was unchanged in putrescine-treated plants, so the exogenous putrescine likely accelerated disease indirectly by affecting host physiology. These results indicate that putrescine is a pathogen-produced virulence metabolite. © 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.
Spatial distribution of xylem embolisms in the stems of Pinus thunbergii at the threshold of fatal drought stress.

PubMed

Umebayashi, Toshihiro; Morita, Toshimitsu; Utsumi, Yasuhiro; Kusumoto, Dai; Yasuda, Yuko; Haishi, Tomoyuki; Fukuda, Kenji

2016-10-01

Although previous studies have suggested that branch dieback and whole-plant death due to drought stress occur at 50-88% loss of stem hydraulic conductivity (P 50 and P 88 , respectively), the dynamics of catastrophic failure in the water-conducting pathways in whole plants subjected to drought remain poorly understood. We examined the dynamics of drought stress tolerance in 3-year-old Japanese black pine (Pinus thunbergii Parl.). We nondestructively monitored (i) the spatial distribution of drought-induced embolisms in the stem at greater than P 50 and (ii) recovery from embolisms following rehydration. Stem water distributions were visualized by cryo-scanning electron microscopy. The percentages of both embolized area and loss of hydraulic conductivity showed similar patterns of increase, although the water loss in xylem increased markedly at -5.0 MPa or less. One seedling that had reached 72% loss of the water-conducting area survived and the xylem water potential recovered to -0.3 MPa. We concluded that Japanese black pines may need to maintain water-filled tracheids within earlywood of the current-year xylem under natural conditions to avoid disconnection of water movement between the stem and the tops of branches. It is necessary to determine the spatial distribution of embolisms around the point of the lethal threshold to gain an improved understanding of plant survival under conditions of drought. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Control of the rate of cell enlargement: Excision, wall relaxation, and growth-induced water potentials.

PubMed

Boyer, J S; Cavalieri, A J; Schulze, E D

1985-04-01

A new guillotine thermocouple psychrometer was used to make continuous measurements of water potential before and after the excision of elongating and mature regions of darkgrown soybean (Glycine max L. Merr.) stems. Transpiration could not occur, but growth took place during the measurement if the tissue was intact. Tests showed that the instrument measured the average water potential of the sampled tissue and responded rapidly to changes in water potential. By measuring tissue osmotic potential (Ψ s ), turgor pressure (Ψ p ) could be calculated. In the intact plant, Ψ s and Ψ p were essentially constant for the entire 22 h measurement, but Ψ s was lower and Ψ p higher in the elongating region than in the mature region. This caused the water potential in the elongating region to be lower than in the mature region. The mature tissue equilibrated with the water potential of the xylem. Therefore, the difference in water potential between mature and elongating tissue represented a difference between the xylem and the elongating region, reflecting a water potential gradient from the xylem to the epidermis that was involved in supplying water for elongation. When mature tissue was excised with the guillotine, Ψ s and Ψ p did not change. However, when elongating tissue was excised, water was absorbed from the xylem, whose water potential decreased. This collapsed the gradient and prevented further water uptake. Tissue Ψ p then decreased rapidly (5 min) by about 0.1 MPa in the elongating tissue. The Ψ p decreased because the cell walls relaxed as extension, caused by Ψ p , continued briefly without water uptake. The Ψ p decreased until the minimum for wall extension (Y) was reached, whereupon elongation ceased. This was followed by a slow further decrease in Y but no additional elongation. In elongating tissue excised with mature tissue attached, there was almost no effect on water potential or Ψ p for several hours. Nevertheless, growth was reduced
Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status.

Treesearch

J-C. Domec; F.G. Scholz; S.J. Bucci; F.C. Meinzer; G. Goldstein; R. Villalobos-Vega

2006-01-01

Vulnerability to water-stress-induced embolism and variation in the degree of native embolism were measured in lateral roots of four co-occuring neotropical savanna tree species. Root embolism varied diurnally and seasonally. Late in the dry season, loss of root xylem conductivity reached 80% in the afternoon when root water potential (ψroot...

Influence of Drought on the Hydraulic Efficiency and the Hydraulic Safety of the Xylem - Case of a Semi-arid Conifer.

NASA Astrophysics Data System (ADS)

Gentine, P.; Guerin, M. F.; von Arx, G.; Martin-Benito, D.; Griffin, K. L.; McDowell, N.; Pockman, W.; Andreu-Hayles, L.

2017-12-01

Recent droughts in the Southwest US have resulted in extensive mortality in the pinion pine population (Pinus Edulis). An important factor for resiliency is the ability of a plant to maintain a functional continuum between soil and leaves, allowing water's motion to be sustained or resumed. During droughts, loss of functional tracheids happens through embolism, which can be partially mitigated by increasing the hydraulic safety of the xylem. However, higher hydraulic safety is usually achieved by building narrower tracheids with thicker walls, resulting in a reduction of the hydraulic efficiency of the xylem (conductivity per unit area). Reduced efficiency constrains water transport, limits photosynthesis and might delay recovery after the drought. Supporting existing research on safety-efficiency tradeoff, we test the hypothesis that under dry conditions, isohydric pinions grow xylem that favor efficiency over safety. Using a seven-year experiment with three watering treatments (drought, control, irrigated) in New Mexico, we investigate the effect of drought on the xylem anatomy of pinions' branches. We also compare the treatment effect with interannual variations in xylem structure. We measure anatomical variables - conductivities, cell wall thicknesses, hydraulic diameter, cell reinforcement and density - and preliminarily conclude that treatment has little effect on hydraulic efficiency while hydraulic safety is significantly reduced under dry conditions. Taking advantage of an extremely dry year occurrence during the experiment, we find a sharp increase in vulnerability for xylem tissues built the same year.
Hydraulic properties of rice and the response of gas exchange to water stress.

PubMed

Stiller, Volker; Lafitte, H Renee; Sperry, John S

2003-07-01

We investigated the role of xylem cavitation, plant hydraulic conductance, and root pressure in the response of rice (Oryza sativa) gas exchange to water stress. In the field (Philippines), the percentage loss of xylem conductivity (PLC) from cavitation exceeded 60% in leaves even in watered controls. The PLC versus leaf water potential relationship indicated diurnal refilling of cavitated xylem. The leaf water potential causing 50 PLC (P(50)) was -1.6 MPa and did not differ between upland versus lowland rice varieties. Greenhouse-grown varieties (Utah) were more resistant to cavitation with a 50 PLC of -1.9 MPa but also showed no difference between varieties. Six-day droughts caused concomitant reductions in leaf-specific photosynthetic rate, leaf diffusive conductance, and soil-leaf hydraulic conductance that were associated with cavitation-inducing water potentials and the disappearance of nightly root pressure. The return of root pressure after drought was associated with the complete recovery of leaf diffusive conductance, leaf-specific photosynthetic rate, and soil-leaf hydraulic conductance. Root pressure after the 6-d drought (61.2 +/- 8.8 kPa) was stimulated 7-fold compared with well-watered plants before drought (8.5 +/- 3.8 kPa). The results indicate: (a) that xylem cavitation plays a major role in the reduction of plant hydraulic conductance during drought, and (b) that rice can readily reverse cavitation, possibly aided by nocturnal root pressure.
Xylem and Leaf Functional Adjustments to Drought in Pinus sylvestris and Quercus pyrenaica at Their Elevational Boundary

PubMed Central

Fernández-de-Uña, Laura; Rossi, Sergio; Aranda, Ismael; Fonti, Patrick; González-González, Borja D.; Cañellas, Isabel; Gea-Izquierdo, Guillermo

2017-01-01

Climatic scenarios for the Mediterranean region forecast increasing frequency and intensity of drought events. Consequently, a reduction in Pinus sylvestris L. distribution range is projected within the region, with this species being outcompeted at lower elevations by more drought-tolerant taxa such as Quercus pyrenaica Willd. The functional response of these species to the projected shifts in water availability will partially determine their performance and, thus, their competitive success under these changing climatic conditions. We studied how the cambial and leaf phenology and xylem anatomy of these two species responded to a 3-year rainfall exclusion experiment set at their elevational boundary in Central Spain. Additionally, P. sylvestris leaf gas exchange, water potential and carbon isotope content response to the treatment were measured. Likewise, we assessed inter-annual variability in the studied functional traits under control and rainfall exclusion conditions. Prolonged exposure to drier conditions did not affect the onset of xylogenesis in either of the studied species, whereas xylem formation ceased 1–3 weeks earlier in P. sylvestris. The rainfall exclusion had, however, no effect on leaf phenology on either species, which suggests that cambial phenology is more sensitive to drought than leaf phenology. P. sylvestris formed fewer, but larger tracheids under dry conditions and reduced the proportion of latewood in the tree ring. On the other hand, Q. pyrenaica did not suffer earlywood hydraulic diameter changes under rainfall exclusion, but experienced a cumulative reduction in latewood width, which could ultimately challenge its hydraulic performance. The phenological and anatomical response of the studied species to drought is consistent with a shift in resource allocation under drought stress from xylem to other sinks. Additionally, the tighter stomatal control and higher intrinsic water use efficiency observed in drought-stressed P. sylvestris
Xylem and Leaf Functional Adjustments to Drought in Pinus sylvestris and Quercus pyrenaica at Their Elevational Boundary.

PubMed

Fernández-de-Uña, Laura; Rossi, Sergio; Aranda, Ismael; Fonti, Patrick; González-González, Borja D; Cañellas, Isabel; Gea-Izquierdo, Guillermo

2017-01-01

Climatic scenarios for the Mediterranean region forecast increasing frequency and intensity of drought events. Consequently, a reduction in Pinus sylvestris L. distribution range is projected within the region, with this species being outcompeted at lower elevations by more drought-tolerant taxa such as Quercus pyrenaica Willd. The functional response of these species to the projected shifts in water availability will partially determine their performance and, thus, their competitive success under these changing climatic conditions. We studied how the cambial and leaf phenology and xylem anatomy of these two species responded to a 3-year rainfall exclusion experiment set at their elevational boundary in Central Spain. Additionally, P. sylvestris leaf gas exchange, water potential and carbon isotope content response to the treatment were measured. Likewise, we assessed inter-annual variability in the studied functional traits under control and rainfall exclusion conditions. Prolonged exposure to drier conditions did not affect the onset of xylogenesis in either of the studied species, whereas xylem formation ceased 1-3 weeks earlier in P. sylvestris . The rainfall exclusion had, however, no effect on leaf phenology on either species, which suggests that cambial phenology is more sensitive to drought than leaf phenology. P. sylvestris formed fewer, but larger tracheids under dry conditions and reduced the proportion of latewood in the tree ring. On the other hand, Q. pyrenaica did not suffer earlywood hydraulic diameter changes under rainfall exclusion, but experienced a cumulative reduction in latewood width, which could ultimately challenge its hydraulic performance. The phenological and anatomical response of the studied species to drought is consistent with a shift in resource allocation under drought stress from xylem to other sinks. Additionally, the tighter stomatal control and higher intrinsic water use efficiency observed in drought-stressed P. sylvestris
Divergent climate response on hydraulic-related xylem anatomical traits of Picea abies along a 900-m altitudinal gradient.

PubMed

Castagneri, Daniele; Petit, Giai; Carrer, Marco

2015-12-01

Climate change can induce substantial modifications in xylem structure and water transport capacity of trees exposed to environmental constraints. To elucidate mechanisms of xylem plasticity in response to climate, we retrospectively analysed different cell anatomical parameters over tree-ring series in Norway spruce (Picea abies L. Karst.). We sampled 24 trees along an altitudinal gradient (1200, 1600 and 2100 m above sea level, a.s.l.) and processed 2335 ± 1809 cells per ring. Time series for median cell lumen area (MCA), cell number (CN), tree-ring width (RW) and tree-ring-specific hydraulic conductivity (Kr) were crossed with daily temperature and precipitation records (1926-2011) to identify climate influence on xylem anatomical traits. Higher Kr at the low elevation site was due to higher MCA and CN. These variables were related to different aspects of intra-seasonal climatic variability under different environmental conditions, with MCA being more sensitive to summer precipitation. Winter precipitation (snow) benefited most parameters in all the sites. Descending the gradient, sensitivity of xylem features to summer climate shifted mostly from temperature to precipitation. In the context of climate change, our results indicate that higher summer temperatures at high elevations will benefit cell production and xylem hydraulic efficiency, whereas reduced water availability at lower elevations could negatively affect tracheids enlargement and thus stem capacity to transport water. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Spatial organization of xylem cell walls by ROP GTPases and microtubule-associated proteins.

PubMed

Oda, Yoshihisa; Fukuda, Hiroo

2013-12-01

Proper patterning of cellulosic cell walls is critical for cell shaping and differentiation of plant cells. Cortical microtubule arrays regulate the deposition patterns of cellulose microfibrils by controlling the targeting and trajectory of cellulose synthase complexes. Although some microtubule-associated proteins (MAPs) regulate the arrangement of cortical microtubules, knowledge about the overall mechanism governing the spacing of cortical microtubules is still limited. Recent studies reveal that ROP GTPases and MAPs spatially regulate the assembly and disassembly of cortical microtubules in developing xylem cells, in which localized secondary cell walls are deposited. Here, we review recent insights into the regulation of xylem cell wall patterning by cortical microtubules, ROP GTPases, and MAPs. Copyright © 2013 Elsevier Ltd. All rights reserved.
Herbicides in vineyards reduce grapevine root mycorrhization and alter soil microorganisms and the nutrient composition in grapevine roots, leaves, xylem sap and grape juice.

PubMed

Zaller, Johann G; Cantelmo, Clemens; Santos, Gabriel Dos; Muther, Sandrina; Gruber, Edith; Pallua, Paul; Mandl, Karin; Friedrich, Barbara; Hofstetter, Ingrid; Schmuckenschlager, Bernhard; Faber, Florian

2018-06-03

Herbicides are increasingly applied in vineyards worldwide. However, not much is known on potential side effects on soil organisms or on the nutrition of grapevines (Vitis vinifera). In an experimental vineyard in Austria, we examined the impacts of three within-row herbicide treatments (active ingredients: flazasulfuron, glufosinate, glyphosate) and mechanical weeding on grapevine root mycorrhization; soil microorganisms; earthworms; and nutrient concentration in grapevine roots, leaves, xylem sap and grape juice. The three herbicides reduced grapevine root mycorrhization on average by 53% compared to mechanical weeding. Soil microorganisms (total colony-forming units, CFU) were significantly affected by herbicides with highest CFUs under glufosinate and lowest under glyphosate. Earthworms (surface casting activity, density, biomass, reproduction) or litter decomposition in soil were unaffected by herbicides. Herbicides altered nutrient composition in grapevine roots, leaves, grape juice and xylem sap that was collected 11 months after herbicide application. Xylem sap under herbicide treatments also contained on average 70% more bacteria than under mechanical weeding; however, due to high variability, this was not statistically significant. We conclude that interdisciplinary approaches should receive more attention when assessing ecological effects of herbicides in vineyard ecosystems.
Drought-induced xylem cavitation and hydraulic deterioration: risk factors for urban trees under climate change?

PubMed

Savi, Tadeja; Bertuzzi, Stefano; Branca, Salvatore; Tretiach, Mauro; Nardini, Andrea

2015-02-01

Urban trees help towns to cope with climate warming by cooling both air and surfaces. The challenges imposed by the urban environment, with special reference to low water availability due to the presence of extensive pavements, result in high rates of mortality of street trees, that can be increased by climatic extremes. We investigated the water relations and xylem hydraulic safety/efficiency of Quercus ilex trees growing at urban sites with different percentages of surrounding impervious pavements. Seasonal changes of plant water potential and gas exchange, vulnerability to cavitation and embolism level, and morpho-anatomical traits were measured. We found patterns of increasing water stress and vulnerability to drought at increasing percentages of impervious pavement cover, with a consequent reduction in gas exchange rates, decreased safety margins toward embolism development, and increased vulnerability to cavitation, suggesting the occurrence of stress-induced hydraulic deterioration. The amount of impermeable surface and chronic exposure to water stress influence the site-specific risk of drought-induced dieback of urban trees under extreme drought. Besides providing directions for management of green spaces in towns, our data suggest that xylem hydraulics is key to a full understanding of the responses of urban trees to global change. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.
Spatial and temporal patterns of xylem sap pH derived from stems and twigs of Populus deltoides L.

Treesearch

Doug Aubrey; Justin Boyles; Laura Krysinsky; Robert Teskey

2011-01-01

Xylem sap pH (pHX) is critical in determining the quantity of inorganic carbon dissolved in xylem solution from gaseous [CO2] measurements. Studies of internal carbon transport have generally assumed that pHX derived from stems and twigs is similar and that pHX remains constant through time; however, no empirical studies have investigated these assumptions. If any of...
Easy Come, Easy Go: Capillary Forces Enable Rapid Refilling of Embolized Primary Xylem Vessels.

PubMed

Rolland, Vivien; Bergstrom, Dana M; Lenné, Thomas; Bryant, Gary; Chen, Hua; Wolfe, Joe; Holbrook, N Michele; Stanton, Daniel E; Ball, Marilyn C

2015-08-01

Protoxylem plays an important role in the hydraulic function of vascular systems of both herbaceous and woody plants, but relatively little is known about the processes underlying the maintenance of protoxylem function in long-lived tissues. In this study, embolism repair was investigated in relation to xylem structure in two cushion plant species, Azorella macquariensis and Colobanthus muscoides, in which vascular water transport depends on protoxylem. Their protoxylem vessels consisted of a primary wall with helical thickenings that effectively formed a pit channel, with the primary wall being the pit channel membrane. Stem protoxylem was organized such that the pit channel membranes connected vessels with paratracheal parenchyma or other protoxylem vessels and were not exposed directly to air spaces. Embolism was experimentally induced in excised vascular tissue and detached shoots by exposing them briefly to air. When water was resupplied, embolized vessels refilled within tens of seconds (excised tissue) to a few minutes (detached shoots) with water sourced from either adjacent parenchyma or water-filled vessels. Refilling occurred in two phases: (1) water refilled xylem pit channels, simplifying bubble shape to a rod with two menisci; and (2) the bubble contracted as the resorption front advanced, dissolving air along the way. Physical properties of the protoxylem vessels (namely pit channel membrane porosity, hydrophilic walls, vessel dimensions, and helical thickenings) promoted rapid refilling of embolized conduits independent of root pressure. These results have implications for the maintenance of vascular function in both herbaceous and woody species, because protoxylem plays a major role in the hydraulic systems of leaves, elongating stems, and roots. © 2015 American Society of Plant Biologists. All Rights Reserved.
Moving beyond the cambium necrosis hypothesis of post-fire tree mortality: cavitation and deformation of xylem in forest fires

Treesearch

S.T. Michaletz; E.A. Johnson; M.T. Tyree

2012-01-01

It is widely assumed that post-fire tree mortality results from necrosis of phloem and vascular cambium in stems, despite strong evidence that reduced xylem conductivity also plays an important role. In this study, experiments with Populus balsamifera were used to demonstrate two mechanisms by which heat reduces the hydraulic conductivity of xylem:...
Infection processes of xylem-colonizing pathogenic bacteria: possible explanations for the scarcity of qualitative disease resistance genes against them in crops.

PubMed

Bae, Chungyun; Han, Sang Wook; Song, Yu-Rim; Kim, Bo-Young; Lee, Hyung-Jin; Lee, Je-Min; Yeam, Inhwa; Heu, Sunggi; Oh, Chang-Sik

2015-07-01

Disease resistance against xylem-colonizing pathogenic bacteria in crops. Plant pathogenic bacteria cause destructive diseases in many commercially important crops. Among these bacteria, eight pathogens, Ralstonia solanacearum, Xanthomonas oryzae pv. oryzae, X. campestris pv. campestris, Erwinia amylovora, Pantoea stewartii subsp. stewartii, Clavibacter michiganensis subsp. michiganensis, Pseudomonas syringae pv. actinidiae, and Xylella fastidiosa, infect their host plants through different infection sites and paths and eventually colonize the xylem tissues of their host plants, resulting in wilting symptoms by blocking water flow or necrosis of xylem tissues. Noticeably, only a relatively small number of resistant cultivars in major crops against these vascular bacterial pathogens except X. oryzae pv. oryzae have been found or generated so far, although these pathogens threaten productivity of major crops. In this review, we summarize the lifestyles of major xylem-colonizing bacterial pathogens and then discuss the progress of current research on disease resistance controlled by qualitative disease resistance genes or quantitative trait loci against them. Finally, we propose infection processes of xylem-colonizing bacterial pathogens as one of possible reasons for why so few qualitative disease resistance genes against these pathogens have been developed or identified so far in crops.
Casting light on xylem vulnerability in an herbaceous species reveals a lack of segmentation.

PubMed

Skelton, Robert P; Brodribb, Timothy J; Choat, Brendan

2017-04-01

Finding thresholds at which loss of plant functionality occurs during drought is critical for predicting future crop productivity and survival. Xylem resistance to embolism has been suggested as a key trait associated with water-stress tolerance. Although a substantial literature exists describing the vulnerability of woody stems to embolism, leaves and roots of herbaceous species remain under-represented. Also, little is known about vulnerability to embolism at a whole-plant scale or propagation of embolism within plants. New techniques to view the process of embolism formation provide opportunities to resolve long-standing questions. Here, we used multiple visual techniques, including X-ray micro-computed tomography and the optical vulnerability method, to investigate the spread of embolism within intact stems, leaves and roots of Solanum lycopersicum (common tomato). We found that roots, stems and leaves of tomato plants all exhibited similar vulnerability to embolism, suggesting that embolism rapidly propagates among tissues. Although we found scarce evidence for differentiation of xylem vulnerability among tissues at the scale of the whole plant, within a leaf the midrib embolized at higher water potentials than lower order veins. Substantial overlap between the onset of cavitation and incipient leaf damage suggests that cavitation represents a substantial damage to plants, but the point of lethal cavitation in this herbaceous species remains uncertain. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.
Nickel affects xylem Sap RNase a and converts RNase A to a urease

PubMed Central

2013-01-01

Background Nickel (Ni) is an essential micronutrient; however, its metabolic or physiological functions in plants and animals are largely uncharacterized. The ribonucleases (RNase, e.g., RNase A) are a large family of hydrolases found in one form or many forms facilitating nitrogen (N) cycling. It is currently unknown how either a deficiency or excess of Ni influences the functionality of ribonucleases, like RNase A. This is especially true for perennial crops possessing relatively high Ni requirements. Results We report that the 'rising’ xylem sap of pecan [Carya illinoinensis (Wangenh.) K. Koch, a long-lived tree] at bud break contains a 14 kDa RNase A (aka, RNase 1), which amount has a 33% greater in Ni-deficient as in Ni-sufficient trees when exposed to Ni ions exhibits ureolytic activity. The homologous 13.4 kDa bovine pancreatic RNase A likewise exhibits ureolytic activity upon exposure to Ni ions. Ni therefore affects enzymatic function of a typically non-metalloenzyme, such as it transforms to an enzyme capable of hydrolyzing a linear amide; thus, converting an endonuclease esterase into a urease. Conclusions We conclude that Ni potentially affects the level and activity of RNase A present in the spring xylem sap of pecan trees, and probably in other crops, it has the same influence. The catalytic property of RNase A appears to shift from a nuclease to a urease relying on Ni exposure. This is suggestive that RNase A might possess novel metabolic functionality regarding N-metabolism in perennial plants. The ability of Ni to convert the activity of plant and animal RNase A from that of a ribonuclease to a urease indicates a possible unrecognized beneficial metabolic function of Ni in organisms, while also identifying a potential detrimental effect of excessive Ni on N related metabolic activity if there is sufficient disruption of Ni homeostasis. PMID:24320827
Data on xylem sap proteins from Mn- and Fe-deficient tomato plants obtained using shotgun proteomics.

PubMed

Ceballos-Laita, Laura; Gutierrez-Carbonell, Elain; Takahashi, Daisuke; Abadía, Anunciación; Uemura, Matsuo; Abadía, Javier; López-Millán, Ana Flor

2018-04-01

This article contains consolidated proteomic data obtained from xylem sap collected from tomato plants grown in Fe- and Mn-sufficient control, as well as Fe-deficient and Mn-deficient conditions. Data presented here cover proteins identified and quantified by shotgun proteomics and Progenesis LC-MS analyses: proteins identified with at least two peptides and showing changes statistically significant (ANOVA; p ≤ 0.05) and above a biologically relevant selected threshold (fold ≥ 2) between treatments are listed. The comparison between Fe-deficient, Mn-deficient and control xylem sap samples using a multivariate statistical data analysis (Principal Component Analysis, PCA) is also included. Data included in this article are discussed in depth in the research article entitled "Effects of Fe and Mn deficiencies on the protein profiles of tomato ( Solanum lycopersicum) xylem sap as revealed by shotgun analyses" [1]. This dataset is made available to support the cited study as well to extend analyses at a later stage.
How do sharpshooter leafhoppers feed and survive on nutritionally depauperate xylem fluid?

USDA-ARS?s Scientific Manuscript database

Sharpshooters (Cicadellidae: Cicadellinae) are large, tropical and semi-tropical leafhoppers that are unique among all non-sessile hemipterans in ingesting primarily from xylem vessels. This presentation will summarize research on behavioral and physiological adaptations that permit sharpshooters ...
Seasonal abundance and spatio-temporal distribution of dominant xylem fluid-feeding hemiptera in vineyards of central Texas and surrounding habitats.

PubMed

Lauzière, Isabelle; Sheather, Simon; Mitchell, Forrest

2008-08-01

A survey of xylem fluid-feeding insects (Hemiptera) exhibiting potential for transmission of Xylella fastidiosa, the bacterium causing Pierce's disease of grapevine, was conducted from 2004 to 2006 in the Hill Country grape growing region of central Texas. Nineteen insect species were collected from yellow sticky traps. Among these, two leafhoppers and one spittlebug comprised 94.57% of the xylem specialists caught in this region. Homalodisca vitripennis (Germar), Graphocephala versuta (Say), and Clastoptera xanthocephala Germar trap catches varied significantly over time, with greatest counts usually recorded between May or June and August and among localities. A comparison of insect counts from traps placed inside and outside vineyards indicated that G. versuta is always more likely captured on the vegetation adjacent to the vineyard. C. xanthocephala was caught inside the vineyard during the summer. Between October and December, the natural habitat offers more suitable host plants, and insects were absent from the vineyards after the first freezes. H. vitripennis was caught in higher numbers inside the vineyards throughout the grape vegetative season. However, insects were also caught in the habitat near the affected crop throughout the year, and residual populations overwintering near vineyards were also recorded. This study shed new light on the fauna of xylem fluid-feeding insects of Texas. These results also provide critical information to vineyard managers for timely applications of insecticides before insect feeding and vectoring to susceptible grapevines.
Divergent hydraulic strategies to cope with freezing in co-occurring temperate tree species with special reference to root and stem pressure generation.

PubMed

Yin, Xiao-Han; Sterck, Frank; Hao, Guang-You

2018-04-23

Some temperate tree species mitigate the negative impacts of frost-induced xylem cavitation by restoring impaired hydraulic function via positive pressures, and may therefore be more resistant to frost fatigue (the phenomenon that post-freezing xylem becomes more susceptible to hydraulic dysfunction) than nonpressure-generating species. We test this hypothesis and investigate underlying anatomical/physiological mechanisms. Using a common garden experiment, we studied key hydraulic traits and detailed xylem anatomical characteristics of 18 sympatric tree species. These species belong to three functional groups, that is, one generating both root and stem pressures (RSP), one generating only root pressure (RP), and one unable to generate such pressures (NP). The three functional groups diverged substantially in hydraulic efficiency, resistance to drought-induced cavitation, and frost fatigue resistance. Most notably, RSP and RP were more resistant to frost fatigue than NP, but this was at the cost of reduced hydraulic conductivity for RSP and reduced resistance to drought-induced cavitation for RP. Our results show that, in environments with strong frost stress: these groups diverge in hydraulic functioning following multiple trade-offs between hydraulic efficiency, resistance to drought and resistance to frost fatigue; and how differences in anatomical characteristics drive such divergence across species. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.
Effects of Grape Xylem Sap and Cell-Wall Constituents on In Vitro Growth, Biofilm Formation and Cellular Aggregation of Xylella fastidiosa

USDA-ARS?s Scientific Manuscript database

Purified cell-wall constituents or grape xylem sap added to media affected in vitro growth, biofilm formation, cell aggregation and gene expression of Xylella fastidiosa. Media containing xylem sap from Pierce’s disease (PD)-susceptible plants provided better support for bacterial growth and biofil...
Verticillium Infection Triggers VASCULAR-RELATED NAC DOMAIN7–Dependent de Novo Xylem Formation and Enhances Drought Tolerance in Arabidopsis[W

PubMed Central

Reusche, Michael; Thole, Karin; Janz, Dennis; Truskina, Jekaterina; Rindfleisch, Sören; Drübert, Christine; Polle, Andrea; Lipka, Volker; Teichmann, Thomas

2012-01-01

The soilborne fungal plant pathogen Verticillium longisporum invades the roots of its Brassicaceae hosts and proliferates in the plant vascular system. Typical aboveground symptoms of Verticillium infection on Brassica napus and Arabidopsis thaliana are stunted growth, vein clearing, and leaf chloroses. Here, we provide evidence that vein clearing is caused by pathogen-induced transdifferentiation of chloroplast-containing bundle sheath cells to functional xylem elements. In addition, our findings suggest that reinitiation of cambial activity and transdifferentiation of xylem parenchyma cells results in xylem hyperplasia within the vasculature of Arabidopsis leaves, hypocotyls, and roots. The observed de novo xylem formation correlates with Verticillium-induced expression of the VASCULAR-RELATED NAC DOMAIN (VND) transcription factor gene VND7. Transgenic Arabidopsis plants expressing the chimeric repressor VND7-SRDX under control of a Verticillium infection-responsive promoter exhibit reduced de novo xylem formation. Interestingly, infected Arabidopsis wild-type plants show higher drought stress tolerance compared with noninfected plants, whereas this effect is attenuated by suppression of VND7 activity. Together, our results suggest that V. longisporum triggers a tissue-specific developmental plant program that compensates for compromised water transport and enhances the water storage capacity of infected Brassicaceae host plants. In conclusion, we provide evidence that this natural plant–fungus pathosystem has conditionally mutualistic features. PMID:23023171

Ceratocystis smalleyi colonization of bitternut hickkory and host responses in the xylem

Treesearch

J.-H. Park; J. Juzwik

2014-01-01

Colonization of Carya cordiformis sapwood by Ceratocystis smalleyi and subsequent host defence responses following artificial inoculation were investigated using anatomical and histological techniques. Hyphae of C. smalleyi were observed in all sapwood xylem features confirming the ability of the pathogen to...
Scapoidus titanus performs a dual-meaning, sharpshooter-style EPG X wave in xylem and phloem: Could S. titanus be a potential vector of Xylella fastidiosa in European vineyards?

USDA-ARS?s Scientific Manuscript database

In phytophagous hemipterans, salivary sheath-feeding species are described as xylem or phloem sap-ingesting specialists. Because these two food sources have different characteristics, two different feeding tactics are associated with this supposed specialization. Study of feeding behavior is crucial...
Evidence for xylem adaptations to drought in ancient Cordaites of the Carboniferous

NASA Astrophysics Data System (ADS)

Medeiros, J. S.; Hewins, C.; Serbet, R.; Taylor, T. N.; Taylor, E. L.; Ward, J. K.

2013-12-01

Ancient land plants faced the same challenges to growth and survival as modern land plants, including the need to resist xylem embolisms imposed by drought in order to main water supply to leaves. Cordaites, considered to be ancestors of the conifers, were some of the first trees on Earth and are often described as the most drought resistant plants in the North American landscape from the Late Missisipian (~320 MYA) to the early Permian (~250 MYA). Cordaites were common in both mires and dry uplands, however, suggesting considerable variation in drought tolerance, but neither the extent of this variation nor the particular xylem features associated with dryland habitats have been previously examined. We measured xylem anatomical traits including tracheid diameter (D) and wall thickness (t), for Cordaites roots and stems from three sites in Central North America: What Cheer IA, Sahara IL and Lewis Creek KY. From these data we calculated mechanical strength (t/b), which was used to estimate vulnerability to drought embolism (P50) based on comparisons with modern plants. In addition, we used the model of Wilson et al. (2008) to calculate the specific conductivity (Ksp), a measure of xylem water transport capacity. D and Ksp of Cordaites stems were similar to that typical of modern conifers but t/b tended to be lower. However, Cordaites exhibited significant variation in D, t, Ksp and t/b across sites. Stem P50 estimated from comparisons with modern plants ranged from approximately -4 at Lewis Creek to as low as -7 MPa at Sahara. We also found differences between stems and roots for Cordaites. Compared to stems, roots had larger D and higher Ksp, but lower t and t/b, resulting in a P50 ranging from approximately -2 to -4 MPa. In the roots of Sahara Cordaites, lower t/b in roots was a result of both significantly larger conduits and significantly thinner conduit walls compared to stems. Thus, hydraulic segmentation in Cordaites could have facilitated their survival in
In vivo Visualization of the Water-refilling Process in Xylem Vessels Using X-ray Micro-imaging

PubMed Central

Lee, Sang-Joon; Kim, Yangmin

2008-01-01

Background and Aims Xylem vessels containing gases (embolized) must be refilled with water if they are to resume transport of water through the plant, so refilling is of great importance for the maintenance of water balance in plants. However, the refilling process is poorly understood because of inadequate examination methods. Simultaneous measurements of plant anatomy and vessel refilling are essential to elucidate the mechanisms involved. In the present work, a new technique based on phase-contrast X-ray imaging is presented that visualizes, in vivo and in real time, both xylem anatomy and refilling of embolized vessels. Methods With the synchrotron X-ray micro-imaging technique, the refilling of xylem vessels of leaves and a stem of Phyllostachys bambusoides with water is demonstrated under different conditions. The technique employs phase contrast imaging of X-ray beams, which are transformed into visible light and are photographed by a charge coupled device camera. X-ray images were captured consecutively at every 0·5 s with an exposure time of 10 ms. Key Results The interface (meniscus) between the water and gas phases in refilling the xylem vessels is displayed. During refilling, the rising menisci in embolized vessels showed repetitive flow, i.e. they temporarily stopped at the end walls of the vessel elements while gas bubbles were removed. The meniscus then passed through the end wall at a faster rate than the speed of flow in the main vessels. In the light, the speed of refilling in a specific vessel was slower than that in the dark, but this rate increased again after repeated periods in darkness. Conclusions Real-time, non-destructive X-ray micro-imaging is an important, useful and novel technique to study the relationship between xylem structure and the refilling of embolized vessels in intact plants. It provides new insight into understanding the mechanisms of water transport and the refilling of embolized vessels, which are not understood well
Xylem Resin in the Resistance of the Pinaceae to Bark Beetles

Treesearch

Richard H. Smith

1972-01-01

Xylem resin of Pinaceae is closely linked with their resistance and suseptibility to tree-killing bark beetles. This review of the literature on attacking adults suggests that all three resistance mechanisms proposed by Painter -- preference, antibiosis, and tolerance -- are active in this relationship: preference by attraction, repellency, and synergism; antibiosis...
Tocochromanols in wood: a potential new tool for dendrometabolomics.

PubMed

Fleta-Soriano, Eva; Fernández-Marín, Beatriz; Olano, José Miguel; Míguez, Fátima; Molinero, Jon; Camarero, Jesús Julio; García-Plazaola, José Ignacio

2014-12-01

Tocochromanols are the most abundant lipid-soluble antioxidants in plants. Among them, α-tocopherol (α-Toc) shows a particularly high sensitivity to environmental stressors and its content is used as a stress biomarker even in non-photosynthetic tissues. Nevertheless, the presence of tocochromanols has not been described yet in the xylem of woody plants, even when their functions regarding cell membrane protection and the transport of photoassimilates may be crucial in this tissue and despite its potential utility in dendrometabolomics. Considering all these, we aimed to determine the presence and distribution of tocochromanols in the xylem of woody plants, to examine their responsiveness to high temperature and to evaluate their potential as environmental bioindicators. The analysis of 29 phyllogenetically diverse species showed that α-Toc is the most abundant and frequent tocochromanol in the xylem and is ubiquitously present in all the studied species, with a concentration ranging from 0.5 to 39.3 μg g(-1) of dry weight. α-Tocopherol appeared to be mainly located in the parenchyma rays and was found in both the sapwood and the heartwood, suggesting that it is present even in dead parenchyma cells. The levels of α-Toc in the xylem did not change in response to locally induced xylem heating, but responded positively to the 3-year moving average of annual precipitation. The present findings suggest that α-Toc may be linked to changes in climatic stress. This should enhance further research on the environmental controls of α-Toc variation in the xylem as a first step towards a deeper understanding of dendrometabolomics. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Leaf vein xylem conduit diameter influences susceptibility to embolism and hydraulic decline

USDA-ARS?s Scientific Manuscript database

Ecosystems worldwide are facing increasingly severe and prolonged droughts during which hydraulic failure from drought-induced embolism can lead to organ or whole plant death. Understanding the determinants of xylem failure across species is critical especially in leaves, the engine of plant growth....
BOREAS RSS-17 Xylem Flux Density Measurements at the SSA-OBS Site

NASA Technical Reports Server (NTRS)

Zimmerman, Reiner; Way, JoBea; McDonald, Kyle; Nickeson, Jaime (Editor); Hall, Forrest G. (Editor); Smith, David E. (Technical Monitor)

2000-01-01

As part of its efforts to determine environmental and phenological states from radar imagery, the Boreal Ecosystem-Atmosphere Study (BOREAS) Remote Sensing Science (RSS)-17 team collected in situ tree xylem flow measurements for one growing season on five Picea mariana (black spruce) trees. The data were collected to obtain information on the temporal and spatial variability in water uptake by trees in the Southern Study Area-Old Black Spruce (SSA-OBS) stand in the BOREAS SSA. Temporally, the data were collected in 30-minute intervals for 120 days from 31 May 1994 until 27 September 1994. The data are stored in tabular ASCII files. The xylem flux data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).
Water transport properties of the grape (V. vinifera L.) pedicel during fruit development: Insights into xylem anatomy and function using microtomography

USDA-ARS?s Scientific Manuscript database

Xylem flow into the fruit decline at the onset of ripening (i.e. veraison) in grapes, and current literature suggests that there is an increase in hydraulic resistance in the pedicel at this time. However, it is unknown how pedicel hydraulic properties change developmentally in relation to xylem an...
Response pattern of amino compounds in phloem and xylem of trees to soil drought depends on drought intensity and root symbiosis.

PubMed

Liu, X-P; Gong, C-M; Fan, Y-Y; Eiblmeier, M; Zhao, Z; Han, G; Rennenberg, H

2013-01-01

This study aimed to identify drought-mediated differences in amino nitrogen (N) composition and content of xylem and phloem in trees having different symbiotic N(2)-fixing bacteria. Under controlled water availability, 1-year-old seedlings of Robinia pseudoacacia (nodules with Rhizobium), Hippophae rhamnoides (symbiosis with Frankia) and Buddleja alternifolia (no such root symbiosis) were exposed to control, medium drought and severe drought, corresponding soil water content of 70-75%, 45-50% and 30-35% of field capacity, respectively. Composition and content of amino compounds in xylem sap and phloem exudates were analysed as a measure of N nutrition. Drought strongly reduced biomass accumulation in all species, but amino N content in xylem and phloem remained unaffected only in R. pseudoacacia. In H. rhamnoides and B. alternifolia, amino N in phloem remained constant, but increased in xylem of both species in response to drought. There were differences in composition of amino compounds in xylem and phloem of the three species in response to drought. Proline concentrations in long-distance transport pathways of all three species were very low, below the limit of detection in phloem of H. rhamnoides and in phloem and xylem of B. alternifolia. Apparently, drought-mediated changes in N composition were much more connected with species-specific changes in C:N ratios. Irrespective of soil water content, the two species with root symbioses did not show similar features for the different types of symbiosis, neither in N composition nor in N content. There was no immediate correlation between symbiotic N fixation and drought-mediated changes in amino N in the transport pathways. © 2012 German Botanical Society and The Royal Botanical Society of the Netherlands.
Analysis of Xylem Sap from Functional (Nonembolized) and Nonfunctional (Embolized) Vessels of Populus nigra: Chemistry of Refilling1[C][W][OA

PubMed Central

Secchi, Francesca; Zwieniecki, Maciej A.

2012-01-01

It is assumed that the refilling of drought-induced embolism requires the creation of an osmotic gradient between xylem parenchyma cells and vessel lumens to generate the water efflux needed to fill the void. To assess the mechanism of embolism repair, it is crucial to determine if plants can up-regulate the efflux of osmotically active substances into embolized vessels and identify the major components of the released osmoticum. Here, we introduce a new approach of sap collection designed to separate water from nonembolized (functional) and embolized (nonfunctional) vessels. This new approach made possible the chemical analysis of liquid collected from both types of vessels in plants subjected to different levels of water stress. The technique also allowed us to determine the water volumes in nonfunctional vessels as a function of stress level. Overall, with the increase of water stress in plants, the osmotic potential of liquid collected from nonfunctional vessels increased while its volume decreased. These results revealed the presence of both sugars and ions in nonfunctional vessels at elevated levels in comparison with liquid collected from functional vessels, in which only traces of sugars were found. The increased sugar concentration was accompanied by decreased xylem sap pH. These results provide new insight into the biology of refilling, underlining the role of sugar and sugar transporters, and imply that a large degree of hydraulic compartmentalization must exist in the xylem during the refilling process. PMID:22837359
How Does Leaf Anatomy Influence Water Transport outside the Xylem?1[OPEN

PubMed Central

Buckley, Thomas N.; Scoffoni, Christine; Sack, Lawren

2015-01-01

Leaves are arguably the most complex and important physicobiological systems in the ecosphere. Yet, water transport outside the leaf xylem remains poorly understood, despite its impacts on stomatal function and photosynthesis. We applied anatomical measurements from 14 diverse species to a novel model of water flow in an areole (the smallest region bounded by minor veins) to predict the impact of anatomical variation across species on outside-xylem hydraulic conductance (Kox). Several predictions verified previous correlational studies: (1) vein length per unit area is the strongest anatomical determinant of Kox, due to effects on hydraulic pathlength and bundle sheath (BS) surface area; (2) palisade mesophyll remains well hydrated in hypostomatous species, which may benefit photosynthesis, (3) BS extensions enhance Kox; and (4) the upper and lower epidermis are hydraulically sequestered from one another despite their proximity. Our findings also provided novel insights: (5) the BS contributes a minority of outside-xylem resistance; (6) vapor transport contributes up to two-thirds of Kox; (7) Kox is strongly enhanced by the proximity of veins to lower epidermis; and (8) Kox is strongly influenced by spongy mesophyll anatomy, decreasing with protoplast size and increasing with airspace fraction and cell wall thickness. Correlations between anatomy and Kox across species sometimes diverged from predicted causal effects, demonstrating the need for integrative models to resolve causation. For example, (9) Kox was enhanced far more in heterobaric species than predicted by their having BS extensions. Our approach provides detailed insights into the role of anatomical variation in leaf function. PMID:26084922
A Plumber's-Eye View of Xylem Water Transport in Woody Plants

ERIC Educational Resources Information Center

Martinez-Vilalta, Jordi; Pinol, Josep

2004-01-01

We present a practical for university-level students aimed at measuring and comparing xylem hydraulic properties of co-existing plant species. After sampling branches of several woody species in the field, their main hydraulic properties were measured using a simple set-up. Hydraulic conductivity ("K[subscript h]") was calculated as the ratio…
Maximum height in a conifer is associated with conflicting requirements for xylem design.

PubMed

Domec, Jean-Christophe; Lachenbruch, Barbara; Meinzer, Frederick C; Woodruff, David R; Warren, Jeffrey M; McCulloh, Katherine A

2008-08-19

Despite renewed interest in the nature of limitations on maximum tree height, the mechanisms governing ultimate and species-specific height limits are not yet understood, but they likely involve water transport dynamics. Tall trees experience increased risk of xylem embolism from air-seeding because tension in their water column increases with height because of path-length resistance and gravity. We used morphological measurements to estimate the hydraulic properties of the bordered pits between tracheids in Douglas-fir trees along a height gradient of 85 m. With increasing height, the xylem structural modifications that satisfied hydraulic requirements for avoidance of runaway embolism imposed increasing constraints on water transport efficiency. In the branches and trunks, the pit aperture diameter of tracheids decreases steadily with height, whereas torus diameter remains relatively constant. The resulting increase in the ratio of torus to pit aperture diameter allows the pits to withstand higher tensions before air-seeding but at the cost of reduced pit aperture conductance. Extrapolations of vertical trends for trunks and branches show that water transport across pits will approach zero at a heights of 109 m and 138 m, respectively, which is consistent with historic height records of 100-127 m for this species. Likewise, the twig water potential corresponding to the threshold for runaway embolism would be attained at a height of approximately 107 m. Our results suggest that the maximum height of Douglas-fir trees may be limited in part by the conflicting requirements for water transport and water column safety.
Primary events regulating stem growth at low water potentials.

