Transduction of the Root Gravitropic Stimulus: Can Apical Calcium Regulate Auxin Distribution?

NASA Technical Reports Server (NTRS)

Edwards, K. L.

1985-01-01

The hypothesis was tested that calcium, asymmetrically distributes in the root cap upon reorientation to gravity, affects auxin transport and thereby auxin distribution at the elongation zone. It is assumed that calcium exists in the root cap and is asymmetrically transported in root caps altered from a vertical to a horizontal position and that the meristem, the tissue immediately adjacent to the root cap and lying between the site of gravity perception and the site of gravity response, is essential for mediation of gravitropism. Tip calcium in root gravicurvature was implicated. The capstone evidence is that the root cap has the capacity to polarly translocate exogenous calcium downward when tissue is oriented horizontally, and that exogenous calcium, when supplied asymmetrically at the root tip, induces curvature and dictates the direction of curvature in both vertical and horizontal corn roots.

Effect of Environmental Density and Buoyancy on Growth and Gravitropic Response in Maize Roots

NASA Astrophysics Data System (ADS)

Robbins, J. L.; Mulkey, T. J.

2008-06-01

The mechanism by which plants sense gravity is not fully understood. The hydrostatic model was proposed as an alternative to the statolith model. These experiments are designed to provide further understanding about the underlying mechanism of the gravitropic sensing. Primary roots of maize with a length of about 1 cm were used. The roots were placed in environments of various density and buoyancy using air, water, sucrose, sucrose/polyethylene glycol 4000 (PEG), PEG 8000, and Ficoll PM 400. The rates of growth and gravitropic curvature were monitored using time-lapse video and digital recordings. Comparison of roots in air to roots in oxygenated water indicate that there is no significant difference in growth rates but the higher density of water and the other test solutions significantly slows the gravitropic response. Altering the environmental density and buoyancy of the solution surrounding the root does not appear to alter sedimentation of statoliths within the root tip.

Characterization of root agravitropism induced by genetic, chemical, and developmental constraints

NASA Technical Reports Server (NTRS)

Moore, R.; Fondren, W. M.; Marcum, H.

1987-01-01

The patterns and rates of organelle redistribution in columella (i.e., putative statocyte) cells of agravitropic agt mutants of Zea mays are not significantly different from those of columella cells in graviresponsive roots. Graviresponsive roots of Z. mays are characterized by a strongly polar movement of 45Ca2+ across the root tip from the upper to the lower side. Horizontally-oriented roots of agt mutants exhibit only a minimal polar transport of 45Ca2+. Exogenously-induced asymmetries of Ca result in curvature of agt roots toward the Ca source. A similar curvature can be induced by a Ca asymmetry in normally nongraviresponsive (i.e., lateral) roots of Phaseolus vulgaris. Similarly, root curvature can be induced by placing the roots perpendicular to an electric field. This electrotropism increased with 1) currents between 8-35 mA, and 2) time between 1-9 hr when the current is constant. Electrotropism is reduced significantly by treating roots with triiodobenzoic acid (TIBA), an inhibitor of auxin transport. These results suggest that 1) if graviperception occurs via the sedimentation of amyloplasts in columella cells, then nongraviresponsive roots apparently sense gravity as do graviresponsive roots, 2) exogenously-induced asymmetries of a gravitropic effector (i.e., Ca) can induce curvature of normally nongraviresponsive roots, 3) the gravity-induced downward movement of exogenously-applied 45Ca2+ across tips of graviresponsive roots does not occur in nongraviresponsive roots, 4) placing roots in an electrical field (i.e., one favoring the movement of ions such as Ca2+) induces root curvature, and 5) electrically-induced curvature is apparently dependent on auxin transport. These results are discussed relative to a model to account for the lack of graviresponsiveness by these roots.

Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism

PubMed Central

Band, Leah R.; Wells, Darren M.; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M.; French, Andrew P.; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H.; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M.; Estelle, Mark; Owen, Markus R.; Vissenberg, Kris; Hodgman, T. Charlie; Pridmore, Tony P.; King, John R.; Vernoux, Teva; Bennett, Malcolm J.

2012-01-01

Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a “tipping point” mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution. PMID:22393022

Root gravitropism is regulated by a transient lateral auxin gradient controlled by a tipping-point mechanism.

PubMed

Band, Leah R; Wells, Darren M; Larrieu, Antoine; Sun, Jianyong; Middleton, Alistair M; French, Andrew P; Brunoud, Géraldine; Sato, Ethel Mendocilla; Wilson, Michael H; Péret, Benjamin; Oliva, Marina; Swarup, Ranjan; Sairanen, Ilkka; Parry, Geraint; Ljung, Karin; Beeckman, Tom; Garibaldi, Jonathan M; Estelle, Mark; Owen, Markus R; Vissenberg, Kris; Hodgman, T Charlie; Pridmore, Tony P; King, John R; Vernoux, Teva; Bennett, Malcolm J

2012-03-20

Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a "tipping point" mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution.

Molecular genetics of root gravitropism and waving in Arabidopsis thaliana

NASA Technical Reports Server (NTRS)

Sedbrook, J.; Boonsirichai, K.; Chen, R.; Hilson, P.; Pearlman, R.; Rosen, E.; Rutherford, R.; Batiza, A.; Carroll, K.; Schulz, T.;

An electric current associated with gravity sensing in maize roots

NASA Technical Reports Server (NTRS)

Bjorkman, T.; Leopold, A. C.

1987-01-01

The study of gravisensing would be greatly enhanced if physiological events associated with gravity sensing could be detected separately from subsequent growth processes. This report presents a means to discriminate sensing from the growth processes. By using a vibrating probe, we have found an electric current generated by the gravity sensing region of the root cap of maize (Zea mays cv Merit) in response to gravistimulation. On the upper surface of the root cap, the change from the endogenous current has a density of 0.55 microampere per square centimeter away from gravity. The onset of the current shift has a characteristic of lag of three to four minutes after gravistimulation, which corresponds to the presentation time for gravity sensing in this tissue. A description of the current provides some information about the sensing mechanism, as well as being a valuable means to detect gravity sensing independently of differential growth.

Reversible loss of gravitropic sensitivity in maize roots after tip application of calcium chelators

NASA Technical Reports Server (NTRS)

Lee, J. S.; Mulkey, T. J.; Evans, M. L.

1983-01-01

The application of calcium chelating agents (EDTA or EGTA) to the tips of maize roots caused a loss of gravitropic sensitivity. When the chelator was replaced with calcium chloride, gravitropic sensitivity was restored. Asymmetric application of calcium chloride near the tip of a vertical root caused curvature toward the calcium source. When the calcium was applied to the upper surface of the tip of a root oriented horizontally, the root curved upward even though control roots exhibited strong downward curvature. Application of calcium chloride to the tips of decapped roots, which are known to be gravitropically insensitive, did not restore gravitropic sensitivity. However, asymmetric application of calcium chloride near the tips of decapped roots caused curvature toward the calcium source. Calcium may play a key role in linking gravity detection to gravitropic curvature in roots.

Actin Turnover-Mediated Gravity Response in Maize Root Apices

PubMed Central

Mancuso, Stefano; Barlow, Peter W; Volkmann, Dieter

2006-01-01

The dynamic actin cytoskeleton has been proposed to be linked to gravity sensing in plants but the mechanistic understanding of these processes remains unknown. We have performed detailed pharmacological analyses of the role of the dynamic actin cytoskeleton in gravibending of maize (Zea mays) root apices. Depolymerization of actin filaments with two drugs having different mode of their actions, cytochalasin D and latrunculin B, stimulated root gravibending. By contrast, drug-induced stimulation of actin polymerization and inhibition of actin turnover, using two different agents phalloidin and jasplakinolide, compromised the root gravibending. Importantly, all these actin drugs inhibited root growth to similar extents suggesting that high actin turnover is essential for the gravity-related growth responses rather than for the general growth process. Both latrunculin B and cytochalasin D treatments inhibited root growth but restored gravibending of the decapped root apices, indicating that there is a strong potential for effective actin-mediated gravity sensing outside the cap. This elusive gravity sensing outside the root cap is dependent not only on the high rate of actin turnover but also on weakening of myosin activities, as general inhibition of myosin ATPases induced stimulation of gravibending of the decapped root apices. Collectively, these data provide evidence for the actin turnover-mediated gravity sensing outside the root cap. PMID:19521476

Effect of inhibitors of auxin transport and of calmodulin on a gravisensing-dependent current in maize roots

NASA Technical Reports Server (NTRS)

Bjorkman, T.; Leopold, A. C.

1987-01-01

Some characteristics of the gravity sensing mechanism in maize root caps were investigated using a bioelectric current as an indicator of gravity sensing. This technique involves the measurement of a change in the current density which arises at the columella region coincidently with the presentation time. Two inhibitors of auxin transport, triiodobenzoic acid and naphthylphthalamic acid, blocked gravitropic curvature but not the change in current density. Two inhibitors of calmodulin activity, compound 48/80 and calmidazolium, blocked both curvature and gravity-induced current. The results suggest that auxin transport is not a component of gravity sensing in the root cap. By contrast, the results suggest that calmodulin plays an intrinsic role in gravity sensing.

Characterizing pathways by which gravitropic effectors could move from the root cap to the root of primary roots of Zea mays

NASA Technical Reports Server (NTRS)

Moore, R.; McClelen, C. E.

1989-01-01

Plasmodesmata linking the root cap and root in primary roots Zea mays are restricted to approx. 400 protodermal cells bordering approx. 110000 microns2 of the calyptrogen of the root cap. This area is less than 10% of the cross-sectional area of the root-tip at the cap junction. Therefore, gravitropic effectors moving from the root cap to the root can move symplastically only through a relatively small area in the centre of the root. Decapped roots are non-responsive to gravity. However, decapped roots whose caps are replaced immediately after decapping are strongly graviresponsive. Thus, gravicurvature occurs only when the root cap contacts the root, and symplastic continuity between the cap and root is not required for gravicurvature. Completely removing mucilage from the root tip renders the root non-responsive to gravity. Taken together, these data suggest that gravitropic effectors move apoplastically through mucilage from the cap to the root.

Nodal endoplasmic reticulum, a specialized form of endoplasmic reticulum found in gravity-sensing root tip columella cells

NASA Technical Reports Server (NTRS)

Zheng, H. Q.; Staehelin, L. A.

2001-01-01

The endoplasmic reticulum (ER) of columella root cap cells has been postulated to play a role in gravity sensing. We have re-examined the ultrastructure of columella cells in tobacco (Nicotiana tabacum) root tips preserved by high-pressure freezing/freeze-substitution techniques to gain more precise information about the organization of the ER in such cells. The most notable findings are: the identification of a specialized form of ER, termed "nodal ER," which is found exclusively in columella cells; the demonstration that the bulk of the ER is organized in the form of a tubular network that is confined to a peripheral layer under the plasma membrane; and the discovery that this ER-rich peripheral region excludes Golgi stacks, vacuoles, and amyloplasts but not mitochondria. Nodal ER domains consist of an approximately 100-nm-diameter central rod composed of oblong subunits to which usually seven sheets of rough ER are attached along their margins. These domains form patches at the interface between the peripheral ER network and the ER-free central region of the cells, and they occupy defined positions within central and flanking columella cells. Over one-half of the nodal ER domains are located along the outer tangential walls of the flanking cells. Cytochalasin D and latrunculin A cause an increase in size and a decrease in numbers of nodal ER domains. We postulate that the nodal ER membranes locally modulate the gravisensing signals produced by the sedimenting amyloplasts, and that the confinement of all ER membranes to the cell periphery serves to enhance the sedimentability of the amyloplasts in the central region of columella cells.

Genetical approach to gravitropism

NASA Astrophysics Data System (ADS)

Boonsirichai, K.; Chen, R.; Guan, C.; Rosen, E.; Young, L.; Masson, P.

Gravitropism guides the growth of plant organs at a defined angle from the gravity vector. Accordingly, most roots grow downward, undergoing positive gravitropism. Gravity perception by roots appears to involve the sedimentation of amyloplasts within the columella cells of the cap. Amyloplast sedimentation triggers a signal transduction pathway that promotes the development of an auxin gradient across the root tip. This gradient is then transmitted to the elongation zones where it promotes a differential cellular elongation, partly responsible for the development of a root-tip curvature. To better understand the mechanisms involved in gravity signal transduction, we have identified and characterized several Arabidopsis thaliana mutants that show specific defects in root gravitropism. Several of these genes were characterized. ARG1 functions in gravity signal transduction, and encodes a dnaJ-like protein whose structure suggests an interaction with the cytoskeleton. Two other genes encode similar proteins (ARL1 and ARL2) in Arabidopsis. One of them (ARL2) also appears to function in gravity signal transduction. Because loss-of-function mutations in ARG1 result in partial alterations of gravitropism, we were able to identify and characterize two genetic enhancers of arg1-2: mar1-1 and mar2-1. These enhancers increased the gravitropism defect of arg1-2 roots and hypocotyls, and changed its orientation. Hence, MAR1 and MAR2 also appear to function in gravity signal transduction. AGR1, on the other hand, encodes a transmembrane component of the auxin efflux carrier complex involved in polar auxin transport through the elongation zones of Arabidopsis root tips. It belongs to a large gene family, several members of which are expressed in the root cap. Upon gravistimulation, the AGR3 protein appears to quickly relocate within the columella cells, accumulating in membranes at the new physical bottom. Hence, the gravity signal transduction pathway that includes the ARG1, ARL2, MAR1 and MAR2 gene products, appears to control the cellular distribution of auxin efflux carriers in the columella cells of the root cap, thereby controlling the polarity of lateral auxin transport in response to gravistimulation. Work is in progress to identify new proteins that interact genetically or physically with ARG1, ARL2 or AGR1, and characterize their involvement in gravitropism.

Actin is an essential component of plant gravitropic signaling pathways

NASA Astrophysics Data System (ADS)

Braun, Markus; Hauslage, Jens; Limbach, Christoph

2003-08-01

A role of the actin cytoskeleton in the different phases of gravitropism in higher plant organs seems obvious, but experimental evidence is still inconclusive and contradictory. In gravitropically tip-growing rhizoids and protonemata, however, it is well documented that actin is an essential component of the tip-growth machinery and is involved either in the cellular mechanisms that lead to gravity sensing and in the processes of the graviresponses that result in the reorientation of the growth direction. All these processes depend on a complexly organized and highly dynamic organization of actin filaments whose diverse functions are coordinated by numerous associated proteins. Actin filaments and myosins mediate the transport of secretory vehicles to the growing tip and precisely control the delivery of cell wall material. In addition, both cell types use a very efficient actomyosin-based system to control and correct the position of their statoliths and to direct sedimenting statoliths to confined graviperception sites at the plasma membrane. The studies presented in this paper provide evidence for the essential role of actin in plant gravity sensing and the gravitropic responses. A unique actin-organizing center exists in the tip of characean rhizoids and protonemata which is associated with and dynamically regulated by a specific set of actin-dynamizing proteins. It is concluded that this highly dynamic apical actin array is an essential prerequisite for gravity sensing and gravity-oriented tip growth.

Actin-based gravity-sensing mechanisms in unicellular plant model systems

NASA Astrophysics Data System (ADS)

Braun, Markus; Limbach, Christoph

2005-08-01

Considerable progress has been made in the understanding of the molecular and cellular mechanisms underlying gravity sensing and gravity-oriented polarized growth in single-celled rhizoids and protonemata of the characean algae. It is well known that the actin cytoskeleton plays a key role in these processes. Numerous actin-binding proteins control apical actin polymerization and the dynamic remodeling of the actin arrangement. An actomyosin-based system mediates the delivery and incorporation of secretory vesicles at the growing tip and coordinates the tip-high gradient of cytoplasmic free calcium which is required for local exocytosis. Additionally, the actomyosin system precisely controls the position of statoliths and, upon a change in orientation relative to the gravity vector, directs sedimenting statoliths to the confined graviperception sites of the plasma membrane where gravitropic signalling is initiated. The upward growth response of protonemata is preceded by an actin-dependent relocalization of the Ca2+-gradient to the upper flank. The downward growth response of rhizoids, however, is caused by differential growth of the opposite flankes due to a local reduction of cytoplasmic free calcium limited to the plasma membrane area where statoliths are sedimented. Thus, constant actin polymerization in the growing tip and the spatiotemporal control of actin remodeling are essential for gravity sensing and gravity-oriented polarized growth of characean rhizoids and protonemata.

The effect of the external medium on the gravitropic curvature of rice (Oryza sativa, Poaceae) roots

NASA Technical Reports Server (NTRS)

Staves, M. P.; Wayne, R.; Leopold, A. C.

1997-01-01

The roots of rice seedlings, growing in artificial pond water, exhibit robust gravitropic curvature when placed perpendicular to the vector of gravity. To determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best accounts for gravity sensing in rice roots, we changed the physical properties of the external medium with impermeant solutes and examined the effect on gravitropism. As the density of the external medium is increased, the rate of gravitropic curvature decreases. The decrease in the rate of gravicurvature cannot be attributed to an inhibition of growth, since rice roots grown in 100 Osm/m3 (0.248 MPa) solutions of different densities all support the same root growth rate but inhibit gravicurvature increasingly with increasing density. By contrast, the sedimentation rate of amyloplasts in the columella cells is unaffected by the external density. These results are consistent with the gravitational pressure theory of gravity sensing, but cannot be explained by the statolith theory.

Root gravitropism: an experimental tool to investigate basic cellular and molecular processes underlying mechanosensing and signal transmission in plants

NASA Technical Reports Server (NTRS)

Boonsirichai, K.; Guan, C.; Chen, R.; Masson, P. H.

2002-01-01

The ability of plant organs to use gravity as a guide for growth, named gravitropism, has been recognized for over two centuries. This growth response to the environment contributes significantly to the upward growth of shoots and the downward growth of roots commonly observed throughout the plant kingdom. Root gravitropism has received a great deal of attention because there is a physical separation between the primary site for gravity sensing, located in the root cap, and the site of differential growth response, located in the elongation zones (EZs). Hence, this system allows identification and characterization of different phases of gravitropism, including gravity perception, signal transduction, signal transmission, and curvature response. Recent studies support some aspects of an old model for gravity sensing, which postulates that root-cap columellar amyloplasts constitute the susceptors for gravity perception. Such studies have also allowed the identification of several molecules that appear to function as second messengers in gravity signal transduction and of potential signal transducers. Auxin has been implicated as a probable component of the signal that carries the gravitropic information between the gravity-sensing cap and the gravity-responding EZs. This has allowed the identification and characterization of important molecular processes underlying auxin transport and response in plants. New molecular models can be elaborated to explain how the gravity signal transduction pathway might regulate the polarity of auxin transport in roots. Further studies are required to test these models, as well as to study the molecular mechanisms underlying a poorly characterized phase of gravitropism that is independent of an auxin gradient.

Basipetal auxin transport is required for gravitropism in roots of Arabidopsis

NASA Technical Reports Server (NTRS)

Rashotte, A. M.; Brady, S. R.; Reed, R. C.; Ante, S. J.; Muday, G. K.; Davies, E. (Principal Investigator)

2000-01-01

Auxin transport has been reported to occur in two distinct polarities, acropetally and basipetally, in two different root tissues. The goals of this study were to determine whether both polarities of indole-3-acetic acid (IAA) transport occur in roots of Arabidopsis and to determine which polarity controls the gravity response. Global application of the auxin transport inhibitor naphthylphthalamic acid (NPA) to roots blocked the gravity response, root waving, and root elongation. Immediately after the application of NPA, the root gravity response was completely blocked, as measured by an automated video digitizer. Basipetal [(3)H]IAA transport in Arabidopsis roots was inhibited by NPA, whereas the movement of [(14)C]benzoic acid was not affected. Inhibition of basipetal IAA transport by local application of NPA blocked the gravity response. Inhibition of acropetal IAA transport by application of NPA at the root-shoot junction only partially reduced the gravity response at high NPA concentrations. Excised root tips, which do not receive auxin from the shoot, exhibited a normal response to gravity. The Arabidopsis mutant eir1, which has agravitropic roots, exhibited reduced basipetal IAA transport but wild-type levels of acropetal IAA transport. These results support the hypothesis that basipetally transported IAA controls root gravitropism in Arabidopsis.

Root phototropism: from dogma to the mechanism of blue light perception.

PubMed

Kutschera, Ulrich; Briggs, Winslow R

2012-03-01

In roots, the "hidden half" of all land plants, gravity is an important signal that determines the direction of growth in the soil. Hence, positive gravitropism has been studied in detail. However, since the 19th century, the response of roots toward unilateral light has also been analyzed. Based on studies on white mustard (Sinapis alba) seedlings, botanists have concluded that all roots are negatively phototropic. This "Sinapis-dogma" was refuted in a seminal study on root phototropism published a century ago, where it was shown that less then half of the 166 plant species investigated behave like S. alba, whereas 53% displayed no phototropic response at all. Here we summarize the history of research on root phototropism, discuss this phenomenon with reference to unpublished data on garden cress (Lepidium sativum) seedlings, and describe the effects of blue light on the negative bending response in Thale cress (Arabidopsis thaliana). The ecological significance of root phototropism is discussed and the relationships between gravi- and phototropism are outlined, with respect to the starch-statolith-theory of gravity perception. Finally, we present an integrative model of gravi- and blue light perception in the root tip of Arabidopsis seedlings. This hypothesis is based on our current view of the starch-statolith-concept and light sensing via the cytoplasmic red/blue light photoreceptor phytochrome A and the plasma membrane-associated blue light receptor phototropin-1. Open questions and possible research agendas for the future are summarized.

UWB Wind Turbine Blade Deflection Sensing for Wind Energy Cost Reduction.

PubMed

Zhang, Shuai; Jensen, Tobias Lindstrøm; Franek, Ondrej; Eggers, Patrick C F; Olesen, Kim; Byskov, Claus; Pedersen, Gert Frølund

2015-08-12

A new application of utilizing ultra-wideband (UWB) technology to sense wind turbine blade deflections is introduced in this paper for wind energy cost reduction. The lower UWB band of 3.1-5.3 GHz is applied. On each blade, there will be one UWB blade deflection sensing system, which consists of two UWB antennas at the blade root and one UWB antenna at the blade tip. The detailed topology and challenges of this deflection sensing system are addressed. Due to the complexity of the problem, this paper will first realize the on-blade UWB radio link in the simplest case, where the tip antenna is situated outside (and on the surface of) a blade tip. To investigate this case, full-blade time-domain measurements are designed and conducted under different deflections. The detailed measurement setups and results are provided. If the root and tip antenna locations are properly selected, the first pulse is always of sufficient quality for accurate estimations under different deflections. The measured results reveal that the blade tip-root distance and blade deflection can be accurately estimated in the complicated and lossy wireless channels around a wind turbine blade. Some future research topics on this application are listed finally.

Cytochalasin D does not inhibit gravitropism in roots

NASA Technical Reports Server (NTRS)

Staves, M. P.; Wayne, R.; Leopold, A. C.

1997-01-01

It is generally thought that sedimenting plastids are responsible for gravity sensing in higher plants. We directly tested the model generated by the current statolith hypothesis that the gravity sensing that leads to gravitropism results from an interaction between the plastids and actin microfilaments. We find that the primary roots of rice, corn, and cress undergo normal gravitropism and growth even when exposed to cytochalasin D, a disruptor of actin microfilaments. These results indicate that an interaction between amyloplasts and the actin cytoskeleton is not critical for gravity sensing in higher plants and weaken the current statolith hypothesis.

UWB Wind Turbine Blade Deflection Sensing for Wind Energy Cost Reduction

PubMed Central

Zhang, Shuai; Jensen, Tobias Lindstrøm; Franek, Ondrej; Eggers, Patrick C. F.; Olesen, Kim; Byskov, Claus; Pedersen, Gert Frølund

2015-01-01

A new application of utilizing ultra-wideband (UWB) technology to sense wind turbine blade deflections is introduced in this paper for wind energy cost reduction. The lower UWB band of 3.1–5.3 GHz is applied. On each blade, there will be one UWB blade deflection sensing system, which consists of two UWB antennas at the blade root and one UWB antenna at the blade tip. The detailed topology and challenges of this deflection sensing system are addressed. Due to the complexity of the problem, this paper will first realize the on-blade UWB radio link in the simplest case, where the tip antenna is situated outside (and on the surface of) a blade tip. To investigate this case, full-blade time-domain measurements are designed and conducted under different deflections. The detailed measurement setups and results are provided. If the root and tip antenna locations are properly selected, the first pulse is always of sufficient quality for accurate estimations under different deflections. The measured results reveal that the blade tip-root distance and blade deflection can be accurately estimated in the complicated and lossy wireless channels around a wind turbine blade. Some future research topics on this application are listed finally. PMID:26274964

Gravity sensing and signal transduction in vascular plant primary roots.

PubMed

Baldwin, Katherine L; Strohm, Allison K; Masson, Patrick H

2013-01-01

During gravitropism, the potential energy of gravity is converted into a biochemical signal. How this transfer occurs remains one of the most exciting mysteries in plant cell biology. New experiments are filling in pieces of the puzzle. In this review, we introduce gravitropism and give an overview of what we know about gravity sensing in roots of vascular plants, with special highlight on recent papers. When plant roots are reoriented sideways, amyloplast resedimentation in the columella cells is a key initial step in gravity sensing. This process somehow leads to cytoplasmic alkalinization of these cells followed by relocalization of auxin efflux carriers (PINs). This changes auxin flow throughout the root, generating a lateral gradient of auxin across the cap that upon transmission to the elongation zone leads to differential cell elongation and gravibending. We will present the evidence for and against the following players having a role in transferring the signal from the amyloplast sedimentation into the auxin signaling cascade: mechanosensitive ion channels, actin, calcium ions, inositol trisphosphate, receptors/ligands, ARG1/ARL2, spermine, and the TOC complex. We also outline auxin transport and signaling during gravitropism.

Tip-localized actin polymerization and remodeling, reflected by the localization of ADF, profilin and villin, are fundamental for gravity-sensing and polar growth in characean rhizoids.

PubMed

Braun, Markus; Hauslage, Jens; Czogalla, Aleksander; Limbach, Christoph

2004-07-01

Polar organization and gravity-oriented, polarized growth of characean rhizoids are dependent on the actin cytoskeleton. In this report, we demonstrate that the prominent center of the Spitzenkörper serves as the apical actin polymerization site in the extending tip. After cytochalasin D-induced disruption of the actin cytoskeleton, the regeneration of actin microfilaments (MFs) starts with the reappearance of a flat, brightly fluorescing actin array in the outermost tip. The actin array rounds up, produces actin MFs that radiate in all directions and is then relocated into its original central position in the center of the Spitzenkörper. The emerging actin MFs rearrange and cross-link to form the delicate, subapical meshwork, which then controls the statolith positioning, re-establishes the tip-high calcium gradient and mediates the reorganization of the Spitzenkörper with its central ER aggregate and the accumulation of secretory vesicles. Tip growth and gravitropic sensing, which includes control of statolith positioning and gravity-induced sedimentation, are not resumed until the original polar actin organization is completely restored. Immunolocalization of the actin-binding proteins, actin-depolymerizing factor (ADF) and profilin, which both accumulate in the center of the Spitzenkörper, indicates high actin turnover and gives additional support for the actin-polymerizing function of this central, apical area. Association of villin immunofluorescence with two populations of thick undulating actin cables with uniform polarity underlying rotational cytoplasmic streaming in the basal region suggests that villin is the major actin-bundling protein in rhizoids. Our results provide evidence that the precise coordination of apical actin polymerization and dynamic remodeling of actin MFs by actin-binding proteins play a fundamental role in cell polarization, gravity sensing and gravity-oriented polarized growth of characean rhizoids.

Root gravitropism: a complex response to a simple stimulus?

NASA Technical Reports Server (NTRS)

Rosen, E.; Chen, R.; Masson, P. H.

1999-01-01

Roots avoid depleting their immediate environment of essential nutrients by continuous growth. Root growth is directed by environmental cues, including gravity. Gravity sensing occurs mainly in the columella cells of the root cap. Upon reorientation within the gravity field, the root-cap amyloplasts sediment, generating a physiological signal that promotes the development of a curvature at the root elongation zones. Recent molecular genetic studies in Arabidopsis have allowed the identification of genes that play important roles in root gravitropism. Among them, the ARG1 gene encodes a DnaJ-like protein involved in gravity signal transduction, whereas the AUX1 and AGR1 genes encode proteins involved in polar auxin transport. These studies have important implications for understanding the intra- and inter-cellular signaling processes that underlie root gravitropism.

Complex physiological and molecular processes underlying root gravitropism

NASA Technical Reports Server (NTRS)

Chen, Rujin; Guan, Changhui; Boonsirichai, Kanokporn; Masson, Patrick H.

2002-01-01

Gravitropism allows plant organs to guide their growth in relation to the gravity vector. For most roots, this response to gravity allows downward growth into soil where water and nutrients are available for plant growth and development. The primary site for gravity sensing in roots includes the root cap and appears to involve the sedimentation of amyloplasts within the columella cells. This process triggers a signal transduction pathway that promotes both an acidification of the wall around the columella cells, an alkalinization of the columella cytoplasm, and the development of a lateral polarity across the root cap that allows for the establishment of a lateral auxin gradient. This gradient is then transmitted to the elongation zones where it triggers a differential cellular elongation on opposite flanks of the central elongation zone, responsible for part of the gravitropic curvature. Recent findings also suggest the involvement of a secondary site/mechanism of gravity sensing for gravitropism in roots, and the possibility that the early phases of graviresponse, which involve differential elongation on opposite flanks of the distal elongation zone, might be independent of this auxin gradient. This review discusses our current understanding of the molecular and physiological mechanisms underlying these various phases of the gravitropic response in roots.

Temperature sensing by primary roots of maize

NASA Technical Reports Server (NTRS)

Poff, K. L.

1990-01-01

Zea mays L. seedlings, grown on agar plates at 26 degrees C, reoriented the original vertical direction of their primary root when exposed to a thermal gradient applied perpendicular to the gravity vector. The magnitude and direction of curvature can not be explained simply by either a temperature or a humidity effect on root elongation. It is concluded that primary roots of maize sense temperature gradients in addition to sensing the gravitational force.

NPY genes play an essential role in root gravitropic responses in Arabidopsis.

PubMed

Li, Yuanting; Dai, Xinhua; Cheng, Youfa; Zhao, Yunde

2011-01-01

Plants can sense the direction of gravity and orient their growth to ensure that roots are anchored in soil and that shoots grow upward. Gravitropism has been studied extensively using Arabidopsis genetics, but the exact mechanisms for gravitropism are not fully understood. Here, we demonstrate that five NPY genes play a key role in Arabidopsis root gravitropism. NPY genes were previously identified as regulators of auxin-mediated organogenesis in a genetic pathway with the AGC kinases PID, PID2, WAG1, and WAG2. We show that all five NPY genes are highly expressed in primary root tips. The single npy mutants do not display obvious gravitropism defects, but the npy1 npy2 npy3 npy4 npy5 quintuple mutants show dramatic gravitropic phenotypes. Systematic analysis of all the npy double, triple, and quadruple combinations demonstrates that the five NPY genes all contribute to gravitropism. Our work indicates that gravitropism, phototropism, and organogenesis use analogous mechanisms in which at least one AGC kinase, one NPH3/NPY gene, and one ARF are required.

Genetic Analysis of Gravity Signal Transduction in Arabidopsis thaliana Seedlings

NASA Astrophysics Data System (ADS)

Boonsirichai, K.; Harrison, B.; Stanga, J.; Young, L.-S.; Neal, C.; Sabat, G.; Murthy, N.; Harms, A.; Sedbrook, J.; Masson, P.

The primary roots of Arabidopsis thaliana seedlings respond to gravity stimulation by developing a tip curvature that results from differential cellular elongation on opposite flanks of the elongation zone. This curvature appears modulated by a lateral gradient of auxin that originates in the gravity-perceiving cells (statocytes) of the root cap through an apparent lateral repositioning of a component the auxin efflux carrier complex within these cells (Friml et al, 2002, Nature 415: 806-809). Unfortunately, little is known about the molecular mechanisms that govern early phases of gravity perception and signal transduction within the root-cap statocytes. We have used a molecular genetic approach to uncover some of these mechanisms. Mutations in the Arabidopsis ARG1 and ARL2 genes, which encode J-domain proteins, resulted in specific alterations in root and hypocotyl gravitropism, without pleiotropic phenotypes. Interestingly, ARG1 and ARL2 appear to function in the same genetic pathway. A combination of molecular genetic, biochemical and cell-biological approaches were used to demonstrate that ARG1 functions in early phases of gravity signal transduction within the root and hypocotyl statocytes, and is needed for efficient lateral auxin transport within the cap. The ARG1 protein is associated with components of the secretory and/or endosomal pathways, suggesting its role in the recycling of components of the auxin efflux carrier complex between plasma membrane and endosome (Boonsirichai et al, 2003, Plant Cell 15:2612-2625). Genetic modifiers of arg1-2 were isolated and shown to enhance the gravitropic defect of arg1-2, while resulting in little or no gravitropic defects in a wild type ARG1 background. A slight tendency for arg1-2;mar1-1 and arg1-2;mar2-1 double-mutant organs to display an opposite gravitropic response compared to wild type suggests that all three genes contribute to the interpretation of the gravity-vector information by seedling organs. The molecular structure of these new loci is being investigated. Furthermore, a proteomic approach is being developed to characterize root-tip proteins that are differentially expressed, modified or targeted in response to gravity stimulation. We acknowledge funding by NASA and NSF.

Directional gravity sensing in gravitropism.

PubMed

Morita, Miyo Terao

2010-01-01

Plants can reorient their growth direction by sensing organ tilt relative to the direction of gravity. With respect to gravity sensing in gravitropism, the classic starch statolith hypothesis, i.e., that starch-accumulating amyloplast movement along the gravity vector within gravity-sensing cells (statocytes) is the probable trigger of subsequent intracellular signaling, is widely accepted. Several lines of experimental evidence have demonstrated that starch is important but not essential for gravity sensing and have suggested that it is reasonable to regard plastids (containers of starch) as statoliths. Although the word statolith means sedimented stone, actual amyloplasts are not static but instead possess dynamic movement. Recent studies combining genetic and cell biological approaches, using Arabidopsis thaliana, have demonstrated that amyloplast movement is an intricate process involving vacuolar membrane structures and the actin cytoskeleton. This review covers current knowledge regarding gravity sensing, particularly gravity susception, and the factors modulating the function of amyloplasts for sensing the directional change of gravity. Specific emphasis is made on the remarkable differences in the cytological properties, developmental origins, tissue locations, and response of statocytes between root and shoot systems. Such an approach reveals a common theme in directional gravity-sensing mechanisms in these two disparate organs.

Proteomic alterations in root tips of Arabidopsis thaliana seedlings under altered gravity conditions

NASA Astrophysics Data System (ADS)

Zheng, H. Q.; Wang, H.

Gravity has a profound influence on plant growth and development Removed the influence of gravitational acceleration by spaceflight caused a wide range of cellular changes in plant Whole seedling that germinated and grown on clinostats showed the absent of gravitropism At the cellular level clinostat treatment has specific effects on plant cells such as induce alterations in cell wall composition increase production of heat-soluble proteins impact on the cellular energy metabolism facilitate a uniform distribution of plastids amyloplasts and increase number and volume of nucleoli A number of recent studies have shown that the exposure of Arabidopsis seedlings and callus cells to gravity stimulation hyper g-forces or clinostat rotation induces alterations in gene expression In our previous study the proteome of the Arabidopsis thaliana callus cells were separated by high resolution two-dimensional electrophoresis 2-DE Image analysis revealed that 80 protein spots showed quantitative and qualitative variations after exposure to clinostat rotation treatment We report here a systematic proteomic approach to investigate the altered gravity responsive proteins in root tip of Arabidopsis thaliana cv Landsberg erecta Three-day-old seedlings were exposed for 12h to a horizontal clinostat rotation H simulated weightlessness altered g-forces by centrifugation 7g hypergravity a vertical clinostat rotation V clinostat control or a stationary control grown conditions Total proteins of roots were extracted

Plant gravity sensing

NASA Technical Reports Server (NTRS)

Sack, F. D.

1991-01-01

This review of plant gravity sensing examines sensing in organ gravitropism, sensing in single-cell gravitropism, and nongravitropic sensing. Topics related to sensing in organ gravitropism are (1) identification of the gravitropic susceptors, including intracellular asymmetry in equilibrium position and after reorientation, susceptor signal-to-noise ratio, signal integration over threshold stimulation periods, intracellular asymmetry and gravitropic competence, and starch deficiency and gravitropic competence; (2) possible root statocytes and receptors, including identification of presumptive statocytes, cytology, and possible receptors and models of sensing; and (3) negatively gravitropic organs, including identification and distribution of presumptive statocytes and cytology and possible receptors. Topics related to nongravitropic sensing include gravitaxis, reaction wood, gravimorphogenesis, other gravity-influenced organ movements, and cytoplasmic streaming.

Calcium movement, graviresponsiveness and the structure of columella cells and columella tissues in roots of Allium cepa L

NASA Technical Reports Server (NTRS)

Moore, R.

1985-01-01

Roots of Allium cepa L. cv. Yellow are differentially responsive to gravity. Long (e.g. 40 mm) roots are strongly graviresponsive, while short (c.g. 4 mm) roots are minimally responsive to gravity. Although columella cells of graviresponsive roots are larger than those of nongraviresponsive roots, they partition their volumes to cellular organelles similarly. The movement of amyloplasts and nuclei in columella cells of horizontally-oriented roots correlates positively with the onset of gravicurvature. Furthermore, there is no significant difference in the rates of organellar redistribution when graviresponsive and nongraviresponsive roots are oriented horizontally. The more pronounced graviresponsiveness of longer roots correlates positively with (1) their caps being 9-6 times more voluminous, (2) their columella tissues being 42 times more voluminous, (3) their caps having 15 times more columella cells, and (4) their columella tissues having relative volumes 4.4 times larger than those of shorter, nongraviresponsive roots. Graviresponsive roots that are oriented horizontally are characterized by a strongly polar movement of 45Ca2+ across the root tip from the upper to the lower side, while similarly oriented nongraviresponsive roots exhibit only a minimal polar transport of 45Ca2+. These results indicate that the differential graviresponsiveness of roots of A. cepa is probably not due to either (1) ultrastructural differences in their columella cells, (2) differences in the rates of organellar redistribution when roots are oriented horizontally. Rather, these results indicate the graviresponsiveness may require an extensive columella tissue, which, in turn, may be necessary for polar movement of 45Ca2+ across the root tip.

Characterizing the Physics of Plant Root Gravitropism: A Systems Modeling Approach

DTIC Science & Technology

1999-01-01

with its root directly downward, the root and stem undergo a gravitropic response. Statoliths (gravity-sensing organelles) within the root cap respond...this study is to model the plant root gravitropic response using classical controls and system identification principles. Specific objectives of this

Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response, and lateral root growth

NASA Technical Reports Server (NTRS)

Rashotte, A. M.; DeLong, A.; Muday, G. K.; Brown, C. S. (Principal Investigator)

2001-01-01

Auxin transport is required for important growth and developmental processes in plants, including gravity response and lateral root growth. Several lines of evidence suggest that reversible protein phosphorylation regulates auxin transport. Arabidopsis rcn1 mutant seedlings exhibit reduced protein phosphatase 2A activity and defects in differential cell elongation. Here we report that reduced phosphatase activity alters auxin transport and dependent physiological processes in the seedling root. Root basipetal transport was increased in rcn1 or phosphatase inhibitor-treated seedlings but showed normal sensitivity to the auxin transport inhibitor naphthylphthalamic acid (NPA). Phosphatase inhibition reduced root gravity response and delayed the establishment of differential auxin-induced gene expression across a gravity-stimulated root tip. An NPA treatment that reduced basipetal transport in rcn1 and cantharidin-treated wild-type plants also restored a normal gravity response and asymmetric auxin-induced gene expression, indicating that increased basipetal auxin transport impedes gravitropism. Increased auxin transport in rcn1 or phosphatase inhibitor-treated seedlings did not require the AGR1/EIR1/PIN2/WAV6 or AUX1 gene products. In contrast to basipetal transport, root acropetal transport was normal in phosphatase-inhibited seedlings in the absence of NPA, although it showed reduced NPA sensitivity. Lateral root growth also exhibited reduced NPA sensitivity in rcn1 seedlings, consistent with acropetal transport controlling lateral root growth. These results support the role of protein phosphorylation in regulating auxin transport and suggest that the acropetal and basipetal auxin transport streams are differentially regulated.

GRAVI-2 space experiment: investigating statoliths displacement and location effects on early stages of gravity perception pathways in lentil roots.

NASA Astrophysics Data System (ADS)

Bizet, François; Eche, Brigitte; Pereda Loth, Veronica; Badel, Eric; Legue, Valerie; Brunel, Nicole; Label, Philippe; Gérard, Joëlle

2016-07-01

The plants ability to orient their growth with respect to external stimuli such as gravity is a key factor for survival and acclimation to their environment. Belowground, plant roots modulate their growth towards gravity, allowing soil exploration and uptake of water and nutrients. In roots, gravity sensing cells called statocytes are located in the center of the root cap. Statocytes contain starch-filled plastids denser than the cytoplasm, which sedimentation along the direction of gravity is widely accepted as being involved into early stages of gravity perception (the starch-statolith hypothesis; Sack, 1991). Root gravitropism following statoliths displacement is based on auxin redistribution in the root apex, inducing differential growth between the root upward and downward sides. However at the cell scale, the chain of transduction starting from statoliths displacement and leading to auxin redistribution remains poorly documented. Signaling molecules such as calcium, reactive oxygen species, nitric oxide and inositol 1,4,5-triphosphate are serious candidates previously shown to be involved within minutes before modification of the expression of auxin-related genes (Morita, 2010; Sato et al., 2015). Here, we observe and quantify statoliths displacements and locations at various levels of gravity to investigate two hypothesis: (i) Are contacts between statoliths and the endoplasmic reticulum necessary to induce gravitropism? (ii) Are very low displacements of statoliths sufficient to initiate transduction pathways such as the calcium's one? These questionings have led to an experiment called GRAVI-2 which took place aboard the ISS in 2014. During the experiment, lentil roots were grown in the European modular cultivation system for several hours in microgravity and were then submitted to short high gravity stimulus (5 and 15 minutes at 2 g) before the return to Earth for analyses. Ongoing cytological measurements will reveal the effects of statoliths displacement and location on intracellular calcium localization. Complementary RNA sequencing was done and current transcriptomic analyses will show the regulation of calcium-downstream gene expression and of auxin dependent pathways at two short time steps following gravistimulus. In addition, some of the lentil roots grown in microgravity aboard the ISS were submitted for several hours to low level of gravity (10-2 g) close to the detection threshold determined on a previous experiment (GRAVI-1; Driss-Ecole et al., 2008). Root gravitropism in response to such a low level of gravity was investigated and compared to the very low statoliths displacement expected. This study give insights about the molecular mechanisms underlying the very high sensitivity of roots to gravity and are among the firsts studies involving global transcriptomic analyses of root material grown in microgravity. Keywords: Calcium; ISS; Microgravity; Root; Statholith; Transcriptomic Acknowledgments: The authors thank G. Perbal, D. Driss-Ecole, the European space agency and the Norwegian user support and operations center team for their considerable help in the preparation and achievement of the GRAVI experiments. This work should not have been possible without the financial supports of the Centre National d'Etudes Spatiales (CNES) through a postdoctoral fellowship. References: Driss-Ecole, D., Legué, V., Carnero-Diaz, E. and Perbal, G. 2008. Gravisensitivity and automorphogenesis of lentil seedling roots grown on board the International Space Station. Physiologia Plantarum. 134, 1 (2008), 191-201. Morita, M. 2010. Directional Gravity Sensing in Gravitropism. Plant Biology. 61, 1 (2010), 705-720. Sack, F.D. 1991. Plant gravity sensing. International review of cytology. 127, (1991), 193-252. Sato, E.M., Hijazi, H., Bennett, M.J., Vissenberg, K. and Swarup, R. 2015. New insights into root gravitropic signalling. Journal of experimental botany. 66, 8 (Apr. 2015), 2155-65.

Drought response transcriptomes are altered in poplar with reduced tonoplast sucrose transporter expression

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

Xue, Liang-Jiao; Frost, Christopher J.; Tsai, Chung-Jui

Transgenic Populus tremula x alba (717-1B4) plants with reduced expression of a tonoplast sucrose efflux transporter, PtaSUT4, exhibit reduced shoot growth compared to wild type (WT) under sustained mild drought. The present study was undertaken to determine whether SUT4-RNAi directly or indirectly altered poplar predisposition and/or response to changes in soil water availability. While sucrose and hexose levels were constitutively elevated in shoot organs, expression responses to drought were most altered in the root tips of SUT4-RNAi plants. Prior to any drought treatment, constitutively elevated transcript levels of abscisic acid biosynthetic genes and bark/vegetative storage proteins suggested altered metabolism inmore » root tips of RNAi plants. Stronger drought-stimulation of stress-inducible genes encoding late-embryogenesis-abundant proteins in transgenic roots was consistent with increased vulnerability to soil drying. Transcript evidence suggested an RNAi effect on intercellular water trafficking by aquaporins in stem xylem during soil drying and recovery. Co-expression network analysis predicted altered integration of abscisic acid sensing/signaling with ethylene and jasmonate sensing/signaling in RNAi compared to WT roots. The overall conclusion is that steepened shoot-root sugar gradient in RNAi plants increased sensitivity of root tips to decreasing soil water availability.« less

Drought response transcriptomes are altered in poplar with reduced tonoplast sucrose transporter expression

DOE PAGES

Xue, Liang-Jiao; Frost, Christopher J.; Tsai, Chung-Jui; ...

2016-09-19

Transgenic Populus tremula x alba (717-1B4) plants with reduced expression of a tonoplast sucrose efflux transporter, PtaSUT4, exhibit reduced shoot growth compared to wild type (WT) under sustained mild drought. The present study was undertaken to determine whether SUT4-RNAi directly or indirectly altered poplar predisposition and/or response to changes in soil water availability. While sucrose and hexose levels were constitutively elevated in shoot organs, expression responses to drought were most altered in the root tips of SUT4-RNAi plants. Prior to any drought treatment, constitutively elevated transcript levels of abscisic acid biosynthetic genes and bark/vegetative storage proteins suggested altered metabolism inmore » root tips of RNAi plants. Stronger drought-stimulation of stress-inducible genes encoding late-embryogenesis-abundant proteins in transgenic roots was consistent with increased vulnerability to soil drying. Transcript evidence suggested an RNAi effect on intercellular water trafficking by aquaporins in stem xylem during soil drying and recovery. Co-expression network analysis predicted altered integration of abscisic acid sensing/signaling with ethylene and jasmonate sensing/signaling in RNAi compared to WT roots. The overall conclusion is that steepened shoot-root sugar gradient in RNAi plants increased sensitivity of root tips to decreasing soil water availability.« less

New insights into root gravitropic signalling

PubMed Central

Sato, Ethel Mendocilla; Hijazi, Hussein; Bennett, Malcolm J.; Vissenberg, Kris; Swarup, Ranjan

2015-01-01

An important feature of plants is the ability to adapt their growth towards or away from external stimuli such as light, water, temperature, and gravity. These responsive plant growth movements are called tropisms and they contribute to the plant’s survival and reproduction. Roots modulate their growth towards gravity to exploit the soil for water and nutrient uptake, and to provide anchorage. The physiological process of root gravitropism comprises gravity perception, signal transmission, growth response, and the re-establishment of normal growth. Gravity perception is best explained by the starch–statolith hypothesis that states that dense starch-filled amyloplasts or statoliths within columella cells sediment in the direction of gravity, resulting in the generation of a signal that causes asymmetric growth. Though little is known about the gravity receptor(s), the role of auxin linking gravity sensing to the response is well established. Auxin influx and efflux carriers facilitate creation of a differential auxin gradient between the upper and lower side of gravistimulated roots. This asymmetric auxin gradient causes differential growth responses in the graviresponding tissue of the elongation zone, leading to root curvature. Cell biological and mathematical modelling approaches suggest that the root gravitropic response begins within minutes of a gravity stimulus, triggering genomic and non-genomic responses. This review discusses recent advances in our understanding of root gravitropism in Arabidopsis thaliana and identifies current challenges and future perspectives. PMID:25547917

The microtubule associated protein END BINDING 1 represses root responses to mechanical cues.

PubMed

Gleeson, Laura; Squires, Shannon; Bisgrove, Sherryl R

2012-05-01

The ability of roots to navigate around rocks and other debris as they grow through the soil requires a mechanism for detecting and responding to input from both touch and gravity sensing systems. The microtubule associated protein END BINDING 1b (EB1b) is involved in this process as mutants have defects responding to combinations of touch and gravity cues. This study investigates the role of EB1b in root responses to mechanical cues. We find that eb1b-1 mutant roots exhibit an increase over wild type in their response to touch and that the expression of EB1b genes in transgenic mutants restores the response to wild type levels, indicating that EB1b is an inhibitor of the response. Mutant roots are also hypersensitive to increased levels of mechanical stimulation, revealing the presence of another process that activates the response. These findings are supported by analyses of double mutants between eb1b-1 and seedlings carrying mutations in PHOSPHOGLUCOMUTASE (PGM), ALTERED RESPONSE TO GRAVITY1 (ARG1), or TOUCH3 (TCH3), genes that encode proteins involved in gravity sensing, signaling, or touch responses, respectively. A model is proposed in which root responses to mechanical cues are modulated by at least two competing regulatory processes, one that promotes touch-mediated growth and another, regulated by EB1b, which dampens root responses to touch and enhances gravitropism. © 2012. Published by Elsevier Ireland Ltd. All rights reserved.

A new centrifuge microscope reveals that mobile plastids trigger gravity sensing in Arabidopsis inflorescence stems

NASA Astrophysics Data System (ADS)

Toyota, Masatsugu; Tasaka, Masao; Morita, Miyo T.; Gilroy, Simon

2012-07-01

The starch-statolith hypothesis is the most widely accepted model for plant gravity sensing and proposes that the sedimentation of high-density starch-filled plastids (amyloplasts) in shoot endodermal cells and root columella cells is important for gravity sensing of each organ. However, starch-deficient phosphoglucomutase (pgm-1) mutants sense gravity and show gravitropism in inflorescence stems, even though most starchless amyloplasts in this mutant fail to sediment toward the gravity vector. These results raise the questions about the role of starch in gravity sensing and the features of statolith/statocyte essential for shoot gravity sensing. To address these questions, we developed a new centrifuge microscope and analyzed two gravitropic mutants, i.e., pgm-1 and endodermal-amyloplast less 1 (eal1). All optical devices (e.g., objective lens, light source and CCD camera) and specimens were rotated on a direct-drive motor, and acquired images were wirelessly transmitted during centrifugation. Live-cell imaging during centrifugation revealed that the starchless amyloplasts sedimented to the hypergravity vector (10 and 30 g) in endodermal cells of pgm-1 stems, indicating that the density of the starchless amyloplasts is higher than that of cytoplasm. Electron micrographs of shoot endodermal cells in pgm-1 mutants suggested that the starchless amyloplast contains an organized thylakoid membrane but not starch granules, which morphologically resembles chloroplasts in the adjacent cortical cells. Therefore, the shoot amyloplasts without starch are possibly as dense as chloroplasts. We examined eal1 mutants, an allele of shoot gravitropism (sgr) 7/short-root (shr), which also have starchless amyloplasts due to abnormal differentiation of amyloplasts and show no gravitropic response at 1 g. Hypergravity up to 30 g induced little gravitropism in eal1 stems and the starchless amyloplasts failed to sediment under 30 g conditions. However, the eal1 mutants treated with latrunculin B, an actin disrupting drug, showed gravitropism under 30 g conditions, during which amyloplasts were artificially sedimented by hypergravity. These results suggest that shoot amyloplasts are intrinsically dense enough to trigger gravity sensing without starch and, rather, intracellular environments that render amyloplasts sedimentable/mobile, such as actin organization, are essential for gravity sensing in Arabidopsis inflorescence stems.

Gravity sensing, a largely misunderstood trigger of plant orientated growth.

PubMed

Lopez, David; Tocquard, Kévin; Venisse, Jean-Stéphane; Legué, Valerie; Roeckel-Drevet, Patricia

2014-01-01

Gravity is a crucial environmental factor regulating plant growth and development. Plants have the ability to sense a change in the direction of gravity, which leads to the re-orientation of their growth direction, so-called gravitropism. In general, plant stems grow upward (negative gravitropism), whereas roots grow downward (positive gravitropism). Models describing the gravitropic response following the tilting of plants are presented and highlight that gravitropic curvature involves both gravisensing and mechanosensing, thus allowing to revisit experimental data. We also discuss the challenge to set up experimental designs for discriminating between gravisensing and mechanosensing. We then present the cellular events and the molecular actors known to be specifically involved in gravity sensing.

PINOID kinase regulates root gravitropism through modulation of PIN2-dependent basipetal auxin transport in Arabidopsis.

PubMed

Sukumar, Poornima; Edwards, Karin S; Rahman, Abidur; Delong, Alison; Muday, Gloria K

2009-06-01

Reversible protein phosphorylation is a key regulatory mechanism governing polar auxin transport. We characterized the auxin transport and gravitropic phenotypes of the pinoid-9 (pid-9) mutant of Arabidopsis (Arabidopsis thaliana) and tested the hypothesis that phosphorylation mediated by PID kinase and dephosphorylation regulated by the ROOTS CURL IN NAPHTHYLPHTHALAMIC ACID1 (RCN1) protein might antagonistically regulate root auxin transport and gravity response. Basipetal indole-3-acetic acid transport and gravitropism are reduced in pid-9 seedlings, while acropetal transport and lateral root development are unchanged. Treatment of wild-type seedlings with the protein kinase inhibitor staurosporine phenocopies the reduced auxin transport and gravity response of pid-9, while pid-9 is resistant to inhibition by staurosporine. Staurosporine and the phosphatase inhibitor, cantharidin, delay the asymmetric expression of DR5revGFP (green fluorescent protein) at the root tip after gravistimulation. Gravity response defects of rcn1 and pid-9 are partially rescued by treatment with staurosporine and cantharidin, respectively. The pid-9 rcn1 double mutant has a more rapid gravitropic response than rcn1. These data are consistent with a reciprocal regulation of gravitropism by RCN1 and PID. Furthermore, the effect of staurosporine is lost in pinformed2 (pin2). Our data suggest that reduced PID kinase function inhibits gravitropism and basipetal indole-3-acetic acid transport. However, in contrast to PID overexpression studies, we observed wild-type asymmetric membrane distribution of the PIN2 protein in both pid-9 and wild-type root tips, although PIN2 accumulates in endomembrane structures in pid-9 roots. Similarly, staurosporine-treated plants expressing a PIN2GFP fusion exhibit endomembrane accumulation of PIN2GFP, but no changes in membrane asymmetries were detected. Our data suggest that PID plays a limited role in root development; loss of PID activity alters auxin transport and gravitropism without causing an obvious change in cellular polarity.