PubMed

Nonami, H; Boyer, J S

1990-08-01

Cell enlargement is inhibited by inadequate water. As a first step toward understanding the mechanism, all the physical parameters affecting enlargement were monitored to identify those that changed first, particularly in coincidence with the inhibition. The osmotic potential, turgor, yield threshold turgor, growth-induced water potential, wall extensibility, and conductance to water were measured in the elongating region, and the water potential was measured in the xylem of stems of dark-grown soybean (Glycine max [L.] Merr.) seedlings. A stepdown in water potential was achieved around the roots by transplanting the seedlings to vermiculite of low water content, and each of the parameters was measured simultaneously in the same plants while intact or within a few minutes of being intact using a newly developed guillotine psychrometer. The gradient of decreasing water potential from the xylem to the enlarging cells (growth-induced water potential) was the first of the parameters to decrease to a growth-limiting level. The kinetics were the same as for the inhibition of growth. The decreased gradient was caused mostly by a decreased water potential of the xylem. This was followed after 5 to 10 hours by a similar decrease in cell wall extensibility and tissue conductance for water. Later, the growth-induced water potential recovered as a result of osmotic adjustment and a rise in the water potential of the xylem. Still later, moderate growth resumed at a rate apparently determined by the low wall extensibility and tissue conductance for water. The turgor did not change significantly during the experiment. These results indicate that the primary event during the growth inhibition was the change in the growth-induced water potential. Because the growth limitation subsequently shifted to the low wall extensibility and tissue conductance for water, the initial change in potential may have set in motion subsequent metabolic changes that altered the characteristics of the
Tyloses and Phenolic Deposits in Xylem Vessels Impede Water Transport in Low-Lignin Transgenic Poplars: A Study by Cryo-Fluorescence Microscopy1[W][OA

PubMed Central

Kitin, Peter; Voelker, Steven L.; Meinzer, Frederick C.; Beeckman, Hans; Strauss, Steven H.; Lachenbruch, Barbara

2010-01-01

Of 14 transgenic poplar genotypes (Populus tremula × Populus alba) with antisense 4-coumarate:coenzyme A ligase that were grown in the field for 2 years, five that had substantial lignin reductions also had greatly reduced xylem-specific conductivity compared with that of control trees and those transgenic events with small reductions in lignin. For the two events with the lowest xylem lignin contents (greater than 40% reduction), we used light microscopy methods and acid fuchsin dye ascent studies to clarify what caused their reduced transport efficiency. A novel protocol involving dye stabilization and cryo-fluorescence microscopy enabled us to visualize the dye at the cellular level and to identify water-conducting pathways in the xylem. Cryo-fixed branch segments were planed in the frozen state on a sliding cryo-microtome and observed with an epifluorescence microscope equipped with a cryo-stage. We could then distinguish clearly between phenolic-occluded vessels, conductive (stain-filled) vessels, and nonconductive (water- or gas-filled) vessels. Low-lignin trees contained areas of nonconductive, brown xylem with patches of collapsed cells and patches of noncollapsed cells filled with phenolics. In contrast, phenolics and nonconductive vessels were rarely observed in normal colored wood of the low-lignin events. The results of cryo-fluorescence light microscopy were supported by observations with a confocal microscope after freeze drying of cryo-planed samples. Moreover, after extraction of the phenolics, confocal microscopy revealed that many of the vessels in the nonconductive xylem were blocked with tyloses. We conclude that reduced transport efficiency of the transgenic low-lignin xylem was largely caused by blockages from tyloses and phenolic deposits within vessels rather than by xylem collapse. PMID:20639405
Cadmium uptake and xylem loading are active processes in the hyperaccumulator Sedum alfredii.

PubMed

Lu, Ling-li; Tian, Sheng-ke; Yang, Xiao-e; Li, Ting-qiang; He, Zhen-li

2009-04-01

Sedum alfredii is a well known cadmium (Cd) hyperaccumulator native to China; however, the mechanism behind its hyperaccumulation of Cd is not fully understood. Through several hydroponic experiments, characteristics of Cd uptake and translocation were investigated in the hyperaccumulating ecotype (HE) of S. alfredii in comparison with its non-hyperaccumulating ecotype (NHE). The results showed that at Cd level of 10 microM measured Cd uptake in HE was 3-4 times higher than the implied Cd uptake calculated from transpiration rate. Furthermore, inhibition of transpiration rate in the HE has no essential effect on Cd accumulation in shoots of the plants. Low temperature treatment (4 degrees C) significantly inhibited Cd uptake and reduced upward translocation of Cd to shoots for 9 times in HE plants, whereas no such effect was observed in NHE. Cadmium concentration was 3-4-fold higher in xylem sap of HE, as compared with that in external uptake solution, whereas opposite results were obtained for NHE. Cadmium concentration in xylem sap of HE was significantly reduced by the addition of metabolic inhibitors, carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP), in the uptake solutions, whereas no such effect was noted in NHE. These results suggest that Cd uptake and translocation is an active process in plants of HE S. alfredii, symplastic pathway rather than apoplastic bypass contributes greatly to root uptake, xylem loading and translocation of Cd to the shoots of HE, in comparison with the NHE plants.
Tryptophan-dependent auxin biosynthesis is required for HD-ZIP III-mediated xylem patterning.

PubMed

Ursache, Robertas; Miyashima, Shunsuke; Chen, Qingguo; Vatén, Anne; Nakajima, Keiji; Carlsbecker, Annelie; Zhao, Yunde; Helariutta, Ykä; Dettmer, Jan

2014-03-01

The development and growth of higher plants is highly dependent on the conduction of water and minerals throughout the plant by xylem vessels. In Arabidopsis roots the xylem is organized as an axis of cell files with two distinct cell fates: the central metaxylem and the peripheral protoxylem. During vascular development, high and low expression levels of the class III HD-ZIP transcription factors promote metaxylem and protoxylem identities, respectively. Protoxylem specification is determined by both mobile, ground tissue-emanating miRNA165/6 species, which downregulate, and auxin concentrated by polar transport, which promotes HD-ZIP III expression. However, the factors promoting high HD-ZIP III expression for metaxylem identity have remained elusive. We show here that auxin biosynthesis promotes HD-ZIP III expression and metaxylem specification. Several auxin biosynthesis genes are expressed in the outer layers surrounding the vascular tissue in Arabidopsis root and downregulation of HD-ZIP III expression accompanied by specific defects in metaxylem development is seen in auxin biosynthesis mutants, such as trp2-12, wei8 tar2 or a quintuple yucca mutant, and in plants treated with L-kynurenine, a pharmacological inhibitor of auxin biosynthesis. Some of the patterning defects can be suppressed by synthetically elevated HD-ZIP III expression. Taken together, our results indicate that polar auxin transport, which was earlier shown to be required for protoxylem formation, is not sufficient to establish a proper xylem axis but that root-based auxin biosynthesis is additionally required.
Photosynthesis and leaf water relations in four American sycamore clones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Z.; Land, S.B. Jr.

1995-11-01

Photosynthesis, transpiration, stomatal conductance, and xylem pressure potential were studied to examine clonal variation and clone-by-season interactions in rooted cuttings of four sycamore clones (Platanus occidentalis L.). These physiological parameters were measured during June through November of the second and third growing seasons in the field. Stomatal conductance, xylem pressure potential, and photosynthesis were higher in June-July than in August-November. The four clones did not differ significantly in yearly average photosynthetic rates, but clone 11 tended to have higher rates early in each growing season (June-July) than did the other three clones. Dry periods during August-September of the second seasonmore » and during October of the third season apparently caused clone 11 to close its stomata more than clone 17, as indicated by significant clone-by-season interactions for reductions in stomatal conductance and transpiration late in the morning. Clone 17 was generally able to maintain high xylem pressure potential, stomatal conductance, and transpiration throughout the growing season, probably because of its large root system. 36 refs., 2 figs., 5 tabs.« less
What HR-CT imaging can teach us about xylem structure and function

USDA-ARS?s Scientific Manuscript database

It is well established that plant xylem is composed of a complex and interconnected system of vascular elements, but little is known about how the three-dimensional (3D) organization of this network influences properties such as plant hydraulics (Tyree & Zimmermann, 2002), and few studies have measu...

Methyl Jasmonate Induces Traumatic Resin Ducts, Terpenoid Resin Biosynthesis, and Terpenoid Accumulation in Developing Xylem of Norway Spruce Stems1

PubMed Central

Martin, Diane; Tholl, Dorothea; Gershenzon, Jonathan; Bohlmann, Jörg

2002-01-01

Norway spruce (Picea abies L. Karst) produces an oleoresin characterized by a diverse array of terpenoids, monoterpenoids, sesquiterpenoids, and diterpene resin acids that can protect conifers against potential herbivores and pathogens. Oleoresin accumulates constitutively in resin ducts in the cortex and phloem (bark) of Norway spruce stems. De novo formation of traumatic resin ducts (TDs) is observed in the developing secondary xylem (wood) after insect attack, fungal elicitation, and mechanical wounding. Here, we characterize the methyl jasmonate-induced formation of TDs in Norway spruce by microscopy, chemical analyses of resin composition, and assays of terpenoid biosynthetic enzymes. The response involves tissue-specific differentiation of TDs, terpenoid accumulation, and induction of enzyme activities of both prenyltransferases and terpene synthases in the developing xylem, a tissue that constitutively lacks axial resin ducts in spruce. The induction of a complex defense response in Norway spruce by methyl jasmonate application provides new avenues to evaluate the role of resin defenses for protection of conifers against destructive pests such as white pine weevils (Pissodes strobi), bark beetles (Coleoptera, Scolytidae), and insect-associated tree pathogens. PMID:12114556
Mixed xylem and phloem sap ingestion in sheath-feeders as normal dietary behavior: Evidence from the leafhopper Scaphoideus titanus.

PubMed

Chuche, Julien; Sauvion, Nicolas; Thiéry, Denis

2017-10-01

In phytophagous piercing-sucking insects, salivary sheath-feeding species are often described as xylem- or phloem-sap feeding specialists. Because these two food sources have very different characteristics, two feeding tactics are often associated with this supposed specialization. Studying the feeding behavior of insects provides substantial information on their biology, ecology, and evolution. Furthermore, study of feeding behavior is of primary importance to elucidate the transmission ability of insects that act as vectors of plant pathogens. In this study, we compared the durations of ingestion performed in xylem versus phloem by a leafhopper species, Scaphoideus titanus Ball, 1932. This was done by characterizing and statistically analyzing electrical signals recorded using the electropenetrography technique, derived from the feeding behaviors of males and females. We identified three groups of S. titanus based on their feeding behavior: 1) a group that reached the phloem quickly and probed for a longer time in phloem tissue than the other groups, 2) a group that reached the xylem quickly and probed for a longer time in xylem tissue than the other groups, and 3) a group where individuals did not ingest much sap. In addition, the numbers and durations of waveforms representing ingestion of xylem and phloem saps differed significantly depending on the sex of the leafhopper, indicating that the two sexes exhibit different feeding behaviors. Males had longer phloem ingestion events than did females, which indicates that males are greater phloem feeders than females. These differences are discussed, specifically in relation to hypotheses about evolution of sap feeding and phytoplasma transmission from plant to plant. Copyright © 2017 Elsevier Ltd. All rights reserved.
Effects of combined drought and heavy metal stresses on xylem structure and hydraulic conductivity in red maple (Acer rubrum L.).

PubMed

de Silva, Nayana Dilini Gardiyehewa; Cholewa, Ewa; Ryser, Peter

2012-10-01

The effects of heavy metal stress, drought stress, and their combination on xylem structure in red maple (Acer rubrum) seedlings were investigated in an outdoor pot experiment. As metal-contaminated substrate, a mixture of 1.5% slag with sand was used, with Ni, Cu, Co, and Cr as the main contaminants. Plants grown on contaminated substrate had increased leaf metal concentrations. The two stresses reduced plant growth in an additive manner. The effects of metal and drought stresses on xylem characteristics were similar to each other, with a reduced proportion of xylem tissue, reduced conduit density in stems, and reduced conduit size in the roots. This resulted, in both stems and roots, in reductions in hydraulic conductance, xylem-specific conductivity, and leaf-specific conductivity. The similarity of the responses to the two stresses suggests that the plants' response to metals was actually a drought response, probably due to the reduced water uptake capacity of the metal-exposed roots. The only plant responses specific to metal stress were decreasing trends of stomatal density and chlorophyll content. In conclusion, the exposure to metals aggravates water stress in an additive manner, making the plants more vulnerable to drought.
Leaf Pressure Volume Data in Caxiuana and Tapajos National Forest, Para, Brazil (2011)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powell, Thomas; Moorcroft, Paul

Pressure volume curve measurements on leaves of canopy trees from the from the Caxiuana and Tapajos National Forests, Para, Brazil. Tapajos samples were harvested from the km 67 forested area, which is adjacent to the decommissioned throughfall exclusion drought experimental plot. Caxiuana samples were harvested from trees growing in the throughfall exclusion plots. Data were collected in 2011. Dataset includes: date of measurement, site ID, plot ID, tree ID (species, tree tag #), leaf area, fresh weight, relative weight, leaf water potential, and leaf water loss. P-V curve parameters (turgor loss point, osmotic potential, and bulk modulus of elasticity) canmore » be found in Powell et al. (2017) Differences in xylem cavitation resistance and leaf hydraulic traits explain differences in drought tolerance among mature Amazon rainforest trees. Global Change Biology.« less
Effects of Fe and Mn deficiencies on the protein profiles of tomato (Solanum lycopersicum) xylem sap as revealed by shotgun analyses.

PubMed

Ceballos-Laita, Laura; Gutierrez-Carbonell, Elain; Takahashi, Daisuke; Abadía, Anunciación; Uemura, Matsuo; Abadía, Javier; López-Millán, Ana Flor

2018-01-06

The aim of this work was to study the effects of Fe and Mn deficiencies on the xylem sap proteome of tomato using a shotgun proteomic approach, with the final goal of elucidating plant response mechanisms to these stresses. This approach yielded 643 proteins reliably identified and quantified with 70% of them predicted as secretory. Iron and Mn deficiencies caused statistically significant and biologically relevant abundance changes in 119 and 118 xylem sap proteins, respectively. In both deficiencies, metabolic pathways most affected were protein metabolism, stress/oxidoreductases and cell wall modifications. First, results suggest that Fe deficiency elicited more stress responses than Mn deficiency, based on the changes in oxidative and proteolytic enzymes. Second, both nutrient deficiencies affect the secondary cell wall metabolism, with changes in Fe deficiency occurring via peroxidase activity, and in Mn deficiency involving peroxidase, Cu-oxidase and fasciclin-like arabinogalactan proteins. Third, the primary cell wall metabolism was affected by both nutrient deficiencies, with changes following opposite directions as judged from the abundances of several glycoside-hydrolases with endo-glycolytic activities and pectin esterases. Fourth, signaling pathways via xylem involving CLE and/or lipids as well as changes in phosphorylation and N-glycosylation also play a role in the responses to these stresses. Biological significance In spite of being essential for the delivery of nutrients to the shoots, our knowledge of xylem responses to nutrient deficiencies is very limited. The present work applies a shotgun proteomic approach to unravel the effects of Fe and Mn deficiencies on the xylem sap proteome. Overall, Fe deficiency seems to elicit more stress in the xylem sap proteome than Mn deficiency, based on the changes measured in proteolytic and oxido-reductase proteins, whereas both nutrients exert modifications in the composition of the primary and secondary
Xylem anatomy correlates with gas exchange, water-use efficiency and growth performance under contrasting water regimes: evidence from Populus deltoides x Populus nigra hybrids.

PubMed

Fichot, Régis; Laurans, Françoise; Monclus, Romain; Moreau, Alain; Pilate, Gilles; Brignolas, Franck

2009-12-01

Six Populus deltoides Bartr. ex Marsh. x P. nigra L. genotypes were selected to investigate whether stem xylem anatomy correlated with gas exchange rates, water-use efficiency (WUE) and growth performance. Clonal copies of the genotypes were grown in a two-plot common garden test under contrasting water regimes, with one plot maintained irrigated and the other one subjected to moderate summer water deficit. The six genotypes displayed a large range of xylem anatomy, mean vessel and fibre diameter varying from about 40 to 60 microm and from 7.5 to 10.5 microm, respectively. Decreased water availability resulted in a reduced cell size and an important rise in vessel density, but the extent of xylem plasticity was both genotype and trait dependent. Vessel diameter and theoretical xylem-specific hydraulic conductivity correlated positively with stomatal conductance, carbon isotope discrimination and growth performance-related traits and negatively with intrinsic WUE, especially under water deficit conditions. Vessel diameter and vessel density measured under water deficit conditions correlated with the relative losses in biomass production in response to water deprivation; this resulted from the fact that a more plastic xylem structure was generally accompanied by a larger loss in biomass production.
Tracing Cationic Nutrients from Xylem into Stem Tissue of French Bean by Stable Isotope Tracers and Cryo-Secondary Ion Mass Spectrometry[W][OA

PubMed Central

Metzner, Ralf; Schneider, Heike Ursula; Breuer, Uwe; Thorpe, Michael Robert; Schurr, Ulrich; Schroeder, Walter Heinz

2010-01-01

Fluxes of mineral nutrients in the xylem are strongly influenced by interactions with the surrounding stem tissues and are probably regulated by them. Toward a mechanistic understanding of these interactions, we applied stable isotope tracers of magnesium, potassium, and calcium continuously to the transpiration stream of cut bean (Phaseolus vulgaris) shoots to study their radial exchange at the cell and tissue level with stem tissues between pith and phloem. For isotope localization, we combined sample preparation with secondary ion mass spectrometry in a completely cryogenic workflow. After 20 min of application, tracers were readily detectable to various degrees in all tissues. The xylem parenchyma near the vessels exchanged freely with the vessels, its nutrient elements reaching a steady state of strong exchange with elements in the vessels within 20 min, mainly via apoplastic pathways. A slow exchange between vessels and cambium and phloem suggested that they are separated from the xylem, parenchyma, and pith, possibly by an apoplastic barrier to diffusion for nutrients (as for carbohydrates). There was little difference in these distributions when tracers were applied directly to intact xylem via a microcapillary, suggesting that xylem tension had little effect on radial exchange of these nutrients and that their movement was mainly diffusive. PMID:19965970
Primary Events Regulating Stem Growth at Low Water Potentials 1

PubMed Central

Nonami, Hiroshi; Boyer, John S.

1990-01-01

Cell enlargement is inhibited by inadequate water. As a first step toward understanding the mechanism, all the physical parameters affecting enlargement were monitored to identify those that changed first, particularly in coincidence with the inhibition. The osmotic potential, turgor, yield threshold turgor, growth-induced water potential, wall extensibility, and conductance to water were measured in the elongating region, and the water potential was measured in the xylem of stems of dark-grown soybean (Glycine max [L.] Merr.) seedlings. A stepdown in water potential was achieved around the roots by transplanting the seedlings to vermiculite of low water content, and each of the parameters was measured simultaneously in the same plants while intact or within a few minutes of being intact using a newly developed guillotine psychrometer. The gradient of decreasing water potential from the xylem to the enlarging cells (growth-induced water potential) was the first of the parameters to decrease to a growth-limiting level. The kinetics were the same as for the inhibition of growth. The decreased gradient was caused mostly by a decreased water potential of the xylem. This was followed after 5 to 10 hours by a similar decrease in cell wall extensibility and tissue conductance for water. Later, the growth-induced water potential recovered as a result of osmotic adjustment and a rise in the water potential of the xylem. Still later, moderate growth resumed at a rate apparently determined by the low wall extensibility and tissue conductance for water. The turgor did not change significantly during the experiment. These results indicate that the primary event during the growth inhibition was the change in the growth-induced water potential. Because the growth limitation subsequently shifted to the low wall extensibility and tissue conductance for water, the initial change in potential may have set in motion subsequent metabolic changes that altered the characteristics of the
Interpreting the Climatic Effects on Xylem Functional Traits in Two Mediterranean Oak Species: The Role of Extreme Climatic Events.

PubMed

Rita, Angelo; Borghetti, Marco; Todaro, Luigi; Saracino, Antonio

2016-01-01

In the Mediterranean region, the widely predicted rise in temperature, change in the precipitation pattern, and increase in the frequency of extreme climatic events are expected to alter the shape of ecological communities and to affect plant physiological processes that regulate ecosystem functioning. Although change in the mean values are important, there is increasing evidence that plant distribution, survival, and productivity respond to extremes rather than to the average climatic condition. The present study aims to assess the effects of both mean and extreme climatic conditions on radial growth and functional anatomical traits using long-term tree-ring time series of two co-existing Quercus spp. from a drought-prone site in Southern Italy. In particular, this is the first attempt to apply the Generalized Additive Model for Location, Scale, and Shape (GAMLSS) technique and Bayesian modeling procedures to xylem traits data set, with the aim of (i) detecting non-linear long-term responses to climate and (ii) exploring relationships between climate extreme and xylem traits variability in terms of probability of occurrence. This study demonstrates the usefulness of long-term xylem trait chronologies as records of environmental conditions at annual resolution. Statistical analyses revealed that most of the variability in tree-ring width and specific hydraulic conductivity might be explained by cambial age. Additionally, results highlighted appreciable relationships between xylem traits and climate variability more than tree-ring width, supporting also the evidence that the plant hydraulic traits are closely linked to local climate extremes rather than average climatic conditions. We reported that the probability of extreme departure in specific hydraulic conductivity (Ks) rises at extreme values of Standardized Precipitation Index (SPI). Therefore, changing frequency or intensity of extreme events might overcome the adaptive limits of vascular transport, resulting
Interpreting the Climatic Effects on Xylem Functional Traits in Two Mediterranean Oak Species: The Role of Extreme Climatic Events

PubMed Central

Rita, Angelo; Borghetti, Marco; Todaro, Luigi; Saracino, Antonio

2016-01-01

In the Mediterranean region, the widely predicted rise in temperature, change in the precipitation pattern, and increase in the frequency of extreme climatic events are expected to alter the shape of ecological communities and to affect plant physiological processes that regulate ecosystem functioning. Although change in the mean values are important, there is increasing evidence that plant distribution, survival, and productivity respond to extremes rather than to the average climatic condition. The present study aims to assess the effects of both mean and extreme climatic conditions on radial growth and functional anatomical traits using long-term tree-ring time series of two co-existing Quercus spp. from a drought-prone site in Southern Italy. In particular, this is the first attempt to apply the Generalized Additive Model for Location, Scale, and Shape (GAMLSS) technique and Bayesian modeling procedures to xylem traits data set, with the aim of (i) detecting non-linear long-term responses to climate and (ii) exploring relationships between climate extreme and xylem traits variability in terms of probability of occurrence. This study demonstrates the usefulness of long-term xylem trait chronologies as records of environmental conditions at annual resolution. Statistical analyses revealed that most of the variability in tree-ring width and specific hydraulic conductivity might be explained by cambial age. Additionally, results highlighted appreciable relationships between xylem traits and climate variability more than tree-ring width, supporting also the evidence that the plant hydraulic traits are closely linked to local climate extremes rather than average climatic conditions. We reported that the probability of extreme departure in specific hydraulic conductivity (Ks) rises at extreme values of Standardized Precipitation Index (SPI). Therefore, changing frequency or intensity of extreme events might overcome the adaptive limits of vascular transport, resulting
Chronological Sequence of Leaf Phenology, Xylem and Phloem Formation and Sap Flow of Quercus pubescens from Abandoned Karst Grasslands

PubMed Central

Lavrič, Martina; Eler, Klemen; Ferlan, Mitja; Vodnik, Dominik; Gričar, Jožica

2017-01-01

Intra-annual variations in leaf development, radial growth, including the phloem part, and sap flow have rarely been studied in deciduous trees from drought-prone environments. In order to understand better the chronological order and temporal course of these processes, we monitored leaf phenology, xylem and phloem formation and sap flow in Quercus pubescens from abandoned karst grasslands in Slovenia during the growing season of 2014. We found that the initial earlywood vessel formation started before bud opening at the beginning of April. Buds started to open in the second half of April and full leaf unfolding occurred by the end of May. LAI values increased correspondingly with leaf development. About 28% of xylem and 22% of phloem annual increment were formed by the time of bud break. Initial earlywood vessels were fully lignified and ready for water transport, indicating that they are essential to provide hydraulic conductivity for axial water flow during leaf development. Sap flow became active and increasing contemporarily with leaf development and LAI values. Similar early spring patterns of xylem sap flow and LAI denoted that water transport in oaks broadly followed canopy leaf area development. In the initial 3 weeks of radial growth, phloem growth preceded that of xylem, indicating its priority over xylem at the beginning of the growing season. This may be related to the fact that after bud break, the developing foliage is a very large sink for carbohydrates but, at the same time, represents a small transpirational area. Whether the interdependence of the chronological sequence of the studied processes is fixed in Q. pubescens needs to be confirmed with more data and several years of analyses, although the ‘correct sequence’ of processes is essential for synchronized plant performance and response to environmental stress. PMID:28321232
Soil water and xylem chemistry in declining sugar maple stands in Pennsylvania

Treesearch

David R. DeWalle; Bryan R. Swistock; William E. Sharpe

1999-01-01

Evidence is accumulating that decline of sugar maple, Acer saccharum Marsh., in northern Pennsylvania may be related to overall site fertility as reflected in the chemistry of soil water and bolewood xylem. In this paper we discuss factors related to varying site fertility, including effects of soil liming, past glacialion, topographic position and...
Invasion of xylem of mature tree stems by Phytophthora ramorum and P. kernoviae

Treesearch

Anna Brown; Clive Brasier

2008-01-01

The aetiology and frequency of Phytophthoras in discoloured xylem tissue beneath phloem lesions was investigated in a range of broadleaved trees infected with P. ramorum, P. kernoviae and several other Phytophthoras. Isolation was attempted from the inner surface of 81, 6 x 4 cm sterilised...
Control of xylem Na+ loading and transport to the shoot in rice and barley as a determinant of differential salinity stress tolerance.

PubMed

Ishikawa, Tetsuya; Shabala, Sergey

2018-05-15

Control of xylem Na + loading has often been named as the essential components of salinity tolerance mechanism. However, it is less clear to what extent the difference in this trait may determine differential salinity tolerance between species. In this study barley (Hordeum vulgare L. cv. CM72) and rice (Oryza sativa L. cv Dongjin) plants were grown under two levels of salinity. Na + and K + concentrations in the xylem sap, and shoot and root tissues were measured at different time points after stress onset. Salt-exposed rice plants prevented xylem Na + loading for several days, but failed to control this process in the longer term, ultimately resulting in a massive Na + shoot loading. Barley plants quickly increased xylem Na + concentration and its delivery to the shoot (most likely for the purpose of osmotic adjustment) but were able to reduce this process later on, keeping most of accumulated Na + in the root, thus maintaining non-toxic shoot Na + level. Rice plants increased shoot K + concentration, while barley plants maintained higher root K + concentration. Control of xylem Na + loading is remarkably different between rice and barley; this difference may differentiate the extent of the salinity tolerance between species. This trait should be investigated in more details to be used in the breeding programs aimed to improve salinity tolerance in crops. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
Metabolic Profiling of Xylem Sap from Pierce’s Disease Resistant and Susceptible Grapevines

USDA-ARS?s Scientific Manuscript database

Pierce’s Disease (PD) of grapevines is caused by a gram-negative, xylem-limited bacterium Xylella fastidiosa (Xf). All Vitis vinifera-based cultivars are highly susceptible to Xf infection. However, some grape species from the southern United States such as V. arizonica, V. Shuttleworthii, and Musca...
Investigating water transport through the xylem network in vascular plants.

PubMed

Kim, Hae Koo; Park, Joonghyuk; Hwang, Ildoo

2014-04-01

Our understanding of physical and physiological mechanisms depends on the development of advanced technologies and tools to prove or re-evaluate established theories, and test new hypotheses. Water flow in land plants is a fascinating phenomenon, a vital component of the water cycle, and essential for life on Earth. The cohesion-tension theory (CTT), formulated more than a century ago and based on the physical properties of water, laid the foundation for our understanding of water transport in vascular plants. Numerous experimental tools have since been developed to evaluate various aspects of the CTT, such as the existence of negative hydrostatic pressure. This review focuses on the evolution of the experimental methods used to study water transport in plants, and summarizes the different ways to investigate the diversity of the xylem network structure and sap flow dynamics in various species. As water transport is documented at different scales, from the level of single conduits to entire plants, it is critical that new results be subjected to systematic cross-validation and that findings based on different organs be integrated at the whole-plant level. We also discuss the functional trade-offs between optimizing hydraulic efficiency and maintaining the safety of the entire transport system. Furthermore, we evaluate future directions in sap flow research and highlight the importance of integrating the combined effects of various levels of hydraulic regulation.
Morphological imaging and quantification of axial xylem tissue in Fraxinus excelsior L. through X-ray micro-computed tomography.

PubMed

Koddenberg, Tim; Militz, Holger

2018-05-05

The popularity of X-ray based imaging methods has continued to increase in research domains. In wood research, X-ray micro-computed tomography (XμCT) is useful for structural studies examining the three-dimensional and complex xylem tissue of trees qualitatively and quantitatively. In this study, XμCT made it possible to visualize and quantify the spatial xylem organization of the angiosperm species Fraxinus excelsior L. on the microscopic level. Through image analysis, it was possible to determine morphological characteristics of the cellular axial tissue (vessel elements, fibers, and axial parenchyma cells) three-dimensionally. X-ray imaging at high resolutions provides very distinct visual insight into the xylem structure. Numerical analyses performed through semi-automatic procedures made it possible to quickly quantify cell characteristics (length, diameter, and volume of cells). Use of various spatial resolutions (0.87-5 μm) revealed boundaries users should be aware of. Nevertheless, our findings, both qualitative and quantitative, demonstrate XμCT to be a valuable tool for studying the spatial cell morphology of F. excelsior. Copyright © 2018. Published by Elsevier Ltd.
Stomatal regulation based on competition for water, stochastic rainfall, and xylem hydraulic vulnerability - a new theoretical model

NASA Astrophysics Data System (ADS)

Lu, Y.; Duursma, R.; Farrior, C.; Medlyn, B. E.

2016-12-01

Stomata control the exchange of soil water for atmospheric CO2, which is one of the most important resource trade-offs for plants. This trade-off has been studied a lot but not in the context of competition. Based on the theory of evolutionarily stable strategy, we search for the uninvadable (or the ESS) response of stomatal conductance to soil water content under stochastic rainfall, with which the dominant plant population should never be invaded by any rare mutants in the water competition due to a higher fitness. In this study, we define the fitness as the difference between the long-term average photosynthetic carbon gain and a carbon cost of stomatal opening. This cost has traditionally been considered an unknown constant. Here we extend this framework by assuming it as the energy required for xylem embolism refilling. With regard to the refilling process, we explore 2 questions 1) to what extent the embolized xylem vessels can be repaired via refilling; and 2) whether this refilling is immediate or has a time delay following the formation of xylem embolism. We compare various assumptions in a total of 5 scenarios and find that the ESS exists only if the xylem damage can be repaired completely. Then, with this ESS, we estimate annual vegetation photosynthesis and water consumption and compare them with empirical results. In conclusion, this study provides a different insight from the existing empirical and mechanistic models as well as the theoretical models based on the optimization theory. In addition, as the model result is a simple quantitative relation between stomatal conductance and soil water content, it can be easily incorporated into other vegetation function models.
Cambial Activity and Intra-annual Xylem Formation in Roots and Stems of Abies balsamea and Picea mariana

PubMed Central

Thibeault-Martel, Maxime; Krause, Cornelia; Morin, Hubert; Rossi, Sergio

2008-01-01

Background and Aims Studies on xylogenesis focus essentially on the stem, whereas there is basically no information about the intra-annual growth of other parts of the tree. As roots strongly influence carbon allocation and tree development, knowledge of the dynamics of xylem production and maturation in roots at a short time scale is required for a better understanding of the phenomenon of tree growth. This study compared cambial activity and xylem formation in stem and roots in two conifers of the boreal forest in Canada. Methods Wood microcores were collected weekly in stem and roots of ten Abies balsamea and ten Picea mariana during the 2004–2006 growing seasons. Cross-sections were cut using a rotary microtome, stained with cresyl violet acetate and observed under visible and polarized light. The number of cells in the cambial zone and in differentiation, plus the number of mature cells, was counted along the developing xylem. Key Results Xylem formation lasted from the end of May to the end of September, with no difference between stem and roots in 2004–2005. On the contrary, in 2006 a 1-week earlier beginning of cell differentiation was observed in the stem, with cell wall thickening and lignification in roots ending up to 22 d later than in the stem. Cell production in the stem was concentrated early in the season, in June, while most cell divisions in roots occurred 1 month later. Conclusions The intra-annual dynamics of growth observed in stem and roots could be related to the different amount of cells produced by the cambium and the patterns of air and soil temperature occurring in spring. PMID:18708643
Water relations in silver birch during springtime: How is sap pressurised?

PubMed

Hölttä, T; Dominguez Carrasco, M D R; Salmon, Y; Aalto, J; Vanhatalo, A; Bäck, J; Lintunen, A

2018-05-06

Positive sap pressures are produced in the xylem of birch trees in boreal conditions during the time between the thawing of the soil and bud break. During this period, xylem embolisms accumulated during wintertime are refilled with water. The mechanism for xylem sap pressurization and its environmental drivers are not well known. We measured xylem sap flow, xylem sap pressure, xylem sap osmotic concentration, xylem and whole stem diameter changes, and stem and root non-structural carbohydrate concentrations, along with meteorological conditions at two sites in Finland during and after the sap pressurisation period. The diurnal dynamics of xylem sap pressure and sap flow during the sap pressurisation period varied, but were more often opposite to the diurnal pattern after bud burst, i.e. sap pressure increased and sap flow rate mostly decreased when temperature increased. Net conversion of soluble sugars to starch in the stem and roots occurred during the sap pressurisation period. Xylem sap osmotic pressure was small in comparison to total sap pressure, and it did not follow changes in environmental conditions or tree water relations. Based on these findings, we suggest that xylem sap pressurisation and embolism refilling occur gradually over a few weeks through water transfer from parenchyma cells to xylem vessels during daytime, and then the parenchyma are refilled mostly during nighttime by water uptake from soil. Possible drivers for water transfer from parenchyma cells to vessels are discussed. Also the functioning of thermal dissipation probes in conditions of changing stem water content is discussed. © 2018 German Society for Plant Sciences and The Royal Botanical Society of the Netherlands.

Polyphenols in ceratocystis minor infected Pinus Taeda: fungal metabolites, phloem, and xylem phenols

Treesearch

R.W. Hemingway; G.W. McGraw; S.J. Barras

1977-01-01

Since Ceratocystis minor is central to the death of pines infested by southern pine beetles, changes in polyphenols of infected loblolly pine were examined with regard to accumulation of fungal metabolites and changes in concentrations of fungitoxic and fungistatic phloem and xylem constitutents. C. minor grown in liquid culture...
Polyphenols in Ceratocystis minor infected Pinus taeda: fungal metabolites, phloem and xylem phenols

Treesearch

Richard W. Hemingway; Gerald W. McGraw; Stanley J. Barras

1977-01-01

Since Ceratocystis minor is central to the death of pines infested by southern pine beetles, changes in polyphenols of infected loblolly pine were examined with regard to accumulation of fungal metabolites and changes in concentrations of fungitoxic and fungistatic phloem and xylem constitutents. C. minor grown in liquid culture...
Modeling the dynamics of pressure propagation and diameter variation in tree sapwood.

PubMed

Perämäki, Martti; Vesala, Timo; Nikinmaa, Eero

2005-09-01

A non-steady-state model of water tension propagation in tree stems was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration together with the elasticity of wood cause variations in the diameter of a tree stem. The change in xylem diameter can be linked to water tension in accordance with Hooke's law. The model was tested against field measurements of the diurnal change in xylem diameter at different heights in a 180-year-old Scots pine tree at Hyytiälä, southern Finland. Model predictions agreed well with measurements. The effect of tree dimensions on pressure propagation was examined with the model. The model outcomes were also consistent with results of several field measurements presented in the literature.
Root-to-shoot Cd translocation via the xylem is the major process determining shoot and grain cadmium accumulation in rice

PubMed Central

Uraguchi, Shimpei; Mori, Shinsuke; Kuramata, Masato; Kawasaki, Akira; Arao, Tomohito; Ishikawa, Satoru

2009-01-01

Physiological properties involved in divergent cadmium (Cd) accumulation among rice genotypes were characterized using the indica cultivar ‘Habataki’ (high Cd in grains) and the japonica cultivar ‘Sasanishiki’ (low Cd in grains). Time-dependence and concentration-dependence of symplastic Cd absorption in roots were revealed not to be responsible for the different Cd accumulation between the two cultivars because root Cd uptake was not greater in the Cd-accumulating cultivar ‘Habataki’ compared with ‘Sasanishiki’. On the other hand, rapid and greater root-to-shoot Cd translocation was observed in ‘Habataki’, which could be mediated by higher abilities in xylem loading of Cd and transpiration rate as a driving force. To verify whether different abilities in xylem-mediated shoot-to-root translocation generally account for the genotypic variation in shoot Cd accumulation in rice, the world rice core collection, consisting of 69 accessions which covers the genetic diversity of almost 32 000 accessions of cultivated rice, was used. The results showed strong correlation between Cd levels in xylem sap and shoots and grains among the 69 rice accessions. Overall, the results presented in this study revealed that the root-to-shoot Cd translocation via the xylem is the major and common physiological process determining the Cd accumulation level in shoots and grains of rice plants. PMID:19401409
Xylem anisotropy and water transport--a model for the double sawcut experiment

Treesearch

Paul J. Schulte; David G. Costa

2010-01-01

Early experiments with overlapping cuts to the stems of trees demonstrated that lateral flow within the stem must be possible to allow such trees to maintain water flow to their leaves. We present a mathematical approach to considering lateral flow in stems by treating the xylem as an anisotropic medium for flow and develop an expression of its conductivity in the form...
Microorganisms under high pressure--adaptation, growth and biotechnological potential.

PubMed

Mota, Maria J; Lopes, Rita P; Delgadillo, Ivonne; Saraiva, Jorge A

2013-12-01

Hydrostatic pressure is a well-known physical parameter which is now considered an important variable of life, since organisms have the ability to adapt to pressure changes, by the development of resistance against this variable. In the past decades a huge interest in high hydrostatic pressure (HHP) technology is increasingly emerging among food and biosciences researchers. Microbial specific stress responses to HHP are currently being investigated, through the evaluation of pressure effects on biomolecules, cell structure, metabolic behavior, growth and viability. The knowledge development in this field allows a better comprehension of pressure resistance mechanisms acquired at sub-lethal pressures. In addition, new applications of HHP could arise from these studies, particularly in what concerns to biotechnology. For instance, the modulation of microbial metabolic pathways, as a response to different pressure conditions, may lead to the production of novel compounds with potential biotechnological and industrial applications. Considering pressure as an extreme life condition, this review intends to present the main findings so far reported in the scientific literature, focusing on microorganisms with the ability to withstand and to grow in high pressure conditions, whether they have innated or acquired resistance, and show the potential of the application of HHP technology for microbial biotechnology. © 2013.
Transgenic poplars with reduced lignin show impaired xylem conductivity, growth efficiency and survival

Treesearch

Steven L. Voelker; Barbara Lachenbruch; Frederick C. Meinzer; Peter Kitin; Steven H. Strauss

2011-01-01

We studied xylem anatomy and hydraulic architecture in 14 transgenic insertion events and a control line of hybrid poplar (Populus spp.) that varied in lignin content. Transgenic events had different levels of down-regulation of two genes encoding 4-coumarate:coenzyme A ligase (4CL). Two-year-old trees were characterized after...
Direct micro-CT observation confirms the induction of embolism upon xylem cutting under tension

USDA-ARS?s Scientific Manuscript database

We used two different Synchrotron-based micro-CT facilities (SLS: Swiss Light Source, Villigen, Switzerland, and ALS: Advanced Light Source, Berkeley, CA USA) to test the excision artifact described by Wheeler et al. (2013). Specifically, we examined the impact of cutting xylem under tension and und...
Maximum height in a conifer is associated with conflicting requirements for xylem design

Treesearch

Jean-Chrisophe Domec; Barbara Lachenbruch; Frederick Meinzer; David R. Woodruff; Jeffrey M. Warren; Katherine A. McCulloh

2008-01-01

Despite renewed interest in the nature of limitations on maximum tree height, the mechanisms governing ultimate and species-specific height limits are not yet understood, but they likely involve water transport dynamics. Tall trees experience increased risk of xylem embolism from air-seeding because tension in their water column increases with height owing to path-...
Plant fluid proteomics: Delving into the xylem sap, phloem sap and apoplastic fluid proteomes

USDA-ARS?s Scientific Manuscript database

The phloem sap, xylem sap and apoplastic fluid play key roles in long and short distance transport of signals and nutrients, and act as a barrier against local and systemic pathogen infection. Among other components, these plant fluids contain proteins which are likely to be important players in the...
Plant fluid proteomics: Delving into the xylem sap, phloem sap and apoplastic fluid proteomes

USDA-ARS?s Scientific Manuscript database

The phloem sap, xylem sap and apoplastic fluid play key roles in long and short distance transport of signals and nutrients, and act as a barrier against local and systemic pathogen infection. Among other components, these plant fluids contain proteins, which are likely to be important players in th...
Effects of dormancy progression and low-temperature response on changes in the sorbitol concentration in xylem sap of Japanese pear during winter season.

PubMed

Ito, Akiko; Sugiura, Toshihiko; Sakamoto, Daisuke; Moriguchi, Takaya

2013-04-01

In order to elucidate which physiological event(s) are involved in the seasonal changes of carbohydrate dynamics during winter, we examined the effects of different low temperatures on the carbohydrate concentrations of Japanese pear (Pyrus pyrifolia (Burm.) Nakai). For four winter seasons, large increases in the sorbitol concentration of shoot xylem sap occurred during mid- to late December, possibly due to the endodormancy completion and low-temperature responses. When trees were kept at 15 °C from 3 November to 3 December in order to postpone the initiation and completion of chilling accumulation that would break endodormancy, sorbitol accumulation in xylem sap was always higher from trees with sufficient chilling accumulation than from trees that received insufficient chilling. However, an additional increase in xylem sap sorbitol occurred around late December in trees regardless of whether their chilling accumulation naturally progressed or was postponed. To examine different temperature effects more closely, we compared the carbohydrate concentrations of trees subjected to either 6 or 0 °C treatment. The sorbitol concentration in xylem sap tremendously increased at 0 °C treatment compared with 6 °C treatment. However, an additional increase in xylem sap sorbitol occurred at both the temperatures when sufficient chilling accumulated with a peak coinciding with the peak expression in shoots of the sorbitol transporter gene (PpSOT2). Interestingly, the total carbohydrate concentration of shoots tremendously increased with exposure to 0 °C compared with exposure to 6 °C, but was not affected by the amount of accumulated chilling. Instead, as chilling accumulated the ratio of sorbitol to total soluble sugars in shoots increased. We presumed that carbohydrates in the shoot tissues may be converted to sorbitol and loaded into the xylem sap so that the sorbitol accumulation patterns were synchronized with the progression of dormancy, whereas the total
Thinning, Fertilization, and Crown Position Interact to Control Physiological Responses of Loblolly Pine

Treesearch

Zhenmin Tang; Jim L. Chambers; Suresh Guddanti; James P. Barnett

1999-01-01

Summary To examine physiological responses to thinning, fertilization, and crown position, we measured net photosynthesis (Pn), transpiration (E), vapor pressure difference (VPD), stomatal conductance (gs), and xylem pressure potential (Yl) between 0930 and 1130 h under ambient conditions in the...
Leaf gas exchange performance and the lethal water potential of five European species during drought.

PubMed

Li, Shan; Feifel, Marion; Karimi, Zohreh; Schuldt, Bernhard; Choat, Brendan; Jansen, Steven

2016-02-01

Establishing physiological thresholds to drought-induced mortality in a range of plant species is crucial in understanding how plants respond to severe drought. Here, five common European tree species were selected (Acer campestre L., Acer pseudoplatanus L., Carpinus betulus L., Corylus avellana L. and Fraxinus excelsior L.) to study their hydraulic thresholds to mortality. Photosynthetic parameters during desiccation and the recovery of leaf gas exchange after rewatering were measured. Stem vulnerability curves and leaf pressure-volume curves were investigated to understand the hydraulic coordination of stem and leaf tissue traits. Stem and root samples from well-watered and severely drought-stressed plants of two species were observed using transmission electron microscopy to visualize mortality of cambial cells. The lethal water potential (ψlethal) correlated with stem P99 (i.e., the xylem water potential at 99% loss of hydraulic conductivity, PLC). However, several plants that were stressed beyond the water potential at 100% PLC showed complete recovery during the next spring, which suggests that the ψlethal values were underestimated. Moreover, we observed a 1 : 1 relationship between the xylem water potential at the onset of embolism and stomatal closure, confirming hydraulic coordination between leaf and stem tissues. Finally, ultrastructural changes in the cytoplasm of cambium tissue and mortality of cambial cells are proposed to provide an alternative approach to investigate the point of no return associated with plant death. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Magnetic resonance imaging of water ascent in embolized xylem vessels of grapevine stem segments

Treesearch

Mingtao Wang; Melvin T. Tyree; Roderick E. Wasylishen

2013-01-01

Temporal and spatial information about water refilling of embolized xylem vessels and the rate of water ascent in these vessels is critical for understanding embolism repair in intact living vascular plants. High-resolution 1H magnetic resonance imaging (MRI) experiments have been performed on embolized grapevine stem segments while they were...
Persistent Supercooling of Reproductive Shoots Is Enabled by Structural Ice Barriers Being Active Despite an Intact Xylem Connection

PubMed Central

Pfaller, Kristian; Wagner, Johanna

2016-01-01

Extracellular ice nucleation usually occurs at mild subzero temperatures in most plants. For persistent supercooling of certain plant parts ice barriers are necessary to prevent the entry of ice from already frozen tissues. The reproductive shoot of Calluna vulgaris is able to supercool down to below -22°C throughout all developmental stages (shoot elongation, flowering, fruiting) despite an established xylem conductivity. After localization of the persistent ice barrier between the reproductive and vegetative shoot at the base of the pedicel by infrared differential thermal analysis, the currently unknown structural features of the ice barrier tissue were anatomically analyzed on cross and longitudinal sections. The ice barrier tissue was recognized as a 250 μm long constriction zone at the base of the pedicel that lacked pith tissue and intercellular spaces. Most cell walls in this region were thickened and contained hydrophobic substances (lignin, suberin, and cutin). A few cell walls had what appeared to be thicker cellulose inclusions. In the ice barrier tissue, the area of the xylem was as much as 5.7 times smaller than in vegetative shoots and consisted of tracheids only. The mean number of conducting units in the xylem per cross section was reduced to 3.5% of that in vegetative shoots. Diameter of conducting units and tracheid length were 70% and 60% (respectively) of that in vegetative shoots. From vegetative shoots water transport into the ice barrier must pass pit membranes that are likely impermeable to ice. Pit apertures were about 1.9 μm x 0.7 μm, which was significantly smaller than in the vegetative shoot. The peculiar anatomical features of the xylem at the base of the pedicel suggest that the diameter of pores in pit membranes could be the critical constriction for ice propagation into the persistently supercooled reproductive shoots of C. vulgaris. PMID:27632365
Persistent Supercooling of Reproductive Shoots Is Enabled by Structural Ice Barriers Being Active Despite an Intact Xylem Connection.