Genetic analysis of gravity signal transduction in roots

NASA Astrophysics Data System (ADS)

Masson, Patrick; Strohm, Allison; Baldwin, Katherine

To grow downward into the soil, roots use gravity as a guide. Specialized cells, named stato-cytes, enable this directional growth response by perceiving gravity. Located in the columella region of the cap, these cells sense a reorientation of the root within the gravity field through the sedimentation of, and/or tension/pressure exerted by, dense amyloplasts. This process trig-gers a gravity signal transduction pathway that leads to a fast alkalinization of the cytoplasm and a change in the distribution of the plasma membrane-associated auxin-efflux carrier PIN3. The latter protein is uniformly distributed within the plasma membrane on all sides of the cell in vertically oriented roots. However, it quickly accumulates at the bottom side upon gravis-timulation. This process correlates with a preferential transport of auxin to the bottom side of the root cap, resulting in a lateral gradient across the tip. This gradient is then transported to the elongation zone where it promotes differential cellular elongation, resulting in downward curvature. We isolated mutations that affect gravity signal transduction at a step that pre-cedes cytoplasmic alkalinization and/or PIN3 relocalization and lateral auxin transport across the cap. arg1 and arl2 mutations identify a common genetic pathway that is needed for all three gravity-induced processes in the cap statocytes, indicating these genes function early in the pathway. On the other hand, adk1 affects gravity-induced PIN3 relocalization and lateral auxin transport, but it does not interfere with cytoplasmic alkalinization. ARG1 and ARL2 encode J-domain proteins that are associated with membranes of the vesicular trafficking path-way whereas ADK1 encodes adenosine kinase, an enzyme that converts adenosine derived from nucleic acid metabolism and the AdoMet cycle into AMP, thereby alleviating feedback inhibi-tion of this important methyl-donor cycle. Because mutations in ARG1 (and ARL2) do not completely eliminate gravitropism, we sought genetic enhancers of arg1 as a way to identify new gravity signal transducers. Two of these modifiers, named mar1 and mar2, were found to affect genes that encode two subunits of the plastidic outer-membrane protein import complex, TOC75 and TOC132, respectively. mar2 did not affect the ultrastructure of amyloplasts in the statocytes nor did it alter their ability to sediment in response to gravistimulation, suggesting a role for the outer membrane of the amyloplasts in gravity signal transduction (reviewed in Stanga et al., 2009, Plant Signal Behavior 4(10): 1-9). The contribution of TOC132 in gravity signal transduction is being investigated by analyzing the regions of this protein that are needed for the pathway, and investigating the contribution of a putative TOC132-interacting protein in gravity signal transduction. We have also isolated additional putative enhancers of arg1-2 in the hope of identifying new plastid-associated gravity signal transducers, and have initiated a screen for genetic enhancers of mar2 to seek new transducers in the ARG1 branch of the pathway.

Ionic signaling in plant gravity and touch responses

NASA Technical Reports Server (NTRS)

Massa, Gioia D.; Fasano, Jeremiah M.; Gilroy, Simon

2003-01-01

Plant roots are optimized to exploit resources from the soil and as each root explores this environment it will encounter a range of biotic and abiotic stimuli to which it must respond. Therefore, each root must possess a sensory array capable of monitoring and integrating these diverse stimuli to direct the appropriate growth response. Touch and gravity represent two of the biophysical stimuli that plants must integrate. As sensing both of these signals requires mechano-transduction of biophysical forces to biochemical signaling events, it is likely that they share signal transduction elements. These common signaling components may allow for cross-talk and so integration of thigmotropic and gravitropic responses. Indeed, signal transduction events in both plant touch and gravity sensing are thought to include Ca(2+)- and pH-dependent events. Additionally, it seems clear that the systems responsible for root touch and gravity response interact to generate an integrated growth response. Thus, primary and lateral roots of Arabidopsis respond to mechanical stimuli by eliciting tropic growth that is likely part of a growth strategy employed by the root to circumvent obstacles in the soil. Also, the mechano-signaling induced by encountering an obstacle apparently down-regulates the graviperception machinery to allow this kind of avoidance response. The challenge for future research will be to define how the cellular signaling events in the root cap facilitate this signal integration and growth regulation. In addition, whether other stimuli are likewise integrated with the graviresponse via signal transduction system cross-talk is an important question that remains to be answered.

Live cell imaging of cytoskeletal and organelle dynamics in gravity-sensing cells in plant gravitropism.

PubMed

Nakamura, Moritaka; Toyota, Masatsugu; Tasaka, Masao; Morita, Miyo Terao

2015-01-01

Plants sense gravity and change their morphology/growth direction accordingly (gravitropism). The early process of gravitropism, gravity sensing, is supposed to be triggered by sedimentation of starch-filled plastids (amyloplasts) in statocytes such as root columella cells and shoot endodermal cells. For several decades, many scientists have focused on characterizing the role of the amyloplasts and observed their intracellular sedimentation in various plants. Recently, it has been discovered that the complex sedimentary movements of the amyloplasts are created not only by gravity but also by cytoskeletal/organelle dynamics, such as those of actin filaments and the vacuolar membrane. Thus, to understand how plants sense gravity, we need to analyze both amyloplast movements and their regulatory systems in statocytes. We have developed a vertical-stage confocal microscope that allows multicolor fluorescence imaging of amyloplasts, actin filaments and vacuolar membranes in vertically oriented plant tissues. We also developed a centrifuge microscope that allows bright-field imaging of amyloplasts during centrifugation. These microscope systems provide new insights into gravity-sensing mechanisms in Arabidopsis.

Spatial separation of light perception and growth response in maize root phototropism.

PubMed

Mullen, J L; Wolverton, C; Ishikawa, H; Hangarter, R P; Evans, M L

2002-09-01

Although the effects of gravity on root growth are well known and interactions between light and gravity have been reported, details of root phototropic responses are less documented. We used high-resolution image analysis to study phototropism in primary roots of Zea mays L. Similar to the location of perception in gravitropism, the perception of light was localized in the root cap. Phototropic curvature away from the light, on the other hand, developed in the central elongation zone, more basal than the site of initiation of gravitropic curvature. The phototropic curvature saturated at approximately 10 micromoles m-2 s-1 blue light with a peak curvature of 29 +/- 4 degrees, in part due to induction of positive gravitropism following displacement of the root tip from vertical during negative phototropism. However, at higher fluence rates, development of phototropic curvature is arrested even if gravitropism is avoided by maintaining the root cap vertically using a rotating feedback system. Thus continuous illumination can cause adaptation in the signalling pathway of the phototropic response in roots.

Spatial separation of light perception and growth response in maize root phototropism

NASA Technical Reports Server (NTRS)

Mullen, J. L.; Wolverton, C.; Ishikawa, H.; Hangarter, R. P.; Evans, M. L.

2002-01-01

Although the effects of gravity on root growth are well known and interactions between light and gravity have been reported, details of root phototropic responses are less documented. We used high-resolution image analysis to study phototropism in primary roots of Zea mays L. Similar to the location of perception in gravitropism, the perception of light was localized in the root cap. Phototropic curvature away from the light, on the other hand, developed in the central elongation zone, more basal than the site of initiation of gravitropic curvature. The phototropic curvature saturated at approximately 10 micromoles m-2 s-1 blue light with a peak curvature of 29 +/- 4 degrees, in part due to induction of positive gravitropism following displacement of the root tip from vertical during negative phototropism. However, at higher fluence rates, development of phototropic curvature is arrested even if gravitropism is avoided by maintaining the root cap vertically using a rotating feedback system. Thus continuous illumination can cause adaptation in the signalling pathway of the phototropic response in roots.

Pinoid kinase regulates root gravitropism through modulation of PIN2-dependent basipetal auxin transport in Arabidopsis thaliana

NASA Astrophysics Data System (ADS)

Muday, Gloria; Sukumar, Poornima; Edwards, Karin; Delong, Alison; Rahman, Abidur

Reversible protein phosphorylation is a key regulatory mechanism governing polar auxin transport. We tested the hypothesis that PINOID (PID)-mediated phosphorylation and RCN1- regulated dephosphorylation might antagonistically regulate auxin transport and gravity response in seedling roots. Here we show that basipetal IAA transport and gravitropism are reduced in pid mutant seedlings, while acropetal transport and lateral root development are unchanged. Treatment of wild-type seedlings with the protein kinase inhibitor, staurosporine, phenocopied the reduced auxin transport and gravity response of pid-9 and reduced formation of asymmetric DR5-revGFP expression at the root tip after reorientation relative to gravity. Gravitropism and auxin transport in pid are resistant to further inhibition by staurosporine. Gravity response defects of rcn1 and pid-9 are partially rescued by treatment with staurosporine or the phosphatase inhibitor, cantharidin, respectively, and in the pid-9 rcn1 double mutant. Furthermore, the effect of staurosporine is lost in pin2, and a PIN2::GFP fusion protein accumulates in endomembrane compartments after staurosporine treatment. In the pid-9 mutant, immunological techniques find a similar PIN2 localization. These data suggest that staurosporine inhibits gravitropism and basipetal IAA transport by blocking PID action and altering PIN2 localization and support the model that PID and RCN1 reciprocally regulate root gravitropic curvature.

Re-Evaluation of the Role of Starch in Gravitropic Sensing

NASA Technical Reports Server (NTRS)

Sack, Fred D.

1998-01-01

Plant organs grow toward or away from gravity as a way to orient those organs for optimizing growth. Starch has long been thought to be important in sensing the direction of the g-vector in gravitropism, but that hypothesis has also evoked controversy. We have previously shown that starch-deficient mutants of Arabidopsis (TC7) and Nicotiana (NS458) are impaired in their gravitropism. While this suggests that starch is not necessary for reduced gravitropism, it also indicates that the mass of the starch contributes to sensing when present and thus is necessary for full gravitropic sensitivity. The research supported by this grant focused on three related projects, (1) the effect of light on hypocotyl gravitropism in NS458, (2) the effects of root phototropism on measurements of gravitropic sensitivity, and (3) the effects of starch overproduction on sedimentation and gravitropism. Collectively, our results provide additional strong support for the importance of starch in gravitropic sensing. First, by accounting for negative phototropism in roots of two starchless mutants of Arabidopsis we have established that these mutants are much less sensitive to gravity than previously thought. This work also demonstrates the importance of designing experimental protocols that remove the influence of root phototropism on measuring root gravitropism. Second, light apparently promotes gravitropism in starch-deficient Nicotiana hypocotyls by increasing the trace amounts of starch in the plastids, by inducing limited plastid sedimentation and thus by presumably increasing the signal provided by plastid mass. And finally, we show that excess starch in Arabidopsis seedlings has little effect on gravitropic sensitivity implying that the sensing system is already saturated. However, in light-grown stems where this mutation results in starch accumulation and where the wild-type practically lacks starch in the sensing cells, the mutant is much more sensitive than the wild-type again showing that the loss of starch depresses gravity sensing.

Salt modulates gravity signaling pathway to regulate growth direction of primary roots in Arabidopsis.

PubMed

Sun, Feifei; Zhang, Wensheng; Hu, Haizhou; Li, Bao; Wang, Youning; Zhao, Yankun; Li, Kexue; Liu, Mengyu; Li, Xia

2008-01-01

Plant root architecture is highly plastic during development and can adapt to many environmental stresses. The proper distribution of roots within the soil under various conditions such as salinity, water deficit, and nutrient deficiency greatly affects plant survival. Salinity profoundly affects the root system architecture of Arabidopsis (Arabidopsis thaliana). However, despite the inhibitory effects of salinity on root length and the number of roots, very little is known concerning influence of salinity on root growth direction and the underlying mechanisms. Here we show that salt modulates root growth direction by reducing the gravity response. Exposure to salt stress causes rapid degradation of amyloplasts in root columella cells of Arabidopsis. The altered root growth direction in response to salt was found to be correlated with PIN-FORMED2 (PIN2) messenger RNA abundance and expression and localization of the protein. Furthermore, responsiveness to gravity of salt overly sensitive (sos) mutants is substantially reduced, indicating that salt-induced altered gravitropism of root growth is mediated by ion disequilibrium. Mutation of SOS genes also leads to reduced amyloplast degradation in root tip columella cells and the defects in PIN2 gene expression in response to salt stress. These results indicate that the SOS pathway may mediate the decrease of PIN2 messenger RNA in salinity-induced modification of gravitropic response in Arabidopsis roots. Our findings provide new insights into the development of a root system necessary for plant adaptation to high salinity and implicate an important role of the SOS signaling pathway in this process.

Cell proliferation and plant development under novel altered gravity environments.

PubMed

Herranz, R; Medina, F J

2014-01-01

Gravity is a key factor for life on Earth. It is the only environmental factor that has remained constant throughout evolution, and plants use it to modulate important physiological activities; gravity removal or alteration produces substantial changes in essential functions. For root gravitropism, gravity is sensed in specialised cells, which are capable of detecting magnitudes of the g vector lower than 10(-3) . Then, the mechanosignal is transduced to upper zones of the root, resulting in changes in the lateral distribution of auxin and in the rate of auxin polar transport. Gravity alteration has consequences for cell growth and proliferation rates in root meristems, which are the basis of the developmental programme of a plant, in which regulation via auxin is involved. The effect is disruption of meristematic competence, i.e. the strict coordination between cell proliferation and growth, which characterises meristematic cells. This effect can be related to changes in the transport and distribution of auxin throughout the root. However, similar effects of gravity alteration have been found in plant cell cultures in vitro, in which neither specialised structures for gravity sensing and signal transduction, nor apparent gravitropism have been described. We postulate that gravity resistance, a general mechanism of cellular origin for developing rigid structures in plants capable of resisting the gravity force, could also be responsible for the changes in cell growth and proliferation parameters detected in non-specialised cells. The mechanisms of gravitropism and graviresistance are complementary, the first being mostly sensitive to the direction of the gravity vector, and the second to its magnitude. At a global molecular level, the consequence of gravity alteration is that the genome should be finely tuned to counteract a type of stress that plants have never encountered before throughout evolution. Multigene families and redundant genes present an advantage in that they can experience changes without the risk of being deleterious and, for this reason, they should play a key role in the response to gravitational stress. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.

Rhizoids and protonemata of characean algae: model cells for research on polarized growth and plant gravity sensing.

PubMed

Braun, M; Limbach, C

2006-12-01

Gravitropically tip-growing rhizoids and protonemata of characean algae are well-established unicellular plant model systems for research on gravitropism. In recent years, considerable progress has been made in the understanding of the cellular and molecular mechanisms underlying gravity sensing and gravity-oriented growth. While in higher-plant statocytes the role of cytoskeletal elements, especially the actin cytoskeleton, in the mechanisms of gravity sensing is still enigmatic, there is clear evidence that in the characean cells actin is intimately involved in polarized growth, gravity sensing, and the gravitropic response mechanisms. The multiple functions of actin are orchestrated by a variety of actin-binding proteins which control actin polymerisation, regulate the dynamic remodelling of the actin filament architecture, and mediate the transport of vesicles and organelles. Actin and a steep gradient of cytoplasmic free calcium are crucial components of a feedback mechanism that controls polarized growth. Experiments performed in microgravity provided evidence that actomyosin is a key player for gravity sensing: it coordinates the position of statoliths and, upon a change in the cell's orientation, directs sedimenting statoliths to specific areas of the plasma membrane, where contact with membrane-bound gravisensor molecules elicits short gravitropic pathways. In rhizoids, gravitropic signalling leads to a local reduction of cytoplasmic free calcium and results in differential growth of the opposite subapical cell flanks. The negative gravitropic response of protonemata involves actin-dependent relocation of the calcium gradient and displacement of the centre of maximal growth towards the upper flank. On the basis of the results obtained from the gravitropic model cells, a similar fine-tuning function of the actomyosin system is discussed for the early steps of gravity sensing in higher-plant statocytes.

Development of Gravity Sensitive Plant Cells (Ceratodon) in Microgravity

NASA Technical Reports Server (NTRS)

Sack, Fred D.

1999-01-01

Protonemata of the moss Ceratodon are tip-growing cells that grow up in the dark. This cell type is unique compared to cells in almost any other organism, since the growth of the plant cell itself is completely oriented by gravity. Thus, both the processes of gravity sensing and the gravity response occur in the same cell. Gravity sensing appears to rely upon amyloplasts (starch-filled plastids) that sediment. This sedimentation occurs in specific zones and plastid zonation is complex with respect to plastid morphology, distribution, and gravity. Microtubules restrict the extent of plastid sedimentation (i.e., they are load-bearing). Light also is important since apical cells have a phytochrome-based positive phototropism, light quality influences plastid zonation and sedimentation (photomorphogenesis), and red light suppresses gravitropism at higher but not lower light intensities. Many of these processes were examined in a 16 day spaceflight experiment, "SPM-A" space moss" or "SPAM)) on STS-87 that landed in December, 1997. The work described here involves the definition of a second flight experiment that builds upon the data and questions arising from STS-87. Effort was directed towards further definition of an experiment for the Shuttle (dubbed "SOS" for "Son of SPAM"). Our current target is STS 107 that is scheduled to fly in January 2001. This definition addressed two goals of the STS107 experiment. The goals of the current experiment were to determine whether the cytoskeleton plays a role in maintaining and generating an apical (non-random) plastid distribution in microgravity and to determine the development and extent of clockwise spiral tip-growth in microgravity.

Transcriptional regulation of PIN genes by FOUR LIPS and MYB88 during Arabidopsis root gravitropism.

PubMed

Wang, Hong-Zhe; Yang, Ke-Zhen; Zou, Jun-Jie; Zhu, Ling-Ling; Xie, Zi Dian; Morita, Miyo Terao; Tasaka, Masao; Friml, Jiří; Grotewold, Erich; Beeckman, Tom; Vanneste, Steffen; Sack, Fred; Le, Jie

2015-11-18

PIN proteins are auxin export carriers that direct intercellular auxin flow and in turn regulate many aspects of plant growth and development including responses to environmental changes. The Arabidopsis R2R3-MYB transcription factor FOUR LIPS (FLP) and its paralogue MYB88 regulate terminal divisions during stomatal development, as well as female reproductive development and stress responses. Here we show that FLP and MYB88 act redundantly but differentially in regulating the transcription of PIN3 and PIN7 in gravity-sensing cells of primary and lateral roots. On the one hand, FLP is involved in responses to gravity stimulation in primary roots, whereas on the other, FLP and MYB88 function complementarily in establishing the gravitropic set-point angles of lateral roots. Our results support a model in which FLP and MYB88 expression specifically determines the temporal-spatial patterns of PIN3 and PIN7 transcription that are closely associated with their preferential functions during root responses to gravity.

Control of root system architecture by DEEPER ROOTING 1 increases rice yield under drought conditions.

PubMed

Uga, Yusaku; Sugimoto, Kazuhiko; Ogawa, Satoshi; Rane, Jagadish; Ishitani, Manabu; Hara, Naho; Kitomi, Yuka; Inukai, Yoshiaki; Ono, Kazuko; Kanno, Noriko; Inoue, Haruhiko; Takehisa, Hinako; Motoyama, Ritsuko; Nagamura, Yoshiaki; Wu, Jianzhong; Matsumoto, Takashi; Takai, Toshiyuki; Okuno, Kazutoshi; Yano, Masahiro

2013-09-01

The genetic improvement of drought resistance is essential for stable and adequate crop production in drought-prone areas. Here we demonstrate that alteration of root system architecture improves drought avoidance through the cloning and characterization of DEEPER ROOTING 1 (DRO1), a rice quantitative trait locus controlling root growth angle. DRO1 is negatively regulated by auxin and is involved in cell elongation in the root tip that causes asymmetric root growth and downward bending of the root in response to gravity. Higher expression of DRO1 increases the root growth angle, whereby roots grow in a more downward direction. Introducing DRO1 into a shallow-rooting rice cultivar by backcrossing enabled the resulting line to avoid drought by increasing deep rooting, which maintained high yield performance under drought conditions relative to the recipient cultivar. Our experiments suggest that control of root system architecture will contribute to drought avoidance in crops.

Gravity-induced cellular and molecular processes in plants studied under altered gravity conditions

NASA Astrophysics Data System (ADS)

Vagt, Nicole; Braun, Markus

With the ability to sense gravity plants possess a powerful tool to adapt to a great variety of environmental conditions and to respond to environmental changes in a most beneficial way. Gravity is the only constant factor that provides organisms with reliable information for their orientation since billions of years. Any deviation of the genetically determined set-point angle of the plants organs from the vector of gravity is sensed by specialized cells, the statocytes of roots and shoots in higher plants. Dense particles, so-called statoliths, sediment in the direction of gravity and activate membrane-bound gravireceptors. A physiological signalling-cascade is initiated that eventually results in the gravitropic curvature response, namely, the readjust-ment of the growth direction. Experiments under microgravity conditions have significantly contributed to our understanding of plant gravity-sensing and gravitropic reorientation. For a gravity-sensing lower plant cell type, the rhizoid of the green alga Chara, and for statocytes of higher plant roots, it was shown that the interactions between statoliths and the actomyosin system consisting of the actin cytoskeleton and motor proteins (myosins) are the basis for highly efficient gravity-sensing processes. In Chara rhizoids, the actomyosin represents a guid-ing system that directs sedimenting statoliths to a specific graviperception site. Parabolic flight experiments aboard the airbus A300 Zero-G have provided evidence that lower and higher plant cells use principally the same statolith-mediated gravireceptor-activation mechanism. Graviper-ception is not dependent on mechanical pressure mediated through the weight of the sedimented statoliths, but on direct interactions between the statoliths's surface and yet unknown gravire-ceptor molecules. In contrast to Chara rhizoids, in the gravity-sensing cells of higher plants, the actin cytoskeleton is not essentially involved in the early phases of gravity sensing. Dis-rupting the actomyosin system did not impair the sedimentation of statoliths and did not prevent the activation of gravireceptors. However, experiments in microgravity and inhibitor experiments have demonstrated that the actomyosin system optimizes the statolith-receptor interactions by keeping the sedimented statoliths in motion causing a consistent activation of different gravireceptor molecules. Thereby, a triggered gravitropic signal is created which is the basis for a highly sensitive control and readjustment mechanism. In addition, the results of recent parabolic flight studies on the effects of altered gravity conditions on the gene expres-sion pattern of Arabidopsis seedlings support these findings and provide new insight into the molecular basis of the plants response to different acceleration conditions. The work was financially supported by DLR on behalf of Bundesministerium für Wirtschaft und Technologie (50WB0815).

Columella cells revisited: novel structures, novel properties, and a novel gravisensing model

NASA Technical Reports Server (NTRS)

Staehelin, L. A.; Zheng, H. Q.; Yoder, T. L.; Smith, J. D.; Todd, P.

2000-01-01

A hundred years of research has not produced a clear understanding of the mechanism that transduces the energy associated with the sedimentation of starch-filled amyloplast statoliths in root cap columella cells into a growth response. Most models postulate that the statoliths interact with microfilaments (MF) to transmit signals to the plasma membrane (or ER), or that sedimentation onto these organelles produces the signals. However, no direct evidence for statolith-MF links has been reported, and no asymmetric structures of columella cells have been identified that might explain how a root turned by 90 degrees knows which side is up. To address these and other questions, we have (1) quantitatively examined the effects of microgravity on the size, number, and spatial distribution of statoliths; (2) re-evaluated the ultrastructure of columella cells in high-pressure frozen/freeze-substituted roots; and (3) followed the sedimentation dynamics of statolith movements in reoriented root tips. The findings have led to the formulation of a new model for the gravity-sensing apparatus of roots, which envisages the cytoplasm pervaded by an actin-based cytoskeletal network. This network is denser in the ER-devoid central region of the cell than in the ER-rich cell cortex and is coupled to receptors in the plasma membrane. Statolith sedimentation is postulated to disrupt the network and its links to receptors in some regions of the cell cortex, while allowing them to reform in other regions and thereby produce a directional signal.

Auxin, ethylene and the regulation of root growth under mechanical impedance

NASA Astrophysics Data System (ADS)

Sharma, Rameshwar; Santisree, Parankusam; Nongmaithem, Sapana; Sreelakshmi, Yellamaraju

2012-07-01

Among the multitude functions performed by plant roots, little information is available about the mechanisms that allow roots to overcome the soil resistance, in order to grow in the soil to obtain water and nutrient. Tomato (Solanum lycopersicum) seedlings grown on horizontally placed agar plates showed a progressive decline in the root length with the increasing impedance of agar media. The incubation with 1-methylcyclopropane (1-MCP), an inhibitor of ethylene perception, led to aerial growth of roots. In contrast, in absence of 1-MCP control roots grew horizontally anchored to the agar surface. Though 1-MCP-treated and control seedlings showed differential ability to penetrate in the agar, the inhibition of root elongation was nearly similar for both treatments. While increased mechanical impedance also progressively impaired hypocotyl elongation in 1-MCP treated seedlings, it did not affect the hypocotyl length of control seedlings. The decline in root elongation was also associated with increased expression of DR5::GUS activity in the root tip signifying accumulation of auxin at the root tip. The increased expression of DR5::GUS activity in the root tip was also observed in 1-MCP treated seedlings, indicating independence of this response from ethylene signaling. Our results indicate operation of a sensing mechanism in root that likely operates independently of ethylene but involves auxin to determine the degree of impedance of the substratum.

Glucose and phytohormone interplay in controlling root directional growth in Arabidopsis.

PubMed

Singh, Manjul; Gupta, Aditi; Laxmi, Ashverya

2014-01-01

Sensing and responding toward gravity vector is a complicated and multistep process. Gravity is a constant factor feeding plants with reliable information for the spatial orientation of their organs. Auxin, cytokinin, ethylene and BRs have been the most explored hormones in relation to gravitropism. We have previously shown that glucose (Glc) could promote brassinosteroid (BR) signaling thereby inducing changes in root directional growth. Auxin signaling and polar transport components are also involved in Glc induced changes in root directional growth. Here, we provide evidence for involvement of cytokinin and ethylene signaling components in regulation of root directional growth downstream to Glc and BR. Altogether, Glc mediated change in root direction is an adaptive feature which is a result of a collaborative effort integrating phytohormonal signaling cues.

Inducing gravitropic curvature of primary roots of Zea mays cv Ageotropic

NASA Technical Reports Server (NTRS)

Moore, R.; Evans, M. L.; Fondren, W. M.

1990-01-01

Primary roots of the mutant 'Ageotropic' cultivar of Zea mays are nonresponsive to gravity. Their root caps secrete little or no mucilage and touch the root only at the extreme apex. A gap separates the cap and root at the periphery of the cap. Applying mucilage from normal roots or substances with a consistency similar to that of mucilage to tips of mutant roots causes these roots to become strongly graviresponsive. Gravicurvature stops when these substances are removed. Caps of some mutants secrete small amounts of mucilage and are graviresponsive. These results indicate that (a) the lack of graviresponsiveness in the mutant results from disrupting the transport pathway between the cap and root, (b) movement of the growth-modifying signal from the cap to the root occurs via an apoplastic pathway, and (c) mucilage is necessary for normal communication between the root cap and root in Zea mays cv Ageotropic.

Mutualism in a Reduced Gravity Environment (MuRGE)

NASA Technical Reports Server (NTRS)

Haire, Timothy C.

2010-01-01

Mutualism in a Reduced Gravity Environment (MuRGE) is a ground research study to determine the feasibility of assessing fungi-plant (Piriformospora indica-Arabidopsis thaliana) interactions in microgravity. Seeds from the plant Arabiddospsis thaliana (At) will be grown in the presence of Piriformospora indica (Pi) an endophytic Sebacinacae family fungus. Pi is capable of colonizing the roots of a wide variety of plant species, including non-mycorrhizal hosts like At, and promoting plant growth similarly to AMF (arbusuclar mychorrizal fungi) unlike most AMF, Pi is not an obligate plant symbiont and can be grown in the absence of a host. In the presence of a suitable plant host, Pi can attach to and colonize root tips. Interaction visualization is accomplished with strong autofluorescence in the roots, followed by root colonization via fungal hyphae, and chlamydospore production. Increased root growth can be observed even before root colonization is detectable. In addition, Pi chlamydospores generated from axenic culture in microgravity will be used to inoculate roots of At grown in 1g to determine the effect of microgravity upon the inherent virulence or beneficial effects. Based on recent reports of increased virulence of S. typhimurium, P. aeruginosa, and S. Pneumoniae in reduced gravity, differences in microbial pathogenic responses and host plant systemic acquired resistance are expected. The focus of this project within MuRGE involved the development P. indica culture media evaluation and microscopy protocol development. High, clean spore harvest yields for the detection of fungi-plant interactions microscopically was the immediate goal of this experiment.

Characterization of a calcium/calmodulin-dependent protein kinase homolog from maize roots showing light-regulated gravitropism

NASA Technical Reports Server (NTRS)

Lu, Y. T.; Hidaka, H.; Feldman, L. J.

1996-01-01

Roots of many species respond to gravity (gravitropism) and grow downward only if illuminated. This light-regulated root gravitropism is phytochrome-dependent, mediated by calcium, and inhibited by KN-93, a specific inhibitor of calcium/calmodulin-dependent protein kinase II (CaMK II). A cDNA encoding MCK1, a maize homolog of mammalian CaMK, has been isolated from roots of maize (Zea mays L.). The MCK1 gene is expressed in root tips, the site of perception for both light and gravity. Using the [35S]CaM gel-overlay assay we showed that calmodulin-binding activity of the MCK1 is abolished by 50 microM KN-93, but binding is not affected by 5 microM KN-93, paralleling physiological findings that light-regulated root gravitropism is inhibited by 50 microM KN-93, but not by 5 microM KN-93. KN-93 inhibits light-regulated gravitropism by interrupting transduction of the light signal, not light perception, suggesting that MCK1 may play a role in transducing light. This is the first report suggesting a physiological function for a CaMK homolog in light signal transduction.

Effects of real or simulated microgravity on plant cell growth and proliferation

NASA Astrophysics Data System (ADS)

Medina, Francisco Javier; Manzano, Ana Isabel; Herranz, Raul; Dijkstra, Camelia; Larkin, Oliver; Hill, Richard; Carnero-Díaz, Eugénie; van Loon, Jack J. W. A.; Anthony, Paul; Davey, Michael R.; Eaves, Laurence

Experiments on seed germination and seedling growth performed in real microgravity on the International Space Station and in different facilities for simulating microgravity in Earth-based laboratories (Random Positioning Machine and Magnetic Levitation), have provided evidence that the absence of gravity (or the artificial compensation of the gravity vector) results in the uncoupling of cell growth and proliferation in root meristematic cells. These are two essential cellular functions that support plant growth and development, which are strictly coordinated under normal ground gravity conditions. Under conditions of altered gravity, we observe that cell proliferation is enhanced, whereas cell growth is reduced, according to different morphometric, cytological and immunocytochemical parameters. Since coordination of cell growth and proliferation are major features of meristematic cells, this observed uncoupling represents a major stress condition for these cells, inducing major alterations in the pattern of plant development. Moreover, the expression of the cyclin B1 gene, a regulator of the entry into mitosis and normally used as an indicator of cell proliferation, appears reduced in the smaller and more actively proliferating cells of samples grown under the conditions of our experiments. These results are compatible with an alteration of the regulation of the cell cycle, producing a shorter G2 period. Interestingly, while cyclin B1 expression is depleted in these conditions in root meristematic cells, it is enhanced in cotyledons of the same seedlings, as shown by qPCR and by the expression of the gus reporter gene. It is known that regulation of root growth (including regulation of root meristematic activity) is driven mainly by auxin, whereas cytokinin is the key hormone regulating cotyledon growth. Therefore, our results indicate a major role of auxin in the sensitivity to altered gravity of root meristematic cells. Auxin is crucial in maintaining the coupling of cell growth and proliferation under normal conditions and it should have a decisive influence in the uncoupling of these processes under altered gravity. Experiments to detect auxin distribution in roots under altered gravity produced by diamagnetic levitation have shown that the lateral balanced distribution of the growth regulator in the root cap is altered slightly and that the total concentration of the auxin detected in root tips is somewhat reduced. These effects are independent of the orientation of statoliths in columella cells.

Hydrostatic factors affect the gravity responses of algae and roots

NASA Technical Reports Server (NTRS)

Staves, Mark P.; Wayne, Randy; Leopold, A. C.

1991-01-01

The hypothesis of Wayne et al. (1990) that plant cells perceive gravity by sensing a pressure differential between the top and the bottom of the cell was tested by subjecting rice roots and cells of Caracean algae to external solutions of various densities. It was found that increasing the density of the external medium had a profound effect on the polar ratio (PR, the ratio between velocities of the downwardly and upwardly streaming cytoplasm) of the Caracean algae cells. When these cells were placed in solutions of denser compound, the PR decreased to less than 1, as the density of the external medium became higher than that of the cell; thus, the normal gravity-induced polarity was reversed, indicating that the osmotic pressure of the medium affects the cell's ability to respond to gravity. In rice roots, an increase of the density of the solution inhibited the rate of gravitropism. These results agree with predictions of a hydrostatic model for graviperception.

Gravity-induced differentiations and deficiency in flower formation observed on Columbus experiment WAICO1

NASA Astrophysics Data System (ADS)

Scherer, Günther; Pietrzyk, Peter

The Arabidopsis Atpla-I-3 knockout mutant (gene nr. At1g61859) is deficient in gravitropism and phototropism indicating a defect in the auxin transport system. The mutant roots form higher numbers of root coils on 45° angle tilted agar. Root tip coils exhibit right-handed spiral pattern of the rhizodermis cells suggesting that torsion of rhizodermis cells could provide a driving force for asymmetrical growth and coiling. WAICO1 was designed to test whether the tendency to for coils by asymmetric tip growth may be provided by torsion of external rhizodermis cells or, alternatively, the asymmetric growth is driven by intrinsic forces in the root. Coil formation is often increased in root agravitropic mutants so that an increase of coils by lack of gravity -and thus absence of gravisensing -was the favoured working hypothesis. Two agar boxes each of wild type and mutant seedlings were grown inside of an outer growth container at 22.5° C in constant light and at a 45° angle tilted, in the 1G rotor and in the microgravity rotor. At first, the samples grown in microgravity could be retrieved from orbit as cooled (4° -8° C) material. They were investigated by microscopy and compared to photographs made in orbit of 1G and µG plants by astronaut. Plants first grown in 1G were retrieved much later (see below). Mutant and wt formed high numbers of coils in microgravity, whereas in 1G none were observed which is comparable to growth experiments on the ground. However, the mutant developed a lower percentage of spiral pattern in the rhizodermal cells despite an even higher number of coils as observed in the wt. The results show that asymmetrical growth of root tips is an intrinsic property and independent of forces that may be exerted by the rhizodermal pattern. Surprisingly, in both wild type and mutant a much higher number of lateral roots were found in µG-grown plants than in plants grown in the 1G-centrifuge after 12 d, suggesting that gravity suppresses lateral root formation. When mutants and wt only grown in the 1G centrifuge were compared the mutant leaves and cotyledons were smaller than in wt and hypocotyls were longer, but when the plants in µG for 12d were compared this difference was not found. Hence, gravity had an influence on leaf expansion and hypocotyl length in the mutant. The samples grown for 12d in 1G were kept in µG after 12d on due to a technical failure of the 1G centrifuge. They were retrieved about a year later. They had grown to full senescence and were preserved in a beautiful state as "straw". The observations on the root patterns by the astronaut photos at day 12 could be confirmed but plants had grown on and newer roots made coils just as the plants grown µG. Leaf sizes were different for wt and mutant. The most striking observation was that the mutants had developed small flower stems with a few flower buds but many flowers were incomplete, without the proper sepal or petal number or without gynaecium. The wild type plants had not developed any clear flower stem but only several malformed cell clumps shortly above the rosette. In ground laboratory experiments the mutants flower earlier which might explain why they developed flowers to some extent whereas the wt not at all. Microgravity might be a "stress" for flower formation. Taken together, several gravity-induced (or microgravity-induced) changes in differentiation occurred.

Genetic ablation of root cap cells in Arabidopsis

NASA Technical Reports Server (NTRS)

Tsugeki, R.; Fedoroff, N. V.

1999-01-01

The root cap is increasingly appreciated as a complex and dynamic plant organ. Root caps sense and transmit environmental signals, synthesize and secrete small molecules and macromolecules, and in some species shed metabolically active cells. However, it is not known whether root caps are essential for normal shoot and root development. We report the identification of a root cap-specific promoter and describe its use to genetically ablate root caps by directing root cap-specific expression of a diphtheria toxin A-chain gene. Transgenic toxin-expressing plants are viable and have normal aerial parts but agravitropic roots, implying loss of root cap function. Several cell layers are missing from the transgenic root caps, and the remaining cells are abnormal. Although the radial organization of the roots is normal in toxin-expressing plants, the root tips have fewer cytoplasmically dense cells than do wild-type root tips, suggesting that root meristematic activity is lower in transgenic than in wild-type plants. The roots of transgenic plants have more lateral roots and these are, in turn, more highly branched than those of wild-type plants. Thus, root cap ablation alters root architecture both by inhibiting root meristematic activity and by stimulating lateral root initiation. These observations imply that the root caps contain essential components of the signaling system that determines root architecture.

Immunolocalization of integrin-like proteins in Arabidopsis and Chara

NASA Technical Reports Server (NTRS)

Katembe, W. J.; Swatzell, L. J.; Makaroff, C. A.; Kiss, J. Z.

1997-01-01

Integrins are a large family of integral plasma membrane proteins that link the extracellular matrix to the cytoskeleton in animal cells. As a first step in determining if integrin-like proteins are involved in gravitropic signal transduction pathways, we have used a polyclonal antibody against the chicken beta1 integrin subunit in western blot analyses and immunofluorescence microscopy to gain information on the size and location of these proteins in plants. Several different polypeptides are recognized by the anti-integrin antibody in roots and shoots of Arabidopsis and in the internodal cells and rhizoids of Chara. These cross-reactive polypeptides are associated with cellular membranes, a feature which is consistent with the known location of integrins in animal systems. In immunofluorescence studies of Arabidopsis roots, a strong signal was obtained from labeling integrin-like proteins in root cap cells, and there was little or no immunolabel in other regions of the root tip. While the antibody stained throughout Chara rhizoids, the highest density of immunolabel was at the tip. Thus, in both Arabidopsis roots and Chara rhizoids, the sites of gravity perception/transduction appear to be enriched in integrin-like molecules.

Trichoderma-Induced Acidification Is an Early Trigger for Changes in Arabidopsis Root Growth and Determines Fungal Phytostimulation

PubMed Central

Pelagio-Flores, Ramón; Esparza-Reynoso, Saraí; Garnica-Vergara, Amira; López-Bucio, José; Herrera-Estrella, Alfredo

2017-01-01

Trichoderma spp. are common rhizosphere inhabitants widely used as biological control agents and their role as plant growth promoting fungi has been established. Although soil pH influences several fungal and plant functional traits such as growth and nutrition, little is known about its influence in rhizospheric or mutualistic interactions. The role of pH in the Trichoderma–Arabidopsis interaction was studied by determining primary root growth and lateral root formation, root meristem status and cell viability, quiescent center (QC) integrity, and auxin inducible gene expression. Primary root growth phenotypes in wild type seedlings and STOP1 mutants allowed identification of a putative root pH sensing pathway likely operating in plant–fungus recognition. Acidification by Trichoderma induced auxin redistribution within Arabidopsis columella root cap cells, causing root tip bending and growth inhibition. Root growth stoppage correlated with decreased cell division and with the loss of QC integrity and cell viability, which were reversed by buffering the medium. In addition, stop1, an Arabidopsis mutant sensitive to low pH, was oversensitive to T. atroviride primary root growth repression, providing genetic evidence that a pH root sensing mechanism reprograms root architecture during the interaction. Our results indicate that root sensing of pH mediates the interaction of Trichoderma with plants. PMID:28567051

Graviresponsiveness of surgically altered primary roots of Zea mays

NASA Technical Reports Server (NTRS)

Maimon, E.; Moore, R.

1991-01-01

We examined the gravitropic responses of surgically altered primary roots of Zea mays to determine the route by which gravitropic inhibitors move from the root tip to the elongating zone. Horizontally oriented roots, from which a 1-mm-wide girdle of epidermis plus 2-10 layers of cortex were removed from the apex of the elongating zone, curve downward. However, curvature occurred only apical to the girdle. Filling the girdle with mucilage-like material transmits curvature beyond the girdle. Vertically oriented roots with a half-girdle' (i.e. the epidermis and 2-10 layers of the cortex removed from half of the circumference of the apex of the elongating zone) curve away from the girdle. Inserting the half-girdle at the base of the elongating zone induces curvature towards the girdle. Filling the half-circumference girdles with mucilage-like material reduced curvature significantly. Stripping the epidermis and outer 2-5 layers of cortex from the terminal 1.5 cm of one side of a primary root induces curvature towards the cut, irrespective of the root's orientation to gravity. This effect is not due to desiccation since treated roots submerged in water also curved towards their cut surface. Coating a root's cut surface with a mucilage-like substance minimizes curvature. These results suggest that the outer cell-layers of the root, especially the epidermis, play an important role in root gravicurvature, and the gravitropic signals emanating from the root tip can move apoplastically through mucilage.

Gravisensing in single-celled systems

NASA Astrophysics Data System (ADS)

Braun, M.; Limbach, C.

Single-celled systems are favourable cell types for studying several aspects of gravisensing and gravitropic responses. Whether and how actin is involved in both processes in higher plant statocytes is still a matter of intensive debate. In single-celled and tip-growing characean rhizoids and protonemata, however, there is clear evidence that actin is a central keyplayer controlling polarized growth and the mechanisms of gravity sensing and growth reorientation. Both cell types exhibit a unique actin polymerization in the extending tip, strictly colocalized with the prominent ER-aggregate in the center of the Spitzenkoerper. The local accumulation of ADF and profilin in this central array suggest that actin polymerization is controlled by these actin-binding proteins, which can be regulated by calcium, pH and a variety of other parameters. Distinct actin filaments extend even into the outermost tip and form a dense meshwork in the apical and subapical region, before they become bundled by villin to form two populations of thick actin cables that generate rotational cytoplasmic streaming in the basal region. Actomyosin not only mediates the delivery of secretory vesicles to the growing tip and controls the incorporation pattern of cell wall material, but also coordinates the tip-focused distribution pattern of calcium channels in the apical membrane. They establish the tip-high calcium gradient, a prerequisite for exocytosis. Microgravity experiments have added much to our understanding that both cell types use an efficient actomyosin-based system to control and correct the position of their statoliths and to direct sedimenting statoliths to confined graviperception sites at the plasma membrane. Actin's involvement in the graviresponses is more indirect. The upward growth of negatively gravitropic protonemata was shown to be preceded by a statolith-induced relocalization the Ca2+-calcium gradient to the upper flank that does not occur in positively gravitropic (downward growing) rhizoids, in which statoliths sedimentation is followed by differential flank growth. Based on these results, it is evident that polymerization, dynamic reorganization and the diverse functions of actin spatiotemporally controlled by numerous actin-binding proteins are fundamental for the processes of gravity sensing and gravity-oriented polarized growth. Financial support by Deutsches Zentrum für Luft- und Raumfahrt (DLR) on behalf of the Bundesministerium für Bildung und Forschung (50WB9998).

Reactive Oxygen Species Tune Root Tropic Responses1[OPEN

PubMed Central

Krieger, Gat

2016-01-01

The default growth pattern of primary roots of land plants is directed by gravity. However, roots possess the ability to sense and respond directionally to other chemical and physical stimuli, separately and in combination. Therefore, these root tropic responses must be antagonistic to gravitropism. The role of reactive oxygen species (ROS) in gravitropism of maize and Arabidopsis (Arabidopsis thaliana) roots has been previously described. However, which cellular signals underlie the integration of the different environmental stimuli, which lead to an appropriate root tropic response, is currently unknown. In gravity-responding roots, we observed, by applying the ROS-sensitive fluorescent dye dihydrorhodamine-123 and confocal microscopy, a transient asymmetric ROS distribution, higher at the concave side of the root. The asymmetry, detected at the distal elongation zone, was built in the first 2 h of the gravitropic response and dissipated after another 2 h. In contrast, hydrotropically responding roots show no transient asymmetric distribution of ROS. Decreasing ROS levels by applying the antioxidant ascorbate, or the ROS-generation inhibitor diphenylene iodonium attenuated gravitropism while enhancing hydrotropism. Arabidopsis mutants deficient in Ascorbate Peroxidase 1 showed attenuated hydrotropic root bending. Mutants of the root-expressed NADPH oxidase RBOH C, but not rbohD, showed enhanced hydrotropism and less ROS in their roots apices (tested in tissue extracts with Amplex Red). Finally, hydrostimulation prior to gravistimulation attenuated the gravistimulated asymmetric ROS and auxin signals that are required for gravity-directed curvature. We suggest that ROS, presumably H2O2, function in tuning root tropic responses by promoting gravitropism and negatively regulating hydrotropism. PMID:27535793

Organelle sedimentation in gravitropic roots of Limnobium is restricted to the elongation zone

NASA Technical Reports Server (NTRS)

Sack, F. D.; Kim, D.; Stein, B.

1994-01-01

Roots of the aquatic angiosperm Limnobium spongia (Bosc) Steud. were evaluated by light and electron microscopy to determine the distribution of organelle sedimentation towards gravity. Roots of Limnobium are strongly gravitropic. The rootcap consists of only two layers of cells. Although small amyloplasts are present in the central cap cells, no sedimentation of any organelle, including amyloplasts, was found. In contrast, both amyloplasts and nuclei sediment consistently and completely in cells of the elongation zone. Sedimentation occurs in one cell layer of the cortex just outside the endodermis. Sedimentation of both amyloplasts and nuclei begins in cells that are in their initial stages of elongation and persists at least to the level of the root where root hairs emerge. This is the first modern report of the presence of sedimentation away from, but not in, the rootcap. It shows that sedimentation in the rootcap is not necessary for gravitropic sensing in at least one angiosperm. If amyloplast sedimentation is responsible for gravitropic sensing, then the site of sensing in Limnobium roots is the elongation zone and not the rootcap. These data do not necessarily conflict with the hypothesis that sensing occurs in the cap in other roots, since Limnobium roots are exceptional in rootcap origin and structure, as well as in the distribution of organelle sedimentation. Similarly, if nuclear sedimentation is involved in gravitropic sensing, then nuclear mass would function in addition to, not instead of, that of amyloplasts.

Effects of inversion on plastid position and gravitropism in Ceratodon protonemata

NASA Technical Reports Server (NTRS)

Schwuchow, J.; Sack, F. D.

1993-01-01

When dark-grown tip cells of protonemata of the moss Ceratodon purpureus are turned to the horizontal, plastids first sediment towards gravity in a specific zone and then the tip curves upward. To determine whether gravitropism and plastid sedimentation occur in other orientations, protonemata were reoriented to angles other than 90 degrees. Qualitative and quantitative light microscopic observations show that plastid sedimentation along the cell axis occurs in both upright and inverted cells. However, only some plastids fall and sedimentation is incomplete; plastids remain distributed throughout the length of the cell, and those plastids that sediment do not fall all the way to the bottom of the cell. Tip cells are gravitropic regardless of stimulation angle, and as in higher plants, the maximal rate of initial curvature is in response to a 120 degrees reorientation. Infrared videomicroscopy, time-lapse studies of living, inverted protonemata indicate that amyloplast sedimentation precedes upward curvature. Together, these data further support (i) the hypothesis that amyloplast sedimentation functions in gravitropic sensing in these cells, and (ii) the idea that gravity affected the evolution of cell organization.

The wavy growth 3 E3 ligase family controls the gravitropic response in Arabidopsis roots.

PubMed

Sakai, Tatsuya; Mochizuki, Susumu; Haga, Ken; Uehara, Yukiko; Suzuki, Akane; Harada, Akiko; Wada, Takuji; Ishiguro, Sumie; Okada, Kiyotaka

2012-04-01

Regulation of the root growth pattern is an important control mechanism during plant growth and propagation. To better understand alterations in root growth direction in response to environmental stimuli, we have characterized an Arabidopsis thaliana mutant, wavy growth 3 (wav3), whose roots show a short-pitch pattern of wavy growth on inclined agar medium. The wav3 mutant shows a greater curvature of root bending in response to gravity, but a smaller curvature in response to light, suggesting that it is a root gravitropism-enhancing mutation. This wav3 phenotype also suggests that enhancement of the gravitropic response in roots strengthens root tip impedance after contact with the agar surface and/or causes an increase in subsequent root bending in response to obstacle-touching stimulus in these mutants. WAV3 encodes a protein with a RING finger domain, and is mainly expressed in root tips. RING-containing proteins often function as an E3 ubiquitin ligase, and the WAV3 protein shows such activity in vitro. There are three genes homologous to WAV3 in the Arabidopsis genome [EMBRYO SAC DEVELOPMENT ARREST 40 (EDA40), WAVH1 and WAVH2 ], and wav3 wavh1 wavh2 triple mutants show marked root gravitropism abnormalities. This genetic study indicates that WAV3 functions positively rather than negatively in root gravitropism, and that enhancement of the gravitropic response in wav3 roots is dependent upon the function of WAVH2 in the absence of WAV3. Hence, our results demonstrate that the WAV3 family of proteins are E3 ligases that are required for root gravitropism in Arabidopsis. © 2011 The Authors. The Plant Journal © 2011 Blackwell Publishing Ltd.

The Mechanism Forming the Cell Surface of Tip-Growing Rooting Cells Is Conserved among Land Plants.

PubMed

Honkanen, Suvi; Jones, Victor A S; Morieri, Giulia; Champion, Clement; Hetherington, Alexander J; Kelly, Steve; Proust, Hélène; Saint-Marcoux, Denis; Prescott, Helen; Dolan, Liam

2016-12-05

To discover mechanisms that controlled the growth of the rooting system in the earliest land plants, we identified genes that control the development of rhizoids in the liverwort Marchantia polymorpha. 336,000 T-DNA transformed lines were screened for mutants with defects in rhizoid growth, and a de novo genome assembly was generated to identify the mutant genes. We report the identification of 33 genes required for rhizoid growth, of which 6 had not previously been functionally characterized in green plants. We demonstrate that members of the same orthogroup are active in cell wall synthesis, cell wall integrity sensing, and vesicle trafficking during M. polymorpha rhizoid and Arabidopsis thaliana root hair growth. This indicates that the mechanism for constructing the cell surface of tip-growing rooting cells is conserved among land plants and was active in the earliest land plants that existed sometime more than 470 million years ago [1, 2]. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Dynamical and Microrheological Analysis of Amyloplasts in the Plant Root Gravity-Sensing Cells

NASA Astrophysics Data System (ADS)

Zheng, Zhongyu; Zou, Junjie; Li, Hanhai; Xue, Shan; Le, Jie; Wang, Yuren

2015-11-01

Gravitropism in plants is one of the most controversial issues. In the most wildly accepted starch-statolith hypothesis the sedimentation movement of amyloplasts in the gravisensing columella cells primarily triggers the asymmetric distribution of auxin which leads to the differential growth of the plant root. It has been gradually recognized that the inhomogeneous structures in statocytes arising from intracellular components such as cytoskeletons significantly affect the complex movements of amyloplasts and the final gravimorphogenesis. In this letter, we implement a diffusive dynamics measurement and inplanta microrheological analysis of amyloplasts in the wild-type plants and actin cytoskeleton mutants for the first time. We found that the intracellular environment of columella cells exhibits the spatial heterogeneity and the cage-confinement on amyloplasts which is the typically characteristics in colloidal suspensions. By comparing the distinct diffusive dynamics of amyloplasts in different types of plants with the behaviors of colloidal systems in different states, we quantitatively characterized the influence of the actin organization dominated intracellular envoronments on the amyloplast movements. Furthermore, the cage-confinement strength was measured by calculating the spatial fluctuation of local apparent viscosity within the columella cells. Finally, a linear association between the initial mechanical stimulation in the columella cells the subsequent intercellular signal transduction and the final gravity response was observed and a possible gravity sensing mechanism was suggested. It suggests the existence of a potential gravity-sensing mechanism that dictates a linear frustration effect of the actin cytoskeleton on the conversion of the mechanical stimulation of amyloplasts into gravitropic signals.

A technique for the determination of center of gravity and rolling resistance for tilt-seat wheelchairs.

PubMed

Lemaire, E D; Lamontagne, M; Barclay, H W; John, T; Martel, G

1991-01-01

A balance platform setup was defined for use in the determination of the center of gravity in the sagittal plane for a wheelchair and patient. Using the center of gravity information, measurements from the wheelchair and patient (weight, tire coefficients of friction), and various assumptions (constant speed, level-concrete surface, patient-wheelchair system is a rigid body), a method for estimating the rolling resistance for a wheelchair was outlined. The center of gravity and rolling resistance techniques were validated against criterion values (center of gravity error = 1 percent, rolling resistance root mean square error = 0.33 N, rolling resistance Pearson correlation coefficient = 0.995). Consistent results were also obtained from a test dummy and five subjects. Once the center of gravity is known, it is possible to evaluate the stability of a wheelchair (in terms of tipping over) and the interaction between the level of stability and rolling resistance. These quantitative measures are expected to be of use in the setup of wheelchairs with a variable seat angle and variable wheelbase length or when making comparisons between different wheelchairs.

A New Model for Root Growth in Soil with Macropores

NASA Astrophysics Data System (ADS)

Landl, M.; Huber, K.; Schnepf, A.; Vanderborght, J.; Javaux, M.; Bengough, G.; Vereecken, H.

2016-12-01

In order to study soil-root interaction processes, dynamic root architecture models which are linked to models that simulate water flow and nutrient transport in the soil-root system are needed. Such models can be used to predict the impact of soil structural features, e.g. the presence of macropores in dense subsoil, on water and nutrient uptake by plants. In dynamic root architecture models, root growth is represented by moving root tips whose growth trajectory results in the creation of linear root segments. Typically, the direction of each new root segment is calculated as the vector sum of various direction-affecting components. The use of these established methods to simulate root growth in soil containing macropores, however, failed to reproduce experimentally observed root growth patterns. We therefore developed an alternative modelling approach where we distinguish between, firstly, the driving force for root growth which is determined by the orientation of the previous root segment as well as the influence of gravitropism and, secondly, soil mechanical resistance to root growth. The latter is expressed by root conductance which represents the inverse of soil penetration resistance and is treated similarly to hydraulic conductivity in Darcy's law. At the presence of macropores, root conductance is anisotropic which leads to a difference between the direction of the driving force and the direction of the root tip movement. The model was tested using data from the literature, at pot scale, at macropore scale, and in a series of simulations where sensitivity to gravity and macropore orientation was evaluated. The model simulated root growth trajectories in structured soil at both single root and whole root-system scales, generating root systems that were similar to images from experiments. Its implementation in the three dimensional soil and root water uptake model R-SWMS enables the use of the model in the future to evaluate the effect of macropores on crop access to water and nutrients.

Multiple roles for membrane-associated protein trafficking and signaling in gravitropism

PubMed Central

Strohm, Allison K.; Baldwin, Katherine L.; Masson, Patrick H.

2012-01-01

Gravitropism is a process that allows plant organs to guide their growth relative to the gravity vector. It requires them to sense changes in their orientation and generate a biochemical signal that they transmit to the tissues that drive organ curvature. Trafficking between the plasma membrane and endosomal compartments is important for all of these phases of the gravitropic response. The sedimentation of starch-filled organelles called amyloplasts plays a key role in sensing reorientation, and vacuolar integrity is required for amyloplast sedimentation in shoots. Other proteins associated with the vesicle trafficking pathway contribute to early gravity signal transduction independently of amyloplast sedimentation in both roots and hypocotyls. Phosphatidylinositol signaling, which starts at the plasma membrane and later affects the localization of auxin efflux facilitators, is a likely second messenger in the signal transduction phase of gravitropism. Finally, membrane-localized auxin influx and efflux facilitators contribute to a differential auxin gradient across the gravistimulated organs, which directs root curvature. PMID:23248632

Multiple roles for membrane-associated protein trafficking and signaling in gravitropism.

PubMed

Strohm, Allison K; Baldwin, Katherine L; Masson, Patrick H

2012-01-01

Gravitropism is a process that allows plant organs to guide their growth relative to the gravity vector. It requires them to sense changes in their orientation and generate a biochemical signal that they transmit to the tissues that drive organ curvature. Trafficking between the plasma membrane and endosomal compartments is important for all of these phases of the gravitropic response. The sedimentation of starch-filled organelles called amyloplasts plays a key role in sensing reorientation, and vacuolar integrity is required for amyloplast sedimentation in shoots. Other proteins associated with the vesicle trafficking pathway contribute to early gravity signal transduction independently of amyloplast sedimentation in both roots and hypocotyls. Phosphatidylinositol signaling, which starts at the plasma membrane and later affects the localization of auxin efflux facilitators, is a likely second messenger in the signal transduction phase of gravitropism. Finally, membrane-localized auxin influx and efflux facilitators contribute to a differential auxin gradient across the gravistimulated organs, which directs root curvature.

The Effect of Weak Combined Magnetic Field on Root Gravitropism and a Role of Ca2+ Ions Therein

NASA Astrophysics Data System (ADS)

Kordyum, Elizabeth; Bogatina, Nina; Kondrachuk, A.

At present, magnetic fields of different types are widely used to study gravity sensing in plants. For instance, magnetic levitation of amyloplasts caused by high gradient magnetic field enables us to alter the effective gravity sensed by plant cells. For the first time we showed that a weak combined magnetic field (CMF), that is the sum of collinear permanent and alternating magnetic fields ( 0.5 gauss, 0-100 Hz), changes a cress and pea root positive gravitropic reaction on a negative one. This effect has the form of resonance and occurs at the frequency of cyclotron resonance of calcium ions. What is especially interesting is that under gravistimulation in the CMF, the displacement of amylopasts in the root cap statocytes is directed to the upper wall of a cell, i.e. in the direction opposite to the gravitational vector. The displacement of amyloplasts, which contain the abundance of free Ca2+ ions in the stroma, is accompanied by Ca2+ redistribution in the same direction, and increasing in the cytosol around amyloplasts near ten times in the CMF in comparison with the state magnetic field. Earlier, we also observed the Ca2+ accumulation in the upper site of a root curvature in the elongation zone in the CMF unlike a positive gravitropic reaction. Thus, it should be stressed that a root is bending in the same direction in which amyloplasts are displacing: downwards when gravitropism is positive and upwards when gravitropism is negative. The obtained data confirm the amyloplast statolithic function and give another striking demonstration of a leading role of Ca2+ ions in root gravitropism. But these data bring the question: what forces can promote amyloplast displacement against gravity? The possible explanation of the effect found is discussed. It is based on the ion cyclotron resonance in biosystems proposed by Liboff.. The original approach based on the use of a weak CMF may be helpful for understanding the mechanisms of plant gravisensing

Calcium/Calmodulin-Mediated Gravitropic Response in Plants

NASA Technical Reports Server (NTRS)

Poovaiah, B. W.

2002-01-01

Plant organs respond to different physical signals such as gravity, light and touch. Gravity gives plants proper orientation, resulting in the proper form that we take for granted; the roots grow down into soil and shoots grow towards the light. Under microgravity conditions, as in space, plant growth patterns lack a clear sense of direction. Calcium and calmodulin (CaM) play an important role in gravity signal transduction. However, the molecular and biochemical mechanisms involved in gravity signal transduction are not clearly understood. The goal of this project was to gain a fundamental understanding of how calcium/calmodulin-mediated signaling is involved in gravity signal transduction in plants. During the grant period, significant progress was made in elucidating the role of calmodulin and its target proteins in gravitropism.

Root cytoskeleton: its role in perception of and response to gravity

NASA Technical Reports Server (NTRS)

Baluska, F.; Hasenstein, K. H.

1997-01-01

We have critically evaluated the possible functions of the plant cytoskeleton in root gravisensing and graviresponse and discussed the evidence that microtubules (MTs) and actin microfilaments (MFs) do not control differential cell growth during bending of roots. On the other hand, MF and MT networks are envisaged to participate in gravisensing because of the mechanical properties of the cytoskeletal structures that interconnect plant cell organelles with the plasma membrane. In restrained gravisensing, forces are suggested to be transmitted to membranes because large-scale gravity-dependent repositioning of organelles is effectively prevented due to the cytoskeleton-mediated anchorage of their envelopes at the plasma membrane. From the cytoskeletal point of view, we can also envisage an unrestrained gravity sensing when cytoskeletal tethers are not strong enough to preserve the tight control over distribution of organelles and the latter, if heavy enough, are allowed to sediment towards the physical bottom of cells. This situation obviously occurs in root cap statocytes because these uniquely organized cells are depleted of prominent actin MF bundles, endoplasmic MT arrays, and ER elements in their internal cytoplasm. Nevertheless, indirect evidence clearly indicates that sedimented root cap statoliths are enmeshed within fine but dynamic MF networks and that their behaviour is obviously under, at least partial, cytoskeletal control. The actomyosin-enriched domain among and around amyloplasts is proposed to increase the perception of gravity due to the grouping effect of sedimenting statoliths. Cytoskeletal links between myosin-rich statoliths, and cell peripheries well equipped with dense cortical MTs, membrane-associated cytoskeleton, as well as with ER elements, would allow efficient restrained gravisensing only at the statocyte cell cortex. As a consequence of cytoskeletal depletion in the internal statocyte cytoplasm and bulk sedimentation of large amyloplasts, restrained gravisensing is spatially restricted to the bottom of the statocyte irrespective of whether roots are vertical or horizontal. This spatial aspect allows for efficient gravisensing via amplification of gravity-induced impacts on the cellular architecture, a phenomenon which is unique to root cap statocytes.

Effects of Gravity, Microgravity or Microgravity Simulation on Early Mammalian Development.

PubMed

Ruden, Douglas M; Bolnick, Alan; Awonuga, Awoniyi; Abdulhasan, Mohammed; Perez, Gloria; Puscheck, Elizabeth E; Rappolee, Daniel A

2018-06-11

Plant and animal life forms evolved mechanisms for sensing and responding to gravity on Earth where homeostatic needs require responses. The lack of gravity, such as in the International Space Station (ISS), causes acute, intra-generational changes in the quality of life. These include maintaining calcium levels in bone, maintaining muscle tone, and disturbances in the vestibular apparatus in the ears. These problems decrease work efficiency and quality of life of humans not only during microgravity exposures but also after return to higher gravity on Earth or destinations such as Mars or the Moon. It has been hypothesized that lack of gravity during mammalian development may cause prenatal, postnatal and transgenerational effects that conflict with the environment, especially if the developing organism and its progeny are returned, or introduced de novo, into the varied gravity environments mentioned above. Although chicken and frog pregastrulation development, and plant root development, have profound effects due to orientation of cues by gravity-sensing mechanisms and responses, mammalian development is not typically characterized as gravity-sensing. Although no effects of microgravity simulation (MGS) on mouse fertilization were observed in two reports, negative effects of MGS on early mammalian development after fertilization and before gastrulation are presented in four reports that vary with the modality of MGS. This review will analyze the positive and negative mammalian early developmental outcomes, and enzymatic and epigenetic mechanisms known to mediate developmental responses to simulated microgravity on Earth and microgravity during spaceflight experiments. We will update experimental techniques that have already been developed or need to be developed for zero gravity molecular, cellular, and developmental biology experiments.

Macromolecular differentiation of Golgi stacks in root tips of Arabidopsis and Nicotiana seedlings as visualized in high pressure frozen and freeze-substituted samples

NASA Technical Reports Server (NTRS)

Staehelin, L. A.; Giddings, T. H. Jr; Kiss, J. Z.; Sack, F. D.

1990-01-01

The plant root tip represents a fascinating model system for studying changes in Golgi stack architecture associated with the developmental progression of meristematic cells to gravity sensing columella cells, and finally to "young" and "old", polysaccharide-slime secreting peripheral cells. To this end we have used high pressure freezing in conjunction with freeze-substitution techniques to follow developmental changes in the macromolecular organization of Golgi stacks in root tips of Arabidopsis and Nicotiana. Due to the much improved structural preservation of all cells under investigation, our electron micrographs reveal both several novel structural features common to all Golgi stacks, as well as characteristic differences in morphology between Golgi stacks of different cell types. Common to all Golgi stacks are clear and discrete differences in staining patterns and width of cis, medial and trans cisternae. Cis cisternae have the widest lumina (approximately 30 nm) and are the least stained. Medial cisternae are narrower (approximately 20 nm) and filled with more darkly staining products. Most trans cisternae possess a completely collapsed lumen in their central domain, giving rise to a 4-6 nm wide dark line in cross-sectional views. Numerous vesicles associated with the cisternal margins carry a non-clathrin type of coat. A trans Golgi network with clathrin coated vesicles is associated with all Golgi stacks except those of old peripheral cells. It is easily distinguished from trans cisternae by its blebbing morphology and staining pattern. The zone of ribosome exclusion includes both the Golgi stack and the trans Golgi network. Intercisternal elements are located exclusively between trans cisternae of columella and peripheral cells, but not meristematic cells. In older peripheral cells only trans cisternae exhibit slime-related staining. Golgi stacks possessing intercisternal elements also contain parallel rows of freeze-fracture particles in their trans cisternal membranes. We propose that intercisternal elements serve as anchors of enzyme complexes involved in the synthesis of polysaccharide slime molecules to prevent the complexes from being dragged into the forming secretory vesicles by the very large slime molecules. In addition, we draw attention to the similarities in composition and apparent site of synthesis of xyloglucans and slime molecules.

Gravity persistent signal 1 reveals a novel cytochrome P450 involved in gravitropic signal transduction

NASA Astrophysics Data System (ADS)

Wyatt, Sarah

Understanding gene expression that occurs during gravitopism is important for studying the processes that link the perception of gravity to the growth response. Arabidopsis plants with a mutation in the GRAVITY PERSISTENT SIGNAL (GPS)1 locus show a "no response" phenotype during gravistimulation experiments. Basepital auxin transport in gps1 mutant was unaffected by the mutation, but auxin was not laterally redistributed after gravistimulation. GPS1 encodes CYP705A22, a cytochrome P450 protein (P450) of unknown function. The wild type CYP705A22 gene was transformed into the gps1 mutant background and successfully rescued the mutant phenotype. Data mining of microarray data collected from gravistimulated root tips of Arabidopsis indicated that although CYP705A22 was not expressed in roots, a family member CYP705A5 was up-regulated within 3 minutes after gravistimulation. Expression profiling of CYP705A5, using real-time quantitative PCR, showed that CYP705A5 was up-regulated nearly five fold within minutes of gravity stimulation. And reporter gene fusions that link the CYP705A5 gene to the green fluorescent protein showed that CYP705A5 was expressed in the root zones of elongation and maturation. Computer modeling of the catalytic domain of CYP705A22 and CYP705A5 and in silico substrate docking simulations generated a list of 130 compounds that are potential substrates of the P450s. Many of the compounds are phenylpropanoid derivatives. Heterologous expression of CYP705A5 in baculovirus and Type 1 binding studies indicate the substrate of the P450 may be quercitin or myricetin. A mutation affecting CYP705A5 expression resulted in a delayed gravity response in roots. The mutant phenotype could be chemically complemented, and DPBA staining in the CYP705A5 mutant indicated a 1.5 fold accumulation of quercetin in mutant roots as compared to WT. These data, taken together, may indicate that we have identified a flavonoid pathway that regulates auxin distribution and thus is involved in gravitropic signal transduction. (Partially support by NSF: 0618506 to SEW)

Plastids and gravitropic sensing

NASA Technical Reports Server (NTRS)

Sack, F. D.

1997-01-01

Data and theories about the identity of the mass that acts in gravitropic sensing are reviewed. Gravity sensing may have evolved several times in plants and algae in processes such as gravitropism of organs and tip-growing cells, gravimorphism, gravitaxis, and the regulation of cytoplasmic streaming in internodal cells of Chara. In the latter and in gravitaxis, the mass of the entire cell may function in sensing. But gravitropic sensing appears to rely upon the mass of amyloplasts that sediment since (i) the location of cells with sedimentation is highly regulated, (ii) such cells contain other morphological specializations favoring sedimentation, (iii) sedimentation always correlates with gravitropic competence in wild-type plants, (iv) magnetophoretic movement of rootcap amyloplasts mimics gravitropism, and (v) starchless and intermediate starch mutants show reduced gravitropic sensitivity. The simplest interpretation of these data is that gravitropic sensing is plastid-based.

A C2H2-type zinc finger protein, SGR5, is involved in early events of gravitropism in Arabidopsis inflorescence stems.

PubMed

Morita, Miyo T; Sakaguchi, Keitaro; Kiyose, Shin-Ichiro; Taira, Kensuke; Kato, Takehide; Nakamura, Moritaka; Tasaka, Masao

2006-08-01

Plants can sense the direction of gravity and change the growth orientation of their organs. To elucidate the molecular mechanisms of gravity perception and the signal transduction of gravitropism, we have characterized a number of shoot gravitropism (sgr) mutants of Arabidopsis. The sgr5-1 mutant shows reduced gravitropism in the inflorescence stem but its root and hypocotyl have normal gravitropism. SGR5 encodes a zinc finger protein with a coiled-coil motif. The SGR5-GFP fusion protein is localized in the nucleus of Arabidopsis protoplasts, suggesting that SGR5 may act as a transcription factor. Analysis of GUS expression under the control of the SGR5 promoter revealed that SGR5 is mainly expressed in the endodermis, the gravity-sensing tissue in inflorescence stems. Furthermore, the observation that endodermis-specific expression of SGR5 using the SCR promoter in the sgr5-1 mutant restores shoot gravitropism indicates that it could function in the gravity-sensing endodermal cell layer. In contrast to other sgr mutants reported previously, almost all amyloplasts in the endodermal cells of the sgr5-1 mutant sedimented in the direction of gravity. Taken together, our results suggest that SGR5 may be involved in an early event in shoot gravitropism such as gravity perception and/or a signaling process subsequent to amyloplast sedimentation as a putative transcription factor in gravity-perceptive cells.

The possible involvement of root-cap mucilage in gravitropism and calcium movement across root tips of Allium cepa L

NASA Technical Reports Server (NTRS)

Moore, R.; Fondren, W. M.

1986-01-01

Roots of Allium cepa L. grown in aerated water elongate rapidly, but are not graviresponsive. These roots (1) possess extensive columella tissues comprised of cells containing numerous sedimented amyloplasts, (2) lack mucilage on their tips, and (3) are characterized by a weakly polar movement of calcium (Ca) across their tips. Placing roots in humid air correlates positively with the (1) onset of gravicurvature, (2) appearance of mucilage on tips of the roots, and (3) onset of the ability to transport Ca polarly to the lower side of the root tip. Gravicurvature of roots previously submerged in aerated water is more rapid when roots are oriented vertically for 1-2 h in humid air prior to being oriented horizontally. The more rapid gravicurvature of these roots correlates positively with the accumulation of mucilage at the tips of roots during the time the roots are oriented vertically. Therefore, the onset of gravicurvature and the ability of roots to transport Ca to the lower sides of their tips correlate positively with the presence of mucilage at their tips. These results suggest that mucilage may be important for the transport of Ca across root caps.

LAZY Genes Mediate the Effects of Gravity on Auxin Gradients and Plant Architecture1[OPEN

PubMed Central

2017-01-01

A rice (Oryza sativa) mutant led to the discovery of a plant-specific LAZY1 protein that controls the orientation of shoots. Arabidopsis (Arabidopsis thaliana) possesses six LAZY genes having spatially distinct expression patterns. Branch angle phenotypes previously associated with single LAZY genes were here studied in roots and shoots of single and higher-order atlazy mutants. The results identify the major contributors to root and shoot branch angles and gravitropic behavior of seedling hypocotyls and primary roots. AtLAZY1 is the principal determinant of inflorescence branch angle. The weeping inflorescence phenotype of atlazy1,2,4 mutants may be due at least in part to a reversal in the gravitropism mechanism. AtLAZY2 and AtLAZY4 determined lateral root branch angle. Lateral roots of the atlazy2,4 double mutant emerged slightly upward, approximately 10° greater than perpendicular to the primary root axis, and they were agravitropic. Etiolated hypocotyls of the quadruple atlazy1,2,3,4 mutant were essentially agravitropic, but their phototropic response was robust. In light-grown seedlings, the root of the atlazy2,3,4 mutant was also agravitropic but when adapted to dim red light it displayed a reversed gravitropic response. A reversed auxin gradient across the root visualized by a fluorescent signaling reporter explained the reversed, upward bending response. We propose that AtLAZY proteins control plant architecture by coupling gravity sensing to the formation of auxin gradients that override a LAZY-independent mechanism that creates an opposing gravity-induced auxin gradient. PMID:28821594

Gravitropism in a starchless mutant of Arabidopsis: implications for the starch-statolith theory of gravity sensing

NASA Technical Reports Server (NTRS)

Caspar, T.; Pickard, B. G.

1989-01-01

The starch-statolith theory of gravity reception has been tested with a mutant of Arabidopsis thaliana (L.) Heynh. which, lacking plastid phosphoglucomutase (EC 2.7.5.1) activity, does not synthesize starch. The hypocotyls and seedling roots of the mutant were examined by light and electron microscopy to confirm that they did not contain starch. In upright wild-type (WT) seedlings, starch-filled plastids in the starch sheath of the hypocotyl and in three of the five columellar layers of the root cap were piled on the cell floors, and sedimented to the ceilings when the plants were inverted. However, starchless plastids of the mutant were not significantly sedimented in these cells in either upright or inverted seedlings. Gravitropism of light-grown seedling roots was vigorous: e.g., 10 degrees curvature developed in mutants rotated on a clinostat following a 5 min induction at 1 g, compared with 14 degrees in the WT. Curvatures induced during intervals from 2.5 to 30 min were 70% as great in the mutant as the WT. Thus under these conditions the presence of starch and the sedimentation of plastids are unnecessary for reception of gravity by Arabidopsis roots. Gravitropism by hypocotyls of light-grown seedlings was less vigorous than that by roots, but the mutant hypocotyls exhibited an average of 70-80% as much curvature as the WT. Roots and hypocotyls of etiolated seedlings and flower stalks of mature plants were also gravitropic, although in these cases the mutant was generally less closely comparable to the WT. Thus, starch is also unnecessary for gravity reception in these tissues.

Induction of hypoxic root metabolism results from physical limitations in O 2 bioavailability in microgravity

NASA Astrophysics Data System (ADS)

Liao, J.; Liu, G.; Monje, O.; Stutte, G. W.; Porterfield, D. M.

2004-01-01

Numerous spaceflight experiments have noted changes in the roots that are consistent with hypoxia in the rootzone. These observations include general ultrastructure analysis and biochemical measurements to direct measurements of stress specific enzymes. In experiments that have monitored alcohol dehydrogenase (ADH), the data shows this hypoxically responsive gene is induced and is associated with increased ADH activity in microgravity. These changes in ADH could be induced either by spaceflight hypoxia resulting from inhibition of gravity mediated O 2 transport, or by a non-specific stress response due to inhibition of gravisensing. We tested these hypotheses in a series of two experiments. The objective of the first experiment was to determine if physical changes in gravity-mediated O 2 transport can be directly measured, while the second series of experiments tested whether disruption of gravisensing can induce a non-specific ADH response. To directly measure O 2 bioavailability as a function of gravity, we designed a sensor that mimics metabolic oxygen consumption in the rhizosphere. Because of these criteria, the sensor is sensitive to any changes in root O 2 bioavailability that may occur in microgravity. In a KC-135 experiment, the sensor was implanted in a moist granular clay media and exposed to microgravity during parabolic flight. The resulting data indicated that root O 2 bioavailability decreased in phase with gravity. In experiments that tested for non-specific induction of ADH, we compared the response of transgenic Arabidopsis plants (ADH promoted GUS marker gene) exposed to clinostat, control, and waterlogged conditions. The plants were grown on agar slats in a growth chamber before being exposed to the experimental treatments. The plants were stained for GUS activity localization, and subjected to biochemical tests for ADH, and GUS enzyme activity. These tests showed that the waterlogging treatment induced significant increases in GUS and ADH enzyme activities, while the control and clinostat treatments showed no response. This work demonstrates: (1) the inhibition of gravity-driven convective transport can reduce the O 2 bioavailability to the root tip, and (2) the perturbation of gravisensing by clinostat rotation does not induce a non-specific stress response involving ADH. Together these experiments support the microgravity convection inhibition model for explaining changes in root metabolism during spaceflight.

Induction of hypoxic root metabolism results from physical limitations in O2 bio-availability in microgravity

NASA Astrophysics Data System (ADS)

Liao, J.; Monje, O.; Porterfield, D.

Numerous spaceflight experiments have noted changes in the roots that are consistent with hypoxia in the rootzone. These observations range from general ultrastructure analysis and biochemical measurements to direct measurements of stress specific enzymes. In experiments that have monitored alcohol dehydrogenase (ADH) the data shows this hypoxically responsive gene is induced and ADH activity is elevated in microgravity. These changes in ADH could be induced either by spaceflight hypoxia resulting from inhibition of gravity mediated O 2 transport, or by a non-specific stress response due to inhibition of gravisensing. We tested these hypotheses in two series of experiments. The objective of the first experiment was to determine if physical changes in gravity mediated O 2 transport can be directly measured, while the second series of experiments tested whether disruption of gravisensing can induce a non-specific ADH response. To directly measure O 2 bioavailability as a function of gravity we designed a sensor that mimics metabolic O 2 consumption from the rhizosphere. Because of these design criteria the sensor is sensitive to any changes in root O 2 bioavailability that may occur in microgravity. In a KC-135 experiment the sensor was implanted in a moist granular clay media and exposed to microgravity during parabolic flight. The resulting data indicated that root O 2 bioavailability decreased in phase with gravity. In experiments that tested for non-specific induction of ADH we compared the response of transgenic Arabidopsis plants (ADH promoted GUS marker gene) exposed to clinostat, control, and waterlogged conditions. The plants were grown on agar slats in a growth chamber before being exposed to the experimental treatments. The plants were stained for GUS activity localization, and subjected to biochemical tests for ADH, and GUS enzyme activity. These tests showed that the waterlogging treatment induced significant increases in GUS and ADH enzyme activities, while the control and clinostat treatments showed no response. This work demonstrates : 1) the inhibition of gravity driven convective transport can reduce the O2 bioavailability to the root tip, and 2) the perturbation of gravisensing by clinostat rotation does not induce a non-specific stress response involving ADH. Together these experiments support the microgravity convection inhibition model for explaining changes in root metabolism during spaceflight. Supported by funding from the Missouri Research Board, and the USDA/NRICGP (2001-35100-10751) to DMP.

Apical control, gravitropic signaling, and the growth of lateral roots in Arabidopsis

NASA Astrophysics Data System (ADS)

Mullen, Jack L.; Wolverton, Chris; Hangarter, Roger P.

Most research on gravity responses in plants has focused on primary roots and shoots, which typically grow in a vertical orientation. However, the patterns of lateral organ growth, which generally have large effects on overall plant architecture, are such that the organs are typically not vertical. In lateral roots of Arabidopsis, growth is initially in a nearly horizontal orientation but changes to a near-vertical orientation as the lateral root develops. Although the non-vertical lateral roots are gravitropically competent, following gravitropic reorientation of seedlings, the lateral roots on the upper flank of the primary root have different growth patterns from those on the lower side of the primary root. The differences are in part dependent on reorientation of the primary root, suggesting that gravitropic signaling from the primary root also contributes to the control of lateral root growth. The hormone auxin appears to play a role in this signaling between the primary and lateral roots, as auxin transport inhibitors applied to the primary root affect lateral root growth. Also, lateral roots of pin3 mutants, which are impaired in polar auxin transport, have altered lateral root orientations. However, other signals from the primary root tip also play an important role in regulating lateral root growth.

Thermotropism by primary roots of maize

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

Fortin, M.-C.; Poff, K.L.

1990-05-01

Sensing in the roots of higher plants has long been recognized to be restricted mainly to gravitropism and thigmotropism. However, root responses to temperature gradients have not been extensively studied. We have designed experiments under controlled conditions to test if and how root direction of maize can be altered by thermal gradients perpendicular to the gravity vector. Primary roots of maize grown on agar plates exhibit positive thermotropism (curvature toward the warmer temperature) when exposed to gradients of 0.5 to 4.2{degree}C cm{sup {minus}1}. The extent of thermotropism depends on the temperature gradient and the temperature at which the root ismore » placed within the gradient. The curvature cannot be accounted for by differential growth as a direct effect of temperature on each side of the root.« less

Red light-induced suppression of gravitropism in moss protonemata

NASA Astrophysics Data System (ADS)

Kern, V. D.; Sack, F. D.

1999-01-01

Moss protonemata are among the few cell types known that both sense and respond to gravity and light. Apical cells of Ceratodon protonemata grow by oriented tip growth which is negatively gravitropic in the dark or positively phototropic in unilateral red light. Phototropism is phytochrome-mediated. To determine whether any gravitropism persists during irradiation, cultures were turned at various angles with respect to gravity and illuminated so that the light and gravity vectors acted either in the same or in different directions. Red light for 24h (≥140nmol m-2s-1) caused the protonemata to be oriented directly towards the light. Similarly, protonemata grew directly towards the light regardless of light position with respect to gravity indicating that all growth is oriented strictly by phototropism, not gravitropism. At light intensities ≤100nmol m-2s-1, no phototropism occurs and the mean protonemal tip angle remains above the horizontal, which is the criterion for negative gravitropism. But those protonemata are not as uniformly upright as they would be in the dark indicating that low intensity red light permits gravitropism but also modulates the response. Protonemata of the aphototropic mutant ptr1 that lacks a functional Pfr chromophore, exhibit gravitropism regardless of red light intensity. This indicates that red light acts via Pfr to modulate gravitropism at low intensities and to suppress gravitropism at intensities ≥140nmol m-2s-1.

Effects of cloning and root-tip size on observations of fungal ITS sequences from Picea glauca roots

Treesearch

Daniel L. Lindner; Mark T. Banik

2009-01-01

To better understand the effects of cloning on observations of fungal ITS sequences from Picea glauca (white spruce) roots two techniques were compared: (i) direct sequencing of fungal ITS regions from individual root tips without cloning and (ii) cloning and sequencing of fungal ITS regions from individual root tips. Effect of root tip size was...

Novel, Moon and Mars, partial gravity simulation paradigms and their effects on the balance between cell growth and cell proliferation during early plant development.

PubMed

Manzano, Aránzazu; Herranz, Raúl; den Toom, Leonardus A; Te Slaa, Sjoerd; Borst, Guus; Visser, Martijn; Medina, F Javier; van Loon, Jack J W A

2018-01-01

Clinostats and Random Positioning Machine (RPM) are used to simulate microgravity, but, for space exploration, we need to know the response of living systems to fractional levels of gravity (partial gravity) as they exist on Moon and Mars. We have developed and compared two different paradigms to simulate partial gravity using the RPM, one by implementing a centrifuge on the RPM (RPM HW ), the other by applying specific software protocols to driving the RPM motors (RPM SW ). The effects of the simulated partial gravity were tested in plant root meristematic cells, a system with known response to real and simulated microgravity. Seeds of Arabidopsis thaliana were germinated under simulated Moon (0.17  g ) and Mars (0.38  g ) gravity. In parallel, seeds germinated under simulated microgravity (RPM), or at 1  g control conditions. Fixed root meristematic cells from 4-day grown seedlings were analyzed for cell proliferation rate and rate of ribosome biogenesis using morphometrical methods and molecular markers of the regulation of cell cycle and nucleolar activity. Cell proliferation appeared increased and cell growth was depleted under Moon gravity, compared with the 1  g control. The effects were even higher at the Moon level than at simulated microgravity, indicating that meristematic competence (balance between cell growth and proliferation) is also affected at this gravity level. However, the results at the simulated Mars level were close to the 1  g static control. This suggests that the threshold for sensing and responding to gravity alteration in the root would be at a level intermediate between Moon and Mars gravity. Both partial g simulation strategies seem valid and show similar results at Moon g -levels, but further research is needed, in spaceflight and simulation facilities, especially around and beyond Mars g levels to better understand more precisely the differences and constrains in the use of these facilities for the space biology community.

Abscisic acid accumulation modulates auxin transport in the root tip to enhance proton secretion for maintaining root growth under moderate water stress.

PubMed

Xu, Weifeng; Jia, Liguo; Shi, Weiming; Liang, Jiansheng; Zhou, Feng; Li, Qianfeng; Zhang, Jianhua

2013-01-01

Maintenance of root growth is essential for plant adaptation to soil drying. Here, we tested the hypothesis that auxin transport is involved in mediating ABA's modulation by activating proton secretion in the root tip to maintain root growth under moderate water stress. Rice and Arabidopsis plants were raised under a hydroponic system and subjected to moderate water stress (-0.47 MPa) with polyethylene glycol (PEG). ABA accumulation, auxin transport and plasma membrane H(+)-ATPase activity at the root tip were monitored in addition to the primary root elongation and root hair density. We found that moderate water stress increases ABA accumulation and auxin transport in the root apex. Additionally, ABA modulation is involved in the regulation of auxin transport in the root tip. The transported auxin activates the plasma membrane H(+)-ATPase to release more protons along the root tip in its adaption to moderate water stress. The proton secretion in the root tip is essential in maintaining or promoting primary root elongation and root hair development under moderate water stress. These results suggest that ABA accumulation modulates auxin transport in the root tip, which enhances proton secretion for maintaining root growth under moderate water stress. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.

Root Tip Shape Governs Root Elongation Rate under Increased Soil Strength1[OPEN

PubMed Central

Kirchgessner, Norbert; Walter, Achim

2017-01-01

Increased soil strength due to soil compaction or soil drying is a major limitation to root growth and crop productivity. Roots need to exert higher penetration force, resulting in increased penetration stress when elongating in soils of greater strength. This study aimed to quantify how the genotypic diversity of root tip geometry and root diameter influences root elongation under different levels of soil strength and to determine the extent to which roots adjust to increased soil strength. Fourteen wheat (Triticum aestivum) varieties were grown in soil columns packed to three bulk densities representing low, moderate, and high soil strength. Under moderate and high soil strength, smaller root tip radius-to-length ratio was correlated with higher genotypic root elongation rate, whereas root diameter was not related to genotypic root elongation. Based on cavity expansion theory, it was found that smaller root tip radius-to-length ratio reduced penetration stress, thus enabling higher root elongation rates in soils with greater strength. Furthermore, it was observed that roots could only partially adjust to increased soil strength. Root thickening was bounded by a maximum diameter, and root tips did not become more acute in response to increased soil strength. The obtained results demonstrated that root tip geometry is a pivotal trait governing root penetration stress and root elongation rate in soils of greater strength. Hence, root tip shape needs to be taken into account when selecting for crop varieties that may tolerate high soil strength. PMID:28600344

Getting to the root of plant biology: impact of the Arabidopsis genome sequence on root research

PubMed Central

Benfey, Philip N.; Bennett, Malcolm; Schiefelbein, John

2010-01-01

Summary Prior to the availability of the genome sequence, the root of Arabidopsis had attracted a small but ardent group of researchers drawn to its accessibility and developmental simplicity. Roots are easily observed when grown on the surface of nutrient agar media, facilitating analysis of responses to stimuli such as gravity and touch. Developmental biologists were attracted to the simple radial organization of primary root tissues, which form a series of concentric cylinders around the central vascular tissue. Equally attractive was the mode of propagation, with stem cells at the tip giving rise to progeny that were confined to cell files. These properties of root development reduced the normal four-dimensional problem of development (three spatial dimensions and time) to a two-dimensional problem, with cell type on the radial axis and developmental time along the longitudinal axis. The availability of the complete Arabidopsis genome sequence has dramatically accelerated traditional genetic research on root biology, and has also enabled entirely new experimental strategies to be applied. Here we review examples of the ways in which availability of the Arabidopsis genome sequence has enhanced progress in understanding root biology. PMID:20409273

Magnetophoretic induction of curvature in coleoptiles and hypocotyls

NASA Technical Reports Server (NTRS)

Kuznetsov, O. A.; Hasenstein, K. H.

1997-01-01

Coleoptiles of barley (Hordeum vulgare) were positioned in a high gradient magnetic field (HGMF, dynamic factor gradient of H(2)/2 of 10(9)-10(10) Oe2 cm-1), generated by a ferromagnetic wedge in a uniform magnetic field and rotated on a 1 rpm clinostat. After 4 h 90% of coleoptiles had curved toward the HGMF. The cells affected by HGMF showed clear intracellular displacement of amyloplasts. Coleoptiles in a magnetic field next to a non-ferromagnetic wedge showed no preferential curvature. The small size of the area of nonuniformity of the HGMF allowed mapping of the sensitivity of the coleoptiles by varying the initial position of the wedge relative to the coleoptile apex. When the ferromagnetic wedge was placed 1 mm below the coleoptile tip only 58% of the coleoptiles curved toward the wedge indicating that the cells most sensitive to intracellular displacement of amyloplasts and thus gravity sensing are confined to the top 1 mm portion of barley coleoptiles. Similar experiments with tomato hypocotyls (Lycopersicum esculentum) also resulted in curvature toward the HGMF. The data strongly support the amyloplast-based gravity-sensing system in higher plants and the usefulness of HGMF to substitute gravity in shoots.

Ammonium-induced loss of root gravitropism is related to auxin distribution and TRH1 function, and is uncoupled from the inhibition of root elongation in Arabidopsis.

PubMed

Zou, Na; Li, Baohai; Dong, Gangqiang; Kronzucker, Herbert J; Shi, Weiming

2012-06-01

Root gravitropism is affected by many environmental stresses, including salinity, drought, and nutrient deficiency. One significant environmental stress, excess ammonium (NH(4)(+)), is well documented to inhibit root elongation and lateral root formation, yet little is known about its effects on the direction of root growth. We show here that inhibition of root elongation upon elevation of external NH(4)(+) is accompanied by a loss in root gravitropism (agravitropism) in Arabidopsis. Addition of potassium (K(+)) to the treatment medium partially rescued the inhibition of root elongation by high NH(4)(+) but did not improve gravitropic root curvature. Expression analysis of the auxin-responsive reporter gene DR5::GUS revealed that NH(4)(+) treatment delayed the development of gravity-induced auxin gradients across the root cap but extended their duration once initiated. Moreover, the β-glucuronidase (GUS) signal intensity in root tip cells was significantly reduced under high NH(4)(+) treatment over time. The potassium carrier mutant trh1 displayed different patterns of root gravitropism and DR5::GUS signal intensity in root apex cells compared with the wild type in response to NH(4)(+). Together, the results demonstrate that the effects of NH(4)(+) on root gravitropism are related to delayed lateral auxin redistribution and the TRH1 pathway, and are largely independent of inhibitory effects on root elongation.

Polar transport of 45Ca2+ across the elongation zone of gravistimulated roots

NASA Technical Reports Server (NTRS)

Lee, J. S.; Evans, M. L.

1985-01-01

The movement of calcium across the elongation zone of gravistimulated primary roots of maize (Zea mays L.) was measured using 45Ca2+. Radioactive calcium was applied to one side of the elongation zone about 4 mm back from the root tip and the distribution of radioactivity across the root in the region of application was determined using scintillation spectrometry. The movement of 45Ca2+ across the elongation zone was non-polar in vertically oriented roots. In gravistimulated roots the movement of label was polarized with about twice as much label moving from top to bottom as from bottom to top. A variety of treatments which interfere with gravitropism was found to eliminate the polar movement of 45Ca2+ across the elongation zone. In maize cultivars which require light for gravitropic competency, dark grown roots exhibited neither gravitropism nor polar movement of 45Ca2+ across the elongation zone. Upon illumination the roots developed but gravitropic competency and gravity-induced polar movement of 45Ca2+ across the elongation zone. Similarly, roots of light-grown seedlings lost both gravitropic competency and 45Ca2+ transport polarity upon transfer to the dark. The results indicate a close correlation between calcium movement and gravitropism in primary roots in maize.

Arabidopsis pdr2 reveals a phosphate-sensitive checkpoint in root development.

PubMed

Ticconi, Carla A; Delatorre, Carla A; Lahner, Brett; Salt, David E; Abel, Steffen

2004-03-01

Plants have evolved complex strategies to maintain phosphate (Pi) homeostasis and to maximize Pi acquisition when the macronutrient is limiting. Adjustment of root system architecture via changes in meristem initiation and activity is integral to the acclimation process. However, the mechanisms that monitor external Pi status and interpret the nutritional signal remain to be elucidated. Here, we present evidence that the Pi deficiency response, pdr2, mutation disrupts local Pi sensing. The sensitivity and amplitude of metabolic Pi-starvation responses, such as Pi-responsive gene expression or accumulation of anthocyanins and starch, are enhanced in pdr2 seedlings. However, the most conspicuous alteration of pdr2 is a conditional short-root phenotype that is specific for Pi deficiency and caused by selective inhibition of root cell division followed by cell death below a threshold concentration of about 0.1 mm external Pi. Measurements of general Pi uptake and of total phosphorus (P) in root tips exclude a defect in high-affinity Pi acquisition. Rescue of root meristem activity in Pi-starved pdr2 by phosphite (Phi), a non-metabolizable Pi analog, and divided-root experiments suggest that pdr2 disrupts sensing of low external Pi availability. Thus, PDR2 is proposed to function at a Pi-sensitive checkpoint in root development, which monitors environmental Pi status, maintains and fine-tunes meristematic activity, and finally adjusts root system architecture to maximize Pi acquisition.

Space Magnets Attracting Interest on Earth: Applications of Physical and Biological Techniques In the Study of Gravisensing and Response System of Plants

NASA Technical Reports Server (NTRS)

Hasenstein, Karl H.; Boody, April; Cox, David (Technical Monitor)

2002-01-01

The BioTube/Magnetic Field Apparatus (MFA) research is designed to provide insight into the organization and operation of the gravity sensing systems of plants and other small organisms. This experiment on STS-107 uses magnetic fields to manipulate sensory cells in plant roots, thus using magnetic fields as a tool to study gravity-related phenomena. The experiment will be located in the SPACEHAB module and is about the size of a household microwave oven. The goal of the experiment is to improve our understanding of the basic phenomenon of how plants respond to gravity. The BioTube/MFA experiment specifically examines how gravitational forces serve as a directional signal for growth in the low-gravity environment of space. As with all basic research, this study will contribute to an improved understanding of how plants grow and will have important implications for improving plant growth and productivity on Earth. In BioTube/MFA, magnetic fields will be used to determine whether the distribution of subcellular starch grains, called amyloplasts, within plant cells predicts the direction in which roots will grow and curve in microgravity.

Control of deep lithospheric roots on crustal scale GOCE gravity and gradient fields evident in Gondwana reconstructions

NASA Astrophysics Data System (ADS)

Braitenberg, Carla; Mariani, Patrizia

2015-04-01

The GOCE gravity field is globally homogeneous at the resolution of about 80km or better allowing for the first time to analyze tectonic structures at continental scale. Geologic correlation studies based on age determination and mineral composition of rock samples propose to continue the tectonic lineaments across continents to the pre-breakup position. Tectonic events which induce density changes, as metamorphic events and magmatic events, should then show up in the gravity field. Therefore gravity can be used as a globally available supportive tool for interpolation of isolated samples. Applying geodynamic plate reconstructions to the GOCE gravity field places today's observed field at the pre-breakup position. In order to test the possible deep control of the crustal features, the same reconstruction is applied to the seismic velocity models, and a joint gravity-velocity analysis is performed. The geophysical fields allow to control the likeliness of the hypothesized continuation of lineations based on sparse surface outcrops. Total absence of a signal, makes the cross-continental continuation of the lineament improbable, as continental-wide lineaments are controlled by rheologic and compositional differences of lithospheric mantle. It is found that the deep lithospheric roots as those found below cratons control the position of the positive gravity values. The explanation is that the deep lithospheric roots focus asthenospheric upwelling outboard of the root protecting the overlying craton from magmatic intrusions. The study is carried out over the African and South American continents. The background for the study can be found in the following publications where the techniques which have been used are described: Braitenberg, C., Mariani, P. and De Min, A. (2013). The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, 54(4), 321-334. doi:10.4430/bgta0105 Braitenberg, C. and Mariani, P. (2015). Geological implications from complete Gondwana GOCE-products reconstructions and link to lithospheric roots. Proceedings of 5th International GOCE User Workshop, 25 - 28 November 2014. Braitenberg, C. (2015). Exploration of tectonic structures with GOCE in Africa and across-continents. Int. J.Appl. Earth Observ. Geoinf. 35, 88-95. http://dx.doi.org/10.1016/j.jag.2014.01.013 Braitenberg, C. (2015). A grip on geological units with GOCE, IAG Symp. 141, in press.

Allelopathy of plants in space

NASA Astrophysics Data System (ADS)

Tomita-Yokotani, K.; Baba, K.; Fujii, Y.; Hashimoto, H.; Nakamura, T.; Yamashita, M.

Allelopathy is a chemical way of interaction among many organisms living together on the earth, and forming ecological systems as the member of the biosphere. Biosynthesis of allelochemicals, their release, transport and sensing mechanism at the recipient organisms, which is associated with allelopathy, are under the influence of gravity in many aspects. Such gravitational action on the allelopathy could be ranged from perturbation on biochemical networks in the cells to macroscopic transportation phenomena around the organisms. If gravity is an environmental factor that governs those processes, allelopathy at the absence of gravity on space craft, or under the different magnitude of gravity on the outer planets might differ from allelopathy on the ground. Another important factor in allelopathy in space application is physical closure of living environment, and lack of natural process to decompose allelopathic chemicals or the sink among material circulation in the biosphere. Many organisms and ecological system may behave differently in spacecrafts or on outer planets, based on the modified inter-organisms and -species interactions associated with alleopahty. In order to examine allelopathy under exotic gravity and closed environment, we imposed pseudo-microgravity and physical closure on a plant-plant allelopathy system. Two plant species were co-cultured in a closed vessel, and gravity vector was randomized by the 3D-clinorotation. Velvet bean (Mucuna pruriens L.) is known to induce strong allelopathic action on many plant species. Velvet bean and lettuce was chosen as the pair. Growth of lettuce seedlings, co-cultured with velvet bean, was analyzed under the 3D-clinorotation, and compared it with growth of the ground control group. The degree of allelopathic suppression on the lettuce root growth was less on the 3D-clinorotation. L-DOPA (L-3,4-dihydroxy-phennylalanine), released from root is the major substance responsible to the allelopathy of velvet bean. The number and growth of adventitious root in velvet bean differed between the clinostated and control group. The distribution of L-DOPA in the root was also different under the 3D-clinorotation. This method was verified to be useful for the screening pair plant species, of which allelopathic interaction could be gravity dependent.

Gravisensing in single-celled systems - update on characean rhizoids and protonemata

NASA Astrophysics Data System (ADS)

Braun, M.; Limbach, C.

Single-celled and tip-growing rhizoids and protonemata of the characean algae have been intensively studied and there is considerable progress in the understanding of the molecular and cellular mechanisms underlying gravisensing and gravity-dependent growth. In higher plant statocytes, the role of actin in both processes is still a matter of intense debate, but there is clear evidence that actin coordinates both processes in characean rhizoids and protonemata. The multiple functions and dynamic nature of the actin cytoskeleton in these cells are based on the concerted action of a variety of actin-binding proteins. Profilin, actin-depolymerizing factor, a spectrin-like protein, villin and fimbrin have been detected which control apical actin polymerization and regulate the dynamic remodeling of the actin arrangement. An actomyosin-based system was shown to (i) mediate the transport of secretory vesicles to the growing tip, (ii) establish the incorporation of cell wall material and (iii) coordinate the tip-focussed distribution of calcium channels which establish the tip-high calcium gradient for local exocytosis. Experiments performed in microgravity have shown that the actomyosin system precisely coordinates the position of statoliths in rhizoids and protonemata and, upon a change in orientation, directs sedimenting statoliths to specific areas at the plasma membrane where physical contact with gravisensor molecules initiates growth reorientation. The upward growth response of protonemata was shown to be preceded by a statolith-induced and actin-dependent relocalization of the Ca2+-gradient to the upper flank that does not occur in positively gravitropic rhizoids, in which sedimented statoliths cause differential growth of the opposite subapical cell flank. Thus, constant actin polymerization in the growing tip and the spatiotemporal control of actin remodeling by numerous actin-binding proteins are essential for gravity sensing and polarized growth of characean rhizoids and protonemata.

The tonoplast intrinsic aquaporin (TIP) subfamily of Eucalyptus grandis: Characterization of EgTIP2, a root-specific and osmotic stress-responsive gene.

PubMed

Rodrigues, Marcela I; Bravo, Juliana P; Sassaki, Flávio T; Severino, Fábio E; Maia, Ivan G

2013-12-01

Aquaporins have important roles in various physiological processes in plants, including growth, development and adaptation to stress. In this study, a gene encoding a root-specific tonoplast intrinsic aquaporin (TIP) from Eucalyptus grandis (named EgTIP2) was investigated. The root-specific expression of EgTIP2 was validated over a panel of five eucalyptus organ/tissues. In eucalyptus roots, EgTIP2 expression was significantly induced by osmotic stress imposed by PEG treatment. Histochemical analysis of transgenic tobacco lines (Nicotiana tabacum SR1) harboring an EgTIP2 promoter:GUS reporter cassette revealed major GUS staining in the vasculature and in root tips. Consistent with its osmotic-stress inducible expression in eucalyptus, EgTIP2 promoter activity was up-regulated by mannitol treatment, but was down-regulated by abscisic acid. Taken together, these results suggest that EgTIP2 might be involved in eucalyptus response to drought. Additional searches in the eucalyptus genome revealed the presence of four additional putative TIP coding genes, which could be individually assigned to the classical TIP1-5 groups. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Geoperception in primary and lateral roots of Phaseolus vulgaris (Fabaceae). III. A model to explain the differential georesponsiveness of primary and lateral roots

NASA Technical Reports Server (NTRS)

Ransom, J. S.; Moore, R.

1985-01-01

Half-tipped primary and lateral roots of Phaseolus vulgaris bend toward the side of the root on which the intact half tip remains. Therefore, tips of lateral and primary roots produce growth effectors capable of inducing gravicurvature. The asymmetrical placement of a tip of a lateral root onto a detipped primary root results in the root bending toward the side of the root onto which the tip was placed. That is, the lesser graviresponsiveness of lateral roots as compared with primary roots is not due to the inability of their caps to produce growth inhibitors. The more pronounced graviresponsiveness of primary roots is positively correlated with the presence of columella tissues that are 3.8 times longer, 1.7 times wider, and 10.5 times more voluminous than the columellas of lateral roots. We propose that the lack of graviresponsiveness exhibited by lateral roots is due to the fact that they (i) produce smaller amounts of the inhibitor than primary (i.e., strongly graviresponsive) roots and (ii) are unable to redistribute the inhibitor so as to be able to create a concentration gradient sufficient to induce a pronounced gravitropic response.

Striking the Right Chord: Signaling Enigma during Root Gravitropism

PubMed Central

Singh, Manjul; Gupta, Aditi; Laxmi, Ashverya

2017-01-01

Plants being sessile can often be judged as passive acceptors of their environment. However, plants are actually even more active in responding to the factors from their surroundings. Plants do not have eyes, ears or vestibular system like animals, still they “know” which way is up and which way is down? This is facilitated by receptor molecules within plant which perceive changes in internal and external conditions such as light, touch, obstacles; and initiate signaling pathways that enable the plant to react. Plant responses that involve a definite and specific movement are called “tropic” responses. Perhaps the best known and studied tropisms are phototropism, i.e., response to light, and geotropism, i.e., response to gravity. A robust root system is vital for plant growth as it can provide physical anchorage to soil as well as absorb water, nutrients and essential minerals from soil efficiently. Gravitropic responses of both primary as well as lateral root thus become critical for plant growth and development. The molecular mechanisms of root gravitropism has been delved intensively, however, the mechanism behind how the potential energy of gravity stimulus converts into a biochemical signal in vascular plants is still unknown, due to which gravity sensing in plants still remains one of the most fascinating questions in molecular biology. Communications within plants occur through phytohormones and other chemical substances produced in plants which have a developmental or physiological effect on growth. Here, we review current knowledge of various intrinsic signaling mechanisms that modulate root gravitropism in order to point out the questions and emerging developments in plant directional growth responses. We are also discussing the roles of sugar signals and their interaction with phytohormone machinery, specifically in context of root directional responses. PMID:28798760

Striking the Right Chord: Signaling Enigma during Root Gravitropism.

PubMed

Singh, Manjul; Gupta, Aditi; Laxmi, Ashverya

2017-01-01

Plants being sessile can often be judged as passive acceptors of their environment. However, plants are actually even more active in responding to the factors from their surroundings. Plants do not have eyes, ears or vestibular system like animals, still they "know" which way is up and which way is down? This is facilitated by receptor molecules within plant which perceive changes in internal and external conditions such as light, touch, obstacles; and initiate signaling pathways that enable the plant to react. Plant responses that involve a definite and specific movement are called "tropic" responses. Perhaps the best known and studied tropisms are phototropism, i.e., response to light, and geotropism, i.e., response to gravity. A robust root system is vital for plant growth as it can provide physical anchorage to soil as well as absorb water, nutrients and essential minerals from soil efficiently. Gravitropic responses of both primary as well as lateral root thus become critical for plant growth and development. The molecular mechanisms of root gravitropism has been delved intensively, however, the mechanism behind how the potential energy of gravity stimulus converts into a biochemical signal in vascular plants is still unknown, due to which gravity sensing in plants still remains one of the most fascinating questions in molecular biology. Communications within plants occur through phytohormones and other chemical substances produced in plants which have a developmental or physiological effect on growth. Here, we review current knowledge of various intrinsic signaling mechanisms that modulate root gravitropism in order to point out the questions and emerging developments in plant directional growth responses. We are also discussing the roles of sugar signals and their interaction with phytohormone machinery, specifically in context of root directional responses.

Molecular genetic analysis of plant gravitropism

NASA Technical Reports Server (NTRS)

Lomax, T. L.

1997-01-01

The analysis of mutants is a powerful approach for elucidating the components of complex biological processes. A growing number of mutants have been isolated which affect plant gravitropism and the classes of mutants found thus far provide important information about the gravity response mechanism. The wide variety of mutants isolated, especially in Arabidopsis, indicates that gravitropism is a complex, multi-step process. The existence of mutants altered in either root gravitropism alone, shoot gravitropism alone, or both indicates that the root and shoot gravitropic mechanisms have both separate and common steps. Reduced starch mutants have confirmed the role of amyloplasts in sensing the gravity signal. The hormone auxin is thought to act as the transducing signal between the sites of gravity perception (the starch parenchyma cells surrounding the vascular tissue in shoots and the columella cells of root caps) and asymmetric growth (the epidermal cells of the elongation zone(s) of each organ). To date, all mutants that are resistant to high concentrations of auxin have also been found to exhibit a reduced gravitropic response, thus supporting the role of auxin. Not all gravitropic mutants are auxin-resistant, however, indicating that there are additional steps which do not involve auxin. Studies with mutants of tomato which exhibit either reduced or reversed gravitropic responses further support the role of auxin redistribution in gravitropism and suggest that both red light and cytokinin interact with gravitropism through controlling lateral auxin transport. Plant responses to gravity thus likely involve changes in both auxin transport and sensitivity.

Root gravitropism and root hair development constitute coupled developmental responses regulated by auxin homeostasis in the Arabidopsis root apex.

PubMed

Rigas, Stamatis; Ditengou, Franck Anicet; Ljung, Karin; Daras, Gerasimos; Tietz, Olaf; Palme, Klaus; Hatzopoulos, Polydefkis

2013-03-01

Active polar transport establishes directional auxin flow and the generation of local auxin gradients implicated in plant responses and development. Auxin modulates gravitropism at the root tip and root hair morphogenesis at the differentiation zone. Genetic and biochemical analyses provide evidence for defective basipetal auxin transport in trh1 roots. The trh1, pin2, axr2 and aux1 mutants, and transgenic plants overexpressing PIN1, all showing impaired gravity response and root hair development, revealed ectopic PIN1 localization. The auxin antagonist hypaphorine blocked root hair elongation and caused moderate agravitropic root growth, also leading to PIN1 mislocalization. These results suggest that auxin imbalance leads to proximal and distal developmental defects in Arabidopsis root apex, associated with agravitropic root growth and root hair phenotype, respectively, providing evidence that these two auxin-regulated processes are coupled. Cell-specific subcellular localization of TRH1-YFP in stele and epidermis supports TRH1 engagement in auxin transport, and hence impaired function in trh1 causes dual defects of auxin imbalance. The interplay between intrinsic cues determining root epidermal cell fate through the TTG/GL2 pathway and environmental cues including abiotic stresses modulates root hair morphogenesis. As a consequence of auxin imbalance in Arabidopsis root apex, ectopic PIN1 mislocalization could be a risk aversion mechanism to trigger root developmental responses ensuring root growth plasticity. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.

Root hydrotropism is controlled via a cortex-specific growth mechanism.

PubMed

Dietrich, Daniela; Pang, Lei; Kobayashi, Akie; Fozard, John A; Boudolf, Véronique; Bhosale, Rahul; Antoni, Regina; Nguyen, Tuan; Hiratsuka, Sotaro; Fujii, Nobuharu; Miyazawa, Yutaka; Bae, Tae-Woong; Wells, Darren M; Owen, Markus R; Band, Leah R; Dyson, Rosemary J; Jensen, Oliver E; King, John R; Tracy, Saoirse R; Sturrock, Craig J; Mooney, Sacha J; Roberts, Jeremy A; Bhalerao, Rishikesh P; Dinneny, José R; Rodriguez, Pedro L; Nagatani, Akira; Hosokawa, Yoichiroh; Baskin, Tobias I; Pridmore, Tony P; De Veylder, Lieven; Takahashi, Hideyuki; Bennett, Malcolm J

2017-05-08

Plants can acclimate by using tropisms to link the direction of growth to environmental conditions. Hydrotropism allows roots to forage for water, a process known to depend on abscisic acid (ABA) but whose molecular and cellular basis remains unclear. Here we show that hydrotropism still occurs in roots after laser ablation removed the meristem and root cap. Additionally, targeted expression studies reveal that hydrotropism depends on the ABA signalling kinase SnRK2.2 and the hydrotropism-specific MIZ1, both acting specifically in elongation zone cortical cells. Conversely, hydrotropism, but not gravitropism, is inhibited by preventing differential cell-length increases in the cortex, but not in other cell types. We conclude that root tropic responses to gravity and water are driven by distinct tissue-based mechanisms. In addition, unlike its role in root gravitropism, the elongation zone performs a dual function during a hydrotropic response, both sensing a water potential gradient and subsequently undergoing differential growth.

From ROOTS to GRAVI-1: Twenty Five Years for Understanding How Plants Sense Gravity

NASA Astrophysics Data System (ADS)

Perbal, Gerald

2009-01-01

In the 1970s, when I started to work on gravitropism at the University Pierre and Marie Curie, Paris), it was well known that statocytes contain voluminous amyloplasts (statoliths) that sediment under the influence of gravity. The role of these organelles in gravisensing was strongly disputed. In 1974, I attended a session of a meeting on gravitropism in Würzburg, where I presented results that supported the involvement of statoliths in the perception of gravity. This meeting had a strong impact on my research, since at that time the Council of Europe was looking for people interested in performing experiments in Space. Our first experiment (ROOTS) was carried out in the Biorack Facility (ESA) in the frame of the Spacelab D1 mission (1985). We had a very efficient help from CNES which developed a very fine hardware to grow lentil seedlings and to chemically fix them at the end of the experiment. The results obtained were surprising since we observed that in microgravity the statoliths were located at one pole of the statocyte and not distributed at random as it was expected. The goal of the following experiment (Spacelab IML-1 mission, 1992) was to determine the threshold stimulation time at 1 × g (created by centrifugation). It was estimated at 25 s. In the frame of the SMM/03 and SMM/06 missions (1996, 1997), we proved that the statoliths are attached to actin filaments by motor proteins (myosin) that make these organelles move in one preferential direction in microgravity. The analysis of gravisensitivity with clinostats incited us to compare gravisensitivity of lentil roots grown in microgravity or on a 1 × g centrifuge (SMM05 mission, 1997). It was found that the latter were less sensitive than the former. We showed that this was due to the fact that the statoliths are not distributed in the same way in both cases (microgravity or 1 × g centrifuge). All these studies led us to propose a mode of gravity sensing by plants in which elements of the cytoskeleton and stretch activated ion channels are involved. The last experiment (GRAVI-1) which has been carried out (in ISS with the EMCS facility, 2007) dealt with the threshold acceleration that is perceived by roots.