PubMed

Kuprian, Edith; Tuong, Tan D; Pfaller, Kristian; Wagner, Johanna; Livingston, David P; Neuner, Gilbert

2016-01-01

Extracellular ice nucleation usually occurs at mild subzero temperatures in most plants. For persistent supercooling of certain plant parts ice barriers are necessary to prevent the entry of ice from already frozen tissues. The reproductive shoot of Calluna vulgaris is able to supercool down to below -22°C throughout all developmental stages (shoot elongation, flowering, fruiting) despite an established xylem conductivity. After localization of the persistent ice barrier between the reproductive and vegetative shoot at the base of the pedicel by infrared differential thermal analysis, the currently unknown structural features of the ice barrier tissue were anatomically analyzed on cross and longitudinal sections. The ice barrier tissue was recognized as a 250 μm long constriction zone at the base of the pedicel that lacked pith tissue and intercellular spaces. Most cell walls in this region were thickened and contained hydrophobic substances (lignin, suberin, and cutin). A few cell walls had what appeared to be thicker cellulose inclusions. In the ice barrier tissue, the area of the xylem was as much as 5.7 times smaller than in vegetative shoots and consisted of tracheids only. The mean number of conducting units in the xylem per cross section was reduced to 3.5% of that in vegetative shoots. Diameter of conducting units and tracheid length were 70% and 60% (respectively) of that in vegetative shoots. From vegetative shoots water transport into the ice barrier must pass pit membranes that are likely impermeable to ice. Pit apertures were about 1.9 μm x 0.7 μm, which was significantly smaller than in the vegetative shoot. The peculiar anatomical features of the xylem at the base of the pedicel suggest that the diameter of pores in pit membranes could be the critical constriction for ice propagation into the persistently supercooled reproductive shoots of C. vulgaris.
Synchrotron microtomography of xylem embolism in Sequoia sempervirens seedlings during cycles of drought and recovery

USDA-ARS?s Scientific Manuscript database

The formation of emboli in xylem conduits can dramatically reduce hydraulic capacity and represents one of the principal mechanisms of drought induced mortality in woody plants. Some angiosperm species possess a mechanism to rapidly repair embolism by dissolving gas back into solution. However, it i...
Intervessel connectivity and relationship with patterns of lateral water exchange within and between xylem sectors in seven xeric shrubs from the great Sahara desert.

PubMed

Halis, Youcef; Mayouf, Rabah; Benhaddya, Mohamed Lamine; Belhamra, Mohamed

2013-03-01

The main objective of this study was to evaluate the role of intervessel contacts in determining the patterns of hydraulic integration both within and between xylem sectors. The degree of intervessel contacts and the lateral exchange capability within and between sectors were examined and correlated in different xeric shrubs. A dye injection method was used to detect the connections between vessels; an apoplastic dye was sucked through a known number of vessels and its distribution in the xylem network was followed. Hydraulic techniques were used to measure axial and tangential conductivity both within and between xylem sectors. The intra- and inter-sector integration indexes were then determined as the ratio of tangential to axial conductance. Species differed significantly in the degree of intervessel contacts, intra- and inter-sector integration index. In all cases, hydraulic integration was observed to be higher within sector than between sectors. From the correlation analyses, the intervessel contacts showed a very weak relationship with inter-sector integration index and a strong positive relationship with intra-sector integration index. Results suggested that (1) the factors affecting patterns of lateral flow within xylem sectors might be relatively different from those between sectors. (2) The degree of intervessel contacts was a major determinant of hydraulic integration within the same xylem sector. (3) Intervessel connectivity alone was a poor predictor of hydraulic integration between different sectors, implying a significant contribution of other anatomical, physiological and environmental factors in determining the patterns of integrated-sectored transport within woody stems.
Microclimate, Water Potential, Transpiration, and Bole Dielectric Constant of Coniferous and Deciduous Tree Species in the Continental Boreal Ecotone of Central Alaska

NASA Technical Reports Server (NTRS)

Zimmermann, R.; McDonald, K.; Way, J.; Oren, R.

1994-01-01

Tree canopy microclimate, xylem water flux and xylem dielectric constant have been monitored in situ since June 1993 in two adjacent natural forest stands in central Alaska. The deciduous stand represents a mature balsam poplar site on the Tanana River floodplain, while the coniferous stand consists of mature white spruce with some black spruce mixed in. During solstice in June and later in summer, diurnal changes of xylem water potential were measured to investigate the occurrence and magnitude of tree transpiration and dielectric constant changes in stems.

Auxin Influx Carriers Control Vascular Patterning and Xylem Differentiation in Arabidopsis thaliana

PubMed Central

Siligato, Riccardo; Alonso, Jose M.; Swarup, Ranjan; Bennett, Malcolm J.; Mähönen, Ari Pekka; Caño-Delgado, Ana I.; Ibañes, Marta

2015-01-01

Auxin is an essential hormone for plant growth and development. Auxin influx carriers AUX1/LAX transport auxin into the cell, while auxin efflux carriers PIN pump it out of the cell. It is well established that efflux carriers play an important role in the shoot vascular patterning, yet the contribution of influx carriers to the shoot vasculature remains unknown. Here, we combined theoretical and experimental approaches to decipher the role of auxin influx carriers in the patterning and differentiation of vascular tissues in the Arabidopsis inflorescence stem. Our theoretical analysis predicts that influx carriers facilitate periodic patterning and modulate the periodicity of auxin maxima. In agreement, we observed fewer and more spaced vascular bundles in quadruple mutants plants of the auxin influx carriers aux1lax1lax2lax3. Furthermore, we show AUX1/LAX carriers promote xylem differentiation in both the shoot and the root tissues. Influx carriers increase cytoplasmic auxin signaling, and thereby differentiation. In addition to this cytoplasmic role of auxin, our computational simulations propose a role for extracellular auxin as an inhibitor of xylem differentiation. Altogether, our study shows that auxin influx carriers AUX1/LAX regulate vascular patterning and differentiation in plants. PMID:25922946
Immunogold scanning electron microscopy can reveal the polysaccharide architecture of xylem cell walls

PubMed Central

Sun, Yuliang; Juzenas, Kevin

2017-01-01

Abstract Immunofluorescence microscopy (IFM) and immunogold transmission electron microscopy (TEM) are the two main techniques commonly used to detect polysaccharides in plant cell walls. Both are important in localizing cell wall polysaccharides, but both have major limitations, such as low resolution in IFM and restricted sample size for immunogold TEM. In this study, we have developed a robust technique that combines immunocytochemistry with scanning electron microscopy (SEM) to study cell wall polysaccharide architecture in xylem cells at high resolution over large areas of sample. Using multiple cell wall monoclonal antibodies (mAbs), this immunogold SEM technique reliably localized groups of hemicellulosic and pectic polysaccharides in the cell walls of five different xylem structures (vessel elements, fibers, axial and ray parenchyma cells, and tyloses). This demonstrates its important advantages over the other two methods for studying cell wall polysaccharide composition and distribution in these structures. In addition, it can show the three-dimensional distribution of a polysaccharide group in the vessel lateral wall and the polysaccharide components in the cell wall of developing tyloses. This technique, therefore, should be valuable for understanding the cell wall polysaccharide composition, architecture and functions of diverse cell types. PMID:28398585
Genomic insights into strategies used by Xanthomonas albilineans with its reduced artillery to spread within sugarcane xylem vessels.

PubMed

Pieretti, Isabelle; Royer, Monique; Barbe, Valérie; Carrere, Sébastien; Koebnik, Ralf; Couloux, Arnaud; Darrasse, Armelle; Gouzy, Jérôme; Jacques, Marie-Agnès; Lauber, Emmanuelle; Manceau, Charles; Mangenot, Sophie; Poussier, Stéphane; Segurens, Béatrice; Szurek, Boris; Verdier, Valérie; Arlat, Matthieu; Gabriel, Dean W; Rott, Philippe; Cociancich, Stéphane

2012-11-21

Xanthomonas albilineans causes leaf scald, a lethal disease of sugarcane. X. albilineans exhibits distinctive pathogenic mechanisms, ecology and taxonomy compared to other species of Xanthomonas. For example, this species produces a potent DNA gyrase inhibitor called albicidin that is largely responsible for inducing disease symptoms; its habitat is limited to xylem; and the species exhibits large variability. A first manuscript on the complete genome sequence of the highly pathogenic X. albilineans strain GPE PC73 focused exclusively on distinctive genomic features shared with Xylella fastidiosa-another xylem-limited Xanthomonadaceae. The present manuscript on the same genome sequence aims to describe all other pathogenicity-related genomic features of X. albilineans, and to compare, using suppression subtractive hybridization (SSH), genomic features of two strains differing in pathogenicity. Comparative genomic analyses showed that most of the known pathogenicity factors from other Xanthomonas species are conserved in X. albilineans, with the notable absence of two major determinants of the "artillery" of other plant pathogenic species of Xanthomonas: the xanthan gum biosynthesis gene cluster, and the type III secretion system Hrp (hypersensitive response and pathogenicity). Genomic features specific to X. albilineans that may contribute to specific adaptation of this pathogen to sugarcane xylem vessels were also revealed. SSH experiments led to the identification of 20 genes common to three highly pathogenic strains but missing in a less pathogenic strain. These 20 genes, which include four ABC transporter genes, a methyl-accepting chemotaxis protein gene and an oxidoreductase gene, could play a key role in pathogenicity. With the exception of hypothetical proteins revealed by our comparative genomic analyses and SSH experiments, no genes potentially involved in any offensive or counter-defensive mechanism specific to X. albilineans were identified, supposing
Water Flow through Xylem: An Investigation of a Fluid Dynamics Principle Applied to Plants

ERIC Educational Resources Information Center

Rice, Stanley A.; McArthur, John

2004-01-01

A study was conducted to prove that a large blood or xylem vessel could conduct 256 times more fluid than a vessel or a pipe that is four times smaller. The result of this study proved that if arteriosclerosis causes an artery to loose half its effective diameter, the blood flow would be reduced by fifteen-sixteenths.
Coexisting oak species, including rear-edge populations, buffer climate stress through xylem adjustments.

PubMed

Granda, E; Alla, A Q; Laskurain, N A; Loidi, J; Sánchez-Lorenzo, A; Camarero, J J

2018-02-01

The ability of trees to cope with climate change is a pivotal feature of forest ecosystems, especially for rear-edge populations facing warm and dry conditions. To evaluate current and future forests threats, a multi-proxy focus on the growth, anatomical and physiological responses to climate change is needed. We examined the long-term xylem adjustments to climate variability of the temperate Quercus robur L. at its rear edge and the sub-Mediterranean Quercus pyrenaica Willd. Both species coexist at a mesic (ME, humid and warmer) and a xeric (XE, dry and cooler) site in northern Spain, the latter experiencing increasing temperatures in recent decades. We compared xylem traits at each site and assessed their trends, relationships and responses to climate (1960-2008). Traits included basal area increment, earlywood vessel hydraulic diameter, density and theoretical-specific hydraulic conductivity together with latewood oxygen (δ18O) stable isotopes and δ13C-derived water-use efficiency (iWUE). Quercus robur showed the highest growth at ME, likely through enhanced cambial activity. Quercus pyrenaica had higher iWUE at XE compared with ME, but limited plasticity of anatomical xylem traits was found for the two oak species. Similar physiological performance was found for both species. The iWUE augmented in recent years especially at XE, likely explained by stomatal closure given the increasing δ18O signal in response to drier and sunnier growing seasons. Overall, traits were more correlated at XE than at ME. The iWUE improvements were linked to higher growth up to a threshold (~85 μmol mol-1) after which reduced growth was found at XE. Our results are consistent with Q. pyrenaica and Q. robur coexisting at the central and dry edge of the climatic species distribution, respectively, showing similar responses to buffer warmer conditions. In fact, the observed adjustments found for Q. robur point towards growth stability of similar rear-edge oak populations under
BRANCH JUNCTIONS AND THE FLOW OF WATER THROUGH XYLEM IN DOUGLAS-FIR AND PONDEROSA PINE STEMS

EPA Science Inventory

Water flowing through the xylem of most plants from the roots to the leaves must pass through junctions where branches have developed from the main stem. These junctions have been studied as both flow constrictions and components of a hydraulic segmentation mechanism to protect ...
Three types of cavitation caused by air seeding.

PubMed

Shen, Fanyi; Wang, Yuansheng; Cheng, Yanxia; Zhang, Li

2012-11-01

There are different opinions of the dynamics of an air bubble entering a xylem conduit. In this paper, we present a thorough mechanical analysis and conclude that there are three types of cavitation caused by air seeding. After an air seed enters a conduit at high xylem pressure P'(1), along with the drop of the water potential, it will expand gradually to a long-shaped bubble and extend continually. This is the first type of air seeding, or the type of expanding gradually. When the xylem pressure is moderate, right after an air seed enters a conduit, it will expand first. Then, as soon as the pressure reaches a threshold the bubble will blow up to form a bubble in long shape, accompanied by acoustic (or ultra-acoustic) emission. It will extend further as xylem pressure decreases continually. This is the second type of air seeding, or the type of expanding-exploding, becoming a long-shaped bubble-lengthening by degrees. In the range of P'(1) ≤ - 3P(o) (P(o) is atmospheric pressure), soon after an air seed is sucked into a conduit it will explode immediately and the conduit will be full of the gas of the bubble instantly. This is the third type of air seeding, or the type of sudden exploding and filling conduit instantly. The third type is the frequent event in daily life of plant.
The dynamic pipeline: hydraulic capacitance and xylem hydraulic safety in four tall conifer species

Treesearch

Katherine A. McCulloh; Daniel M. Johnson; Frederick C. Meinzer; David R. Woodruff

2013-01-01

Recent work has suggested that plants differ in their relative reliance on structural avoidance of embolism versus maintenance of the xylem water column through dynamic traits such as capacitance, but we still know little about how and why species differ along this continuum. It is even less clear how or if different parts of a plant vary along this spectrum. Here we...
A mathematical model of water and nutrient transport in xylem vessels of a wheat plant.

PubMed

Payvandi, S; Daly, K R; Jones, D L; Talboys, P; Zygalakis, K C; Roose, T

2014-03-01

At a time of increasing global demand for food, dwindling land and resources, and escalating pressures from climate change, the farming industry is undergoing financial strain, with a need to improve efficiency and crop yields. In order to improve efficiencies in farming, and in fertiliser usage in particular, understanding must be gained of the fertiliser-to-crop-yield pathway. We model one aspect of this pathway; the transport of nutrients within the vascular tissues of a crop plant from roots to leaves. We present a mathematical model of the transport of nutrients within the xylem vessels in response to the evapotranspiration of water. We determine seven different classes of flow, including positive unidirectional flow, which is optimal for nutrient transport from the roots to the leaves; and root multidirectional flow, which is similar to the hydraulic lift process observed in plants. We also investigate the effect of diffusion on nutrient transport and find that diffusion can be significant at the vessel termini especially if there is an axial efflux of nutrient, and at night when transpiration is minimal. Models such as these can then be coupled to whole-plant models to be used for optimisation of nutrient delivery scenarios.
New insights into pioneer root xylem development: evidence obtained from Populus trichocarpa plants grown under field conditions

PubMed Central

Bagniewska-Zadworna, Agnieszka; Arasimowicz-Jelonek, Magdalena; Smoliński, Dariusz J.; Stelmasik, Agnieszka

2014-01-01

Background and Aims Effective programmed xylogenesis is critical to the structural framework of the plant root system and its central role in the acquisition and long-distance transport of water and nutrients. The process of xylem differentiation in pioneer roots under field conditions is poorly understood. In this study it is hypothesized that xylogenesis, an example of developmental programmed cell death (PCD), in the roots of woody plants demonstrates a clearly defined sequence of events resulting in cell death. A comprehensive analysis was therefore undertaken to identify the stages of xylogenesis in pioneer roots from procambial cells to fully functional vessels with lignified cell walls and secondary cell wall thickenings. Methods Xylem differentiation was monitored in the pioneer roots of Populus trichocarpa at the cytological level using rhizotrons under field conditions. Detection and localization of the signalling molecule nitric oxide (NO) and hydrogen peroxide (H2O2) was undertaken and a detailed examination of nuclear changes during xylogenesis was conducted. In addition, analyses of the expression of genes involved in secondary cell wall synthesis were performed in situ. Key Results The primary event in initially differentiating tracheary elements (TEs) was a burst of NO in thin-walled cells, followed by H2O2 synthesis and the appearance of TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling)-positive nuclei. The first changes in nuclear structure were observed in the early stages of xylogenesis of pioneer roots, prior to lignification; however, the nucleus was detectable under transmission electron microscopy in differentiating cells until the stage at which vacuole integrity was maintained, indicating that their degradation was slow and prolonged. The subsequent sequence of events involved secondary cell wall formation and autophagy. Potential gene markers from the cinnamyl alcohol dehydrogenase (CAD) gene family that were
Different cation stresses affect specifically osmotic root hydraulic conductance, involving aquaporins, ATPase and xylem loading of ions in Capsicum annuum, L. plants.

PubMed

Cabañero, Francisco J; Carvajal, Micaela

2007-10-01

In order to study the effect of nutrient stress on water uptake in pepper plants (Capsicum annuum L.), the excess or deficiency of the main cations involved in plant nutrition (K(+), Mg(2+), Ca(2+)) and two different degrees of salinity were related to the activity of plasma membrane H(+)-ATPase, the pH of the xylem sap, nutrient flux into the xylem (J(s)) and to a number of parameters related to water relations, such as root hydraulic conductance (L(0)), stomatal conductance (g(s)) and aquaporin activity. Excess of K(+), Ca(+) and NaCl produced a toxic effect on L(0) while Mg(2+) starvation produced a positive effect, which was in agreement with aquaporin functionality, but not with ATPase activity. The xylem pH was altered only by Ca treatments. The results obtained with each treatment could suggest that detection of the quality of the nutrient supply being received by roots can be related to aquaporins functionality, but also that each cation stress triggers specific responses that have to be assessed individually.
Characterization of Optimum Physiological Responses of Field-Grown Loblolly Pine

Treesearch

Zhenmin Tang; Jim L. Chambers; James P. Barnett

1999-01-01

Photosynthetic photon flux density (PPFD), air temperature (Ta), needle net photosynthesis (Pn), vapor pressure difference (VPD), stomata1 conductance (gw), transpiration (E), and predawn and daytime xylem pressure potentials (XPP) were measured in a loblolly pine (Pinus taeda L.) plantation in 1995 and 1996. Boundary-line analyses were conducted...
Tree-ring anatomy and carbon isotope ratio show both direct and legacy effects of climate on bimodal xylem formation in Pinus pinea.

PubMed

Castagneri, Daniele; Battipaglia, Giovanna; von Arx, Georg; Pacheco, Arturo; Carrer, Marco

2018-04-24

Understanding how climate affects xylem formation is critical for predicting the impact of future conditions on tree growth and functioning in the Mediterranean region, which is expected to face warmer and drier conditions. However, mechanisms of growth response to climate at different temporal scales are still largely unknown, being complicated by separation between spring and autumn xylogenesis (bimodal temporal pattern) in most species such as Mediterranean pines. We investigated wood anatomical characteristics and carbon stable isotope composition in Mediterranean Pinus pinea L. along tree-ring series at intra-ring resolution to assess xylem formation processes and responses to intra-annual climate variability. Xylem anatomy was strongly related to environmental conditions occurring a few months before and during the growing season, but was not affected by summer drought. In particular, the lumen diameter of the first earlywood tracheids was related to winter precipitation, whereas the size of tracheids produced later was influenced by mid-spring precipitation. Diameter of latewood tracheids was associated with precipitation in mid-autumn. In contrast, tree-ring carbon isotope composition was mostly related to climate of the previous seasons. Earlywood was likely formed using both recently and formerly assimilated carbon, while latewood relied mostly on carbon accumulated many months prior to its formation. Our integrated approach provided new evidence on the short-term and carry-over effects of climate on the bimodal temporal xylem formation in P. pinea. Investigations on different variables and time scales are necessary to disentangle the complex climate influence on tree growth processes under Mediterranean conditions.
Impacts of long-term precipitation manipulation on hydraulic architecture and xylem anatomy of piñon and juniper in Southwest USA.

PubMed

Hudson, P J; Limousin, J M; Krofcheck, D J; Boutz, A L; Pangle, R E; Gehres, N; McDowell, N G; Pockman, W T

2018-02-01

Hydraulic architecture imposes a fundamental control on water transport, underpinning plant productivity, and survival. The extent to which hydraulic architecture of mature trees acclimates to chronic drought is poorly understood, limiting accuracy in predictions of forest responses to future droughts. We measured seasonal shoot hydraulic performance for multiple years to assess xylem acclimation in mature piñon (Pinus edulis) and juniper (Juniperus monosperma) after 3+ years of precipitation manipulation. Our treatments consisted of water addition (+20% ambient precipitation), partial precipitation-exclusion (-45% ambient precipitation), and exclusion-structure control. Supplemental watering elevated leaf water potential, sapwood-area specific hydraulic conductivity, and leaf-area specific hydraulic conductivity relative to precipitation exclusion. Shifts in allocation of leaf area to sapwood area enhanced differences between irrigated and droughted K L in piñon but not juniper. Piñon and juniper achieved similar K L under ambient conditions, but juniper matched or outperformed piñon in all physiological measurements under both increased and decreased precipitation treatments. Embolism vulnerability and xylem anatomy were unaffected by treatments in either species. Absence of significant acclimation combined with inferior performance for both hydraulic transport and safety suggests piñon has greater risk of local extirpation if aridity increases as predicted in the southwestern USA. © 2017 John Wiley & Sons Ltd.
A Revised Similarity Law in Botanic Describes the Genesis of the Vulnerability Curve Shape in Vascular Plants

NASA Astrophysics Data System (ADS)

Mrad, A.; Domec, J. C.; Huang, C. W.; Katul, G. G.

2017-12-01

Xylem tissues are specialized in offering the least possible resistance to water flow. However, this is not guaranteed when ascending sap reaches large negative pressures during periods of water stress when embolism within the xylem occurs, an inevitable step toward potential drought-induced mortality. Ongoing research into changing forest patterns and plant survival due to droughts rarely dispute the significance of Vulnerability Curves (VCs), plots that feature loss in relative conductance with declining liquid pressure (ψ). While Earth-Systems models routinely employ various VC functions, the theoretical underpinnings describing their shape remains lacking. VCs are the outcome of microscopic phenomena describing embolism formation, bubble-scale xylem properties allowing embolism spread, and hydraulic processes that dictate the water potential along the flow path. The work here explores how the upscaled version of these gives rise to popular mathematical shapes used to describe VC measurements: The Logistic and Weibull exceedance equations. Each of these two captures a distinct type of embolism spread: The Logistic VC arises when the probability that embolized vessels interact with intact ones describe embolism spread as water pressure decreases (labeled as a similarity law in botanic [1]). The Weibull VC arises when the aforementioned description includes the effects of ψ explicitly. Variability in xylem properties along the flow path is explored analytically using novel approaches borrowed from `super-statistics' and numerical simulations. The numerical simulations intend to single out which xylem network property is significant in describing the VC shape. The model results corroborate previous research (experimental and 3-dimensional high-resolution simulations) on the effect of vessel size and network topology. It is shown that (i) initial embolism locations alter air-seeding pressure and VC slope; (ii) redundancy and size variations decrease bubble
Influence of soil texture on hydraulic properties and water relations of a dominant warm-desert phreatophyte.

PubMed

Hultine, K R; Koepke, D F; Pockman, W T; Fravolini, A; Sperry, J S; Williams, D G

2006-03-01

We investigated hydraulic constraints on water uptake by velvet mesquite (Prosopis velutina Woot.) at a site with sandy-loam soil and at a site with loamy-clay soil in southeastern Arizona, USA. We predicted that trees on sandy-loam soil have less negative xylem and soil water potentials during drought and a lower resistance to xylem cavitation, and reach E(crit) (the maximum steady-state transpiration rate without hydraulic failure) at higher soil water potentials than trees on loamy-clay soil. However, minimum predawn leaf xylem water potentials measured during the height of summer drought were significantly lower at the sandy-loam site (-3.5 +/- 0.1 MPa; all errors are 95% confidence limits) than at the loamy-clay site (-2.9 +/- 0.1 MPa). Minimum midday xylem water potentials also were lower at the sandy-loam site (-4.5 +/- 0.1 MPa) than at the loamy-clay site (-4.0 +/- 0.1 MPa). Despite the differences in leaf water potentials, there were no significant differences in either root or stem xylem embolism, mean cavitation pressure or Psi(95) (xylem water potential causing 95% cavitation) between trees at the two sites. A soil-plant hydraulic model parameterized with the field data predicted that E(crit) approaches zero at a substantially higher bulk soil water potential (Psi(s)) on sandy-loam soil than on loamy-clay soil, because of limiting rhizosphere conductance. The model predicted that transpiration at the sandy-loam site is limited by E(crit) and is tightly coupled to Psi(s) over much of the growing season, suggesting that seasonal transpiration fluxes at the sandy-loam site are strongly linked to intra-annual precipitation pulses. Conversely, the model predicted that trees on loamy-clay soil operate below E(crit) throughout the growing season, suggesting that fluxes on fine-textured soils are closely coupled to inter-annual changes in precipitation. Information on the combined importance of xylem and rhizosphere constraints to leaf water supply across soil
Spatial variation of vessel grouping in the xylem of Betula platyphylla Roth.

PubMed

Zhao, Xiping

2016-01-01

Vessel grouping in angiosperms may improve hydraulic integration and increase the spread of cavitations through redundancy pathways. Although disputed, it is increasingly attracting research interest as a potentially significant hydraulic trait. However, the variation of vessel grouping in a tree is poorly understood. I measured the number of solitary and grouped vessels in the xylem of Betula platyphylla Roth. from the pith to the bark along the water flow path. The vessel grouping parameters included the mean number of vessels per vessel group (VG), percentage of solitary vessels (SVP), percentage of radial multiple vessels (MVP), and percentage of cluster vessels (CVP). The effects of cambial age (CA) and flow path-length (PL) on the vessel grouping were analyzed using a linear mixed model.VG and CVP increased nonlinearly, SVP decreased nonlinearly with PL. In trunks and branches, VG and CVP decreased nonlinearly, and SVP increased nonlinearly with CA. In roots, the parameters had no change with CA. MVP was almost constant with PL or CA. The results suggest that vessel grouping has a nonrandom variation pattern, which is affected deeply by cambial age and water flow path.
Chemical and anatomical changes in Liquidambar styraciflua L.xylem after long term exposure to elevated CO

Treesearch

Keonhee Kim; Nicole Labbé; Jeffrey M. Warren; Thomas Elder; Timothy G. Rials

2015-01-01

The anatomical and chemical characteristics of sweetgum were studied after 11 years of elevated CO₂(544 ppm, ambient at 391 ppm) exposure. Anatomically, branch xylem cells were larger for elevated CO2 trees, and the cell wall thickness was thinner. Chemically, elevated CO₂ exposure did not...
The zonal-mean and regional tropospheric pressure responses to changes in ionospheric potential

NASA Astrophysics Data System (ADS)

Zhou, Limin; Tinsley, Brian; Wang, Lin; Burns, Gary

2018-06-01

Global reanalysis data reveal daily surface pressure responses to changes in the global ionospheric potential in both polar and sub-polar regions. We use 21 years of data to show that the pressure response to externally-induced ionospheric potential changes, that are due to the interplanetary magnetic field east-west (IMF By) component, are present in two separate decadal intervals, and follow the opposite ionospheric potential changes in the Arctic and Antarctic for a given By. We use the 4 years of available data to show that the pressure responses to changes in internally generated ionospheric potential, that are caused by low-latitude thunderstorms and highly electrified clouds, agree in sign and sensitivity with those externally generated. We have determined that the daily varying pressure responses are stronger in local winter and spring. The pressure responses at polar latitudes are predominantly over the Antarctic and Greenland ice caps, and those at sub-polar latitudes are of opposite sign, mainly over oceans. A lead-lag analysis confirms that the responses maximize within two days of the ionospheric potential input. Regions of surface pressure fluctuating by about 4 hPa in winter are found with ionospheric potential changes of about 40 kV. The consistent pressure response to the independent external and internal inputs strongly supports the reality of a cloud microphysical mechanism affected by the global electric circuit. A speculative mechanism involves the ionosphere-earth current density Jz, which produces space charge at cloud boundaries and electrically charged droplets and aerosol particles. Ultrafine aerosol particles, under the action of electro-anti-scavenging, are enabled to grow to condensation nuclei size, affecting cloud microphysics and cloud opacity and surface pressure on time scales of hours.
Golgi Enrichment and Proteomic Analysis of Developing Pinus radiata Xylem by Free-Flow Electrophoresis

PubMed Central

Macdonald, Lucy J.; Adams, Paul D.; Petzold, Christopher J.; Strabala, Timothy J.; Wagner, Armin; Heazlewood, Joshua L.

2013-01-01

Our understanding of the contribution of Golgi proteins to cell wall and wood formation in any woody plant species is limited. Currently, little Golgi proteomics data exists for wood-forming tissues. In this study, we attempted to address this issue by generating and analyzing Golgi-enriched membrane preparations from developing xylem of compression wood from the conifer Pinus radiata. Developing xylem samples from 3-year-old pine trees were harvested for this purpose at a time of active growth and subjected to a combination of density centrifugation followed by free flow electrophoresis, a surface charge separation technique used in the enrichment of Golgi membranes. This combination of techniques was successful in achieving an approximately 200-fold increase in the activity of the Golgi marker galactan synthase and represents a significant improvement for proteomic analyses of the Golgi from conifers. A total of thirty known Golgi proteins were identified by mass spectrometry including glycosyltransferases from gene families involved in glucomannan and glucuronoxylan biosynthesis. The free flow electrophoresis fractions of enriched Golgi were highly abundant in structural proteins (actin and tubulin) indicating a role for the cytoskeleton during compression wood formation. The mass spectrometry proteomics data associated with this study have been deposited to the ProteomeXchange with identifier PXD000557. PMID:24416096

A synthetic leaf: the biomimetic potential of graphene oxide

NASA Astrophysics Data System (ADS)

Lamb, Marilla; Koch, George W.; Morgan, Eric R.; Shafer, Michael W.

2015-03-01

Emerging materials such as graphene oxide (GO) have micro and nano features that are functionally similar to those in plant cell walls involved in water transport. Therefore, it may now be possible to design and build biomimetic trees to lift water via mechanisms similar to those employed by trees, allowing for potential applications such as passive water pumping, filtering, and evaporative cooling. The tallest trees can raise large volumes of water to over 100 meters using only the vapor pressure gradient between their leaves and the atmosphere. This phenomenon occurs in all terrestrial plants when capillary forces generated in the microscopic pores in the cell walls of leaves are collectively applied to large diameter xylem conduits. The design of a synthetic tree that mimics these mechanisms will allow water to be moved to heights greater than is currently possible by any engineered system that does not require the use of a positive pressure pump. We are testing the suitability of membranous GO as the leaf of a synthetic tree and present an analysis in support of this design. In addition, we include results from a preliminary design using ceramics.
Ion-mediated enhancement of xylem hydraulic conductivity in four Acer species: relationships with ecological and anatomical features.

PubMed

Nardini, Andrea; Dimasi, Federica; Klepsch, Matthias; Jansen, Steven

2012-12-01

The 'ionic effect', i.e., changes in xylem hydraulic conductivity (k(xyl)) due to variation of the ionic sap composition in vessels, was studied in four Acer species growing in contrasting environments differing in water availability. Hydraulic measurements of the ionic effect were performed together with measurements on the sap electrical conductivity, leaf water potential and vessel anatomy. The low ionic effect recorded in Acer pseudoplatanus L. and Acer campestre L. (15.8 and 14.7%, respectively), which represented two species from shady and humid habitats, was associated with a low vessel grouping index, high sap electrical conductivity and least negative leaf water potential. Opposite traits were found for Acer monspessulanum L. and Acer platanoides L., which showed an ionic effect of 23.6 and 23.1%, respectively, and represent species adapted to higher irradiance and/or lower water availability. These findings from closely related species provide additional support that the ionic effect could function as a compensation mechanism for embolism-induced loss of k(xyl), either as a result of high evaporative demand or increased risk of hydraulic failure.
Relationships among foliar phenology, radial growth rate, and xylem density in a young Douglas-fir plantation

Treesearch

Warren D. Devine; Constance A. Harrington

2009-01-01

We related intraannual patterns in radial growth rate and xylem density to foliar phenology and second growth flushes in a young Douglas-fir plantation in western Washington. Three foliar maturity classes were defined: (1) shoots and needles elongating; (2) elongation complete, needles maturing; and (3) needles mature. Diameter growth rate had two peaks, one about the...
Xylem transport and gene expression play decisive roles in cadmium accumulation in shoots of two oilseed rape cultivars (Brassica napus).

PubMed

Wu, Zhichao; Zhao, Xiaohu; Sun, Xuecheng; Tan, Qiling; Tang, Yafang; Nie, Zhaojun; Hu, Chengxiao

2015-01-01

Cadmium (Cd) is a toxic metal which harms human health through food chains. The mechanisms underlying Cd accumulation in oilseed rape are still poorly understood. Here, we investigated the physiological and genetic processes involved in Cd uptake and transport of two oilseed rape cultivars (Brassica napus). L351 accumulates more Cd in shoots but less in roots than L338. A scanning ion-selective electrode technique (SIET) and uptake kinetics of Cd showed that roots were not responsible for the different Cd accumulation in shoots since L351 showed a lower Cd uptake ability. However, concentration-dependent and time-dependent dynamics of Cd transport by xylem showed L351 exhibited a superordinate capacity of Cd translocation to shoots. Additionally, the Cd concentrations of shoots and xylem sap showed a great correlation in both cultivars. Furthermore, gene expression levels related to Cd uptake by roots (IRT1) and Cd transport by xylem (HMA2 and HMA4) were consistent with the tendencies of Cd absorption and transport at the physiological level respectively. In other words, L351 had stronger gene expression for Cd transport but lower for Cd uptake. Overall, results revealed that the process of Cd translocation to shoots is a determinative factor for Cd accumulation in shoots, both at physiological and genetic levels. Crown Copyright © 2014. Published by Elsevier Ltd. All rights reserved.
Frost fatigue and spring recovery of xylem vessels in three diffuse-porous trees in situ.

PubMed

Christensen-Dalsgaard, Karen K; Tyree, Melvin T

2014-05-01

Frost has been shown to cause frost fatigue (reduced cavitation resistance) in branch segments in the lab. Here, we studied the change in cavitation resistance and percent loss of conductivity (PLC) from fall to spring over 2 consecutive years in three diffuse-porous species in situ. We used the cavitron technique to measure P25 , P50 and P90 (the xylem pressure causing a 25, 50 and 90% conductivity loss) and PLC and stained functioning vessels. Cavitation resistance was reduced by 64-87% (in terms of P50 ), depending on the species and year. P25 was impacted the most and P90 the least, changing the vulnerability curves from s- to r-shaped over the winter in all three species. The branches suffered an almost complete loss of conductivity, but frost fatigue did not necessarily occur concurrently with increases in PLC. In two species, there was a trade-off between conduit size and vulnerability. Spring recovery occurred by growth of new vessels, and in two species by partial refilling of embolized conduits. Although newly grown and functioning conduits appeared more vulnerable to cavitation than year-old vessels, cavitation resistance generally improved in spring, suggesting other mechanisms for partial frost fatigue repair. © 2013 John Wiley & Sons Ltd.
Mind the bubbles: achieving stable measurements of maximum hydraulic conductivity through woody plant samples

PubMed Central

Espino, Susana; Schenk, H. Jochen

2011-01-01

The maximum specific hydraulic conductivity (kmax) of a plant sample is a measure of the ability of a plants’ vascular system to transport water and dissolved nutrients under optimum conditions. Precise measurements of kmax are needed in comparative studies of hydraulic conductivity, as well as for measuring the formation and repair of xylem embolisms. Unstable measurements of kmax are a common problem when measuring woody plant samples and it is commonly observed that kmax declines from initially high values, especially when positive water pressure is used to flush out embolisms. This study was designed to test five hypotheses that could potentially explain declines in kmax under positive pressure: (i) non-steady-state flow; (ii) swelling of pectin hydrogels in inter-vessel pit membranes; (iii) nucleation and coalescence of bubbles at constrictions in the xylem; (iv) physiological wounding responses; and (v) passive wounding responses, such as clogging of the xylem by debris. Prehydrated woody stems from Laurus nobilis (Lauraceae) and Encelia farinosa (Asteraceae) collected from plants grown in the Fullerton Arboretum in Southern California, were used to test these hypotheses using a xylem embolism meter (XYL'EM). Treatments included simultaneous measurements of stem inflow and outflow, enzyme inhibitors, stem-debarking, low water temperatures, different water degassing techniques, and varied concentrations of calcium, potassium, magnesium, and copper salts in aqueous measurement solutions. Stable measurements of kmax were observed at concentrations of calcium, potassium, and magnesium salts high enough to suppress bubble coalescence, as well as with deionized water that was degassed using a membrane contactor under strong vacuum. Bubble formation and coalescence under positive pressure in the xylem therefore appear to be the main cause for declining kmax values. Our findings suggest that degassing of water is essential for achieving stable and precise
Ralstonia solanacearum uses inorganic nitrogen metabolism for virulence, ATP production, and detoxification in the oxygen-limited host xylem environment.

PubMed

Dalsing, Beth L; Truchon, Alicia N; Gonzalez-Orta, Enid T; Milling, Annett S; Allen, Caitilyn

2015-03-17

Genomic data predict that, in addition to oxygen, the bacterial plant pathogen Ralstonia solanacearum can use nitrate (NO3(-)), nitrite (NO2(-)), nitric oxide (NO), and nitrous oxide (N2O) as terminal electron acceptors (TEAs). Genes encoding inorganic nitrogen reduction were highly expressed during tomato bacterial wilt disease, when the pathogen grows in xylem vessels. Direct measurements found that tomato xylem fluid was low in oxygen, especially in plants infected by R. solanacearum. Xylem fluid contained ~25 mM NO3(-), corresponding to R. solanacearum's optimal NO3(-) concentration for anaerobic growth in vitro. We tested the hypothesis that R. solanacearum uses inorganic nitrogen species to respire and grow during pathogenesis by making deletion mutants that each lacked a step in nitrate respiration (ΔnarG), denitrification (ΔaniA, ΔnorB, and ΔnosZ), or NO detoxification (ΔhmpX). The ΔnarG, ΔaniA, and ΔnorB mutants grew poorly on NO3(-) compared to the wild type, and they had reduced adenylate energy charge levels under anaerobiosis. While NarG-dependent NO3(-) respiration directly enhanced growth, AniA-dependent NO2(-) reduction did not. NO2(-) and NO inhibited growth in culture, and their removal depended on denitrification and NO detoxification. Thus, NO3(-) acts as a TEA, but the resulting NO2(-) and NO likely do not. None of the mutants grew as well as the wild type in planta, and strains lacking AniA (NO2(-) reductase) or HmpX (NO detoxification) had reduced virulence on tomato. Thus, R. solanacearum exploits host NO3(-) to respire, grow, and cause disease. Degradation of NO2(-) and NO is also important for successful infection and depends on denitrification and NO detoxification systems. The plant-pathogenic bacterium Ralstonia solanacearum causes bacterial wilt, one of the world's most destructive crop diseases. This pathogen's explosive growth in plant vascular xylem is poorly understood. We used biochemical and genetic approaches to show
An improved method and data analysis for ultrasound acoustic emissions and xylem vulnerability in conifer wood.

PubMed

Wolkerstorfer, Silviya V; Rosner, Sabine; Hietz, Peter

2012-10-01

The vulnerability of the xylem to cavitation is an important trait in plant drought resistance and has been quantified by several methods. We present a modified method for the simultaneous measurement of cavitations, recorded as ultrasound acoustic emissions (UAEs), and the water potential, measured with a thermocouple psychrometer, in small samples of conifer wood. Analyzing the amplitude of the individual signals showed that a first phase, during which the mean amplitude increased, was followed by a second phase with distinctly lower signal amplitudes. We provide a method to separate the two groups of signals and show that for many samples plausible vulnerability curves require rejecting late low-energy UAEs. These very likely do not result from cavitations. This method was used to analyze the differences between juvenile wood, and early and late mature wood in Picea abies (L.) Karst. Juvenile earlywood was more resistant to cavitation than mature earlywood or latewood, which we relate to the tracheid anatomy of the samples. Copyright © Physiologia Plantarum 2012.
Measurement of imidacloprid in xylem fluid from eastern hemlock (Tsuga canadensis) by derivitization/GC/MS and ELISA

Treesearch

Anthony Lagalante; Peter Greenbacker; Jonathan Jones; Richard Turcotte; Bradley Onken

2007-01-01

Imidacloprid is a nonvolatile insecticide and its direct quantification is not possible by gas chromatography. In order to ascertain imidacloprid levels in soil and trunk injection treated trees, a sensitive and selective method has been developed using GC/MS to measure the imidacloprid levels in xylem fluid exudates. In May 2005, a stand of hemlock trees in West...
Post-fire Tree Mortality: Heating Increases Vulnerability to Cavitation in Longleaf Pine Branches

NASA Astrophysics Data System (ADS)

Lodge, A.; Kavanagh, K.; Dickinson, M. B.

2016-12-01

Tree mortality following wild and prescribed fires is of interest to both researchers and land managers. While some models exist that can predict mortality following fires, process-based models that incorporate physiological mechanisms of mortality are still being developed and improved. Delayed post-fire tree mortality has recently received increased attention, in part due to an increased use of prescribed fire as a restoration and management tool. One hypothesized mechanism of delayed mortality in trees is disruption of water transport in xylem due to exposure to the heat plume of a fire. This heat plume rapidly increases the vapor pressure deficit in the tree canopy, quickly increasing the tension on the water held in the xylem and leaves, potentially leading to cavitation. Cavitated xylem conduits can no longer transport water, eventually leading to tree death. We conducted a laboratory experiment examining whether heating stems increases their vulnerability to cavitation. We placed longleaf pine (Pinus palustris) branches in a water bath at sub-lethal temperatures (<60°C) and applied pressure in a cavitation chamber to simulate a range of xylem tension levels that may occur during fire. Percent loss of conductivity was measured following cavitation induced by various levels of applied pressure. When we compared the resulting vulnerability curves of heated branches to those of branches pressurized at room temperature, we observed increased vulnerability to cavitation in the heated samples especially at lower pressures. P50, or the pressure at which 50% of conductivity has been lost, decreased by 18% on branches heated to approximately 54°C. This suggests that stems heated during fires may be more vulnerable to cavitation, and provides some support for hydraulic disruption as a mechanism for post-fire tree mortality. Continued advancement in understanding of the mechanisms leading to delayed mortality will improve models predicting tree mortality.
Grapevine species from varied native habitats exhibit differences in embolism formation/repair associated with leaf gas exchange and root pressure.

PubMed

Knipfer, Thorsten; Eustis, Ashley; Brodersen, Craig; Walker, Andrew M; McElrone, Andrew J

2015-08-01

Drought induces xylem embolism formation, but grapevines can refill non-functional vessels to restore transport capacity. It is unknown whether vulnerability to embolism formation and ability to repair differ among grapevine species. We analysed in vivo embolism formation and repair using x-ray computed microtomography in three wild grapevine species from varied native habitats (Vitis riparia, V. arizonica, V. champinii) and related responses to measurements of leaf gas exchange and root pressure. Vulnerability to embolism formation was greatest in V. riparia, intermediate in V. arizonica and lowest in V. champinii. After re-watering, embolism repair was rapid and pronounced in V. riparia and V. arizonica, but limited or negligible in V. champinii even after numerous days. Similarly, root pressure measured after re-watering was positively correlated with drought stress severity for V. riparia and V. arizonica (species exhibiting embolism repair) but not for V. champinii. Drought-induced reductions in transpiration were greatest for V. riparia and least in V. champinii. Recovery of transpiration after re-watering was delayed for all species, but was greatest for V. champinii and most rapid in V. arizonica. These species exhibit varied responses to drought stress that involve maintenance/recovery of xylem transport capacity coordinated with root pressure and gas exchange responses. © 2014 John Wiley & Sons Ltd.
Sanio's laws revisited. Size-dependent changes in the xylem architecture of trees.

PubMed

Mencuccini, Maurizio; Hölttä, Teemu; Petit, Giai; Magnani, Federico

2007-11-01

Early observations led Sanio [Wissen. Bot., 8, (1872) 401] to state that xylem conduit diameters and lengths in a coniferous tree increase from the apex down to a height below which they begin to decrease towards the tree base. Sanio's law of vertical tapering has been repeatedly tested with contradictory results and the debate over the scaling of conduit diameters with distance from the apex has not been settled. The debate has recently acquired new vigour, as an accurate knowledge of the vertical changes in wood anatomy has been shown to be crucial to scaling metabolic properties to plant and ecosystem levels. Contrary to Sanio's hypothesis, a well known model (MST, metabolic scaling theory) assumes that xylem conduits monotonically increase in diameter with distance from the apex following a power law. This has been proposed to explain the three-fourth power scaling between size and metabolism seen across plants. Here, we (i) summarized available data on conduit tapering in trees and (ii) propose a new numerical model that could explain the observed patterns. Data from 101 datasets grouped into 48 independent profiles supported the notions that phylogenetic group (angiosperms versus gymnosperms) and tree size strongly affected the vertical tapering of conduit diameter. For both angiosperms and gymnosperms, within-tree tapering also varied with distance from the apex. The model (based on the concept that optimal conduit tapering occurs when the difference between photosynthetic gains and wall construction costs is maximal) successfully predicted all three major empirical patterns. Our results are consistent with Sanio's law only for large trees and reject the MST assumptions that vertical tapering in conduit diameter is universal and independent of rank number.
During measurements of root hydraulics with pressure probes, the contribution of unstirred layers is minimized in the pressure relaxation mode: comparison with pressure clamp and high-pressure flowmeter.