Direct amplification of DNA from fresh and preserved ectomycorrhizal root tips

Treesearch

Elizabeth Bent; D. Lee Taylor

2009-01-01

Methods are described by which DNA can be amplified directly from ectomycorrhizal root tip homogenates of a variety of plant species (Picea mariana (black spruce), Betula papyrifera (paper birch), Populus tremuloides (trembling aspen) and Alnus sp.(alder)), including root tips that have...

Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots.

PubMed

Wang, Shengyin; Ren, Xiaoyan; Huang, Bingru; Wang, Ge; Zhou, Peng; An, Yuan

2016-07-20

The objective of this study was to investigate Al(3+)-induced IAA transport, distribution, and the relation of these two processes to Al(3+)-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L(-1) IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress significantly decreased the IAA concentration in apical buds and root tips. The distribution of IAA fluorescence signals in root tips was disturbed, and the IAA transportation from shoot base to root tip was inhibited. The highest intensity of fluorescence signals was detected in the apical meristematic zone. Exogenous application of IAA markedly alleviated the Al(3+)-induced inhibition of root growth by increasing IAA accumulation and recovering the damaged cell structure in root tips. In addition, Al(3+) stress up-regulated expression of AUX1 and PIN2 genes. These results indicate that Al(3+)-induced reduction of root growth could be associated with the inhibitions of IAA synthesis in apical buds and IAA transportation in roots, as well as the imbalance of IAA distribution in root tips.

Aluminium-induced reduction of plant growth in alfalfa (Medicago sativa) is mediated by interrupting auxin transport and accumulation in roots

PubMed Central

Wang, Shengyin; Ren, Xiaoyan; Huang, Bingru; Wang, Ge; Zhou, Peng; An, Yuan

2016-01-01

The objective of this study was to investigate Al3+-induced IAA transport, distribution, and the relation of these two processes to Al3+-inhibition of root growth in alfalfa. Alfalfa seedlings with or without apical buds were exposed to 0 or 100 μM AlCl3 and were foliar sprayed with water or 6 mg L−1 IAA. Aluminium stress resulted in disordered arrangement of cells, deformed cell shapes, altered cell structure, and a shorter length of the meristematic zone in root tips. Aluminium stress significantly decreased the IAA concentration in apical buds and root tips. The distribution of IAA fluorescence signals in root tips was disturbed, and the IAA transportation from shoot base to root tip was inhibited. The highest intensity of fluorescence signals was detected in the apical meristematic zone. Exogenous application of IAA markedly alleviated the Al3+-induced inhibition of root growth by increasing IAA accumulation and recovering the damaged cell structure in root tips. In addition, Al3+ stress up-regulated expression of AUX1 and PIN2 genes. These results indicate that Al3+-induced reduction of root growth could be associated with the inhibitions of IAA synthesis in apical buds and IAA transportation in roots, as well as the imbalance of IAA distribution in root tips. PMID:27435109

Gel-free/label-free proteomic analysis of root tip of soybean over time under flooding and drought stresses.

PubMed

Wang, Xin; Oh, MyeongWon; Sakata, Katsumi; Komatsu, Setsuko

2016-01-01

Growth in the early stage of soybean is markedly inhibited under flooding and drought stresses. To explore the responsive mechanisms of soybean, temporal protein profiles of root tip under flooding and drought stresses were analyzed using gel-free/label-free proteomic technique. Root tip was analyzed because it was the most sensitive organ against flooding, and it was beneficial to root penetration under drought. UDP glucose: glycoprotein glucosyltransferase was decreased and increased in soybean root under flooding and drought, respectively. Temporal protein profiles indicated that fermentation and protein synthesis/degradation were essential in root tip under flooding and drought, respectively. In silico protein-protein interaction analysis revealed that the inductive and suppressive interactions between S-adenosylmethionine synthetase family protein and B-S glucosidase 44 under flooding and drought, respectively, which are related to carbohydrate metabolism. Furthermore, biotin/lipoyl attachment domain containing protein and Class II aminoacyl tRNA/biotin synthetases superfamily protein were repressed in the root tip during time-course stresses. These results suggest that biotin and biotinylation might be involved in energy management to cope with flooding and drought in early stage of soybean-root tip. Copyright © 2015 Elsevier B.V. All rights reserved.

Dispersion of near-infrared laser energy through radicular dentine when using plain or conical tips.

PubMed

Teo, Christine Yi Jia; George, Roy; Walsh, Laurence J

2018-02-01

The aim of this study was to investigate the influence of tip design on patterns of laser energy dispersion through the dentine of tooth roots when using near-infrared diode lasers. Diode laser emissions of 810 or 940 nm were used in combination with optical fiber tips with either conventional plain ends or conical ends, to irradiate tooth roots of oval or round cross-sectional shapes. The lasers were operated in continuous wave mode at 0.5 W for 5 s with the distal end of the fiber tip placed in the apical or coronal third of the root canal at preset positions. Laser light exiting through the roots and apical foramen was imaged, and the extent of lateral spread calculated. There was a significant difference in infrared light exiting the root canal apex between plain and conical fiber tips for both laser wavelengths, with more forward transmission of laser energy through the apex for plain tips. For both laser wavelengths, there were no significant differences in emission patterns when the variable of canal shape was used and all other variables were kept the same (plain vs conical tip, tip position). To ensure optimal treatment effect and to prevent the risks of inadvertent laser effects on the adjacent periapical tissues, it is important to have a good understanding of laser transmission characteristics of the root canal and root dentine. Importantly, it is also essential to understand transmission characteristics of plain and conical fibers tips.

Automorphosis of higher plants on a 3-D clinostat

NASA Astrophysics Data System (ADS)

Hoson, T.; Kamisaka, S.; Yamashita, M.; Masuda, Y.

On a three-dimensional (3-D) clinostat, various plant organs developed statocytes capable of responding to the gravity vector. The graviresponse of primary roots of garden cress and maize grown on the clinostat was the same as the control roots, whereas that of maize coleoptiles was reduced. When maize seedlings were grown in the presence of 10^-4 M gibberellic acid and kinetin, the graviresponse of both roots and shoots was suppressed. The corresponding suppression of amyloplast development was observed in the clinostatted and the hormone-treated seedlings. Maize roots and shoots showed spontaneous curvatures in different portions on the 3-D clinostat. The hormone treatment did not significantly influence such an automorphic curvature. When the root cap was removed, maize roots did not curve gravitropically. However, the removal suppressed the automorphic curvatures only slightly. On the other hand, the removal of coleoptile tip did not influence its graviresponse, whereas the spontaneous curvature of decapitated coleoptiles on the clinostat was strongly suppressed. Also, cytochalasin B differently affected the gravitropic and the automorphic curvatures of maize roots and shoots. From these results it is concluded that the graviperception and the early processes of signal transmission are unnecessary for automorphoses under simulated microgravity conditions. Moreover, the results support the view that the amyloplasts act as statoliths probably via an interaction with microfilaments.

Root tips moving through soil

PubMed Central

Curlango-Rivera, Gilberto

2011-01-01

Root elongation occurs by the generation of new cells from meristematic tissue within the apical 1–2 mm region of root tips. Therefore penetration of the soil environment is carried out by newly synthesized plant tissue, whose cells are inherently vulnerable to invasion by pathogens. This conundrum, on its face, would seem to reflect an intolerable risk to the successful establishment of root systems needed for plant life. Yet root tip regions housing the meristematic tissues repeatedly have been found to be free of microbial infection and colonization. Even when spore germination, chemotaxis, and/or growth of pathogens are stimulated by signals from the root tip, the underlying root tissue can escape invasion. Recent insights into the functions of root border cells, and the regulation of their production by transient exposure to external signals, may shed light on long-standing observations. PMID:21455030

Fixation procedure for transmission electron microscopy of Chara rhizoids under microgravity in a Spacelab (IML-2).

PubMed

Braun, M; Buchen, B; Sievers, A

1996-06-27

A special fixation device and fixation procedure have been developed to investigate for the first time the ultrastructure of gravity-sensing, unicellular Chara rhizoids grown for 30 h under microgravity (MG) conditions during the IML-2 mission. The fixation unit allowed culture, fixation and storage of Chara rhizoids in the same chamber without transferring the samples. The procedure was easy and safe to perform and required a minimum of crew time. Rhizoids fixated with glutaraldehyde in space and further processed for electron microscopy on ground showed that the fixation was of high quality and corresponded to the fixation quality of rhizoids in the ground controls. Thus, the equipment accomplished the manifold problems related to the physical effects of MG. The polarity of the rhizoids was maintained in MG. Well-preserved organelles and microtubules showed no obvious difference in ultrastructure or distribution after 30-h growth in MG compared to ground controls. The statoliths were more randomly distributed, however, only up to 50 microns basal to the tip. Thus, changing the gravity conditions does to disturb the cellular organisation of the rhizoids enabling the tip-growing cells to follow their genetic program in development and growth also under MG.

Aluminum and calcium in fine root tips of red spruce collected from the forest floor

Treesearch

K.T. Smith; W.C. Shortle; W.D. Ostrofsky

1995-01-01

Root chemistry is being increasingly used as a marker of biologically relevant soil chemistry. To evaluate this marker, we determined the precision of measurement, the effect of organic soil horizon, and the effect of stand elevation on the chemistry of fine root tips of red spruce (Picea rubens Sarg.) Fine root tips were collected from the F and H...

Modeling the Kinetics of Root Gravireaction

NASA Astrophysics Data System (ADS)

Kondrachuk, Alexander V.; Starkov, Vyacheslav N.

2011-02-01

The known "sun-flower equation" (SFE), which was originally proposed to model root circumnutating, was used to describe the simplest tip root graviresponse. Two forms of the SFE (integro-differential and differential-delayed) were solved, analyzed and compared with each other. The numerical solutions of these equations were found to be matching with arbitrary accuracy. The analysis of the solutions focused on time-lag effects on the kinetics of tip root bending. The results of the modeling are in good correlation with an experiment at the initial stages of root tips graviresponse. Further development of the model calls for its systematic comparison with some specially designed experiments, which would include measuring the kinetics of root tip bending before gravistimulation over the period of time longer than the time lag.

Effect of ultrasonic tip and root-end filling material on bond strength.

PubMed

Vivan, Rodrigo Ricci; Guerreiro-Tanomaru, Juliane Maria; Bernardes, Ricardo Affonso; Reis, José Mauricio Santos Nunes; Hungaro Duarte, Marco Antonio; Tanomaru-Filho, Mário

2016-11-01

The objective of this study was to evaluate the bond strength of three root-end filling materials (MTAA-MTA Angelus, MTAS-experimental MTA Sealer, and ZOE- zinc oxide and eugenol cement) in retrograde preparations performed with different ultrasonic tips (CVD, Trinity, and Satelec). Ninety 2-mm root sections from single-rooted human teeth were used. The retrograde cavities were prepared by using the ultrasonic tips, coupled to a device for position standardization. The specimens were randomly divided into nine groups: CVD MTAA; CVD MTAS; CVD ZOE; Trinity MTAA; Trinity MTAS; Trinity ZOE; Satelec MTAA; Satelec MTAS; Satelec ZOE. Each resin disc/dentin/root-end filling material was placed in the machine to perform the push-out test. The specimens were examined in a stereomicroscope to evaluate the type of failure. Data were submitted to statistical analysis using ANOVA and Tukey tests (α = 0.05). The highest bond strength was observed for the CVD tip irrespective of the material used (P < 0.05). There was no significant difference for the Trinity TU-18 diamond and S12 Satelec tips (P > 0.05). MTAA and MTAS showed highest bond strength. The most common type of failure was adhesion between the filling material and dentin wall, except for ZOE, where mixed failure was predominant. The CVD tip favored higher bond strength of the root-end filling materials. MTA Angelus and experimental MTAS presented bond strength to dentin prepared with ultrasonic tips. Root-end preparation with the CVD tip positively influences the bond strength of root-end filling materials. MTA Angelus and experimental MTAS present bond strength to be used as root-end filling materials.

Root elongation against a constant force: experiment with a computerized feedback-controlled device

NASA Technical Reports Server (NTRS)

Kuzeja, P. S.; Lintilhac, P. M.; Wei, C.

2001-01-01

Axial force was applied to the root tip of corn (Zea mays L. cv. Merit) seedlings using a computerized, feedback-controlled mechanical device. The system's feedback capability allowed continuous control of a constant tip load, and the attached displacement transducer provided the time course of root elongation. Loads up to 7.5 g decreased the root elongation rate by 0.13 mm h-1 g-1, but loads 7.5 to 17.5 g decreased the growth rate by only 0.04 mm h-1 g-1. Loads higher than 18 g stopped root elongation completely. Measurement of the cross-sectional areas of the root tips indicated that the 18 g load had applied about 0.98 MPa of axial pressure to the root, thereby exceeding the root's ability to respond with increased turgor pressure. Recorded time-lapse images of loaded roots showed that radial thickening (swelling) occurred behind the root cap, whose cross-sectional area increased with tip load.

Observations on the Feeding and Symptomatology of Xiphinema and Longidorus on Selected Host Roots

PubMed Central

Cohn, E.

1970-01-01

In vitro feeding of Xiphinema brevicolle, X. index and Longidorus africanus on roots of host seedlings is described. Both Xiphinema spp. fed mainly along roots rather than at tips and up to several days at a single site. Feeding of L. africanus was confined to root tips and lasted up to 15 min. No visible short term reaction of roots parasitized by the Xiphinema spp. could be discerned, but both swelling and cessation of growth of root tips were observed within 20 hr after feeding by L. africanus. Long-term (12-month) symptoms on roots of several host plants caused by cultured populations of X. brevicolle, X. index, X. italiae, L. africanus and L. brevicaudatus are described. All the Xiphinema spp. caused a thinning and distinct darkening of root systems and, at some sites, a breakdown of the cortex. Both species of Longidorus caused stubby and swollen root tips. Root symptom severity was in proportion to nematode population levels. PMID:19322291

Intensity of hydrostimulation for the induction of root hydrotropism and its sensing by the root cap

NASA Technical Reports Server (NTRS)

Takahashi, H.; Scott, T. K.

1993-01-01

Roots of Pisum sativum L. and Zea mays L. were exposed to different moisture gradients established by placing both wet cheesecloth (hydrostimulant) and saturated aqueous solutions of various salts in a closed chamber. Atmospheric conditions with different relative humidity (RH) in a range between 98 and 86% RH were obtained at root level, 2 to 3mm from the water-saturated hydrostimulant. Roots of Silver Queen corn placed vertically with the tips down curved sideways toward the hydrostimulant in response to approximately 94% RH but did not respond positively to RH higher than approximately 95%. The positive hydrotropic response increased linearly as RH was lowered from 95 to 90%. A maximum response was observed at RH between 90 and 86%. However, RH required for the induction of hydrotropism as well as the responsiveness differed among plant species used; gravitropically sensitive roots appeared to require a somewhat greater moisture gradient for the induction of hydrotropism. Decapped roots of corn failed to curve hydrotropically, suggesting the root cap as a major site of hydrosensing.

A novel tracking tool for the analysis of plant-root tip movements.

PubMed

Russino, A; Ascrizzi, A; Popova, L; Tonazzini, A; Mancuso, S; Mazzolai, B

2013-06-01

The growth process of roots consists of many activities, such as exploring the soil volume, mining minerals, avoiding obstacles and taking up water to fulfil the plant's primary functions, that are performed differently, depending on environmental conditions. Root movements are strictly related to a root decision strategy, which helps plants to survive under stressful conditions by optimizing energy consumption. In this work, we present a novel image-analysis tool to study the kinematics of the root tip (apex), named analyser for root tip tracks (ARTT). The software implementation combines a segmentation algorithm with additional software imaging filters in order to realize a 2D tip detection. The resulting paths, or tracks, arise from the sampled tip positions through the acquired images during the growth. ARTT allows work with no markers and deals autonomously with new emerging root tips, as well as handling a massive number of data relying on minimum user interaction. Consequently, ARTT can be used for a wide range of applications and for the study of kinematics in different plant species. In particular, the study of the root growth and behaviour could lead to the definition of novel principles for the penetration and/or control paradigms for soil exploration and monitoring tasks. The software capabilities were demonstrated by experimental trials performed with Zea mays and Oryza sativa.

Proteomic and metabolomic analyses of soybean root tips under flooding stress.

PubMed

Komatsu, Setsuko; Nakamura, Takuji; Sugimoto, Yurie; Sakamoto, Kazunori

2014-01-01

Flooding is one of the serious problems for soybean plants because it inhibits growth. Proteomic and metabolomic techniques were used to determine whether proteins and metabolites are altered in the root tips of soybeans under flooding stress. Two-day-old soybean plants were flooded for 2 days, and proteins and metabolites were extracted from root tips. Flooding-responsive proteins were identified using two-dimensional- or SDS-polyacrylamide gel electrophoresis- based proteomics techniques. Using both techniques, 172 proteins increased and 105 proteins decreased in abundance in the root tips of flood-stressed soybean. The abundance of methionine synthase, heat shock cognate protein, urease, and phosphoenol pyruvate carboxylase was significantly increased by flooding stress. Furthermore, 73 flooding-responsive metabolites were identified using capillary electrophoresis-mass spectrometry. The levels of gamma-aminobutyric acid, glycine, NADH2, and phosphoenol pyruvate were increased by flooding stress. Taken together, these results suggest that synthesis of phosphoenol pyruvate by way of oxaloacetate produced in the tricarboxylic acid cycle is activated in soybean root tips in response to flooding stress, and that flooding stress also leads to modulation of the urea cycle in the root tips.

Aluminium localization in root tips of the aluminium-accumulating plant species buckwheat (Fagopyrum esculentum Moench)

PubMed Central

Klug, Benjamin; Specht, André; Horst, Walter J.

2011-01-01

Aluminium (Al) uptake and transport in the root tip of buckwheat is not yet completely understood. For localization of Al in root tips, fluorescent dyes and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were compared. The staining of Al with morin is an appropriate means to study qualitatively the radial distribution along the root tip axis of Al which is complexed by oxalate and citrate in buckwheat roots. The results compare well with the distribution of total Al determined by LA-ICP-MS which could be reliably calibrated to compare with Al contents by conventional total Al determination using graphite furnace atomic absorption spectrometry. The Al localization in root cross-sections along the root tip showed that in buckwheat Al is highly mobile in the radial direction. The root apex predominantly accumulated Al in the cortex. The subapical root section showed a homogenous Al distribution across the whole section. In the following root section Al was located particularly in the pericycle and the xylem parenchyma cells. With further increasing distance from the root apex Al could be detected only in individual xylem vessels. The results support the view that the 10 mm apical root tip is the main site of Al uptake into the symplast of the cortex, while the subapical 10–20 mm zone is the main site of xylem loading through the pericycle and xylem parenchyma cells. Progress in the better molecular understanding of Al transport in buckwheat will depend on the consideration of the tissue specificity of Al transport and complexation. PMID:21831842

Defective secretion of mucilage is the cellular basis for agravitropism in primary roots of Zea mays cv. Ageotropic

NASA Technical Reports Server (NTRS)

Miller, I.; Moore, R.

1990-01-01

Root caps of primary, secondary, and seminal roots of Z. mays cv. Kys secrete large amounts of mucilage and are in close contact with the root all along the root apex. These roots are strongly graviresponsive. Secondary and seminal roots of Z. mays cv. Ageotropic are also strongly graviresponsive. Similarly, their caps secrete mucilage and closely appress the root all along the root apex. However, primary roots of Z. mays cv. Ageotropic are non-responsive to gravity. Their caps secrete negligible amounts of mucilage and contact the root only at the extreme apex of the root along the calyptrogen. These roots become graviresponsive when their tips are coated with mucilage or mucilage-like materials. Peripheral cells of root caps of roots of Z. mays cv. Kys contain many dictyosomes associated with vesicles that migrate to and fuse with the plasmalemma. Root-cap cells of secondary and seminal (i.e. graviresponsive) roots of Z. mays cv. Ageotropic are similar to those of primary roots of Z. mays cv. Kys. However, root-cap cells of primary (i.e. non-graviresponsive) roots of Z. mays cv. Ageotropic have distended dictyosomal cisternae filled with an electron-dense, granular material. Large vesicles full of this material populate the cells and apparently do not fuse with the plasmalemma. Taken together, these results suggest that non-graviresponsiveness of primary roots of Z. mays cv. Ageotropic results from the lack of apoplastic continuity between the root and the periphery of the root cap. This is a result of negligible secretion of mucilage by cells along the edge of the root cap which, in turn, appears to be due to the malfunctioning of dictyosomes in these cells.

Cytological and ultrastructural studies on root tissues

NASA Technical Reports Server (NTRS)

Slocum, R. D.; Gaynor, J. J.; Galston, A. W.

1984-01-01

The anatomy and fine structure of roots from oat and mung bean seedlings, grown under microgravity conditions for 8 days aboard the Space Shuttle, was examined and compared to that of roots from ground control plants grown under similar conditions. Roots from both sets of oat seedlings exhibited characteristic monocotyledonous tissue organization and normal ultrastructural features, except for cortex cell mitochondria, which exhibited a 'swollen' morphology. Various stages of cell division were observed in the meristematic tissues of oat roots. Ground control and flight-grown mung bean roots also showed normal tissue organization, but root cap cells in the flight-grown roots were collapsed and degraded in appearance, especially at the cap periphery. At the ultrastructural level, these cells exhibited a loss of organelle integrity and a highly-condensed cytoplasm. This latter observation perhaps suggests a differing tissue sensitivity for the two species to growth conditions employed in space flight. The basis for abnormal root cap cell development is not understood, but the loss of these putative gravity-sensing cells holds potential significance for long term plant growth orientation during space flight.

Gravity Maps of Antarctic Lithospheric Structure from Remote-Sensing and Seismic Data

NASA Astrophysics Data System (ADS)

Tenzer, Robert; Chen, Wenjin; Baranov, Alexey; Bagherbandi, Mohammad

2018-02-01

Remote-sensing data from altimetry and gravity satellite missions combined with seismic information have been used to investigate the Earth's interior, particularly focusing on the lithospheric structure. In this study, we use the subglacial bedrock relief BEDMAP2, the global gravitational model GOCO05S, and the ETOPO1 topographic/bathymetric data, together with a newly developed (continental-scale) seismic crustal model for Antarctica to compile the free-air, Bouguer, and mantle gravity maps over this continent and surrounding oceanic areas. We then use these gravity maps to interpret the Antarctic crustal and uppermost mantle structure. We demonstrate that most of the gravity features seen in gravity maps could be explained by known lithospheric structures. The Bouguer gravity map reveals a contrast between the oceanic and continental crust which marks the extension of the Antarctic continental margins. The isostatic signature in this gravity map confirms deep and compact orogenic roots under the Gamburtsev Subglacial Mountains and more complex orogenic structures under Dronning Maud Land in East Antarctica. Whereas the Bouguer gravity map exhibits features which are closely spatially correlated with the crustal thickness, the mantle gravity map reveals mainly the gravitational signature of the uppermost mantle, which is superposed over a weaker (long-wavelength) signature of density heterogeneities distributed deeper in the mantle. In contrast to a relatively complex and segmented uppermost mantle structure of West Antarctica, the mantle gravity map confirmed a more uniform structure of the East Antarctic Craton. The most pronounced features in this gravity map are divergent tectonic margins along mid-oceanic ridges and continental rifts. Gravity lows at these locations indicate that a broad region of the West Antarctic Rift System continuously extends between the Atlantic-Indian and Pacific-Antarctic mid-oceanic ridges and it is possibly formed by two major fault segments. Gravity lows over the Transantarctic Mountains confirms their non-collisional origin. Additionally, more localized gravity lows closely coincide with known locations of hotspots and volcanic regions (Marie Byrd Land, Balleny Islands, Mt. Erebus). Gravity lows also suggest a possible hotspot under the South Orkney Islands. However, this finding has to be further verified.

Effects of ultrasonic root-end cavity preparation with different surgical-tips and at different power-settings on glucose-leakage of root-end filling material.

PubMed

Gunes, Betul; Aydinbelge, Hale Ali

2014-09-01

The aim of this in vitro study was to evaluate the effects of different ultrasonic surgical-tips and power-settings on micro-leakage of root-end filling material. The root canals were instrumented using rotary-files and were filled with tapered gutta-percha and root canal sealer using a single-cone technique. The apical 3 mm of each root was resected and the roots were divided into six experimental groups; negative and positive control groups. Root-end cavities were prepared with diamond-coated, zirconum-nitride-coated and stainless-steel ultrasonic retro-tips at half-power and high-power settings. The time required to prepare the root-end cavities for each group was recorded. Root-end cavities were filled with Super-EBA. Leakage values of all samples evaluated with glucose penetration method on 7, 14, 21 and 28(th) days. The results were statistically analyzed with Kruskal-Wallis and Hollander-Wolfe tests. The mean time required to prepare retro cavities using diamond-coated surgical tip at high-power setting was significantly less than other groups (P < 0.01). There were no statistically significant differences in the glucose penetration between the groups at first and second weeks (P > 0.01). Diamond-coated surgical tip showed the least leakage at high-power setting at 3(rd) and 4(th) weeks (P < 0.01). Under the conditions of this study, cavity preparation time was the shortest and the leakage of the root-end filling was the least when diamond-coated retro-tip used at high-power setting.

A role for CSLD3 during cell-wall synthesis in apical plasma membranes of tip-growing root-hair cells.

PubMed

Park, Sungjin; Szumlanski, Amy L; Gu, Fangwei; Guo, Feng; Nielsen, Erik

2011-07-17

In plants, cell shape is defined by the cell wall, and changes in cell shape and size are dictated by modification of existing cell walls and deposition of newly synthesized cell-wall material. In root hairs, expansion occurs by a process called tip growth, which is shared by root hairs, pollen tubes and fungal hyphae. We show that cellulose-like polysaccharides are present in root-hair tips, and de novo synthesis of these polysaccharides is required for tip growth. We also find that eYFP-CSLD3 proteins, but not CESA cellulose synthases, localize to a polarized plasma-membrane domain in root hairs. Using biochemical methods and genetic complementation of a csld3 mutant with a chimaeric CSLD3 protein containing a CESA6 catalytic domain, we provide evidence that CSLD3 represents a distinct (1→4)-β-glucan synthase activity in apical plasma membranes during tip growth in root-hair cells.

A Receptor-Like Kinase Mediates Ammonium Homeostasis and Is Important for the Polar Growth of Root Hairs in Arabidopsis[W

PubMed Central

Bai, Ling; Ma, Xiaonan; Zhang, Guozeng; Song, Shufei; Zhou, Yun; Gao, Lijie; Miao, Yuchen; Song, Chun-Peng

2014-01-01

Ammonium (NH4+) is both a necessary nutrient and an important signal in plants, but can be toxic in excess. Ammonium sensing and regulatory mechanisms in plant cells have not been fully elucidated. To decipher the complex network of NH4+ signaling, we analyzed [Ca2+]cyt-associated protein kinase (CAP) genes, which encode signaling components that undergo marked changes in transcription levels in response to various stressors. We demonstrated that CAP1, a tonoplast-localized receptor-like kinase, regulates root hair tip growth by maintaining cytoplasmic Ca2+ gradients. A CAP1 knockout mutant (cap1-1) produced elevated levels of cytoplasmic NH4+. Furthermore, root hair growth of cap1-1 was inhibited on Murashige and Skoog medium, but NH4+ depletion reestablished the Ca2+ gradient necessary for normal growth. The lower net NH4+ influx across the vacuolar membrane and relatively alkaline cytosolic pH of cap1-1 root hairs implied that mutation of CAP1 increased NH4+ accumulation in the cytoplasm. Furthermore, CAP1 functionally complemented the npr1 (nitrogen permease reactivator protein) kinase yeast mutant, which is defective in high-affinity NH4+ uptake via MEP2 (methylammonium permease 2), distinguishing CAP1 as a cytosolic modulator of NH4+ levels that participates in NH4+ homeostasis-regulated root hair growth by modulating tip-focused cytoplasmic Ca2+ gradients. PMID:24769480

Joint effects of microwave and chromium trioxide on root tip cells of Vicia faba *

PubMed Central

Qian, Xiao-Wei; Luo, Wei-Hua; Zheng, Ou-Xiang

2006-01-01

The mutagenic effects of microwave and chromium trioxide (CrO3) on Vicia faba root tip were studied. Micronucleus assay and chromosomal aberration assay were used to determine the mitotic index, the micronucleus frequency and chromosomal aberration frequency of Vicia faba root tip cells induced by microwave and CrO3. The results showed that the micronucleus frequency decreased, and that the mitotic index and chromosomal aberration frequency showed linear dose responses to CrO3, in treatment of microwave for 5 s. In microwave of 25 s, the mitotic index decreased, the micronucleus frequency and chromosomal aberration frequency increased with increase of CrO3 concentration. We concluded that microwave and CrO3 had antagonistic effect on the mitotic index of Vicia faba root tip cells, but had synergetic effect on micronucleus frequency and chromosomal aberration frequency of Vicia faba root tip cells. PMID:16502510

Joint effects of microwave and chromium trioxide on root tip cells of Vicia faba.

PubMed

Qian, Xiao-wei; Luo, Wei-hua; Zheng, Ou-xiang

2006-03-01

The mutagenic effects of microwave and chromium trioxide (CrO(3)) on Vicia faba root tip were studied. Micronucleus assay and chromosomal aberration assay were used to determine the mitotic index, the micronucleus frequency and chromosomal aberration frequency of Vicia faba root tip cells induced by microwave and CrO(3). The results showed that the micronucleus frequency decreased, and that the mitotic index and chromosomal aberration frequency showed linear dose responses to CrO(3), in treatment of microwave for 5 s. In microwave of 25 s, the mitotic index decreased, the micronucleus frequency and chromosomal aberration frequency increased with increase of CrO(3) concentration. We concluded that microwave and CrO(3) had antagonistic effect on the mitotic index of Vicia faba root tip cells, but had synergetic effect on micronucleus frequency and chromosomal aberration frequency of Vicia faba root tip cells.

[Study on teratogenic effect of potassium dichromate on Vicia faba root tip cells].

PubMed

Qian, Xiao-Wei

2004-05-01

We studied the aberrant effects of different concentrations of potassium dichromate on Vicia faba root tip cells. The micronucleus and chromosome aberration assay was conducted to determine the micronucleus rate and chromosome aberration rate of Vicia faba root tip cells induced by potassium dichromate. The result indicated that potassium dichromate could increase the micronucleus rate of Vicia faba root tip cells. Within certain range of concentration the rate of micronucleus was found to be increased with the increase of potassium dichromate concentration,but beyond this range the rate of micronucleus decreased with further increase of potassium dichromate concentration. The potassium dichromate at different concentrations could increase the cell mitosis index. Besides,it also caused various types of chromosome aberration,and the rates of chromosome aberration were always higher than that of the control group. The conclusion of this study was that potassium dichromate has obvious teratogenic effect on Vicia faba root tip cells.

Mathematical modeling and experimental validation of the spatial distribution of boron in the root of Arabidopsis thaliana identify high boron accumulation in the tip and predict a distinct root tip uptake function.

PubMed

Shimotohno, Akie; Sotta, Naoyuki; Sato, Takafumi; De Ruvo, Micol; Marée, Athanasius F M; Grieneisen, Verônica A; Fujiwara, Toru

2015-04-01

Boron, an essential micronutrient, is transported in roots of Arabidopsis thaliana mainly by two different types of transporters, BORs and NIPs (nodulin26-like intrinsic proteins). Both are plasma membrane localized, but have distinct transport properties and patterns of cell type-specific accumulation with different polar localizations, which are likely to affect boron distribution. Here, we used mathematical modeling and an experimental determination to address boron distributions in the root. A computational model of the root is created at the cellular level, describing the boron transporters as observed experimentally. Boron is allowed to diffuse into roots, in cells and cell walls, and to be transported over plasma membranes, reflecting the properties of the different transporters. The model predicts that a region around the quiescent center has a higher concentration of soluble boron than other portions. To evaluate this prediction experimentally, we determined the boron distribution in roots using laser ablation-inductivity coupled plasma-mass spectrometry. The analysis indicated that the boron concentration is highest near the tip and is lower in the more proximal region of the meristem zone, similar to the pattern of soluble boron distribution predicted by the model. Our model also predicts that upward boron flux does not continuously increase from the root tip toward the mature region, indicating that boron taken up in the root tip is not efficiently transported to shoots. This suggests that root tip-absorbed boron is probably used for local root growth, and that instead it is the more mature root regions which have a greater role in transporting boron toward the shoots. © The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.

Mathematical Modeling and Experimental Validation of the Spatial Distribution of Boron in the Root of Arabidopsis thaliana Identify High Boron Accumulation in the Tip and Predict a Distinct Root Tip Uptake Function

PubMed Central

Shimotohno, Akie; Sotta, Naoyuki; Sato, Takafumi; De Ruvo, Micol; Marée, Athanasius F.M.; Grieneisen, Verônica A.; Fujiwara, Toru

2015-01-01

Boron, an essential micronutrient, is transported in roots of Arabidopsis thaliana mainly by two different types of transporters, BORs and NIPs (nodulin26-like intrinsic proteins). Both are plasma membrane localized, but have distinct transport properties and patterns of cell type-specific accumulation with different polar localizations, which are likely to affect boron distribution. Here, we used mathematical modeling and an experimental determination to address boron distributions in the root. A computational model of the root is created at the cellular level, describing the boron transporters as observed experimentally. Boron is allowed to diffuse into roots, in cells and cell walls, and to be transported over plasma membranes, reflecting the properties of the different transporters. The model predicts that a region around the quiescent center has a higher concentration of soluble boron than other portions. To evaluate this prediction experimentally, we determined the boron distribution in roots using laser ablation-inductivity coupled plasma-mass spectrometry. The analysis indicated that the boron concentration is highest near the tip and is lower in the more proximal region of the meristem zone, similar to the pattern of soluble boron distribution predicted by the model. Our model also predicts that upward boron flux does not continuously increase from the root tip toward the mature region, indicating that boron taken up in the root tip is not efficiently transported to shoots. This suggests that root tip-absorbed boron is probably used for local root growth, and that instead it is the more mature root regions which have a greater role in transporting boron toward the shoots. PMID:25670713

Extracellular ATP inhibits root gravitropism at concentrations that inhibit polar auxin transport

NASA Technical Reports Server (NTRS)

Tang, Wenqiang; Brady, Shari R.; Sun, Yu; Muday, Gloria K.; Roux, Stanley J.

2003-01-01

Raising the level of extracellular ATP to mM concentrations similar to those found inside cells can block gravitropism of Arabidopsis roots. When plants are grown in Murashige and Skoog medium supplied with 1 mM ATP, their roots grow horizontally instead of growing straight down. Medium with 2 mM ATP induces root curling, and 3 mM ATP stimulates lateral root growth. When plants are transferred to medium containing exogenous ATP, the gravity response is reduced or in some cases completely blocked by ATP. Equivalent concentrations of ADP or inorganic phosphate have slight but usually statistically insignificant effects, suggesting the specificity of ATP in these responses. The ATP effects may be attributable to the disturbance of auxin distribution in roots by exogenously applied ATP, because extracellular ATP can alter the pattern of auxin-induced gene expression in DR5-beta-glucuronidase transgenic plants and increase the response sensitivity of plant roots to exogenously added auxin. The presence of extracellular ATP also decreases basipetal auxin transport in a dose-dependent fashion in both maize (Zea mays) and Arabidopsis roots and increases the retention of [(3)H]indole-3-acetic acid in root tips of maize. Taken together, these results suggest that the inhibitory effects of extracellular ATP on auxin distribution may happen at the level of auxin export. The potential role of the trans-plasma membrane ATP gradient in auxin export and plant root gravitropism is discussed.

The Electrical Network of Maize Root Apex is Gravity Dependent

PubMed Central

Masi, Elisa; Ciszak, Marzena; Comparini, Diego; Monetti, Emanuela; Pandolfi, Camilla; Azzarello, Elisa; Mugnai, Sergio; Baluška, Frantisek; Mancuso, Stefano

2015-01-01

Investigations carried out on maize roots under microgravity and hypergravity revealed that gravity conditions have strong effects on the network of plant electrical activity. Both the duration of action potentials (APs) and their propagation velocities were significantly affected by gravity. Similarly to what was reported for animals, increased gravity forces speed-up APs and enhance synchronized electrical events also in plants. The root apex transition zone emerges as the most active, as well as the most sensitive, root region in this respect. PMID:25588706

The electrical network of maize root apex is gravity dependent.

PubMed

Masi, Elisa; Ciszak, Marzena; Comparini, Diego; Monetti, Emanuela; Pandolfi, Camilla; Azzarello, Elisa; Mugnai, Sergio; Baluška, Frantisek; Mancuso, Stefano

2015-01-15

Investigations carried out on maize roots under microgravity and hypergravity revealed that gravity conditions have strong effects on the network of plant electrical activity. Both the duration of action potentials (APs) and their propagation velocities were significantly affected by gravity. Similarly to what was reported for animals, increased gravity forces speed-up APs and enhance synchronized electrical events also in plants. The root apex transition zone emerges as the most active, as well as the most sensitive, root region in this respect.

[Effects of chlorobenzene stress on seedling growth and cell division of Vicia faba].

PubMed

Liu, Wan; Zhou, Qixing; Li, Peijun; Sun, Tieheng; Tai, Peidong; Xu, Huaxia; Zhang, Chungui; Zhang, Hairong

2003-04-01

Effects of 1, 2, 4-trichlorobenzene (TCB) stress on seedling growth, cell division and chromosomal aberration frequency of root-tip cells of Vicia faba were studied. The results indicated that the growth of the root length and mitotic index of root tip cells were successively decreased and even stopped with the increase of TCB concentrations and treatment duration. Numerical and structural chromosomal aberrations at metaphase and anaphase of root-tip cells in Vicia faba seedlings were produced by 50-300 micrograms.g-1 TCB treatment for 12-96 h. The percentage of c-mitosis, chromosomal bridge and chromosomal asymmetry array in root tip cells exposed to 50-100 micrograms.g-1 TCB for 12-24 h was up to 1.0-10.3%. The percentage of chromosomal stickness (S), chromosomal stickiness + chromosomal breakage (S + B), chromosomal stickness + chromosomal ring (S + R), chromosomal stickiness + chromosomal asymmetry array (S + A) and chromosomal stickness + chromosomal bridge (S + Be) in root tip cells reached 47.9-88.9%, and 18.1-29.6% for different kinds of chromosomal breakage at 300 micrograms.g-1 TCB for 12-96 h. Thus, the chromosomal aberration of root tip cells in Vicia faba seedlings could be used as a sensitive biomarker of monitoring soil contaminated with TCB.

Collection of gravitropic effectors from mucilage of electrotropically-stimulated roots of Zea mays L

NASA Technical Reports Server (NTRS)

Fondren, W. M.; Moore, R.

1987-01-01

We placed agar blocks adjacent to tips of electrotropically stimulated primary roots of Zea mays. Blocks placed adjacent to the anode-side of the roots for 3 h induced significant curvature when subsequently placed asymmetrically on tips of vertically-oriented roots. Curvature was always toward the side of the root unto which the agar block was placed. Agar blocks not contacting roots and blocks placed adjacent to the cathode-side of electrotropically stimulated roots did not induce significant curvature when placed asymmetrically on tips of vertically-oriented roots. Atomic absorption spectrophotometry indicated that blocks adjacent to the anode-side of electrotropically-stimulated roots contained significantly more calcium than (1) blocks not contacting roots, and (2) blocks contacting the cathode-side of roots. These results demonstrate the presence of a gradient of endogenous Ca in mucilage of electrotropically-stimulated roots (i.e. roots undergoing gravitropic-like curvature).

Turbine bucket for use in gas turbine engines and methods for fabricating the same

DOEpatents

Garcia-Crespo, Andres

2014-06-03

A turbine bucket for use with a turbine engine. The turbine bucket includes an airfoil that extends between a root end and a tip end. The airfoil includes an outer wall that defines a cavity that extends from the root end to the tip end. The outer wall includes a first ceramic matrix composite (CMC) substrate that extends a first distance from the root end to the tip end. An inner wall is positioned within the cavity. The inner wall includes a second CMC substrate that extends a second distance from the root end towards the tip end that is different than the first distance.

Abscisic Acid Regulates Auxin Homeostasis in Rice Root Tips to Promote Root Hair Elongation

PubMed Central

Wang, Tao; Li, Chengxiang; Wu, Zhihua; Jia, Yancui; Wang, Hong; Sun, Shiyong; Mao, Chuanzao; Wang, Xuelu

2017-01-01

Abscisic acid (ABA) plays an essential role in root hair elongation in plants, but the regulatory mechanism remains to be elucidated. In this study, we found that exogenous ABA can promote rice root hair elongation. Transgenic rice overexpressing SAPK10 (Stress/ABA-activated protein kinase 10) had longer root hairs; rice plants overexpressing OsABIL2 (OsABI-Like 2) had attenuated ABA signaling and shorter root hairs, suggesting that the effect of ABA on root hair elongation depends on the conserved PYR/PP2C/SnRK2 ABA signaling module. Treatment of the DR5-GUS and OsPIN-GUS lines with ABA and an auxin efflux inhibitor showed that ABA-induced root hair elongation depends on polar auxin transport. To examine the transcriptional response to ABA, we divided rice root tips into three regions: short root hair, long root hair and root tip zones; and conducted RNA-seq analysis with or without ABA treatment. Examination of genes involved in auxin transport, biosynthesis and metabolism indicated that ABA promotes auxin biosynthesis and polar auxin transport in the root tip, which may lead to auxin accumulation in the long root hair zone. Our findings shed light on how ABA regulates root hair elongation through crosstalk with auxin biosynthesis and transport to orchestrate plant development. PMID:28702040

In vitro performance of DIAGNOdent laser fluorescence device for dental calculus detection on human tooth root surfaces.

PubMed

Rams, Thomas E; Alwaqyan, Abdulaziz Y

2017-10-01

This study assessed the reproducibility of a red diode laser device, and its capability to detect dental calculus in vitro on human tooth root surfaces. On each of 50 extracted teeth, a calculus-positive and calculus-free root surface was evaluated by two independent examiners with a low-power indium gallium arsenide phosphide diode laser (DIAGNOdent) fitted with a periodontal probe-like sapphire tip and emitting visible red light at 655 nm wavelength. Laser autofluorescence intensity readings of examined root surfaces were scored on a 0-99 scale, with duplicate assessments performed using the laser probe tip directed both perpendicular and parallel to evaluated tooth root surfaces. Pearson correlation coefficients of untransformed measurements, and kappa analysis of data dichotomized with a >40 autofluorescence intensity threshold, were calculated to assess intra- and inter-examiner reproducibility of the laser device. Mean autofluorescence intensity scores of calculus-positive and calculus-free root surfaces were evaluated with the Student's t -test. Excellent intra- and inter-examiner reproducibility was found for DIAGNOdent laser autofluorescence intensity measurements, with Pearson correlation coefficients above 94%, and kappa values ranging between 0.96 and 1.0, for duplicate readings taken with both laser probe tip orientations. Significantly higher autofluorescence intensity values were measured when the laser probe tip was directed perpendicular, rather than parallel, to tooth root surfaces. However, calculus-positive roots, particularly with calculus in markedly-raised ledges, yielded significantly greater mean DIAGNOdent laser autofluorescence intensity scores than calculus-free surfaces, regardless of probe tip orientation. DIAGNOdent autofluorescence intensity values >40 exhibited a stronger association with calculus (36.6 odds ratio) then measurements of ≥5 (20.1 odds ratio) when the laser probe tip was advanced parallel to root surfaces. Excellent intra- and inter-examiner reproducibility of autofluorescence intensity measurements was obtained with the DIAGNOdent laser fluorescence device on human tooth roots. Calculus-positive root surfaces exhibited significantly greater DIAGNOdent laser autofluorescence than calculus-free tooth roots, even with the laser probe tip directed parallel to root surfaces. These findings provide further in vitro validation of the potential utility of a DIAGNOdent laser fluorescence device for identifying dental calculus on human tooth root surfaces.

A three-dimensional gravity study of the 95.5°W propagating rift in the Galapagos spreading center

NASA Astrophysics Data System (ADS)

Phipps Morgan, Jason; Parmentier, E. M.

1987-01-01

Seafloor at the Galapagos 95.5°W propagating rift (PR) has a varied morphological expression that can be spatially correlated with the predicted kinematic history of the PR. A median valley-like depression occurs near the tip of the growing ridge axis. To test if this bathymetry is a dynamic feature supported by mantle or lithosphere strength or if it is due to isostatically compensated crustal thickness variations, we use three-dimensional gravity modelling to constrain the crustal structure in this region, from data collected by Hey in 1979 and 1982. The gravity anomaly at the PR tip depression suggests that the tip depression is not caused by crustal thinning. The data are consistent with a stress-supported PR tip depression caused by asthenospheric along-axis flow into the growing ridge axis (Phipps Morgan and Parmentier [1]). In contrast to the tip depression, seafloor in the sheared zone of material transferred through transform migration from the Cocos to Nazca plate is anomalously shallow and has a pronounced regional 300-400 m tilt towards the growing ridge axis over the 20 km width of the sheared zone. The gravity data also suggest that the sheared zone is not compensated by crustal thickening.

The role of the distal elongation zone in the response of maize roots to auxin and gravity

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Evans, M. L.

1993-01-01

We used a video digitizer system to (a) measure changes in the pattern of longitudinal surface extension in primary roots of maize (Zea mays L.) upon application and withdrawal of auxin and (b) compare these patterns during gravitropism in control roots and roots pretreated with auxin. Special attention was paid to the distal elongation zone (DEZ), arbitrarily defined as the region between the meristem and the point within the elongation zone at which the rate of elongation reaches 0.3 of the peak rate. For roots in aqueous solution, the basal limit of the DEZ is about 2.5 mm behind the tip of the root cap. Auxin suppressed elongation throughout the elongation zone, but, after 1 to 3 h, elongation resumed, primarily as a result of induction of rapid elongation in the DEZ. Withdrawal of auxin during the period of strong inhibition resulted in exceptionally rapid elongation attributable to the initiation of rapid elongation in the DEZ plus recovery in the main elongation zone. Gravistimulation of auxin-inhibited roots induced rapid elongation in the DEZ along the top of the root. This resulted in rapid gravitropism even though the elongation rate of the root was zero before gravistimulation. The results indicate that cells of the DEZ differ from cells in the bulk of the elongation zone with respect to auxin sensitivity and that DEZ cells play an important role in gravitropism.

Root Border Cells and Their Role in Plant Defense.

PubMed

Hawes, Martha; Allen, Caitilyn; Turgeon, B Gillian; Curlango-Rivera, Gilberto; Minh Tran, Tuan; Huskey, David A; Xiong, Zhongguo

2016-08-04

Root border cells separate from plant root tips and disperse into the soil environment. In most species, each root tip can produce thousands of metabolically active cells daily, with specialized patterns of gene expression. Their function has been an enduring mystery. Recent studies suggest that border cells operate in a manner similar to mammalian neutrophils: Both cell types export a complex of extracellular DNA (exDNA) and antimicrobial proteins that neutralize threats by trapping pathogens and thereby preventing invasion of host tissues. Extracellular DNases (exDNases) of pathogens promote virulence and systemic spread of the microbes. In plants, adding DNase I to root tips eliminates border cell extracellular traps and abolishes root tip resistance to infection. Mutation of genes encoding exDNase activity in plant-pathogenic bacteria (Ralstonia solanacearum) and fungi (Cochliobolus heterostrophus) results in reduced virulence. The study of exDNase activities in plant pathogens may yield new targets for disease control.

Intracellular magnetophoresis of amyloplasts and induction of root curvature

NASA Technical Reports Server (NTRS)

Kuznetsov, O. A.; Hasenstein, K. H.

1996-01-01

High-gradient magnetic fields (HGMFs) were used to induce intracellular magnetophoresis of amyloplasts. The HGMFs were generated by placing a small ferromagnetic wedge into a uniform magnetic field or at the gap edge between two permanent magnets. In the vicinity of the tip of the wedge the dynamic factor of the magnetic field, delta(H2/2), was about 10(9) Oe2.cm-1, which subjected the amyloplasts to a force comparable to that of gravity. When roots of 2-d-old seedlings of flax (Linum usitatissimum L.) were positioned vertically and exposed to an HGMF, curvature away from the wedge was transient and lasted approximately 1 h. Average curvature obtained after placing magnets, wedge and seedlings on a 1-rpm clinostat for 2 h was 33 +/- 5 degrees. Roots of horizontally placed control seedlings without rotation curved about 47 +/- 4 degrees. The time course of curvature and changes in growth rate were similar for gravicurvature and for root curvature induced by HGMFs. Microscopy showed displacement of amyloplasts in vitro and in vivo. Studies with Arabidopsis thaliana (L.) Heynh. showed that the wild type responded to HGMFs but the starchless mutant TC7 did not. The data indicate that a magnetic force can be used to study the gravisensing and response system of roots.

On the role of convective motion during dendrite growth: Experiments under variable gravity, revised

NASA Technical Reports Server (NTRS)

Hallett, J.; Cho, N.; Harrison, K.; Lord, A.; Wedum, E.; Purcell, R.; Saunders, C. P. R.

1987-01-01

Experiments show the effect of self induced convection on individual dendrite growth in uniformly supercooled samples and solidification of the resulting mush under conditions of high and low g. Convection is visualized by a Schlieren optical system or a Mach Zender interferometer. For ice crystals growing from the vapor in air, a slight reduction in linear growth rate occur under low g. For ice crystals growing from NaCl solution, dendrite tip velocities are unchanged, but subsequent mush solidification is enhanced through drainage channels under higher g. By contrast, sodium sulfate decahydrate dendrites growing from solution produce convective plumes which lead to higher tip growth rate only as the crystal growth direction approaches that of gravity. Convective plumes are laminar for small crystals under conditions of these experiments; the rise velocity of such plumes is greater than individual vortex rings under identical conditions. Convection effects are only present in solution under a critical supercooling less than about 5 C for sodium sulfate and 2 C for ice in NaCl since at higher supercooling the crystallization velocity, proportional to the square of the supercooling, exceeds the convective velocity, proportional to the square root of the supercooling. The role of convective velocity in bulk solidification is to give a large scale flow which under extreme cases may lead to extensive secondary crystal production, which alters the resulting crystal texture of the completely solidified melt.

The Microtubule-Associated Protein MAP18 Affects ROP2 GTPase Activity during Root Hair Growth1[OPEN

PubMed Central

Kang, Erfang; Zheng, Mingzhi; Zhang, Yan; Yuan, Ming; Fu, Ying

2017-01-01

Establishment and maintenance of the polar site are important for root hair tip growth. We previously reported that Arabidopsis (Arabidopsis thaliana) MICROTUBULE-ASSOCIATED PROTEIN18 (MAP18) functions in controlling the direction of pollen tube growth and root hair elongation. Additionally, the Rop GTPase ROP2 was reported as a positive regulator of both root hair initiation and tip growth in Arabidopsis. Both loss of function of ROP2 and knockdown of MAP18 lead to a decrease in root hair length, whereas overexpression of either MAP18 or ROP2 causes multiple tips or a branching hair phenotype. However, it is unclear whether MAP18 and ROP2 coordinately regulate root hair growth. In this study, we demonstrate that MAP18 and ROP2 interact genetically and functionally. MAP18 interacts physically with ROP2 in vitro and in vivo and preferentially binds to the inactive form of the ROP2 protein. MAP18 promotes ROP2 activity during root hair tip growth. Further investigation revealed that MAP18 competes with RhoGTPase GDP DISSOCIATION INHIBITOR1/SUPERCENTIPEDE1 for binding to ROP2, in turn affecting the localization of active ROP2 in the plasma membrane of the root hair tip. These results reveal a novel function of MAP18 in the regulation of ROP2 activation during root hair growth. PMID:28314794

Influence of electrical fields and asymmetric application of mucilage on curvature of primary roots of Zea mays

NASA Technical Reports Server (NTRS)

Marcum, H.; Moore, R.

1990-01-01

Primary roots of Zea mays cv. Yellow Dent growing in an electric field curve towards the anode. Roots treated with EDTA and growing in electric field do not curve. When root cap mucilage is applied asymmetrically to tips of vertically-oriented roots, the roots curve toward the mucilage. Roots treated with EDTA curve toward the side receiving mucilage and toward blocks containing 10 mM CaCl2, but not toward "empty" agar blocks or the cut surfaces of severed root tips. These results suggest that 1) free calcium (Ca) is necessary for root electrotropism, 2) mucilage contains effector(s) that induce gravitropiclike curvature, and 3) mucilage can replace gravitropic effectors chelated by EDTA. These results are consistent with the hypothesis that the downward movement of gravitropic effectors to the lower sides of tips of horizontally-oriented roots occurs at least partially in the apoplast.

Effects of mechanostimulation on gravitropism and signal persistence in flax roots.

PubMed

John, Susan P; Hasenstein, Karl H

2011-09-01

Gravitropism describes curvature of plants in response to gravity or differential acceleration and clinorotation is commonly used to compensate unilateral effect of gravity. We report on experiments that examine the persistence of the gravity signal and separate mechanostimulation from gravistimulation. Flax roots were reoriented (placed horizontally for 5, 10 or 15 min) and clinorotated at a rate of 0.5 to 5 rpm either vertically (parallel to the gravity vector and root axis) or horizontally (perpendicular to the gravity vector and parallel to the root axis). Image sequences showed that horizontal clinorotation did not affect root growth rate (0.81 ± 0.03 mm h-1) but vertical clinorotation reduced root growth by about 7%. The angular velocity (speed of clinorotation) did not affect growth for either direction. However, maximal curvature for vertical clinorotation decreased with increasing rate of rotation and produced straight roots at 5 rpm. In contrast, horizontal clinorotation increased curvature with increasing angular velocity. The point of maximal curvature was used to determine the longevity (memory) of the gravity signal, which lasted about 120 min. The data indicate that mechanostimulation modifies the magnitude of the graviresponse but does not affect memory persistence.

Root Apex Transition Zone As Oscillatory Zone

PubMed Central

Baluška, František; Mancuso, Stefano

2013-01-01

Root apex of higher plants shows very high sensitivity to environmental stimuli. The root cap acts as the most prominent plant sensory organ; sensing diverse physical parameters such as gravity, light, humidity, oxygen, and critical inorganic nutrients. However, the motoric responses to these stimuli are accomplished in the elongation region. This spatial discrepancy was solved when we have discovered and characterized the transition zone which is interpolated between the apical meristem and the subapical elongation zone. Cells of this zone are very active in the cytoskeletal rearrangements, endocytosis and endocytic vesicle recycling, as well as in electric activities. Here we discuss the oscillatory nature of the transition zone which, together with several other features of this zone, suggest that it acts as some kind of command center. In accordance with the early proposal of Charles and Francis Darwin, cells of this root zone receive sensory information from the root cap and instruct the motoric responses of cells in the elongation zone. PMID:24106493

Changes in root cap pH are required for the gravity response of the Arabidopsis root

NASA Technical Reports Server (NTRS)

Fasano, J. M.; Swanson, S. J.; Blancaflor, E. B.; Dowd, P. E.; Kao, T. H.; Gilroy, S.

2001-01-01

Although the columella cells of the root cap have been identified as the site of gravity perception, the cellular events that mediate gravity signaling remain poorly understood. To determine if cytoplasmic and/or wall pH mediates the initial stages of root gravitropism, we combined a novel cell wall pH sensor (a cellulose binding domain peptide-Oregon green conjugate) and a cytoplasmic pH sensor (plants expressing pH-sensitive green fluorescent protein) to monitor pH dynamics throughout the graviresponding Arabidopsis root. The root cap apoplast acidified from pH 5.5 to 4.5 within 2 min of gravistimulation. Concomitantly, cytoplasmic pH increased in columella cells from 7.2 to 7.6 but was unchanged elsewhere in the root. These changes in cap pH preceded detectable tropic growth or growth-related pH changes in the elongation zone cell wall by 10 min. Altering the gravity-related columella cytoplasmic pH shift with caged protons delayed the gravitropic response. Together, these results suggest that alterations in root cap pH likely are involved in the initial events that mediate root gravity perception or signal transduction.

jsc2018m000256_Rooting_for_Answers

NASA Image and Video Library

2018-03-22

Rooting for Answers: Simulating G-Force in Plants---------On Earth, plants use gravity and light to orient their roots and shoots, but in space, microgravity is too weak to provide a growth cue. The Gravity Perception Systems (Plant Gravity Perception) investigation germinates normal and variant forms of thale cress, a model research plant, to study the plants’ gravity and light perception. Results provide new information about plants’ ability to detect gravity and adapt to an environment without it. The investigation continues efforts to grow plants for food on future missions.

Induction of numerical chromosomal aberrations during DNA synthesis using the fungicides nimrod and rubigan-4 in root tips of Vicia faba L.

PubMed

Shahin, S A; el-Amoodi, K H

1991-11-01

The 2 fungicides nimrod and rubigan-4 were tested for genotoxicity using Vicia faba root tips as the biological test system. Treating lateral roots with different concentrations of each fungicide for different periods showed that both fungicides were able to produce numerical but not structural chromosomal aberrations. The percentage of total aberrations in root tips exposed to nimrod reached 54.39% at 250 ppm for 4 h, and 64.69% in root tips exposed to rubigan-4 at 250 ppm for 6 h. The types of numerical chromosomal aberrations produced by both fungicides included: binucleate cells, c-metaphases, sticky chromosomes, polyploid cells, and laggards. Recovery experiments for 24, 48, and 96 h showed no significant differences between the percentage of total aberrations in treated and control groups.

Electron microscopic analysis of gravisensing Chara rhizoids developed under microgravity conditions.

PubMed

Braun, M; Buchen, B; Sievers, A

1999-01-01

Tip-growing, unicellular Chara rhizoids that react gravitropically on Earth developed in microgravity. In microgravity, they grew out from the nodes of the green thallus in random orientation. Development and morphogenesis followed an endogenous program that is not affected by the gravitational field. The cell shape, the polar cytoplasmic organization, and the polar distribution of cell organelles, except for the statoliths, were not different from controls that had grown on earth (ground controls). The ultrastructure of the organelles and the microtubules were well preserved. Microtubules were excluded from the apical zone in both ground controls as well as microgravity-grown rhizoids. The statoliths (vesicles containing BaSO4 crystals in a matrix) in microgravity-grown rhizoids were spread over a larger area (up to 50 microm basal to the tip) than the statoliths of ground controls (10-30 microm). Some statoliths were even located in the subapical zone close to microtubules, which was not observed in ground controls. The crystals in statoliths from microgravity-grown rhizoids appeared more loosely arranged in the vesicle matrix compared with ground controls. The chemical composition of the crystals was identified as BaSO4 by X-ray microanalysis. There is evidence that the amount of BaSO4 in statoliths of rhizoids developed in microgravity is lower than in ground controls, indicating that the gravisensitivity of microgravity-developed rhizoids might be reduced compared with ground controls. Lack of gravity, however, does not affect the process of tip growth and does not inhibit the development of the structures needed for the gravity-sensing machinery.

Characterization of closely related delta-TIP genes encoding aquaporins which are differentially expressed in sunflower roots upon water deprivation through exposure to air.

PubMed

Sarda, X; Tousch, D; Ferrare, K; Cellier, F; Alcon, C; Dupuis, J M; Casse, F; Lamaze, T

1999-05-01

We isolated five sunflower (Helianthus annuus) cDNAs belonging to the TIP (tonoplast intrinsic protein) family. SunRb7 and Sun gammaTIP (partial sequence) are homologous to tobacco TobRb7 and Arabidopsis gamma-TIP, respectively. SunTIP7, 18 and 20 (SunTIPs) are closely related and homologous to Arabidopsis delta-TIP (SunTIP7 and 20 have already been presented in Sarda et al., Plant J. 12 (1997) 1103-1111). As was previously shown for SunTIP7 and 20, expression of SunTIP18 and SunRb7 in Xenopus oocytes caused an increase in osmotic water permeability demonstrating that they are aquaporins. In roots, in situ hybridization revealed that SunTIP7 and 18 mRNAs accumulate in phloem tissues. The expression of TIP-like genes was studied in roots during 24 h water deprivation through exposure to air. During the course of the treatment, each SunTIP gene displayed an individual response: SunTIP7 transcript abundance increased, SunTIP18 decreased whereas that of SunTIP20 was transitorily enhanced. By contrast, SunRb7 and Sun gammaTIP mRNA levels did not fluctuate. Due to the changes in their transcript levels, it is proposed that SUNTIP aquaporins encoded by delta-TIP-like genes play a role in the sunflower response to drought.

Reductions in maize root-tip elongation by salt and osmotic stress do not correlate with apoplastic O2*- levels.

PubMed

Bustos, Dolores; Lascano, Ramiro; Villasuso, Ana Laura; Machado, Estela; Senn, María Eugenia; Córdoba, Alicia; Taleisnik, Edith

2008-10-01

Experimental evidence in the literature suggests that O(2)(*-) produced in the elongation zone of roots and leaves by plasma membrane NADPH oxidase activity is required for growth. This study explores whether growth changes along the root tip induced by hyperosmotic treatments in Zea mays are associated with the distribution of apoplastic O(2)(*-). Stress treatments were imposed using 150 mm NaCl or 300 mM sorbitol. Root elongation rates and the spatial distribution of growth rates in the root tip were measured. Apoplastic O(2)(*-) was determined using nitro blue tetrazolium, and H(2)O(2) was determined using 2', 7'-dichlorofluorescin. In non-stressed plants, the distribution of accelerating growth and highest O(2)(*-) levels coincided along the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation, but O(2)(*-) levels increased in sorbitol-treated roots and decreased in NaCl-treated roots. The lack of association between apoplastic O(2)(*-) levels and root growth inhibition under hyper-osmotic stress leads us to hypothesize that under those conditions the role of apoplastic O(2)(*-) may be to participate in signalling processes, that convey information on the nature of the substrate that the growing root is exploring.

A complete system for 3D reconstruction of roots for phenotypic analysis.

PubMed

Kumar, Pankaj; Cai, Jinhai; Miklavcic, Stanley J

2015-01-01

Here we present a complete system for 3D reconstruction of roots grown in a transparent gel medium or washed and suspended in water. The system is capable of being fully automated as it is self calibrating. The system starts with detection of root tips in root images from an image sequence generated by a turntable motion. Root tips are detected using the statistics of Zernike moments on image patches centred on high curvature points on root boundary and Bayes classification rule. The detected root tips are tracked in the image sequence using a multi-target tracking algorithm. Conics are fitted to the root tip trajectories using a novel ellipse fitting algorithm which weighs the data points by its eccentricity. The conics projected from the circular trajectory have a complex conjugate intersection which are image of the circular points. Circular points constraint the image of the absolute conics which are directly related to the internal parameters of the camera. The pose of the camera is computed from the image of the rotation axis and the horizon. The silhouettes of the roots and camera parameters are used to reconstruction the 3D voxel model of the roots. We show the results of real 3D reconstruction of roots which are detailed and realistic for phenotypic analysis.

Aluminum-induced cell death of barley-root border cells is correlated with peroxidase- and oxalate oxidase-mediated hydrogen peroxide production.

PubMed

Tamás, L; Budíková, S; Huttová, J; Mistrík, I; Simonovicová, M; Siroká, B

2005-06-01

The function of root border cells (RBC) during aluminum (Al) stress and the involvement of oxalate oxidase, peroxidase and H(2)O(2) generation in Al toxicity were studied in barley roots. Our results suggest that RBC effectively protect the barley root tip from Al relative to the situation in roots cultivated in hydroponics where RBC are not sustained in the area surrounding the root tip. The removal of RBC from Al-treated roots increased root growth inhibition, Al and Evans blue uptake, inhibition of RBC production, the level of dead RBC, peroxidase and oxalate oxidase activity and the production of H(2)O(2). Our results suggest that even though RBC actively produce active oxygen species during Al stress, their role in the protection of root tips against Al toxicity is to chelate Al in their dead cell body.

Mechanotransduction molecules in the plant gravisensory response: amyloplast/statolith membranes contain a beta 1 integrin-like protein

NASA Technical Reports Server (NTRS)

Lynch, T. M.; Lintilhac, P. M.; Domozych, D.

1998-01-01

It has been hypothesized that the sedimentation of amyloplasts within root cap cells is the primary event in the plant gravisensory-signal transduction cascade. Statolith sedimentation, with its ability to generate weighty mechanical signals, is a legitimate means for organisms to discriminate the direction of the gravity vector. However, it has been demonstrated that starchless mutants with reduced statolith densities maintain some ability to sense gravity, calling into question the statolith sedimentation hypothesis. Here we report on the presence of a beta 1 integrin-like protein localized inside amyloplasts of tobacco NT-1 suspension culture, callus cells, and whole-root caps. Two different antibodies to the beta 1 integrin, one to the cytoplasmic domain and one to the extracellular domain, localize in the vicinity of the starch grains within amyloplasts of NT-1. Biochemical data reveals a 110-kDa protein immunoprecipitated from membrane fractions of NT-1 suspension culture indicating size homology to known beta 1 integrin in animals. This study provides the first direct evidence for the possibility of integrin-mediated signal transduction in the perception of gravity by higher plants. An integrin-mediated pathway, initiated by starch grain sedimentation within the amyloplast, may provide the signal amplification necessary to explain the gravitropic response in starch-depleted cultivars.

The Earth Gravitational Observatory (EGO): Nanosat Constellations For Advanced Gravity Mapping

NASA Astrophysics Data System (ADS)

Yunck, T.; Saltman, A.; Bettadpur, S. V.; Nerem, R. S.; Abel, J.

2017-12-01

The trend to nanosats for space-based remote sensing is transforming system architectures: fleets of "cellular" craft scanning Earth with exceptional precision and economy. GeoOptics Inc has been selected by NASA to develop a vision for that transition with an initial focus on advanced gravity field mapping. Building on our spaceborne GNSS technology we introduce innovations that will improve gravity mapping roughly tenfold over previous missions at a fraction of the cost. The power of EGO is realized in its N-satellite form where all satellites in a cluster receive dual-frequency crosslinks from all other satellites, yielding N(N-1)/2 independent measurements. Twelve "cells" thus yield 66 independent links. Because the cells form a 2D arc with spacings ranging from 200 km to 3,000 km, EGO senses a wider range of gravity wavelengths and offers greater geometrical observing strength. The benefits are two-fold: Improved time resolution enables observation of sub-seasonal processes, as from hydro-meteorological phenomena; improved measurement quality enhances all gravity solutions. For the GRACE mission, key limitations arise from such spacecraft factors as long-term accelerometer error, attitude knowledge and thermal stability, which are largely independent from cell to cell. Data from a dozen cells reduces their impact by 3x, by the "root-n" averaging effect. Multi-cell closures improve on this further. The many closure paths among 12 cells provide strong constraints to correct for observed range changes not compatible with a gravity source, including accelerometer errors in measuring non-conservative forces. Perhaps more significantly from a science standpoint, system-level estimates with data from diverse orbits can attack the many scientifically limiting sources of temporal aliasing.

Nitric oxide is involved in the oxytetracycline-induced suppression of root growth through inhibiting hydrogen peroxide accumulation in the root meristem

NASA Astrophysics Data System (ADS)

Yu, Qing-Xiang; Ahammed, Golam Jalal; Zhou, Yan-Hong; Shi, Kai; Zhou, Jie; Yu, Yunlong; Yu, Jing-Quan; Xia, Xiao-Jian

2017-02-01

Use of antibiotic-contaminated manure in crop production poses a severe threat to soil and plant health. However, few studies have studied the mechanism by which plant development is affected by antibiotics. Here, we used microscopy, flow cytometry, gene expression analysis and fluorescent dyes to study the effects of oxytetracycline (OTC), a widely used antibiotic in agriculture, on root meristem activity and the accumulation of hydrogen peroxide (H2O2) and nitric oxide (NO) in the root tips of tomato seedlings. We found that OTC caused cell cycle arrest, decreased the size of root meristem and inhibited root growth. Interestingly, the inhibition of root growth by OTC was associated with a decline in H2O2 levels but an increase in NO levels in the root tips. Diphenyliodonium (DPI), an inhibitor of H2O2 production, showed similar effects on root growth as those of OTC. However, exogenous H2O2 partially reversed the effects on the cell cycle, meristem size and root growth. Importantly, cPTIO (the NO scavenger) and tungstate (an inhibitor of nitrate reductase) significantly increased H2O2 levels in the root tips and reversed the inhibition of root growth by OTC. Out results suggest that OTC-induced NO production inhibits H2O2 accumulation in the root tips, thus leading to cell cycle arrest and suppression of root growth.

The effect of gravity on plant germination

NASA Astrophysics Data System (ADS)

Takakura, T.; Goto, E.; Tanaka, M.

1996-01-01

An axis clinostat was constructed to create micro and negative gravity also a rotated flat disk was constructed with different rotation rates to give increased gravity, by centrifugal force up to 48g. Rice seeds were grown on agar in tubes at the constant air temperature of 20 degC under an average light condition of 110 mumol/m^2/sec(PPF). Humidity was not controlled but was maintained above 90%. Since the tube containers were not large enough for long cultivation, shoot and root growth were observed every 12 hours until the sixth day from seeding. The lengths of shoots and roots for each individual plant were measured on the last day. The stem lengths were increased by microgravity but the root lengths were not. Under the negative gravity, negative orthogeotropism and under micro gravity, diageotropism was observed. No significant effect of increased gravity was observed on shoot and root growth.

UV-B Radiation Induces Root Bending Through the Flavonoid-Mediated Auxin Pathway in Arabidopsis.

PubMed

Wan, Jinpeng; Zhang, Ping; Wang, Ruling; Sun, Liangliang; Wang, Wenying; Zhou, Huakun; Xu, Jin

2018-01-01

Ultraviolet (UV)-B radiation-induced root bending has been reported; however, the underlying mechanisms largely remain unclear. Here, we investigate whether and how auxin and flavonoids are involved in UV-B radiation-induced root bending in Arabidopsis using physiological, pharmacological, and genetic approaches. UV-B radiation modulated the direction of root growth by decreasing IAA biosynthesis and affecting auxin distribution in the root tips, where reduced auxin accumulation and asymmetric auxin distribution were observed. UV-B radiation increased the distribution of auxin on the nonradiated side of the root tips, promoting growth and causing root bending. Further analysis indicated that UV-B induced an asymmetric accumulation of flavonoids; this pathway is involved in modulating the accumulation and asymmetric distribution of auxin in root tips and the subsequent redirection of root growth by altering the distribution of auxin carriers in response to UV-B radiation. Taken together, our results indicate that UV-B radiation-induced root bending occurred through a flavonoid-mediated phototropic response to UV-B radiation.

UV-B Radiation Induces Root Bending Through the Flavonoid-Mediated Auxin Pathway in Arabidopsis

PubMed Central

Wan, Jinpeng; Zhang, Ping; Wang, Ruling; Sun, Liangliang; Wang, Wenying; Zhou, Huakun; Xu, Jin

2018-01-01

Ultraviolet (UV)-B radiation-induced root bending has been reported; however, the underlying mechanisms largely remain unclear. Here, we investigate whether and how auxin and flavonoids are involved in UV-B radiation-induced root bending in Arabidopsis using physiological, pharmacological, and genetic approaches. UV-B radiation modulated the direction of root growth by decreasing IAA biosynthesis and affecting auxin distribution in the root tips, where reduced auxin accumulation and asymmetric auxin distribution were observed. UV-B radiation increased the distribution of auxin on the nonradiated side of the root tips, promoting growth and causing root bending. Further analysis indicated that UV-B induced an asymmetric accumulation of flavonoids; this pathway is involved in modulating the accumulation and asymmetric distribution of auxin in root tips and the subsequent redirection of root growth by altering the distribution of auxin carriers in response to UV-B radiation. Taken together, our results indicate that UV-B radiation-induced root bending occurred through a flavonoid-mediated phototropic response to UV-B radiation. PMID:29868074

Systemic control of cell division and endoreduplication by NAA and BAP by modulating CDKs in root tip cells of Allium cepa.

PubMed

Tank, Jigna G; Thaker, Vrinda S

2014-01-01

Molecular mechanism regulated by auxin and cytokinin during endoreduplication, cell division, and elongation process is studied by using Allium cepa roots as a model system. The activity of CDK genes modulated by auxin and cytokinin during cell division, elongation, and endoreduplication process is explained in this research work. To study the significance of auxin and cytokinin in the management of cell division and endoreduplication process in plant meristematic cells at molecular level endoreduplication was developed in root tips of Allium cepa by giving colchicine treatment. There were inhibition of vegetative growth, formation of c-tumor at root tip, and development of endoreduplicated cells after colchicine treatment. This c-tumor was further treated with NAA and BAP to reinitiate vegetative growth in roots. BAP gave positive response in reinitiation of vegetative growth of roots from center of c-tumor. However, NAA gave negative response in reinitiation of vegetative growth of roots from c-tumor. Further, CDKs gene expression analysis from normal, endoreduplicated, and phytohormone (NAA or BAP) treated root tip was done and remarkable changes in transcription level of CDK genes in normal, endoreduplicated, and phytohormones treated cells were observed.

Systemic Control of Cell Division and Endoreduplication by NAA and BAP by Modulating CDKs in Root Tip Cells of Allium cepa

PubMed Central

Tank, Jigna G.; Thaker, Vrinda S.

2014-01-01

Molecular mechanism regulated by auxin and cytokinin during endoreduplication, cell division, and elongation process is studied by using Allium cepa roots as a model system. The activity of CDK genes modulated by auxin and cytokinin during cell division, elongation, and endoreduplication process is explained in this research work. To study the significance of auxin and cytokinin in the management of cell division and endoreduplication process in plant meristematic cells at molecular level endoreduplication was developed in root tips of Allium cepa by giving colchicine treatment. There were inhibition of vegetative growth, formation of c-tumor at root tip, and development of endoreduplicated cells after colchicine treatment. This c-tumor was further treated with NAA and BAP to reinitiate vegetative growth in roots. BAP gave positive response in reinitiation of vegetative growth of roots from center of c-tumor. However, NAA gave negative response in reinitiation of vegetative growth of roots from c-tumor. Further, CDKs gene expression analysis from normal, endoreduplicated, and phytohormone (NAA or BAP) treated root tip was done and remarkable changes in transcription level of CDK genes in normal, endoreduplicated, and phytohormones treated cells were observed. PMID:24955358

Severely Reduced Gravitropism in Dark-Grown Hypocotyls of a Starch-Deficient Mutant of Nicotiana sylvestris1

PubMed Central

Kiss, John Z.; Sack, Fred D.

1990-01-01

Gravitropism in dark-grown hypocotyls of the wild type was compared with a starch-deficient Nicotiana sylvestris mutant (NS 458) to test the effects of starch deficiency on gravity sensing. In a time course of curvature measured using infrared video, the response of the mutant was greatly reduced compared to the wild type; 72 hours after reorientation, curvature was about 10° for NS 458 and about 70° for wild type. In dishes maintained in a vertical orientation, wild-type hypocotyls were predominantly vertical, whereas NS 458 hypocotyls were severely disoriented with about 5 times more orientational variability than wild type. Since the growth rates were equal for both genotypes and phototropic curvature was only slightly inhibited in NS 458, the mutation probably affects gravity perception rather than differential growth. Our data suggest that starch deficiency reduces gravitropic sensitivity more in dark-grown hypocotyls than in dark- or light-grown roots in this mutant and support the hypothesis that amyloplasts function as statoliths in shoots as well as roots. Images Figure 2 Figure 3 Figure 4 PMID:11537476

Severely reduced gravitropism in dark-grown hypocotyls of a starch-deficient mutant of Nicotiana sylvestris

NASA Technical Reports Server (NTRS)

Kiss, J. Z.; Sack, F. D.

1990-01-01

Gravitropism in dark-grown hypocotyls of the wild type was compared with a starch-deficient Nicotiana sylvestris mutant (NS 458) to test the effects of starch deficiency on gravity sensing. In a time course of curvature measured using infrared video, the response of the mutant was greatly reduced compared to the wild type; 72 hours after reorientation, curvature was about 10 degrees for NS 458 and about 70 degrees for wild type. In dishes maintained in a vertical orientation, wild-type hypocotyls were predominantly vertical, whereas NS 458 hypocotyls were severely disoriented with about 5 times more orientational variability than wild type. Since the growth rates were equal for both genotypes and phototropic curvature was only slightly inhibited in NS 458, the mutation probably affects gravity perception rather than differential growth. Our data suggest that starch deficiency reduces gravitropic sensitivity more in dark-grown hypocotyls than in dark- or light-grown roots in this mutant and support the hypothesis that amyloplasts function as statoliths in shoots as well as roots.

Regulation of H+ Extrusion and Cytoplasmic pH in Maize Root Tips Acclimated to a Low-Oxygen Environment.

PubMed

Xia, J. H.; Roberts, JKM.

1996-05-01

We tested the hypothesis that H+ extrusion contributes to cytoplasmic pH regulation and tolerance of anoxia in maize (Zea mays) root tips. We studied root tips of whole seedlings that were acclimated to a low-oxygen environment by pretreatment in 3% (v/v) O2. Acclimated root tips characteristically regulate cytoplasmic pH near neutrality and survive prolonged anoxia, whereas nonacclimated tips undergo severe cytoplasmic acidosis and die much more quickly. We show that the plasma membrane H+-ATPase can operate under anoxia and that net H+ extrusion increases when cytoplasmic pH falls. However, at an external pH near 6.0, H+ extrusion contributes little to cytoplasmic pH regulation. At more acidic external pH values, net H+ flux into root tips increases dramatically, leading to a decrease in cytoplasmic pH and reduced tolerance of anoxia. We present evidence that, under these conditions, H+ pumps are activated to partly offset acidosis due to H+ influx and, thereby, contribute to cytoplasmic pH regulation and tolerance of anoxia. The regulation of H+ extrusion under anoxia is discussed with respect to the acclimation response and mechanisms of intracellular pH regulation in aerobic plant cells.

Plant Roots: The Hidden Half. Chapter 16; Calcium and Gravitropism; Revised

NASA Technical Reports Server (NTRS)

Poovaiah, B. W.; Reedy, A. S. N.

1995-01-01

Environmental signals such as light and gravity control many aspects of plant growth and development. In higher plants, the directional growth of an organ in response to stimuli such as gravity and light is considered a tropic movement. Such movement could be either positive or negative with respect to a specific stimulus. In general, stems show a positive response to light and negative response to gravity. In contrast, most roots show a positive response to gravity and a negative response to light. Investigations on plant tropism date back a century when Darwin studied the phototropic responses of maize seedlings (Darwin). Although the precise mechanism of signal perception and transduction in roots is not understood, Darwin recognized over 100 years ago that the root cap is the probable site of signal perception. He discovered that the removal of the root cap eliminates the ability of roots to respond to gravity. Other investigators have since confirmed Darwin's observation (Konings; Evans et al.). In recent years, especially with the advent of the U.S. Space Program, there has been a renewed interest in understanding how plants respond to extracellular signals such as gravity (Halstead and Dutcher). Studies on the mechanisms involved in perception and transduction of gravity signal by roots would ultimately help us to better understand gravitropism and also to grow plants under microgravity conditions as in space. In this chapter, we restrict ourselves to the role of calcium in transduction of the gravity signal. In doing so, emphasis is given to the role of calcium-modulated proteins and their role in signal transduction in gravitropism. Detailed reviews on various other aspects of gravitropism (Scott, Torrey, Wilkins, Fim and Digby, Feldman, Pickard, Moore and Evans, Halstead and Dutcher, Poovaiah et al.) and on the role of calcium as a messenger in signal transduction in general have been published (Helper and Wayne, Poovaiah and Reddy, Roberts and Hartnon, Bowler and Chua, Gilroy and Trewavas). Plant roots have been widely used to study the transduction of gravity and light signals (Poovaiah et al., Roux and Serlin). Most roots show positive gravitropic response in either dark or light. However, roots of some varieties of plants (e.g., Zea mays L., cv Merit, and Zea rwvs L., cv Golden Cross Bantam 70) show positive gravitropic response only in light (Feldman, Miyazaki et al.). Investigations from various laboratories indicate that calcium acts as a messenger in transducing gravity and light signals in plant roots(Pickard, Evans et al., Pooviah et al.).

Gibberellin Biosynthesis in Developing Pumpkin Seedlings12

PubMed Central

Lange, Theo; Kappler, Jeannette; Fischer, Andreas; Frisse, Andrea; Padeffke, Tania; Schmidtke, Sabine; Lange, Maria João Pimenta

2005-01-01

A gibberellin (GA) biosynthetic pathway was discovered operating in root tips of 7-d-old pumpkin (Cucurbita maxima) seedlings. Stepwise analysis of GA metabolism in cell-free systems revealed the conversion of GA12-aldehyde to bioactive GA4 and inactive GA34. Highest levels of endogenous GA4 and GA34 were found in hypocotyls and root tips of 3-d-old seedlings. cDNA molecules encoding two GA oxidases, CmGA20ox3 and CmGA3ox3, were isolated from root tips of 7-d-old LAB150978-treated seedlings. Recombinant CmGA20ox3 fusion protein converted GA12 to GA9, GA24 to GA9, GA14 to GA4, and, less efficiently, GA53 to GA20, and recombinant CmGA3ox3 protein oxidized GA9 to GA4. Transcript profiles were determined for four GA oxidase genes from pumpkin revealing relatively high transcript levels for CmGA7ox in shoot tips and cotyledons, for CmGA20ox3 in shoot tips and hypocotyls, and for CmGA3ox3 in hypocotyls and roots of 3-d-old seedlings. Transcripts of CmGA2ox1 were mainly found in roots of 7-d-old seedlings. In roots of 7-d-old seedlings, transcripts of CmGA7ox, CmGA20ox3, and CmGA3ox3 were localized in the cap and the rhizodermis by in situ hybridization. We conclude that hypocotyls and root tips are important sites of GA biosynthesis in the developing pumpkin seedling. PMID:16126862

Effects of different types of tooth movement and force magnitudes on the amount of tooth movement and root resorption in rats.

PubMed

Nakano, Takako; Hotokezaka, Hitoshi; Hashimoto, Megumi; Sirisoontorn, Irin; Arita, Kotaro; Kurohama, Takeshi; Darendeliler, M Ali; Yoshida, Noriaki

2014-11-01

To investigate differences in the amount of tooth movement and root resorption that occurred after tipping and bodily movement of the maxillary first molar in rats. Ten-week-old female Wistar rats were divided into two groups according to type of tooth movement and subdivided into four subgroups according to the magnitude of applied force. Nickel-titanium closed-coil springs exerting forces of 10, 25, 50, or 100 g were applied to the maxillary left first molars to induce mesial tooth movement. We designed a novel orthodontic appliance for bodily tooth movement. Tooth movement distance and root resorption were measured using microcomputed tomography and scanning electron and scanning laser microscopy. The amount of tooth movement in the bodily tooth movement group was less than half that in the tipping tooth movement group. The greatest amount of tooth movement occurred in the 10-g tipping and 50-g bodily tooth movement subgroups, and the amount of tooth movement decreased with the application of an excessive magnitude of force. Conversely, root resorption increased when the heavier orthodontic force was applied in both groups. Root resorption in the tipping tooth movement group was approximately twice that in the bodily tooth movement group. Root resorption in the tipping tooth movement group was more pronounced than that in the bodily tooth movement group. Although the amount of tooth movement decreased when extremely heavy forces were applied, root resorption increased in both the tipping and bodily tooth movement groups in rats.

Microgravity

NASA Image and Video Library

1997-11-15

The Isothermal Dendritic Growth Experiment (IDGE), flown on three Space Shuttle missions, is yielding new insights into virtually all industrially relevant metal and alloy forming operations. IDGE used transparent organic liquids that form dendrites (treelike structures) similar to those inside metal alloys. Comparing Earth-based and space-based dendrite growth velocity, tip size and shape provides a better understanding of the fundamentals of dentritic growth, including gravity's effects. Shalowgraphic images of pivalic acid (PVA) dendrites forming from the melt show the subtle but distinct effects of gravity-driven heat convection on dentritic growth. In orbit, the dendrite grows as its latent heat is liberated by heat conduction. This yields a blunt dendrite tip. On Earth, heat is carried away by both conduction and gravity-driven convection. This yields a sharper dendrite tip. In addition, under terrestrial conditions, the sidebranches growing in the direction of gravity are augmented as gravity helps carry heat out of the way of the growing sidebranches as opposed to microgravity conditions where no augmentation takes place. IDGE was developed by Rensselaer Polytechnic Institute and NASA/Glenn Research Center. Advanced follow-on experiments are being developed for flight on the International Space Station. Photo Credit: NASA/Glenn Research Center

Mechanism of dynamic reorientation of cortical microtubules due to mechanical stress.

PubMed

Muratov, Alexander; Baulin, Vladimir A

2015-12-01

Directional growth caused by gravitropism and corresponding bending of plant cells has been explored since 19th century, however, many aspects of mechanisms underlying the perception of gravity at the molecular level are still not well known. Perception of gravity in root and shoot gravitropisms is usually attributed to gravisensitive cells, called statocytes, which exploit sedimentation of macroscopic and heavy organelles, amyloplasts, to sense the direction of gravity. Gravity stimulus is then transduced into distal elongation zone, which is several mm far from statocytes, where it causes stretching. It is suggested that gravity stimulus is conveyed by gradients in auxin flux. We propose a theoretical model that may explain how concentration gradients and/or stretching may indirectly affect the global orientation of cortical microtubules, attached to the cell membrane and induce their dynamic reorientation perpendicular to the gradients. In turn, oriented microtubule arrays direct the growth and orientation of cellulose microfibrils, forming part of the cell external skeleton and determine the shape of the cell. Reorientation of microtubules is also observed in reaction to light in phototropism and mechanical bending, thus suggesting universality of the proposed mechanism. Copyright © 2015 Elsevier B.V. All rights reserved.

Statolith positioning by microfilaments in Chara rhizoids and protonemata

NASA Astrophysics Data System (ADS)

Hodick, Dieter; Buchen, Brigitte; Sievers, Andreas

The rhizoids of the green alga Chara are tip-growing cells with a precise positive gravitropism. In rhizoids growing downwards the statoliths never sediment upon the cell wall at the very tip but keep a minimal distance of approximately 10 μm from the cell vertex. It has been argued that this position is attained by a force acting upon the statoliths in the basal direction and that this force is generated by an interaction between actin microfilaments and myosin on the statolith membrane. This hypothesis received experimental support from (1) effects of the actin-attacking drug cytochalasin, (2) experiments under microgravity conditions, and (3) clinostat experiments. Using video-microscopy it is now shown that this basipetal force also acts on statoliths during sedimentation. As a result, many statoliths in Chara rhizoids do not simply fall along the plumb line while sedimenting during gravistimulation, but move basipetally. This statolith movement is compared to the ones occurring in the unicellular Chara protonemata during gravistimulation. Dark-grown protonemata morphologically closely resemble the rhizoids but respond negatively gravitropic. In contrast to the rhizoids a gravistimulation of the protonemata induces a transport of statoliths towards the tip. This transport is mainly along the cell axis and not parallel to the gravity vector. It is stressed that the sedimentation of statoliths in Chara rhizoids and protonemata as well as in gravity sensing cells in mosses and higher plants is accompanied by statolith movements based on interactions with the cytoskeleton. In tip-growing cells these movements direct the statoliths to a definite region of the cell where they can sediment and elicit a gravitropic curvature. In the statocytes of higher plants the interactions of the statoliths with the cytoskeleton probably do not serve primarily to move the statoliths but to transduce mechanical stresses from the sedimenting statoliths to the plasma membrane.

Statolith positioning by microfilaments in Chara rhizoids and protonemata.

PubMed

Hodick, D; Buchen, B; Sievers, A

1998-01-01

The rhizoids of the green alga Chara are tip-growing cells with a precise positive gravitropism. In rhizoids growing downwards the statoliths never sediment upon the cell wall at the very tip but keep a minimal distance of approximately 10 micrometers from the cell vertex. It has been argued that this position is attained by a force acting upon the statoliths in the basal direction and that this force is generated by an interaction between actin microfilaments and myosin on the statolith membrane. This hypothesis received experimental support from (1) effects of the actin-attacking drug cytochalasin, (2) experiments under microgravity conditions, and (3) clinostat experiments. Using video-microscopy it is now shown that this basipetal force also acts on statoliths during sedimentation. As a result, many statoliths in Chara rhizoids do not simply fall along the plumb line while sedimenting during gravistimulation, but move basipetally. This statolith movement is compared to the ones occurring in the unicellular Chara protonemata during gravistimulation. Dark-grown protonemata morphologically closely resemble the rhizoids but respond negatively gravitropic. In contrast to the rhizoids a gravistimulation of the protonemata induces a transport of statoliths towards the tip. This transport is mainly along the cell axis and not parallel to the gravity vector. It is stressed that the sedimentation of statoliths in Chara rhizoids and protonemata as well as in gravity sensing cells in mosses and higher plants is accompanied by statolith movements based on interactions with the cytoskeleton. In tip-growing cells these movements direct the statoliths to a definite region of the cell where they can sediment and elicit a gravitropic curvature. In the statocytes of higher plants the interactions of the statoliths with the cytoskeleton probably do not serve primarily to move the statoliths but to transduce mechanical stresses from the sedimenting statoliths to the plasma membrane.

How roots perceive and respond to gravity

NASA Technical Reports Server (NTRS)

Moore, R.; Evans, M. L.

1986-01-01

Graviperception by plant roots is believed to occur via the sedimentation of amyloplasts in columella cells of the root cap. This physical stimulus results in an accumulation of calcium on the lower side of the cap, which in turn induces gravicurvature. In this paper we present a model for root gravitropism integrating gravity-induced changes in electrical potential, cytochemical localization of calcium in cells of gravistimulated roots, and the interdependence of calcium and auxin movement. Key features of the model are that 1) gravity-induced redistribution of calcium is an early event in the transduction mechanism, and 2) apoplastic movement of calcium through the root-cap mucilage may be an important component of the pathway for calcium movement.

Tip cell-specific requirement for an atypical Gpr124- and Reck-dependent Wnt/β-catenin pathway during brain angiogenesis

PubMed Central

Vanhollebeke, Benoit; Stone, Oliver A; Bostaille, Naguissa; Cho, Chris; Zhou, Yulian; Maquet, Emilie; Gauquier, Anne; Cabochette, Pauline; Fukuhara, Shigetomo; Mochizuki, Naoki; Nathans, Jeremy; Stainier, Didier YR

2015-01-01

Despite the critical role of endothelial Wnt/β-catenin signaling during central nervous system (CNS) vascularization, how endothelial cells sense and respond to specific Wnt ligands and what aspects of the multistep process of intra-cerebral blood vessel morphogenesis are controlled by these angiogenic signals remain poorly understood. We addressed these questions at single-cell resolution in zebrafish embryos. We identify the GPI-anchored MMP inhibitor Reck and the adhesion GPCR Gpr124 as integral components of a Wnt7a/Wnt7b-specific signaling complex required for brain angiogenesis and dorsal root ganglia neurogenesis. We further show that this atypical Wnt/β-catenin signaling pathway selectively controls endothelial tip cell function and hence, that mosaic restoration of single wild-type tip cells in Wnt/β-catenin-deficient perineural vessels is sufficient to initiate the formation of CNS vessels. Our results identify molecular determinants of ligand specificity of Wnt/β-catenin signaling and provide evidence for organ-specific control of vascular invasion through tight modulation of tip cell function. DOI: http://dx.doi.org/10.7554/eLife.06489.001 PMID:26051822

Seeking the Light: Gravity Without the Influence of Gravity

NASA Technical Reports Server (NTRS)

Sack, Fred; Kern, Volker; Reed, Dave; Etheridge, Guy (Technical Monitor)

2002-01-01

All living things sense gravity like humans might sense light or sound. The Biological Research In Canisters (BRIC-14) experiment, explores how moss cells sense and respond to gravity and light. This experiment studies how gravity influences the internal structure of moss cells and seeks to understand the influences of the spaceflight environment on cell growth. This knowledge will help researchers understand the role of gravity in the evolution of cells and life on earth.

Abscisic Acid Stimulates Elongation of Excised Pea Root Tips

PubMed Central

Gaither, Douglas H.; Lutz, Donald H.; Forrence, Leonard E.

1975-01-01

Excised Pisum sativum L. root tips were incubated in a pH 5.2 sucrose medium containing abscisic acid. Elongation growth was inhibited by 100 μm abscisic acid. However, decreasing the abscisic acid concentration caused stimulation of elongation, the maximum response (25% to 30%) occurring at 1 μm abscisic acid. Prior to two hours, stimulation of elongation by 1 μm abscisic acid was not detectable. Increased elongation did not occur in abscisic acid-treated root tips of Lens culinaris L., Phaseolus vulgaris L., or Zea mays L. PMID:16659198

Auxin increases the hydrogen peroxide (H2O2) concentration in tomato (Solanum lycopersicum) root tips while inhibiting root growth

PubMed Central

Ivanchenko, Maria G.; den Os, Désirée; Monshausen, Gabriele B.; Dubrovsky, Joseph G.; Bednářová, Andrea; Krishnan, Natraj

2013-01-01

Background and Aims The hormone auxin and reactive oxygen species (ROS) regulate root elongation, but the interactions between the two pathways are not well understood. The aim of this study was to investigate how auxin interacts with ROS in regulating root elongation in tomato, Solanum lycopersicum. Methods Wild-type and auxin-resistant mutant, diageotropica (dgt), of tomato (S. lycopersicum ‘Ailsa Craig’) were characterized in terms of root apical meristem and elongation zone histology, expression of the cell-cycle marker gene Sl-CycB1;1, accumulation of ROS, response to auxin and hydrogen peroxide (H2O2), and expression of ROS-related mRNAs. Key Results The dgt mutant exhibited histological defects in the root apical meristem and elongation zone and displayed a constitutively increased level of hydrogen peroxide (H2O2) in the root tip, part of which was detected in the apoplast. Treatments of wild-type with auxin increased the H2O2 concentration in the root tip in a dose-dependent manner. Auxin and H2O2 elicited similar inhibition of cell elongation while bringing forth differential responses in terms of meristem length and number of cells in the elongation zone. Auxin treatments affected the expression of mRNAs of ROS-scavenging enzymes and less significantly mRNAs related to antioxidant level. The dgt mutation resulted in resistance to both auxin and H2O2 and affected profoundly the expression of mRNAs related to antioxidant level. Conclusions The results indicate that auxin regulates the level of H2O2 in the root tip, so increasing the auxin level triggers accumulation of H2O2 leading to inhibition of root cell elongation and root growth. The dgt mutation affects this pathway by reducing the auxin responsiveness of tissues and by disrupting the H2O2 homeostasis in the root tip. PMID:23965615

Changes in the Expression and the Enzymic Properties of the 20S Proteasome in Sugar-Starved Maize Roots. Evidence for an in Vivo Oxidation of the Proteasome1

PubMed Central

Basset , Gilles; Raymond, Philippe; Malek, Lada; Brouquisse, Renaud

2002-01-01

The 20S proteasome (multicatalytic proteinase) was purified from maize (Zea mays L. cv DEA 1992) roots through a five-step procedure. After biochemical characterization, it was shown to be similar to most eukaryotic proteasomes. We investigated the involvement of the 20S proteasome in the response to carbon starvation in excised maize root tips. Using polyclonal antibodies, we showed that the amount of proteasome increased in 24-h-carbon-starved root tips compared with freshly excised tips, whereas the mRNA levels of α3 and β6 subunits of 20S proteasome decreased. Moreover, in carbon-starved tissues, chymotrypsin-like and caseinolytic activities of the 20S proteasome were found to increase, whereas trypsin-like activities decreased. The measurement of specific activities and kinetic parameters of 20S proteasome purified from 24-h-starved root tips suggested that it was subjected to posttranslational modifications. Using dinitrophenylhydrazine, a carbonyl-specific reagent, we observed an increase in carbonyl residues in 20S proteasome purified from starved root tips. This means that 20S proteasome was oxidized during starvation treatment. Moreover, an in vitro mild oxidative treatment of 20S proteasome from non-starved material resulted in the activation of chymotrypsin-like, peptidyl-glutamyl-peptide hydrolase and caseinolytic-specific activities and in the inhibition of trypsin-like specific activities, similar to that observed for proteasome from starved root tips. Our results provide the first evidence, to our knowledge, for an in vivo carbonylation of the 20S proteasome. They suggest that sugar deprivation induces an oxidative stress, and that oxidized 20S proteasome could be associated to the degradation of oxidatively damaged proteins in carbon starvation situations. PMID:11891269

Alleviation effect of alginate-derived oligosaccharides on Vicia faba root tip cells damaged by cadmium.

PubMed

Ma, L J; Zhang, Y; Bu, N; Wang, S H

2010-02-01

Cadmium has been shown to prevent Vicia faba growth by inhibiting cell mitosis. In this study we investigated the role of Alginate-derived Oligosaccharides (ADO) in alleviating Vicia faba root tip cells damaged by 6 and 8 mg L(-1) CdCl2. Micronucleus assay and chromosomal aberration assay were used to determine mitotic index, micronucleus frequency and chromosomal aberration frequency. The results showed that micronucleus frequency of Vicia faba root tip cells was inhibited under all the ADO concentrations. Especially, the inhibition ratio of 0.125% ADO highly reached 66.11 and 67.17% in 6 and 8 mg L(-1) CdCl2, respectively. Furthermore, the mitotic index increased (p < 0.05) and chromosomal aberration frequency decreased (p < 0.05) under all the ADO concentrations. This indicated that ADO had a significant alleviation effect on Vicia faba root tip cells damaged by cadmium.

GraPhoBox: Gravitropism and phototropism in Arabidopsis thaliana

NASA Astrophysics Data System (ADS)

Buizer, K.

2007-09-01

The morphology of plants is directed by the directional growth of roots and shoots. Gravity and light direction are the two major environmental stimuli important for directional growth. The 'GraPhoBox' experiment, flown on the Dutch DELTA mission to the ISS in April 2004, tries to elucidate the different effects of gravitropism and phototropism on plants, and their combined effects on plant morphology. Wild-type Arabidopsis thaliana (L.), phototropic-deficient mutants phot1 and gravitropic-deficient mutant pgm1 seeds were germinated in microgravity and in Earth gravity, in low light conditions and darkness. The angle of directional growth of roots and shoots was then assessed. Light is -even in the absense of gravity- the most important environmental cue for directional growth of shoots, while for roots gravity is by far the most important cue, and light is only a very minor factor due to their poor phototropic capacity. Compared to roots, shoots are deviated more than roots in microgravity and therefore less gravity-dependent. All results together suggests that environmental cues are differently percepted by roots and shoots which also adapt differently. Furthermore, environmental cues are probably transferred little or not to the opposite side of the plant.

Gravity-regulated differential auxin transport from columella to lateral root cap cells

NASA Technical Reports Server (NTRS)

Ottenschlager, Iris; Wolff, Patricia; Wolverton, Chris; Bhalerao, Rishikesh P.; Sandberg, Goran; Ishikawa, Hideo; Evans, Mike; Palme, Klaus

2003-01-01

Gravity-induced root curvature has long been considered to be regulated by differential distribution of the plant hormone auxin. However, the cells establishing these gradients, and the transport mechanisms involved, remain to be identified. Here, we describe a GFP-based auxin biosensor to monitor auxin during Arabidopsis root gravitropism at cellular resolution. We identify elevated auxin levels at the root apex in columella cells, the site of gravity perception, and an asymmetric auxin flux from these cells to the lateral root cap (LRC) and toward the elongation zone after gravistimulation. We differentiate between an efflux-dependent lateral auxin transport from columella to LRC cells, and an efflux- and influx-dependent basipetal transport from the LRC to the elongation zone. We further demonstrate that endogenous gravitropic auxin gradients develop even in the presence of an exogenous source of auxin. Live-cell auxin imaging provides unprecedented insights into gravity-regulated auxin flux at cellular resolution, and strongly suggests that this flux is a prerequisite for root gravitropism.

Actin polymerization drives polar growth in Arabidopsis root hair cells.

PubMed

Vazquez, Luis Alfredo Bañuelos; Sanchez, Rosana; Hernandez-Barrera, Alejandra; Zepeda-Jazo, Isaac; Sánchez, Federico; Quinto, Carmen; Torres, Luis Cárdenas

2014-01-01

In plants, the actin cytoskeleton is a prime regulator of cell polarity, growth, and cytoplasmic streaming. Tip growth, as observed in root hairs, caulonema, and pollen tubes, is governed by many factors, including calcium gradients, exocytosis and endocytosis, reactive oxygen species, and the cytoskeleton. Several studies indicate that the polymerization of G-actin into F-actin also contributes to tip growth. The structure and function of F-actin within the apical dome is variable, ranging from a dense meshwork to sparse single filaments. The presence of multiple F-actin structures in the elongating apices of tip-growing cells suggests that this cytoskeletal array is tightly regulated. We recently reported that sublethal concentrations of fluorescently labeled cytochalasin could be used to visualize the distribution of microfilament plus ends using fluorescence microscopy, and found that the tip region of the growing root hair cells of a legume plant exhibits a clear response to the nodulation factors secreted by Rhizobium. (1) In this current work, we expanded our analysis using confocal microscopy and demonstrated the existence of highly dynamic fluorescent foci along Arabidopsis root hair cells. Furthermore, we show that the strongest fluorescence signal accumulates in the tip dome of the growing root hair and seems to be in close proximity to the apical plasma membrane. Based on these findings, we propose that actin polymerization within the dome of growing root hair cells regulates polar growth.

Calcium-Dependent Protein Kinase Genes in Corn Roots

NASA Technical Reports Server (NTRS)

Takezawa, D.; Patil, S.; Bhatia, A.; Poovaiah, B. W.

1996-01-01

Two cDNAs encoding Ca-2(+) - Dependent Protein Kinases (CDPKs), Corn Root Protein Kinase 1 and 2 (CRPK 1, CRPK 2) were isolated from the root tip library of corn (Zea mays L., cv. Merit) and their nucleotide sequences were determined. Deduced amino acid sequences of both the clones have features characteristic of plant CDPKS, including all 11 conserved serine/threonine kinase subdomains, a junction domain and a calmodulin-like domain with four Ca-2(+), -binding sites. Northern analysis revealed that CRPKI mRNA is preferentially expressed in roots, especially in the root tip; whereas, the expression of CRPK2 mRNA was very low in all the tissues tested. In situ hybridization experiments revealed that CRPKI mRNA is highly expressed in the root apex, as compared to other parts of the root. Partially purified CDPK from the root tip phosphorylates syntide-2, a common peptide substrate for plant CDPKs, and the phosphorylation was stimulated 7-fold by the addition of Ca-2(+). Our results show that two CDPK isoforms are expressed in corn roots and they may be involved in the Ca-2(+)-dependent signal transduction process.

Changes in the proteomic and metabolic profiles of Beta vulgaris root tips in response to iron deficiency and resupply

PubMed Central

2010-01-01

Background Plants grown under iron deficiency show different morphological, biochemical and physiological changes. These changes include, among others, the elicitation of different strategies to improve the acquisition of Fe from the rhizosphere, the adjustment of Fe homeostasis processes and a reorganization of carbohydrate metabolism. The application of modern techniques that allow the simultaneous and untargeted analysis of multiple proteins and metabolites can provide insight into multiple processes taking place in plants under Fe deficiency. The objective of this study was to characterize the changes induced in the root tip proteome and metabolome of sugar beet plants in response to Fe deficiency and resupply. Results Root tip extract proteome maps were obtained by 2-D isoelectric focusing polyacrylamide gel electrophoresis, and approximately 140 spots were detected. Iron deficiency resulted in changes in the relative amounts of 61 polypeptides, and 22 of them were identified by mass spectrometry (MS). Metabolites in root tip extracts were analyzed by gas chromatography-MS, and more than 300 metabolites were resolved. Out of 77 identified metabolites, 26 changed significantly with Fe deficiency. Iron deficiency induced increases in the relative amounts of proteins and metabolites associated to glycolysis, tri-carboxylic acid cycle and anaerobic respiration, confirming previous studies. Furthermore, a protein not present in Fe-sufficient roots, dimethyl-8-ribityllumazine (DMRL) synthase, was present in high amounts in root tips from Fe-deficient sugar beet plants and gene transcript levels were higher in Fe-deficient root tips. Also, a marked increase in the relative amounts of the raffinose family of oligosaccharides (RFOs) was observed in Fe-deficient plants, and a further increase in these compounds occurred upon short term Fe resupply. Conclusions The increases in DMRL synthase and in RFO sugars were the major changes induced by Fe deficiency and resupply in root tips of sugar beet plants. Flavin synthesis could be involved in Fe uptake, whereas RFO sugars could be involved in the alleviation of oxidative stress, C trafficking or cell signalling. Our data also confirm the increase in proteins and metabolites related to carbohydrate metabolism and TCA cycle pathways. PMID:20565974

Magnet pole tips

DOEpatents

Thorn, Craig E.; Chasman, Chellis; Baltz, Anthony J.

1984-04-24

An improved magnet which more easily provides a radially increasing magnetic field, as well as reduced fringe field and requires less power for a given field intensity. The subject invention comprises a pair of spaced, opposed magnetic poles which further comprise a pair of pole roots, each having a pole tip attached to its center. The pole tips define the gap between the magnetic poles and at least a portion of each pole tip is separated from its associated pole root. The separation begins at a predetermined distance from the center of the pole root and increases with increasing radial distance while being constant with azimuth within that portion. Magnets in accordance with the subject invention have been found to be particularly advantageous for use in large isochronous cyclotrons.

Magnet pole tips

DOEpatents

Thorn, C.E.; Chasman, C.; Baltz, A.J.

1981-11-19

An improved magnet more easily provides a radially increasing magnetic field, as well as reduced fringe field and requires less power for a given field intensity. The subject invention comprises a pair of spaced, opposed magnetic poles which further comprise a pair of pole roots, each having a pole tip attached to its center. The pole tips define the gap between the magnetic poles and at least a portion of each pole tip is separated from its associated pole root. The separation begins at a predetermined distance from the center of the pole root and increases with increasing radial distance while being constant with azimuth within that portion. Magnets in accordance with the subject invention have been found to be particularly advantageous for use in large isochronous cyclotrons.

Calcium ion dependency of ethylene production in segments of primary roots of Zea mays

NASA Technical Reports Server (NTRS)

Hasenstein, K. H.; Evans, M. L.

1986-01-01

We investigated the effect of Ca2+ on ethylene production in 2-cm long apical segments from primary roots of corn (Zea mays L., B73 x Missouri 17) seedlings. The seedlings were raised under different conditions of Ca2+ availability. Low-Ca and high-Ca seedlings were raised by soaking the grains and watering the seedlings with distilled water or 10 mM CaCl2, respectively. Segments from high-Ca roots produced more than twice as much ethylene as segments from low-Ca roots. Indoleacetic acid (IAA; 1 micromole) enhanced ethylene production in segments from both low-Ca and high-Ca roots but auxin-induced promotion of ethylene production was consistently higher in segments from high-Ca roots. Addition of 1-aminocyclopropane-1-carboxylic acid (ACC) to root segments from low-Ca seedlings doubled total ethylene production and the rate of production remained fairly constant during a 24 h period of monitoring. In segments from high-Ca seedlings ACC also increased total ethylene production but most of the ethylene was produced within the first 6 h. The data suggest that Ca2+ enhances the conversion of ACC to ethylene. The terminal 2 mm of the root tip were found to be especially important to ethylene biosynthesis by apical segments and, experiments using 45Ca2+ as tracer indicated that the apical 2 mm of the root is the region of strongest Ca2+ accumulation. Other cations such as Mn2+, Mg2+, and K+ could largely substitute for Ca2+. The significance of these findings is discussed with respect to recent evidence for gravity-induced Ca2+ redistribution and its relationship to the establishment of asymmetric growth during gravitropic curvature.

Adenosine kinase modulates root gravitropism and cap morphogenesis in Arabidopsis.

PubMed

Young, Li-Sen; Harrison, Benjamin R; Narayana Murthy, U M; Moffatt, Barbara A; Gilroy, Simon; Masson, Patrick H

2006-10-01

Adenosine kinase (ADK) is a key enzyme that regulates intra- and extracellular levels of adenosine, thereby modulating methyltransferase reactions, production of polyamines and secondary compounds, and cell signaling in animals. Unfortunately, little is known about ADK's contribution to the regulation of plant growth and development. Here, we show that ADK is a modulator of root cap morphogenesis and gravitropism. Upon gravistimulation, soluble ADK levels and activity increase in the root tip. Mutation in one of two Arabidopsis (Arabidopsis thaliana) ADK genes, ADK1, results in cap morphogenesis defects, along with alterations in root sensitivity to gravistimulation and slower kinetics of root gravitropic curvature. The kinetics defect can be partially rescued by adding spermine to the growth medium, whereas the defects in cap morphogenesis and gravitropic sensitivity cannot. The root morphogenesis and gravitropism defects of adk1-1 are accompanied by altered expression of the PIN3 auxin efflux facilitator in the cap and decreased expression of the auxin-responsive DR5-GUS reporter. Furthermore, PIN3 fails to relocalize to the bottom membrane of statocytes upon gravistimulation. Consequently, adk1-1 roots cannot develop a lateral auxin gradient across the cap, necessary for the curvature response. Interestingly, adk1-1 does not affect gravity-induced cytoplasmic alkalinization of the root statocytes, suggesting either that ADK1 functions between cytoplasmic alkalinization and PIN3 relocalization in a linear pathway or that the pH and PIN3-relocalization responses to gravistimulation belong to distinct branches of the pathway. Our data are consistent with a role for ADK and the S-adenosyl-L-methionine pathway in the control of root gravitropism and cap morphogenesis.

Adenosine Kinase Modulates Root Gravitropism and Cap Morphogenesis in Arabidopsis1[W][OA

PubMed Central

Young, Li-Sen; Harrison, Benjamin R.; U.M., Narayana Murthy; Moffatt, Barbara A.; Gilroy, Simon; Masson, Patrick H.