PubMed

Knipfer, Thorsten; Das, Debasish; Steudle, Ernst

2007-07-01

The effects of unstirred layers (USLs) at the endodermis of roots of young maize plants (Zea mays L.) were quantified, when measuring the water permeability of roots using a root pressure probe (RPP) in the pressure relaxation (PR) and pressure clamp (PC) modes. Different from PRs, PCs were performed by applying a constant pressure for certain periods of time. Experimental data were compared with results from simulations based on a convection versus diffusion (C/D) model, with the endodermis being the main barrier for solutes and water. Solute profiles in the stele were calculated as they occurred during rapid water flows across the root. The model quantitatively predicted the experimental finding of two distinct phases during PRs, in terms of a build-up of concentration profiles in the stele between endodermis and xylem vessels. It also predicted that, following a PC, half-times (T1/2) of PRs increased as the time used for clamping (and the build-up of USLs) increased. Following PCs of durations of 15, 30 and 60 s, T1/2 increased by factors of between 2.5 and 7.0, and water permeability of roots (root hydraulic conductivity, Lpr) was reduced by the same factors. When root pressure was immediately taken back to the original equilibrium root pressure following a PC, there was a transient uptake of water into the root stele (transient increase of root pressure), and the size of transients rose with time of clamping, as predicted by the model. The results indicated that the 'real' hydraulic conductivity of roots should be measured during initial water flows, such as during the rapid phase of PRs, when the effect of USLs was minimized. It was discussed that 'pressure-propagation effects' could not explain the finding of two phases during PRs. The results of USL effects threw some doubt on the use of PC and high-pressure flowmeter (HPFM) techniques with roots, where rigorous estimates of USLs were still missing despite the fact that large quantities of water were forced
A rhamnose-rich O-antigen mediates adhesion, virulence, and host colonization for the xylem-limited phytopathogen Xylella fastidiosa.

PubMed

Clifford, Jennifer C; Rapicavoli, Jeannette N; Roper, M Caroline

2013-06-01

Xylella fastidiosa is a gram-negative, xylem-limited bacterium that causes a lethal disease of grapevine called Pierce's disease. Lipopolysaccharide (LPS) composes approximately 75% of the outer membrane of gram-negative bacteria and, because it is largely displayed on the cell surface, it mediates interactions between the bacterial cell and its surrounding environment. LPS is composed of a conserved lipid A-core oligosaccharide component and a variable O-antigen portion. By targeting a key O-antigen biosynthetic gene, we demonstrate the contribution of the rhamnose-rich O-antigen to surface attachment, cell-cell aggregation, and biofilm maturation: critical steps for successful infection of the host xylem tissue. Moreover, we have demonstrated that a fully formed O-antigen moiety is an important virulence factor for Pierce's disease development in grape and that depletion of the O-antigen compromises its ability to colonize the host. It has long been speculated that cell-surface polysaccharides play a role in X. fastidiosa virulence and this study confirms that LPS is a major virulence factor for this important agricultural pathogen.
Fast-growing Acer rubrum differs from slow-growing Quercus alba in leaf, xylem and hydraulic trait coordination responses to simulated acid rain.

PubMed

Medeiros, Juliana S; Tomeo, Nicholas J; Hewins, Charlotte R; Rosenthal, David M

2016-08-01

We investigated the effects of historic soil chemistry changes associated with acid rain, i.e., reduced soil pH and a shift from nitrogen (N)- to phosphorus (P)-limitation, on the coordination of leaf water demand and xylem hydraulic supply traits in two co-occurring temperate tree species differing in growth rate. Using a full-factorial design (N × P × pH), we measured leaf nutrient content, water relations, leaf-level and canopy-level gas exchange, total biomass and allocation, as well as stem xylem anatomy and hydraulic function for greenhouse-grown saplings of fast-growing Acer rubrum (L.) and slow-growing Quercus alba (L.). We used principle component analysis to characterize trait coordination. We found that N-limitation, but not P-limitation, had a significant impact on plant water relations and hydraulic coordination of both species. Fast-growing A. rubrum made hydraulic adjustments in response to N-limitation, but trait coordination was variable within treatments and did not fully compensate for changing allocation across N-availability. For slow-growing Q. alba, N-limitation engendered more strict coordination of leaf and xylem traits, resulting in similar leaf water content and hydraulic function across all treatments. Finally, low pH reduced the propensity of both species to adjust leaf water relations and xylem anatomical traits in response to nutrient manipulations. Our data suggest that a shift from N- to P-limitation has had a negative impact on the water relations and hydraulic function of A. rubrum to a greater extent than for Q. alba We suggest that current expansion of A. rubrum populations could be tempered by acidic N-deposition, which may restrict it to more mesic microsites. The disruption of hydraulic acclimation and coordination at low pH is emphasized as an interesting area of future study. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits.

PubMed

Kröber, W; Heklau, H; Bruelheide, H

2015-03-01

We explored potential of morphological and anatomical leaf traits for predicting ecophysiological key functions in subtropical trees. We asked whether the ecophysiological parameters stomatal conductance and xylem cavitation vulnerability could be predicted from microscopy leaf traits. We investigated 21 deciduous and 19 evergreen subtropical tree species, using individuals of the same age and from the same environment in the Biodiversity-Ecosystem Functioning experiment at Jiangxi (BEF-China). Information-theoretic linear model selection was used to identify the best combination of morphological and anatomical predictors for ecophysiological functions. Leaf anatomy and morphology strongly depended on leaf habit. Evergreen species tended to have thicker leaves, thicker spongy and palisade mesophyll, more palisade mesophyll layers and a thicker subepidermis. Over 50% of all evergreen species had leaves with multi-layered palisade parenchyma, while only one deciduous species (Koelreuteria bipinnata) had this. Interactions with leaf habit were also included in best multi-predictor models for stomatal conductance (gs ) and xylem cavitation vulnerability. In addition, maximum gs was positively related to log ratio of palisade to spongy mesophyll thickness. Vapour pressure deficit (vpd) for maximum gs increased with the log ratio of palisade to spongy mesophyll thickness in species having leaves with papillae. In contrast, maximum specific hydraulic conductivity and xylem pressure at which 50% loss of maximum specific xylem hydraulic conductivity occurred (Ψ50 ) were best predicted by leaf habit and density of spongy parenchyma. Evergreen species had lower Ψ50 values and lower maximum xylem hydraulic conductivities. As hydraulic leaf and wood characteristics were reflected in structural leaf traits, there is high potential for identifying further linkages between morphological and anatomical leaf traits and ecophysiological responses. © 2014 German Botanical Society
Plant fluid proteomics: Delving into the xylem sap, phloem sap and apoplastic fluid proteomes.

PubMed

Rodríguez-Celma, Jorge; Ceballos-Laita, Laura; Grusak, Michael A; Abadía, Javier; López-Millán, Ana-Flor

2016-08-01

The phloem sap, xylem sap and apoplastic fluid play key roles in long and short distance transport of signals and nutrients, and act as a barrier against local and systemic pathogen infection. Among other components, these plant fluids contain proteins which are likely to be important players in their functionalities. However, detailed information about their proteomes is only starting to arise due to the difficulties inherent to the collection methods. This review compiles the proteomic information available to date in these three plant fluids, and compares the proteomes obtained in different plant species in order to shed light into conserved functions in each plant fluid. Inter-species comparisons indicate that all these fluids contain the protein machinery for self-maintenance and defense, including proteins related to cell wall metabolism, pathogen defense, proteolysis, and redox response. These analyses also revealed that proteins may play more relevant roles in signaling in the phloem sap and apoplastic fluid than in the xylem sap. A comparison of the proteomes of the three fluids indicates that although functional categories are somewhat similar, proteins involved are likely to be fluid-specific, except for a small group of proteins present in the three fluids, which may have a universal role, especially in cell wall maintenance and defense. This article is part of a Special Issue entitled: Plant Proteomics--a bridge between fundamental processes and crop production, edited by Dr. Hans-Peter Mock. Copyright © 2016 Elsevier B.V. All rights reserved.
Stomatal closure of Pelargonium × hortorum in response to soil water deficit is associated with decreased leaf water potential only under rapid soil drying.

PubMed

Boyle, Richard K A; McAinsh, Martin; Dodd, Ian C

2016-01-01

Soil water deficits applied at different rates and for different durations can decrease both stomatal conductance (gs ) and leaf water potential (Ψleaf ). Understanding the physiological mechanisms regulating these responses is important in sustainable irrigation scheduling. Glasshouse-grown, containerized Pelargonium × hortorum BullsEye plants were irrigated either daily at various fractions of plant evapotranspiration (100, 75 and 50% ET) for 20 days or irrigation was withheld for 4 days. Xylem sap was collected and gs and Ψleaf were measured on days 15 and 20, and on days 16-19 for the respective treatments. Xylem sap pH and NO3 (-) and Ca(2+) concentrations did not differ between irrigation treatments. Xylem abscisic acid (ABA) concentrations ([ABA]xyl ) increased within 24 h of irrigation being withheld whilst gs and Ψleaf decreased. Supplying irrigation at a fraction of daily ET produced a similar relationship between [ABA]xyl and gs , but did not change Ψleaf . Treatment differences occurred independently of whether Ψleaf was measured in whole leaves with a pressure chamber, or in the lamina with a thermocouple psychrometer. Plants that were irrigated daily showed lower [ABA]xyl than plants from which irrigation was withheld, even at comparable soil moisture content. This implies that regular re-watering attenuates ABA signaling due to maintenance of soil moisture in the upper soil levels. Crucially, detached leaves supplied with synthetic ABA showed a similar relationship between [ABA]xyl and gs as intact plants, suggesting that stomatal closure of P. hortorum in response to soil water deficit is primarily an ABA-induced response, independent of changes in Ψleaf . © 2015 Scandinavian Plant Physiology Society.
Quantifying the impact of daily and seasonal variation in sap pH on xylem dissolved inorganic carbon estimates in plum trees.

PubMed

Erda, F G; Bloemen, J; Steppe, K

2014-01-01

In studies on internal CO2 transport, average xylem sap pH (pH(x)) is one of the factors used for calculation of the concentration of dissolved inorganic carbon in the xylem sap ([CO2 *]). Lack of detailed pH(x) measurements at high temporal resolution could be a potential source of error when evaluating [CO2*] dynamics. In this experiment, we performed continuous measurements of CO2 concentration ([CO2]) and stem temperature (T(stem)), complemented with pH(x) measurements at 30-min intervals during the day at various stages of the growing season (Day of the Year (DOY): 86 (late winter), 128 (mid-spring) and 155 (early summer)) on a plum tree (Prunus domestica L. cv. Reine Claude d'Oullins). We used the recorded pH(x) to calculate [CO2*] based on T(stem) and the corresponding measured [CO2]. No statistically significant difference was found between mean [CO2*] calculated with instantaneous pH(x) and daily average pH(x). However, using an average pH(x) value from a different part of the growing season than the measurements of [CO2] and T(stem) to estimate [CO2*] led to a statistically significant error. The error varied between 3.25 ± 0.01% under-estimation and 3.97 ± 0.01% over-estimation, relative to the true [CO2*] data. Measured pH(x) did not show a significant daily variation, unlike [CO2], which increased during the day and declined at night. As the growing season progressed, daily average [CO2] (3.4%, 5.3%, 7.4%) increased and average pH(x) (5.43, 5.29, 5.20) decreased. Increase in [CO2] will increase its solubility in xylem sap according to Henry's law, and the dissociation of [CO2*] will negatively affect pH(x). Our results are the first quantifying the error in [CO2*] due to the interaction between [CO2] and pH(x) on a seasonal time scale. We found significant changes in pH(x) across the growing season, but overall the effect on the calculation of [CO2*] remained within an error range of 4%. However, it is possible that the error could be more
The Mechanism of Freezing Injury in Xylem of Winter Apple Twigs 1

PubMed Central

Quamme, H.; Weiser, C. J.; Stushnoff, C.

1973-01-01

In acclimated winter twigs of Haralson apple (Pyrus Malus L.), a lag in temperature during cooling at a constant rate was observed at about −41 C by differential thermal analysis. The temperature at which this low temperature exotherm occurred was essentially unaffected by the cooling rate. During thawing there was no lag in temperature (endotherm) near the temperature at which the low temperature exotherm occurred, but upon subsequent refreezing the exotherm reappeared at a somewhat higher temperature when twigs were rewarmed to at least −5 C before refreezing. These observations indicate that a small fraction of water may remain unfrozen to as low as −42 C after freezing of the bulk water in stems. The low temperature exotherm was not present in twigs freeze-dried to a water content below 8.5% (per unit fresh weight), but it reappeared when twigs were rehydrated to 20% water. When freeze-dried twigs were ground to a fine powder prior to rehydration, no exotherm was observed. Previous work has shown that the low temperature exotherm arises from xylem and pith tissues, and that injury to living cells in these tissues invariably occurs only when twigs are cooled below, but not above the temperature of the low temperature exotherm. This study revealed that the low temperature exotherm resulted from the freezing of a water fraction, that the freezing of this water was independent of the freezing of the bulk water, that the exotherm was associated with some gross structural feature but not the viability of the tissue, and that injury to living cells in the xylem and pith was closely and perhaps causally related to the initial freezing of this water. PMID:16658314

Down-regulation of SlIAA15 in tomato altered stem xylem development and production of volatile compounds in leaf exudates.

PubMed

Deng, Wei; Yan, Fang; Liu, Minchun; Wang, Xinyu; Li, Zhengguo

2012-08-01

The Aux/IAA family genes encode short-lived nuclear proteins that function as transcriptional regulators in auxin signal transduction. Aux/IAA genes have been reported to control many processes of plant development. Our recent study showed that down-regulation of SlIAA15 in tomato reduced apical dominance, altered pattern of axillary shoot development, increased lateral root formation and leaves thickness. The SlIAA15 suppressed lines display strong reduction of trichome density, suggesting that SlIAA15 is involved in trichome formation. Here, we reported that SlIAA15-suppressed transgenic lines display increased number of xylem cells compared to wild-type plants. Moreover, the monoterpene content in trichome exudates are significantly reduced in SlIAA15 down-regulated leaves. The results provide the roles of SlIAA15 in production of volatile compounds in leaf exudates and xylem development, clearly indicating that members of the Aux/IAA gene family can play distinct and specific functions.
An evaluation of potential decompression hazards in small pressurized aircraft.

DOT National Transportation Integrated Search

1967-06-01

Over 300 decompression tests were conducted to determine potential hazards of ejection or incapacitating or fatal head injuries in small volume pressurized aircraft in the event of sudden decompression following the loss of a window, emergency exit, ...
Comparison of water potentials measured by in situ psychrometry and pressure chamber in morphologically different species.

PubMed

Turner, N C; Spurway, R A; Schulze, E D

1984-02-01

Leaf water potentials measured by in situ psychrometry were compared with leaf water potentials measured by the pressure chamber technique at various values of water potential in Helianthus annuus, Helianthus nuttallii, Vigna unguiculata, Nerium oleander, Pistacia vera, and Corylus avellana. In V. unguiculata, the leaf water potentials measured by the in situ psychrometer oscillated at the same periodicity as, and proportional to, the leaf conductance. In all species, potentials measured by in situ psychrometers operating in the psychrometric mode were linearly correlated with potentials measured with the pressure chamber. However, the in situ psychrometers underestimated the leaf water potential in the two Helianthus species at low water potentials and overestimated the water potential in P. vera, N. oleander, and C. avellana. The underestimation in the two Helianthus species at low water potentials resulted from differences in water potential across the leaf. The overestimation in P. vera, N. oleander, and C. avellana was considered to arise from low epidermal conductances in these species even after abrasion of the cuticle. Pressure-volume studies with Lycopersicon esculentum showed that less water was expressed from distal than proximal leaflets when the whole leaf was slowly pressurized. The implication of this for water relations characteristics obtained by pressure-volume techniques is discussed. We conclude that in situ psychrometers are suitable for following dynamic changes in leaf water potential, but should be used with caution on leaves with low epidermal conductances.
Pattern of xylem phenology in conifers of cold ecosystems at the Northern Hemisphere.

PubMed

Rossi, Sergio; Anfodillo, Tommaso; Čufar, Katarina; Cuny, Henri E; Deslauriers, Annie; Fonti, Patrick; Frank, David; Gričar, Jožica; Gruber, Andreas; Huang, Jian-Guo; Jyske, Tuula; Kašpar, Jakub; King, Gregory; Krause, Cornelia; Liang, Eryuan; Mäkinen, Harri; Morin, Hubert; Nöjd, Pekka; Oberhuber, Walter; Prislan, Peter; Rathgeber, Cyrille B K; Saracino, Antonio; Swidrak, Irene; Treml, Václav

2016-11-01

The interaction between xylem phenology and climate assesses forest growth and productivity and carbon storage across biomes under changing environmental conditions. We tested the hypothesis that patterns of wood formation are maintained unaltered despite the temperature changes across cold ecosystems. Wood microcores were collected weekly or biweekly throughout the growing season for periods varying between 1 and 13 years during 1998-2014 and cut in transverse sections for assessing the onset and ending of the phases of xylem differentiation. The data set represented 1321 trees belonging to 10 conifer species from 39 sites in the Northern Hemisphere and covering an interval of mean annual temperature exceeding 14 K. The phenological events and mean annual temperature of the sites were related linearly, with spring and autumnal events being separated by constant intervals across the range of temperature analysed. At increasing temperature, first enlarging, wall-thickening and mature tracheids appeared earlier, and last enlarging and wall-thickening tracheids occurred later. Overall, the period of wood formation lengthened linearly with the mean annual temperature, from 83.7 days at -2 °C to 178.1 days at 12 °C, at a rate of 6.5 days °C -1 . April-May temperatures produced the best models predicting the dates of wood formation. Our findings demonstrated the uniformity of the process of wood formation and the importance of the environmental conditions occurring at the time of growth resumption. Under warming scenarios, the period of wood formation might lengthen synchronously in the cold biomes of the Northern Hemisphere. © 2016 John Wiley & Sons Ltd.
Pressure-strain energy redistribution in compressible turbulence: return-to-isotropy versus kinetic-potential energy equipartition

NASA Astrophysics Data System (ADS)

Lee, Kurnchul; Venugopal, Vishnu; Girimaji, Sharath S.

2016-08-01

Return-to-isotropy and kinetic-potential energy equipartition are two fundamental pressure-moderated energy redistributive processes in anisotropic compressible turbulence. Pressure-strain correlation tensor redistributes energy among various Reynolds stress components and pressure-dilatation is responsible for energy reallocation between dilatational kinetic and potential energies. The competition and interplay between these pressure-based processes are investigated in this study. Direct numerical simulations (DNS) of low turbulent Mach number dilatational turbulence are performed employing the hybrid thermal Lattice Boltzman method (HTLBM). It is found that a tendency towards equipartition precedes proclivity for isotropization. An evolution towards equipartition has a collateral but critical effect on return-to-isotropy. The preferential transfer of energy from strong (rather than weak) Reynolds stress components to potential energy accelerates the isotropization of dilatational fluctuations. Understanding of these pressure-based redistributive processes is critical for developing insight into the character of compressible turbulence.
Decoding intravesical pressure from local field potentials in rat lumbosacral spinal cord

NASA Astrophysics Data System (ADS)

Im, Changkyun; Park, Hae Yong; Koh, Chin Su; Ryu, Sang Baek; Seo, In Seok; Kim, Yong Jung; Kim, Kyung Hwan; Shin, Hyung-Cheul

2016-10-01

Chronic monitoring of intravesical pressure is required to detect the onset of intravesical hypertension and the progression of a more severe condition. Recent reports demonstrate the bladder state can be monitored from the spiking activity of the dorsal root ganglia or lumbosacral spinal cord. However, one of the most serious challenges for these methods is the difficulty of sustained spike signal acquisition due to the high-electrode-location-sensitivity of spikes or neuro-degeneration. Alternatively, it has been demonstrated that local field potential recordings are less affected by encapsulation reactions or electrode location changes. Here, we hypothesized that local field potential (LFP) from the lumbosacral dorsal horn may provide information concerning the intravesical pressure. LFP and spike activities were simultaneously recorded from the lumbosacral spinal cord of anesthetized rats during bladder filling. The results show that the LFP activities carry significant information about intravesical pressure along with spiking activities. Importantly, the intravesical pressure is decoded from the power in high-frequency bands (83.9-256 Hz) with a substantial performance similar to that of the spike train decoding. These findings demonstrate that high-frequency LFP activity can be an alternative intravesical pressure monitoring signal, which could lead to a proper closed loop system for urinary control.
Seasonal and diel variation in xylem CO2 concentration and sap pH in sub-Mediterranean oak stems.

PubMed

Salomón, Roberto; Valbuena-Carabaña, María; Teskey, Robert; McGuire, Mary Anne; Aubrey, Doug; González-Doncel, Inés; Gil, Luis; Rodríguez-Calcerrada, Jesús

2016-04-01

Since a substantial portion of respired CO2 remains within the stem, diel and seasonal trends in stem CO2 concentration ([CO2]) are of major interest in plant respiration and carbon budget research. However, continuous long-term stem [CO2] studies are scarce, and generally absent in Mediterranean climates. In this study, stem [CO2] was monitored every 15min together with stem and air temperature, sap flow, and soil water storage during a growing season in 16 stems of Quercus pyrenaica to elucidate the main drivers of stem [CO2] at different temporal scales. Fluctuations in sap pH were also assessed during two growing seasons to evaluate potential errors in estimates of the concentration of CO2 dissolved in xylem sap ([CO2*]) calculated using Henry's law. Stem temperature was the best predictor of stem [CO2] and explained more than 90% and 50% of the variability in stem [CO2] at diel and seasonal scales, respectively. Under dry conditions, soil water storage was the main driver of stem [CO2]. Likewise, the first rains after summer drought caused intense stem [CO2] pulses, suggesting enhanced stem and root respiration and increased resistance to radial CO2 diffusion. Sap flow played a secondary role in controlling stem [CO2] variations. We observed night-time sap pH acidification and progressive seasonal alkalinization. Thus, if the annual mean value of sap pH (measured at midday) was assumed to be constant, night-time sap [CO2*] was substantially overestimated (40%), and spring and autumn sap [CO2*] were misestimated by 25%. This work highlights that diel and seasonal variations in temperature, tree water availability, and sap pH substantially affect xylem [CO2] and sap [CO2*]. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.
Seasonal patterns of leaf photosynthetic and secondary xylem vascular traits in current-year stems of three Sorbus species with contrasting growth habits.

PubMed

Ďurkovič, J; Čaňová, I; Kardošová, M; Kurjak, D

2014-09-01

Seasonal effects of environmental variables on photosynthetic activity and secondary xylem formation provide data to demonstrate how environmental factors together with leaf ageing during the season control tree growth. In this study, we assessed physiological responses in photosynthetic behaviour to seasonal climate changes, and also identified seasonal differences in vascular traits within differentiating secondary xylem tissue from three diploid species of the taxonomically complex genus Sorbus. From sampling day 150, a clear physiological segregation of S. chamaemespilus from S. torminalis and S. aria was evident. The shrubby species S. chamaemespilus could be distinguished by a higher photosynthetic capacity between days 150 and 206. This was reflected in its associations with net CO2 assimilation rate (PN), maximum photochemical efficiency of PSII (F(v)/F(m)), variable-to-initial fluorescence ratio (F(v)/F(0)), potential electron acceptor capacity ('area') in multivariate space, and also its associations with log-transformed vessel area and log-transformed relative conductivity between days 239 and 268. The maximum segregation and differentiation among the examined Sorbus species was on sampling day 206. The largest differences between S. torminalis and S. aria were found on day 115, when the latter species clearly showed closer associations with high values of vessel density and transpiration (E). Sampling day clusters were arranged along an arch-like gradient that reflected the positioning of the entire growing season in multivariate space. This arch-like pattern was most apparent in the case of S. chamaemespilus, but was also observed in S. torminalis and S. aria. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.
Comparison of Water Potentials Measured by In Situ Psychrometry and Pressure Chamber in Morphologically Different Species 1

PubMed Central

Turner, Neil C.; Spurway, R. A.; Schulze, E.-D.

1984-01-01

Leaf water potentials measured by in situ psychrometry were compared with leaf water potentials measured by the pressure chamber technique at various values of water potential in Helianthus annuus, Helianthus nuttallii, Vigna unguiculata, Nerium oleander, Pistacia vera, and Corylus avellana. In V. unguiculata, the leaf water potentials measured by the in situ psychrometer oscillated at the same periodicity as, and proportional to, the leaf conductance. In all species, potentials measured by in situ psychrometers operating in the psychrometric mode were linearly correlated with potentials measured with the pressure chamber. However, the in situ psychrometers underestimated the leaf water potential in the two Helianthus species at low water potentials and overestimated the water potential in P. vera, N. oleander, and C. avellana. The underestimation in the two Helianthus species at low water potentials resulted from differences in water potential across the leaf. The overestimation in P. vera, N. oleander, and C. avellana was considered to arise from low epidermal conductances in these species even after abrasion of the cuticle. Pressure-volume studies with Lycopersicon esculentum showed that less water was expressed from distal than proximal leaflets when the whole leaf was slowly pressurized. The implication of this for water relations characteristics obtained by pressure-volume techniques is discussed. We conclude that in situ psychrometers are suitable for following dynamic changes in leaf water potential, but should be used with caution on leaves with low epidermal conductances. PMID:16663415
A global analysis of parenchyma tissue fractions in secondary xylem of seed plants.

PubMed

Morris, Hugh; Plavcová, Lenka; Cvecko, Patrick; Fichtler, Esther; Gillingham, Mark A F; Martínez-Cabrera, Hugo I; McGlinn, Daniel J; Wheeler, Elisabeth; Zheng, Jingming; Ziemińska, Kasia; Jansen, Steven

2016-03-01

Parenchyma is an important tissue in secondary xylem of seed plants, with functions ranging from storage to defence and with effects on the physical and mechanical properties of wood. Currently, we lack a large-scale quantitative analysis of ray parenchyma (RP) and axial parenchyma (AP) tissue fractions. Here, we use data from the literature on AP and RP fractions to investigate the potential relationships of climate and growth form with total ray and axial parenchyma fractions (RAP). We found a 29-fold variation in RAP fraction, which was more strongly related to temperature than with precipitation. Stem succulents had the highest RAP values (mean ± SD: 70.2 ± 22.0%), followed by lianas (50.1 ± 16.3%), angiosperm trees and shrubs (26.3 ± 12.4%), and conifers (7.6 ± 2.6%). Differences in RAP fraction between temperate and tropical angiosperm trees (21.1 ± 7.9% vs 36.2 ± 13.4%, respectively) are due to differences in the AP fraction, which is typically three times higher in tropical than in temperate trees, but not in RP fraction. Our results illustrate that both temperature and growth form are important drivers of RAP fractions. These findings should help pave the way to better understand the various functions of RAP in plants. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.
Photosynthesis, water relations, and growth of planted Pinus strobus L. on burned sites in the southern Appalachians

Treesearch

Katherine J. Elliott; James M. Vose

1994-01-01

We measured net photosynthesis,leaf conductance, xylem water potential, and growth of Pinus strbus L. seedlings two years after planting on two clear-cut and burned sites in the southern Appalachians. Multiple regression analysis was used to relate seedling net pholosynthesis to vapor pressure deficit, seedling crown temperature, photosynthetically active radiation (...
Riparian Plant Water Relations Along the North Fork Kings River, California

Treesearch

Janet L. Nachlinger; Stanley D. Smith; Roland J. Risser

1989-01-01

Plant water relations of five obligate riparian species were studied along California's North Fork Kings River. Diurnal stomatal conductance, transpiration, and xylem pressure potentials were measured throughout the 1986 growing season and in mid-season in 1987. Patterns were similar for all species although absolute values varied considerably. Maximum stomatal...
Stem girdling manipulates leaf sugar concentrations and anthocyanin expression in sugar maples trees during autumn

Treesearch

P.F. Murakami; P.G. Schaberg; J.B. Shane

2008-01-01

To better understand the effects of sugar accumulation on red color development of foliage during autumn, we compared carbohydrate concentration, anthocyanin expression and xylem pressure potential of foliage on girdled versus non-girdled (control) branches of 12 mature, open-grown sugar maple (Acer saccharum Marsh.) trees. Half of the study trees...
Effects of Fe and Mn deficiencies on the protein profiles of tomato (Solanum lycopersicum) xylem sap as revealed by shotgun analyses

USDA-ARS?s Scientific Manuscript database

The aim of this work was to study the effects of Fe and Mn deficiencies on the xylem sap proteome of tomato using a shotgun proteomic approach, with the final goal of elucidating plant response mechanisms to these stresses. This approach yielded 643 proteins reliably identified and quantified with 7...
Tyloses and phenolic deposits in xylem vessels impede water transport in low-lignin transgenic poplars: a study by cryo-fluorescence microscopy

Treesearch

Peter Kitin; Steven L. Voelker; Frederick C. Meinzer; Hans Beekman; Steven H. Strauss; Barbara Lachenbruch

2010-01-01

Of 14 transgenic poplar genotypes (Populus tremula x Populus alba) with antisense 4-coumarate:coenzynle A ligase that were grown in the field for 2 years, five that had substantial lignin reductions also had greatly reduced xylem-specific conductivity compared with that of control trees and those transgenic events with small...
Bordered pit structure and function determine spatial patterns of air-seeding thresholds in xylem of Douglas-fir (Pseudotsuga menziesii; Pinaceae) trees.

Treesearch

J.C. Domec; B. Lachenbruch; F.C. Meinzer

2006-01-01

The air-seeding hypothesis predicts that xylem embolism resistance is linked directly to bordered pit functioning. We tested this prediction in trunks, roots, and branches at different vertical and radial locations in young and old trees of Pseudotsuga menziesii. Dimensions of bordered pits were measured from light and scanning electron micrographs...
Crystal Thermoelasticity at Extreme Loading Rates and Pressures: Analysis of Higher-Order Energy Potentials

DTIC Science & Technology

2015-07-01

ARL-RP-0526 ● JULY 2015 US Army Research Laboratory Crystal Thermoelasticity at Extreme Loading Rates and Pressures : Analysis of...ARL-RP-0526 ● JULY 2015 US Army Research Laboratory Crystal Thermoelasticity at Extreme Loading Rates and Pressures : Analysis of...2015 4. TITLE AND SUBTITLE Crystal Thermoelasticity at Extreme Loading Rates and Pressures : Analysis of Higher-Order Energy Potentials 5a. CONTRACT
Specific Fluorescence in Situ Hybridization (FISH) Test to Highlight Colonization of Xylem Vessels by Xylella fastidiosa in Naturally Infected Olive Trees (Olea europaea L.)

PubMed Central

Cardinale, Massimiliano; Luvisi, Andrea; Meyer, Joana B.; Sabella, Erika; De Bellis, Luigi; Cruz, Albert C.; Ampatzidis, Yiannis; Cherubini, Paolo

2018-01-01

The colonization behavior of the Xylella fastidiosa strain CoDiRO, the causal agent of olive quick decline syndrome (OQDS), within the xylem of Olea europaea L. is still quite controversial. As previous literature suggests, even if xylem vessel occlusions in naturally infected olive plants were observed, cell aggregation in the formation of occlusions had a minimal role. This observation left some open questions about the whole behavior of the CoDiRO strain and its actual role in OQDS pathogenesis. In order to evaluate the extent of bacterial infection in olive trees and the role of bacterial aggregates in vessel occlusions, we tested a specific fluorescence in situ hybridization (FISH) probe (KO 210) for X. fastidiosa and quantified the level of infection and vessel occlusion in both petioles and branches of naturally infected and non-infected olive trees. All symptomatic petioles showed colonization by X. fastidiosa, especially in the larger innermost vessels. In several cases, the vessels appeared completely occluded by a biofilm containing bacterial cells and extracellular matrix and the frequent colonization of adjacent vessels suggested a horizontal movement of the bacteria. Infected symptomatic trees had 21.6 ± 10.7% of petiole vessels colonized by the pathogen, indicating an irregular distribution in olive tree xylem. Thus, our observations point out the primary role of the pathogen in olive vessel occlusions. Furthermore, our findings indicate that the KO 210 FISH probe is suitable for the specific detection of X. fastidiosa. PMID:29681910
Drought resistance in early and late secondary successional species from a tropical dry forest: the interplay between xylem resistance to embolism, sapwood water storage and leaf shedding.

PubMed

Pineda-García, Fernando; Paz, Horacio; Meinzer, Frederick C

2013-02-01

The mechanisms of drought resistance that allow plants to successfully establish at different stages of secondary succession in tropical dry forests are not well understood. We characterized mechanisms of drought resistance in early and late-successional species and tested whether risk of drought differs across sites at different successional stages, and whether early and late-successional species differ in resistance to experimentally imposed soil drought. The microenvironment in early successional sites was warmer and drier than in mature forest. Nevertheless, successional groups did not differ in resistance to soil drought. Late-successional species resisted drought through two independent mechanisms: high resistance of xylem to embolism, or reliance on high stem water storage capacity. High sapwood water reserves delayed the effects of soil drying by transiently decoupling plant and soil water status. Resistance to soil drought resulted from the interplay between variations in xylem vulnerability to embolism, reliance on sapwood water reserves and leaf area reduction, leading to a tradeoff of avoidance against tolerance of soil drought, along which successional groups were not differentiated. Overall, our data suggest that ranking species' performance under soil drought based solely on xylem resistance to embolism may be misleading, especially for species with high sapwood water storage capacity. © 2012 Blackwell Publishing Ltd.
Physiological changes in red spruce seedlings during a simulated winter thaw

Treesearch

P.G. Schaberg; J.B. Shane; G.J. Hawley; G.R. Strimbeck; D.H. DeHayes; P.F. Cali; J.R. Donnelly

1996-01-01

We evaluated net photosynthesis, respiration, leaf conductance, xylem pressure potential (XPP) and cold hardiness in red spruce (Picea rubens Sarg.) seedlings exposed to either a continuous thaw (CT) or a daytime thaw with freezing nights (FN) for 8 days during mid-winter. Physiological differences between CT and FN seedlings were evident for all...

Shoot dieback during prolonged drought in Ceanothus (Rhamnaceae) chaparral of California: a possible case of hydraulic failure.

PubMed

Davis, Stephen D; Ewers, Frank W; Sperry, John S; Portwood, Kimberly A; Crocker, Michelle C; Adams, Gerard C

2002-05-01

Progressive diebacks of outer canopy branchlets of Ceanothus crassifolius were repeatedly observed after rainless periods up to 9 mo in duration in the Santa Monica Mountains of southern California. Mean xylem pressures of branchlets near the end of drought were as low as -11.2 MPa (N = 22) with a mean of about 60 dead branchlets per shrub. Inoculation (N = 15) with three species of fungi previously isolated from the same population of C. crassifolius did not promote dieback, suggesting that the observed decline was not fungal induced, as had been proposed. Further, at least 50% of healthy-appearing twigs, without symptoms of dieback, contained isolatible endophytic fungi. We used a centrifugal force method to determine the range of xylem pressure causing cavitation (vulnerability curves) for branchlets (N = 12) and roots (N = 16). We combined vulnerability curves with soil texture data (N = 6) into a water transport model that estimated the critical values (P(Lcrit)) of leaf xylem pressure associated with the loss of water from soil to foliage. Maximum P(Lcrit) was between -10 and -11 MPa and within the range of minimum measured xylem pressures of branchlets during drought and dieback. Branchlet dieback correlated with seasonal declines in xylem pressure in concert with declining safety margins from hydraulic failure. Symptoms of dieback were duplicated in the field by partially severing stem xylem that normally supplied branchlets with water. Taken together, these results indicate that loss of hydraulic conductance to foliage was the probable cause of the observed dieback in C. crassifolius. Partial dieback of peripheral branchlets, and its attendant reduction in evaporative surface area, may be a last-resort mechanism for whole-plant water conservation and drought survival in this species.
Pressure induced structural phase transition in metal nitrides: An effective interionic potential calculations

NASA Astrophysics Data System (ADS)

Soni, Shubhangi; Choudhary, K. K.; Kaurav, Netram

2018-05-01

Structural and elastic properties of transition metal nitrides, XN (X = Co, Fe and Cu), are investigated through an effective inter-ionic potential method. The B3(ZnS) type ambient crystal structure of these compounds undergoes to B1(NaCl) type structure with pressure. Structural phase transition pressure in CoN, FeN and CuN was 35, 55 and 35 GPa, respectively, predicated by computing Gibbs' free energy (G) as a function of pressure and has good agreement with available theoretical results. The elastic properties were also estimated as a function of pressure. It is found that the elastic constants increased linearly with increasing pressure due to stronger hybridization, bonding and covalent properties of constituent elements of a compound.
Influence of xylem ray integrity and degree of polymerization on bending strength of beech wood decayed by Pleurotus ostreatus and Trametes versicolor

Treesearch

Ehsan Bari; Reza Oladi; Olaf Schmidt; Carol A. Clausen; Katie Ohno; Darrel D. Nicholas; Mehrdad Ghodskhah Daryaei; Maryam Karim

2015-01-01

The scope of this research was to evaluate the influence of xylem ray (XR) and degree of polymerization (DP) of holocellulose in Oriental beech wood (Fagus orientalis Lipsky.) on impact bending strength against two white-rot fungi. Beech wood specimens, exposed to Pleurotus ostreatus and Trametes versicolor, were evaluated for...
Studying global change through investigation of the plastic responses of xylem anatomy in tree rings.

PubMed

Fonti, Patrick; von Arx, Georg; García-González, Ignacio; Eilmann, Britta; Sass-Klaassen, Ute; Gärtner, Holger; Eckstein, Dieter

2010-01-01

Variability in xylem anatomy is of interest to plant scientists because of the role water transport plays in plant performance and survival. Insights into plant adjustments to changing environmental conditions have mainly been obtained through structural and functional comparative studies between taxa or within taxa on contrasting sites or along environmental gradients. Yet, a gap exists regarding the study of hydraulic adjustments in response to environmental changes over the lifetimes of plants. In trees, dated tree-ring series are often exploited to reconstruct dynamics in ecological conditions, and recent work in which wood-anatomical variables have been used in dendrochronology has produced promising results. Environmental signals identified in water-conducting cells carry novel information reflecting changes in regional conditions and are mostly related to short, sub-annual intervals. Although the idea of investigating environmental signals through wood anatomical time series goes back to the 1960s, it is only recently that low-cost computerized image-analysis systems have enabled increased scientific output in this field. We believe that the study of tree-ring anatomy is emerging as a promising approach in tree biology and climate change research, particularly if complemented by physiological and ecological studies. This contribution presents the rationale, the potential, and the methodological challenges of this innovative approach.
Effect of confining wall potential on charged collimated dust beam in low-pressure plasma

NASA Astrophysics Data System (ADS)

Kausik, S. S.; Kakati, B.; Saikia, B. K.

2013-05-01

The effect of confining wall potential on charged collimated dust beam in low-pressure plasma has been studied in a dusty plasma experimental setup by applying electrostatic field to each channel of a multicusp magnetic cage. Argon plasma is produced by hot cathode discharge method at a pressure of 5×10-4 millibars and is confined by a full line cusped magnetic field confinement system. Silver dust grains are produced by gas-evaporation technique and move upward in the form of a collimated dust beam due to differential pressure maintained between the dust and plasma chambers. The charged grains in the beam after coming out from the plasma column enter into the diagnostic chamber and are deflected by a dc field applied across a pair of deflector plates at different confining potentials. Both from the amount of deflection and the floating potential, the number of charges collected by the dust grains is calculated. Furthermore, the collimated dust beam strikes the Faraday cup, which is placed above the deflector plates, and the current (˜pA) so produced is measured by an electrometer at different confining potentials. The experimental results demonstrate the significant effect of confining wall potential on charging of dust grains.
Effect of vegetative competition on the moisture and nutrient status of loblolly pine

Treesearch

G.A. Carter; J.H. Miller; D.E. Davis; R.M. Patterson

1984-01-01

A field study examined the effects of competing vegetation on the moisture and nutrient status of 5-year-old loblolly pines (Pinus taeda L.). Similar experiments were conducted on a Piedmont site and a Coastal Plain site using individual pines as experimental units. Predawn measurements of xylem pressure potential were made using detached needle...
Testing the 'microbubble effect' using the Cavitron technique to measure xylem water extraction curves.

PubMed

Pivovaroff, Alexandria L; Burlett, Régis; Lavigne, Bruno; Cochard, Hervé; Santiago, Louis S; Delzon, Sylvain

2016-01-01

Plant resistance to xylem cavitation is a major drought adaptation trait and is essential to characterizing vulnerability to climate change. Cavitation resistance can be determined with vulnerability curves. In the past decade, new techniques have increased the ease and speed at which vulnerability curves are produced. However, these new techniques are also subject to new artefacts, especially as related to long-vesselled species. We tested the reliability of the 'flow rotor' centrifuge technique, the so-called Cavitron, and investigated one potential mechanism behind the open vessel artefact in centrifuge-based vulnerability curves: the microbubble effect. The microbubble effect hypothesizes that microbubbles introduced to open vessels, either through sample flushing or injection of solution, travel by buoyancy or mass flow towards the axis of rotation where they artefactually nucleate cavitation. To test the microbubble effect, we constructed vulnerability curves using three different rotor sizes for five species with varying maximum vessel length, as well as water extraction curves that are constructed without injection of solution into the rotor. We found that the Cavitron technique is robust to measure resistance to cavitation in tracheid-bearing and short-vesselled species, but not for long-vesselled ones. Moreover, our results support the microbubble effect hypothesis as the major cause for the open vessel artefact in long-vesselled species. Published by Oxford University Press on behalf of the Annals of Botany Company.
Coordination of xylem hydraulics and stomatal regulation in keeping the integrity of xylem water transport in shoots of two compound-leaved tree species.

PubMed

Liu, Yan-Yan; Song, Jia; Wang, Miao; Li, Na; Niu, Cun-Yang; Hao, Guang-You

2015-12-01

Hydraulic segmentation between proximal and distal organs has been hypothesized to be an important protective mechanism for plants to minimize the detrimental effects of drought-induced hydraulic failure. Uncertainties still exist regarding the degree of segmentation and the role of stomatal regulation in keeping hydraulic integrity of organs at different hierarchies. In the present study, we measured hydraulic conductivity and vulnerability in stems, compound leaf petioles and leaflet laminas of Fraxinus mandshurica Rupr. and Juglans mandshurica Maxim. growing in Changbai Mountain of Northeast China to identify the main locality where hydraulic segmentation occurs along the shoot water transport pathway. Stomatal conductance in response to leaf water potential change was also measured to investigate the role of stomatal regulation in avoiding extensive transpiration-induced embolism. No major contrasts were found between stems and compound leaf petioles in either hydraulic conductivity or vulnerability to drought-induced embolism, whereas a large difference in hydraulic vulnerability exists between compound leaf petioles and leaflet laminas. Furthermore, in contrast to the relatively large safety margins in stems (4.13 and 2.04 MPa) and compound leaf petioles (1.33 and 1.93 MPa), leaflet lamina hydraulic systems have substantially smaller or even negative safety margins (-0.17 and 0.47 MPa) in F. mandshurica and J. mandshurica. Under unstressed water conditions, gas exchange may be better optimized by allowing leaflet vascular system function with small safety margins. In the meantime, hydraulic safety of compound leaf petioles and stems are guaranteed by their large safety margins. In facing severe drought stress, larger safety margins in stems than in compound leaf petioles would allow plants to minimize the risk of catastrophic embolism in stems by sacrificing the whole compound leaves. A strong coordination between hydraulic and stomatal regulation
Pressure potential and stability analysis in an acoustical noncontact transportation

NASA Astrophysics Data System (ADS)

Li, J.; Liu, C. J.; Zhang, W. J.

2017-01-01

Near field acoustic traveling wave is one of the most popular principles in noncontact manipulations and transportations. The stability behavior is a key factor in the industrial applications of acoustical noncontact transportation. We present here an in-depth analysis of the transportation stability of a planar object levitated in near field acoustic traveling waves. To more accurately describe the pressure distributions on the radiation surface, a 3D nonlinear traveling wave model is presented. A closed form solution is derived based on the pressure potential to quantitatively calculate the restoring forces and moments under small disturbances. The physical explanations of the effects of fluid inertia and the effects of non-uniform pressure distributions are provided in detail. It is found that a vibration rail with tapered cross section provides more stable transportation than a rail with rectangular cross section. The present study sheds light on the issue of quantitative evaluation of stability in acoustic traveling waves and proposes three main factors that influence the stability: (a) vibration shape, (b) pressure distribution and (c) restoring force/moment. It helps to provide a better understanding of the physics behind the near field acoustic transportation and provide useful design and optimization tools for industrial applications.
How does climate influence xylem morphogenesis over the growing season? Insights from long-term intra-ring anatomy in Picea abies

PubMed Central

Fonti, Patrick; von Arx, Georg; Carrer, Marco

2017-01-01

Background and Aims During the growing season, the cambium of conifer trees produces successive rows of xylem cells, the tracheids, that sequentially pass through the phases of enlargement and secondary wall thickening before dying and becoming functional. Climate variability can strongly influence the kinetics of morphogenetic processes, eventually affecting tracheid shape and size. This study investigates xylem anatomical structure in the stem of Picea abies to retrospectively infer how, in the long term, climate affects the processes of cell enlargement and wall thickening. Methods Tracheid anatomical traits related to the phases of enlargement (diameter) and wall thickening (wall thickness) were innovatively inspected at the intra-ring level on 87-year-long tree-ring series in Picea abies trees along a 900 m elevation gradient in the Italian Alps. Anatomical traits in ten successive tree-ring sectors were related to daily temperature and precipitation data using running correlations. Key Results Close to the altitudinal tree limit, low early-summer temperature negatively affected cell enlargement. At lower elevation, water availability in early summer was positively related to cell diameter. The timing of these relationships shifted forward by about 20 (high elevation) to 40 (low elevation) d from the first to the last tracheids in the ring. Cell wall thickening was affected by climate in a different period in the season. In particular, wall thickness of late-formed tracheids was strongly positively related to August–September temperature at high elevation. Conclusions Morphogenesis of tracheids sequentially formed in the growing season is influenced by climate conditions in successive periods. The distinct climate impacts on cell enlargement and wall thickening indicate that different morphogenetic mechanisms are responsible for different tracheid traits. Our approach of long-term and high-resolution analysis of xylem anatomy can support and extend short
How does climate influence xylem morphogenesis over the growing season? Insights from long-term intra-ring anatomy in Picea abies.