2006-01-01

Adenosine kinase (ADK) is a key enzyme that regulates intra- and extracellular levels of adenosine, thereby modulating methyltransferase reactions, production of polyamines and secondary compounds, and cell signaling in animals. Unfortunately, little is known about ADK's contribution to the regulation of plant growth and development. Here, we show that ADK is a modulator of root cap morphogenesis and gravitropism. Upon gravistimulation, soluble ADK levels and activity increase in the root tip. Mutation in one of two Arabidopsis (Arabidopsis thaliana) ADK genes, ADK1, results in cap morphogenesis defects, along with alterations in root sensitivity to gravistimulation and slower kinetics of root gravitropic curvature. The kinetics defect can be partially rescued by adding spermine to the growth medium, whereas the defects in cap morphogenesis and gravitropic sensitivity cannot. The root morphogenesis and gravitropism defects of adk1-1 are accompanied by altered expression of the PIN3 auxin efflux facilitator in the cap and decreased expression of the auxin-responsive DR5-GUS reporter. Furthermore, PIN3 fails to relocalize to the bottom membrane of statocytes upon gravistimulation. Consequently, adk1-1 roots cannot develop a lateral auxin gradient across the cap, necessary for the curvature response. Interestingly, adk1-1 does not affect gravity-induced cytoplasmic alkalinization of the root statocytes, suggesting either that ADK1 functions between cytoplasmic alkalinization and PIN3 relocalization in a linear pathway or that the pH and PIN3-relocalization responses to gravistimulation belong to distinct branches of the pathway. Our data are consistent with a role for ADK and the S-adenosyl-l-methionine pathway in the control of root gravitropism and cap morphogenesis. PMID:16891550

A novel blue-light phototropic response is revealed in roots of Arabidopsis thaliana in microgravity.

PubMed

Vandenbrink, Joshua P; Herranz, Raul; Medina, F Javier; Edelmann, Richard E; Kiss, John Z

2016-12-01

Blue-light positive phototropism in roots is masked by gravity and revealed in conditions of microgravity. In addition, the magnitude of red-light positive phototropic curvature is correlated to the magnitude of gravity. Due to their sessile nature, plants utilize environmental cues to grow and respond to their surroundings. Two of these cues, light and gravity, play a substantial role in plant orientation and directed growth movements (tropisms). However, very little is currently known about the interaction between light- (phototropic) and gravity (gravitropic)-mediated growth responses. Utilizing the European Modular Cultivation System on board the International Space Station, we investigated the interaction between phototropic and gravitropic responses in three Arabidopsis thaliana genotypes, Landsberg wild type, as well as mutants of phytochrome A and phytochrome B. Onboard centrifuges were used to create a fractional gravity gradient ranging from reduced gravity up to 1g. A novel positive blue-light phototropic response of roots was observed during conditions of microgravity, and this response was attenuated at 0.1g. In addition, a red-light pretreatment of plants enhanced the magnitude of positive phototropic curvature of roots in response to blue illumination. In addition, a positive phototropic response of roots was observed when exposed to red light, and a decrease in response was gradual and correlated with the increase in gravity. The positive red-light phototropic curvature of hypocotyls when exposed to red light was also confirmed. Both red-light and blue-light phototropic responses were also shown to be affected by directional light intensity. To our knowledge, this is the first characterization of a positive blue-light phototropic response in Arabidopsis roots, as well as the first description of the relationship between these phototropic responses in fractional or reduced gravities.

A novel blue-light phototropic response is revealed in roots of Arabidopsis thaliana in microgravity

PubMed Central

Vandenbrink, Joshua P.; Herranz, Raul; Medina, F. Javier; Edelmann, Richard E.

2017-01-01

Main conclusion Blue-light positive phototropism in roots is masked by gravity and revealed in conditions of microgravity. In addition, the magnitude of red-light positive phototropic curvature is correlated to the magnitude of gravity. Due to their sessile nature, plants utilize environmental cues to grow and respond to their surroundings. Two of these cues, light and gravity, play a substantial role in plant orientation and directed growth movements (tropisms). However, very little is currently known about the interaction between light- (phototropic) and gravity (gravitropic)-mediated growth responses. Utilizing the European Modular Cultivation System on board the International Space Station, we investigated the interaction between phototropic and gravitropic responses in three Arabidopsis thaliana genotypes, Landsberg wild type, as well as mutants of phytochrome A and phytochrome B. Onboard centrifuges were used to create a fractional gravity gradient ranging from reduced gravity up to 1g. A novel positive blue-light phototropic response of roots was observed during conditions of microgravity, and this response was attenuated at 0.1g. In addition, a red-light pretreatment of plants enhanced the magnitude of positive phototropic curvature of roots in response to blue illumination. In addition, a positive phototropic response of roots was observed when exposed to red light, and a decrease in response was gradual and correlated with the increase in gravity. The positive red-light phototropic curvature of hypocotyls when exposed to red light was also confirmed. Both red-light and blue-light phototropic responses were also shown to be affected by directional light intensity. To our knowledge, this is the first characterization of a positive blue-light phototropic response in Arabidopsis roots, as well as the first description of the relationship between these phototropic responses in fractional or reduced gravities. PMID:27507239

Gravitropism in lateral roots of Arabidopsis pgm-1 mutants is indistinguishable from that of wild-type

PubMed Central

Bai, Hanwen

2011-01-01

The majority of understanding of root gravity responses comes from the study of primary roots, even though lateral roots make a far greater contribution to root system architecture. The focus of this report is the analysis of gravitropic responses in lateral roots of wild-type background and pgm-1 mutants. Despite the significant reduction in gravitropic response of primary roots of pgm-1 mutants, the lateral roots of this mutant demonstrate wild-type rates of gravitropism, suggesting a significant difference in gravity signal transduction between primary and lateral roots. PMID:21921698

Gravitropism in lateral roots of Arabidopsis pgm-1 mutants is indistinguishable from that of wild-type.

PubMed

Bai, Hanwen; Wolverton, Chris

2011-10-01

The majority of understanding of root gravity responses comes from the study of primary roots, even though lateral roots make a far greater contribution to root system architecture. The focus of this report is the analysis of gravitropic responses in lateral roots of wild-type background and pgm-1 mutants. Despite the significant reduction in gravitropic response of primary roots of pgm-1 mutants, the lateral roots of this mutant demonstrate wild-type rates of gravitropism, suggesting a significant difference in gravity signal transduction between primary and lateral roots.

Nitric Oxide Is Associated with Long-Term Zinc Tolerance in Solanum nigrum1[W

PubMed Central

Xu, Jin; Yin, Hengxia; Li, Yulong; Liu, Xiaojing

2010-01-01

Nitric oxide (NO) has been identified as a signal molecule that interplays with reactive oxygen species in response to heavy metal stresses. Roles of NO in regulating cadmium toxicity and iron deficiency have been proposed; however, the function of NO in zinc (Zn) tolerance in plants remains unclear. Here, we investigated NO accumulation and its role in plant Zn tolerance. Zn-induced NO production promoted an increase in reactive oxygen species accumulation in Solanum nigrum roots by modulating the expression and activity of antioxidative enzymes. Subsequently, programmed cell death (PCD) was observed in primary root tips. Inhibiting NO accumulation by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (a specific NO scavenger) or NG-nitro-l-arginine-methyl ester (a NO synthase inhibitor) prevented the increase of superoxide radical and hydrogen peroxide as well as the subsequent cell death in the root tips, supporting the role of NO in Zn-induced PCD in the root tips. Zn-induced NO production affected the length of primary roots, the number of lateral roots, and root hair growth and thereby modulated root system architecture and activity. Investigation of metal contents in Zn-treated roots suggests that NO is required for metal (especially iron) uptake and homeostasis in plants exposed to excess Zn. Taken together, our results indicate that NO production and the subsequent PCD in root tips exposed to excess Zn are favorable for the S. nigrum seedling response to long-term Zn toxicity by modulating root system architecture and subsequent adaptation to Zn stress. PMID:20855519

Rhodamine B induces long nucleoplasmic bridges and other nuclear anomalies in Allium cepa root tip cells.

PubMed

Tan, Dehong; Bai, Bing; Jiang, Donghua; Shi, Lin; Cheng, Shunchang; Tao, Dongbing; Ji, Shujuan

2014-03-01

The cytogenetic toxicity of rhodamine B on root tip cells of Allium cepa was investigated. A. cepa were cultured in water (negative control), 10 ppm methyl methanesulfonate (positive control), and three concentrations of rhodamine B (200, 100, and 50 ppm) for 7 days. Rhodamine B inhibited mitotic activity; increased nuclear anomalies, including micronuclei, nuclear buds, and bridged nuclei; and induced oxidative stress in A. cepa root tissues. Furthermore, a substantial amount of long nucleoplasmic bridges were entangled together, and some nuclei were simultaneously linked to several other nuclei and to nuclear buds with nucleoplasmic bridges in rhodamine B-treated cells. In conclusion, rhodamine B induced cytogenetic effects in A. cepa root tip cells, which suggests that the A. cepa root is an ideal model system for detecting cellular interactions.

Effects of Mg{sup 2+}, Co{sup 2+}, and Hg{sup 2+} on the nucleus and nucleolus in root tip cells of allium cepa

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

Liu, D.; Jiang, W.; Wang, W.

Metal toxicity in plants has been known for a long time. Much importance has increasingly been attached to the problems of metal pollution with the development of modern industry and agriculture. If metals in plants are accumulated to a large extent, it might seriously affect them. The cytological effects of cobalt and mercury have been studied in Allium cepa by documentation of c-mitosis. Also, the quantification of chromosome aberration in Vicia faba root-tip cells treated by magnesium sulphate and in Allium cepa by metyl mercury chloride and mercuric chloride has been reported. Cytological research on the poisoning effects of Mg,more » Co and Hg on the nuclei and nucleoli in root-tip cells of plants has hardly been reported. The aim of this study was to determine the effects of different concentrations of magnesium, cobalt and mercury ions on root growth, and on the nuclei and nucleoli of root tip cells of Allium-cepa. 20 refs., 3 figs.« less

Control of gravitropic orientation. I. Non-vertical orientation by primary roots of maize results from decay of competence for orthogravitropic induction

NASA Technical Reports Server (NTRS)

LaMotte, Clifford E.; Pickard, Barbara G.

2004-01-01

Plant organs may respond to gravity by vertical (orthogravitropic), oblique (plagiogravitropic) or horizontal (diagravitropic) growth. Primary roots of maize (Zea mays L.) provide a good system for studying such behaviours because they are reportedly capable of displaying all three responses. In current work using maize seedlings of the Silver Queen cultivar, stabilisation of growth at an oblique orientation was commonplace. Hypothetically, plagiogravitropism may be accomplished either by a process we call graded orthogravitropism or by hunting about a sensed non-vertical setpoint. In graded orthotropism primary bending is unidirectional and depends on facilitative stimuli that determine its extent. The hallmark of the setpoint mechanism is restorative curvature of either sign following a displacement; both diagravitropism and orthogravitropism are based on setpoints. Roots settled in a plagiogravitropic orientation were tested with various illumination and displacement protocols designed to distinguish between these two hypotheses. The tests refuted the setpoint hypothesis and supported that of graded orthotropism. No evidence of diagravitropism could be found, thus, earlier claims were likely based on inadequately controlled observations of graded orthotropism. We propose that orthotropism is graded by the sequential action of dual gravity receptors: induction of a vectorial gravitropic response requires gravitational induction of a separate facilitative response, whose decay in the absence of fresh stimuli can brake gravitropism at plagiotropic angles.

Combined effects of thinning and decline on fine root dynamics in a Quercus robur L. forest adjoining the Italian Pre-Alps.

PubMed

Mosca, E; Montecchio, L; Barion, G; Dal Cortivo, C; Vamerali, T

2017-05-01

Oak decline is a complex phenomenon, characterized by symptoms of canopy transparency, bark cracks and root biomass reduction. Root health status is one of the first stress indicators, and root turnover is a key process in plant adaptation to unfavourable conditions. In this study, the combined effects of decline and thinning were evaluated on fine root dynamics in an oak forest adjoining the Italian Pre-Alps by comparison of acute declining trees with non-declining trees, both with and without thinning treatment of surrounding trees. Dynamics of volumetric root length density (RLD V ) and tip density (RTD V ), root tip density per unit length of root (RTD L ), diameter, branching index (BI) and mycorrhizal colonization were monitored by soil coring over 2 years as possible descriptors of decline. At the beginning of the experiment, the relationship between canopy transparency and root status was weak, declining trees having slightly lower RLD V (-20 %) and RTD V (-11 %). After a 1 year lag, during which the parameters were almost unaffected, BI and RLD V , together with tip density, tip vitality and mycorrhizal colonization, became the descriptors most representative of both decline class and thinning. Thinning of declining trees increased RLD V (+12 %) and RTD V (+32 %), but reduced tip mycorrhizal colonization and vitality over time compared with non-thinned trees, whereas the opposite occurred in healthy trees, together with a marked decrease in branching. After thinning, there was an initial reduction in the structure of the ectomycorrhizal community, although recovery occurred about 10 months later, regardless of decline severity. Decline causes losses of fine root length, and a moderate recovery can be achieved by thinning, allowing better soil exploration by oak roots. The close correlation between root vitality and mycorrhizal colonization and their deterioration after thinning indicates that decline does not benefit from reduced root competition, excluding the hypothesis of limited water and nutrient availability as a possible cause of the syndrome in this forest. © 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

Combined effects of thinning and decline on fine root dynamics in a Quercus robur L. forest adjoining the Italian Pre-Alps

PubMed Central

Montecchio, L.; Barion, G.; Dal Cortivo, C.; Vamerali, T.

2017-01-01

Abstract Aims Oak decline is a complex phenomenon, characterized by symptoms of canopy transparency, bark cracks and root biomass reduction. Root health status is one of the first stress indicators, and root turnover is a key process in plant adaptation to unfavourable conditions. In this study, the combined effects of decline and thinning were evaluated on fine root dynamics in an oak forest adjoining the Italian Pre-Alps by comparison of acute declining trees with non-declining trees, both with and without thinning treatment of surrounding trees. Methods Dynamics of volumetric root length density (RLDV) and tip density (RTDV), root tip density per unit length of root (RTDL), diameter, branching index (BI) and mycorrhizal colonization were monitored by soil coring over 2 years as possible descriptors of decline. Key Results At the beginning of the experiment, the relationship between canopy transparency and root status was weak, declining trees having slightly lower RLDV (–20 %) and RTDV (–11 %). After a 1 year lag, during which the parameters were almost unaffected, BI and RLDV, together with tip density, tip vitality and mycorrhizal colonization, became the descriptors most representative of both decline class and thinning. Thinning of declining trees increased RLDV (+12 %) and RTDV (+32 %), but reduced tip mycorrhizal colonization and vitality over time compared with non-thinned trees, whereas the opposite occurred in healthy trees, together with a marked decrease in branching. After thinning, there was an initial reduction in the structure of the ectomycorrhizal community, although recovery occurred about 10 months later, regardless of decline severity. Conclusions Decline causes losses of fine root length, and a moderate recovery can be achieved by thinning, allowing better soil exploration by oak roots. The close correlation between root vitality and mycorrhizal colonization and their deterioration after thinning indicates that decline does not benefit from reduced root competition, excluding the hypothesis of limited water and nutrient availability as a possible cause of the syndrome in this forest. PMID:28334145

The Brassicaceae species Heliophila coronopifolia produces root border-like cells that protect the root tip and secrete defensin peptides.

PubMed

Weiller, Florent; Moore, John P; Young, Philip; Driouich, Azeddine; Vivier, Melané A

2017-03-01

Root border cells and border-like cells (BLCs), the latter originally described in Arabidopsis thaliana , have been described as cells released at the root tips of the species in which they occur. BLCs are thought to provide protection to root meristems similar to classical root border cells. In addition, four defensin peptides (Hc-AFP1-4) have previously been characterized from Heliophila coronopifolia , a South African semi-desert flower, and found to be strongly antifungal. This provided an opportunity to evaluate if the BLCs of H. coronopifolia indeed produce these defensins, which would provide evidence towards a defence role for BLCs. Fluorescence microscopy, using live-cell-imaging technology, was used to characterize the BLCs of H. coronopifolia . Quantitative real-time PCR (qRT-PCR) analysis and immunofluorescence microscopy was used to characterize these defensin peptides. BLCs originated at the root apical meristem and formed a protective sheath at the tip and along the sides as the root elongated in solid medium. BLCs have a cellulose-enriched cell wall, intact nuclei and are embedded in a layer of pectin-rich mucilage. Pectinase treatments led to the dissolution of the sheath and dissociation of the root BLCs. Hc-AFP1-4 genes were all expressed in root tissues, but Hc-AFP3 transcripts were the most abundant in these tissues as measured by qRT-PCR. A polyclonal antibody that was cross-reactive with all four defensins, and probably recognizing a general plant defensin epitope, was used in fluorescence microscopy analysis to examine the presence of the peptides in the root tip and BLCs. Data confirmed the peptides present in the root tip tissues, the mucilage sheath and the BLCs. This study provides a link between defensin peptides and BLCs, both embedded in a protective pectin mucilage sheath, during normal plant growth and development. The presence of the Hc-AFP3 defensin peptides in the BLCs suggests a role for these cells in root protection. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com

The Brassicaceae species Heliophila coronopifolia produces root border-like cells that protect the root tip and secrete defensin peptides

PubMed Central

Weiller, Florent; Young, Philip; Driouich, Azeddine; Vivier, Melané A.

2017-01-01

Background and Aims Root border cells and border-like cells (BLCs), the latter originally described in Arabidopsis thaliana, have been described as cells released at the root tips of the species in which they occur. BLCs are thought to provide protection to root meristems similar to classical root border cells. In addition, four defensin peptides (Hc-AFP1–4) have previously been characterized from Heliophila coronopifolia, a South African semi-desert flower, and found to be strongly antifungal. This provided an opportunity to evaluate if the BLCs of H. coronopifolia indeed produce these defensins, which would provide evidence towards a defence role for BLCs. Methods Fluorescence microscopy, using live-cell-imaging technology, was used to characterize the BLCs of H. coronopifolia. Quantitative real-time PCR (qRT-PCR) analysis and immunofluorescence microscopy was used to characterize these defensin peptides. Key Results BLCs originated at the root apical meristem and formed a protective sheath at the tip and along the sides as the root elongated in solid medium. BLCs have a cellulose-enriched cell wall, intact nuclei and are embedded in a layer of pectin-rich mucilage. Pectinase treatments led to the dissolution of the sheath and dissociation of the root BLCs. Hc-AFP1–4 genes were all expressed in root tissues, but Hc-AFP3 transcripts were the most abundant in these tissues as measured by qRT-PCR. A polyclonal antibody that was cross-reactive with all four defensins, and probably recognizing a general plant defensin epitope, was used in fluorescence microscopy analysis to examine the presence of the peptides in the root tip and BLCs. Data confirmed the peptides present in the root tip tissues, the mucilage sheath and the BLCs. Conclusions This study provides a link between defensin peptides and BLCs, both embedded in a protective pectin mucilage sheath, during normal plant growth and development. The presence of the Hc-AFP3 defensin peptides in the BLCs suggests a role for these cells in root protection. PMID:27481828

Patterns of auxin and abscisic acid movement in the tips of gravistimulated primary roots of maize

NASA Technical Reports Server (NTRS)

Young, L. M.; Evans, M. L.

1996-01-01

Because both abscisic acid (ABA) and auxin (IAA) have been suggested as possible chemical mediators of differential growth during root gravitropism, we compared with redistribution of label from applied 3H-IAA and 3H-ABA during maize root gravitropism and examined the relative basipetal movement of 3H-IAA and 3H-ABA applied to the caps of vertical roots. Lateral movement of 3H-ABA across the tips of vertical roots was non-polar and about 2-fold greater than lateral movement of 3H-IAA (also non-polar). The greater movement of ABA was not due to enhanced uptake since the uptake of 3H-IAA was greater than that of 3H-ABA. Basipetal movement of label from 3H-IAA or 3H-ABA applied to the root cap was determined by measuring radioactivity in successive 1 mm sections behind the tip 90 minutes after application. ABA remained largely in the first mm (point of application) whereas IAA was concentrated in the region 2-4 mm from the tip with substantial levels found 7-8 mm from the tip. Pretreatment with inhibitors of polar auxin transport decreased both gravicurvature and the basipetal movement of IAA. When roots were placed horizontally, the movement of 3H-IAA from top to bottom across the cap was enhanced relative to movement from bottom to top whereas the pattern of movement of label from 3H-ABA was unaffected. These results are consistent with the hypothesis that IAA plays a role in root gravitropism but contrary to the idea that gravi-induced asymmetric distribution of ABA contributes to the response.

Mechanisms of gravitropism in single-celled systems

NASA Astrophysics Data System (ADS)

Greuel, Nicole; Braun, Markus; Hauslage, Jens; Wiemann, Katharina

Physiological processes in plants are influenced by a variety of external stimuli. Gravity is the only constant factor that provides plants with reliable information for their orientation. Gravity-oriented growth responses, called gravitropism, enable plants to adapt to a diversity of habitats on Earth and to survive changing environmental conditions. For instance, the ability to respond gravitropically prevents crop, flattened by a windstorm, from decay. Even small deviations from the genetically programmed set-point angle of plant organs are recognized by specialized cells, the statocytes, in which dense particles, the statoliths, sediment in the direction of gravity and activate gravity sensors - membrane bound gravity-receptor proteins. Activation of receptor proteins creates a physiological signal that initiates a stimulus-specific signal transduction cascade causing the gravitropic response. To unravel the gravitropic signalling pathways in plant statocytes, our research focused on a unicellular model system, the rhizoid of the green alga Chara. Experiments under microgravity conditions during sounding-rocket and parabolic plane flights have shown that the actin cytoskeleton is a key element of the gravityinduced statolith-sedimentation process in characean rhizoids. Actomyosin, consisting of a dense meshwork of mainly axially oriented actin microfilaments and motor proteins (myosins), actively guides sedimenting statoliths to gravisensitive plasma membrane areas where gravireceptor molecules are exclusively located. TEXUS and MAXUS sounding rocket missions were performed to determine the threshold acceleration level (< 0.1g) required for lateral statolith displacement. parabolic flight experiments aboard the airbus A300 Zero-G have shown that sedimented but weightless statoliths are still capable of activating the membrane-bound gravireceptor in characean rhizoids. The results contradict the classical model of a mechanoreceptor that is activated by the pressure exerted by sedimented statoliths. Instead, the experiments provide evidence that graviperception depends on direct interactions between statoliths and a yet unknown gravireceptor.Graviperception in higher plant statocytes was also found to be not dependent on mechanical pressure but on direct interactions between gravireceptors and statoliths. In contrast to Chara rhizoids, however, the actin system of higher plant statocytes is not essentially required for gravity-sensing. Parabolic flight experiments and ground controls indicated that disruption of the actin cytoskeleton in root statocytes by using Latrunculin B results in an increased gravisensitivity and in a promoted gravitropic curvature rather than in an inhibition. It is speculated that the actomyosin system in statocytes has a fine-tuning function in the early phases of gravity sensing. Actin in higher plant statocytes may be required to optimize statolith-receptor interactions and to keep the sensing system highly sensitive on one hand, but on the other hand actomyosin-statolith interactions seem to avoid unfavourable responses to only transient stimuli.Investigating the unicellular characean rhizoid has greatly enhanced our understanding of gravity sensing processes in plants and there is increasing evidence that higher plants and characean rhizoids share common processes in the signalling pathway of gravity-oriented growth.

Tip-growing cells of the moss Ceratodon purpureus Are gravitropic in high-density media

NASA Technical Reports Server (NTRS)

Schwuchow, Jochen Michael; Kern, Volker Dieter; Sack, Fred David

2002-01-01

Gravity sensing in plants and algae is hypothesized to rely upon either the mass of the entire cell or that of sedimenting organelles (statoliths). Protonemata of the moss Ceratodon purpureus show upward gravitropism and contain amyloplasts that sediment. If moss sensing were whole-cell based, then media denser than the cell should prevent gravitropism or reverse its direction. Cells that were inverted or reoriented to the horizontal displayed distinct negative gravitropism in solutions of iodixanol with densities of 1.052 to 1.320 as well as in bovine serum albumin solutions with densities of 1.037 to 1.184 g cm(-3). Studies using tagged molecules of different sizes and calculations of diffusion times suggest that both types of media penetrate through the apical cell wall. Estimates of the density of the apical cell range from 1.004 to 1.085. Because protonemata grow upward when the cells have a density that is lower than the surrounding medium, gravitropic sensing probably utilizes an intracellular mass in moss protonemata. These data provide additional support for the idea that sedimenting amyloplasts function as statoliths in gravitropism.

Redox-mediated quorum sensing in plants.

PubMed

Fuller, Alexandra W; Young, Phoebe; Pierce, B Daniel; Kitson-Finuff, Jamie; Jain, Purvi; Schneider, Karl; Lazar, Stephen; Taran, Olga; Palmer, Andrew G; Lynn, David G

2017-01-01

The rhizosphere, the narrow zone of soil around plant roots, is a complex network of interactions between plants, bacteria, and a variety of other organisms. The absolute dependence on host-derived signals, or xenognosins, to regulate critical developmental checkpoints for host commitment in the obligate parasitic plants provides a window into the rhizosphere's chemical dynamics. These sessile intruders use H2O2 in a process known as semagenesis to chemically modify the mature root surfaces of proximal host plants and generate p-benzoquinones (BQs). The resulting redox-active signaling network regulates the spatial and temporal commitments necessary for host attachment. Recent evidence from non-parasites, including Arabidopsis thaliana, establishes that reactive oxygen species (ROS) production regulates similar redox circuits related to root recognition, broadening xenognosins' role beyond the parasites. Here we compare responses to the xenognosin dimethoxybenzoquinone (DMBQ) between the parasitic plant Striga asiatica and the non-parasitic A. thaliana. Exposure to DMBQ simulates the proximity of a mature root surface, stimulating an increase in cytoplasmic Ca2+ concentration in both plants, but leads to remarkably different phenotypic responses in the parasite and non-parasite. In S. asiatica, DMBQ induces development of the host attachment organ, the haustorium, and decreases ROS production at the root tip, while in A. thaliana, ROS production increases and further growth of the root tip is arrested. Obstruction of Ca2+ channels and the addition of antioxidants both lead to a decrease in the DMBQ response in both parasitic and non-parasitic plants. These results are consistent with Ca2+ regulating the activity of NADPH oxidases, which in turn sustain the autocatalytic production of ROS via an external quinone/hydroquinone redox cycle. Mechanistically, this chemistry is similar to black and white photography with the emerging dynamic reaction-diffusion network laying the foundation for the precise temporal and spatial control underlying rhizosphere architecture.

Investigation of buoyancy effects on turbulent nonpremixed jet flames by using normal and low-gravity conditions

NASA Astrophysics Data System (ADS)

Idicheria, Cherian Alex

An experimental study was performed with the aim of investigating the structure of transitional and turbulent nonpremixed jet flames under different gravity conditions. In particular, the focus was to determine the effect of buoyancy on the mean and fluctuating characteristics of the jet flames. Experiments were conducted under three gravity levels, viz. 1 g, 20 mg and 100 mug. The milligravity and microgravity conditions were achieved by dropping a jet-flame rig in the UT-Austin 1.25-second and the NASA-Glenn Research Center 2.2-second drop towers, respectively. The principal diagnostics employed were time-resolved, cinematographic imaging of the visible soot luminosity and planar laser Mie scattering (PLMS). For the cinematographic flame luminosity imaging experiments, the flames studied were piloted nonpremixed propane, ethylene and methane jet flames at source Reynolds numbers ranging from 2000 to 10500. From the soot luminosity images, mean and root-mean square (RMS) images were computed, and volume rendering of the image sequences was used to investigate the large-scale structure evolution and flame tip dynamics. The relative importance of buoyancy was quantified with the parameter, xL , as defined by Becker and Yamazaki [1978]. The results show, in contrast to previous microgravity studies, that the high Reynolds number flames have the same flame length irrespective of the gravity level. The RMS fluctuations and volume renderings indicate that the large-scale structure and flame tip dynamics are essentially identical to those of purely momentum driven flames provided xL is approximately less than 2. The volume-renderings show that the luminous structure celerities (normalized by jet exit velocity) are approximately constant for xL < 6, but are substantially larger for xL > 8. The celerity values for xL > 8 are seen to follow a x3/2L scaling, which can be predicted with a simplified momentum equation analysis for the buoyancy-dominated regime. The underlying turbulent structure and mean mixture fraction characteristics were investigated in nonreacting and reacting jets with a PLMS diagnostic system developed for the UT-Austin 1.25-second drop tower. (Abstract shortened by UMI.)

Determinate Root Growth and Meristem Maintenance in Angiosperms

PubMed Central

Shishkova, S.; Rost, T. L.; Dubrovsky, J. G.

2008-01-01

Background The difference between indeterminate and determinate growth in plants consists of the presence or absence of an active meristem in the fully developed organ. Determinate root growth implies that the root apical meristem (RAM) becomes exhausted. As a consequence, all cells in the root tip differentiate. This type of growth is widely found in roots of many angiosperm taxa and might have evolved as a developmental adaptation to water deficit (in desert Cactaceae), or low mineral content in the soil (proteoid roots in various taxa). Scope and Conclusions This review considers the mechanisms of determinate root growth to better understand how the RAM is maintained, how it functions, and the cellular and genetic bases of these processes. The role of the quiescent centre in RAM maintenance and exhaustion will be analysed. During root ageing, the RAM becomes smaller and its organization changes; however, it remains unknown whether every root is truly determinate in the sense that its RAM becomes exhausted before senescence. We define two types of determinate growth: constitutive where determinacy is a natural part of root development; and non-constitutive where determinacy is induced usually by an environmental factor. Determinate root growth is proposed to include two phases: the indeterminate growth phase, when the RAM continuously produces new cells; and the termination growth phase, when cell production gradually decreases and eventually ceases. Finally, new concepts regarding stem cells and a stem cell niche are discussed to help comprehend how the meristem is maintained in a broad taxonomic context. PMID:17954472

Growth is required for perception of water availability to pattern root branches in plants.

PubMed

Robbins, Neil E; Dinneny, José R

2018-01-23

Water availability is a potent regulator of plant development and induces root branching through a process termed hydropatterning. Hydropatterning enables roots to position lateral branches toward regions of high water availability, such as wet soil or agar media, while preventing their emergence where water is less available, such as in air. The mechanism by which roots perceive the spatial distribution of water during hydropatterning is unknown. Using primary roots of Zea mays (maize) we reveal that developmental competence for hydropatterning is limited to the growth zone of the root tip. Past work has shown that growth generates gradients in water potential across an organ when asymmetries exist in the distribution of available water. Using mathematical modeling, we predict that substantial growth-sustained water potential gradients are also generated in the hydropatterning competent zone and that such biophysical cues inform the patterning of lateral roots. Using diverse chemical and environmental treatments we experimentally demonstrate that growth is necessary for normal hydropatterning of lateral roots. Transcriptomic characterization of the local response of tissues to a moist surface or air revealed extensive regulation of signaling and physiological pathways, some of which we show are growth-dependent. Our work supports a "sense-by-growth" mechanism governing hydropatterning, by which water availability cues are rendered interpretable through growth-sustained water movement. Copyright © 2018 the Author(s). Published by PNAS.

Growth is required for perception of water availability to pattern root branches in plants

PubMed Central

2018-01-01

Water availability is a potent regulator of plant development and induces root branching through a process termed hydropatterning. Hydropatterning enables roots to position lateral branches toward regions of high water availability, such as wet soil or agar media, while preventing their emergence where water is less available, such as in air. The mechanism by which roots perceive the spatial distribution of water during hydropatterning is unknown. Using primary roots of Zea mays (maize) we reveal that developmental competence for hydropatterning is limited to the growth zone of the root tip. Past work has shown that growth generates gradients in water potential across an organ when asymmetries exist in the distribution of available water. Using mathematical modeling, we predict that substantial growth-sustained water potential gradients are also generated in the hydropatterning competent zone and that such biophysical cues inform the patterning of lateral roots. Using diverse chemical and environmental treatments we experimentally demonstrate that growth is necessary for normal hydropatterning of lateral roots. Transcriptomic characterization of the local response of tissues to a moist surface or air revealed extensive regulation of signaling and physiological pathways, some of which we show are growth-dependent. Our work supports a “sense-by-growth” mechanism governing hydropatterning, by which water availability cues are rendered interpretable through growth-sustained water movement. PMID:29317538

The kinetics of root gravitropism in PIN mutants suggest redundancy in the signal transduction pathway

NASA Astrophysics Data System (ADS)

Wolverton, Chris

As nonmotile organisms, plants rely on differential growth responses to maximize exposure to the resources necessary for growth and reproduction. One of the primary environmental cues causing differential growth in roots is gravity, which is thought to be sensed predominately in the root cap. This gravity perception event is thought to be transduced into information in the form of an auxin gradient across the cap and propagating basipetally toward the elongation zone. The discovery of several families of auxin efflux and influx carriers has provided significant insight into the mechanisms of directional auxin transport, and the identification of mutants in the genes encoding these carriers provides the opportunity to test the roles of these transporters in plant gravitropism. In this study, we report the results of a systematic, high-resolution study of the kinetics of root gravitropism of mutants in the PIN family of auxin efflux carriers. Based on reported expression and localization patterns, we predicted mutations in PIN2, PIN3, PIN4, and PIN7 to cause the greatest reduction in root gravitropism. While pin2 mutants showed severe gravitropic deficiencies in roots as reported previously, several alleles of pin3, pin4 and pin7 remained strongly gravitropic. PIN3 has been localized to the central columella cells, the purported gravisensing cells in the root, and shown to rapidly relocate to the lower flank of the columella cells upon gravistimulation, suggesting an early role in auxin gradient formation. Mutant alleles of PIN3 showed an early delay in response, with just 7 deg of curvature in the first hour compared to approximately 15 deg h-1 in wild-type, but their rate of curvature recovered to near wild-type levels over the ensuing 3 h. Pin3 mutants also showed a slower overall growth rate (124 µm h-1 ), elongating at approximately half the rate of wild-type roots (240 µm h-1 ). PIN4 has been localized to the quiescent center in the root, where it presumably plays a role in efflux to the columella. Pin4 mutants showed no deficiencies in gravitropism, in fact responding at a greater rate than wild-type roots over the first hour (22 deg h-1 ). PIN7 has been localized to the vascular tissue of the elongation zone and to the central columella. Like pin4 mutants, pin7 mutants did not show a significantly reduced gravitropic response relative to wild-type roots. Interestingly, roots of pin3pin7 double mutants showed curvature and growth rates similar to pin7 single mutants and wild-type roots, suggesting a genetic interaction between PIN3 and PIN7 in this pathway. These results suggest a significant degree of redundancy in the regulation of directional auxin transport and perhaps in the gravity signaling pathway in roots in general.

Measurement of pressure changes during laser-activated irrigant by an erbium, chromium: yttrium, scandium, gallium, garnet laser.

PubMed

Peeters, Harry Huiz; De Moor, Roeland J G

2015-07-01

The use of Er,Cr:YSGG laser to activate irrigants results in the creation of vapour bubbles and shockwaves. The present study evaluated the magnitude of pressure changes in the root canal during laser-activated irrigation. The root canal of a single extracted maxillary canine was enlarged to a size 40/0.06 file. A pressure sensor was inserted apically into the root canal. The tooth was processed as follows. In the EDTA condition, the tooth was irrigated with 17 % EDTA; in the NaOCl condition, the tooth was irrigated with 3 % NaOCl. In all conditions, the irrigants were activated at 0.75 and 1.75 W for 60 s using RFT2 and MZ2 tips; to analyse the effect of tip placement, the tip was activated at the orifice and after inserting the tip 5 mm deeper than the orifice. Data showed no significant difference between irrigation regimens (p > 0.05). There were no significant differences of the pressure between RFT2 and MZ2 tips (p > 0.05). The placement of tips closer to the apex resulted in significantly higher pressure than at the orifice (p < 0.001). The use of 1.75 W power resulted in a significantly higher increase of pressure compared to 0.75 W (p < 0.001), regardless either the type of solutions or tips used. The magnitude of the pressure changes in the root canal at 0.75 W was significantly lower than 1.75 W regardless of either type of tips or solutions used. The closer the insertion of the tip to the apex, the higher the pressure.

ZIFL1.1 transporter modulates polar auxin transport by stabilizing membrane abundance of multiple PINs in Arabidopsis root tip

PubMed Central

Remy, Estelle; Baster, Pawel; Friml, Jiří; Duque, Paula

2013-01-01

Cell-to-cell directional flow of the phytohormone auxin is primarily established by polar localization of the PIN auxin transporters, a process tightly regulated at multiple levels by auxin itself. We recently reported that, in the context of strong auxin flows, activity of the vacuolar ZIFL1.1 transporter is required for fine-tuning of polar auxin transport rates in the Arabidopsis root. In particular, ZIFL1.1 function protects plasma-membrane stability of the PIN2 carrier in epidermal root tip cells under conditions normally triggering PIN2 degradation. Here, we show that ZIFL1.1 activity at the root tip also promotes PIN1 plasma-membrane abundance in central cylinder cells, thus supporting the notion that ZIFL1.1 acts as a general positive modulator of polar auxin transport in roots. PMID:23857365

AtPIN2 defines a locus of Arabidopsis for root gravitropism control.

PubMed Central

Müller, A; Guan, C; Gälweiler, L; Tänzler, P; Huijser, P; Marchant, A; Parry, G; Bennett, M; Wisman, E; Palme, K

1998-01-01

The molecular mechanisms underlying gravity perception and signal transduction which control asymmetric plant growth responses are as yet unknown, but are likely to depend on the directional flux of the plant hormone auxin. We have isolated an Arabidopsis mutant of the AtPIN2 gene using transposon mutagenesis. Roots of the Atpin2::En701 null-mutant were agravitropic and showed altered auxin sensitivity, a phenotype characteristic of the agravitropic wav6-52 mutant. The AtPIN2 gene was mapped to chromosome 5 (115.3 cM) corresponding to the WAV6 locus and subsequent genetic analysis indicated that wav6-52 and Atpin2::En701 were allelic. The AtPIN2 gene consists of nine exons defining an open reading frame of 1944 bp which encodes a 69 kDa protein with 10 putative transmembrane domains interrupted by a central hydrophilic loop. The topology of AtPIN2p was found to be similar to members of the major facilitator superfamily of transport proteins. We have shown that the AtPIN2 gene was expressed in root tips. The AtPIN2 protein was localized in membranes of root cortical and epidermal cells in the meristematic and elongation zones revealing a polar localization. These results suggest that AtPIN2 plays an important role in control of gravitropism regulating the redistribution of auxin from the stele towards the elongation zone of roots. PMID:9843496

Hydrotropism and its interaction with gravitropism in maize roots

NASA Technical Reports Server (NTRS)

Takahashi, H.; Scott, T. K.

1991-01-01

We have partially characterized root hydrotropism and its interaction with gravitropism in maize (Zea mays L.). Roots of Golden Cross Bantam 70, which require light for orthogravitropism, showed positive hydrotropism; bending upward when placed horizontally below a hydrostimulant (moist cheesecloth) in 85% relative humidity (RH) and in total darkness. However, the light-exposed roots of Golden Cross Bantam 70 or roots of a normal maize cultivar, Burpee Snow Cross, showed positive gravitropism under the same conditions; bending downward when placed horizontally below the hydrostimulant in 85% RH. Light-exposed roots of Golden Cross Bantam 70 placed at 70 degrees below the horizontal plane responded positively hydrotropically, but gravitropism overcame the hydrotropism when the roots were placed at 45 degrees below the horizontal. Roots placed vertically with the tip down in 85% RH bent to the side toward the hydrostimulant in both cultivars, and light conditions did not affect the response. Such vertical roots did not respond when the humidity was maintained near saturation. These results suggest that hydrotropic and gravitropic responses interact with one another depending on the intensity of one or both factors. Removal of the approximately 1.5 millimeter root tip blocked both hydrotropic and gravitropic responses in the two cultivars. However, removal of visible root tip mucilage did not affect hydrotropism or gravitropism in either cultivar.

Plasma membrane NADH oxidase of maize roots responds to gravity and imposed centrifugal forces

NASA Technical Reports Server (NTRS)

Bacon, E.; Morre, D. J.

2001-01-01

NADH oxidase activities measured with excised roots of dark-grown maize (Zea mays) seedlings and with isolated plasma membrane vesicles from roots of dark-grown maize oscillated with a regular period length of 24 min and were inhibited by the synthetic auxin 2,4-dichlorophenoxyacetic [correction of dichorophenoxyacetic] acid. The activities also responded to orientation with respect to gravity and to imposed centrifugal forces. Turning the roots upside down resulted in stimulation of the activity with a lag of about 10 min. Returning the sections to the normal upright position resulted in a return to initial rates. The activity was stimulated reversibly to a maximum of about 2-fold with isolated plasma membrane vesicles, when subjected to centrifugal forces of 25 to 250 x g for 1 to 4 min duration. These findings are the first report of a gravity-responsive enzymatic activity of plant roots inhibited by auxin and potentially related to the gravity-induced growth response. c2001 Editions scientifiques et medicales Elsevier SAS.

Operationally Defined Apoplastic and Symplastic Aluminum Fractions in Root Tips of Aluminum-Intoxicated Wheat

PubMed Central

Tice, Kathy R.; Parker, David R.; DeMason, Darleen A.

1992-01-01

Knowledge of the mechanistic basis of differential aluminum (Al) tolerance depends, in part, on an improved ability to quantify Al located in the apoplastic and symplastic compartments of the root apex. Using root tips excised from seedlings of an Al-tolerant wheat cultivar (Triticum aestivum L. cv Yecora Rojo) grown in Al solutions for 2 d, we established an operationally defined apoplastic Al fraction determined with six sequential 30-min washes using 5 mm CaCl2 (pH 4.3). Soluble symplastic Al was eluted by freezing root tips to rupture cell membranes and performing four additional 30-min CaCl2 washes, and a residual fraction was determined via digestion of root tips with HNO3. The three fractions were then determined in Yecora Rojo and a sensitive wheat cultivar (Tyler) grown at 18, 55, or 140 μm total solution Al (AlT). When grown at equal AlT, Tyler contained more Al than Yecora Rojo in all fractions, but both total Al and fractional distribution were similar in the two cultivars grown at AlT levels effecting a 50% reduction in root growth. Residual Al was consistently 50 to 70% of the total, and its location was elucidated by staining root tips with the fluorophore morin and examining them using fluorescence and confocal laser scanning microscopy. Wall-associated Al was only observed in tips prior to any washing, and the residual fraction was manifested as distinct staining of the cytoplasm and nucleus but not of the apoplastic space. Accordingly, the residual fraction was allocated to the symplastic compartment for both cultivars, and recalculated apoplastic Al was consistently approximately 30 to 40% of the total. Distributions of Al in the two cultivars did not support a symplastic detoxification hypothesis, but the role of cytoplasmic exclusion remains unsettled. Images Figure 4 Figure 5 PMID:16652962

Amyloplast sedimentation dynamics in maize columella cells support a new model for the gravity-sensing apparatus of roots

NASA Technical Reports Server (NTRS)

Yoder, T. L.; Zheng, H. Q.; Todd, P.; Staehelin, L. A.

2001-01-01

Quantitative analysis of statolith sedimentation behavior was accomplished using videomicroscopy of living columella cells of corn (Zea mays) roots, which displayed no systematic cytoplasmic streaming. Following 90 degrees rotation of the root, the statoliths moved downward along the distal wall and then spread out along the bottom with an average velocity of 1.7 microm min(-1). When statolith trajectories traversed the complete width or length of the cell, they initially moved horizontally toward channel-initiation sites and then moved vertically through the channels to the lower side of the reoriented cell where they again dispersed. These statoliths exhibited a significantly lower average velocity than those sedimenting on distal-to-side trajectories. In addition, although statoliths undergoing distal-to-side sedimentation began at their highest velocity and slowed monotonically as they approached the lower cell membrane, statoliths crossing the cell's central region remained slow initially and accelerated to maximum speed once they reached a channel. The statoliths accelerated sooner, and the channeling effect was less pronounced in roots treated with cytochalasin D. Parallel ultrastructural studies of high-pressure frozen-freeze-substituted columella cells suggest that the low-resistance statolith pathway in the cell periphery corresponds to the sharp interface between the endoplasmic reticulum (ER)-rich cortical and the ER-devoid central region of these cells. The central region is also shown to contain an actin-based cytoskeletal network in which the individual, straight, actin-like filaments are randomly distributed. To explain these findings as well as the results of physical simulation experiments, we have formulated a new, tensegrity-based model of gravity sensing in columella cells. This model envisages the cytoplasm as pervaded by an actin-based cytoskeletal network that is denser in the ER-devoid central region than in the ER-rich cell cortex and is linked to stretch receptors in the plasma membrane. Sedimenting statoliths are postulated to produce a directional signal by locally disrupting the network and thereby altering the balance of forces acting on the receptors in different plasma membrane regions.

Amyloplast Sedimentation Dynamics in Maize Columella Cells Support a New Model for the Gravity-Sensing Apparatus of Roots1

PubMed Central

Yoder, Thomas L.; Zheng, Hui-qiong; Todd, Paul; Staehelin, L. Andrew

2001-01-01

Quantitative analysis of statolith sedimentation behavior was accomplished using videomicroscopy of living columella cells of corn (Zea mays) roots, which displayed no systematic cytoplasmic streaming. Following 90° rotation of the root, the statoliths moved downward along the distal wall and then spread out along the bottom with an average velocity of 1.7 μm min−1. When statolith trajectories traversed the complete width or length of the cell, they initially moved horizontally toward channel-initiation sites and then moved vertically through the channels to the lower side of the reoriented cell where they again dispersed. These statoliths exhibited a significantly lower average velocity than those sedimenting on distal-to-side trajectories. In addition, although statoliths undergoing distal-to-side sedimentation began at their highest velocity and slowed monotonically as they approached the lower cell membrane, statoliths crossing the cell's central region remained slow initially and accelerated to maximum speed once they reached a channel. The statoliths accelerated sooner, and the channeling effect was less pronounced in roots treated with cytochalasin D. Parallel ultrastructural studies of high-pressure frozen-freeze-substituted columella cells suggest that the low-resistance statolith pathway in the cell periphery corresponds to the sharp interface between the endoplasmic reticulum (ER)-rich cortical and the ER-devoid central region of these cells. The central region is also shown to contain an actin-based cytoskeletal network in which the individual, straight, actin-like filaments are randomly distributed. To explain these findings as well as the results of physical simulation experiments, we have formulated a new, tensegrity-based model of gravity sensing in columella cells. This model envisages the cytoplasm as pervaded by an actin-based cytoskeletal network that is denser in the ER-devoid central region than in the ER-rich cell cortex and is linked to stretch receptors in the plasma membrane. Sedimenting statoliths are postulated to produce a directional signal by locally disrupting the network and thereby altering the balance of forces acting on the receptors in different plasma membrane regions. PMID:11161060

Amyloplast sedimentation dynamics in maize columella cells support a new model for the gravity-sensing apparatus of roots.

PubMed

Yoder, T L; Zheng, H Q; Todd, P; Staehelin, L A

2001-02-01

Quantitative analysis of statolith sedimentation behavior was accomplished using videomicroscopy of living columella cells of corn (Zea mays) roots, which displayed no systematic cytoplasmic streaming. Following 90 degrees rotation of the root, the statoliths moved downward along the distal wall and then spread out along the bottom with an average velocity of 1.7 microm min(-1). When statolith trajectories traversed the complete width or length of the cell, they initially moved horizontally toward channel-initiation sites and then moved vertically through the channels to the lower side of the reoriented cell where they again dispersed. These statoliths exhibited a significantly lower average velocity than those sedimenting on distal-to-side trajectories. In addition, although statoliths undergoing distal-to-side sedimentation began at their highest velocity and slowed monotonically as they approached the lower cell membrane, statoliths crossing the cell's central region remained slow initially and accelerated to maximum speed once they reached a channel. The statoliths accelerated sooner, and the channeling effect was less pronounced in roots treated with cytochalasin D. Parallel ultrastructural studies of high-pressure frozen-freeze-substituted columella cells suggest that the low-resistance statolith pathway in the cell periphery corresponds to the sharp interface between the endoplasmic reticulum (ER)-rich cortical and the ER-devoid central region of these cells. The central region is also shown to contain an actin-based cytoskeletal network in which the individual, straight, actin-like filaments are randomly distributed. To explain these findings as well as the results of physical simulation experiments, we have formulated a new, tensegrity-based model of gravity sensing in columella cells. This model envisages the cytoplasm as pervaded by an actin-based cytoskeletal network that is denser in the ER-devoid central region than in the ER-rich cell cortex and is linked to stretch receptors in the plasma membrane. Sedimenting statoliths are postulated to produce a directional signal by locally disrupting the network and thereby altering the balance of forces acting on the receptors in different plasma membrane regions.

Sport Utility Vehicles: Traffic Safety Tips

DOT National Transportation Integrated Search

1996-01-01

This fact sheet, NHTSA Facts: Summer 1996, describe traffic safety tips for driving sport utility vehicles. Because sport utility vehicles have a higher center of gravity, making them more top heavy than cars, they handle and maneuver differently tha...

Effect of biweekly shoot tip harvests on the growth and yield of Georgia Jet sweet potato grown hydroponically

NASA Technical Reports Server (NTRS)

Ogbuehi, Cyriacus R.; Loretan, Phil A.; Bonsi, C. K.; Hill, Walter A.; Morris, Carlton E.; Biswas, P. K.; Mortley, Desmond G.

1989-01-01

Sweet potato shoot tips have been shown to be a nutritious green vegetable. A study was conducted to determine the effect of biweekly shoot tip harvests on the growth and yield of Georgia Jet sweet potato grown in the greenhouse using the nutrient film technique (NFT). The nutrient solution consisted of a modified half Hoagland solution. Biweekly shoot tip harvests, beginning 42 days after planting, provided substantial amounts of vegetable greens and did not affect the fresh and dry foliage weights or the storage root number and fresh and dry storage root weights at final harvest. The rates of anion and cation uptake were not affected by tip harvests.

Nuclear Proteomics Reveals the Role of Protein Synthesis and Chromatin Structure in Root Tip of Soybean during the Initial Stage of Flooding Stress.

PubMed

Yin, Xiaojian; Komatsu, Setsuko

2016-07-01

To identify the upstream events controlling the regulation of flooding-responsive proteins in soybean, proteomic analysis of nuclear proteins in root tip was performed. By using nuclear fractions, which were highly enriched, a total of 365 nuclear proteins were changed in soybean root tip at initial stage of flooding stress. Four exon-junction complex-related proteins and NOP1/NOP56, which function in upstream of 60S preribosome biogenesis, were decreased in flooded soybean. Furthermore, proteomic analysis of crude protein extract revealed that the protein translation was suppressed by continuous flooding stress. Seventeen chromatin structure-related nuclear proteins were decreased in response to flooding stress. Out of them, histone H3 was clearly decreased with protein abundance and mRNA expression levels at the initial flooding stress. Additionally, a number of protein synthesis-, RNA-, and DNA-related nuclear proteins were decreased in a time-dependent manner. mRNA expressions of genes encoding the significantly changed flooding-responsive nuclear proteins were inhibited by the transcriptional inhibitor, actinomycin D. These results suggest that protein translation is suppressed through inhibition of preribosome biogenesis- and mRNA processing-related proteins in nuclei of soybean root tip at initial flooding stress. In addition, flooding stress may regulate histone variants with gene expression in root tip.

Forensic DNA typing from teeth using demineralized root tips.

PubMed

Corrêa, Heitor Simões Dutra; Pedro, Fabio Luis Miranda; Volpato, Luiz Evaristo Ricci; Pereira, Thiago Machado; Siebert Filho, Gilberto; Borges, Álvaro Henrique

2017-11-01

Teeth are widely used samples in forensic human genetic identification due to their persistence and practical sampling and processing. Their processing, however, has changed very little in the last 20 years, usually including powdering or pulverization of the tooth. The objective of this study was to present demineralized root tips as DNA sources while, at the same time, not involving powdering the samples or expensive equipment for teeth processing. One to five teeth from each of 20 unidentified human bodies recovered from midwest Brazil were analyzed. Whole teeth were demineralized in EDTA solution with daily solution change. After a maximum of approximately seven days, the final millimeters of the root tip was excised. This portion of the sample was used for DNA extraction through a conventional organic protocol. DNA quantification and STR amplification were performed using commercial kits followed by capillary electrophoresis on 3130 or 3500 genetic analyzers. For 60% of the unidentified bodies (12 of 20), a full genetic profile was obtained from the extraction of the first root tip. By the end of the analyses, full genetic profiles were obtained for 85% of the individuals studied, of which 80% were positively identified. This alternative low-tech approach for postmortem teeth processing is capable of extracting DNA in sufficient quantity and quality for forensic casework, showing that root tips are viable nuclear DNA sources even after demineralization. Copyright © 2017 Elsevier B.V. All rights reserved.

Analysis of amyloplast dynamics involved in gravity sensing using a novel centrifuge microscope

NASA Astrophysics Data System (ADS)

Toyota, Masatsugu; Tasaka, Masao; Morita, Miyo T.

Plants sense gravity and change their growth orientation, a phenomenon known as gravitropism. According to the starch-statolith hypothesis, sedimentation of high-density starch-filled plastids (amyloplasts) within endodermal cells appears to be involved in gravity sensing of Arabidop-sis shoots. Recent studies suggest, however, that amyloplasts are never static but continu-ously show dynamic and complicated movements due to interaction with vacuole/cytoskeleton. Therefore, it remains unclear what movement/state of amyloplasts is required for gravity sens-ing. To address this critical issue, we analyzed gravitropism and amyloplast dynamics under hypergravity condition where sedimentation by gravity is more dominant than other movements. Segments of Arabidopsis inflorescence stem showed a gravitropism in response to hypergrav-ity (10g) that had been applied perpendicularly to the growth axis for 30 s in a conventional centrifuge, suggesting that amyloplast dynamics during this short time period is involved in gravity sensing. Real-time imaging of amyloplasts during the 10g stimulation was performed using a novel centrifuge microscope (NSK Ltd, Japan): all optical devices including objective lens, light source (LED) and CCD camera are mounted on an AC motor, enabling bright-field imaging with a temporal resolution of 30 frames/sec during rotation. Almost all amyloplasts started to move toward 10g and some reached the one side of endodermal cell within 30 s. These results clearly support the starch-statolith hypothesis that redistribution of amyloplasts to gravity is important for gravity sensing. Furthermore, we analyzed the shoot gravitropic mutant, sgr2, that has non-sedimentable amyloplasts and shows little gravitropism at 1g. An obvious gravitropism was induced by 30g for 5 min where amyloplasts were moved to the hyper-gravity but not by 10g where amyloplasts were not moved. These results not only suggest that gravity sensing of Arabidopsis inflorescence stems is triggered by the amyloplast redistribution resulting from the directional movement to gravity, but also provide a new interpretation of sgr2 that sgr2 has a gravity-sensing mechanism, which is inactivated at 1g probably due to non-sedimentable amyloplasts.

Autoradiography and the Cell Cycle.

ERIC Educational Resources Information Center

Jones, C. Weldon

1992-01-01

Outlines the stages of a cell biology "pulse-chase" experiment in which the students apply autoradiography techniques to learn about the concept of the cell cycle. Includes (1) seed germination and plant growth; (2) radioactive labeling and fixation of root tips; (3) feulgen staining of root tips; (4) preparation of autoradiograms; and…

Accurate real-time sensing tip for aqueous NO with optical fibers embedded in active hydrogel waveguide

NASA Astrophysics Data System (ADS)

Chung, Chieh-Wen; Tsai, May-Jywan; Lin, Peng-Wei; Huang, Ding-Wen; Wang, Kuan-Hsun; Chen, Yu-An; Meng, Hsin-Fei; Zan, Hsiao-Wen; Cheng, Henrich; Tong, Limin; Zhang, Lei; Horng, Sheng-Fu; Hung, Cheng-Hsiung

2018-02-01

A NO sensing tip is made by inserting two parallel optical fibers inside a poly 2-hydroxyethyl methacrylate (PolyHEMA) hydrogel waveguide mixed with the probe molecule 1, 2-Diaminoanthraquinone (DAQ). There is a length difference of 1 mm between the two fibers, and the light has to propagate through the difference from the short fiber to the long fiber. The total cross section area of the active hydrogel waveguide embedded with the fibers is only 3mm x 1.2 mm. For practical use the tip is housed in a needle for mechanical protection and the sensing tip is able to detect aqueous NO concentration around 1 μM with time resolution about 5 minutes. Such a sensing tip can be used to monitor the medical conditions inside the brain after a stroke or a brain injury.

Micromanipulation of statoliths in gravity-sensing Chara rhizoids by optical tweezers.

PubMed

Leitz, G; Schnepf, E; Greulich, K O

1995-09-01

Infrared laser traps (optical tweezers) were used to micromanipulate statoliths in gravity-sensing rhizoids of the green alga Chara vulgaris Vail. We were able to hold and move statoliths with high accuracy and to observe directly the effects of statolith position on cell growth in horizontally positioned rhizoids. The first step in gravitropism, namely the physical action of gravity on statoliths, can be simulated by optical tweezers. The direct laser microirradiation of the rhizoid apex did not cause any visible damage to the cells. Through lateral positioning of statoliths a differential growth of the opposite flank of the cell wall could be induced, corresponding to bending growth in gravitropism. The acropetal displacement of the statolith complex into the extreme apex of the rhizoid caused a temporary decrease in cell growth rate. The rhizoids regained normal growth after remigration of the statoliths to their initial position 10-30 micrometers basal to the rhizoid apex. During basipetal displacement of statoliths, cell growth continued and the statoliths remigrated towards the rhizoid tip after release from the optical trap. The resistance to statolith displacement increased towards the nucleus. The basipetal displacement of the whole complex of statoliths for a long distance (>100 micrometers) caused an increase in cell diameter and a subsequent regaining of normal growth after the statoliths reappeared in the rhizoid apex. We conclude that the statolith displacement interferes with the mechanism of tip growth, i.e. with the transport of Golgi vesicles, either directly by mechanically blocking their flow and/or, indirectly, by disturbing the actomyosin system. In the presence of the actin inhibitor cytochalasin B the optical forces required for acropetal and basipetal displacement of statoliths were significantly reduced to a similar level. The lateral displacement of statoliths was not changed by cytochalasin B. The results indicate: (i) the viscous resistance to optical displacement of statoliths depend mainly on actin, (ii) the lateral displacement of statoliths is not impeded by actin filaments, (iii) the axially directed actin-mediated forces against optical displacement of statoliths (for a distance of 10 micrometers) are stronger in the basipetal than in the acropetal direction, (iv) the forces acting on single statoliths by axially oriented actin filaments are estimated to be in the range of 11-110 pN for acropetal and of 18-180 pN for basipetal statolith displacements.

The Fast and Transient Transcriptional Network of Gravity and Mechanical Stimulation in the Arabidopsis Root Apex1[w

PubMed Central

Kimbrough, Jeffery M.; Salinas-Mondragon, Raul; Boss, Wendy F.; Brown, Christopher S.; Sederoff, Heike Winter

2004-01-01

Plant root growth is affected by both gravity and mechanical stimulation (Massa GD, Gilroy S [2003] Plant J 33: 435–445). A coordinated response to both stimuli requires specific and common elements. To delineate the transcriptional response mechanisms, we carried out whole-genome microarray analysis of Arabidopsis root apices after gravity stimulation (reorientation) and mechanical stimulation and monitored transcript levels of 22,744 genes in a time course during the first hour after either stimulus. Rapid, transient changes in the relative abundance of specific transcripts occurred in response to gravity or mechanical stimulation, and these transcript level changes reveal clusters of coordinated events. Transcriptional regulation occurs in the root apices within less than 2 min after either stimulus. We identified genes responding specifically to each stimulus as well as transcripts regulated in both signal transduction pathways. Several unknown genes were specifically induced only during gravitropic stimulation (gravity induced genes). We also analyzed the network of transcriptional regulation during the early stages of gravitropism and mechanical stimulation. PMID:15347791

Towards systems biology of the gravity response of higher plants -multiscale analysis of Arabidopsis thaliana root growth

NASA Astrophysics Data System (ADS)

Palme, Klaus; Aubry, D.; Bensch, M.; Schmidt, T.; Ronneberger, O.; Neu, C.; Li, X.; Wang, H.; Santos, F.; Wang, B.; Paponov, I.; Ditengou, F. A.; Teale, W. T.; Volkmann, D.; Baluska, F.; Nonis, A.; Trevisan, S.; Ruperti, B.; Dovzhenko, A.

Gravity plays a fundamental role in plant growth and development. Up to now, little is known about the molecular organisation of the signal transduction cascades and networks which co-ordinate gravity perception and response. By using an integrated systems biological approach, a systems analysis of gravity perception and the subsequent tightly-regulated growth response is planned in the model plant Arabidopsis thaliana. This approach will address questions such as: (i) what are the components of gravity signal transduction pathways? (ii) what are the dynamics of these components? (iii) what is their spatio-temporal regulation in different tis-sues? Using Arabidopsis thaliana as a model-we use root growth to obtain insights in the gravity response. New techniques enable identification of the individual genes affected by grav-ity and further integration of transcriptomics and proteomics data into interaction networks and cell communication events that operate during gravitropic curvature. Using systematic multiscale analysis we have identified regulatory networks consisting of transcription factors, the protein degradation machinery, vesicle trafficking and cellular signalling during the gravire-sponse. We developed approach allowing to incorporate key features of the root system across all relevant spatial and temporal scales to describe gene-expression patterns and correlate them with individual gene and protein functions. Combination of high-resolution microscopy and novel computational tools resulted in development of the root 3D model in which quantitative descriptions of cellular network properties and of multicellular interactions important in root growth and gravitropism can be integrated for the first time.

Thermal effects from modified endodontic laser tips used in the apical third of root canals with erbium-doped yttrium aluminium garnet and erbium, chromium-doped yttrium scandium gallium garnet lasers.

PubMed

George, Roy; Walsh, Laurence J

2010-04-01

To evaluate the temperature changes occurring on the apical third of root surfaces when erbium-doped yttrium aluminium garnet (Er:YAG) and erbium, chromium-doped yttrium scandium gallium garnet (Er,Cr:YSGG) laser energy was delivered with a tube etched, laterally emitting conical tip and a conventional bare design optical fiber tip. Thermal effects of root canal laser treatments on periodontal ligament cells and alveolar bone are of concern in terms of safety. A total of 64 single-rooted extracted teeth were prepared 1 mm short of the working length using rotary nickel-titanium Pro-Taper files to an apical size corresponding to a F5 Pro-Taper instrument. A thermocouple located 2 mm from the apex was used to record temperature changes arising from delivery of laser energy through laterally emitting conical tips or plain tips, using an Er:YAG or Er,Cr:YSGG laser. For the Er:YAG and Er,Cr:YSGG systems, conical fibers showed greater lateral emissions (452 + 69% and 443 + 64%) and corresponding lower forward emissions (48 + 5% and 49 + 5%) than conventional plain-fiber tips. All four combinations of laser system and fiber design elicited temperature increases less than 2.5 degrees C during lasing. The use of water irrigation attenuated completely the thermal effects of individual lasing cycles. Laterally emitting conical fiber tips can be used safely under defined conditions for intracanal irradiation without harmful thermal effects on the periodontal apparatus.

Root hairs aid soil penetration by anchoring the root surface to pore walls

PubMed Central

Bengough, A. Glyn; Loades, Kenneth; McKenzie, Blair M.

2016-01-01

The physical role of root hairs in anchoring the root tip during soil penetration was examined. Experiments using a hairless maize mutant (Zea mays: rth3–3) and its wild-type counterpart measured the anchorage force between the primary root of maize and the soil to determine whether root hairs enabled seedling roots in artificial biopores to penetrate sandy loam soil (dry bulk density 1.0–1.5g cm−3). Time-lapse imaging was used to analyse root and seedling displacements in soil adjacent to a transparent Perspex interface. Peak anchorage forces were up to five times greater (2.5N cf. 0.5N) for wild-type roots than for hairless mutants in 1.2g cm−3 soil. Root hair anchorage enabled better soil penetration for 1.0 or 1.2g cm−3 soil, but there was no significant advantage of root hairs in the densest soil (1.5g cm−3). The anchorage force was insufficient to allow root penetration of the denser soil, probably because of less root hair penetration into pore walls and, consequently, poorer adhesion between the root hairs and the pore walls. Hairless seedlings took 33h to anchor themselves compared with 16h for wild-type roots in 1.2g cm−3 soil. Caryopses were often pushed several millimetres out of the soil before the roots became anchored and hairless roots often never became anchored securely.The physical role of root hairs in anchoring the root tip may be important in loose seed beds above more compact soil layers and may also assist root tips to emerge from biopores and penetrate the bulk soil. PMID:26798027

Root hairs aid soil penetration by anchoring the root surface to pore walls.

PubMed

Bengough, A Glyn; Loades, Kenneth; McKenzie, Blair M

2016-02-01

The physical role of root hairs in anchoring the root tip during soil penetration was examined. Experiments using a hairless maize mutant (Zea mays: rth3-3) and its wild-type counterpart measured the anchorage force between the primary root of maize and the soil to determine whether root hairs enabled seedling roots in artificial biopores to penetrate sandy loam soil (dry bulk density 1.0-1.5g cm(-3)). Time-lapse imaging was used to analyse root and seedling displacements in soil adjacent to a transparent Perspex interface. Peak anchorage forces were up to five times greater (2.5N cf. 0.5N) for wild-type roots than for hairless mutants in 1.2g cm(-3) soil. Root hair anchorage enabled better soil penetration for 1.0 or 1.2g cm(-3) soil, but there was no significant advantage of root hairs in the densest soil (1.5g cm(-3)). The anchorage force was insufficient to allow root penetration of the denser soil, probably because of less root hair penetration into pore walls and, consequently, poorer adhesion between the root hairs and the pore walls. Hairless seedlings took 33h to anchor themselves compared with 16h for wild-type roots in 1.2g cm(-3) soil. Caryopses were often pushed several millimetres out of the soil before the roots became anchored and hairless roots often never became anchored securely.The physical role of root hairs in anchoring the root tip may be important in loose seed beds above more compact soil layers and may also assist root tips to emerge from biopores and penetrate the bulk soil. © The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Proline Accumulation in Maize (Zea mays L.) Primary Roots at Low Water Potentials. II. Metabolic Source of Increased Proline Deposition in the Elongation Zone1

PubMed Central

Verslues, Paul E.; Sharp, Robert E.

1999-01-01

The proline (Pro) concentration increases greatly in the growing region of maize (Zea mays L.) primary roots at low water potentials (ψw), largely as a result of an increased net rate of Pro deposition. Labeled glutamate (Glu), ornithine (Orn), or Pro was supplied specifically to the root tip of intact seedlings in solution culture at high and low ψw to assess the relative importance of Pro synthesis, catabolism, utilization, and transport in root-tip Pro deposition. Labeling with [3H]Glu indicated that Pro synthesis from Glu did not increase substantially at low ψw and accounted for only a small fraction of the Pro deposition. Labeling with [14C]Orn showed that Pro synthesis from Orn also could not be a substantial contributor to Pro deposition. Labeling with [3H]Pro indicated that neither Pro catabolism nor utilization in the root tip was decreased at low ψw. Pro catabolism occurred at least as rapidly as Pro synthesis from Glu. There was, however, an increase in Pro uptake at low ψw, which suggests increased Pro transport. Taken together, the data indicate that increased transport of Pro to the root tip serves as the source of low-ψw-induced Pro accumulation. The possible significance of Pro catabolism in sustaining root growth at low ψw is also discussed. PMID:10198094

A RAPID DNA EXTRACTION METHOD IS SUCCESSFULLY APPLIED TO ITS-RFLP ANALYSIS OF MYCORRHIZAL ROOT TIPS

EPA Science Inventory

A rapid method for extracting DNA from intact, single root tips using a Xanthine solution was developed to handle very large numbers of analyses of ectomycorrhizas. By using an extraction without grinding we have attempted to bias the extraction towards the fungal DNA in the man...

Calcium-regulated in vivo protein phosphorylation in Zea mays L. root tips

NASA Technical Reports Server (NTRS)

Raghothama, K. G.; Reddy, A. S.; Friedmann, M.; Poovaiah, B. W.

1987-01-01

Calcium dependent protein phosphorylation was studied in corn (Zea mays L.) root tips. Prior to in vivo protein phosphorylation experiments, the effect of calcium, ethyleneglycol-bis-(beta-aminoethyl ether)-N-N' -tetraacetic acid (EGTA) and calcium ionophore (A-23187) on phosphorus uptake was studied. Calcium increased phosphorus uptake, whereas EGTA and A-23187 decreased it. Consequently, phosphorus concentration in the media was adjusted so as to attain similar uptake in different treatments. Phosphoproteins were analyzed by two-dimensional gel electrophoresis. Distinct changes in phosphorylation were observed following altered calcium levels. Calcium depletion in root tips with EGTA and A-23187 decreased protein phosphorylation. However, replenishment of calcium following EGTA and ionophore pretreatment enhanced phosphorylation of proteins. Preloading of the root tips with 32P in the presence of EGTA and A-23187 followed by a ten minute calcium treatment, resulted in increased phosphorylation indicating the involvement of calcium, calcium and calmodulin-dependent kinases. Calmodulin antagonist W-7 was effective in inhibiting calcium-promoted phosphorylation. These studies suggest a physiological role for calcium-dependent phosphorylation in calcium-mediated processes in plants.

Analysis of gene expression during parabolic flights reveals distinct early gravity responses in Arabidopsis roots.

PubMed

Aubry-Hivet, D; Nziengui, H; Rapp, K; Oliveira, O; Paponov, I A; Li, Y; Hauslage, J; Vagt, N; Braun, M; Ditengou, F A; Dovzhenko, A; Palme, K

2014-01-01

Plant roots are among most intensively studied biological systems in gravity research. Altered gravity induces asymmetric cell growth leading to root bending. Differential distribution of the phytohormone auxin underlies root responses to gravity, being coordinated by auxin efflux transporters from the PIN family. The objective of this study was to compare early transcriptomic changes in roots of Arabidopsis thaliana wild type, and pin2 and pin3 mutants under parabolic flight conditions and to correlate these changes to auxin distribution. Parabolic flights allow comparison of transient 1-g, hypergravity and microgravity effects in living organisms in parallel. We found common and mutation-related genes differentially expressed in response to transient microgravity phases. Gene ontology analysis of common genes revealed lipid metabolism, response to stress factors and light categories as primarily involved in response to transient microgravity phases, suggesting that fundamental reorganisation of metabolic pathways functions upstream of a further signal mediating hormonal network. Gene expression changes in roots lacking the columella-located PIN3 were stronger than in those deprived of the epidermis and cortex cell-specific PIN2. Moreover, repetitive exposure to microgravity/hypergravity and gravity/hypergravity flight phases induced an up-regulation of auxin responsive genes in wild type and pin2 roots, but not in pin3 roots, suggesting a critical function of PIN3 in mediating auxin fluxes in response to transient microgravity phases. Our study provides important insights towards understanding signal transduction processes in transient microgravity conditions by combining for the first time the parabolic flight platform with the transcriptome analysis of different genetic mutants in the model plant, Arabidopsis. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.

The TacTip Family: Soft Optical Tactile Sensors with 3D-Printed Biomimetic Morphologies

PubMed Central

Pestell, Nicholas; Cramphorn, Luke; Winstone, Benjamin; Giannaccini, Maria Elena; Rossiter, Jonathan; Lepora, Nathan F.

2018-01-01

Abstract Tactile sensing is an essential component in human–robot interaction and object manipulation. Soft sensors allow for safe interaction and improved gripping performance. Here we present the TacTip family of sensors: a range of soft optical tactile sensors with various morphologies fabricated through dual-material 3D printing. All of these sensors are inspired by the same biomimetic design principle: transducing deformation of the sensing surface via movement of pins analogous to the function of intermediate ridges within the human fingertip. The performance of the TacTip, TacTip-GR2, TacTip-M2, and TacCylinder sensors is here evaluated and shown to attain submillimeter accuracy on a rolling cylinder task, representing greater than 10-fold super-resolved acuity. A version of the TacTip sensor has also been open-sourced, enabling other laboratories to adopt it as a platform for tactile sensing and manipulation research. These sensors are suitable for real-world applications in tactile perception, exploration, and manipulation, and will enable further research and innovation in the field of soft tactile sensing. PMID:29297773

The TacTip Family: Soft Optical Tactile Sensors with 3D-Printed Biomimetic Morphologies.

PubMed

Ward-Cherrier, Benjamin; Pestell, Nicholas; Cramphorn, Luke; Winstone, Benjamin; Giannaccini, Maria Elena; Rossiter, Jonathan; Lepora, Nathan F

2018-04-01

Tactile sensing is an essential component in human-robot interaction and object manipulation. Soft sensors allow for safe interaction and improved gripping performance. Here we present the TacTip family of sensors: a range of soft optical tactile sensors with various morphologies fabricated through dual-material 3D printing. All of these sensors are inspired by the same biomimetic design principle: transducing deformation of the sensing surface via movement of pins analogous to the function of intermediate ridges within the human fingertip. The performance of the TacTip, TacTip-GR2, TacTip-M2, and TacCylinder sensors is here evaluated and shown to attain submillimeter accuracy on a rolling cylinder task, representing greater than 10-fold super-resolved acuity. A version of the TacTip sensor has also been open-sourced, enabling other laboratories to adopt it as a platform for tactile sensing and manipulation research. These sensors are suitable for real-world applications in tactile perception, exploration, and manipulation, and will enable further research and innovation in the field of soft tactile sensing.

ARG1 and ARL2 contribute to gravity signal transduction in the statocytes of Arabidopsis thaliana roots and hypocotyls

NASA Astrophysics Data System (ADS)

Masson, Patrick; Harrison, Benjamin; Stanga, John; Otegui, Marisa; Sedbrook, John

Gravity is an important cue that plant organs use to guide their growth. Each organ is characterized by a defined gravity set point angle that dictates its optimal orientation within the gravity field. Specialized cells, named statocytes, enable this directional growth response by perceiving gravity via the sedimentation of, and/or tension/pressure exerted by, starch-filled plastids within their cytoplasm. Located in the columella region of the cap in roots and in the endodermis of hypocotyls and stems, these cells modulate the lateral transport of auxin across the corresponding organ in a gravistimulus-dependent manner. Upon plant reorientation within the gravity field, a gravity signal transduction pathway is activated within those cells, which in roots leads to a relocalization of the PIN3 auxin efflux carrier toward the lower membrane and an alkalinization of the cytoplasm. In turn, these events appear to promote a lateral transport of auxin toward the bottom side of the stimulated organ, which promotes a curvature. We previously uncovered ARG1 and ARL2 as essential contributors to these cellular processes. Mutations in these genes result in altered root and hypocotyl gravitropism. In roots, this abnormal growth behavior is associated with a lack of PIN3 relocalization within the statocytes and an absence of preferential downward auxin transport upon gravistimulation. These two genes encode paralogous J-domain proteins that are associated with the plasma membrane and other membranes of the vesicular trafficking pathway, and appear to modulate protein trafficking within the statocytes. An analysis of the root gravitropic phenotypes associated with different double mutant configurations affecting ARG1, ARL2 and PIN3 suggest that all three proteins function in a common gravity-signaling pathway. Surprisingly, when a mutation that affects starch biosynthesis (pgm) is introgressed into an arg1-2 mutant, the gravitropic defects are dramatically enhanced relative to those of the single mutants. We used this observation to design a genetic screen for the identification of new loci that contribute to the pgm gravity-signaling pathway. Two genetic enhancers of arg1-2 were identified this way, called mar1-1 and mar2-1. These mutations were shown to affect components of the protein-import complex found in the outer membrane of plastids. Interestingly, the columellar amyloplasts of arg1-2 mar2-1 mutant roots display wild-type ultra-structure, accumulate starch and sediment at wild-type rates upon gravistimulation. We conclude that the plastid outer envelope may contribute directly to gravity signal transduction within the statocytes.

A Novel Growing Device Inspired by Plant Root Soil Penetration Behaviors

PubMed Central

Sadeghi, Ali; Tonazzini, Alice; Popova, Liyana; Mazzolai, Barbara

2014-01-01

Moving in an unstructured environment such as soil requires approaches that are constrained by the physics of this complex medium and can ensure energy efficiency and minimize friction while exploring and searching. Among living organisms, plants are the most efficient at soil exploration, and their roots show remarkable abilities that can be exploited in artificial systems. Energy efficiency and friction reduction are assured by a growth process wherein new cells are added at the root apex by mitosis while mature cells of the root remain stationary and in contact with the soil. We propose a new concept of root-like growing robots that is inspired by these plant root features. The device penetrates soil and develops its own structure using an additive layering technique: each layer of new material is deposited adjacent to the tip of the device. This deposition produces both a motive force at the tip and a hollow tubular structure that extends to the surface of the soil and is strongly anchored to the soil. The addition of material at the tip area facilitates soil penetration by omitting peripheral friction and thus decreasing the energy consumption down to 70% comparing with penetration by pushing into the soil from the base of the penetration system. The tubular structure provides a path for delivering materials and energy to the tip of the system and for collecting information for exploratory tasks. PMID:24587244

Effect of aluminum on metabolism of organic acids and chemical forms of aluminum in root tips of Eucalyptus camaldulensis Dehnh.

PubMed

Ikka, Takashi; Ogawa, Tsuyoshi; Li, Donghua; Hiradate, Syuntaro; Morita, Akio

2013-10-01

Eucalyptus (Eucalyptus camaldulensis) has relatively high resistance to aluminum (Al) toxicity than the various herbaceous plants and model plant species. To investigate Al-tolerance mechanism, the metabolism of organic acids and the chemical forms of Al in the target site (root tips) in Eucalyptus was investigated. To do this, 2-year old rooted cuttings of E. camaldulensis were cultivated in half-strength Hoagland solution (pH 4.0) containing Al (0, 0.25, 0.5, 1.0, 2.5 and 5.0mM) salts for 5weeks; growth was not affected at concentrations up to 2.5mM even with Al concentration reaching 6000μgg(-1) DW. In roots, the citrate content also increased with increasing Al application. Concurrently, the activities of aconitase and NADP(+)-isocitrate dehydrogenase, which catalyze the decomposition of citrate, decreased. On the other hand, the activity of citrate synthase was not affected at concentrations up to 2.5mM Al. (27)Al-NMR spectroscopic analyses were carried out where it was found that Al-citrate complexes were a major chemical form present in cell sap of root tips. These findings suggested that E. camaldulensis detoxifies Al by forming Al-citrate complexes, and that this is achieved through Al-induced citrate accumulation in root tips via suppression of the citrate decomposition pathway. Copyright © 2013 Elsevier Ltd. All rights reserved.

Unusual square roots in the ghost-free theory of massive gravity

NASA Astrophysics Data System (ADS)

Golovnev, Alexey; Smirnov, Fedor

2017-06-01

A crucial building block of the ghost free massive gravity is the square root function of a matrix. This is a problematic entity from the viewpoint of existence and uniqueness properties. We accurately describe the freedom of choosing a square root of a (non-degenerate) matrix. It has discrete and (in special cases) continuous parts. When continuous freedom is present, the usual perturbation theory in terms of matrices can be critically ill defined for some choices of the square root. We consider the new formulation of massive and bimetric gravity which deals directly with eigenvalues (in disguise of elementary symmetric polynomials) instead of matrices. It allows for a meaningful discussion of perturbation theory in such cases, even though certain non-analytic features arise.

The effect of cyanide compounds, fluorides, aluminum, and inorganic oxides present in spent pot liner on germination and root tip cells of Lactuca sativa.

PubMed

Andrade, L F; Davide, L C; Gedraite, L S

2010-05-01

SPL (spent pot liner) is a solid waste produced by the aluminum industry. This waste has a highly variable composition, consisting of cyanides, fluorides, organics, and metals. The aim of this work was to study the effect of SPL on root tips of Lactuca sativa using current plant bioassays. We observed a decrease in the germination rate with increasing concentrations of SPL. In addition, SPL was found to reduce root growth, which is correlated with a decrease in the mitotic index. Nevertheless, we noticed a significant enhancement in the percentage of stickiness, c-metaphase, anaphase bridges, and laggard chromosomes in dividing cells and also an increase in the number of cells with condensed nuclei. Moreover, SPL was found to alter the root tip surface, resulting in a reduction in the amount of root hair. These results demonstrate that SPL is a toxic agent that leads to cell damage and disturbance. Copyright 2009 Elsevier Inc. All rights reserved.

Long-term fertilization, but not warming, shifts rates of ectomycorrhizal nutrient cycling in Arctic tussock tundra.

NASA Astrophysics Data System (ADS)

Dunleavy, H.; Mack, M. C.

2017-12-01

The role of ectomycorrhizae (ECM) in Arctic nutrient cycling may be changing as temperature, nutrient availability, and ECM shrub abundance and size increase. A shift in ECM function has been proposed as a possible mechanism for shrub expansion. While several studies demonstrate a higher abundance of ECM as well as community compositional shifts in response to long-term experimental warming and fertilization, direct measurements of functional responses are missing. To understand the potential role of ECM in soil biogeochemical processes of the changing Arctic, we investigated the functional response of ECM to 30 years of summer warming and increased nutrient availability by measuring potential activities of extracellular enzymes associated with nitrogen (N) and phosphorous (P) acquisition on ECM root tips. We hypothesize ECM enzyme activities will be higher with warmer temperatures. Conversely, fertilization will lower ECM enzyme activities as N and P become less limiting to host plants. Preliminary results strongly support our latter hypothesis, but not the first. Warming decreased hydrolytic P-associated and labile N-associated enzyme activities on individual root tips (pmol/min/mm2 root tip) by 30% and 83%, respectively. However, warming increased ECM abundance and did not alter community-level activities (pmol/min/cm3 soil). Fertilization decreased hydrolytic and oxidative enzymatic activities on individual root tips by 34 to 80% as well as on a community level by 67 to 93%, even though ECM shrubs were almost monodominant. The combined effect of warming and fertilization decreased labile N-associated enzyme activity by 82%, but had little effect on oxidative and other hydrolytic enzyme activities. Although both warming and fertilization decreased root tip activities, reflecting a potential reduction in plant allocation to mycorrhizal nutrient acquisition, only fertilization lowered rates of ECM nutrient cycling. The indirect relationship between ECM abundance and individual root tip activity highlights the importance of measuring ECM function to assess the role of this symbiosis in nutrient cycling.

CASIROZ: Root parameters and types of ectomycorrhiza of young beech plants exposed to different ozone and light regimes.

PubMed

Zeleznik, P; Hrenko, M; Then, C; Koch, N; Grebenc, T; Levanic, T; Kraigher, H

2007-03-01

Tropospheric ozone (O(3)) triggers physiological changes in leaves that affect carbon source strength leading to decreased carbon allocation below-ground, thus affecting roots and root symbionts. The effects of O(3) depend on the maturity-related physiological state of the plant, therefore adult and young forest trees might react differently. To test the applicability of young beech plants for studying the effects of O(3) on forest trees and forest stands, beech seedlings were planted in containers and exposed for two years in the Kranzberg forest FACOS experiment (Free-Air Canopy O(3) Exposure System, http://www.casiroz.de ) to enhanced ozone concentration regime (ambient [control] and double ambient concentration, not exceeding 150 ppb) under different light conditions (sun and shade). After two growing seasons the biomass of the above- and below-ground parts, beech roots (using WinRhizo programme), anatomical and molecular (ITS-RFLP and sequencing) identification of ectomycorrhizal types and nutrient concentrations were assessed. The mycorrhization of beech seedlings was very low ( CA. 5 % in shade, 10 % in sun-grown plants), no trends were observed in mycorrhization (%) due to ozone treatment. The number of Cenococcum geophilum type of ectomycorrhiza, as an indicator of stress in the forest stands, was not significantly different under different ozone treatments. It was predominantly occurring in sun-exposed plants, while its majority share was replaced by Genea hispidula in shade-grown plants. Different light regimes significantly influenced all parameters except shoot/root ratio and number of ectomycorrhizal types. In the ozone fumigated plants the number of types, number of root tips per length of 1 to 2 mm root diameter, root length density per volume of soil and concentration of Mg were significantly lower than in control plants. Trends to a decrease were found in root, shoot, leaf, and total dry weights, total number of root tips, number of vital mycorrhizal root tips, fine root (mass) density, root tip density per surface, root area index, concentration of Zn, and Ca/Al ratio. Due to the general reduction in root growth indices and nutrient cycling in ozone-fumigated plants, alterations in soil carbon pools could be predicted.

How to detect when cells in space perceive gravity

NASA Technical Reports Server (NTRS)

Bjoerkman, Thomas

1989-01-01

It is useful to be able to measure when and whether cells detect gravity during spaceflights. For studying gravitational physiology, gravity perception is the response the experimentalist needs to measure. Also, for growing plants in space, plant cells may have a non-directional requirement for gravity as a development cue. The main goals of spaceflight experiments in which gravity perception would be measured are to determine the properties of the gravity receptor and how it is activated, and to determine fundamental characteristics of the signal generated. The main practical difficulty with measuring gravity sensing in space is that gravity sensing cannot be measured with certainty on earth. Almost all experiments measure gravitropic curvature. Reciprocity and intermittent stimulation are measurements which were made to some degree on earth using clinostatting, but which would provide clearer results if done with microgravity rather than clinostatting. These would be important uses of the space laboratory for determining the nature of gravity sensing in plants. Those techniques which do not use gravitropic curvature to measure gravity sensing are electrophysiological. The vibrating probe would be somewhat easier to adapt to space conditions than the intracellular microelectrode because it can be positioned with less precision. Ideally, a non-invasive technique would be best suited if an appropriate measure could be developed. Thus, the effect of microgravity on cultured cells is more likely to be by large-scale physical events than gravity sensing in the culture cells. It is not expected that it will be necessary to determine whether individual cultured cells perceive gravity unless cells grow abnormally even after the obvious microgravity effects on the culture as a whole can be ruled out as the cause.

Floating retained root lesion mimicking apical periodontitis.

PubMed

Chung, Ming-Pang; Chen, Chih-Ping; Shieh, Yi-Shing

2009-10-01

A case of a retained root tip simulating apical periodontitis on radiographic examination is described. The retained root tip, originating from the left lower first molar, floated under the left lower second premolar apical region mimicking apical periodontitis. It appeared as an ill-defined periapical radiolucency containing a smaller radiodense mass on radiograph. The differential diagnosis included focal sclerosing osteomyelitis (condensing osteitis) and ossifying fibroma. Upon exicisional biopsy, a retained root associated with granulation tissue was found. After 1-year follow-up, the patient was asymptomatic and the periradicular lesion was healing. Meanwhile, the associated tooth showed a normal response to stimulation testing.

[Evaluation of the cavity cleaning of ultrasonic instruments and slow-speed handpiece in posterior teeth root-end preparation].

PubMed

Zhang, Ping-juan; Chen, Wen-xia; Zeng, Qi-xin; Xie, Fang-fang

2013-04-01

To compare the cleanliness of root end preparations by using ultrasonic instrumentation and slow-speed handpiece. Thirty-two mesial roots of the first mandibular molars with two canals and mature root apices were assigned randomly to 2 groups, each group had 16 teeth. The root-end preparations were made respectively using ultrasonic diamond tip Berutti and NiTi tip RE2 and slow-speed handpiece with No.2 round bur. Root end cavities were examined under scanning electron microscope for further evaluation of the superficial debris and smear layer of the root end preparations. SPSS 13.0 software package was used for Kruskal Wallis test. Ultrasonic preparation had significantly less superficial debris and smear layer than slow-speed handpiece preparation (P<0.05). Ultrasonic instrument creates cleaner surfaces for root end cavities than slow-speed handpiece preparation in posterior teeth root end preparation.

Genotoxicity effects of silver nanoparticles on wheat (Triticum aestivum L.) root tip cells.

PubMed

Abdelsalam, Nader R; Abdel-Megeed, Ahmed; Ali, Hayssam M; Salem, Mohamed Z M; Al-Hayali, Muwafaq F A; Elshikh, Mohamed S

2018-07-15

The distribution and use of nanoparticles have rapidly increased over recent years, but the available knowledge regarding their mode of action, ecological tolerance and biodegradability remains insufficient. Wheat (Triticum aestivum L.) is the most important crop worldwide. In the current study, the effects of silver nanoparticles (AgNPs) obtained from two different sources, namely, green and chemical syntheses, on chromosomal aberrations and cell division were investigated. Wheat root tips were treated with four different AgNP concentrations (10, 20, 40 and 50 ppm) for three different exposure durations (8, 16 and 24 h), and the different concentrations of the nanoparticles were added to the tested grains until the root lengths reached 1.5-2 cm. For each concentration, the mitotic indexes (%) were obtained from an analysis of ~ 2000 cells. The treated root-tip cells exhibited various types of chromosomal aberrations, such as incorrect orientation at metaphase, chromosomal breakage, metaphasic plate distortion, spindle dysfunction, stickiness, aberrant movement at metaphase, fragmentation, scattering, unequal separation, scattering, chromosomal gaps, multipolar anaphase, erosion, and distributed and lagging chromosomes. These results demonstrate that the root tip cells of wheat can readily internalize the AgNPs and that the internalized AgNPs can interfere with the cells' normal function. Copyright © 2018 Elsevier Inc. All rights reserved.

A high-yield procedure for isolation of metaphase chromosomes from root tips of Vicia faba L.

PubMed

Doležel, J; Cíhalíková, J; Lucretti, S

1992-08-01

A new method is described for the isolation of large quantities of Vicia faba metaphase chromosomes. Roots were treated with 2.5 mM hydroxyurea for 18 h to accumulate meristem tip cells at the G1/S interface. After release from the block, the cells re-entered the cell cycle with a high degree of synchrony. A treatment with 2.5 μM amiprophos-methyl (APM) was used to accumulate mitotic cells in metaphase. The highest metaphase index (53.9%) was achieved when, 6 h after the release from the hydroxyurea block, the roots were exposed to APM for 4 h. The chromosomes were released from formaldehyde-fixed root tips by chopping with a scalpel in LB01 lysis buffer. Both the quality and the quantity of isolated chromosomes, examined microscopically and by flow cytometry, depended on the extent of the fixation. The best results were achieved after fixation with 6% formaldehyde for 30 min. Under these conditions, 1 · 10(6) chromosomes were routinely obtained from 30 root tips. The chromosomes were morphologically intact and suitable both for high-resolution chromosome studies and for flow-cytometric analysis and sorting. After the addition of hexylene glycol, the chromosome suspensions could be stored at 4° C for six months without any signs of deterioration.

New theories of root growth modelling

NASA Astrophysics Data System (ADS)

Landl, Magdalena; Schnepf, Andrea; Vanderborght, Jan; Huber, Katrin; Javaux, Mathieu; Bengough, A. Glyn; Vereecken, Harry

2016-04-01

In dynamic root architecture models, root growth is represented by moving root tips whose line trajectory results in the creation of new root segments. Typically, the direction of root growth is calculated as the vector sum of various direction-affecting components. However, in our simulations this did not reproduce experimental observations of root growth in structured soil. We therefore developed a new approach to predict the root growth direction. In this approach we distinguish between, firstly, driving forces for root growth, i.e. the force exerted by the root which points in the direction of the previous root segment and gravitropism, and, secondly, the soil mechanical resistance to root growth or penetration resistance. The latter can be anisotropic, i.e. depending on the direction of growth, which leads to a difference between the direction of the driving force and the direction of the root tip movement. Anisotropy of penetration resistance can be caused either by microscale differences in soil structure or by macroscale features, including macropores. Anisotropy at the microscale is neglected in our model. To allow for this, we include a normally distributed random deflection angle α to the force which points in the direction of the previous root segment with zero mean and a standard deviation σ. The standard deviation σ is scaled, so that the deflection from the original root tip location does not depend on the spatial resolution of the root system model. Similarly to the water flow equation, the direction of the root tip movement corresponds to the water flux vector while the driving forces are related to the water potential gradient. The analogue of the hydraulic conductivity tensor is the root penetrability tensor. It is determined by the inverse of soil penetration resistance and describes the ease with which a root can penetrate the soil. By adapting the three dimensional soil and root water uptake model R-SWMS (Javaux et al., 2008) in this way, we were able to simulate root growth and root water uptake in soil with macropores. The model was parametrized using experimental results of studies by Hirth et al. (2005) and Stirzaker et al. (1996). It proved to be capable of reproducing observed root growth responses to structured soil both at the single root and the plant root system scale. This new approach enables us to investigate how plant roots use macropores to gain access to water and nutrient reservoirs in deeper, highly dense soil layers. Acknowledgements: Funding by German Research Foundation within the Research Unit 888 is gratefully acknowledged. The James Hutton Institute receives funding from the Scottish Government.

Effect of IOP based infusion system with and without balanced phaco tip on cumulative dissipated energy and estimated fluid usage in comparison to gravity fed infusion in torsional phacoemulsification.

PubMed

Malik, Praveen K; Dewan, Taru; Patidar, Arun Kr; Sain, Ekta

2017-01-01

To evaluate the effect of three different combinations of tip designs and infusion systems in torsional phacoemulsification (INFINITI and CENTURION) in patients with cataract. According to the manufacturer, two unique improvements in the Centurion are: active fluid dynamic management system and use of an intrepid balanced tip. The study specifically aimed to evaluate the beneficial effects, if any, of change in tip design and infusion system individually and in combination on both per-operative parameters as well as endothelial health over 6 months. One hundred and twenty six consenting patients of grade 4.0-6.9 senile cataract were randomized into three groups for phacoemulsification: Group A ( n  = 42): Gravity fed infusion system and 45 0 Kelman miniflared ABS phaco tip; Group B ( n  = 42): intraocular pressure (IOP) based infusion system and 45 0 Kelman miniflared ABS phaco tip; Group C ( n  = 42): IOP based infusion system and 45 0 Intrepid balanced phaco tip. The cumulative dissipated energy (CDE), estimated fluid usage (EFU) and total aspiration time (TAT) were compared peroperatively. The endothelial parameters were followed up postoperatively for six months. The three arms were matched for age ( p  = 0.525), gender ( p  = 0.96) and grade of cataract ( p  = 0.177). Group C was associated with significant reductions in CDE ( p  = 0.001), EFU ( p  < 0.0005) as well as TAT ( p  = 0.001) in comparison to the other groups. All three groups had comparable baseline endothelial cell density ( p  = 0.876) and central corneal thickness ( p  = 0.561). On post-operative evaluation, although all groups were comparable till 3 months, by 6 months, the percentage losses in endothelial cell density were significantly lower in group C as compared to the other groups. Use of an IOP based phacoemulsification system in association with use of the Intrepid balanced tip reduces the CDE, EFU and TAT in comparison to a gravity fed system with a mini flared tip or IOP based system with a mini flared tip while also providing better endothelial preservation thus favouring the use of an IOP fed system with a balanced tip. Trial registration No.: CTRI/2016/06/007022.

A Finite Element Analysis of a Carbon Fiber Composite Micro Air Vehicle Wing

DTIC Science & Technology

2012-03-22

3. Errors in the manufacturing of the laminate resulting in errors in ply orientation. Each of these was examined in order to determine a root ...material properties. 4.2.4. Vein Width The widths of the individual veins of the manufactured wing were varied linearly from root to tip of the...wing. In the sizing of the engineered wing, the width of the veins were varied linearly from the root of the vein to the tip. For manufacturing

Aluminum fractions in root tips of slash pine and loblolly pine families differing in Al resistance

Treesearch

Jaroslaw Nowak; Alexander L. Friend

2005-01-01

Aluminum (Al) distribution among several cellular fractions was investigated in root tips of seedlings of one Al-resistant and one Al-sensitive family of slash pine (Pinus elliottii Engelm.) and loblolly pine (Pinus taeda L.) grown in nutrient solution containing 100 M AlCl3 (pH 4) for 167 h....

Amyloplast Distribution Directs a Root Gravitropic Reaction

NASA Astrophysics Data System (ADS)

Kordyum, Elizabeth

Immobile higher plants are oriented in the gravitational field due to gravitropim that is a physiological growth reaction and consists of three phases: reception of a gravitational signal by statocytes, its transduction to the elongation zone, and finally the organ bending. As it is known, roots are characterized with positive gravitropism, i. e. they grow in the direction of a gravitational vector, stems - with negative gravitropism, i. e. they grow in the direction opposite to a gravitational vector. According to the Nemec’s and Haberlandt’s starch-statolith hypothesis, amyloplasts in diameter of 1.5 - 3 μ in average, which appear to act as gravity sensors and fulfill a statolythic function in the specialized graviperceptive cells - statocytes, sediment in the direction of a gravitational vector in the distal part of a cell, while a nucleus is in the proximal one. There are reasonable data that confirm the amyloplasts-statoliths participation in gravity perception: 1) correlation between the statoliths localization and the site of gravity sensing, 2) significant redistribution (sedimentation) of amyloplasts in statocytes under gravistimulation in comparison with other cell organelles, 3) root decreased ability to react on gravity under starch removal from amyloplasts, 4) starchless Arabidopsis thaliana mutants are agravitropic, 5) amyloplasts-statoliths do not sediment in the absence of the gravitational vector and are in different parts or more concentrated in the center of statocytes. Plant tropisms have been intensively studied for many decades and continue to be investigated. Nevertheless, the mechanisms by which plants do so is still not clearly explained and many questions on gravisensing and graviresponse remain unanswered. Even accepted hypotheses are now being questioned and recent data are critically evaluated. Although the available data show the Ca2+ and cytoskeleton participation in graviperception and signal transduction, the clear evidence with regard to the participation of calcium ions and cytoskeletal elements in these processes is therefore substantial but still circumstantial and requires new experimental data. Using a new model - weak combined magnetic fields (CMFs), which elicit a variety of responses in plants, growth rate and fresh weight, seed germination, Ca2+ concentration, membrane permeability, with a frequency resonance to cyclotron frequency of calcium ions, we firstly showed that a root positive gravitropic reaction changes on a negative one. In this case, the paradoxical displacement of amylopasts-statoliths to the upper longitudinal cell wall of statocytes occurred in the direction opposite to a gravitational vector. Displacement of amyloplasts, which contain the abundance of free Ca2+ in the stroma, was accompanied with Ca2+ redistribution in the same direction in the cytosol and increasing around amyloplasts in comparison with the state magnetic field. In the elongation zone, calcium ions accumulated in the upper site of a gravistimulated root unlike a positive gravitropic reaction, and a root is bending in the same direction in which amyloplasts are displacing. It seems that a root gravitropic reaction, if it began, occurs by an usual physiological way resulting in root bending with an opposite sign. It is of a special interest that a root is bending to the same direction with displacing of amyloplasts: in positive gravitropism - downwards, in negative gravitropism - upwards. Peculiarities of calcium ion redistribution in statocytes under gravistimulation in such combined magnetic field are a new additional evidence of a Ca2+ ion significant role in gravitropism. Thus, our data support the starch-statolith hypothesis but also pose the question as to which forces displace amyloplasts against the gravity vector? We hope that these data will stimulate new research to better understand the mechanisms of plant graviperception and graviresponse. Gravistimulation of a root in the CMF with the frequency resonance to the cyclotron frequency of Ca2+ ions is an effective model for future research of the mechanism of plant gravitropism, including a Ca2+ role in plant physiological growth reactions.

Block of ATP-Binding Cassette B19 Ion Channel Activity by 5-Nitro-2-(3-Phenylpropylamino)-Benzoic Acid Impairs Polar Auxin Transport and Root Gravitropism1[OPEN

PubMed Central

Cho, Misuk; Henry, Elizabeth M.; Lewis, Daniel R.; Wu, Guosheng; Muday, Gloria K.

2014-01-01

Polar transport of the hormone auxin through tissues and organs depends on membrane proteins, including some B-subgroup members of the ATP-binding cassette (ABC) transporter family. The messenger RNA level of at least one B-subgroup ABCB gene in Arabidopsis (Arabidopsis thaliana), ABCB19, increases upon treatment with the anion channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), possibly to compensate for an inhibitory effect of the drug on ABCB19 activity. Consistent with this hypothesis, NPPB blocked ion channel activity associated with ABCB19 expressed in human embryonic kidney cells as measured by patch-clamp electrophysiology. NPPB inhibited polar auxin transport through Arabidopsis seedling roots similarly to abcb19 mutations. NPPB also inhibited shootward auxin transport, which depends on the related ABCB4 protein. NPPB substantially decreased ABCB4 and ABCB19 protein levels when cycloheximide concomitantly inhibited new protein synthesis, indicating that blockage by NPPB enhances the degradation of ABCB transporters. Impairing the principal auxin transport streams in roots with NPPB caused aberrant patterns of auxin signaling reporters in root apices. Formation of the auxin-signaling gradient across the tips of gravity-stimulated roots, and its developmental consequence (gravitropism), were inhibited by micromolar concentrations of NPPB that did not affect growth rate. These results identify ion channel activity of ABCB19 that is blocked by NPPB, a compound that can now be considered an inhibitor of polar auxin transport with a defined molecular target. PMID:25324509

Block of ATP-binding cassette B19 ion channel activity by 5-nitro-2-(3-phenylpropylamino)-benzoic acid impairs polar auxin transport and root gravitropism.

PubMed

Cho, Misuk; Henry, Elizabeth M; Lewis, Daniel R; Wu, Guosheng; Muday, Gloria K; Spalding, Edgar P

2014-12-01

Polar transport of the hormone auxin through tissues and organs depends on membrane proteins, including some B-subgroup members of the ATP-binding cassette (ABC) transporter family. The messenger RNA level of at least one B-subgroup ABCB gene in Arabidopsis (Arabidopsis thaliana), ABCB19, increases upon treatment with the anion channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), possibly to compensate for an inhibitory effect of the drug on ABCB19 activity. Consistent with this hypothesis, NPPB blocked ion channel activity associated with ABCB19 expressed in human embryonic kidney cells as measured by patch-clamp electrophysiology. NPPB inhibited polar auxin transport through Arabidopsis seedling roots similarly to abcb19 mutations. NPPB also inhibited shootward auxin transport, which depends on the related ABCB4 protein. NPPB substantially decreased ABCB4 and ABCB19 protein levels when cycloheximide concomitantly inhibited new protein synthesis, indicating that blockage by NPPB enhances the degradation of ABCB transporters. Impairing the principal auxin transport streams in roots with NPPB caused aberrant patterns of auxin signaling reporters in root apices. Formation of the auxin-signaling gradient across the tips of gravity-stimulated roots, and its developmental consequence (gravitropism), were inhibited by micromolar concentrations of NPPB that did not affect growth rate. These results identify ion channel activity of ABCB19 that is blocked by NPPB, a compound that can now be considered an inhibitor of polar auxin transport with a defined molecular target. © 2014 American Society of Plant Biologists. All Rights Reserved.

Theoretical parametric study of the relative advantages of winglets and wing-tip extensions

NASA Technical Reports Server (NTRS)

Heyson, H. H.; Riebe, G. D.; Fulton, C. L.

1977-01-01

It was found that for identical increases in bending moment, a winglet provides a greater gain in induced efficiency than a tip extension. Winglet toe-in angle allows design trades between efficiency and root moment. A winglet showed the greatest benefit when the wing loads were heavy near the tip. Washout diminished the benefit of either tip modification, and the gain in induced efficiency became a function of lift coefficient; heavy wing loadings obtained the greatest benefit from a winglet, and low speed performance was enhanced even more than cruise performance. Both induced efficiency and bending moment increased with winglet length and outward cant. The benefit of a winglet relative to a tip extension was greatest for a nearly vertical winglet. Root bending moment was proportional to the minimum weight of bending material required in the wing; it is a valid index of the impact of tip modifications on a new wing design.

Theoretical Parametric Study of the Relative Advantages of Winglets and Wing-Tip Extensions

NASA Technical Reports Server (NTRS)

Heyson, H. H.; Riebe, G. D.; Fulton, C. L.

1977-01-01

For identical increases in bending moment, a winglet provides a greater gain in induced efficiency than tip extension. Winglet toe angle allows design trades between efficiency and root moment. A winglet shows the greatest benefit when the wing loads are heavy near the tip. Washout diminishes the benefit of either tip modification, and the gain in induced efficiency becomes a function of lift coefficient; thus, heavy wing loadings obtain the greatest benefit from a winglet, and low-speed performance is enhanced even more than cruise performance. Both induced efficiency and bending moment increase with winglet length and outward cant. The benefit of a winglet relative to a tip extension is greatest for a nearly vertical winglet. Root bending moment is proportional to the minimum weight of bending material required in the wing; thus, it is a valid index of the impact of tip modifications on a new wing design.

Flowering shoots of ornamental crops as a model to study cellular and molecular aspects of plant gravitropism.

PubMed

Philosoph-Hadas, Sonia; Friedman, Haya; Meir, Shimon

2015-01-01

Flowering shoots offer a very convenient and excellent model system for in-depth study of shoot gravitropism in regular stems rather than in special aboveground organs, showing how plants cope with the force of gravity on Earth and change in orientation. Regarding the emerging notion that roots and shoots execute their gravitropic bending by different mechanisms, the use of flowering shoots offers additional confirmation for the suggested shoot-sensing mechanisms initially found in Arabidopsis. As a part of confirming this mechanism, studying this unique model system also enabled elucidation of the sequence of events operating in gravity signalling in shoots. Hence, using the system of flowering shoots provided an additional dimension to our understanding of shoot gravitropism and its hormonal regulation, which has been less advanced than root gravitropism. This is particularly important since the term "shoots" includes various aboveground organs. Hence, unlike other aboveground organs such as pulvini, the asymmetric growth in response to change in shoot orientation is accompanied in cut ornamental spikes by a continuous growth process. This chapter provides an overview of the basic methods, specifically developed or adapted from other graviresponding systems, for determining the main components which play a key role in gravistimulation signalling in flowering shoots.

Protein and carotenoid synthesis and turnover in gravistimulated root caps

NASA Technical Reports Server (NTRS)

Feldman, L. J.

1984-01-01

In certain cultivars of corn gravitropic bending occurs only after the root cap, the site of gravity perception, is exposed to light. Light appears to trigger or to remove some block in the gravity translation process. Using light sensitive cultivars of corn, it was shown that light affects various processes in the cap. The roles of these light-induced processes in gravitropic bending in roots were studied.

Abiotic stresses modulate expression of major intrinsic proteins in barley (Hordeum vulgare).

PubMed

Ligaba, Ayalew; Katsuhara, Maki; Shibasaka, Mineo; Djira, Gemechis

2011-02-01

In one of the most important crops, barley (Hordeum vulgare L.), gene expression and physiological roles of most major intrinsic proteins (MIPs) remained to be elucidated. Here we studied expression of five tonoplast intrinsic protein isoforms (HvTIP1;2, HvTIP2;1, HvTIP2;2, HvTIP2;3 and HvTIP4;1), a NOD26-like intrinsic protein (HvNIP2;1) and a plasma membrane intrinsic protein (HvPIP2;1) by using the quantitative real-time RT-PCR. Five-day-old seedlings were exposed to abiotic stresses (salt, heavy metals and nutrient deficiency), abscisic acid (ABA) and gibberellic acid (GA) for 24 h. Treatment with 100 mM NaCl, 0.1 mM ABA and 1 mM GA differentially regulated gene expression in roots and shoots. Nitrogen and prolonged P-deficiency downregulated expression of most MIP genes in roots. Intriguingly, gene expression was restored to the values in the control three days after nutrient supply was resumed. Heavy metals (0.2 mM each of Cd, Cu, Zn and Cr) downregulated the transcript levels by 60-80% in roots, whereas 0.2 mM Hg upregulated expressions of most genes in roots. This was accompanied by a 45% decrease in the rate of transpiration. In order to study the physiological role of the MIPs, cDNA of three genes (HvTIP2;1, HvTIP2;3 and HvNIP2;1) have been cloned and heterologous expression was performed in Xenopus laevis oocytes. Osmotic water permeability was determined by a swelling assay. However, no water uptake activity was observed for the three proteins. Hence, the possible physiological role of the proteins is discussed. Copyright © 2010 Académie des sciences. Published by Elsevier SAS. All rights reserved.

Restoring directional growth sense to plants in space

NASA Astrophysics Data System (ADS)

Gorgolewski, S.

Introduction of new plant classification: electrotropic (Et) and non-electrotropic (nEt) plants gives us a criterion which plants need electric field to grow "normally" in space. The electric field: E is measured in V/m (volt per meter). Do not confuse "electrotropism" understood by some as the response to current flow transversely through the plant's root. This effect was previously described in biological textbooks. I suggest to call it as (Ct) (here C stands for current and t for tropism). In the laboratory we have in the plant growth chamber two transparent to light (wire mesh) conducting sheets separated by m(meters) and V volts potential difference. It has been shown in laboratory that Et is a very important factor in electrotropic plant development. Space experiments with plants grown in orbit from seed to seed have been fully successful only (in my very best knowledge) with nEt plants. The most common nEt plants are grasses (more than 50% of all plants). The nEt plants in space use phototropism as their sensor of direction. In space (and most greenhouses) we have to provide the electric field at least for the Et plants. It has been shown that the electric field is also beneficial to nEt plants which also acquire the sense of direction imposed by stronger than the normal 130V/m E field (vector). The stronger horizontal E field of 1.6kV/m (slightly more than 12 times stronger than 130V/m) does not influence the rate of growth of maize (which is nEt) in 130V/m vertical field or even in the Faraday cage 0V/m. Yet when the maize gets its leaves, they all lean in the horizontal field (1.6kV/m) towards the anode. The direction of the E vector is defined by the E field lines running from the positive to the negative charges. Because the electric forces are a factor of 1038 times stronger than the gravitational forces, it is not important for the E field whether it acts on ions in the gravity or in weightlessness. We have to recall that on the Earth and in space Et is due to the E vector acting selectively on negative ions (anions) giving them their directional growth sense towards the anode (+). It is obvious that the Et shall completely ignore the difference between terrestrial gravity or microgravity in space. The gravity acts on the plant as a whole and has nothing to do with Et, Ct or nEt. In Ct the roots also bend towards the anode. Besides we do not connect any current carrying electrodes to the plant roots or leaves in the true electrotropism Et as they do it in the Ct. They connect current carrying electrodes transversely to the roots exposed to the air, and removed from the soil. I hope these exact definitions of Et and Ct shall avoid confusion between the two completely different phenomena.