PubMed

Castagneri, Daniele; Fonti, Patrick; von Arx, Georg; Carrer, Marco

2017-04-01

During the growing season, the cambium of conifer trees produces successive rows of xylem cells, the tracheids, that sequentially pass through the phases of enlargement and secondary wall thickening before dying and becoming functional. Climate variability can strongly influence the kinetics of morphogenetic processes, eventually affecting tracheid shape and size. This study investigates xylem anatomical structure in the stem of Picea abies to retrospectively infer how, in the long term, climate affects the processes of cell enlargement and wall thickening. Tracheid anatomical traits related to the phases of enlargement (diameter) and wall thickening (wall thickness) were innovatively inspected at the intra-ring level on 87-year-long tree-ring series in Picea abies trees along a 900 m elevation gradient in the Italian Alps. Anatomical traits in ten successive tree-ring sectors were related to daily temperature and precipitation data using running correlations. Close to the altitudinal tree limit, low early-summer temperature negatively affected cell enlargement. At lower elevation, water availability in early summer was positively related to cell diameter. The timing of these relationships shifted forward by about 20 (high elevation) to 40 (low elevation) d from the first to the last tracheids in the ring. Cell wall thickening was affected by climate in a different period in the season. In particular, wall thickness of late-formed tracheids was strongly positively related to August-September temperature at high elevation. Morphogenesis of tracheids sequentially formed in the growing season is influenced by climate conditions in successive periods. The distinct climate impacts on cell enlargement and wall thickening indicate that different morphogenetic mechanisms are responsible for different tracheid traits. Our approach of long-term and high-resolution analysis of xylem anatomy can support and extend short-term xylogenesis observations, and increase our
The potential for health risks from intrusion of contaminants into the distribution system from pressure transients.

PubMed

LeChevallier, Mark W; Gullick, Richard W; Karim, Mohammad R; Friedman, Melinda; Funk, James E

2003-03-01

The potential for public health risks associated with intrusion of contaminants into water supply distribution systems resulting from transient low or negative pressures is assessed. It is shown that transient pressure events occur in distribution systems; that during these negative pressure events pipeline leaks provide a potential portal for entry of groundwater into treated drinking water; and that faecal indicators and culturable human viruses are present in the soil and water exterior to the distribution system. To date, all observed negative pressure events have been related to power outages or other pump shutdowns. Although there are insufficient data to indicate whether pressure transients are a substantial source of risk to water quality in the distribution system, mitigation techniques can be implemented, principally the maintenance of an effective disinfectant residual throughout the distribution system, leak control, redesign of air relief venting, and more rigorous application of existing engineering standards. Use of high-speed pressure data loggers and surge modelling may have some merit, but more research is needed.
Generation and analysis of expressed sequence tags from six developing xylem libraries in Pinus radiata D. Don

PubMed Central

Li, Xinguo; Wu, Harry X; Dillon, Shannon K; Southerton, Simon G

2009-01-01

Background Wood is a major renewable natural resource for the timber, fibre and bioenergy industry. Pinus radiata D. Don is the most important commercial plantation tree species in Australia and several other countries; however, genomic resources for this species are very limited in public databases. Our primary objective was to sequence a large number of expressed sequence tags (ESTs) from genes involved in wood formation in radiata pine. Results Six developing xylem cDNA libraries were constructed from earlywood and latewood tissues sampled at juvenile (7 yrs), transition (11 yrs) and mature (30 yrs) ages, respectively. These xylem tissues represent six typical development stages in a rotation period of radiata pine. A total of 6,389 high quality ESTs were collected from 5,952 cDNA clones. Assembly of 5,952 ESTs from 5' end sequences generated 3,304 unigenes including 952 contigs and 2,352 singletons. About 97.0% of the 5,952 ESTs and 96.1% of the unigenes have matches in the UniProt and TIGR databases. Of the 3,174 unigenes with matches, 42.9% were not assigned GO (Gene Ontology) terms and their functions are unknown or unclassified. More than half (52.1%) of the 5,952 ESTs have matches in the Pfam database and represent 772 known protein families. About 18.0% of the 5,952 ESTs matched cell wall related genes in the MAIZEWALL database, representing all 18 categories, 91 of all 174 families and possibly 557 genes. Fifteen cell wall-related genes are ranked in the 30 most abundant genes, including CesA, tubulin, AGP, SAMS, actin, laccase, CCoAMT, MetE, phytocyanin, pectate lyase, cellulase, SuSy, expansin, chitinase and UDP-glucose dehydrogenase. Based on the PlantTFDB database 41 of the 64 transcription factor families in the poplar genome were identified as being involved in radiata pine wood formation. Comparative analysis of GO term abundance revealed a distinct transcriptome in juvenile earlywood formation compared to other stages of wood development
Presence of supercooling-facilitating (anti-ice nucleation) hydrolyzable tannins in deep supercooling xylem parenchyma cells in Cercidiphyllum japonicum.

PubMed

Wang, Donghui; Kasuga, Jun; Kuwabara, Chikako; Endoh, Keita; Fukushi, Yukiharu; Fujikawa, Seizo; Arakawa, Keita

2012-04-01

Xylem parenchyma cells (XPCs) in trees adapt to subzero temperatures by deep supercooling. Our previous study indicated the possibility of the presence of diverse kinds of supercooling-facilitating (SCF; anti-ice nucleation) substances in XPCs of katsura tree (Cercidiphyllum japonicum), all of which might have an important role in deep supercooling of XPCs. In the previous study, a few kinds of SCF flavonol glycosides were identified. Thus, in the present study, we tried to identify other kinds of SCF substances in XPCs of katsura tree. SCF substances were purified from xylem extracts by silica gel column chromatography and Sephadex LH-20 column chromatography. Then, four SCF substances isolated were identified by UV, mass and nuclear magnetic resonance analyses. The results showed that the four kinds of hydrolyzable gallotannins, 2,2',5-tri-O-galloyl-α,β-D-hamamelose (trigalloyl Ham or kurigalin), 1,2,6-tri-O-galloyl-β-D-glucopyranoside (trigalloyl Glc), 1,2,3,6-tetra-O-galloyl-β-D-glucopyranoside (tetragalloyl Glc) and 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranoside (pentagalloyl Glc), in XPCs exhibited supercooling capabilities in the range of 1.5-4.5°C, at a concentration of 1 mg mL⁻¹. These SCF substances, including flavonol glycosides and hydrolyzable gallotannins, may contribute to the supercooling in XPCs of katsura tree.
Infrared nanospectroscopy reveals the chemical nature of pit membranes in water-conducting cells of the plant xylem.

PubMed

Pereira, Luciano; Flores-Borges, Denisele; Bittencourt, Paulo; Mayer, Juliana; Kiyota, Eduardo; Araújo, Pedro; Jansen, Steven; Freitas, Raul; Oliveira, Rafael; Mazzafera, Paulo

2018-06-05

In the xylem of angiosperm plants, microscopic pits through the secondary cell walls connect the water-conducting vessels. Cellulosic meshes originated from primary walls and middle lamella between adjacent vessels, called pit membrane, separates one conduit from another. The intricate structure of the nano-sized pores in pit membranes enables the passage of water under negative pressure without hydraulic failure due to obstruction by gas bubbles (i.e., embolism) under normal conditions or mild drought stress. Since the chemical composition of pit membranes affects embolism formation and bubble behavior, we directly measured pit membrane composition in Populus nigra wood. Here, we characterized the chemical composition of cell wall structures by synchrotron infrared nanospectroscopy and atomic force microscopy-infrared nanospectroscopy with high spatial resolution. Characteristic peaks of cellulose, phenolic compounds, and proteins were found in the intervessel pit membrane of P. nigra wood. In addition, vessel to parenchyma pit membranes and developing cell walls of the vascular cambium showed clear signals of cellulose, proteins, and pectin. We did not find a distinct peak of lignin and other compounds in these structures. Our investigation of the complex chemical composition of intervessel pit membranes furthers our understanding of the flow of water and bubbles between neighboring conduits. The advances presented here pave the way for further label-free studies related to the nano-chemistry of plant cell components. {copyright, serif} 2018 American Society of Plant Biologists. All rights reserved.
Winter drought impairs xylem phenology, anatomy and growth in Mediterranean Scots pine forests.

PubMed

Camarero, J J; Guada, G; Sánchez-Salguero, R; Cervantes, E

2016-12-01

Continental Mediterranean forests face drought but also cold spells and both climate extremes can impair the resilience capacity of these forests. Climate warming could amplify the negative effects of cold spells by inducing premature dehardening. Here we capitalize on a winter drought-induced dieback triggered by a cold spell which occurred in December 2001 affecting Scots pine forests in eastern Spain. We assessed post-dieback recovery by quantifying and comparing radial growth and xylem anatomy of non-declining (ND, crown cover >50%) and declining (D, crown cover ≤50%) trees in two sites (VP, Villarroya de los Pinares; TO, Torrijas). We also characterized xylogenesis in both sites and aboveground productivity in site VP. Dieback caused legacy effects since needle loss, a 60% reduction in litter fall and radial-growth decline characterized D-trees 3 years after dieback symptoms started appearing in spring 2002. D-trees formed collapsed tracheids in the 2002-ring, particularly in the most affected VP site where xylogenesis differences between ND and D trees were most noticeable. The lower growth rates of D-trees were caused by a shorter duration of their major xylogenesis phases. In site VP the radial-enlargement and wall-thickening of tracheids were significantly reduced in D-trees as compared to ND-trees because these xylogenesis phases tended to start earlier and end later in ND-trees. Gompertz models fitted to tracheid production predicted that maximum growth rates occurred 11-12 days earlier in ND than in D-trees. The formation of radially-enlarging tracheids was enhanced by longer days in both study sites and also by wetter conditions in the driest TO site, but xylogenesis sensitivity to climate was reduced in D-trees. Winter-drought dieback impairs xylem anatomy and phenology, aboveground productivity, xylogenesis and growth in Mediterranean Scots pine populations. Affected stands show a costly post-dieback recovery challenging their resilience ability
New perspectives on potential hydrogen storage materials using high pressure.

PubMed

Song, Yang

2013-09-21

In addressing the global demand for clean and renewable energy, hydrogen stands out as the most suitable candidate for many fuel applications that require practical and efficient storage of hydrogen. Supplementary to the traditional hydrogen storage methods and materials, the high-pressure technique has emerged as a novel and unique approach to developing new potential hydrogen storage materials. Static compression of materials may result in significant changes in the structures, properties and performance that are important for hydrogen storage applications, and often lead to the formation of unprecedented phases or complexes that have profound implications for hydrogen storage. In this perspective article, 22 types of representative potential hydrogen storage materials that belong to four major classes--simple hydride, complex hydride, chemical hydride and hydrogen containing materials--were reviewed. In particular, their structures, stabilities, and pressure-induced transformations, which were reported in recent experimental works together with supporting theoretical studies, were provided. The important contextual aspects pertinent to hydrogen storage associated with novel structures and transitions were discussed. Finally, the summary of the recent advances reviewed and the insight into the future research in this direction were given.
Distribution of pines in the Iberian Peninsula agrees with species differences in foliage frost tolerance, not with vulnerability to freezing-induced xylem embolism.

PubMed

Fernández-Pérez, Laura; Villar-Salvador, Pedro; Martínez-Vilalta, Jordi; Toca, Andrei; Zavala, Miguel A

2018-04-01

Drought and frosts are major determinants of plant functioning and distribution. Both stresses can cause xylem embolism and foliage damage. The objective of this study was to analyse if the distribution of six common pine species along latitudinal and altitudinal gradients in Europe is related to their interspecific differences in frost tolerance and to the physiological mechanisms underlying species-specific frost tolerance. We also evaluate if frost tolerance depends on plant water status. We studied survival to a range of freezing temperatures in 2-year-old plants and assessed the percentage loss of hydraulic conductivity (PLC) due xylem embolism formation and foliage damage determined by needle electrolyte leakage (EL) after a single frost cycle to -15 °C and over a range of predawn water potential (ψpd) values. Species experiencing cold winters in their range (Pinus nigra J.F. Arnold, Pinus sylvestris L. and Pinus uncinata Raymond ex A. DC.) had the highest frost survival rates and lowest needle EL and soluble sugar (SS) concentration. In contrast, the pines inhabiting mild or cool winter locations (especially Pinus halepensis Mill. and Pinus pinea L. and, to a lesser extent, Pinus pinaster Ait.) had the lowest frost survival and highest needle EL and SS values. Freezing-induced PLC was very low and differences among species were not related to frost damage. Reduction in ψpd decreased leaf frost damage in P. pinea and P. sylvestris, increased it in P. uncinata and had a neutral effect on the rest of the species. This study demonstrates that freezing temperatures are a major environmental driver for pine distribution and suggests that interspecific differences in leaf frost sensitivity rather than vulnerability to freezing-induced embolism or SS explain pine juvenile frost survival.
Application of total-reflection X-ray fluorescence spectrometry and high-performance liquid chromatography for the chemical characterization of xylem saps of nickel contaminated cucumber plants

NASA Astrophysics Data System (ADS)

Mihucz, Victor G.; Tatár, Eniko; Varga, Anita; Záray, Gyula; Cseh, Edit

2001-11-01

Total-reflection X-ray fluorescence (TXRF) spectrometry, reversed-phase (RP) and size-exclusion (SE) high-performance liquid chromatography (HPLC) methods were applied for the characterization of low-volume xylem sap of control and nickel contaminated cucumber plants growing in hydroponics containing urea as the sole nitrogen source. In these saps collected for 1 h, Ca, K, Fe, Mn, Ni, Zn, as well as malic, citric and fumaric acids were determined. The SEC measurements showed that macromolecules were not detectable in the samples. Nickel contamination had minimum impact on the organic acid transport, however, the transport of Zn, K and Fe was reduced by 50, 22 and 11%, respectively. This observation supports the results of our earlier experiments when nitrate ions were used as the sole nitrogen form. At the same time, the fresh root weight and the volume of the collected xylem sap increased by 36 and 85%, respectively. Therefore, nickel addition seemed to decrease the urea toxicity of the plants. By pooling the eluting fractions of the SEC column, which were 10-fold concentrated by freeze-drying, the series of the resulted samples were analyzed by the TXRF spectrometry and RP-HPLC. The three organic acids could be identified in only one of the fractions, which contained Fe and, in the case of the contaminated plants, Ni in detectable concentration. However, considerable parts of these two elements and Mn, as well as practically the total amounts of Cu may be transported by unidentified organic compounds in the xylem.
First insights into the functional role of vasicentric tracheids and parenchyma in eucalyptus species with solitary vessels: do they contribute to xylem efficiency or safety?

PubMed

Barotto, Antonio José; Fernandez, María Elena; Gyenge, Javier; Meyra, Ariel; Martinez-Meier, Alejandro; Monteoliva, Silvia

2016-12-01

The relationship between hydraulic specific conductivity (k s ) and vulnerability to cavitation (VC) with size and number of vessels has been studied in many angiosperms. However, few of the studies link other cell types (vasicentric tracheids (VT), fibre-tracheids, parenchyma) with these hydraulic functions. Eucalyptus is one of the most important genera in forestry worldwide. It exhibits a complex wood anatomy, with solitary vessels surrounded by VT and parenchyma, which could serve as a good model to investigate the functional role of the different cell types in xylem functioning. Wood anatomy (several traits of vessels, VT, fibres and parenchyma) in conjunction with maximum k s and VC was studied in adult trees of commercial species with medium-to-high wood density (Eucalyptus globulus Labill., Eucalyptus viminalis Labill. and Eucalyptus camaldulensis Dehnh.). Traits of cells accompanying vessels presented correlations with functional variables suggesting that they contribute to both increasing connectivity between adjacent vessels-and, therefore, to xylem conduction efficiency-and decreasing the probability of embolism propagation into the tissue, i.e., xylem safety. All three species presented moderate-to-high resistance to cavitation (mean P 50 values = -2.4 to -4.2 MPa) with no general trade-off between efficiency and safety at the interspecific level. The results in these species do not support some well-established hypotheses of the functional meaning of wood anatomy. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Pressure mapping to assess seated pressure distributions and the potential risk for skin ulceration in a population of sledge hockey players and control subjects.

PubMed

Berthold, Justin; Dicianno, Brad E; Cooper, Rory A

2013-09-01

Ice sledge (or sled) hockey is a fast-paced sport that enables individuals with physical disabilities to play ice hockey. As the attraction to the sport continues to rise, the need for developing better equipment and installing preventative measures for injury will become increasingly important. One such injury includes skin pressure ulceration. A total of 26 subjects including active controls and those with spinal cord injury, multiple sclerosis, limb amputation and traumatic brain injury were studied using a pressure mapping device at the 2012 National Disabled Veterans Winter Sports Clinic to determine the risk for skin pressure ulceration and the impact of cushioning and knee angle positioning on seated pressure distributions. Sledge hockey athletes may be at increased risk for skin pressure ulceration based on seated pressure distribution data. This experiment failed to demonstrate a benefit for specialty cushioning in either group. Interestingly, knee angle positioning, particularly, knee extension significantly lowered the average seated pressures. When considering the risk for skin pressure ulceration, knee angle positioning is of particular clinical importance. More research is warranted, specifically targeting novel cushion and sledge designs and larger groups of individuals with sensory loss and severe spinal deformities. Implications for Rehabilitation Ice sledge (or sled) hockey is a fast-paced and growing adaptive sport played at the Paralympic level. Rehabilitation professionals should consider the potential for skin ulceration in this population of athletes. The effects of cushioning used in the sledge design warrants further investigation. Knee angle positioning; particularly, knee extension significantly lowers seated pressures and may reduce the potential for skin ulceration.
Toward a better δDalkanes paleoclimate proxy; Partitioning of seasonal water sources and xylem-leaf deuterium enrichment according to plant growth form and phenology

NASA Astrophysics Data System (ADS)

Wispelaere, Lien; Bodé, Samuel; Herve-Fernández, Pedro; Hemp, Andreas; Verschuren, Dirk; Boeckx, Pascal

2016-04-01

The DeepCHALLA consortium is preparing an ICDP (International Continental Drilling Program) deep-drilling project on Lake Challa, a crater lake near Mt. Kilimanjaro in equatorial East Africa, where the climate is tropical semi-arid climate and characterized by two distinct rainy seasons. The main objective of this project is to acquire high-resolution and accurately dated proxy data of continental climate and ecosystem change near the Equator over 250,000 years. One of the paleoclimate proxies to be used is the hydrogen-isotopic composition of sedimentary n-alkanes (δDalkanes) derived from fossil plant leaf wax. However, this requires a better understanding of seasonal variability in the isotopic composition of precipitation, and of the fractionation of its hydrogen during incorporation in the plant waxes. In addition, recent studies have described the existence of "two water worlds", resulting in an additional deviation of the isotopic composition of the water taken up by plants. In this study, we measured the δD and δ18O of local precipitation, lake water, and xylem and leaf water from different plant species, seasons and sites with varying distances to Lake Challa. We use these data to set up a local meteoric water line (LMWL), and to assess spatial and temporal patterns of water utilization by local plants. Our data show a seasonal change in water-isotope partitioning with plants tapping water from isotopically lighter water sources during the dry seasons, as indicated by more negative xylem δD values and higher offsets from precipitation (i.e. greater distances from the LMWL), therefore supporting the "two water worlds" hypothesis. Surprisingly, trees appear to preferentially exploit isotopically more enriched sources of soil water, suggesting shallower water sources, than shrubs. Plants located at the lake shore use a mixture of precipitation and lake water, reflected in enriched xylem δD values and in the intersection of 2H and 18O with the LMWL. Leaf
Lignin composition is related to xylem embolism resistance and leaf life span in trees in a tropical semiarid climate.

PubMed

Lima, Taysla R A; Carvalho, Ellen C D; Martins, Fernando R; Oliveira, Rafael S; Miranda, Rafael S; Müller, Caroline S; Pereira, Luciano; Bittencourt, Paulo R L; Sobczak, Jullyana C M S M; Gomes-Filho, Enéas; Costa, Rafael C; Araújo, Francisca S

2018-05-16

Wood properties influence the leaf life span (LL) of tree crowns. As lignin is an important component of wood and the water transport system, we investigated its relationship with embolism resistance and the LL of several tree species in a seasonally dry tropical ecosystem. We determined total lignin and the monomer contents of guaiacyl (G) and syringyl (S) and related them to wood traits and xylem vulnerability to embolism (Ψ 50 ) for the most common species of the Brazilian semiarid, locally known as Caatinga. Leaf life span was negatively related to Ψ 50 and positively related to S : G, which was negatively related to Ψ 50 . This means that greater S : G increases LL by reducing Ψ 50 . Lignin content was not correlated with any variable. We found two apparently unrelated axes of drought resistance. One axis, associated with lignin monomeric composition, increases LL in the dry season as a result of lower xylem embolism vulnerability. The other, associated with wood density and stem water content, helps leafless trees to withstand drought and allows them to resprout at the end of the dry season. The monomeric composition of lignin (S : G) is therefore an important functional wood attribute affecting several key functional aspects of tropical tree species in a semiarid climate. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.
Proton-Dependent Coniferin Transport, a Common Major Transport Event in Differentiating Xylem Tissue of Woody Plants1[W

PubMed Central

Tsuyama, Taku; Kawai, Ryo; Shitan, Nobukazu; Matoh, Toru; Sugiyama, Junji; Yoshinaga, Arata; Takabe, Keiji; Fujita, Minoru; Yazaki, Kazufumi

2013-01-01

Lignin biosynthesis is an essential physiological activity of vascular plants if they are to survive under various environmental stresses on land. The biosynthesis of lignin proceeds in the cell wall by polymerization of precursors; the initial step of lignin polymerization is the transportation of lignin monomers from the cytosol to the cell wall, which is critical for lignin formation. There has been much debate on the transported form of the lignin precursor, either as free monolignols or their glucosides. In this study, we performed biochemical analyses to characterize the membrane transport mechanism of lignin precursors using angiosperms, hybrid poplar (Populus sieboldii × Populus grandidentata) and poplar (Populus sieboldii), as well gymnosperms, Japanese cypress (Chamaecyparis obtusa) and pine (Pinus densiflora). Membrane vesicles prepared from differentiating xylem tissues showed clear ATP-dependent transport activity of coniferin, whereas less than 4% of the coniferin transport activity was seen for coniferyl alcohol. Bafilomycin A1 and proton gradient erasers markedly inhibited coniferin transport in hybrid poplar membrane vesicles; in contrast, vanadate had no effect. Cis-inhibition experiments suggested that this transport activity was specific for coniferin. Membrane fractionation of hybrid poplar microsomes demonstrated that transport activity was localized to the tonoplast- and endomembrane-rich fraction. Differentiating xylem of Japanese cypress exhibited almost identical transport properties, suggesting the involvement of a common endomembrane-associated proton/coniferin antiport mechanism in the lignifying tissues of woody plants, both angiosperms and gymnosperms. PMID:23585651
Successive measurements of streaming potential and electroosmotic pressure with the same core-holder

NASA Astrophysics Data System (ADS)

Yin, Chenggang; Hu, Hengshan; Yu, Chunhao; Wang, Jun

2018-05-01

Successive measurements of the streaming potential and electroosmotic pressure of each core sample are important for understanding the mechanisms of electrokinetic effects. In previous studies, one plug of the core-holder needs to be replaced in these two experiments, which causes the change of the fluid parameters and the boundary conditions in the core. We design a new core-holder to permit successive experiments without plug replacement, which ensures the consistency of the measurement environment. A two-direction harmonic pressure-driving source is accordingly designed. Using this new equipment, electrokinetic experiments conducted ten core samples at 0.4 mol/L NaCl solution. The results show good agreement between the electrokinetically deduced permeability and premeasured gas permeability. For high salinity saturated samples, the permeability can be inverted from electroosmotic effect instead of the streaming potential.
Xylem specific activation of 5' upstream regulatory region of two NAC transcription factors (MusaVND6 and MusaVND7) in banana is regulated by SNBE-like sites.

PubMed

Negi, Sanjana; Tak, Himanshu; Ganapathi, T R

2018-01-01

Deposition of secondary cell wall in the xylem elements is controlled by a subgroup of NAC (NAM, ATAF, CUC) family, known as vascular-related NAC transcription factors (VNDs). In the present study, we analyzed the 5' upstream regulatory region of two banana NAC transcription factors (MusaVND6 and MusaVND7) for tissue specific expression and presence of 19-bp secondary-wall NAC binding element (SNBE)-like motifs. Transgenic banana plants of Musa cultivar Rasthali harboring either PMusaVND7::GUS or PMusaVND6::GUS showed specific GUS (β-D-Glucuronidase) activity in cells of the xylem tissue. Approximately 1.2kb promoter region of either MusaVND6 or MusaVND7 showed presence of at least two SNBE-like motifs. This 1.2kb promoter region was retarded in a gel shift assay by three banana VND protein (VND1,VND2 and VND3). The banana VND1-VND3 could also retard the mobility of isolated SNBE-like motifs of MusaVND6 or MusaVND7 in a gel shift assay. Transcript levels of MusaVND6 and MusaVND7 were elevated in transgenic banana overexpressing either banana VND1, VND2 or VND3. Present study suggested a probable regulation of banana VND6 and VND7 expression through direct interaction of banana VND1- VND3 with SNBE-like motifs. Our study also indicated two promoter elements for possible utilization in cell wall modifications in plants especially banana, which is being recently considered as a potential biofuel crop.
End-boundary sheath potential, electron and ion energy distribution in the low-pressure non-ambipolar electron plasma

NASA Astrophysics Data System (ADS)

Chen, Lee; Chen, Zhiying; Funk, Merritt

2013-12-01

The end-boundary floating-surface sheath potential, electron and ion energy distribution functions (EEDf, IEDf) in the low-pressure non-ambipolar electron plasma (NEP) are investigated. The NEP is heated by an electron beam extracted from an inductively coupled electron-source plasma (ICP) through a dielectric injector by an accelerator located inside the NEP. This plasma's EEDf has a Maxwellian bulk followed by a broad energy continuum connecting to the most energetic group with energies around the beam energy. The NEP pressure is 1-3 mTorr of N2 and the ICP pressure is 5-15 mTorr of Ar. The accelerator is biased positively from 80 to 600 V and the ICP power range is 200-300 W. The NEP EEDf and IEDf are determined using a retarding field energy analyser. The EEDf and IEDf are measured at various NEP pressures, ICP pressures and powers as a function of accelerator voltage. The accelerator current and sheath potential are also measured. The IEDf reveals mono-energetic ions with adjustable energy and it is proportionally controlled by the sheath potential. The NEP end-boundary floating surface is bombarded by a mono-energetic, space-charge-neutral plasma beam. When the injected energetic electron beam is adequately damped by the NEP, the sheath potential is linearly controlled at almost a 1 : 1 ratio by the accelerator voltage. If the NEP parameters cannot damp the electron beam sufficiently, leaving an excess amount of electron-beam power deposited on the floating surface, the sheath potential will collapse and become unresponsive to the accelerator voltage.
Analysis of the pressure-induced potential arising through composite membranes with selective surface layers.

PubMed

Szymczyk, Anthony; Sbaï, Mohammed; Fievet, Patrick

2005-03-01

When a pressure gradient is applied through a charged selective membrane, the transmembrane electrical potential difference, called the filtration potential, results from both the applied pressure and induced concentration difference across the membrane. In this work we investigate the electrokinetic properties relative to both active and support layers of a composite ceramic membrane close to the nanofiltration range. First, the volume charge density of the active layer is obtained by fitting a transport model to experimental rejection rates (which are controlled by the active layer only). Next, the value of the volume charge density is used to compute the theoretical filtration potential through the active layer. For sufficiently high permeate volume fluxes, the concentration difference across the active layer becomes constant, which allows assessing the membrane potential of the active layer. Experimental measurements of the overall filtration potential arising through the whole membrane are performed. The contribution of the support layer to this overall filtration potential is put in evidence. That implies that the membrane potential of the active layer cannot be deduced directly from the overall filtration potential measurements. Finally, the contribution of the support layer is singled out by subtracting the theoretical filtration potential of the active layer from the experimental filtration potential measured across the whole membrane (i.e., support + active layers). The amphoteric behavior of both layers is put in evidence, which is confirmed by electrophoretic measurements carried out with the powdered support layer and by recently reported tangential streaming potential measurements.
Stem Hydraulic Conductivity depends on the Pressure at Which It Is Measured and How This Dependence Can Be Used to Assess the Tempo of Bubble Pressurization in Recently Cavitated Vessels.

PubMed

Wang, Yujie; Liu, Jinyu; Tyree, Melvin T

2015-12-01

Cavitation of water in xylem vessels followed by embolism formation has been authenticated for more than 40 years. Embolism formation involves the gradual buildup of bubble pressure (air) to atmospheric pressure as demanded by Henry's law of equilibrium between gaseous and liquid phases. However, the tempo of pressure increase has not been quantified. In this report, we show that the rate of pressurization of embolized vessels is controlled by both fast and slow kinetics, where both tempos are controlled by diffusion but over different spatial scales. The fast tempo involves a localized diffusion from endogenous sources: over a distance of about 0.05 mm from water-filled wood to the nearest embolized vessels; this process, in theory, should take <2 min. The slow tempo involves diffusion of air from exogenous sources (outside the stem). The latter diffusion process is slower because of the increased distance of diffusion of up to 4 mm. Radial diffusion models and experimental measurements both confirm that the average time constant is >17 h, with complete equilibrium requiring 1 to 2 d. The implications of these timescales for the standard methods of measuring percentage loss of hydraulic conductivity are discussed in theory and deserve more research in future. © 2015 American Society of Plant Biologists. All Rights Reserved.
Oxygen-Rich Lithium Oxide Phases Formed at High Pressure for Potential Lithium-Air Battery Electrode.

PubMed

Yang, Wenge; Kim, Duck Young; Yang, Liuxiang; Li, Nana; Tang, Lingyun; Amine, Khalil; Mao, Ho-Kwang

2017-09-01

The lithium-air battery has great potential of achieving specific energy density comparable to that of gasoline. Several lithium oxide phases involved in the charge-discharge process greatly affect the overall performance of lithium-air batteries. One of the key issues is linked to the environmental oxygen-rich conditions during battery cycling. Here, the theoretical prediction and experimental confirmation of new stable oxygen-rich lithium oxides under high pressure conditions are reported. Three new high pressure oxide phases that form at high temperature and pressure are identified: Li 2 O 3 , LiO 2 , and LiO 4 . The LiO 2 and LiO 4 consist of a lithium layer sandwiched by an oxygen ring structure inherited from high pressure ε-O 8 phase, while Li 2 O 3 inherits the local arrangements from ambient LiO 2 and Li 2 O 2 phases. These novel lithium oxides beyond the ambient Li 2 O, Li 2 O 2 , and LiO 2 phases show great potential in improving battery design and performance in large battery applications under extreme conditions.
Elevated temperature and CO(2) concentration effects on xylem anatomy of Scots pine.

PubMed

Kilpeläinen, Antti; Gerendiain, Ane Zubizarreta; Luostarinen, Katri; Peltola, Heli; Kellomäki, Seppo

2007-09-01

We studied the effects of elevated temperature and carbon dioxide concentration ([CO(2)]) alone and together on wood anatomy of 20-year-old Scots pine (Pinus sylvestris L.) trees. The study was conducted in 16 closed chambers, providing a factorial combination of two temperature regimes and two CO(2) concentrations (ambient and elevated), with four trees in each treatment. The climate scenario included a doubling of [CO(2)] and a corresponding increase of 2-6 degrees C in temperature at the site depending on the season. Anatomical characteristics analyzed were annual earlywood, latewood and ring widths, intra-ring wood densities (earlywood, latewood and mean wood density), tracheid width, length, wall thickness, lumen diameter, wall thickness:lumen diameter ratio and mass per unit length (coarseness), and numbers of rays, resin canals and tracheids per xylem cross-sectional area. Elevated [CO(2)] increased ring width in four of six treatment years; earlywood width increased in the first two years and latewood width in the third year. Tracheid walls in both the earlywood and latewood tended to become thicker over the 6-year treatment period when temperature or [CO(2)] was elevated alone, whereas in the combined treatment they tended to become thinner relative to the tracheids of trees grown under ambient conditions. Latewood tracheid lumen diameters were larger in all the treatments relative to ambient conditions over the 6-year period, whereas lumen diameters in earlywood increased only in response to elevated [CO(2)] and were 3-6% smaller in the treatments with elevated temperature than in ambient conditions. Tracheid width, length and coarseness were greater in trees grown in elevated than in ambient temperature. The number of resin canals per mm(2) decreased in the elevated [CO(2)] treatment and increased in the elevated temperature treatments relative to ambient conditions. The treatments decreased the number of rays and tracheids per mm(2) of cross
Xylem specific activation of 5’ upstream regulatory region of two NAC transcription factors (MusaVND6 and MusaVND7) in banana is regulated by SNBE-like sites

PubMed Central

2018-01-01

Deposition of secondary cell wall in the xylem elements is controlled by a subgroup of NAC (NAM, ATAF, CUC) family, known as vascular-related NAC transcription factors (VNDs). In the present study, we analyzed the 5’ upstream regulatory region of two banana NAC transcription factors (MusaVND6 and MusaVND7) for tissue specific expression and presence of 19-bp secondary-wall NAC binding element (SNBE)-like motifs. Transgenic banana plants of Musa cultivar Rasthali harboring either PMusaVND7::GUS or PMusaVND6::GUS showed specific GUS (β-D-Glucuronidase) activity in cells of the xylem tissue. Approximately 1.2kb promoter region of either MusaVND6 or MusaVND7 showed presence of at least two SNBE-like motifs. This 1.2kb promoter region was retarded in a gel shift assay by three banana VND protein (VND1,VND2 and VND3). The banana VND1-VND3 could also retard the mobility of isolated SNBE-like motifs of MusaVND6 or MusaVND7 in a gel shift assay. Transcript levels of MusaVND6 and MusaVND7 were elevated in transgenic banana overexpressing either banana VND1, VND2 or VND3. Present study suggested a probable regulation of banana VND6 and VND7 expression through direct interaction of banana VND1- VND3 with SNBE-like motifs. Our study also indicated two promoter elements for possible utilization in cell wall modifications in plants especially banana, which is being recently considered as a potential biofuel crop. PMID:29438404
Investigating the potential of Bacillus subtilis alpha-amylase as a pressure-temperature-time indicator for high hydrostatic pressure pasteurization processes.

PubMed

Grauwet, Tara; Van der Plancken, Iesel; Vervoort, Liesbeth; Hendrickx, Marc E; Van Loey, Ann

2009-01-01

The potential of Bacillus subtilis alpha-amylase (BSA) as a pressure-temperature-time indicator (pTTI) for high pressure pasteurization processing (400-600 MPa; T(i) 10-40 degrees C; 1-15 min) was investigated. A stepwise approach was followed for the development of an enzyme-based, extrinsic, isolated pTTI. First, based on literature data on the pressure stability, BSA was selected as a candidate indicator. Next to the accuracy and ease of the measurement of the indicator's response (residual activity) to the pressure treatment, the storage and handling stability of BSA at atmospheric pressure was verified. Second, the stability of BSA at a constant temperature (T) and time in function of pressure (p) was investigated. Solvent engineering was used to shift the inactivation window of BSA in the processing range of interest. Third, the enzyme (1 g/L BSA-MES 0.05 M pH 5.0) was kinetically calibrated under isobaric-isothermal conditions. Time dependent changes in activity could be modeled best by a first-order model. Except for low pressures and high temperatures, a synergistic effect between pressure and temperature could be observed. Based on the model selected to describe the combined p,T-dependency of the inactivation rate constant, an elliptically shaped isorate contour plot could be constructed, illustrating the processing range where BSA can be used to demonstrate temperature gradients. Fourth, the validity of the kinetic model was tested successfully under dynamic conditions similar to those used in food industry. Finally, the indicator was found suitable to demonstrate nonuniformity in two-sectional planes of a vertical, single vessel system. (c) 2009 American Institute of Chemical Engineers. Biotechnol. Prog., 2009.
Stem Hydraulic Conductivity depends on the Pressure at Which It Is Measured and How This Dependence Can Be Used to Assess the Tempo of Bubble Pressurization in Recently Cavitated Vessels1[OPEN

PubMed Central

Liu, Jinyu; Tyree, Melvin T.

2015-01-01

Cavitation of water in xylem vessels followed by embolism formation has been authenticated for more than 40 years. Embolism formation involves the gradual buildup of bubble pressure (air) to atmospheric pressure as demanded by Henry’s law of equilibrium between gaseous and liquid phases. However, the tempo of pressure increase has not been quantified. In this report, we show that the rate of pressurization of embolized vessels is controlled by both fast and slow kinetics, where both tempos are controlled by diffusion but over different spatial scales. The fast tempo involves a localized diffusion from endogenous sources: over a distance of about 0.05 mm from water-filled wood to the nearest embolized vessels; this process, in theory, should take <2 min. The slow tempo involves diffusion of air from exogenous sources (outside the stem). The latter diffusion process is slower because of the increased distance of diffusion of up to 4 mm. Radial diffusion models and experimental measurements both confirm that the average time constant is >17 h, with complete equilibrium requiring 1 to 2 d. The implications of these timescales for the standard methods of measuring percentage loss of hydraulic conductivity are discussed in theory and deserve more research in future. PMID:26468516
Hydraulic safety margins and air-seeding thresholds in roots, trunks, branches and petioles of four northern hardwood trees.

PubMed

Wason, Jay W; Anstreicher, Katherine S; Stephansky, Nathan; Huggett, Brett A; Brodersen, Craig R

2018-04-16

During drought, xylem sap pressures can approach or exceed critical thresholds where gas embolisms form and propagate through the xylem network, leading to systemic hydraulic dysfunction. The vulnerability segmentation hypothesis (VSH) predicts that low-investment organs (e.g. leaf petioles) should be more vulnerable to embolism spread compared to high-investment, perennial organs (e.g. trunks, stems), as a means of mitigating embolism spread and excessive negative pressures in the perennial organs. We tested this hypothesis by measuring air-seeding thresholds using the single-vessel air-injection method and calculating hydraulic safety margins in four northern hardwood tree species of the northeastern United States, in both saplings and canopy height trees, and at five points along the soil-plant-atmosphere continuum. Acer rubrum was the most resistant to air-seeding and generally supported the VSH. However, Fagus grandifolia, Fraxinus americana and Quercus rubra showed little to no variation in air-seeding thresholds across organ types within each species. Leaf-petiole xylem operated at water potentials close to or exceeding their hydraulic safety margins in all species, whereas roots, trunks and stems of A. rubrum, F. grandifolia and Q. rubra operated within their safety margins, even during the third-driest summer in the last 100 yr. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.
Climate-related trends in sapwood biophysical properties in two conifers: avoidance of hydraulic dysfunction through coordinated adjustments in xylem efficiency, safety and capacitance.

PubMed

Barnard, David M; Meinzer, Frederick C; Lachenbruch, Barbara; McCulloh, Katherine A; Johnson, Daniel M; Woodruff, David R

2011-04-01

In the Pacific north-west, the Cascade Mountain Range blocks much of the precipitation and maritime influence of the Pacific Ocean, resulting in distinct climates east and west of the mountains. The current study aimed to investigate relationships between water storage and transport properties in populations of Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) adapted to both climates. Sapwood thickness, capacitance, vulnerability to embolism, and axial and radial conductivity were measured on samples collected from trunks of mature trees. The sapwood of ponderosa pine was three to four times thicker than Douglas-fir. Radial conductivity was higher in west-side populations of both species, but axial conductivity was higher in the east-side populations and in Douglas-fir. Eastern populations of both species had sapwood that was more vulnerable to embolism than west-side populations. Sapwood capacitance was similar between species, but was about twice as great in east-side populations (580 kg m⁻³ MPa⁻¹) as in west-side populations (274 kg m⁻³ MPa⁻¹). Capacitance was positively correlated with both mean embolism pressure and axial conductivity across species and populations, suggesting that coordinated adjustments in xylem efficiency, safety and water storage capacity may serve to avoid embolism along a gradient of increasing aridity. © 2011 Blackwell Publishing Ltd.
Xylem transport of root-derived CO2: An alternative flux pathway of substantial importance for understanding the components of ecosystem respiration

NASA Astrophysics Data System (ADS)

Aubrey, D. P.; Teskey, R. O.

2011-12-01

Forest ecosystem respiration releases one of the largest annual CO2 fluxes of the global carbon cycle and is dominated by belowground autotrophic and heterotrophic contributions. A mechanistic understanding of forest respiratory flux pathways is imperative to understanding carbon cycling in forests. We recently demonstrated that, on a daily basis, the amount of CO2 that fluxes upward from tree root systems into stems via the xylem stream rivals the amount of CO2 diffusing from the soil surface. However, our original observations were limited to only four individual eastern cottonwood (Populus deltoides L.) trees over a single week where environmental conditions remained similar. Here, we expand our investigation to an entire growing season using nine trees. We calculated the internal transport of root-derived CO2 as the product of sap flow and dissolved CO2 concentration ([CO2]) in the xylem at the base of the stem and measured soil CO2 efflux using the [CO2] gradient approach. We then compared the magnitude of these two flux pathways throughout the growing season. The internal transport of root-derived CO2 was equivalent to one-third of the total belowground respiration throughout the growing season. This indicates that autotrophic respiration was substantially higher than previously estimated, and also higher than heterotrophic soil respiration. The quantity of internally transported CO2 was influenced by both seasonal and daily environmental factors that influenced sap flow rates. We observed high concentrations of CO2 in xylem sap which ranged from 1% to 20% [CO2] among and within individual trees through time. Our results provide evidence that belowground autotrophic respiration consumes a larger amount-and stem respiration consumes a smaller amount-of carbohydrates than previously realized. The magnitude of the internal pathway for root-derived CO2 flux highlights the inadequacy of using the CO2 efflux from the soil surface to the atmosphere alone to measure
Interaction of poly(ethylene-glycols) with air-water interfaces and lipid monolayers: investigations on surface pressure and surface potential.

PubMed Central

Winterhalter, M; Bürner, H; Marzinka, S; Benz, R; Kasianowicz, J J

1995-01-01

We have characterized the surface activity of different-sized poly(ethylene-glycols) (PEG; M(r) 200-100,000 Da) in the presence or absence of lipid monolayers and over a wide range of bulk PEG concentrations (10(-8)-10% w/v). Measurements of the surface potential and surface pressure demonstrate that PEGs interact with the air-water and lipid-water interfaces. Without lipid, PEG added either to the subphase or to the air-water interface forms relatively stable monolayers. Except for very low molecular weight polymers (PEGs < 1000 Da), low concentrations of PEG in the subphase (between 10(-5) and 10(-4)% w/v) increase the surface potential from zero (with respect to the potential of a pure air-water interface) to a plateau value of approximately 440 mV. At much higher polymer concentrations, > 10(-1)% (w/v), depending on the molecular weight of the PEG and corresponding to the concentration at which the polymers in solution are likely to overlap, the surface potential decreases. High concentrations of PEG in the subphase cause a similar decrease in the surface potential of densely packed lipid monolayers spread from either diphytanoyl phosphatidylcholine (DPhPC), dipalmitoyl phosphatidylcholine (DPPC), or dioleoyl phosphatidylserine (DOPS). Adding PEG as a monolayer at the air-water interface also affects the surface activity of DPhPC or DPPC monolayers. At low lipid concentration, the surface pressure and potential are determined by the polymer. For intermediate lipid concentrations, the surface pressure-area and surface potential-area isotherms show that the effects due to lipid and PEG are not always additive and that the polymer's effect is distinct for the two lipids. When PEG-lipid-mixed monolayers are compressed to surface pressures greater than the collapse pressure for a PEG monolayer, the surface pressure-area and surface potential-area isotherms approach that of the lipid alone, suggesting that for this experimental condition PEG is expelled from the
Salt stress induces the formation of a novel type of 'pressure wood' in two Populus species.

PubMed

Janz, Dennis; Lautner, Silke; Wildhagen, Henning; Behnke, Katja; Schnitzler, Jörg-Peter; Rennenberg, Heinz; Fromm, Jörg; Polle, Andrea

2012-04-01

• Salinity causes osmotic stress and limits biomass production of plants. The goal of this study was to investigate mechanisms underlying hydraulic adaptation to salinity. • Anatomical, ecophysiological and transcriptional responses to salinity were investigated in the xylem of a salt-sensitive (Populus × canescens) and a salt-tolerant species (Populus euphratica). • Moderate salt stress, which suppressed but did not abolish photosynthesis and radial growth in P. × canescens, resulted in hydraulic adaptation by increased vessel frequencies and decreased vessel lumina. Transcript abundances of a suite of genes (FLA, COB-like, BAM, XET, etc.) previously shown to be activated during tension wood formation, were collectively suppressed in developing xylem, whereas those for stress and defense-related genes increased. A subset of cell wall-related genes was also suppressed in salt-exposed P. euphratica, although this species largely excluded sodium and showed no anatomical alterations. Salt exposure influenced cell wall composition involving increases in the lignin : carbohydrate ratio in both species. • In conclusion, hydraulic stress adaptation involves cell wall modifications reciprocal to tension wood formation that result in the formation of a novel type of reaction wood in upright stems named 'pressure wood'. Our data suggest that transcriptional co-regulation of a core set of genes determines reaction wood composition. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.
Big and small: menisci in soil pores affect water pressures, dynamics of groundwater levels, and catchment-scale average matric potentials

NASA Astrophysics Data System (ADS)

de Rooij, G. H.

2010-09-01

Soil water is confined behind the menisci of its water-air interface. Catchment-scale fluxes (groundwater recharge, evaporation, transpiration, precipitation, etc.) affect the matric potential, and thereby the interface curvature and the configuration of the phases. In turn, these affect the fluxes (except precipitation), creating feedbacks between pore-scale and catchment-scale processes. Tracking pore-scale processes beyond the Darcy scale is not feasible. Instead, for a simplified system based on the classical Darcy's Law and Laplace-Young Law we i) clarify how menisci transfer pressure from the atmosphere to the soil water, ii) examine large-scale phenomena arising from pore-scale processes, and iii) analyze the relationship between average meniscus curvature and average matric potential. In stagnant water, changing the gravitational potential or the curvature of the air-water interface changes the pressure throughout the water. Adding small amounts of water can thus profoundly affect water pressures in a much larger volume. The pressure-regulating effect of the interface curvature showcases the meniscus as a pressure port that transfers the atmospheric pressure to the water with an offset directly proportional to its curvature. This property causes an extremely rapid rise of phreatic levels in soils once the capillary fringe extends to the soil surface and the menisci flatten. For large bodies of subsurface water, the curvature and vertical position of any meniscus quantify the uniform hydraulic potential under hydrostatic equilibrium. During unit-gradient flow, the matric potential corresponding to the mean curvature of the menisci should provide a good approximation of the intrinsic phase average of the matric potential.

High-pressure synthesis of mesoporous stishovite: potential applications in mineral physics

NASA Astrophysics Data System (ADS)

Stagno, Vincenzo; Mandal, Manik; Landskron, Kai; Fei, Yingwei

2015-06-01

Recently, we have described a successful synthesis route to obtain mesoporous quartz and its high-pressure polymorph coesite by nanocasting at high pressure using periodic mesostructured precursors, such as SBA-16 and FDU-12/carbon composite as starting materials. Periodic mesoporous high-pressure silica polymorphs are of particular interest as they combine transport properties and physical properties such as hardness that potentially enable the industrial use of these materials. In addition, synthesis of mesoporous crystalline silica phases can allow more detailed geology-related studies such as water/mineral interaction, dissolution/crystallization rate and the surface contribution to the associated thermodynamic stability (free energy and enthalpy) of the various polymorphs and their crossover. Here, we present results of synthesis of mesoporous stishovite from cubic large-pore periodic mesoporous silica LP-FDU-12/C composite as precursor with an fcc lattice. We describe the synthesis procedure using multi-anvil apparatus at 9 GPa (about 90,000 atm) and temperature of 500 °C. The synthetic mesoporous stishovite is, then, characterized by wide and small-angle X-ray diffraction, scanning/transmission electron microscopy and gas adsorption. Results show that this new material is characterized by accessible mesopores with wide pore size distribution, surface area of ~45 m2/g and volume of pores of ~0.15 cm3/g. Results from gas adsorption indicate that both porosity and permeability are retained at the high pressures of synthesis but with weak periodic order of the pores.
Influence of headspace pressure on methane production in Biochemical Methane Potential (BMP) tests.

PubMed

Valero, David; Montes, Jesús A; Rico, José Luis; Rico, Carlos

2016-02-01

The biochemical methane potential test is the most commonly applied method to determine methane production from organic wastes. One of the parameters measured is the volume of biogas produced which can be determined manometrically by keeping the volume constant and measuring increases in pressure. In the present study, the effect of pressure accumulation in the headspace of the reactors has been studied. Triplicate batch trials employing cocoa shell, waste coffee grounds and dairy manure as substrates have been performed under two headspace pressure conditions. The results obtained in the study showed that headspace overpressures higher than 600mbar affected methane production for waste coffee grounds. On the contrary, headspace overpressures within a range of 600-1000mbar did not affect methane production for cocoa shell and dairy manure. With the analyses performed in the present work it has not been possible to determine the reasons for the lower methane yield value obtained for the waste coffee grounds under high headspace pressures. Copyright © 2015 Elsevier Ltd. All rights reserved.
Potential pressurized payloads: Fluid and thermal experiments

NASA Technical Reports Server (NTRS)

Swanson, Theodore D.

1992-01-01

Space Station Freedom (SSF) presents the opportunity to perform long term fluid and thermal experiments in a microgravity environment. This presentation provides perspective on the need for fluids/thermal experimentation in a microgravity environment, addresses previous efforts, identifies possible experiments, and discusses the capabilities of a proposed fluid physics/dynamics test facility. Numerous spacecraft systems use fluids for their operation. Thermal control, propulsion, waste management, and various operational processes are examples of such systems. However, effective ground testing is very difficult. This is because the effect of gravity induced phenomena, such as hydrostatic pressure, buoyant convection, and stratification, overcome such forces as surface tension, diffusion, electric potential, etc., which normally dominate in a microgravity environment. Hence, space experimentation is necessary to develop and validate a new fluid based technology. Two broad types of experiments may be performed on SSF: basic research and applied research. Basic research might include experiments focusing on capillary phenomena (with or without thermal and/or solutal gradients), thermal/solutal convection, phase transitions, and multiphase flow. Representative examples of applied research might include two-phase pressure drop, two-phase flow instabilities, heat transfer coefficients, fluid tank fill/drain, tank slosh dynamics, condensate removal enhancement, and void formation within thermal energy storage materials. In order to better support such fluid/thermal experiments on board SSF, OSSA has developed a conceptual design for a proposed Fluid Physics/Dynamics Facility (FP/DF). The proposed facility consists of one facility rack permanently located on SSF and one experimenter rack which is changed out as needed to support specific experiments. This approach will minimize the on-board integration/deintegration required for specific experiments. The FP/DF will have
Evidence for an Elongation/Reduction/C1-Elimination Pathway in the Biosynthesis of n-Heptane in Xylem of Jeffrey Pine.

PubMed Central

Savage, T. J.; Hristova, M. K.; Croteau, R.

1996-01-01

The biosynthetic pathway to n-heptane was investigated by examining the effect of the [beta]-keto acyl-acyl carrier protein synthase inhibitor (2R,3S)-2,3-epoxy-4-oxo-7E,10E-dodecadienamide (cerulenin), a thiol reagent ([beta]-mercaptoethanol), and an aldehydetrapping reagent (hydroxylamine) on the biosynthesis of n-[14C]heptane and putative intermediates in xylem sections of Jeffrey pine (Pinus jeffreyi Grev.& Balf.) incubated with [14C]acetate. Cerulenin inhibited C18 fatty acid biosynthesis but had relatively little effect on radiolabel incorporation into C8 fatty acyl groups and n-heptane. [beta]-Mercaptoethanol inhibited n-heptane biosynthesis, with a corresponding accumulation of radiolabel into both octanal and 1-octanol, whereas hydroxylamine inhibited both n-heptane and 1-octanol biosynthesis, with radiolabel accumulation in octyl oximes. [14C]Octanal was converted to both n-heptane and 1-octanol when incubated with xylem sections, whereas [14C]1-octanol was converted to octanal and n-heptane in a hydroxylamine-sensitive reaction. These results suggest a pathway for the biosynthesis of n-heptane whereby acetate is polymerized via a typical fatty acid synthase reaction sequence to yield a C8 thioester, which subsequently undergoes a two-electron reduction to generate a free thiol and octanal, the latter of which alternately undergoes an additional, reversible reduction to form 1-octanol or loss of C1 to generate n-heptane. PMID:12226360
Psychrometric measurement of soil water potential: Stability of calibration and test of pressure-plate samples

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, T.L.; Gee, G.W.; Heller, P.R.

1990-08-01

A commercially available thermocouple psychrometer sample changer (Decagon SC-10A) was used to measure the water potential of field soils ranging in texture from sand to silty clay loam over a range of {minus}0.5 to {minus}20.0 MPa. The standard error of prediction based on regression statistics was generally between 0.04 and 0.14 MPa at {minus}5 MPa. Replacing the measuring junction of the unit changed the calibration slightly; however, it did not significantly alter measurement accuracy. Calibration curves measured throughout a year of testing are consistent and indicate no systematic drift in calibration. Most measurement uncertainty is produced by shifts in themore » intercept in the calibration equation rather than the slope. Both the variability in intercept and the regression error seem to be random. Measurements taken with the SC-10A show that water potential in both sand and silt loam samples removed from 1.5-MPa pressure plates was often 0.5 to 1.0 MPa greater than the 1.5-MPa applied pressure. Limited data from 0.5-MPa pressure plates show close agreement between SC-10A measurements and pressure applied to these more permeable plates.« less
ELECTRIC CURRENT FILAMENTATION AT A NON-POTENTIAL MAGNETIC NULL-POINT DUE TO PRESSURE PERTURBATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jelínek, P.; Karlický, M.; Murawski, K., E-mail: pjelinek@prf.jcu.cz

2015-10-20

An increase of electric current densities due to filamentation is an important process in any flare. We show that the pressure perturbation, followed by an entropy wave, triggers such a filamentation in the non-potential magnetic null-point. In the two-dimensional (2D), non-potential magnetic null-point, we generate the entropy wave by a negative or positive pressure pulse that is launched initially. Then, we study its evolution under the influence of the gravity field. We solve the full set of 2D time dependent, ideal magnetohydrodynamic equations numerically, making use of the FLASH code. The negative pulse leads to an entropy wave with amore » plasma density greater than in the ambient atmosphere and thus this wave falls down in the solar atmosphere, attracted by the gravity force. In the case of the positive pressure pulse, the plasma becomes evacuated and the entropy wave propagates upward. However, in both cases, owing to the Rayleigh–Taylor instability, the electric current in a non-potential magnetic null-point is rapidly filamented and at some locations the electric current density is strongly enhanced in comparison to its initial value. Using numerical simulations, we find that entropy waves initiated either by positive or negative pulses result in an increase of electric current densities close to the magnetic null-point and thus the energy accumulated here can be released as nanoflares or even flares.« less
A Constrained Maximization Model for inspecting the impact of leaf shape on optimal leaf size and stoma resistance

NASA Astrophysics Data System (ADS)

Ding, J.; Johnson, E. A.; Martin, Y. E.

2017-12-01

Leaf is the basic production unit of plants. Water is the most critical resource of plants. Its availability controls primary productivity of plants by affecting leaf carbon budget. To avoid the damage of cavitation from lowering vein water potential t caused by evapotranspiration, the leaf must increase the stomatal resistance to reduce evapotranspiration rate. This comes at the cost of reduced carbon fixing rate as increasing stoma resistance meanwhile slows carbon intake rate. Studies suggest that stoma will operate at an optimal resistance to maximize the carbon gain with respect to water. Different plant species have different leaf shapes, a genetically determined trait. Further, on the same plant leaf size can vary many times in size that is related to soil moisture, an indicator of water availability. According to metabolic scaling theory, increasing leaf size will increase total xylem resistance of vein, which may also constrain leaf carbon budget. We present a Constrained Maximization Model of leaf (leaf CMM) that incorporates metabolic theory into the coupling of evapotranspiration and carbon fixation to examine how leaf size, stoma resistance and maximum net leaf primary productivity change with petiole xylem water potential. The model connects vein network structure to leaf shape and use the difference between petiole xylem water potential and the critical minor vein cavitation forming water potential as the budget. The CMM shows that both maximum net leaf primary production and optimal leaf size increase with petiole xylem water potential while optimal stoma resistance decreases. Narrow leaf has overall lower optimal leaf size and maximum net leaf carbon gain and higher optimal stoma resistance than those of broad leaf. This is because with small width to length ratio, total xylem resistance increases faster with leaf size. Total xylem resistance of narrow leaf increases faster with leaf size causing higher average and marginal cost of xylem water
PRESSURE EFFECTS IN POLYCYCLIC AROMATIC NITROGENATED HETEROCYCLES (PANHs): DIAGNOSTIC QUALITIES AND COSMOBAROMETRY POTENTIAL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montgomery, Wren; Sephton, Mark A., E-mail: w.montgomery@imperial.ac.uk

2016-03-01

The influence of polycyclic aromatic nitrogen heterocycles (PANHs), which have been suggested as contributors to the interstellar IR emission bands, on interstellar emission features is difficult to constrain because their infrared characteristics are strongly similar to those for polycyclic aromatic hydrocarbons (PAHs). One possible solution is to seek a means of visualizing the presence of PANHs that provides information that is distinct from that for PAHs. Although PANHs and PAHs have similar infrared characteristics in many settings, this relationship may not be universally maintained. We have used in situ high-pressure synchrotron-source Fourier transform infrared spectroscopy to determine that the responsesmore » of two representative molecules, acridine and anthracene, differ at high pressures (>ca. 1 GPa). Because there are a number of high-pressure environments that can be remotely observed by infrared spectroscopy, they represent a potential to glimpse the distribution of PANHs across the cosmos.« less
Streaming potential generated by a pressure-driven flow over a super-hydrophobic surface

NASA Astrophysics Data System (ADS)

Zhao, Hui

2010-11-01

The streaming potential generated by a pressured-driven flow over a weakly charged striped slip-stick surface (the zeta potential of the surface is smaller than the thermal potential (25 mV) with an arbitrary double layer thickness is theoretically studied by solving the Poisson-Boltzmann equation and Stokes equation. A series solution of the streaming potential is derived. Approximate expressions for the streaming potential in the limits of thin double layers and thick double layers are also presented, in excellent agreement with the full solution. The streaming potential is compared against that over a homogenously charged smooth surface. Our results indicate that the streaming potential over a super-hydrophobic surface only can be enhanced when the liquid-gas interface is charged. In addition, as the double layer thickness increases, the advantage of the super-hydrophobic surface diminishes. The impact of a slip-stick surface on the streaming potential might provide guidance for designing novel and efficient microfludic energy conversion devices using a super-hydrophobic surface.
Measurement of compartment elasticity using pressure related ultrasound: a method to identify patients with potential compartment syndrome.

PubMed

Sellei, R M; Hingmann, S J; Kobbe, P; Weber, C; Grice, J E; Zimmerman, F; Jeromin, S; Gansslen, A; Hildebrand, F; Pape, H C

2015-01-01

PURPOSE OF THE STUDY Decision-making in treatment of an acute compartment syndrome is based on clinical assessment, supported by invasive monitoring. Thus, evolving compartment syndrome may require repeated pressure measurements. In suspected cases of potential compartment syndromes clinical assessment alone seems to be unreliable. The objective of this study was to investigate the feasibility of a non-invasive application estimating whole compartmental elasticity by ultrasound, which may improve accuracy of diagnostics. MATERIAL AND METHODS In an in-vitro model, using an artificial container simulating dimensions of the human anterior tibial compartment, intracompartmental pressures (p) were raised subsequently up to 80 mm Hg by infusion of saline solution. The compartmental depth (mm) in the cross-section view was measured before and after manual probe compression (100 mm Hg) upon the surface resulting in a linear compartmental displacement (Δd). This was repeated at rising compartmental pressures. The resulting displacements were related to the corresponding intra-compartmental pressures simulated in our model. A hypothesized relationship between pressures related compartmental displacement and the elasticity at elevated compartment pressures was investigated. RESULTS With rising compartmental pressures, a non-linear, reciprocal proportional relation between the displacement (mm) and the intra-compartmental pressure (mm Hg) occurred. The Pearson's coefficient showed a high correlation (r2 = -0.960). The intraobserver reliability value kappa resulted in a statistically high reliability (κ = 0.840). The inter-observer value indicated a fair reliability (κ = 0.640). CONCLUSIONS Our model reveals that a strong correlation between compartmental strain displacements assessed by ultrasound and the intra-compartmental pressure changes occurs. Further studies are required to prove whether this assessment is transferable to human muscle tissue. Determining the complete
[The changes in contents and composition of phenolic acids during cell xylem growth in scots pine].

PubMed

Antonova, G F; Zheliznichenko, T V; Stasova, V V

2011-01-01

The contents and composition of alcohol soluble phenolic acids were studied during cell xylem growth in the course of wood annual increment formation in the stems of Scots pine. The cells of cambium zone, of two stages of expansion growth and the outset of secondary thickening zone (before lignification) were successively gathered from the stem segments of 25-old pine trees in the period of earlywood xylem formation with constant anatomical and histochemical control. The contents of free and bound forms of phenolic acids, isolated by 80% ethanol from tissues, as well as of their ethers and esters were calculated both per dry weight and per cell. The content and relation of the fractions and the composition of phenolic acid have been found to change significantly from cambium zone to the outset of tracheid secondary thickening. The character of the variations depends on a calculation method. According to the calculation per cell the amount of free and bound phenolic acids and in their composition of esters and especially ethers increased at the first step of expansion growth zone, decreased at the second one and rose again in the outset of secondary wall deposition. In dependence on the stage of cell development the pool of bound phenolic acids exceeded of free acid pool in 2-5 times. Sinapic and ferulic acids dominated in the composition of free hydroxycinnamic acids. The content and composition of hydroxycinnamic acids in ethers and esters depended on cell development phase. In cambium p-coumaric and sinapic acids were principal aglycons in ethers, at other stages these were sinapic and caffeic acids. The esters in cambium zone included essentially p-coumaric acid and at the other stages - sinapic and ferulic acids. At the first phase of growth benzoic acid was connected principally by ester bonds. The pool of these esters decreased from the first phase of growth to the outset of cell wall thickening and in proportion to this the level of free benzoic acid rose.
Assessing plant hydraulic architecture with ultrasonic acoustic emission techniques

NASA Astrophysics Data System (ADS)

Meinzer, F. C.; Johnson, D.; McCulloh, K.; Woodruff, D.

2012-12-01

Water is transported through the xylem of plants under tension (negative pressure). If the tension within a xylem conduit exceeds a critical value, cavitation can occur, which if followed by embolism leads to blockage of water transport through the conduit. Plant species and different organs within the plant such as roots, stems and leaves vary widely in the xylem tension thresholds at which cavitation events begin to occur. Massive cavitation and embolism can lead to catastrophic hydraulic failure and plant death from dehydration. Ultrasonic acoustic emission (UAE) transducers provide a non-invasive means of detecting cavitation events in plants and recording the accumulation of these events through time. When used in combination with other techniques, recording of UAEs can be a powerful tool for characterizing and understanding plant hydraulic architecture; the collection of properties that determine the efficiency and vulnerability of water transport from roots to leaves. The hydraulic architecture of leaves is particularly complex because water must traverse the dead cells of the xylem plus an extra-xylary pathway consisting of living cells and intercellular spaces before it arrives at the internal evaporating surfaces. We used UAE, imaging and other techniques to determine the extent to which dehydration-induced declines in leaf hydraulic conductance were associated with xylem cavitation and embolism versus changes in the conductance of the extra-xylary pathway. In most of the evergreen and deciduous tree species studied there was a close correspondence between the trajectories of cumulative UAEs and loss of whole-leaf hydraulic conductance during dehydration. The mean amplitude of UAEs was positively correlated with mean conduit diameter indicating that in addition to detecting cavitation events, analysis of UAE features can provide information about relative changes in xylem hydraulic conductivity because conductivity is a function of conduit radius to the
Coordination and trade-offs among hydraulic safety, efficiency and drought avoidance traits in Amazonian rainforest canopy tree species.

PubMed

Santiago, Louis S; De Guzman, Mark E; Baraloto, Christopher; Vogenberg, Jacob E; Brodie, Max; Hérault, Bruno; Fortunel, Claire; Bonal, Damien

2018-05-01

Predicting responses of tropical forests to climate change-type drought is challenging because of high species diversity. Detailed characterization of tropical tree hydraulic physiology is necessary to evaluate community drought vulnerability and improve model parameterization. Here, we measured xylem hydraulic conductivity (hydraulic efficiency), xylem vulnerability curves (hydraulic safety), sapwood pressure-volume curves (drought avoidance) and wood density on emergent branches of 14 common species of Eastern Amazonian canopy trees in Paracou, French Guiana across species with the densest and lightest wood in the plot. Our objectives were to evaluate relationships among hydraulic traits to identify strategies and test the ability of easy-to-measure traits as proxies for hard-to-measure hydraulic traits. Xylem efficiency was related to capacitance, sapwood water content and turgor loss point, and other drought avoidance traits, but not to xylem safety (P 50 ). Wood density was correlated (r = -0.57 to -0.97) with sapwood pressure-volume traits, forming an axis of hydraulic strategy variation. In contrast to drier sites where hydraulic safety plays a greater role, tropical trees in this humid tropical site varied along an axis with low wood density, high xylem efficiency and high capacitance at one end of the spectrum, and high wood density and low turgor loss point at the other. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.
Assessment of xylem phenology: a first attempt to verify its accuracy and precision.

PubMed

Lupi, C; Rossi, S; Vieira, J; Morin, H; Deslauriers, A

2014-01-01

This manuscript aims to evaluate the precision and accuracy of current methodology for estimating xylem phenology and tracheid production in trees. Through a simple approach, sampling at two positions on the stem of co-dominant black spruce trees in two sites of the boreal forest of Quebec, we were able to quantify variability among sites, between trees and within a tree for different variables. We demonstrated that current methodology is accurate for the estimation of the onset of xylogenesis, while the accuracy for the evaluation of the ending of xylogenesis may be improved by sampling at multiple positions on the stem. The pattern of variability in different phenological variables and cell production allowed us to advance a novel hypothesis on the shift in the importance of various drivers of xylogenesis, from factors mainly varying at the level of site (e.g., climate) at the beginning of the growing season to factors varying at the level of individual trees (e.g., possibly genetic variability) at the end of the growing season.
Changes in wood density, wood anatomy and hydraulic properties of the xylem along the root-to-shoot flow path in tropical rainforest trees.

PubMed

Schuldt, Bernhard; Leuschner, Christoph; Brock, Nicolai; Horna, Viviana

2013-02-01

It is generally assumed that the largest vessels are occurring in the roots and that vessel diameters and the related hydraulic conductance in the xylem are decreasing acropetally from roots to leaves. With this study in five tree species of a perhumid tropical rainforest in Sulawesi (Indonesia), we searched for patterns in hydraulic architecture and axial conductivity along the flow path from small-diameter roots through strong roots and the trunk to distal sun-canopy twigs. Wood density differed by not more than 10% across the different flow path positions in a species, and branch and stem wood density were closely related in three of the five species. Other than wood density, the wood anatomical and xylem hydraulic traits varied in dependence on the position along the flow path, but were unrelated to wood density within a tree. In contrast to reports from conifers and certain dicotyledonous species, we found a hump-shaped variation in vessel diameter and sapwood area--specific conductivity along the flow path in all five species with a maximum in the trunk and strong roots and minima in both small roots and twigs; the vessel size depended on the diameter of the organ. This pattern might be an adaptation to the perhumid climate with a low risk of hydraulic failure. Despite a similar mean vessel diameter in small roots and twigs, the two distal organs, hydraulically weighted mean vessel diameters were on average 30% larger in small roots, resulting in ∼ 85% higher empirical and theoretical specific conductivities. Relative vessel lumen area in percent of sapwood area decreased linearly by 70% from roots to twigs, reflecting the increase in sclerenchymatic tissue and tracheids in acropetal direction in the xylem. Vessel size was more closely related to the organ diameter than to the distance along the root-to-shoot flow path. We conclude that (i) the five co-occurring tree species show convergent patterns in their hydraulic architecture despite different growth
Insights into plant water uptake from xylem-water isotope measurements in two tropical catchments with contrasting moisture conditions

USGS Publications Warehouse

Evaristo, Jaivime; McDonnell, Jeffrey J.; Scholl, Martha A.; Bruijnzeel, L. Adrian; Chun, Kwok P.

2016-01-01

Water transpired by trees has long been assumed to be sourced from the same subsurface water stocks that contribute to groundwater recharge and streamflow. However, recent investigations using dual water stable isotopes have shown an apparent ecohydrological separation between tree-transpired water and stream water. Here we present evidence for such ecohydrological separation in two tropical environments in Puerto Rico where precipitation seasonality is relatively low and where precipitation is positively correlated with primary productivity. We determined the stable isotope signature of xylem water of 30 mahogany (Swietenia spp.) trees sampled during two periods with contrasting moisture status. Our results suggest that the separation between transpiration water and groundwater recharge/streamflow water might be related less to the temporal phasing of hydrologic inputs and primary productivity, and more to the fundamental processes that drive evaporative isotopic enrichment of residual soil water within the soil matrix. The lack of an evaporative signature of both groundwater and streams in the study area suggests that these water balance components have a water source that is transported quickly to deeper subsurface storage compared to waters that trees use. A Bayesian mixing model used to partition source water proportions of xylem water showed that groundwater contribution was greater for valley-bottom, riparian trees than for ridge-top trees. Groundwater contribution was also greater at the xeric site than at the mesic–hydric site. These model results (1) underline the utility of a simple linear mixing model, implemented in a Bayesian inference framework, in quantifying source water contributions at sites with contrasting physiographic characteristics, and (2) highlight the informed judgement that should be made in interpreting mixing model results, of import particularly in surveying groundwater use patterns by vegetation from regional to global scales.
A 6-Year-Long Manipulation with Soil Warming and Canopy Nitrogen Additions does not Affect Xylem Phenology and Cell Production of Mature Black Spruce

PubMed Central

Dao, Madjelia C. E.; Rossi, Sergio; Walsh, Denis; Morin, Hubert; Houle, Daniel

2015-01-01

The predicted climate warming and increased atmospheric inorganic nitrogen deposition are expected to have dramatic impacts on plant growth. However, the extent of these effects and their interactions remains unclear for boreal forest trees. The aim of this experiment was to investigate the effects of increased soil temperature and nitrogen (N) depositions on stem intra-annual growth of two mature stands of black spruce [Picea mariana (Mill.) BSP] in Québec, QC, Canada. During 2008–2013, the soil around mature trees was warmed up by 4°C with heating cables during the growing season and precipitations containing three times the current inorganic N concentration were added by frequent canopy applications. Xylem phenology and cell production were monitored weekly from April to October. The 6-year-long experiment performed in two sites at different altitude showed no substantial effect of warming and N-depositions on xylem phenological phases of cell enlargement, wall thickening and lignification. Cell production, in terms of number of tracheids along the radius, also did not differ significantly and followed the same patterns in control and treated trees. These findings allowed the hypothesis of a medium-term effect of soil warming and N depositions on the growth of mature black spruce to be rejected. PMID:26617610
A new method of tree xylem water extraction for isotopic analysis

NASA Astrophysics Data System (ADS)

Gierke, C.; Newton, B. T.

2011-12-01

The Sacramento Mountain Watershed Study in the southern Sacramento Mountains of New Mexico is designed to assess the forest restoration technique of tree thinning in mountain watersheds as an effective method of increasing local and regional groundwater recharge. The project is using a soil water balance approach to quantify the partitioning of local precipitation within this watershed before and after thinning trees. Understanding what sources trees extract their water from (e.g. shallow groundwater, unsaturated fractured bedrock, and soils) is difficult due to a complex hydrologic system and heterogeneous distribution of soil thicknesses. However, in order to accurately quantify the soil water balance and to assess how thinning trees will affect this water balance, it is important determine the sources from which trees extract their water. We plan to use oxygen and hydrogen stable isotopic analysis of various end member waters to identify these different sources. We are in the process of developing a new method of determining the isotopic composition of tree water that has several advantages over conventional methods. Within the tree there is the xylem which transports water from the roots to the leaves and the phloem which transports starches and sugars in a water media throughout the tree. Previous studies have shown that the isotopic composition of xylem water accurately reflects that of source water, while phloem water has undergone isotopic fractionation during photosynthesis and metabolism. The distillation of water from twigs, which is often used to extract tree water for isotopic analysis, is very labor intensive. Other disadvantages to distillation methods include possible fractionation due to phase changes and the possible extraction of fractionated phloem waters. Employing a new mixing method, the composition of the twig water (TW) can be determined by putting twigs of unknown isotopic water composition into waters of known compositions or initial
Repeated freeze-thaw cycles induce embolism in drought stressed conifers (Norway spruce, stone pine).

PubMed

Mayr, Stefan; Gruber, Andreas; Bauer, Helmut

2003-07-01

Freezing and thawing lead to xylem embolism when gas bubbles caused by ice formation expand during the thaw process. However, previous experimental studies indicated that conifers are resistant to freezing-induced embolism, unless xylem pressure becomes very negative during the freezing. In this study, we show that conifers experienced freezing-induced embolism when exposed to repeated freeze-thaw cycles and simultaneously to drought. Simulating conditions at the alpine timberline (128 days with freeze-thaw events and thawing rates of up to 9.5 K h(-1) in the xylem of exposed twigs during winter), young trees of Norway spruce [Picea abies (L.) Karst.] and stone pine (Pinus cembra L.) were exposed to 50 and 100 freeze-thaw cycles. This treatment caused a significant increase in embolism rates in drought-stressed samples. Upon 100 freeze-thaw cycles, vulnerability thresholds (50% loss of conductivity) were shifted 1.8 MPa (Norway spruce) and 0.8 MPa (stone pine) towards less negative water potentials. The results demonstrate that freeze-thaw cycles are a possible reason for winter-embolism in conifers observed in several field studies. Freezing-induced embolism may contribute to the altitudinal limits of conifers.
Long-term acclimatization of hydraulic properties, xylem conduit size, wall strength and cavitation resistance in Phaseolus vulgaris in response to different environmental effects.

PubMed

Holste, Ellen K; Jerke, Megan J; Matzner, Steven L

2006-05-01

Phaseolus vulgaris grown under various environmental conditions was used to assess long-term acclimatization of xylem structural characteristics and hydraulic properties. Conduit diameter tended to be reduced and 'wood' density (of 'woody' stems) increased under low moisture ('dry'), increased soil porosity ('porous soil') and low phosphorus ('low P') treatments. Dry and low P had the largest percentage of small vessels. Dry, low light ('shade') and porous soil treatments decreased P50 (50% loss in conductivity) by 0.15-0.25 MPa (greater cavitation resistance) compared with 'controls'. By contrast, low P increased P50 by 0.30 MPa (less cavitation resistance) compared with porous soil (the control for low P). Changes in cavitation resistance were independent of conduit diameter. By contrast, changes in cavitation resistance were correlated with wood density for the control, dry and porous soil treatments, but did not appear to be a function of wood density for the shade and low P treatments. In a separate experiment comparing control and porous soil plants, stem hydraulic conductivity (kh), specific conductivity (ks), leaf specific conductivity (LSC), total pot water loss, plant biomass and leaf area were all greater for control plants compared to porous soil plants. Porous soil plants, however, demonstrated higher midday stomatal conductance to water vapour (gs), apparently because they experienced proportionally less midday xylem cavitation.

Effect of Leaf Water Potential on Internal Humidity and CO2 Dissolution: Reverse Transpiration and Improved Water Use Efficiency under Negative Pressure

PubMed Central

Vesala, Timo; Sevanto, Sanna; Grönholm, Tiia; Salmon, Yann; Nikinmaa, Eero; Hari, Pertti; Hölttä, Teemu

2017-01-01

The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but with much lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flat surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO2, thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Our results indicate that the reduction in vapor pressures of water and CO2 could enhance plant water use efficiency up to about 10% at a leaf water potential of −2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. The omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO2 concentration based on leaf gas exchange
Effect of Leaf Water Potential on Internal Humidity and CO2 Dissolution: Reverse Transpiration and Improved Water Use Efficiency under Negative Pressure.

PubMed

Vesala, Timo; Sevanto, Sanna; Grönholm, Tiia; Salmon, Yann; Nikinmaa, Eero; Hari, Pertti; Hölttä, Teemu

2017-01-01

The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but with much lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flat surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO 2 , thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO 2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Our results indicate that the reduction in vapor pressures of water and CO 2 could enhance plant water use efficiency up to about 10% at a leaf water potential of -2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. The omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO 2 concentration based on leaf gas exchange
Transcriptomic analysis of wound xylem formation in Pinus canariensis.

PubMed

Chano, V; Collada, C; Soto, A

2017-12-04

Woody plants, especially trees, usually must face several injuries caused by different agents during their lives. Healing of injuries in stem and branches, affecting the vascular cambium and xylem can take several years. In conifers, healing takes place mainly from the remaining vascular cambium in the margin of the wound. The woundwood formed in conifers during healing usually presents malformed and disordered tracheids as well as abundant traumatic resin ducts. These characteristics affect its functionality as water conductor and its technological properties. In this work we analyze for the first time the transcriptomic basis of the formation of traumatic wood in conifers, and reveal some differences with normal early- and late-wood. Microarray analysis of the differentiating traumatic wood, confirmed by quantitative RT-PCR, has revealed alterations in the transcription profile of up to 1408 genes during the first period of healing. We have grouped these genes in twelve clusters, according to their transcription profiles, and have distinguished accordingly two main phases during this first healing. Wounding induces a complete rearrangement of the transcriptional program in the cambial zone close to the injuries. At the first instance, radial growth is stopped, and a complete set of defensive genes, mostly related to biotic stress, are induced. Later on, cambial activity is restored in the lateral borders of the wound, even at a high rate. During this second stage certain genes related to early-wood formation, including genes involved in cell wall formation and transcription factors, are significantly overexpressed, while certain late-wood related genes are repressed. Additionally, significant alterations in the transcription profile of abundant non annotated genes are reported.
Two phloem nitrate transporters, NRT1.11 and NRT1.12, are important for redistributing xylem-borne nitrate to enhance plant growth.

PubMed

Hsu, Po-Kai; Tsay, Yi-Fang

2013-10-01

This study of the Arabidopsis (Arabidopsis thaliana) nitrate transporters NRT1.11 and NRT1.12 reveals how the interplay between xylem and phloem transport of nitrate ensures optimal nitrate distribution in leaves for plant growth. Functional analysis in Xenopus laevis oocytes showed that both NRT1.11 and NRT1.12 are low-affinity nitrate transporters. Quantitative reverse transcription-polymerase chain reaction and immunoblot analysis showed higher expression of these two genes in larger expanded leaves. Green fluorescent protein and β-glucuronidase reporter analyses indicated that NRT1.11 and NRT1.12 are plasma membrane transporters expressed in the companion cells of the major vein. In nrt1.11 nrt1.12 double mutants, more root-fed (15)NO3(-) was translocated to mature and larger expanded leaves but less to the youngest tissues, suggesting that NRT1.11 and NRT1.12 are required for transferring root-derived nitrate into phloem in the major veins of mature and larger expanded leaves for redistributing to the youngest tissues. Distinct from the wild type, nrt1.11 nrt1.12 double mutants show no increase of plant growth at high nitrate supply. These data suggested that NRT1.11 and NRT1.12 are involved in xylem-to-phloem transfer for redistributing nitrate into developing leaves, and such nitrate redistribution is a critical step for optimal plant growth enhanced by increasing external nitrate.
Metabolite profiling reveals a role for atypical cinnamyl alcohol dehydrogenase CAD1 in the synthesis of coniferyl alcohol in tobacco xylem.

PubMed

Damiani, Isabelle; Morreel, Kris; Danoun, Saïda; Goeminne, Geert; Yahiaoui, Nabila; Marque, Christiane; Kopka, Joachim; Messens, Eric; Goffner, Deborah; Boerjan, Wout; Boudet, Alain-Michel; Rochange, Soizic

2005-11-01

In angiosperms, lignin is built from two main monomers, coniferyl and sinapyl alcohol, which are incorporated respectively as G and S units in the polymer. The last step of their synthesis has so far been considered to be performed by a family of dimeric cinnamyl alcohol dehydrogenases (CAD2). However, previous studies on Eucalyptus gunnii xylem showed the presence of an additional, structurally unrelated, monomeric CAD form named CAD1. This form reduces coniferaldehyde to coniferyl alcohol, but is inactive on sinapaldehyde. In this paper, we report the functional characterization of CAD1 in tobacco (Nicotiana tabacum L.). Transgenic tobacco plants with reduced CAD1 expression were obtained through an RNAi strategy. These plants displayed normal growth and development, and detailed biochemical studies were needed to reveal a role for CAD1. Lignin analyses showed that CAD1 down-regulation does not affect Klason lignin content, and has a moderate impact on G unit content of the non-condensed lignin fraction. However, comparative metabolic profiling of the methanol-soluble phenolic fraction from basal xylem revealed significant differences between CAD1 down-regulated and wild-type plants. Eight compounds were less abundant in CAD1 down-regulated lines, five of which were identified as dimers or trimers of monolignols, each containing at least one moiety derived from coniferyl alcohol. In addition, 3-trans-caffeoyl quinic acid accumulated in the transgenic plants. Together, our results support a significant contribution of CAD1 to the synthesis of coniferyl alcohol in planta, along with the previously characterized CAD2 enzymes.
Hydraulic Limits on Maximum Plant Transpiration

NASA Astrophysics Data System (ADS)

Manzoni, S.; Vico, G.; Katul, G. G.; Palmroth, S.; Jackson, R. B.; Porporato, A. M.

2011-12-01

Photosynthesis occurs at the expense of water losses through transpiration. As a consequence of this basic carbon-water interaction at the leaf level, plant growth and ecosystem carbon exchanges are tightly coupled to transpiration. In this contribution, the hydraulic constraints that limit transpiration rates under well-watered conditions are examined across plant functional types and climates. The potential water flow through plants is proportional to both xylem hydraulic conductivity (which depends on plant carbon economy) and the difference in water potential between the soil and the atmosphere (the driving force that pulls water from the soil). Differently from previous works, we study how this potential flux changes with the amplitude of the driving force (i.e., we focus on xylem properties and not on stomatal regulation). Xylem hydraulic conductivity decreases as the driving force increases due to cavitation of the tissues. As a result of this negative feedback, more negative leaf (and xylem) water potentials would provide a stronger driving force for water transport, while at the same time limiting xylem hydraulic conductivity due to cavitation. Here, the leaf water potential value that allows an optimum balance between driving force and xylem conductivity is quantified, thus defining the maximum transpiration rate that can be sustained by the soil-to-leaf hydraulic system. To apply the proposed framework at the global scale, a novel database of xylem conductivity and cavitation vulnerability across plant types and biomes is developed. Conductivity and water potential at 50% cavitation are shown to be complementary (in particular between angiosperms and conifers), suggesting a tradeoff between transport efficiency and hydraulic safety. Plants from warmer and drier biomes tend to achieve larger maximum transpiration than plants growing in environments with lower atmospheric water demand. The predicted maximum transpiration and the corresponding leaf water
Widening of xylem conduits in a conifer tree depends on the longer time of cell expansion downwards along the stem

PubMed Central

Anfodillo, Tommaso; Deslauriers, Annie; Menardi, Roberto; Tedoldi, Laura; Petit, Giai; Rossi, Sergio

2012-01-01

The diameter of vascular conduits increases towards the stem base. It has been suggested that this profile is an efficient anatomical feature for reducing the hydraulic resistance when trees grow taller. However, the mechanism that controls the cell diameter along the plant is not fully understood. The timing of cell differentiation along the stem was investigated. Cambial activity and cell differentiation were investigated in a Picea abies tree (11.5 m in height) collecting microsamples at nine different heights (from 1 to 9 m) along the stem with a 4 d time interval. Wood sections (8–12 μm thick) were stained and observed under a light microscope with polarized light to differentiate the developing xylem cells. Cell wall lignification was detected using cresyl violet acetate. The first enlarging cells appeared almost simultaneously along the tree axis indicating that cambium activation is not height-dependent. A significant increase in the duration of the cell expansion phase was observed towards the tree base: at 9 m from the ground, xylem cells expanded for 7 d, at 6 m for 14 d, and at 3 m for 19 d. The duration of the expansion phase is positively correlated with the lumen area of the tracheids (r2=0.68, P < 0.01) at the same height. By contrast, thickness of the cell wall of the earlywood did not show any trend with height. The lumen area of the conduits down the stem appeared linearly dependent on time during which differentiating cells remained in the expansion phase. However, the inductive signal of such long-distance patterned differentiation remains to be identified. PMID:22016427
Widening of xylem conduits in a conifer tree depends on the longer time of cell expansion downwards along the stem.

PubMed

Anfodillo, Tommaso; Deslauriers, Annie; Menardi, Roberto; Tedoldi, Laura; Petit, Giai; Rossi, Sergio

2012-01-01

The diameter of vascular conduits increases towards the stem base. It has been suggested that this profile is an efficient anatomical feature for reducing the hydraulic resistance when trees grow taller. However, the mechanism that controls the cell diameter along the plant is not fully understood. The timing of cell differentiation along the stem was investigated. Cambial activity and cell differentiation were investigated in a Picea abies tree (11.5 m in height) collecting microsamples at nine different heights (from 1 to 9 m) along the stem with a 4 d time interval. Wood sections (8-12 μm thick) were stained and observed under a light microscope with polarized light to differentiate the developing xylem cells. Cell wall lignification was detected using cresyl violet acetate. The first enlarging cells appeared almost simultaneously along the tree axis indicating that cambium activation is not height-dependent. A significant increase in the duration of the cell expansion phase was observed towards the tree base: at 9 m from the ground, xylem cells expanded for 7 d, at 6 m for 14 d, and at 3 m for 19 d. The duration of the expansion phase is positively correlated with the lumen area of the tracheids (r(2)=0.68, P < 0.01) at the same height. By contrast, thickness of the cell wall of the earlywood did not show any trend with height. The lumen area of the conduits down the stem appeared linearly dependent on time during which differentiating cells remained in the expansion phase. However, the inductive signal of such long-distance patterned differentiation remains to be identified.
A split-root technique for measuring root water potential.

PubMed

Adeoye, K B; Rawlins, S L

1981-07-01

Water encounters various resistances in moving along a path of decreasing potential energy from the soil through the plant to the atmosphere. The reported relative magnitudes of these pathway resistances vary widely and often these results are conflicting. One reason for such inconsistency is the difficulty in measuring the potential drop across various segments of the soil-plant-atmosphere continuum. The measurement of water potentials at the soil-root interface and in the root xylem of a transpiring plant remains a challenging problem.In the divided root experiment reported here, the measured water potential of an enclosed, nonabsorbing branch of the root system of young corn (Bonanza) plants to infer the water potential of the remaining roots growing in soil was used. The selected root branch of the seedling was grown in a specially constructed Teflon test tube into which a screen-enclosed thermocouple psychrometer was inserted and sealed to monitor the root's water potential. The root and its surrounding atmosphere were assumed to be in vapor equilibrium.
A Split-Root Technique for Measuring Root Water Potential

PubMed Central

Adeoye, Kingsley B.; Rawlins, Stephen L.

1981-01-01

Water encounters various resistances in moving along a path of decreasing potential energy from the soil through the plant to the atmosphere. The reported relative magnitudes of these pathway resistances vary widely and often these results are conflicting. One reason for such inconsistency is the difficulty in measuring the potential drop across various segments of the soil-plant-atmosphere continuum. The measurement of water potentials at the soil-root interface and in the root xylem of a transpiring plant remains a challenging problem. In the divided root experiment reported here, the measured water potential of an enclosed, nonabsorbing branch of the root system of young corn (Bonanza) plants to infer the water potential of the remaining roots growing in soil was used. The selected root branch of the seedling was grown in a specially constructed Teflon test tube into which a screen-enclosed thermocouple psychrometer was inserted and sealed to monitor the root's water potential. The root and its surrounding atmosphere were assumed to be in vapor equilibrium. Images PMID:16661886
Vascular functioning and the water balance of ripening kiwifruit (Actinidia chinensis) berries

PubMed Central

Clearwater, Michael J.; Luo, Zhiwei; Ong, Sam Eng Chye; Blattmann, Peter; Thorp, T. Grant

2012-01-01

Indirect evidence suggests that water supply to fleshy fruits during the final stages of development occurs through the phloem, with the xylem providing little water, or acting as a pathway for water loss back to the plant. This inference was tested by examining the water balance and vascular functioning of ripening kiwifruit berries (Actinidia chinensis var. chinensis ‘Hort16A’) exhibiting a pre-harvest ‘shrivel’ disorder in California, and normal development in New Zealand. Dye labelling and mass balance experiments indicated that the xylem and phloem were both functional and contributed approximately equally to the fruit water supply during this stage of development. The modelled fruit water balance was dominated by transpiration, with net water loss under high vapour pressure deficit (Da) conditions in California, but a net gain under cooler New Zealand conditions. Direct measurement of pedicel sap flow under controlled conditions confirmed inward flows in both the phloem and xylem under conditions of both low and high Da. Phloem flows were required for growth, with gradual recovery after a step increase in Da. Xylem flows alone were unable to support growth, but did supply transpiration and were responsive to Da-induced pressure fluctuations. The results suggest that the shrivel disorder was a consequence of a high fruit transpiration rate, and that the perception of complete loss or reversal of inward xylem flows in ripening fruits should be re-examined. PMID:22155631
How to become a tree without wood--biomechanical analysis of the stem of Carica papaya L.

PubMed

Kempe, A; Lautenschläger, T; Lange, A; Neinhuis, C

2014-01-01

Carica papaya L. does not contain wood, according to the botanical definition of wood as lignified secondary xylem. Despite its parenchymatous secondary xylem, these plants are able to grow up to 10-m high. This is surprising, as wooden structural elements are the ubiquitous strategy for supporting height growth in plants. Proposed possible alternative principles to explain the compensation for lack of wood in C. papaya are turgor pressure of the parenchyma, lignified phloem fibres in the bark, or a combination of the two. Interestingly, lignified tissue comprises only 5-8% of the entire stem mass. Furthermore, the phloem fibres do not form a compact tube enclosing the xylem, but instead form a mesh tubular structure. To investigate the mechanism of papaya's unusually high mechanical strength, a set of mechanical measurements were undertaken on whole stems and tissue sections of secondary phloem and xylem. The structural Young's modulus of mature stems reached 2.5 GPa. Since this is low compared to woody plants, the flexural rigidity of papaya stem construction may mainly be based on a higher second moment of inertia. Additionally, stem turgor pressure was determined indirectly by immersing specimens in sucrose solutions of different osmolalities, followed by mechanical tests; turgor pressure was between 0.82 and 1.25 MPa, indicating that turgor is essential for flexural rigidity of the entire stem. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.
The challenge of tree height in Eucalyptus regnans: when xylem tapering overcomes hydraulic resistance.

PubMed

Petit, Giai; Pfautsch, Sebastian; Anfodillo, Tommaso; Adams, Mark A

2010-09-01

*Recent research suggests that increasing conduit tapering progressively reduces hydraulic constraints caused by tree height. Here, we tested this hypothesis using the tallest hardwood species, Eucalyptus regnans. *Vertical profiles of conduit dimensions and vessel density were measured for three mature trees of height 47, 51 and 63 m. *Mean hydraulic diameter (Dh) increased rapidly from the tree apex to the point of crown insertion, with the greatest degree of tapering yet reported (b > 0.33). Conduit tapering was such that most of the total resistance was found close to the apex (82-93% within the first 1 m of stem) and the path length effect was reduced by a factor of 2000. Vessel density (VD) declined from the apex to the base of each tree, with scaling parameters being similar for all trees (a = 4.6; b = -0.5). *Eucalyptus regnans has evolved a novel xylem design that ensures a high hydraulic efficiency. This feature enables the species to grow quickly to heights of 50-60 m, beyond the maximum height of most other hardwood trees.
Effect of Leaf Water Potential on Internal Humidity and CO 2 Dissolution: Reverse Transpiration and Improved Water Use Efficiency under Negative Pressure

DOE PAGES

Vesala, Timo; Sevanto, Sanna; Grönholm, Tiia; ...

2017-02-06

The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but with much lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flatmore » surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO 2, thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO 2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Here, our results indicate that the reduction in vapor pressures of water and CO 2 could enhance plant water use efficiency up to about 10% at a leaf water potential of -2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. Lastly, the omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO 2 concentration based on
Effect of Leaf Water Potential on Internal Humidity and CO 2 Dissolution: Reverse Transpiration and Improved Water Use Efficiency under Negative Pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vesala, Timo; Sevanto, Sanna; Grönholm, Tiia

The pull of water from the soil to the leaves causes water in the transpiration stream to be under negative pressure decreasing the water potential below zero. The osmotic concentration also contributes to the decrease in leaf water potential but with much lesser extent. Thus, the surface tension force is approximately balanced by a force induced by negative water potential resulting in concavely curved water-air interfaces in leaves. The lowered water potential causes a reduction in the equilibrium water vapor pressure in internal (sub-stomatal/intercellular) cavities in relation to that over water with the potential of zero, i.e., over the flatmore » surface. The curved surface causes a reduction also in the equilibrium vapor pressure of dissolved CO 2, thus enhancing its physical solubility to water. Although the water vapor reduction is acknowledged by plant physiologists its consequences for water vapor exchange at low water potential values have received very little attention. Consequences of the enhanced CO 2 solubility to a leaf water-carbon budget have not been considered at all before this study. We use theoretical calculations and modeling to show how the reduction in the vapor pressures affects transpiration and carbon assimilation rates. Here, our results indicate that the reduction in vapor pressures of water and CO 2 could enhance plant water use efficiency up to about 10% at a leaf water potential of -2 MPa, and much more when water potential decreases further. The low water potential allows for a direct stomatal water vapor uptake from the ambient air even at sub-100% relative humidity values. This alone could explain the observed rates of foliar water uptake by e.g., the coastal redwood in the fog belt region of coastal California provided the stomata are sufficiently open. Lastly, the omission of the reduction in the water vapor pressure causes a bias in the estimates of the stomatal conductance and leaf internal CO 2 concentration based on
Plant adaptation to low atmospheric pressures: potential molecular responses

NASA Technical Reports Server (NTRS)

Ferl, Robert J.; Schuerger, Andrew C.; Paul, Anna-Lisa; Gurley, William B.; Corey, Kenneth; Bucklin, Ray

2002-01-01

There is an increasing realization that it may be impossible to attain Earth normal atmospheric pressures in orbital, lunar, or Martian greenhouses, simply because the construction materials do not exist to meet the extraordinary constraints imposed by balancing high engineering requirements against high lift costs. This equation essentially dictates that NASA have in place the capability to grow plants at reduced atmospheric pressure. Yet current understanding of plant growth at low pressures is limited to just a few experiments and relatively rudimentary assessments of plant vigor and growth. The tools now exist, however, to make rapid progress toward understanding the fundamental nature of plant responses and adaptations to low pressures, and to develop strategies for mitigating detrimental effects by engineering the growth conditions or by engineering the plants themselves. The genomes of rice and the model plant Arabidopsis thaliana have recently been sequenced in their entirety, and public sector and commercial DNA chips are becoming available such that thousands of genes can be assayed at once. A fundamental understanding of plant responses and adaptation to low pressures can now be approached and translated into procedures and engineering considerations to enhance plant growth at low atmospheric pressures. In anticipation of such studies, we present here the background arguments supporting these contentions, as well as informed speculation about the kinds of molecular physiological responses that might be expected of plants in low-pressure environments.
Insight into the hydraulics and resilience of Ponderosa pine seedlings using a mechanistic ecohydrologic model

NASA Astrophysics Data System (ADS)

Maneta, M. P.; Simeone, C.; Dobrowski, S.; Holden, Z.; Sapes, G.; Sala, A.; Begueria, S.

2017-12-01

In semiarid regions, drought-induced seedling mortality is considered to be caused by failure in the tree hydraulic column. Understanding the mechanisms that cause hydraulic failure and death in seedlings is important, among other things, to diagnose where some tree species may fail to regenerate, triggering demographic imbalances in the forest that could result in climate-driven shifts of tree species. Ponderosa pine is a common lower tree line species in the western US. Seedlings of ponderosa pine are often subject to low soil water potentials, which require lower water potentials in the xylem and leaves to maintain the negative pressure gradient that drives water upward. The resilience of the hydraulic column to hydraulic tension is species dependent, but from greenhouse experiments, we have identified general tension thresholds beyond which loss of xylem conductivity becomes critical, and mortality in Ponderosa pine seedlings start to occur. We describe this hydraulic behavior of plants using a mechanistic soil-vegetation-atmosphere transfer model. Before we use this models to understand water-stress induced seedling mortality at the landscape scale, we perform a modeling analysis of the dynamics of soil moisture, transpiration, leaf water potential and loss of plant water conductivity using detailed data from our green house experiments. The analysis is done using a spatially distributed model that simulates water fluxes, energy exchanges and water potentials in the soil-vegetation-atmosphere continuum. Plant hydraulic and physiological parameters of this model were calibrated using Monte Carlo methods against information on soil moisture, soil hydraulic potential, transpiration, leaf water potential and percent loss of conductivity in the xylem. This analysis permits us to construct a full portrait of the parameter space for Ponderosa pine seedling and generate posterior predictive distributions of tree response to understand the sensitivity of transpiration
Response of the water status of soybean to changes in soil water potentials controlled by the water pressure in microporous tubes.

PubMed

Steinberg, S L; Henninger, D L

1997-12-01

Water transport through a microporous tube-soil-plant system was investigated by measuring the response of soil and plant water status to step change reductions in the water pressure within the tubes. Soybeans were germinated and grown in a porous ceramic 'soil' at a porous tube water pressure of -0.5 kpa for 28 d. During this time, the soil matric potential was nearly in equilibrium with tube water pressure. Water pressure in the porous tubes was then reduced to either -1.0, -1.5 or -2.0 kPa. Sap flow rates, leaf conductance and soil, root and leaf water potentials were measured before and after this change. A reduction in porous tube water pressure from -0.5 to -1.0 or -1.5 kPa did not result in any significant change in soil or plant water status. A reduction in porous tube water pressure to -2.0 kPa resulted in significant reductions in sap flow, leaf conductance, and soil, root and leaf water potentials. Hydraulic conductance, calculated as the transpiration rate/delta psi between two points in the water transport pathway, was used to analyse water transport through the tube-soil-plant continuum. At porous tube water pressures of -0.5 to-1.5 kPa soil moisture was readily available and hydraulic conductance of the plant limited water transport. At -2.0 kPa, hydraulic conductance of the bulk soil was the dominant factor in water movement.
Response of the water status of soybean to changes in soil water potentials controlled by the water pressure in microporous tubes

NASA Technical Reports Server (NTRS)

Steinberg, S. L.; Henninger, D. L.

1997-01-01

Water transport through a microporous tube-soil-plant system was investigated by measuring the response of soil and plant water status to step change reductions in the water pressure within the tubes. Soybeans were germinated and grown in a porous ceramic 'soil' at a porous tube water pressure of -0.5 kpa for 28 d. During this time, the soil matric potential was nearly in equilibrium with tube water pressure. Water pressure in the porous tubes was then reduced to either -1.0, -1.5 or -2.0 kPa. Sap flow rates, leaf conductance and soil, root and leaf water potentials were measured before and after this change. A reduction in porous tube water pressure from -0.5 to -1.0 or -1.5 kPa did not result in any significant change in soil or plant water status. A reduction in porous tube water pressure to -2.0 kPa resulted in significant reductions in sap flow, leaf conductance, and soil, root and leaf water potentials. Hydraulic conductance, calculated as the transpiration rate/delta psi between two points in the water transport pathway, was used to analyse water transport through the tube-soil-plant continuum. At porous tube water pressures of -0.5 to-1.5 kPa soil moisture was readily available and hydraulic conductance of the plant limited water transport. At -2.0 kPa, hydraulic conductance of the bulk soil was the dominant factor in water movement.
Cellulose synthase complexes display distinct dynamic behaviors during xylem transdifferentiation.

PubMed

Watanabe, Yoichiro; Schneider, Rene; Barkwill, Sarah; Gonzales-Vigil, Eliana; Hill, Joseph L; Samuels, A Lacey; Persson, Staffan; Mansfield, Shawn D

2018-06-05

In plants, plasma membrane-embedded CELLULOSE SYNTHASE (CESA) enzyme complexes deposit cellulose polymers into the developing cell wall. Cellulose synthesis requires two different sets of CESA complexes that are active during cell expansion and secondary cell wall thickening, respectively. Hence, developing xylem cells, which first undergo cell expansion and subsequently deposit thick secondary walls, need to completely reorganize their CESA complexes from primary wall- to secondary wall-specific CESAs. Using live-cell imaging, we analyzed the principles underlying this remodeling. At the onset of secondary wall synthesis, the primary wall CESAs ceased to be delivered to the plasma membrane and were gradually removed from both the plasma membrane and the Golgi. For a brief transition period, both primary wall- and secondary wall-specific CESAs coexisted in banded domains of the plasma membrane where secondary wall synthesis is concentrated. During this transition, primary and secondary wall CESAs displayed discrete dynamic behaviors and sensitivities to the inhibitor isoxaben. As secondary wall-specific CESAs were delivered and inserted into the plasma membrane, the primary wall CESAs became concentrated in prevacuolar compartments and lytic vacuoles. This adjustment in localization between the two CESAs was accompanied by concurrent decreased primary wall CESA and increased secondary wall CESA protein abundance. Our data reveal distinct and dynamic subcellular trafficking patterns that underpin the remodeling of the cellulose biosynthetic machinery, resulting in the removal and degradation of the primary wall CESA complex with concurrent production and recycling of the secondary wall CESAs. Copyright © 2018 the Author(s). Published by PNAS.

Arabidopsis VASCULAR-RELATED UNKNOWN PROTEIN1 Regulates Xylem Development and Growth by a Conserved Mechanism That Modulates Hormone Signaling1[W][OPEN

PubMed Central

Grienenberger, Etienne; Douglas, Carl J.

2014-01-01

Despite a strict conservation of the vascular tissues in vascular plants (tracheophytes), our understanding of the genetic basis underlying the differentiation of secondary cell wall-containing cells in the xylem of tracheophytes is still far from complete. Using coexpression analysis and phylogenetic conservation across sequenced tracheophyte genomes, we identified a number of Arabidopsis (Arabidopsis thaliana) genes of unknown function whose expression is correlated with secondary cell wall deposition. Among these, the Arabidopsis VASCULAR-RELATED UNKNOWN PROTEIN1 (VUP1) gene encodes a predicted protein of 24 kD with no annotated functional domains but containing domains that are highly conserved in tracheophytes. Here, we show that the VUP1 expression pattern, determined by promoter-β-glucuronidase reporter gene expression, is associated with vascular tissues, while vup1 loss-of-function mutants exhibit collapsed morphology of xylem vessel cells. Constitutive overexpression of VUP1 caused dramatic and pleiotropic developmental defects, including severe dwarfism, dark green leaves, reduced apical dominance, and altered photomorphogenesis, resembling brassinosteroid-deficient mutants. Constitutive overexpression of VUP homologs from multiple tracheophyte species induced similar defects. Whole-genome transcriptome analysis revealed that overexpression of VUP1 represses the expression of many brassinosteroid- and auxin-responsive genes. Additionally, deletion constructs and site-directed mutagenesis were used to identify critical domains and amino acids required for VUP1 function. Altogether, our data suggest a conserved role for VUP1 in regulating secondary wall formation during vascular development by tissue- or cell-specific modulation of hormone signaling pathways. PMID:24567189
High pressure processing's potential to inactivate norovirus and other fooodborne viruses

USDA-ARS?s Scientific Manuscript database

High pressure processing (HPP) can inactivate human norovirus. However, all viruses are not equally susceptible to HPP. Pressure treatment parameters such as required pressure levels, initial pressurization temperatures, and pressurization times substantially affect inactivation. How food matrix ...
Applying Chemical Potential and Partial Pressure Concepts to Understand the Spontaneous Mixing of Helium and Air in a Helium-Inflated Balloon

ERIC Educational Resources Information Center

Jee-Yon Lee; Hee-Soo Yoo; Jong Sook Park; Kwang-Jin Hwang; Jin Seog Kim

2005-01-01

The spontaneous mixing of helium and air in a helium-inflated balloon is described in an experiment in which the partial pressure of the gases in the balloon are determined from the mole factions and the total pressure measured in the balloon. The results described provide a model for teaching concepts of partial pressure, chemical potential, and…
Osmotic potential and projected drought tolerance of four phreatophytic shrub species in Owens Valley, California

USGS Publications Warehouse

Dileanis, Peter D.; Groeneveld, David P.

1989-01-01

A substantial quantity of the water used by plant communities growing on the floor of Owens Valley, California, is derived from a shallow unconfined aquifer. Fluctuations in the water table caused by ground-water withdrawal may result in periods when this water supply is not accessible to plants. The capacity of the plants to adapt to these periods of water loss depends on the availability of water stored in the soil and on physiological characteristics related to the ability of the plants to resist dehydration and wilting. Osmotic adjustment occurred in four phreatophytic shrub species at sites near Bishop, California, where the water table had been lowered by a system of pump-equipped wells installed in the vicinity of vegetation transects. The pressure-volume technique was used to determine osmotic potential and cell-wall elasticity between March 1985 and September 1986 for Atriplex torreyi, Chrysothamnus nauseosus , Sarcobatus verm iculatus , and Artemisia tridentata. Although not usually classified as a phreatophyte, Artemisia tridentata, where it grows on the valley floor, is apparently dependent on the depth to the water table. During late summer, osmotic potentials were 0.37 to 0.41 MPa (megapascal) lower in plants growing on the site where the water table had been lowered compared to an adjacent site where the water table remained at its natural levels. Measurements of soil matric potential at the two sites indicated that osmotic adjustment occurred in response to stress caused by lowering the water table. A theoretical lower limit of osmotic adjustment was determined by comparing initial cell osmotic potentials with initial xylem water potentials. These experimentally derived limits indicated that Atriplex torreyi and S. vermiculatus may maintain leaf cell turgor at significantly lower cell water potentials (about -4.5 MPa) than C. nauseosus or Artemisia tridentata (about -2.5 MPa), which allows them to function in drier soil environments.
Osmotic potential and projected drought tolerance of four phreatophytic shrub species in Owens Valley, California

USGS Publications Warehouse

Dileanis, Peter D.; Groeneveld, D.P.

1988-01-01

A large part of the water used by plant communities growing on the floor of Owens Valley, California, is derived from a shallow unconfined aquifer. Fluctuations in the water table caused by groundwater withdrawal may result in periods when this water supply is not accessible to plants. The capacity of the plants to adapt to these periods of water loss depend on the availability of water stored in the soil and on physiological characteristics related to the ability of the plants to resist dehydration and wilting. Osmotic adjustment occurred in four phreatophytic shrub species at sites near bishop, California, where the water table had been lowered by a system of pump-equipped wells installed in the vicinity of vegetation transects. The pressure-volume techniques was used to determine osmotic potential and cell-wall elasticity between March 1985 and September 1986 for Atriplex torreyi, Chrysothamnus nauseosus , Sarcobatus vermiculatus, and Artemisia tridentata. Although not usually classified as a phreatophyte, Artemisia tridentata, where it grows on the valley floor, is apparently dependent on the depth to the water table. During late summer, osmotic potentials were 0.37 to 0.41 megapascal lower in plants growing on the site where the water table had been lowered compared to an adjacent site where the water table remained at its natural levels. Measurements of soil matric potential at the two sites indicated that osmotic adjustment occurred in response to stress caused by lowering the water table. A theoretical lower limit of osmotic adjustment was determined by comparing initial cell osmotic potentials with initial xylem water potentials. These experimentally derived limits indicated that A. torreyi and S. vermiculatus may maintain leaf cell turgor at significantly lower cell water potentials (about -4.5 megapascals) than C. nauseosus or A. tridentata (about -2.5 megapascals) and allows them to function in dryer soil environments. (Author 's abstract)
Hydraulic limits on maximum plant transpiration and the emergence of the safety-efficiency trade-off.

PubMed

Manzoni, Stefano; Vico, Giulia; Katul, Gabriel; Palmroth, Sari; Jackson, Robert B; Porporato, Amilcare

2013-04-01

Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water transport and hence carbon uptake by leaves. While more negative xylem water potentials provide a larger driving force for water transport, they also cause cavitation that limits hydraulic conductivity. An optimum balance between driving force and cavitation occurs at intermediate water potentials, thus defining the maximum transpiration rate the xylem can sustain (denoted as E(max)). The presence of this maximum raises the question as to whether plants regulate transpiration through stomata to function near E(max). To address this question, we calculated E(max) across plant functional types and climates using a hydraulic model and a global database of plant hydraulic traits. The predicted E(max) compared well with measured peak transpiration across plant sizes and growth conditions (R = 0.86, P < 0.001) and was relatively conserved among plant types (for a given plant size), while increasing across climates following the atmospheric evaporative demand. The fact that E(max) was roughly conserved across plant types and scales with the product of xylem saturated conductivity and water potential at 50% cavitation was used here to explain the safety-efficiency trade-off in plant xylem. Stomatal conductance allows maximum transpiration rates despite partial cavitation in the xylem thereby suggesting coordination between stomatal regulation and xylem hydraulic characteristics. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.
Impact of Laurel Wilt, Caused by Raffaelea lauricola, on Leaf Gas Exchange and Xylem Sap Flow in Avocado, Persea americana.

PubMed

Ploetz, Randy C; Schaffer, Bruce; Vargas, Ana I; Konkol, Joshua L; Salvatierra, Juanpablo; Wideman, Ronney

2015-04-01

Laurel wilt, caused by Raffaelea lauricola, is a destructive disease of avocado (Persea americana). The susceptibility of different cultivars and races was examined previously but more information is needed on how this host responds to the disease. In the present study, net CO2 assimilation (A), stomatal conductance of H2O (gs), transpiration (E), water use efficiency (WUE), and xylem sap flow rates were assessed in cultivars that differed in susceptibility. After artificial inoculation with R. lauricola, there was a close relationship between symptom development and reductions in A, gs, E, WUE, and mean daily sap flow in the most susceptible cultivar, 'Russell', and significantly greater disease and lower A, gs, E, WUE, and sap flow rates were usually detected after 15 days compared with the more tolerant 'Brogdon' and 'Marcus Pumpkin'. Significant differences in preinoculation A, gs, E, and WUE were generally not detected among the cultivars but preinoculation sap flow rates were greater in Russell than in Brogdon and Marcus Pumpkin. Preinoculation sap flow rates and symptom severity for individual trees were correlated at the end of an experiment (r=0.46), indicating that a plant's susceptibility to laurel wilt was related to its ability to conduct water. The potential management of this disease with clonal rootstocks that reduce sap flow rates is discussed.
Functional relationships between wood structure and vulnerability to xylem cavitation in races of Eucalyptus globulus differing in wood density.

PubMed

Barotto, Antonio José; Monteoliva, Silvia; Gyenge, Javier; Martinez-Meier, Alejandro; Fernandez, María Elena

2018-02-01

Wood density can be considered as a measure of the internal wood structure, and it is usually used as a proxy measure of other mechanical and functional traits. Eucalyptus is one of the most important commercial forestry genera worldwide, but the relationship between wood density and vulnerability to cavitation in this genus has been little studied. The analysis is hampered by, among other things, its anatomical complexity, so it becomes necessary to address more complex techniques and analyses to elucidate the way in which the different anatomical elements are functionally integrated. In this study, vulnerability to cavitation in two races of Eucalyptus globulus Labill. with different wood density was evaluated through Path analysis, a multivariate method that allows evaluation of descriptive models of causal relationship between variables. A model relating anatomical variables with wood properties and functional parameters was proposed and tested. We found significant differences in wood basic density and vulnerability to cavitation between races. The main exogenous variables predicting vulnerability to cavitation were vessel hydraulic diameter and fibre wall fraction. Fibre wall fraction showed a direct impact on wood basic density and the slope of vulnerability curve, and an indirect and negative effect over the pressure imposing 50% of conductivity loss (P50) through them. Hydraulic diameter showed a direct negative effect on P50, but an indirect and positive influence over this variable through wood density on one hand, and through maximum hydraulic conductivity (ks max) and slope on the other. Our results highlight the complexity of the relationship between xylem efficiency and safety in species with solitary vessels such as Eucalyptus spp., with no evident compromise at the intraspecific level. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Wall relaxation in growing stems: comparison of four species and assessment of measurement techniques

NASA Technical Reports Server (NTRS)

Cosgrove, D. J.

1987-01-01

This study was carried out to develop improved methods for measuring in-vivo stress relaxation of growing tissues and to compare relaxation in the stems of four different species. When water uptake by growing tissue is prevented, in-vivo stress relaxation occurs because continued wall loosening reduces wall stress and cell turgor pressure. With this procedure one may measure the yield threshold for growth (Y), the turgor pressure in excess of the yield threshold (P-Y), and the physiological wall extensibility (phi). Three relaxation techniques proved useful: "turgor-relaxation", "balance-pressure" and "pressure-block". In the turgor-relaxation method, water is withheld from growing tissue and the reduction in turgor is measured directly with the pressure probe. This technique gives absolute values for P and Y, but requires tissue excision. In the balance-pressure technique, the excised growing region is sealed in a pressure chamber, and the subsequent reduction in water potential is measured as the applied pressure needed to return xylem sap to the cut surface. This method is simple, but only measures (P-Y), not the individual values of P and Y. In the pressure-block technique, the growing tissue is sealed into a pressure chamber, growth is monitored continuously, and just sufficient pressure is applied to the chamber to block growth. The method gives high-resolution kinetics of relaxation and does not require tissue excision, but only measures (P-Y). The three methods gave similar results when applied to the growing stems of pea (Pisum sativum L.), cucumber (Cucumis sativus L.), soybean (Glycine max (L.) Merr.) and zucchini (Curcubita pepo L.) seedlings. Values for (P-Y) averaged between 1.4 and 2.7 bar, depending on species. Yield thresholds averaged between 1.3 and 3.0 bar. Compared with the other methods, relaxation by pressure-block was faster and exhibited dynamic changes in wall-yielding properties. The two pressure-chamber methods were also used to measure
Sensing of blood pressure increase by transient receptor potential vanilloid 1 receptors on baroreceptors.

PubMed

Sun, Hao; Li, De-Pei; Chen, Shao-Rui; Hittelman, Walter N; Pan, Hui-Lin

2009-12-01

The arterial baroreceptor is critically involved in the autonomic regulation of homoeostasis. The transient receptor potential vanilloid 1 (TRPV1) receptor is expressed on both somatic and visceral sensory neurons. Here, we examined the TRPV1 innervation of baroreceptive pathways and its functional significance in the baroreflex. Resiniferatoxin (RTX), an ultrapotent analog of capsaicin, was used to ablate TRPV1-expressing afferent neurons and fibers in adult rats. Immunofluorescence labeling revealed that TRPV1 immunoreactivity was present on nerve fibers and terminals in the adventitia of the ascending aorta and aortic arch, the nodose ganglion neurons, and afferent fibers in the solitary tract of the brainstem. RTX treatment eliminated TRPV1 immunoreactivities in the aorta, nodose ganglion, and solitary tract. Renal sympathetic nerve activity, blood pressure, and heart rate were recorded in anesthetized rats. The baroreflex was triggered by lowering and raising blood pressure through intravenous infusion of sodium nitroprusside and phenylephrine, respectively. Inhibition of sympathetic nerve activity and heart rate by the phenylephrine-induced increase in blood pressure was largely impaired in RTX-treated rats. The maximum gain of the baroreflex function was significantly lower in RTX-treated than vehicle-treated rats. Furthermore, blocking of TRPV1 receptors significantly blunted the baroreflex and decreased the maximum gain of baroreflex function in the high blood pressure range. Our findings provide important new information that TRPV1 is expressed along the entire baroreceptive afferent pathway. TRPV1 receptors expressed on baroreceptive nerve endings can function as mechanoreceptors to detect the increase in blood pressure and maintain the homoeostasis.
Sensing of Blood Pressure Increase by Transient Receptor Potential Vanilloid 1 Receptors on Baroreceptors

PubMed Central

Sun, Hao; Li, De-Pei; Chen, Shao-Rui; Hittelman, Walter N.

2009-01-01

The arterial baroreceptor is critically involved in the autonomic regulation of homoeostasis. The transient receptor potential vanilloid 1 (TRPV1) receptor is expressed on both somatic and visceral sensory neurons. Here, we examined the TRPV1 innervation of baroreceptive pathways and its functional significance in the baroreflex. Resiniferatoxin (RTX), an ultrapotent analog of capsaicin, was used to ablate TRPV1-expressing afferent neurons and fibers in adult rats. Immunofluorescence labeling revealed that TRPV1 immunoreactivity was present on nerve fibers and terminals in the adventitia of the ascending aorta and aortic arch, the nodose ganglion neurons, and afferent fibers in the solitary tract of the brainstem. RTX treatment eliminated TRPV1 immunoreactivities in the aorta, nodose ganglion, and solitary tract. Renal sympathetic nerve activity, blood pressure, and heart rate were recorded in anesthetized rats. The baroreflex was triggered by lowering and raising blood pressure through intravenous infusion of sodium nitroprusside and phenylephrine, respectively. Inhibition of sympathetic nerve activity and heart rate by the phenylephrine-induced increase in blood pressure was largely impaired in RTX-treated rats. The maximum gain of the baroreflex function was significantly lower in RTX-treated than vehicle-treated rats. Furthermore, blocking of TRPV1 receptors significantly blunted the baroreflex and decreased the maximum gain of baroreflex function in the high blood pressure range. Our findings provide important new information that TRPV1 is expressed along the entire baroreceptive afferent pathway. TRPV1 receptors expressed on baroreceptive nerve endings can function as mechanoreceptors to detect the increase in blood pressure and maintain the homoeostasis. PMID:19726694
No evidence for an open vessel effect in centrifuge-based vulnerability curves of a long-vesselled liana (Vitis vinifera).

PubMed

Jacobsen, Anna L; Pratt, R Brandon

2012-06-01

Vulnerability to cavitation curves are used to estimate xylem cavitation resistance and can be constructed using multiple techniques. It was recently suggested that a technique that relies on centrifugal force to generate negative xylem pressures may be susceptible to an open vessel artifact in long-vesselled species. Here, we used custom centrifuge rotors to measure different sample lengths of 1-yr-old stems of grapevine to examine the influence of open vessels on vulnerability curves, thus testing the hypothesized open vessel artifact. These curves were compared with a dehydration-based vulnerability curve. Although samples differed significantly in the number of open vessels, there was no difference in the vulnerability to cavitation measured on 0.14- and 0.271-m-long samples of Vitis vinifera. Dehydration and centrifuge-based curves showed a similar pattern of declining xylem-specific hydraulic conductivity (K(s)) with declining water potential. The percentage loss in hydraulic conductivity (PLC) differed between dehydration and centrifuge curves and it was determined that grapevine is susceptible to errors in estimating maximum K(s) during dehydration because of the development of vessel blockages. Our results from a long-vesselled liana do not support the open vessel artifact hypothesis. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.
Mean circulatory filling pressure: potential problems with measurement.

PubMed

Gaddis, M L; Rothe, C F; Tunin, R S; Moran, M; MacAnespie, C L

1986-10-01

Three experimental series using 22 acutely splenectomized mongrel dogs were completed to 1) compare fibrillation (Fib) and acetylcholine (ACh) injection as methods to stop the heart for the mean circulatory filling pressure (Pmcf) maneuver, and 2) test whether Pmcf equals portal venous pressure 7 s after heart stoppage (Pportal7s). Blood volume changes of -10, -20, +10, or +20 ml/kg were imposed and Pmcf and Pportal measurements were obtained. Pportal7s and Pmcf were significantly different with volume depletion but were similar under control conditions. Pmcf with ACh and Pmcf with Fib were significantly different only after a volume change of -20 ml/kg. However, severe pulmonary congestion and atelectasis were detected in animals where Ach was used to stop the heart. In some cases (with injection directly into the pulmonary artery) the damage was severe enough to cause irreversible arterial hypoxia. Thus we conclude that the repeated use of ACh may exert a detrimental influence on pulmonary function, changing the physiological status of the experimental animal. Also, the central venous pressure at 7 s of heart stoppage (Pcv7s) is not a fully accurate estimate of the true mean circulatory filling pressure during the Pmcf maneuver, because Pcv7s did not equal the Pportal7s under all experimental conditions.
Long-distance abscisic acid signalling under different vertical soil moisture gradients depends on bulk root water potential and average soil water content in the root zone.

PubMed

Puértolas, Jaime; Alcobendas, Rosalía; Alarcón, Juan J; Dodd, Ian C

2013-08-01

To determine how root-to-shoot abscisic acid (ABA) signalling is regulated by vertical soil moisture gradients, root ABA concentration ([ABA](root)), the fraction of root water uptake from, and root water potential of different parts of the root zone, along with bulk root water potential, were measured to test various predictive models of root xylem ABA concentration [RX-ABA](sap). Beans (Phaseolus vulgaris L. cv. Nassau) were grown in soil columns and received different irrigation treatments (top and basal watering, and withholding water for varying lengths of time) to induce different vertical soil moisture gradients. Root water uptake was measured at four positions within the column by continuously recording volumetric soil water content (θv). Average θv was inversely related to bulk root water potential (Ψ(root)). In turn, Ψ(root) was correlated with both average [ABA](root) and [RX-ABA](sap). Despite large gradients in θv, [ABA](root) and root water potential was homogenous within the root zone. Consequently, unlike some split-root studies, root water uptake fraction from layers with different soil moisture did not influence xylem sap (ABA). This suggests two different patterns of ABA signalling, depending on how soil moisture heterogeneity is distributed within the root zone, which might have implications for implementing water-saving irrigation techniques. © 2013 John Wiley & Sons Ltd.
Gas flow in plant microfluidic networks controlled by capillary valves

NASA Astrophysics Data System (ADS)

Capron, M.; Tordjeman, Ph.; Charru, F.; Badel, E.; Cochard, H.

2014-03-01

The xylem vessels of trees constitute a model natural microfluidic system. In this work, we have studied the mechanism of air flow in the Populus xylem. The vessel microstructure was characterized by optical microscopy, transmission electronic microscopy (TEM), and atomic force microscopy (AFM) at different length scales. The xylem vessels have length ≈15 cm and diameter ≈20μm. Flow from one vessel to the next occurs through ˜102 pits, which are grouped together at the ends of the vessels. The pits contain a thin, porous pit membrane with a thickness of 310 nm. We have measured the Young's moduli of the vessel wall and of the pits (both water-saturated and after drying) by specific nanoindentation and nanoflexion experiments with AFM. We found that both the dried and water-saturated pit membranes have Young's modulus around 0.4 MPa, in agreement with values obtained by micromolding of pits deformed by an applied pressure difference. Air injection experiments reveal that air flows through the xylem vessels when the differential pressure across a sample is larger than a critical value ΔPc=1.8 MPa. In order to model the air flow rate for ΔP ⩾ΔPc, we assumed the pit membrane to be a porous medium that is strained by the applied pressure difference. Water menisci in the pit pores play the role of capillary valves, which open at ΔP =ΔPc. From the point of view of the plant physiology, this work presents a basic understanding of the physics of bordered pits.
Novel wave power analysis linking pressure-flow waves, wave potential, and the forward and backward components of hydraulic power.

PubMed

Mynard, Jonathan P; Smolich, Joseph J

2016-04-15

Wave intensity analysis provides detailed insights into factors influencing hemodynamics. However, wave intensity is not a conserved quantity, so it is sensitive to diameter variations and is not distributed among branches of a junction. Moreover, the fundamental relation between waves and hydraulic power is unclear. We, therefore, propose an alternative to wave intensity called "wave power," calculated via incremental changes in pressure and flow (dPdQ) and a novel time-domain separation of hydraulic pressure power and kinetic power into forward and backward wave-related components (ΠP±and ΠQ±). Wave power has several useful properties:1) it is obtained directly from flow measurements, without requiring further calculation of velocity;2) it is a quasi-conserved quantity that may be used to study the relative distribution of waves at junctions; and3) it has the units of power (Watts). We also uncover a simple relationship between wave power and changes in ΠP±and show that wave reflection reduces transmitted power. Absolute values of ΠP±represent wave potential, a recently introduced concept that unifies steady and pulsatile aspects of hemodynamics. We show that wave potential represents the hydraulic energy potential stored in a compliant pressurized vessel, with spatial gradients producing waves that transfer this energy. These techniques and principles are verified numerically and also experimentally with pressure/flow measurements in all branches of a central bifurcation in sheep, under a wide range of hemodynamic conditions. The proposed "wave power analysis," encompassing wave power, wave potential, and wave separation of hydraulic power provides a potent time-domain approach for analyzing hemodynamics. Copyright © 2016 the American Physiological Society.
On the relationship between the tree and its environment, based on electrical potential difference monitoring on trunk of trees

NASA Astrophysics Data System (ADS)

Koppan, A.; Fenyvesi, A.; Szarka, L.; Wesztergom, V.

2002-05-01

Electrical potential differences (EPD) in the trunk of a Turkey oak tree (measured by using non-polarising electrodes deepened in the sap wood) have been continuously recorded in the Geophysical Observatory "Istv n Széchenyi" of the Hungarian Academy of Sciences since 1997. Besides of various geophysical observations, meteorological and direct sap-flow measurements have also been carried out in the observatory. As it was found (Kopp n A., Szarka L., Wesztergom V., 2000: Annual fluctuation in amplitudes of daily variations of electrical signals measured in the trunk of a standing tree. C.R. Acad. Sci. Paris, Life Sciences 323, 559-563), the measured electric potential difference data have a characteristic sinusoidal daily fluctuation, and the intensity of the diurnal variations has a double-peak annual characteristics, which coincides with the life activity maximums of the tree. We have found a remarkable inter-correlation between trunk EPD, water potential of air (derived from meteorological data), and direct sap flow velocity data from a neighboring tree. All these results clearly demonstrate that the sap streaming due to the transpiration and root pressure generates the largest part of measured potential differences. The ratio of the flow velocity of a diluted solution forced through stems and the potential differences was found to be constant (Gindl, W., L”ppert, H.-G., Wimmer, R., 1999: Relationship between streaming potential and sap velocity in Salix alba L. Phyton, 39, 217-224.). On the contrary in our in-vivo experiments the relationship between the measured sap flow velocity and EPD is non-linear, which means that the conductivity (i.e. ion concentration) of the xylem sap itself also has a daily fluctuation.
Hydraulic safety margins and embolism reversal in stems and leaves: Why are conifers and angiosperms so different?

Treesearch

Daniel M. Johnson; Katherine A. McCulloh; David R. Woodruff; Frederick C. Meinzer

2012-01-01

Angiosperm and coniferous tree species utilize a continuum of hydraulic strategies. Hydraulic safety margins (defined as differences between naturally occurring xylem pressures and pressures that would cause hydraulic dysfunction, or differences between pressures resulting in loss of hydraulic function in adjacent organs (e.g., stems vs. leaves) tend to be much greater...
Ventilation loss and pressurization in the NASA launch/entry suit: Potential for heat stress

NASA Technical Reports Server (NTRS)

Kaufman, Jonathan W.; Dejneka, Katherine Y.; Askew, Gregory K.

1989-01-01

The potential of the NASA Launch/Entry Suit (LES) for producing heat stress in a simulated Space Shuttle cabin environment was studied. The testing was designed to identify potential heat stress hazards if the LES were pressurized or if ventilation were lost. Conditions were designed to simulate an extreme pre-launch situation with chamber temperatures maintained at dry bulb temperature = 27.2 +/- 0.1 C, globe temperature = 27.3 +/- 0.1 C, and wet bulb temperature = 21.1 +/- 0.3 C. Two females and two males, 23 to 34 years of age, were employed in this study, with two subjects having exposures in all 3 conditions. Test durations in the ventilated (V) and unventilated (UV) conditions were designed for 480 minutes, which all subjects achieved. Pressurized runs (Pr) were designed for 45 minutes, which all subjects also achieved. While some significant differences related to experimental conditions were noted in rectal and mean skin temperatures, evaporation rates, sweat rates, and heart rate, these differences were not thought to be physiologically significant. The results indicate that the LES garment, in either the Pr or UV state, poses no danger of inducing unacceptable heat stress under the conditions expected within the Space Shuttle cabin during launch or reentry.
Phloem networks in leaves.

PubMed

Carvalho, Mónica R; Losada, Juan M; Niklas, Karl J

2018-06-01

The survival of all vascular plants depends on phloem and xylem, which comprise a hydraulically coupled tissue system that transports photosynthates, water, and a variety of other molecules and ions. Although xylem hydraulics has been extensively studied, until recently, comparatively little is known quantitatively about the phloem hydraulic network and how it is functionally coupled to the xylem network, particularly in photosynthetic leaves. Here, we summarize recent advances in quantifying phloem hydraulics in fully expanded mature leaves with different vascular architectures and show that (1) the size of phloem conducting cells across phylogenetically different taxa scales isometrically with respect to xylem conducting cell size, (2) cell transport areas and lengths increase along phloem transport pathways in a manner that can be used to model Münch's pressure-flow hypothesis, and (3) report observations that invalidate da Vinci's and Murray's hydraulic models as plausible constructs for understanding photosynthate transport in the leaf lamina. Copyright © 2017 Elsevier Ltd. All rights reserved.

Anatomical regulation of ice nucleation and cavitation helps trees to survive freezing and drought stress

PubMed Central

Lintunen, A.; Hölttä, T.; Kulmala, M.

2013-01-01

Water in the xylem, the water transport system of plants, is vulnerable to freezing and cavitation, i.e. to phase change from liquid to ice or gaseous phase. The former is a threat in cold and the latter in dry environmental conditions. Here we show that a small xylem conduit diameter, which has previously been shown to be associated with lower cavitation pressure thus making a plant more drought resistant, is also associated with a decrease in the temperature required for ice nucleation in the xylem. Thus the susceptibility of freezing and cavitation are linked together in the xylem of plants. We explain this linkage by the regulation of the sizes of the nuclei catalysing freezing and drought cavitation. Our results offer better understanding of the similarities of adaption of plants to cold and drought stress, and offer new insights into the ability of plants to adapt to the changing environment. PMID:23778457
Height-related trends in leaf xylem anatomy and shoot hydraulic characteristics in a tall conifer: safety versus efficiency in water transport.

PubMed

Woodruff, D R; Meinzer, F C; Lachenbruch, B

2008-01-01

Hydraulic vulnerability of Douglas-fir (Pseudotsuga menziesii) branchlets decreases with height, allowing shoots at greater height to maintain hydraulic conductance (K shoot) at more negative leaf water potentials (Psi l). To determine the basis for this trend shoot hydraulic and tracheid anatomical properties of foliage from the tops of Douglas-fir trees were analysed along a height gradient from 5 to 55 m. Values of Psi l at which K shoot was substantially reduced, declined with height by 0.012 Mpa m(-1). Maximum K shoot was reduced by 0.082 mmol m(-2) MPa(-1) s(-1) for every 1 m increase in height. Total tracheid lumen area per needle cross-section, hydraulic mean diameter of leaf tracheid lumens, total number of tracheids per needle cross-section and leaf tracheid length decreased with height by 18.4 microm(2) m(-1), 0.029 microm m(-1), 0.42 m(-1) and 5.3 microm m(-1), respectively. Tracheid thickness-to-span ratio (tw/b)2 increased with height by 1.04 x 10(-3) m(-1) and pit number per tracheid decreased with height by 0.07 m(-1). Leaf anatomical adjustments that enhanced the ability to cope with vertical gradients of increasing xylem tension were attained at the expense of reduced water transport capacity and efficiency, possibly contributing to height-related decline in growth of Douglas fir.
Avian predation pressure as a potential driver of periodical cicada cycle length.

PubMed

Koenig, Walter D; Liebhold, Andrew M

2013-01-01

The extraordinarily long life cycles, synchronous emergences at 13- or 17-year intervals, and complex geographic distribution of periodical cicadas (Magicicada spp.) in eastern North America are a long-standing evolutionary enigma. Although a variety of factors, including satiation of aboveground predators and avoidance of interbrood hybridization, have been hypothesized to shape the evolution of this system, no empirical support for these mechanisms has previously been reported, beyond the observation that bird predation can extirpate small, experimentally mistimed emergences. Here we show that periodical cicada emergences appear to set populations of potential avian predators on numerical trajectories that result in significantly lower potential predation pressure during the subsequent emergence. This result provides new support for the importance of predators in shaping periodical cicada life history, offers an ecological rationale for why emergences are synchronized at the observed multiyear intervals, and may explain some of the developmental plasticity observed in these unique insects.
Effects of hydrostatic pressure on the donor impurity in a cylindrical quantum dot with Morse confining potential

NASA Astrophysics Data System (ADS)

Hayrapetyan, David B.; Kotanjyan, Tigran V.; Tevosyan, Hovhannes Kh.; Kazaryan, Eduard M.

2016-12-01

The effects of hydrostatic pressure and size quantization on the binding energies of a hydrogen-like donor impurity in cylindrical GaAs quantum dot (QD) with Morse confining potential are studied using the variational method and effective-mass approximation. In the cylindrical QD, the effect of hydrostatic pressure on the binding energy of electron has been investigated and it has been found that the application of the hydrostatic pressure leads to the blue shift. The dependence of the absorption edge on geometrical parameters of cylindrical QD is obtained. Selection rules are revealed for transitions between levels with different quantum numbers. It is shown that for the radial quantum number, transitions are allowed between the levels with the same quantum numbers, and any transitions between different levels are allowed for the principal quantum number.
Potential benefits of exercise on blood pressure and vascular function.

PubMed

Pal, Sebely; Radavelli-Bagatini, Simone; Ho, Suleen

2013-01-01

Physical activity seems to enhance cardiovascular fitness during the course of the lifecycle, improve blood pressure, and is associated with decreased prevalence of hypertension and coronary heart disease. It may also delay or prevent age-related increases in arterial stiffness. It is unclear if specific exercise types (aerobic, resistance, or combination) have a better effect on blood pressure and vascular function. This review was written based on previous original articles, systematic reviews, and meta-analyses indexed on PubMed from years 1975 to 2012 to identify studies on different types of exercise and the associations or effects on blood pressure and vascular function. In summary, aerobic exercise (30 to 40 minutes of training at 60% to 85% of predicted maximal heart rate, most days of the week) appears to significantly improve blood pressure and reduce augmentation index. Resistance training (three to four sets of eight to 12 repetitions at 10 repetition maximum, 3 days a week) appears to significantly improve blood pressure, whereas combination exercise training (15 minutes of aerobic and 15 minutes of resistance, 5 days a week) is beneficial to vascular function, but at a lower scale. Aerobic exercise seems to better benefit blood pressure and vascular function. Copyright © 2013 American Society of Hypertension. Published by Elsevier Inc. All rights reserved.
SGLT2 inhibitors: their potential reduction in blood pressure.

PubMed

Maliha, George; Townsend, Raymond R

2015-01-01

The sodium glucose co-transporter 2 (SGLT2) inhibitors represent a promising treatment option for diabetes and its common comorbidity, hypertension. Emerging data suggests that the SGLT2 inhibitors provide a meaningful reduction in blood pressure, although the precise mechanism of the blood pressure drop remains incompletely elucidated. Based on current data, the blood pressure reduction is partially due to a combination of diuresis, nephron remodeling, reduction in arterial stiffness, and weight loss. While current trials are underway focusing on cardiovascular endpoints, the SGLT2 inhibitors present a novel treatment modality for diabetes and its associated hypertension as well as an opportunity to elucidate the pathophysiology of hypertension in diabetes. Copyright © 2015 American Society of Hypertension. Published by Elsevier Inc. All rights reserved.
Xylem traits, leaf longevity and growth phenology predict growth and mortality response to defoliation in northern temperate forests.

PubMed

Foster, Jane R

2017-09-01

Defoliation outbreaks are biological disturbances that alter tree growth and mortality in temperate forests. Trees respond to defoliation in many ways; some recover rapidly, while others decline gradually or die. Functional traits such as xylem anatomy, growth phenology or non-structural carbohydrate (NSC) storage could explain these responses, but idiosyncratic measures used by defoliation studies have frustrated efforts to generalize among species. Here, I test for functional differences with published growth and mortality data from 37 studies, including 24 tree species and 11 defoliators from North America and Eurasia. I synthesized data into standardized variables suitable for numerical models and used linear mixed-effects models to test the hypotheses that responses to defoliation vary among species and functional groups. Standardized data show that defoliation responses vary in shape and degree. Growth decreased linearly or curvilinearly, least in ring-porous Quercus and deciduous conifers (by 10-40% per 100% defoliation), whereas growth of diffuse-porous hardwoods and evergreen conifers declined by 40-100%. Mortality increased exponentially with defoliation, most rapidly for evergreen conifers, then diffuse-porous, then ring-porous species and deciduous conifers (Larix). Goodness-of-fit for functional-group models was strong (R2c = 0.61-0.88), if lower than species-specific mixed-models (R2c = 0.77-0.93), providing useful alternatives when species data are lacking. These responses are consistent with functional differences in leaf longevity, wood growth phenology and NSC storage. When defoliator activity lags behind wood-growth, either because xylem-growth precedes budburst (Quercus) or defoliator activity peaks later (sawflies on Larix), impacts on annual wood-growth will always be lower. Wood-growth phenology of diffuse-porous species and evergreen conifers coincides with defoliation and responds more drastically, and lower axial NSC storage makes them
Interpolating a consumption variable for scaling and generalizing potential population pressure on urbanizing natural areas

USGS Publications Warehouse

Varanka, Dalia; Jiang, Bin; Yao, Xiaobai

2010-01-01

Measures of population pressure, referring in general to the stress upon the environment by human consumption of resources, are imperative for environmental sustainability studies and management. Development based on resource consumption is the predominant factor of population pressure. This paper presents a spatial model of population pressure by linking consumption associated with regional urbanism and ecosystem services. Maps representing relative geographic degree and extent of natural resource consumption and degree and extent of impacts on surrounding areas are new, and this research represents the theoretical research toward this goal. With development, such maps offer a visualization tool for planners of various services, amenities for people, and conservation planning for ecologist. Urbanization is commonly generalized by census numbers or impervious surface area. The potential geographical extent of urbanism encompasses the environmental resources of the surrounding region that sustain cities. This extent is interpolated using kriging of a variable based on population wealth data from the U.S. Census Bureau. When overlayed with land-use/land-cover data, the results indicate that the greatest estimates of population pressure fall within mixed forest areas. Mixed forest areas result from the spread of cedar woods in previously disturbed areas where further disturbance is then suppressed. Low density areas, such as suburbanization and abandoned farmland are characteristic of mixed forest areas.
Species climate range influences hydraulic and stomatal traits in Eucalyptus species.

PubMed

Bourne, Aimee E; Creek, Danielle; Peters, Jennifer M R; Ellsworth, David S; Choat, Brendan

2017-07-01

Plant hydraulic traits influence the capacity of species to grow and survive in water-limited environments, but their comparative study at a common site has been limited. The primary aim of this study was to determine whether selective pressures on species originating in drought-prone environments constrain hydraulic traits among related species grown under common conditions. Leaf tissue water relations, xylem anatomy, stomatal behaviour and vulnerability to drought-induced embolism were measured on six Eucalyptus species growing in a common garden to determine whether these traits were related to current species climate range and to understand linkages between the traits. Hydraulically weighted xylem vessel diameter, leaf turgor loss point, the water potential at stomatal closure and vulnerability to drought-induced embolism were significantly ( P < 0·05) correlated with climate parameters from the species range. There was a co-ordination between stem and leaf parameters with the water potential at turgor loss, 12 % loss of conductivity and the point of stomatal closure significantly correlated. The correlation of hydraulic, stomatal and anatomical traits with climate variables from the species' original ranges suggests that these traits are genetically constrained. The conservative nature of xylem traits in Eucalyptus trees has important implications for the limits of species responses to changing environmental conditions and thus for species survival and distribution into the future, and yields new information for physiological models. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com
Increased vapor pressure deficit due to higher temperature leads to greater transpiration and faster mortality during drought for tree seedlings common to the forest-grassland ecotone.

PubMed

Will, Rodney E; Wilson, Stuart M; Zou, Chris B; Hennessey, Thomas C

2013-10-01

Tree species growing along the forest-grassland ecotone are near the moisture limit of their range. Small increases in temperature can increase vapor pressure deficit (VPD) which may increase tree water use and potentially hasten mortality during severe drought. We tested a 40% increase in VPD due to an increase in growing temperature from 30 to 33°C (constant dewpoint 21°C) on seedlings of 10 tree species common to the forest-grassland ecotone in the southern Great Plains, USA. Measurement at 33 vs 30°C during reciprocal leaf gas exchange measurements, that is, measurement of all seedlings at both growing temperatures, increased transpiration for seedlings grown at 30°C by 40% and 20% for seedlings grown at 33°C. Higher initial transpiration of seedlings in the 33°C growing temperature treatment resulted in more negative xylem water potentials and fewer days until transpiration decreased after watering was withheld. The seedlings grown at 33°C died 13% (average 2 d) sooner than seedlings grown at 30°C during terminal drought. If temperature and severity of droughts increase in the future, the forest-grassland ecotone could shift because low seedling survival rate may not sufficiently support forest regeneration and migration. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.
The transcriptome of sesquiterpenoid biosynthesis in heartwood xylem of Western Australian sandalwood (Santalum spicatum).

PubMed

Moniodis, Jessie; Jones, Christopher G; Barbour, E Liz; Plummer, Julie A; Ghisalberti, Emilio L; Bohlmann, Joerg

2015-05-01

The fragrant heartwood oil of West Australian sandalwood (Santalum spicatum) contains a mixture of sesquiterpene olefins and alcohols, including variable levels of the valuable sesquiterpene alcohols, α- and β-santalol, and often high levels of E,E-farnesol. Transcriptome analysis revealed sequences for a nearly complete set of genes of the sesquiterpenoid biosynthetic pathway in this commercially valuable sandalwood species. Transcriptome sequences were produced from heartwood xylem tissue of a farnesol-rich individual tree. From the assembly of 12,537 contigs, seven different terpene synthases (TPSs), several cytochromes P450, and allylic phosphatases were identified, as well as transcripts of the mevalonic acid and methylerythritol phosphate pathways. Five of the S. spicatum TPS sequences were previously unknown. The full-length cDNA of SspiTPS4 was cloned and the enzyme functionally characterized as a multi-product sesquisabinene B synthase, which complements previous characterization of santalene and bisabolol synthases in S. spicatum. While SspiTPS4 and previously cloned sandalwood TPSs do not explain the prevalence of E,E-farnesol in S. spicatum, the genes identified in this and previous work can form a basis for future studies on natural variation of sandalwood terpenoid oil profiles. Copyright © 2014 Elsevier Ltd. All rights reserved.
Comparison of ionospheric convection and the transpolar potential before and after solar wind dynamic pressure fronts: implications for magnetospheric reconnection

NASA Astrophysics Data System (ADS)

Boudouridis, A.; Zesta, E.; Lyons, L. R.; Kim, H.-J.; Lummerzheim, D.; Wiltberger, M.; Weygand, J. M.; Ruohoniemi, J. M.; Ridley, A. J.

2012-04-01

The solar wind dynamic pressure, both through its steady state value and through its variations, plays an important role in the determination of the state of the terrestrial magnetosphere and ionosphere, its effects being only secondary to those of the Interplanetary Magnetic Field (IMF). Recent studies have demonstrated the significant effect solar wind dynamic pressure enhancements have on ionospheric convection and the transpolar potential. Further studies have shown a strong response of the polar cap boundary and thus the open flux content of the magnetosphere. These studies clearly illustrate the strong coupling of solar wind dynamic pressure fronts to the terrestrial magnetosphere-ionosphere system. We present statistical studies of the response of Super Dual Auroral Radar Network (SuperDARN) flows, and Assimilative Mapping of Ionospheric Electrodynamics (AMIE) transpolar potentials to sudden enhancements in solar wind dynamic pressure. The SuperDARN results show that the convection is enhanced within both the dayside and nightside ionosphere. The dayside response is more clear and immediate, while the response on the nightside is slower and more evident for low IMF By values. AMIE results show that the overall convection, represented by the transpolar potential, has a strong response immediately after an increase in pressure, with magnitude and duration modulated by the background IMF Bz conditions. We compare the location of the SuperDARN convection enhancements with the location and motion of the polar cap boundary, as determined by POLAR Ultra-Violet Imager (UVI) images and runs of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic model for specific events. We find that the boundary exhibits a poleward motion after the increase in dynamic pressure. The enhanced ionospheric flows and the poleward motion of the boundary on the nightside are both signatures of enhanced tail reconnection, a conclusion that is reinforced by the observation of the
Comparisons of xylem sap flow and water vapour flux at the stand level and derivation of canopy conductance for Scots pine

NASA Astrophysics Data System (ADS)

Granier, A.; Biron, P.; Köstner, B.; Gay, L. W.; Najjar, G.

1996-03-01

Simultaneous measurements of xylem sap flow and water vapour flux over a Scots pine ( Pinus sylvestris) forest (Hartheim, Germany), were carried out during the Hartheim Experiment (HartX), an intensive observation campaign of the international programme REKLIP. Sap flow was measured every 30 min using both radial constant heating (Granier, 1985) and two types of Cermak sap flowmeters installed on 24 trees selected to cover a wide range of the diameter classes of the stand (min 8 cm; max 17.5 cm). Available energy was high during the observation period (5.5 to 6.9 mm.day-1), and daily cumulated sap flow on a ground area basis varied between 2.0 and 2.7 mm day-1 depending on climate conditions. Maximum hourly values of sap flow reached 0.33 mm h-1, i.e., 230 W m-2. Comparisons of sap flow with water vapour flux as measured with two OPEC (One Propeller Eddy Correlation, University of Arizona) systems showed a time lag between the two methods, sap flow lagging about 90 min behind vapour flux. After taking into account this time lag in the sap flow data set, a good agreement was found between both methods: sap flow = 0.745* vapour flux, r 2 = 0.86. The difference between the two estimates was due to understory transpiration. Canopy conductance ( g c ) was calculated from sap flow measurements using the reverse form of Penman-Monteith equation and climatic data measured 4 m above the canopy. Variations of g c were well correlated ( r 2 = 0.85) with global radiation ( R) and vapour pressure deficit ( vpd). The quantitative expression for g c = f ( R, vpd) was very similar to that previously found with maritime pine ( Pinus pinaster) in the forest of Les Landes, South Western France.
Intermittent blood pressure control: potential consequences for outcome.

PubMed

Leenen, F H

1999-05-01

Although both blood pressure (BP) and left ventricular (LV) mass at initial evaluation predict future cardiovascular risk, the actual BP and LV mass achieved over years of treatment more clearly relate to cardiovascular event rates. Intermittent compliance or noncompliance is the major reason for uncontrolled hypertension and presumably persistent LV hypertrophy. In general, drugs with rapid onset and short duration of action are not desirable because this profile may lead to large variations in BP lowering effect during actual drug intake and rapid disappearance of the antihypertensive effect with missed doses. In addition, intermittent compliance per se introduces the potential for adverse events. For drugs requiring several dose-titrations (e.g., alpha1-blockers), restarting at full doses may lead to excessive drug action and symptomatic hypotension. For other drugs (e.g., short acting beta-blockers or clonidine-like drugs), sudden discontinuation with intermittent compliance may lead to rebound-enhanced sympathetic responsiveness after one to two days, resulting not only in side effects, but also in adverse events, particularly in patients with (silent) coronary artery disease. The rapid onset, short acting dihydropyridines cause intermittent BP control at each dosing, particularly at higher doses. This intermittent control of BP is even more apparent at dosing intervals that are long relative to the duration of action. Thus, sympathetic activation and potential for adverse events can be anticipated at each dosing unless these drugs are being taken frequently at relatively low doses. For diuretics, angiotensin-converting enzyme inhibitors and angiotensin I receptor blockers, no adverse effects have been identified with intermittent compliance. Intermittent BP control is, in general, not an appropriate approach to the management of hypertension and introduces additional risks depending on the type of antihypertensive drug. In contrast, drugs with slow onset and
Sequence/structural analysis of xylem proteome emphasizes pathogenesis-related proteins, chitinases and β-1, 3-glucanases as key players in grapevine defense against Xylella fastidiosa.

PubMed

Chakraborty, Sandeep; Nascimento, Rafael; Zaini, Paulo A; Gouran, Hossein; Rao, Basuthkar J; Goulart, Luiz R; Dandekar, Abhaya M

2016-01-01

Background. Xylella fastidiosa, the causative agent of various plant diseases including Pierce's disease in the US, and Citrus Variegated Chlorosis in Brazil, remains a continual source of concern and economic losses, especially since almost all commercial varieties are sensitive to this Gammaproteobacteria. Differential expression of proteins in infected tissue is an established methodology to identify key elements involved in plant defense pathways. Methods. In the current work, we developed a methodology named CHURNER that emphasizes relevant protein functions from proteomic data, based on identification of proteins with similar structures that do not necessarily have sequence homology. Such clustering emphasizes protein functions which have multiple copies that are up/down-regulated, and highlights similar proteins which are differentially regulated. As a working example we present proteomic data enumerating differentially expressed proteins in xylem sap from grapevines that were infected with X. fastidiosa. Results. Analysis of this data by CHURNER highlighted pathogenesis related PR-1 proteins, reinforcing this as the foremost protein function in xylem sap involved in the grapevine defense response to X. fastidiosa. β-1, 3-glucanase, which has both anti-microbial and anti-fungal activities, is also up-regulated. Simultaneously, chitinases are found to be both up and down-regulated by CHURNER, and thus the net gain of this protein function loses its significance in the defense response. Discussion. We demonstrate how structural data can be incorporated in the pipeline of proteomic data analysis prior to making inferences on the importance of individual proteins to plant defense mechanisms. We expect CHURNER to be applicable to any proteomic data set.
Pressure demagnetization - a potential approach to improve successfulabsolute paleointensity experiments

NASA Astrophysics Data System (ADS)

Volk, M.; Gilder, S.

2016-12-01

Natural rocks rarely consist of ideal single-domain grains but rather contain mixtures of larger, non-ideal magnetic recorders (pseudo single PSD and multidomain grains MD), which often lead to non-linear trends on an Arai diagram. Here we present results using pressure demagnetization as a way to improve the quality of paleointensity determinations using the Coe modified Thellier method. Experiments were conducted on thermally stable obsidian containing titanomagnetite grains within the PSD range. A thermal remanent magnetization (TRM) in a 35 μT magnetic field was imparted on 20 specimens. Thellier-type paleointensity experiments were carried out at ambient conditions and after pressure cycling to 0.6, 1.2 and 1.8 GPa. Unpressurized samples yielded concave up Arai diagrams that underestimated paleointensities by 10-15%. Pressure cycling under hydrostatic conditions lowered the magnetic moment of the samples by 10%/GPa, yet produced more linear Arai plots. Normalizing the data with the initial, pre-compressed NRM value resulted in corrected paleointensity values of 35.7 ± 0.6, 35.3 ± 0.8 and 35.5 ± 0.9 μT after pressure cycling to 0.6, 1.2 and 1.8 GPa. Furthermore, the mean quality factors increased from 27 to 34, 47 and 47 for the pressure runs at 0.6, 1.2 and 1.8 GPa, respectively. These results suggest that pressure cycling preferentially demagnetizes the remanence held by PSD and MD grains, while leaving the remanence held by SD grains largely intact, leading to much greater retention rates and accuracy of paleointensity data.
Turgidity-dependent petiole flexibility enables efficient water use by a tree subjected to water stress.

PubMed

Gonzalez-Rodriguez, David; Cournède, Paul-Henry; de Langre, Emmanuel

2016-06-07

Water stress is a major cause of tree mortality. In response to drought, leaves wilt due to an increase in petiole flexibility. We present an analytical model coupling petiole mechanics, thermal balance, and xylem hydraulics to investigate the role of petiole flexibility in protecting a tree from water stress. Our model suggests that turgidity-dependent petiole flexibility can significantly attenuate the minimal xylem pressure and thus reduce the risk of cavitation. Moreover, we show that petiole flexibility increases water use efficiency by trees under water stress. Copyright © 2016 Elsevier Ltd. All rights reserved.
Activation of transient receptor potential vanilloid-1 (TRPV1) influences how retinal ganglion cell neurons respond to pressure-related stress

PubMed Central

Sappington, Rebecca M; Sidorova, Tatiana; Ward, Nicholas J; Chakravarthy, Rohini; Ho, Karen W; Calkins, David J

2015-01-01

Our recent studies implicate the transient receptor potential vanilloid-1 (TRPV1) channel as a mediator of retinal ganglion cell (RGC) function and survival. With elevated pressure in the eye, TRPV1 increases in RGCs, supporting enhanced excitability, while Trpv1 -/- accelerates RGC degeneration in mice. Here we find TRPV1 localized in monkey and human RGCs, similar to rodents. Expression increases in RGCs exposed to acute changes in pressure. In retinal explants, contrary to our animal studies, both Trpv1 -/- and pharmacological antagonism of the channel prevented pressure-induced RGC apoptosis, as did chelation of extracellular Ca2+. Finally, while TRPV1 and TRPV4 co-localize in some RGC bodies and form a protein complex in the retina, expression of their mRNA is inversely related with increasing ocular pressure. We propose that TRPV1 activation by pressure-related insult in the eye initiates changes in expression that contribute to a Ca2+-dependent adaptive response to maintain excitatory signaling in RGCs. PMID:25713995
Wasted water pressure and potential energy generation. A feasibility study of the hydroelectric potential in part of the domestic water system of Boulder, Colorado. Draft final

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stern, P.S.; Kiel, J.; Fey, L.

1980-11-01

Colorado Project/Tip's study of the feasibility of using the City of Boulder's domestic water system for the generation of electricity was funded by an Appropriate Technology Grant from the Department of Energy, Region VIII. It has looked at how the extreme pressure being generated in this gravity water system can be used for a beneficial use rather than the current practice of simply venting or releasing it to the atmosphere. Turbines or pumps are studied as the means of converting the wasted pressure into energy. A review of the water system showed that five potential sites exist for installations ofmore » turbines or pumps: Silver Lake, Kossler, Sunshine, Orodell and 6th and Canyon. Data on water flows, elevation differences, pressures and operating procedures were integrated into an optimized flow control strategy for operating the water system while gaining maximum potential for the generation of electricity. Water from the mountain watersheds would continue to flow into the Betasso Water Treatment Plant as now. However, flows from the Silver Lake Line would be made constant as possible on a daily basis with the Kossler Line supplying additional needs. Flows of treated water from the Betasso Plant would be split 85/15 into the Sunshine/Orodell Lines rather than the current 60/40 split. Using the optimized flow control strategy, the power available for each site can be calculated from the pressures experienced, or elevation differences. Turbines can then be selected which would be appropriate for each site. Finally, the cost of the installed turbine plus auxiliary equipment to connect it to a load can be calculated and related to the minimum price which would be necessary to allow the project to break even.« less
Blood Pressure Responses to Endovascular Stimulation: A Potential Therapy for Autonomic Disorders With Vasodilatation.

PubMed

Naksuk, Niyada; Killu, Ammar M; Yogeswaran, Vidhushei; Desimone, Christopher V; Suddendorf, Scott H; Ladewig, Dorothy J; Powers, Joanne M; Weber, Sarah; Madhavan, Malini; Cha, Yong-Mei; Kapa, Suraj; Asirvatham, Samuel J

2016-09-01

We have previously shown that sympathetic ganglia stimulation via the renal vein rapidly increases blood pressure. This study further investigated the optimal target sites and effective energy levels for stimulation of the renal vasculatures and nearby sympathetic ganglia for rapid increase in blood pressure. The pre-study protocol for endovascular stimulations included 2 minutes of stimulation (1-150 V and 10 pulses per second) and at least 2 minutes of rest during poststimulation. If blood pressure and/or heart rate were changed during the stimulation, time to return to baseline was allowed prior to the next stimulation. In 11 acute canine studies, we performed 85 renal artery, 30 renal vein, and 8 hepatic vasculature stimulations. The mean arterial pressure (MAP) rapidly increased during stimulation of renal artery (95 ± 18 mmHg vs. 103 ± 15 mmHg; P < 0.0001), renal vein (90 ± 16 mmHg vs. 102 ± 20 mmHg; P = 0.001), and hepatic vasculatures (74 ± 8 mmHg vs. 82 ± 11 mmHg; P = 0.04). Predictors of a significant increase in MAP were energy >10 V focused on the left renal artery, bilateral renal arteries, and bilateral renal veins (especially the mid segment). Overall, heart rate was unchanged, but muscle fasciculation was observed in 22.0% with an output >10 V (range 15-150 V). Analysis after excluding the stimulations that resulted in fasciculation yielded similar results to the main findings. Stimulation of intra-abdominal vasculatures promptly increased the MAP and thus may be a potential treatment option for hypotension in autonomic disorders. Predictors of optimal stimulation include energy delivery and the site of stimulation (for the renal vasculatures), which informs the design of subsequent research. © 2016 Wiley Periodicals, Inc.

Genome-wide transcriptome analysis of Clavibacter michiganensis subsp. michiganensis grown in xylem mimicking medium.

PubMed

Hiery, Eva; Adam, Susanne; Reid, Stephen; Hofmann, Jörg; Sonnewald, Sophia; Burkovski, Andreas

2013-12-01

The interaction between Clavibacter michiganensis subsp. michiganensis with its host, the tomato plant (Solanum lycopersicum), is poorly understood and only few virulence factors are known. While studying of the bacteria in planta is time-consuming and difficult, the analysis in vitro would facilitate research. Therefore, a xylem mimicking medium (XMM) for C. michiganensis subsp. michiganensis was established in this study based on an apoplast medium for Xanthomonas campestris pv. vesicatoria. In contrast to the apoplast medium, XMM contains no sugars, but amino acids which serve as nitrogen and carbon source. As a result, growth in XMM induced transcriptional changes of genes encoding putative sugar, amino acid and iron uptake systems. In summary, mRNA levels of about 8% of all C. michiganensis subsp. michiganensis genes were changed when XMM-grown bacteria were compared to M9 minimal medium-grown cells. Almost no transcriptional changes of genes encoding hydrolytic enzymes were detected, leading to the idea that XMM reflects the situation in the beginning of infection and therefore allows the characterization of virulence factors in this early stage of infection. The addition of the plant wound substance acetosyringone to the XMM medium led to a change in transcript amount, including genes coding for proteins involved in protein transport, iron uptake and regulation processes. Copyright © 2013 Elsevier B.V. All rights reserved.
Coordination of leaf and stem water transport properties in tropical forest trees

Treesearch

Frederick C. Meinzer; David R. Woodruff; Jean-Christophe Domec; Guillermo Goldstein; Paula I. Campanello; Genoveva M. Gatti; Randol Villalobos-Vega

2008-01-01

Stomatal regulation of transpiration constrains leaf water potential (ψ l) within species-specific ranges that presumably avoid excessive tension and embolism in the stem xylem upstream. However, the hydraulic resistance of leaves can be highly variable over short time scales, uncoupling tension in the xylem of leaves from that in the...
Application of point-process statistical tools to stable isotopes in xylem water for the study of inter- and intra-specific interactions in water uptake patterns in a mixed stand of Pinus halepensis Mill. and Quercus ilex L.

NASA Astrophysics Data System (ADS)

Comas, Carles; del Castillo, Jorge; Voltas, Jordi; Ferrio, Juan Pedro

2013-04-01

The stable isotope composition of xylem water reflects has been used to assess inter-specific differences in uptake patterns, revealing synergistic and competition processes in the use of water resources (see e.g. Dawson et al. 1993). However, there is a lack of detailed studies on spatial and temporal variability of inter- and intra-specific competition within forest stands. In this context, the aim of this work was to compare the isotope composition of xylem water (δ18O , δ2H) in two common Mediterranean tree species, Quercus ilex L. and Pinus halepensis Mill, in order to understand their water uptake patterns throughout the growing season. In addition, we analyze the spatial variability of xylem water, to get insight into inter-specific strategies employed to cope with drought and the interaction between the individuals. Our first hypothesis was that both species used different strategies to cope with drought by uptaking water at different depths; and our second hypothesis was that individual trees would behave in different manner according to the distance to their neighbours as well as to whether the neighbour is from one species or the other. The study was performed in a mixed stand where both species are nearly co-dominant, adding up to a total of 33 oaks and 77 pines (plot area= 893 m2). We sampled sun-exposed branches of each tree six times over the growing season, and extracted the xylem water with a cryogenic trap. The isotopic composition of the water was determined using a Picarro Water Analizer L2130-i. Tree mapping for spatial analysis was done using a high resolution GPS technology (Trimble GeoExplorer 6000). For the spatial analysis, we used the pair-correlation function to study intra-specific tree configuration and the bivariate pair correlation function to analyse the inter-specific spatial configurations (Stoyan et al 1995). Moreover, the isotopic composition of xylem water was assumed to be a mark associated to each tree and analysed as a
Red Xylem and Higher Lignin Extractability by Down-Regulating a Cinnamyl Alcohol Dehydrogenase in Poplar.

PubMed

Baucher, M.; Chabbert, B.; Pilate, G.; Van Doorsselaere, J.; Tollier, M. T.; Petit-Conil, M.; Cornu, D.; Monties, B.; Van Montagu, M.; Inze, D.; Jouanin, L.; Boerjan, W.

1996-12-01

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the last step in the biosynthesis of the lignin precursors, the monolignols. We have down-regulated CAD in transgenic poplar (Populus tremula X Populus alba) by both antisense and co-suppression strategies. Several antisense and sense CAD transgenic poplars had an approximately 70% reduced CAD activity that was associated with a red coloration of the xylem tissue. Neither the lignin amount nor the lignin monomeric composition (syringyl/guaiacyl) were significantly modified. However, phloroglucinol-HCl staining was different in the down-regulated CAD plants, suggesting changes in the number of aldehyde units in the lignin. Furthermore, the reactivity of the cell wall toward alkali treatment was altered: a lower amount of lignin was found in the insoluble, saponified residue and more lignin could be precipitated from the soluble alkali fraction. Moreover, large amounts of phenolic compounds, vanillin and especially syringaldehyde, were detected in the soluble alkali fraction of the CAD down-regulated poplars. Alkaline pulping experiments on 3-month-old trees showed a reduction of the kappa number without affecting the degree of cellulose degradation. These results indicate that reducing the CAD activity in trees might be a valuable strategy to optimize certain processes of the wood industry, especially those of the pulp and paper industry.
Cell-Type Specificity of the Expression of Os BOR1, a Rice Efflux Boron Transporter Gene, Is Regulated in Response to Boron Availability for Efficient Boron Uptake and Xylem Loading

PubMed Central

Nakagawa, Yuko; Hanaoka, Hideki; Kobayashi, Masaharu; Miyoshi, Kazumaru; Miwa, Kyoko; Fujiwara, Toru

2007-01-01

We describe a boron (B) transporter, Os BOR1, in rice (Oryza sativa). Os BOR1 is a plasma membrane–localized efflux transporter of B and is required for normal growth of rice plants under conditions of limited B supply (referred to as -B). Disruption of Os BOR1 reduced B uptake and xylem loading of B. The accumulation of Os BOR1 transcripts was higher in roots than that in shoots and was not affected by B deprivation; however, Os BOR1 was detected in the roots of wild-type plants under -B conditions, but not under normal conditions, suggesting regulation of protein accumulation in response to B nutrition. Interestingly, tissue specificity of Os BOR1 expression is affected by B treatment. Transgenic rice plants containing an Os BOR1 promoter–β-glucuronidase (GUS) fusion construct grown with a normal B supply showed the strongest GUS activity in the steles, whereas after 3 d of -B treatment, GUS activity was elevated in the exodermis. After 6 d of -B treatment, GUS activity was again strong in the stele. Our results demonstrate that Os BOR1 is required both for efficient B uptake and for xylem loading of B. Possible roles of the temporal changes in tissue-specific patterns of Os BOR1 expression in response to B condition are discussed. PMID:17675406
Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure

PubMed Central

Liu, Hanyu; Naumov, Ivan I.; Hoffmann, Roald; Ashcroft, N. W.; Hemley, Russell J.

2017-01-01

A systematic structure search in the La–H and Y–H systems under pressure reveals some hydrogen-rich structures with intriguing electronic properties. For example, LaH10 is found to adopt a sodalite-like face-centered cubic (fcc) structure, stable above 200 GPa, and LaH8 a C2/m space group structure. Phonon calculations indicate both are dynamically stable; electron phonon calculations coupled to Bardeen–Cooper–Schrieffer (BCS) arguments indicate they might be high-Tc superconductors. In particular, the superconducting transition temperature Tc calculated for LaH10 is 274–286 K at 210 GPa. Similar calculations for the Y–H system predict stability of the sodalite-like fcc YH10 and a Tc above room temperature, reaching 305–326 K at 250 GPa. The study suggests that dense hydrides consisting of these and related hydrogen polyhedral networks may represent new classes of potential very high-temperature superconductors. PMID:28630301
Cellular Pressure-Actuated Joint

NASA Technical Reports Server (NTRS)

McGuire, John R.

2003-01-01

A modification of a pressure-actuated joint has been proposed to improve its pressure actuation in such a manner as to reduce the potential for leakage of the pressurizing fluid. The specific joint for which the modification is proposed is a field joint in a reusable solid-fuel rocket motor (RSRM), in which the pressurizing fluid is a mixture of hot combustion gases. The proposed modification could also be applicable to other pressure-actuated joints of similar configuration.
Potential application of high hydrostatic pressure to eliminate Escherichia coli O157:H7 on alfalfa sprouted seeds.

PubMed

Neetoo, Hudaa; Ye, Mu; Chen, Haiqiang

2008-12-10

Sprouts eaten raw are increasingly being perceived as hazardous foods as they have been implicated in Escherichia coli O157:H7 outbreaks where the seeds were found to be the likely source of contamination. The objective of our study was to evaluate the potential of using high hydrostatic pressure (HHP) technology for alfalfa seed decontamination. Alfalfa seeds inoculated with a cocktail of five strains of E. coli O157:H7 were subjected to pressures of 500 and 600 MPa for 2 min at 20 degrees C in a dry or wet (immersed in water) state. Immersing seeds in water during pressurization considerably enhanced inactivation of E. coli O157:H7 achieving reductions of 3.5 log and 5.7 log at 500 and 600 MPa, respectively. When dry seeds were pressurized, both pressure levels reduced the counts by <0.7 log. To test the efficacy of HHP to completely decontaminate seeds whilst meeting the FDA requirement of 5 log reductions, seeds inoculated with a ~5 log CFU/g of E. coli O157:H7 were pressure-treated at 600 and 650 MPa at 20 degrees C for holding times of 2 to 20 min. A >5 log reduction in the population was achieved when 600 MPa was applied for durations of > or =6 min although survivors were still detected by enrichment. When the pressure was stepped up to 650 MPa, the threshold time required to achieve complete elimination was 15 min. Un-inoculated seeds pressure-treated at 650 MPa for 15 min at 20 degrees C successfully sprouted achieving a germination rate identical to untreated seeds after eight days of sprouting. These results therefore demonstrate the promising application of HHP on alfalfa seeds to eliminate the risk of E. coli O157:H7 infections associated with consumption of raw alfalfa sprouts.
Xylem Development and Cell Wall Changes of Soybean Seedlings Grown in Space

PubMed Central

de Micco, Veronica; Aronne, Giovanna; Joseleau, Jean-Paul; Ruel, Katia

2008-01-01

Background and Aims Plants growing in altered gravity conditions encounter changes in vascular development and cell wall deposition. The aim of this study was to investigate xylem anatomy and arrangement of cellulose microfibrils in vessel walls of different organs of soybean seedlings grown in Space. Methods Seeds germinated and seedlings grew for 5 d in Space during the Foton-M2 mission. The environmental conditions, other than gravity, of the ground control repeated those experienced in orbit. The seedlings developed in space were compared with those of the control test on the basis of numerous anatomical and ultrastructural parameters such as number of veins, size and shape of vessel lumens, thickness of cell walls and deposition of cellulose microfibrils. Key Results Observations made with light, fluorescence and transmission electron microscopy, together with the quantification of the structural features through digital image analysis, showed that the alterations due to microgravity do not occur at the same level in the various organs of soybean seedlings. The modifications induced by microgravity or by the indirect effect of space-flight conditions, became conspicuous only in developing vessels at the ultrastructural level. The results suggested that the orientation of microfibrils and their assembly in developing vessels are perturbed by microgravity at the beginning of wall deposition, while they are still able to orient and arrange in thicker and ordered structures at later stages of secondary wall deposition. Conclusions The process of proper cell-wall building, although not prevented, is perturbed in Space at the early stage of development. This would explain the almost unaltered anatomy of mature structures, accompanied by a slower growth observed in seedlings grown in Space than on Earth. PMID:18252765
Xylem development and cell wall changes of soybean seedlings grown in space.

PubMed

de Micco, Veronica; Aronne, Giovanna; Joseleau, Jean-Paul; Ruel, Katia

2008-04-01

Plants growing in altered gravity conditions encounter changes in vascular development and cell wall deposition. The aim of this study was to investigate xylem anatomy and arrangement of cellulose microfibrils in vessel walls of different organs of soybean seedlings grown in Space. Seeds germinated and seedlings grew for 5 d in Space during the Foton-M2 mission. The environmental conditions, other than gravity, of the ground control repeated those experienced in orbit. The seedlings developed in space were compared with those of the control test on the basis of numerous anatomical and ultrastructural parameters such as number of veins, size and shape of vessel lumens, thickness of cell walls and deposition of cellulose microfibrils. Observations made with light, fluorescence and transmission electron microscopy, together with the quantification of the structural features through digital image analysis, showed that the alterations due to microgravity do not occur at the same level in the various organs of soybean seedlings. The modifications induced by microgravity or by the indirect effect of space-flight conditions, became conspicuous only in developing vessels at the ultrastructural level. The results suggested that the orientation of microfibrils and their assembly in developing vessels are perturbed by microgravity at the beginning of wall deposition, while they are still able to orient and arrange in thicker and ordered structures at later stages of secondary wall deposition. The process of proper cell-wall building, although not prevented, is perturbed in Space at the early stage of development. This would explain the almost unaltered anatomy of mature structures, accompanied by a slower growth observed in seedlings grown in Space than on Earth.
Effects of water storage in the stele on measurements of the hydraulics of young roots of corn and barley.

PubMed

Joshi, Ankur; Knipfer, Thorsten; Steudle, Ernst

2009-11-01

In standard techniques (root pressure probe or high-pressure flowmeter), the hydraulic conductivity of roots is calculated from transients of root pressure using responses following step changes in volume or pressure, which may be affected by a storage of water in the stele. Storage effects were examined using both experimental data of root pressure relaxations and clamps and a physical capacity model. Young roots of corn and barley were treated as a three-compartment system, comprising a serial arrangement of xylem/probe, stele and outside medium/cortex. The hydraulic conductivities of the endodermis and of xylem vessels were derived from experimental data. The lower limit of the storage capacity of stelar tissue was caused by the compressibility of water. This was subsequently increased to account for realistic storage capacities of the stele. When root water storage was varied over up to five orders of magnitude, the results of simulations showed that storage effects could not explain the experimental data, suggesting a major contribution of effects other than water storage. It is concluded that initial water flows may be used to measure root hydraulic conductivity provided that the volumes of water used are much larger than the volumes stored.
Pragmatic hydraulic theory predicts stomatal responses to climatic water deficits.

PubMed

Sperry, John S; Wang, Yujie; Wolfe, Brett T; Mackay, D Scott; Anderegg, William R L; McDowell, Nate G; Pockman, William T

2016-11-01

Ecosystem models have difficulty predicting plant drought responses, partially from uncertainty in the stomatal response to water deficits in soil and atmosphere. We evaluate a 'supply-demand' theory for water-limited stomatal behavior that avoids the typical scaffold of empirical response functions. The premise is that canopy water demand is regulated in proportion to threat to supply posed by xylem cavitation and soil drying. The theory was implemented in a trait-based soil-plant-atmosphere model. The model predicted canopy transpiration (E), canopy diffusive conductance (G), and canopy xylem pressure (P canopy ) from soil water potential (P soil ) and vapor pressure deficit (D). Modeled responses to D and P soil were consistent with empirical response functions, but controlling parameters were hydraulic traits rather than coefficients. Maximum hydraulic and diffusive conductances and vulnerability to loss in hydraulic conductance dictated stomatal sensitivity and hence the iso- to anisohydric spectrum of regulation. The model matched wide fluctuations in G and P canopy across nine data sets from seasonally dry tropical forest and piñon-juniper woodland with < 26% mean error. Promising initial performance suggests the theory could be useful in improving ecosystem models. Better understanding of the variation in hydraulic properties along the root-stem-leaf continuum will simplify parameterization. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.
Generation of nanobubbles by ceramic membrane filters: The dependence of bubble size and zeta potential on surface coating, pore size and injected gas pressure.

PubMed

Ahmed, Ahmed Khaled Abdella; Sun, Cuizhen; Hua, Likun; Zhang, Zhibin; Zhang, Yanhao; Zhang, Wen; Marhaba, Taha

2018-07-01

Generation of gaseous nanobubbles (NBs) by simple, efficient, and scalable methods is critical for industrialization and applications of nanobubbles. Traditional generation methods mainly rely on hydrodynamic, acoustic, particle, and optical cavitation. These generation processes render issues such as high energy consumption, non-flexibility, and complexity. This research investigated the use of tubular ceramic nanofiltration membranes to generate NBs in water with air, nitrogen and oxygen gases. This system injects pressurized gases through a tubular ceramic membrane with nanopores to create NBs. The effects of membrane pores size, surface energy, and the injected gas pressures on the bubble size and zeta potential were examined. The results show that the gas injection pressure had considerable effects on the bubble size, zeta potential, pH, and dissolved oxygen of the produced NBs. For example, increasing the injection air pressure from 69 kPa to 414 kPa, the air bubble size was reduced from 600 to 340 nm respectively. Membrane pores size and surface energy also had significant effects on sizes and zeta potentials of NBs. The results presented here aim to fill out the gaps of fundamental knowledge about NBs and development of efficient generation methods. Copyright © 2018 Elsevier Ltd. All rights reserved.
Pressure and Chemical Potential: Effects Hydrophilic Soils Have on Adsorption and Transport

NASA Astrophysics Data System (ADS)

Bennethum, L. S.; Weinstein, T.

2003-12-01

Using the assumption that thermodynamic properties of fluid is affected by its proximity to the solid phase, a theoretical model has been developed based on upscaling and fundamental thermodynamic principles (termed Hybrid Mixture Theory). The theory indicates that Darcy's law and the Darcy-scale chemical potential (which determines the rate of adsorption and diffusion) need to be modified in order to apply to soils containing hydrophilic soils. In this talk we examine the Darcy-scale definition of pressure and chemical potential, especially as it applies to hydrophilic soils. To arrive at our model, we used hybrid mixture theory - first pioneered by Hassanizadeh and Gray in 1979. The technique involves averaging the field equations (i.e. conservation of mass, momentum balance, energy balance, etc.) to obtain macroscopic field equations, where each field variable is defined precisely in terms of its microscale counterpart. To close the system consistently with classical thermodynamics, the entropy inequality is exploited in the sense of Coleman and Noll. With the exceptions that the macroscale field variables are defined precisely in terms of their microscale counterparts and that microscopic interfacial equations can also be treated in a similar manner, the resulting system of equations is consistent with those derived using classical mixture theory. Hence the terminology, Hybrid Mixture Theory.
The accumulation pattern of ferruginol in the heartwood-forming Cryptomeria japonica xylem as determined by time-of-flight secondary ion mass spectrometry and quantity analysis

PubMed Central

Kuroda, Katsushi; Fujiwara, Takeshi; Hashida, Koh; Imai, Takanori; Kushi, Masayoshi; Saito, Kaori; Fukushima, Kazuhiko

2014-01-01

Background and Aims Heartwood formation is a unique phenomenon of tree species. Although the accumulation of heartwood substances is a well-known feature of the process, the accumulation mechanism remains unclear. The aim of this study was to determine the accumulation process of ferruginol, a predominant heartwood substance of Cryptomeria japonica, in heartwood-forming xylem. Methods The radial accumulation pattern of ferruginol was examined from sapwood and through the intermediate wood to the heartwood by direct mapping using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The data were compared with quantitative results obtained from a novel method of gas chromatography analysis using laser microdissection sampling and with water distribution obtained from cryo-scanning electron microscopy. Key Results Ferruginol initially accumulated in the middle of the intermediate wood, in the earlywood near the annual ring boundary. It accumulated throughout the entire earlywood in the inner intermediate wood, and in both the earlywood and the latewood in the heartwood. The process of ferruginol accumulation continued for more than eight annual rings. Ferruginol concentration peaked at the border between the intermediate wood and heartwood, while the concentration was less in the latewood compared wiht the earlywood in each annual ring. Ferruginol tended to accumulate around the ray parenchyma cells. In addition, at the border between the intermediate wood and heartwood, the accumulation was higher in areas without water than in areas with water. Conclusions TOF-SIMS clearly revealed ferruginol distribution at the cellular level. Ferruginol accumulation begins in the middle of intermediate wood, initially in the earlywood near the annual ring boundary, then throughout the entire earlywood, and finally across to the whole annual ring in the heartwood. The heterogeneous timing of ferruginol accumulation could be related to the distribution of ray parenchyma cells
Characterization of the startup transient electrokinetic flow in rectangular channels of arbitrary dimensions, zeta potential distribution, and time-varying pressure gradient.

PubMed

Miller, Andrew; Villegas, Arturo; Diez, F Javier

2015-03-01

The solution to the startup transient EOF in an arbitrary rectangular microchannel is derived analytically and validated experimentally. This full 2D transient solution describes the evolution of the flow through five distinct periods until reaching a final steady state. The derived analytical velocity solution is validated experimentally for different channel sizes and aspect ratios under time-varying pressure gradients. The experiments used a time resolved micro particle image velocimetry technique to calculate the startup transient velocity profiles. The measurements captured the effect of time-varying pressure gradient fields derived in the analytical solutions. This is tested by using small reservoirs at both ends of the channel which allowed a time-varying pressure gradient to develop with a time scale on the order of the transient EOF. Results showed that under these common conditions, the effect of the pressure build up in the reservoirs on the temporal development of the transient startup EOF in the channels cannot be neglected. The measurements also captured the analytical predictions for channel walls made of different materials (i.e., zeta potentials). This was tested in channels that had three PDMS and one quartz wall, resulting in a flow with an asymmetric velocity profile due to variations in the zeta potential between the walls. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Pressure Relief Devices

NASA Astrophysics Data System (ADS)

Manha, William D.

2010-09-01

Pressure relief devices are used in pressure systems and on pressure vessels to prevent catastrophic rupture or explosion from excessive pressure. Pressure systems and pressure vessels have manufacturers maximum rated operating pressures or maximum design pressures(MDP) for which there are relatively high safety factors and minimum risk of rupture or explosion. Pressure systems and pressure vessels that have a potential to exceed the MDP by being connected to another higher pressure source, a compressor, or heat to water(boiler) are required to have over-pressure protecting devices. Such devices can be relief valves and/or burst discs to safely relieve potentially excessive pressure and prevent unacceptable ruptures and explosions which result in fail-safe pressure systems and pressure vessels. Common aerospace relief valve and burst disc requirements and standards will be presented. This will include the NASA PSRP Interpretation Letter TA-88-074 Fault Tolerance of Systems Using Specially Certified Burst Disks that dictates burst disc requirements for payloads on Shuttle. Two recent undesirable manned space payloads pressure relief devices and practices will be discussed, as well as why these practices should not be continued. One example for discussion is the use of three burst discs that have been placed in series to comply with safety requirements of three controls to prevent a catastrophic hazard of the over-pressurization and rupture of pressure system and/or vessels. The cavities between the burst discs are evacuated and are the reference pressures for activating the two upstream burst discs. If the upstream burst disc leaks into the reference cavity, the reference pressure increases and it can increase the burst disc activating pressure and potentially result in the burst disc assembly being ineffective for over pressure protection. The three burst discs-in-series assembly was found acceptable because the burst discs are designed for minimum risk(DFMR) of
The dynamics of carbon stored in xylem sapwood to drought-induced hydraulic stress in mature trees

PubMed Central

Yoshimura, Kenichi; Saiki, Shin-Taro; Yazaki, Kenichi; Ogasa, Mayumi Y.; Shirai, Makoto; Nakano, Takashi; Yoshimura, Jin; Ishida, Atsushi

2016-01-01

Climate-induced forest die-off is widespread in multiple biomes, strongly affecting the species composition, function and primary production in forest ecosystems. Hydraulic failure and carbon starvation in xylem sapwood are major hypotheses to explain drought-induced tree mortality. Because it is difficult to obtain enough field observations on drought-induced mortality in adult trees, the current understanding of the physiological mechanisms for tree die-offs is still controversial. However, the simultaneous examination of water and carbon uses throughout dehydration and rehydration processes in adult trees will contribute to clarify the roles of hydraulic failure and carbon starvation in tree wilting. Here we show the processes of the percent loss of hydraulic conductivity (PLC) and the content of nonstructural carbohydrates (NSCs) of distal branches in woody plants with contrasting water use strategy. Starch was converted to soluble sugar during PLC progression under drought, and the hydraulic conductivity recovered following water supply. The conversion of NSCs is strongly associated with PLC variations during dehydration and rehydration processes, indicating that stored carbon contributes to tree survival under drought; further carbon starvation can advance hydraulic failure. We predict that even slow-progressing drought degrades forest ecosystems via carbon starvation, causing more frequent catastrophic forest die-offs than the present projection. PMID:27079677
The dynamics of carbon stored in xylem sapwood to drought-induced hydraulic stress in mature trees

NASA Astrophysics Data System (ADS)

Yoshimura, Kenichi; Saiki, Shin-Taro; Yazaki, Kenichi; Ogasa, Mayumi Y.; Shirai, Makoto; Nakano, Takashi; Yoshimura, Jin; Ishida, Atsushi

2016-04-01

Climate-induced forest die-off is widespread in multiple biomes, strongly affecting the species composition, function and primary production in forest ecosystems. Hydraulic failure and carbon starvation in xylem sapwood are major hypotheses to explain drought-induced tree mortality. Because it is difficult to obtain enough field observations on drought-induced mortality in adult trees, the current understanding of the physiological mechanisms for tree die-offs is still controversial. However, the simultaneous examination of water and carbon uses throughout dehydration and rehydration processes in adult trees will contribute to clarify the roles of hydraulic failure and carbon starvation in tree wilting. Here we show the processes of the percent loss of hydraulic conductivity (PLC) and the content of nonstructural carbohydrates (NSCs) of distal branches in woody plants with contrasting water use strategy. Starch was converted to soluble sugar during PLC progression under drought, and the hydraulic conductivity recovered following water supply. The conversion of NSCs is strongly associated with PLC variations during dehydration and rehydration processes, indicating that stored carbon contributes to tree survival under drought; further carbon starvation can advance hydraulic failure. We predict that even slow-progressing drought degrades forest ecosystems via carbon starvation, causing more frequent catastrophic forest die-offs than the present projection.
The Integrated Role of Water Availability, Nutrient Dynamics, and Xylem Hydraulic Dysfunction on Plant Rooting Strategies in Managed and Natural Ecosystems

NASA Astrophysics Data System (ADS)

Mackay, D. S.; Savoy, P.; Pleban, J. R.; Tai, X.; Ewers, B. E.

2015-12-01

Plants adapt or acclimate to changing environments in part by allocating biomass to roots and leaves to strike a balance between water and nutrient uptake requirements on the one hand and growth and hydraulic safety on the other hand. In a recent study examining experimental drought with the TREES model, which couples plant ecophysiology with rhizosphere-and-xylem hydraulics, we hypothesized that the asynchronous nature of soil water availability and xylem repair supported root-to-leaf area (RLA) proportionality that favored long-term survival over short-term carbon gain or water use. To investigate this as a possible general principal of plant adjustment to changing environmental conditions, TREES was modified to allocate carbon to fine and coarse roots organized in ten orders differing in biomass allocated per unit absorbing root area, root lifespan, and total absorbing root area in each of several soil-root zones with depth. The expanded model allowed for adjustment of absorbing root area and rhizosphere volume based on available carbohydrate production and nitrogen (N) availability, resulting in dynamic expansion and contraction of the supply-side of the rhizosphere-plant hydraulics and N uptake capacity in response to changing environmental conditions and plant-environment asynchrony. The study was conducted partly in a controlled experimental setting with six genotypes of a widely grown crop species, Brassica rapa. The implications for forests were investigated in controlled experiments and at Fluxnet sites representing temperate mixed forests, semi-arid evergreen needle-leaf, and Mediterranean biomes. The results showed that the effects of N deficiency on total plant growth was modulated by a relative increase in fine root biomass representing a larger absorbing root volume per unit biomass invested. We found that the total absorbing root area per unit leaf area was consistently lower than that needed to maximize short-term water uptake and carbohydrate gain

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