Overexpression of OsRAA1 Causes Pleiotropic Phenotypes in Transgenic Rice Plants, including Altered Leaf, Flower, and Root Development and Root Response to Gravity1

PubMed Central

Ge, Lei; Chen, Hui; Jiang, Jia-Fu; Zhao, Yuan; Xu, Ming-Li; Xu, Yun-Yuan; Tan, Ke-hui; Xu, Zhi-Hong; Chong, Kang

2004-01-01

There are very few root genes that have been described in rice as a monocotyledonous model plant so far. Here, the OsRAA1 (Oryza sativa Root Architecture Associated 1) gene has been characterized molecularly. OsRAA1 encodes a 12.0-kD protein that has 58% homology to the AtFPF1 (Flowering Promoting Factor 1) in Arabidopsis, which has not been reported as modulating root development yet. Data of in situ hybridization and OsRAA1∷GUS transgenic plant showed that OsRAA1 expressed specifically in the apical meristem, the elongation zone of root tip, steles of the branch zone, and the young lateral root. Constitutive expression of OsRAA1 under the control of maize (Zea mays) ubiquitin promoter resulted in phenotypes of reduced growth of primary root, increased number of adventitious roots and helix primary root, and delayed gravitropic response of roots in seedlings of rice (Oryza sativa), which are similar to the phenotypes of the wild-type plant treated with auxin. With overexpression of OsRAA1, initiation and growth of adventitious root were more sensitive to treatment of auxin than those of the control plants, while their responses to 9-hydroxyfluorene-9-carboxylic acid in both transgenic line and wild type showed similar results. OsRAA1 constitutive expression also caused longer leaves and sterile florets at the last stage of plant development. Analysis of northern blot and GUS activity staining of OsRAA1∷GUS transgenic plants demonstrated that the OsRAA1 expression was induced by auxin. At the same time, overexpression of OsRAA1 also caused endogenous indole-3-acetic acid to increase. These data suggested that OsRAA1 as a new gene functions in the development of rice root systems, which are mediated by auxin. A positive feedback regulation mechanism of OsRAA1 to indole-3-acetic acid metabolism may be involved in rice root development in nature. PMID:15247372

Better to light a candle than curse the darkness: illuminating spatial localization and temporal dynamics of rapid microbial growth in the rhizosphere

PubMed Central

Herron, Patrick M.; Gage, Daniel J.; Arango Pinedo, Catalina; Haider, Zane K.; Cardon, Zoe G.

2013-01-01

The rhizosphere is a hotbed of microbial activity in ecosystems, fueled by carbon compounds from plant roots. Basic questions about the location and dynamics of plant-spurred microbial growth in the rhizosphere are difficult to answer with standard, destructive soil assays mixing a multitude of microbe-scale microenvironments in a single, often sieved, sample. Soil microbial biosensors designed with the luxCDABE reporter genes fused to a promoter of interest enable continuous imaging of the microbial perception of (and response to) environmental conditions in soil. We used the common soil bacterium Pseudomonas putida KT2440 as host to plasmid pZKH2 containing a fusion between the strong constitutive promoter nptII and luxCDABE (coding for light-emitting proteins) from Vibrio fischeri. Experiments in liquid media demonstrated that high light production by KT2440/pZKH2 was associated with rapid microbial growth supported by high carbon availability. We applied the biosensors in microcosms filled with non-sterile soil in which corn (Zea mays L.), black poplar (Populus nigra L.), or tomato (Solanum lycopersicum L.) was growing. We detected minimal light production from microbiosensors in the bulk soil, but biosensors reported continuously from around roots for as long as six days. For corn, peaks of luminescence were detected 1–4 and 20–35 mm along the root axis behind growing root tips, with the location of maximum light production moving farther back from the tip as root growth rate increased. For poplar, luminescence around mature roots increased and decreased on a coordinated diel rhythm, but was not bright near root tips. For tomato, luminescence was dynamic, but did not exhibit a diel rhythm, appearing in acropetal waves along roots. KT2440/pZKH2 revealed that root tips are not always the only, or even the dominant, hotspots for rhizosphere microbial growth, and carbon availability is highly variable in space and time around roots. PMID:24032034

Nitric Oxide Inhibits Al-Induced Programmed Cell Death in Root Tips of Peanut (Arachis hypogaea L.) by Affecting Physiological Properties of Antioxidants Systems and Cell Wall

PubMed Central

Pan, Chun-Liu; Yao, Shao-Chang; Xiong, Wei-Jiao; Luo, Shu-Zhen; Wang, Ya-Lun; Wang, Ai-Qin; Xiao, Dong; Zhan, Jie; He, Long-Fei

2017-01-01

It has been reported that nitric oxide (NO) is a negative regulator of aluminum (Al)-induced programmed cell death (PCD) in peanut root tips. However, the inhibiting mechanism of NO on Al-induced PCD is unclear. In order to investigate the mechanism by which NO inhibits Al-induced PCD, the effects of co-treatment Al with the exogenous NO donor or the NO-specific scavenger on peanut root tips, the physiological properties of antioxidants systems and cell wall (CW) in root tip cells of NO inhibiting Al-induced PCD were studied with two peanut cultivars. The results showed that Al exposure induced endogenous NO accumulation, and endogenous NO burst increased antioxidant enzyme activity in response to Al stress. The addition of NO donor sodium nitroprusside (SNP) relieved Al-induced root elongation inhibition, cell death and Al adsorption in CW, as well as oxidative damage and ROS accumulation. Furthermore, co-treatment with the exogenous NO donor decreased MDA content, LOX activity and pectin methylesterase (PME) activity, increased xyloglucan endotransglucosylase (XET) activity and relative expression of the xyloglucan endotransglucosylase/hydrolase (XTH-32) gene. Taken together, exogenous NO alleviated Al-induced PCD by inhibiting Al adsorption in CW, enhancing antioxidant defense and reducing peroxidation of membrane lipids, alleviating the inhibition of Al on root elongation by maintaining the extensibility of CW, decreasing PME activity, and increasing XET activity and relative XTH-32 expression of CW. PMID:29311970

Nitric Oxide Inhibits Al-Induced Programmed Cell Death in Root Tips of Peanut (Arachis hypogaea L.) by Affecting Physiological Properties of Antioxidants Systems and Cell Wall.

PubMed

Pan, Chun-Liu; Yao, Shao-Chang; Xiong, Wei-Jiao; Luo, Shu-Zhen; Wang, Ya-Lun; Wang, Ai-Qin; Xiao, Dong; Zhan, Jie; He, Long-Fei

2017-01-01

It has been reported that nitric oxide (NO) is a negative regulator of aluminum (Al)-induced programmed cell death (PCD) in peanut root tips. However, the inhibiting mechanism of NO on Al-induced PCD is unclear. In order to investigate the mechanism by which NO inhibits Al-induced PCD, the effects of co-treatment Al with the exogenous NO donor or the NO-specific scavenger on peanut root tips, the physiological properties of antioxidants systems and cell wall (CW) in root tip cells of NO inhibiting Al-induced PCD were studied with two peanut cultivars. The results showed that Al exposure induced endogenous NO accumulation, and endogenous NO burst increased antioxidant enzyme activity in response to Al stress. The addition of NO donor sodium nitroprusside (SNP) relieved Al-induced root elongation inhibition, cell death and Al adsorption in CW, as well as oxidative damage and ROS accumulation. Furthermore, co-treatment with the exogenous NO donor decreased MDA content, LOX activity and pectin methylesterase (PME) activity, increased xyloglucan endotransglucosylase (XET) activity and relative expression of the xyloglucan endotransglucosylase/hydrolase ( XTH-32 ) gene. Taken together, exogenous NO alleviated Al-induced PCD by inhibiting Al adsorption in CW, enhancing antioxidant defense and reducing peroxidation of membrane lipids, alleviating the inhibition of Al on root elongation by maintaining the extensibility of CW, decreasing PME activity, and increasing XET activity and relative XTH-32 expression of CW.

Reactive oxygen species triggering systemic programmed cell death process via elevation of nuclear calcium ion level in tomatoes resisting tobacco mosaic virus.

PubMed

Li, Yang; Li, Qi; Hong, Qiang; Lin, Yichun; Mao, Wang; Zhou, Shumin

2018-05-01

Programmed cell death (PCD) plays a positive role in the systemic response of plants to pathogen resistance. It has been confirmed that local tobacco mosaic virus (TMV) infecting tomato leaves can induce systemic PCD process in root-tip tissues. But up to now the underlying physiological mechanisms are poorly understood. This study focused on the detailed investigation of the physiological responses of root-tip cells during the initiation of systemic PCD. Physiological, biochemical examination and cytological observation showed that 1 day post-inoculation (dpi) of TMV inoculation there was an increase in calcium fluorescence intensity in root tip tissue cells. Then at 2 dpi, 4 dpi, 8 dpi and 15 dpi, the fluorescence intensity of calcium ion continued to increase. However, at 5 dpi, the reactive oxygen species (ROS) began to accumulate in the root-tip cells. And finally at 20 dpi, the obvious PCD reaction was detected. In addition, the experimental results also showed that the above process involved the elevation of two types of intracellular Ca 2+ , including cytoplasmic calcium ([Ca 2+ ] cyt ) and nuclear calcium ([Ca 2+ ] nuc ). The [Ca 2+ ] cyt , as a pilot signal could lead to the subsequent elevation of intracellular ROS concentration. Then, the high levels of ROS stimulated an increase of [Ca 2+ ] nuc and eventually caused PCD reactions in the root-tip tissues. In particular, the high level of nuclear calcium is an essential mediator in systemic PCD of plants. Copyright © 2018 Elsevier B.V. All rights reserved.

The persistence of the gravity signal in flax roots

NASA Astrophysics Data System (ADS)

Hasenstein, Karl H.

Although the presentation time of gravitropism has been studied, no data exist as to how long a reorientation stimulus affects the gravitropic response of a root. We tested the duration of gravitropic curvature in roots of Linum usitatissimum after reversing a one hour, 90 degree gravistimulus by increasing time intervals in vertical orientation before clinorotating the roots and acquiring infrared digital images. Clinorotation was performed either parallel or perpendicular to the gravity vector. Under either condition the gravistimulus affected curvature during clinorotation only between two to three minutes. Maximal curvature after one minute of vertical reorientation was 15 degrees within one hour. After three minutes in vertical orientation the observed curvature was not statistically different from vertically growing roots. In both orientations, maximum curvature occurred after 1hr. Perpendicular (horizontal) clinorotation showed decreasing curvature with increasing reorientation time. Parallel (vertical) clinorotation resulted in greater variability to the reorientation time. These data indicate that the gravity stimulus operates essentially memory free and that clinorotation affects the gravity response. Therefore all aspects of clinorotation need to be studied before an assessment of clinostats for the simulation of microgravity is possible and a time limit for memory effects of mechanostimulation can be determined.

Radial and tangential gravity rates from GRACE in areas of glacial isostatic adjustment

NASA Astrophysics Data System (ADS)

van der Wal, Wouter; Kurtenbach, Enrico; Kusche, Jürgen; Vermeersen, Bert

2011-11-01

In areas dominated by Glacial Isostatic Adjustment (GIA), the free-air gravity anomaly rate can be converted to uplift rate to good approximation by using a simple spectral relation. We provide quantitative comparisons between gravity rates derived from monthly gravity field solutions (GFZ Potsdam, CSR Texas, IGG Bonn) from the Gravity Recovery and Climate Experiment (GRACE) satellite mission with uplift rates measured by GPS in these areas. The band-limited gravity data from the GRACE satellite mission can be brought to very good agreement with the point data from GPS by using scaling factors derived from a GIA model (the root-mean-square of differences is 0.55 mm yr-1 for a maximum uplift rate signal of 10 mm yr-1). The root-mean-square of the differences between GRACE derived uplift rates and GPS derived uplift rates decreases with increasing GRACE time period to a level below the uncertainty that is expected from GRACE observations, GPS measurements and the conversion from gravity rate to uplift rate. With the current length of time-series (more than 8 yr) applying filters and a hydrology correction to the GRACE data does not reduce the root-mean-square of differences significantly. The smallest root-mean-square was obtained with the GFZ solution in Fennoscandia and with the CSR solution in North America. With radial gravity rates in excellent agreement with GPS uplift rates, more information on the GIA process can be extracted from GRACE gravity field solutions in the form of tangential gravity rates, which are equivalent to a rate of change in the deflection of the vertical scaled by the magnitude of gravity rate vector. Tangential gravity rates derived from GRACE point towards the centre of the previously glaciated area, and are largest in a location close to the centre of the former ice sheet. Forward modelling showed that present day tangential gravity rates have maximum sensitivity between the centre and edge of the former ice sheet, while radial gravity rates are most sensitive in the centre of the former ice sheet. As a result, tangential gravity rates offer constraints on a two-layer mantle viscosity profile that are different from radial gravity rates, which can be exploited in future GIA studies.

Methods for quantifying simple gravity sensing in Drosophila melanogaster.

PubMed

Inagaki, Hidehiko K; Kamikouchi, Azusa; Ito, Kei

2010-01-01

Perception of gravity is essential for animals: most animals possess specific sense organs to detect the direction of the gravitational force. Little is known, however, about the molecular and neural mechanisms underlying their behavioral responses to gravity. Drosophila melanogaster, having a rather simple nervous system and a large variety of molecular genetic tools available, serves as an ideal model for analyzing the mechanisms underlying gravity sensing. Here we describe an assay to measure simple gravity responses of flies behaviorally. This method can be applied for screening genetic mutants of gravity perception. Furthermore, in combination with recent genetic techniques to silence or activate selective sets of neurons, it serves as a powerful tool to systematically identify neural substrates required for the proper behavioral responses to gravity. The assay requires 10 min to perform, and two experiments can be performed simultaneously, enabling 12 experiments per hour.

[Introduction of hexaploid of Chinese narcissus and analysis of its chromosome change].

PubMed

Wang, Rui; Zhang, Ya Nan; Wang, Ya Ying; Tian, Hui Qiao

2007-06-01

Anthers of Chinese narcissus (Narcissus tazetta L. var chinesis Roem) were used as explants for callus induction and plant regeneration. About 80% anthers produced callus and 28% of the callus differentiated out bulbs, making a good experiment system of tissue culture of Chinese narcissus for further cellular and gene engineering. The 700 callus were treated by 0.5% colchicin for 5-6 days and then transformed into a MS medium containing 3 mg/L 6-BA to induce differentiation. 90 bulbs were obtained and 55 bulbs among them were checked the chromosome number from their root tips for three times. 29 bulbs (53%, 29/55) still kept triploidy and the most cells of root tips contained 30 chromosomes. 22 bulbs (40%, 22/55) displayed aneuploidy and the most cells of its root tips contained 10-50 chromosomes. 4 bulbs displayed hexaploidy and contained 60 chromosomes. After three months growing, the cells of root tips containing aneuploidy chromosomes disappeared, and the bulbs became triploidy. The chromosomes of 4 hexaploidy bulbs did not changed during three checks. The origin and disappearance of aneuploidy cells of Chinese narcissus after treated by colchicin were discussed.

Initiation and elongation of lateral roots in Lactuca sativa

NASA Technical Reports Server (NTRS)

Zhang, N.; Hasenstein, K. H.

1999-01-01

Lactuca sativa cv. Baijianye seedlings do not normally produce lateral roots, but removal of the root tip or application of auxin, especially indole-butyric acid, triggered the formation of lateral roots. Primordia initiated within 9 h and were fully developed after 24 h by activating the pericycle cells opposite the xylem pole. The pericycle cells divided asymmetrically into short and long cells. The short cells divided further to form primordia. The effect of root tip removal and auxin application was reversed by 6-benzylaminopurine at concentrations >10(-8) M. The cytokinin oxidase inhibitor N1-(2chloro4pyridyl)-N2-phenylurea also suppressed auxin-induced lateral rooting. The elongation of primary roots was promoted by L-alpha-(2-aminoethoxyvinyl) glycine and silver ions, but only the latter enhanced elongation of lateral roots. The data indicate that the induction of lateral roots is controlled by basipetally moving cytokinin and acropetally moving auxin. Lateral roots appear to not produce ethylene.

The kinetics of root gravitropism: dual motors and sensors

NASA Technical Reports Server (NTRS)

Wolverton, Chris; Ishikawa, Hideo; Evans, Michael L.

2002-01-01

The Cholodny-Went theory of tropisms has served as a framework for investigation of root gravitropism for nearly three quarters of a century. Recent investigations using modern techniques have generated findings consistent with the classical theory, including confirmation of asymmetrical distribution of polar auxin transport carriers, molecular evidence for auxin asymmetry following gravistimulation, and generation of auxin response mutants with predictable lesions in gravitropism. Other results indicate that the classical model is inadequate to account for key features of root gravitropism. Initiation of curvature, for example, occurs outside the region of most rapid elongation and is driven by differential acceleration rather than differential inhibition of elongation. The evidence indicates that there are two motors driving root gravitropism, one of which appears not to be auxin regulated. We have recently developed technology that is capable of maintaining a constant angle of gravistimulation at any selected target region of a root while continuously monitoring growth and curvature kinetics. This review elaborates on the advantages of this new technology for analyzing gravitropism and describes applications of the technology that reveal (1) the existence of at least two phases to gravitropic motor output, even under conditions of constant stimulus input and (2) the existence of gravity sensing outside of the root cap. We propose a revised model of root gravitropism including dual sensors and dual motors interacting to accomplish root gravitropism, with only one of the systems linked to the classical Cholodny-Went theory.

The kinetics of root gravitropism: dual motors and sensors.

PubMed

Wolverton, Chris; Ishikawa, Hideo; Evans, Michael L

2002-06-01

The Cholodny-Went theory of tropisms has served as a framework for investigation of root gravitropism for nearly three quarters of a century. Recent investigations using modern techniques have generated findings consistent with the classical theory, including confirmation of asymmetrical distribution of polar auxin transport carriers, molecular evidence for auxin asymmetry following gravistimulation, and generation of auxin response mutants with predictable lesions in gravitropism. Other results indicate that the classical model is inadequate to account for key features of root gravitropism. Initiation of curvature, for example, occurs outside the region of most rapid elongation and is driven by differential acceleration rather than differential inhibition of elongation. The evidence indicates that there are two motors driving root gravitropism, one of which appears not to be auxin regulated. We have recently developed technology that is capable of maintaining a constant angle of gravistimulation at any selected target region of a root while continuously monitoring growth and curvature kinetics. This review elaborates on the advantages of this new technology for analyzing gravitropism and describes applications of the technology that reveal (1) the existence of at least two phases to gravitropic motor output, even under conditions of constant stimulus input and (2) the existence of gravity sensing outside of the root cap. We propose a revised model of root gravitropism including dual sensors and dual motors interacting to accomplish root gravitropism, with only one of the systems linked to the classical Cholodny-Went theory.

Fine root morphological adaptations in Scots pine, Norway spruce and silver birch along a latitudinal gradient in boreal forests.

PubMed

Ostonen, Ivika; Lõhmus, Krista; Helmisaari, Heljä-Sisko; Truu, Jaak; Meel, Signe

2007-11-01

Variability in short root morphology of the three main tree species of Europe's boreal forest (Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth)) was investigated in four stands along a latitudinal gradient from northern Finland to southern Estonia. Silver birch and Scots pine were present in three stands and Norway spruce was present in all stands. For three fertile Norway spruce stands, fine root biomass and number of root tips per stand area or unit basal area were assessed from north to south. Principal component analysis indicated that short root morphology was significantly affected by tree species and site, which together explained 34.7% of the total variability. The range of variation in mean specific root area (SRA) was 51-74, 60-70 and 84-124 m(2) kg(-1) for Norway spruce, Scots pine and silver birch, respectively, and the corresponding ranges for specific root length were 37-47, 40-48 and 87-97 m g(-1). The range of variation in root tissue density of Norway spruce, Scots pine and silver birch was 113-182, 127-158 and 81-156 kg m(-3), respectively. Sensitivity of short root morphology to site conditions decreased in the order: Norway spruce > silver birch > Scots pine. Short root SRA increased with site fertility in all species. In Norway spruce, fine root biomass and number of root tips per m(2) decreased from north to south. The differences in morphological parameters among sites were significant but smaller than the site differences in fine root biomass and number of root tips.

Assessment of arsenic toxicity using Allium/Vicia root tip micronucleus assays.

PubMed

Wu, Lihua; Yi, Huilan; Yi, Min

2010-04-15

Arsenic is ubiquitous in the environment and is a potential human carcinogen. Its carcinogenicity has been demonstrated in several models. In this study, broad bean (Vicia faba L.) and common onion (Allium cepa L.), two plant species which are commonly used for detecting the genotoxic effects of environmental pollutants, were used to measure possible genotoxic effect of arsenite (0.3-30 mg/l). Present results showed that arsenite (As(III)) induced micronuclei (MN) formation in both Allium and Vicia root tips. MN frequency significantly increased in Vicia root cells exposed to 0.3-10 mg/l arsenite and in Allium root cells exposed to 1-30 mg/l arsenite, which indicated that Vicia root tip cells are more sensitive to arsenite than Allium. Mitotic index (MI) decreased in a concentration-dependent manner and showed significant differences in Vicia/Allium roots among treatments and the control, after exposure to 1-30 mg/l arsenite for at least 4 h. In the present study, MN frequency was positively associated with lipid peroxidation, which indicated that arsenite exposure can induce oxidative stress, cytotoxicity and genotoxicity in plant cells. The results also suggested that Vicia/Allium root micronucleus (MN) assays are simple, efficient and reproducible methods for the genotoxicity monitoring of arsenic water contamination. 2009 Elsevier B.V. All rights reserved.

Family of columns isospectral to gravity-loaded columns with tip force: A discrete approach

NASA Astrophysics Data System (ADS)

Ramachandran, Nirmal; Ganguli, Ranjan

2018-06-01

A discrete model is introduced to analyze transverse vibration of straight, clamped-free (CF) columns of variable cross-sectional geometry under the influence of gravity and a constant axial force at the tip. The discrete model is used to determine critical combinations of loading parameters - a gravity parameter and a tip force parameter - that cause onset of dynamic instability in the CF column. A methodology, based on matrix-factorization, is described to transform the discrete model into a family of models corresponding to weightless and unloaded clamped-free (WUCF) columns, each with a transverse vibration spectrum isospectral to the original model. Characteristics of models in this isospectral family are dependent on three transformation parameters. A procedure is discussed to convert the isospectral discrete model description into geometric description of realistic columns i.e. from the discrete model, we construct isospectral WUCF columns with rectangular cross-sections varying in width and depth. As part of numerical studies to demonstrate efficacy of techniques presented, frequency parameters of a uniform column and three types of tapered CF columns under different combinations of loading parameters are obtained from the discrete model. Critical combinations of these parameters for a typical tapered column are derived. These results match with published results. Example CF columns, under arbitrarily-chosen combinations of loading parameters are considered and for each combination, isospectral WUCF columns are constructed. Role of transformation parameters in determining characteristics of isospectral columns is discussed and optimum values are deduced. Natural frequencies of these WUCF columns computed using Finite Element Method (FEM) match well with those of the given gravity-loaded CF column with tip force, hence confirming isospectrality.

Analysis of changes in relative elemental growth rate patterns in the elongation zone of Arabidopsis roots upon gravistimulation

NASA Technical Reports Server (NTRS)

Mullen, J. L.; Ishikawa, H.; Evans, M. L.

1998-01-01

Although Arabidopsis is an important system for studying root physiology, the localized growth patterns of its roots have not been well defined, particularly during tropic responses. In order to characterize growth rate profiles along the apex of primary roots of Arabidopsis thaliana (L.) Heynh (ecotype Columbia) we applied small charcoal particles to the root surface and analyzed their displacement during growth using an automated video digitizer system with custom software for tracking the markers. When growing vertically, the maximum elongation rate occurred 481 +/- 50 microns back from the extreme tip of the root (tip of root cap), and the elongation zone extended back to 912 +/- 137 microns. The distal elongation zone (DEZ) has previously been described as the apical region of the elongation zone in which the relative elemental growth rate (REGR) is < or = 30% of the peak rate in the central elongation zone. By this definition, our data indicate that the basal limit of the DEZ was located 248 +/- 30 microns from the root tip. However, after gravistimulation, the growth patterns of the root changed. Within the first hour of graviresponse, the basal limit of the DEZ and the position of peak REGR shifted apically on the upper flank of the root. This was due to a combination of increased growth in the DEZ and growth inhibition in the central elongation zone. On the lower flank, the basal limit of the DEZ shifted basipetally as the REGR decreased. These factors set up the gradient of growth rate across the root, which drives curvature.

Rhizosphere Microbial Community Structure in Relation to Root Location and Plant Iron Nutritional Status

PubMed Central

Yang, Ching-Hong; Crowley, David E.

2000-01-01

Root exudate composition and quantity vary in relation to plant nutritional status, but the impact of the differences on rhizosphere microbial communities is not known. To examine this question, we performed an experiment with barley (Hordeum vulgare) plants under iron-limiting and iron-sufficient growth conditions. Plants were grown in an iron-limiting soil in root box microcosms. One-half of the plants were treated with foliar iron every day to inhibit phytosiderophore production and to alter root exudate composition. After 30 days, the bacterial communities associated with different root zones, including the primary root tips, nonelongating secondary root tips, sites of lateral root emergence, and older roots distal from the tip, were characterized by using 16S ribosomal DNA (rDNA) fingerprints generated by PCR-denaturing gradient gel electrophoresis (DGGE). Our results showed that the microbial communities associated with the different root locations produced many common 16S rDNA bands but that the communities could be distinguished by using correspondence analysis. Approximately 40% of the variation between communities could be attributed to plant iron nutritional status. A sequence analysis of clones generated from a single 16S rDNA band obtained at all of the root locations revealed that there were taxonomically different species in the same band, suggesting that the resolving power of DGGE for characterization of community structure at the species level is limited. Our results suggest that the bacterial communities in the rhizosphere are substantially different in different root zones and that a rhizosphere community may be altered by changes in root exudate composition caused by changes in plant iron nutritional status. PMID:10618246

Density of the continental roots: Compositional and thermal contributions

USGS Publications Warehouse

Kaban, M.K.; Schwintzer, P.; Artemieva, I.M.; Mooney, W.D.

2003-01-01

The origin and evolution of cratonic roots has been debated for many years. Precambrian cratons are underlain by cold lithospheric roots that are chemically depleted. Thermal and petrologic data indicate that Archean roots are colder and more chemically depleted than Proterozoic roots. This observation has led to the hypothesis that the degree of depletion in a lithospheric root depends mostly on its age. Here we test this hypothesis using gravity, thermal, petrologic, and seismic data to quantify differences in the density of cratonic roots globally. In the first step in our analysis we use a global crustal model to remove the crustal contribution to the observed gravity. The result is the mantle gravity anomaly field, which varies over cratonic areas from -100 to +100 mGal. Positive mantle gravity anomalies are observed for cratons in the northern hemisphere: the Baltic shield, East European Platform, and the Siberian Platform. Negative anomalies are observed over cratons in the southern hemisphere: Western Australia, South America, the Indian shield, and Southern Africa. This indicates that there are significant differences in the density of cratonic roots, even for those of similar age. Root density depends on temperature and chemical depletion. In order to separate these effects we apply a lithospheric temperature correction using thermal estimates from a combination of geothermal modeling and global seismic tomography models. Gravity anomalies induced by temperature variations in the uppermost mantle range from -200 to +300 mGal, with the strongest negative anomalies associated with mid-ocean ridges and the strongest positive anomalies associated with cratons. After correcting for thermal effects, we obtain a map of density variations due to lithospheric compositional variations. These maps indicate that the average density decrease due to the chemical depletion within cratonic roots varies from 1.1% to 1.5%, assuming the chemical boundary layer has the same thickness as the thermal boundary layer. The maximal values of the density drop are in the range 1.7-2.5%, and correspond to the Archean portion of each craton. Temperatures within cratonic roots vary strongly, and our analysis indicates that density variations in the roots due to temperature are larger than the variations due to chemical differences. ?? 2003 Elsevier Science B.V. All rights reserved.

Reciprocal trade of Carbon and Nitrogen at the root-fungus interface in ectomycorrhizal beech plants

NASA Astrophysics Data System (ADS)

Kaiser, Christina; Mayerhofer, Werner; Dietrich, Marlies; Gorka, Stefan; Schintlmeister, Arno; Reipert, Siegfried; Schweiger, Peter; Weidinger, Marieluise; Wiesenbauer, Julia; Martin, Victoria; Richter, Andreas; Woebken, Dagmar

2017-04-01

Plants deliver recently assimilated carbon (C) to mycorrhizal fungi, and receive nutrients, such as N and P, in exchange. A reciprocal exchange of C and nutrients between plants and mycorrhizal fungi (i.e., fungi which deliver more nutrients receive more plant C in return and vice versa) has been suggested for arbuscular mycorrhizal symbioses by some studies, but challenged by others. For ectomycorrhizal associations even less is known on how the exchange of C for nutrients is regulated, and whether it is based on reciprocity, or other controls. The aim of this study was to test the concept of reciprocal rewards between beech (Fagus sylvatica) and their associated ectomycorrhizal fungi on different scales, namely (a) across associations between individual root tips of beech and different fungal partners, and (b) at the subcellular scale at the plant-fungus interface. We exposed young beech trees associated with natural mycorrhizal fungal communities to a 13CO2 atmosphere and added 15N-labelled amino acids to a 'litter compartment', that mycorrhizal hyphae, but not plant roots could access. Plants were harvested within 2 days after application of 15N and less than one day after applying 13CO2. If the trading of C for N was reciprocal, we expect that 13C would be correlated to 15N across individual plant-fungal connections and at the subcellular scale within one mycorrhizal root tip, respectively. We collected individual mycorrhizal root-tips from 8 plants right after harvest, analyzed their 13C and 15N content by isotope-ratio mass spectrometry (EA-IRMS) and performed ITS sequencing to identify fungal communities associated with individual root tips. Selected mycorrhizal root tips were also prepared for nano-scale secondary ion mass spectrometry (NanoSIMS) to visualize the spatial distribution of 13C and 15N in cross-sections of mycorrhizal root-tips at the subcellular scale. Our results showed a significant, albeit weak correlation between 13C and 15N across collected mycorrhizal root-tips, the variability of which was seemingly influenced by fungal colonization pattern. Within a cross-section of an individual root-tip, however, NanoSIMS imaging revealed not only a high spatial heterogeneity of 13C and 15N across plant and fungal cells, but also a strong spatial correlation between 13C and 15N in both, plant cells and fungal cells of the Hartig Net, the fungal mantle and external hyphae. Intriguingly, individual 'hotspots' of external fungal hyphae that were highly enriched in 15N (delivering high amounts of the added 15N to the plant), were also always extraordinarily enriched in 13C (receiving more 13C in return). Our results provide first evidence for a reciprocal exchange of C for N between plants and ectomycorrhizal fungi at the subcellular scale. This indicates that a mechanism at the cellular level exists, that (i) either allows plants to direct their C flow into N-delivering parts of the mycorrhizal hyphal network or (ii) allow the fungus to 'draw' more C from the plant (develop a higher sink strength) when it has access to N. While such a mechanism still remains to be elucidated, our study shows, for the first time, direct evidence for its existence.

Stand age and fine root biomass, distribution and morphology in a Norway spruce chronosequence in southeast Norway.

PubMed

Børja, Isabella; De Wit, Heleen A; Steffenrem, Arne; Majdi, Hooshang

2008-05-01

We assessed the influence of stand age on fine root biomass and morphology of trees and understory vegetation in 10-, 30-, 60- and 120-year-old Norway spruce stands growing in sandy soil in southeast Norway. Fine root (< 1, 1-2 and 2-5 mm in diameter) biomass of trees and understory vegetation (< 2 mm in diameter) was sampled by soil coring to a depth of 60 cm. Fine root morphological characteristics, such as specific root length (SRL), root length density (RLD), root surface area (RSA), root tip number and branching frequency (per unit root length or mass), were determined based on digitized root data. Fine root biomass and morphological characteristics related to biomass (RLD and RSA) followed the same tendency with chronosequence and were significantly higher in the 30-year-old stand and lower in the 10-year-old stand than in the other stands. Among stands, mean fine root (< 2 mm) biomass ranged from 49 to 398 g m(-2), SLR from 13.4 to 19.8 m g(-1), RLD from 980 to 11,650 m m(-3) and RSA from 2.4 to 35.4 m(2) m(-3). Most fine root biomass of trees was concentrated in the upper 20 cm of the mineral soil and in the humus layer (0-5 cm) in all stands. Understory fine roots accounted for 67 and 25% of total fine root biomass in the 10- and 120-year-old stands, respectively. Stand age had no affect on root tip number or branching frequency, but both parameters changed with soil depth, with increasing number of root tips and decreasing branching frequency with increasing soil depth for root fractions < 2 mm in diameter. Specific (mass based) root tip number and branching density were highest for the finest roots (< 1 mm) in the humus layer. Season (spring or fall) had no effect on tree fine root biomass, but there was a small and significant increase in understory fine root biomass in fall relative to spring. All morphological characteristics showed strong seasonal variation, especially the finest root fraction, with consistently and significantly higher values in spring than in fall. We conclude that fine root biomass, especially in the finest fraction (< 1 mm in diameter), is strongly dependent on stand age. Among stands, carbon concentration in fine root biomass was highest in the 30-year-old stand, and appeared to be associated with the high tree and canopy density during the early stage of stand development. Values of RLD and RSA, morphological features indicative of stand nutrient-uptake efficiency, were higher in the 30-year-old stand than in the other stands.

Rapid changes in protein phosphorylation associated with light-induced gravity perception in corn roots

NASA Technical Reports Server (NTRS)

McFadden, J. J.; Poovaiah, B. W.

1988-01-01

The effect of light and calcium depletion on in vivo protein phosphorylation was tested using dark-grown roots of Merit corn. Light caused rapid and specific promotion of phosphorylation of three polypeptides. Pretreatment of roots with ethylene glycol bis N,N,N',N' tetraacetic acid and A23187 prevented light-induced changes in protein phosphorylation. We postulate that these changes in protein phosphorylation are involved in the light-induced gravity response.

NASA Workshop on Animal Gravity-Sensing Systems

NASA Technical Reports Server (NTRS)

Corcoran, M. L. (Editor)

1986-01-01

The opportunity for space flight has brought about the need for well-planned research programs that recognize the significance of space flight as a scientific research tool for advancing knowledge of life on Earth, and that utilize each flight opportunity to its fullest. For the first time in history, gravity can be almost completely eliminated. Thus, studies can be undertaken that will help to elucidate the importance of gravity to the normal functioning of living organisms, and to determine the effects microgravity may have on an organism. This workshop was convened to organize a plan for space research on animal gravity-sensing systems and the role that gravity plays in the development and normal functioning of these systems. Scientists working in the field of animal gravity-sensing systems use a wide variety of organisms in their research. The workshop presentations dealt with topics which ranged from the indirect gravity receptor of the water flea, Daphnia (whose antennal setae apparently act as current-sensing receptors as the animal moves up and down in water), through specialized statocyst structures found in jellyfish and gastropods, to the more complex vestibular systems that are characteristic of amphibians, avians, and mammals.

Roothairless5, which functions in maize (Zea mays L.) root hair initiation and elongation encodes a monocot-specific NADPH oxidase.

PubMed

Nestler, Josefine; Liu, Sanzhen; Wen, Tsui-Jung; Paschold, Anja; Marcon, Caroline; Tang, Ho Man; Li, Delin; Li, Li; Meeley, Robert B; Sakai, Hajime; Bruce, Wesley; Schnable, Patrick S; Hochholdinger, Frank

2014-09-01

Root hairs are instrumental for nutrient uptake in monocot cereals. The maize (Zea mays L.) roothairless5 (rth5) mutant displays defects in root hair initiation and elongation manifested by a reduced density and length of root hairs. Map-based cloning revealed that the rth5 gene encodes a monocot-specific NADPH oxidase. RNA-Seq, in situ hybridization and qRT-PCR experiments demonstrated that the rth5 gene displays preferential expression in root hairs but also accumulates to low levels in other tissues. Immunolocalization detected RTH5 proteins in the epidermis of the elongation and differentiation zone of primary roots. Because superoxide and hydrogen peroxide levels are reduced in the tips of growing rth5 mutant root hairs as compared with wild-type, and Reactive oxygen species (ROS) is known to be involved in tip growth, we hypothesize that the RTH5 protein is responsible for establishing the high levels of ROS in the tips of growing root hairs required for elongation. Consistent with this hypothesis, a comparative RNA-Seq analysis of 6-day-old rth5 versus wild-type primary roots revealed significant over-representation of only two gene ontology (GO) classes related to the biological functions (i.e. oxidation/reduction and carbohydrate metabolism) among 893 differentially expressed genes (FDR <5%). Within these two classes the subgroups 'response to oxidative stress' and 'cellulose biosynthesis' were most prominently represented. © 2014 The Authors The Plant Journal © 2014 John Wiley & Sons Ltd.

Geological Implications From Complete Gondwana GOCE- Products Reconstructions and Link to Lithospheric Roots

NASA Astrophysics Data System (ADS)

Braitenberg, Carla; Mariani, Patrizia

2015-03-01

The GOCE gravity field is globally homogeneous at the resolution of about 80km or better allowing for the first time to analyze tectonic structures at continental scale. Geologic correlation studies propose to continue the tectonic lineaments across continents to the pre-breakup position. Tectonic events that induce density changes, as metamorphic events and magmatic events, should then show up in the gravity field. Applying geodynamic plate reconstructions to the GOCE gravity field places today’s observed field at the pre-breakup position. The same reconstruction can be applied to the seismic velocity models, to allow a joint gravity-velocity analysis. The geophysical fields allow to control the likeliness of the hypothesized continuation of lineations based on sparse surface outcrops. Total absence of a signal, makes the cross-continental continuation of the lineament improbable, as continental-wide lineaments are controlled by rheologic and compositional differences of lithospheric mantle. It is found that the deep lithospheric roots as those found below cratons control the position of the positive gravity values. The explanation is that the deep lithospheric roots focus asthenospheric upwelling outboard of the root protecting the overlying craton from magmatic intrusions. The study is carried out over the African and South American continents.

Waving and skewing: how gravity and the surface of growth media affect root development in Arabidopsis.

PubMed

Oliva, Michele; Dunand, Christophe

2007-01-01

Arabidopsis seedlings growing on inclined agar surfaces exhibit characteristic root behaviours called 'waving' and 'skewing': the former consists of a series of undulations, whereas the latter is a deviation from the direction of gravity. Even though the precise basis of these growth patterns is not well understood, both gravity and the contact between the medium and the root are considered to be the major players that result in these processes. The influence of these forces on root surface-dependent behaviours can be verified by growing seedlings at different gel pitches: plants growing on vertical plates present roots with slight waving and skewing when compared with seedlings grown on plates held at minor angles of < 90 degrees . However, other factors are thought to modulate root growth on agar; for instance, it has been demonstrated that the presence and concentration of certain compounds in the medium (such as sucrose) and of drugs able to modify the plant cell cytoskeleton also affect skewing and waving. The recent discovery of an active role of ethylene on surface-dependent root behaviour, and the finding of new mutants showing anomalous growth, pave the way for a more detailed description of these phenomena.

Trans-Golgi network localized small GTPase RabA1d is involved in cell plate formation and oscillatory root hair growth.

PubMed

Berson, Tobias; von Wangenheim, Daniel; Takáč, Tomáš; Šamajová, Olga; Rosero, Amparo; Ovečka, Miroslav; Komis, George; Stelzer, Ernst H K; Šamaj, Jozef

2014-09-27

Small Rab GTPases are important regulators of vesicular trafficking in plants. AtRabA1d, a member of the RabA1 subfamily of small GTPases, was previously found in the vesicle-rich apical dome of growing root hairs suggesting a role during tip growth; however, its specific intracellular localization and role in plants has not been well described. The transient expression of 35S::GFP:RabA1d construct in Allium porrum and Nicotiana benthamiana revealed vesicular structures, which were further corroborated in stable transformed Arabidopsis thaliana plants. GFP-RabA1d colocalized with the trans-Golgi network marker mCherry-VTI12 and with early FM4-64-labeled endosomal compartments. Late endosomes and endoplasmic reticulum labeled with FYVE-DsRed and ER-DsRed, respectively, were devoid of GFP-RabA1d. The accumulation of GFP-RabA1d in the core of brefeldin A (BFA)-induced-compartments and the quantitative upregulation of RabA1d protein levels after BFA treatment confirmed the association of RabA1d with early endosomes/TGN and its role in vesicle trafficking. Light-sheet microscopy revealed involvement of RabA1d in root development. In root cells, GFP-RabA1d followed cell plate expansion consistently with cytokinesis-related vesicular trafficking and membrane recycling. GFP-RabA1d accumulated in disc-like structures of nascent cell plates, which progressively evolved to marginal ring-like structures of the growing cell plates. During root hair growth and development, GFP-RabA1d was enriched at root hair bulges and at the apical dome of vigorously elongating root hairs. Importantly, GFP-RabA1d signal intensity exhibited an oscillatory behavior in-phase with tip growth. Progressively, this tip localization dissapeared in mature root hairs suggesting a link between tip localization of RabA1d and root hair elongation. Our results support a RabA1d role in events that require vigorous membrane trafficking. RabA1d is located in early endosomes/TGN and is involved in vesicle trafficking. RabA1d participates in both cell plate formation and root hair oscillatory tip growth. The specific GFP-RabA1d subcellular localization confirms a correlation between its specific spatio-temporal accumulation and local vesicle trafficking requirements during cell plate and root hair formation.

Reduced gravitropic sensitivity in roots of a starch-deficient mutant of Nicotiana sylvestris

NASA Technical Reports Server (NTRS)

Kiss, J. Z.; Sack, F. D.

1989-01-01

Gravitropism was studied in seedlings of Nicotiana sylvestris Speg. et Comes wild-type (WT) and mutant NS 458 which has a defective plastid phosphoglucomutase (EC 2.7.5.1.). Starch was greatly reduced in NS 458 compared to the WT, but small amounts of starch were detected in rootcap columella cells in NS 458 by light and electron microscopy. The roots of WT are more sensitive to gravity than mutant NS 458 roots since: (1) in mutant roots, curvature was reduced and delayed in the time course of curvature; (2) curvature of mutant roots was 24-56% that of WT roots over the range of induction periods tested; (3) in intermittent-stimulation experiments, curvature of mutant roots was 37% or less than that of WT roots in all treatments tested. The perception time, determined by intermittent-stimulation experiments, was < or = 5 s for WT roots and 30-60 s for mutant roots. The growth rates for WT and NS 458 roots were essentially equal. These results and our previous results with WT and starchless mutant Arabidopsis roots (Kiss et al. 1989, Planta 177, 198-206) support the conclusions that a full complement of starch is necessary for full gravitropic sensitivity and that amyloplasts function in gravity perception. Since a presumed relatively small increase in plastid buoyant mass (N. sylvestris mutant versus Arabidopsis mutant) significantly improves the orientation of the N. sylvestris mutant roots, we suggest that plastids are the likeliest candidates to be triggering gravity perception in roots of both mutants.

Mapping of sugar and amino acid availability in soil around roots with bacterial sensors of sucrose and tryptophan

PubMed

Jaeger; Lindow; Miller; Clark; Firestone

1999-06-01

We developed a technique to map the availability of sugars and amino acids along live roots in an intact soil-root matrix with native microbial soil flora and fauna present. It will allow us to study interactions between root exudates and soil microorganisms at the fine spatial scale necessary to evaluate mechanisms of nitrogen cycling in the rhizosphere. Erwinia herbicola 299R harboring a promoterless ice nucleation reporter gene, driven by either of two nutrient-responsive promoters, was used as a biosensor. Strain 299RTice exhibits tryptophan-dependent ice nucleation activity, while strain 299R(p61RYice) expresses ice nucleation activity proportional to sucrose concentration in its environment. Both biosensors exhibited up to 100-fold differences in ice nucleation activity in response to varying substrate abundance in culture. The biosensors were introduced into the rhizosphere of the annual grass Avena barbata and, as a control, into bulk soil. Neither strain exhibited significant ice nucleation activity in the bulk soil. Both tryptophan and sucrose were detected in the rhizosphere, but they showed different spatial patterns. Tryptophan was apparently most abundant in soil around roots 12 to 16 cm from the tip, while sucrose was most abundant in soil near the root tip. The largest numbers of bacteria (determined by acridine orange staining and direct microscopy) occurred near root sections with the highest apparent sucrose or tryptophan exudation. High sucrose availability at the root tip is consistent with leakage of photosynthate from immature, rapidly growing root tissues, while tryptophan loss from older root sections may result from lateral root perforation of the root epidermis.

Alginate-encapsulation of shoot tips of jojoba [Simmondsia chinensis (Link) Schneider] for germplasm exchange and distribution.

PubMed

Kumar, Sunil; Rai, Manoj K; Singh, Narender; Mangal, Manisha

2010-12-01

Shoot tips excised from in vitro proliferated shoots derived from nodal explants of jojoba [Simmondsia chinensis (Link) Schneider] were encapsulated in calcium alginate beads for germplasm exchange and distribution. A gelling matrix of 3 % sodium alginate and 100 mM calcium chloride was found most suitable for formation of ideal calcium alginate beads. Best response for shoot sprouting from encapsulated shoot tips was recorded on 0.8 % agar-solidified full-strength MS medium. Rooting was induced upon transfer of sprouted shoots to 0.8 % agar-solidified MS medium containing 1 mg l(-1) IBA. About 70 % of encapsulated shoot tips were rooted and converted into plantlets. Plants regenerated from encapsulated shoot tips were acclimatized successfully. The present encapsulation approach could also be applied as an alternative method of propagation of desirable elite genotype of jojoba.

RNA-seq for gene identification and transcript profiling in relation to root growth of bermudagrass (Cynodon dactylon) under salinity stress.

PubMed

Hu, Longxing; Li, Huiying; Chen, Liang; Lou, Yanhong; Amombo, Erick; Fu, Jinmin

2015-08-04

Soil salinity is one of the most significant abiotic stresses affecting plant shoots and roots growth. The adjustment of root architecture to spatio-temporal heterogeneity in salinity is particularly critical for plant growth and survival. Bermudagrass (Cynodon dactylon) is a widely used turf and forage perennial grass with a high degree of salinity tolerance. Salinity appears to stimulate the growth of roots and decrease their mortality in tolerant bermudagrass. To estimate a broad spectrum of genes related to root elongation affected by salt stress and the molecular mechanisms that control the positive response of root architecture to salinity, we analyzed the transcriptome of bermudagrass root tips in response to salinity. RNA-sequencing was performed in root tips of two bermudagrass genotypes contrasting in salt tolerance. A total of 237,850,130 high quality clean reads were generated and 250,359 transcripts were assembled with an average length of 1115 bp. Totally, 103,324 unigenes obtained with 53,765 unigenes (52 %) successfully annotated in databases. Bioinformatics analysis indicated that major transcription factor (TF) families linked to stress responses and growth regulation (MYB, bHLH, WRKY) were differentially expressed in root tips of bermudagrass under salinity. In addition, genes related to cell wall loosening and stiffening (xyloglucan endotransglucosylase/hydrolases, peroxidases) were identified. RNA-seq analysis identified candidate genes encoding TFs involved in the regulation of lignin synthesis, reactive oxygen species (ROS) homeostasis controlled by peroxidases, and the regulation of phytohormone signaling that promote cell wall loosening and therefore root growth under salinity.

Influence of microgravity on root-cap regeneration and the structure of columella cells in Zea mays

NASA Technical Reports Server (NTRS)

Moore, R.; McClelen, C. E.; Fondren, W. M.; Wang, C. L.

1987-01-01

We launched imbibed seeds and seedlings of Zea mays into outer space aboard the space shuttle Columbia to determine the influence of microgravity on 1) root-cap regeneration, and 2) the distribution of amyloplasts and endoplasmic reticulum (ER) in the putative statocytes (i.e., columella cells) of roots. Decapped roots grown on Earth completely regenerated their caps within 4.8 days after decapping, while those grown in microgravity did not regenerate caps. In Earth-grown seedlings, the ER was localized primarily along the periphery of columella cells, and amyloplasts sedimented in response to gravity to the lower sides of the cells. Seeds germinated on Earth and subsequently launched into outer space had a distribution of ER in columella cells similar to that of Earth-grown controls, but amyloplasts were distributed throughout the cells. Seeds germinated in outer space were characterized by the presence of spherical and ellipsoidal masses of ER and randomly distributed amyloplasts in their columella cells. These results indicate that 1) gravity is necessary for regeneration of the root cap, 2) columella cells can maintain their characteristic distribution of ER in microgravity only if they are exposed previously to gravity, and 3) gravity is necessary to distribute the ER in columella cells of this cultivar of Z. mays.

Dynamic response of tapered optical multimode fiber coated with carbon nanotubes for ethanol sensing application.

PubMed

Shabaneh, Arafat; Girei, Saad; Arasu, Punitha; Mahdi, Mohd; Rashid, Suraya; Paiman, Suriati; Yaacob, Mohd

2015-05-04

Ethanol is a highly combustible chemical universally designed for biomedical applications. In this paper, optical sensing performance of tapered multimode fiber tip coated with carbon nanotube (CNT) thin film towards aqueous ethanol with different concentrations is investigated. The tapered optical multimode fiber tip is coated with CNT using drop-casting technique and is annealed at 70 °C to enhance the binding of the nanomaterial to the silica fiber tip. The optical fiber tip and the CNT sensing layer are micro-characterized using FESEM and Raman spectroscopy techniques. When the developed sensor was exposed to different concentrations of ethanol (5% to 80%), the sensor reflectance reduced proportionally. The developed sensors showed high sensitivity, repeatability and fast responses (<55 s) towards ethanol.

Dynamic Response of Tapered Optical Multimode Fiber Coated with Carbon Nanotubes for Ethanol Sensing Application

PubMed Central

Shabaneh, Arafat; Girei, Saad; Arasu, Punitha; Mahdi, Mohd; Rashid, Suraya; Paiman, Suriati; Yaacob, Mohd

2015-01-01

Ethanol is a highly combustible chemical universally designed for biomedical applications. In this paper, optical sensing performance of tapered multimode fiber tip coated with carbon nanotube (CNT) thin film towards aqueous ethanol with different concentrations is investigated. The tapered optical multimode fiber tip is coated with CNT using drop-casting technique and is annealed at 70 °C to enhance the binding of the nanomaterial to the silica fiber tip. The optical fiber tip and the CNT sensing layer are micro-characterized using FESEM and Raman spectroscopy techniques. When the developed sensor was exposed to different concentrations of ethanol (5% to 80%), the sensor reflectance reduced proportionally. The developed sensors showed high sensitivity, repeatability and fast responses (<55 s) towards ethanol. PMID:25946634

Differentiation and Tropisms in Space-Grown Moss

NASA Technical Reports Server (NTRS)

Sack, Fred D.; Kern, Volker

1999-01-01

This grant supported a Space Shuttle experiment on the effects of microgravity on moss cells. Moss provides a rich system for gravitational and spaceflight research. The early phase of the moss life cycle consists of chains of cells that only grow only at their tips. In the moss Ceratodon purpureus these filaments (protonemata) grow away from gravity in the dark, in a process called gravitropism. The tipmost cells, the apical cells, contain heavy starch-filled bodies called amyloplasts that probably function in g-sensing and that sediment within the apical cell. The SPM-A (Space Moss aka SPAM) experiment flew in November - December, 1997 on STS-87 as part of the Collaborative US Ukrainian Experiment (CLTE). The experiment was accommodated in hardware purpose-built by NASA KSC and Bionetics and included Petri Dish Fixation Units (PDFU) and BRIC-LEDs. Together, this hardware allowed for the culture of the moss on agar in commercial petri dishes, for unilateral illumination with red light of varying intensity, and for chemical fixation in situ. The key findings of the spaceflight were quite unexpected. Neither the orientation of tip-growth nor the distribution of amyloplasts was random in microgravity.

Identification and validation of reference genes for quantification of target gene expression with quantitative real-time PCR for tall fescue under four abiotic stresses.

PubMed

Yang, Zhimin; Chen, Yu; Hu, Baoyun; Tan, Zhiqun; Huang, Bingru

2015-01-01

Tall fescue (Festuca arundinacea Schreb.) is widely utilized as a major forage and turfgrass species in the temperate regions of the world and is a valuable plant material for studying molecular mechanisms of grass stress tolerance due to its superior drought and heat tolerance among cool-season species. Selection of suitable reference genes for quantification of target gene expression is important for the discovery of molecular mechanisms underlying improved growth traits and stress tolerance. The stability of nine potential reference genes (ACT, TUB, EF1a, GAPDH, SAND, CACS, F-box, PEPKR1 and TIP41) was evaluated using four programs, GeNorm, NormFinder, BestKeeper, and RefFinder. The combinations of SAND and TUB or TIP41 and TUB were most stably expressed in salt-treated roots or leaves. The combinations of GAPDH with TIP41 or TUB were stable in roots and leaves under drought stress. TIP41 and PEPKR1 exhibited stable expression in cold-treated roots, and the combination of F-box, TIP41 and TUB was also stable in cold-treated leaves. CACS and TUB were the two most stable reference genes in heat-stressed roots. TIP41 combined with TUB and ACT was stably expressed in heat-stressed leaves. Finally, quantitative real-time polymerase chain reaction (qRT-PCR) assays of the target gene FaWRKY1 using the identified most stable reference genes confirmed the reliability of selected reference genes. The selection of suitable reference genes in tall fescue will allow for more accurate identification of stress-tolerance genes and molecular mechanisms conferring stress tolerance in this stress-tolerant species.

Cutting efficiency of apical preparation using ultrasonic tips with microprojections: confocal laser scanning microscopy study.

PubMed

Kwak, Sang-Won; Moon, Young-Mi; Yoo, Yeon-Jee; Baek, Seung-Ho; Lee, WooCheol; Kim, Hyeon-Cheol

2014-11-01

The purpose of this study was to compare the cutting efficiency of a newly developed microprojection tip and a diamond-coated tip under two different engine powers. The apical 3-mm of each root was resected, and root-end preparation was performed with upward and downward pressure using one of the ultrasonic tips, KIS-1D (Obtura Spartan) or JT-5B (B&L Biotech Ltd.). The ultrasonic engine was set to power-1 or -4. Forty teeth were randomly divided into four groups: K1 (KIS-1D / Power-1), J1 (JT-5B / Power-1), K4 (KIS-1D / Power-4), and J4 (JT-5B / Power-4). The total time required for root-end preparation was recorded. All teeth were resected and the apical parts were evaluated for the number and length of cracks using a confocal scanning micrscope. The size of the root-end cavity and the width of the remaining dentin were recorded. The data were statistically analyzed using two-way analysis of variance and a Mann-Whitney test. There was no significant difference in the time required between the instrument groups, but the power-4 groups showed reduced preparation time for both instrument groups (p < 0.05). The K4 and J4 groups with a power-4 showed a significantly higher crack formation and a longer crack irrespective of the instruments. There was no significant difference in the remaining dentin thickness or any of the parameters after preparation. Ultrasonic tips with microprojections would be an option to substitute for the conventional ultrasonic tips with a diamond coating with the same clinical efficiency.

Cutting efficiency of apical preparation using ultrasonic tips with microprojections: confocal laser scanning microscopy study

PubMed Central

Kwak, Sang-Won; Moon, Young-Mi; Yoo, Yeon-Jee; Baek, Seung-Ho; Lee, WooCheol

2014-01-01

Objectives The purpose of this study was to compare the cutting efficiency of a newly developed microprojection tip and a diamond-coated tip under two different engine powers. Materials and Methods The apical 3-mm of each root was resected, and root-end preparation was performed with upward and downward pressure using one of the ultrasonic tips, KIS-1D (Obtura Spartan) or JT-5B (B&L Biotech Ltd.). The ultrasonic engine was set to power-1 or -4. Forty teeth were randomly divided into four groups: K1 (KIS-1D / Power-1), J1 (JT-5B / Power-1), K4 (KIS-1D / Power-4), and J4 (JT-5B / Power-4). The total time required for root-end preparation was recorded. All teeth were resected and the apical parts were evaluated for the number and length of cracks using a confocal scanning micrscope. The size of the root-end cavity and the width of the remaining dentin were recorded. The data were statistically analyzed using two-way analysis of variance and a Mann-Whitney test. Results There was no significant difference in the time required between the instrument groups, but the power-4 groups showed reduced preparation time for both instrument groups (p < 0.05). The K4 and J4 groups with a power-4 showed a significantly higher crack formation and a longer crack irrespective of the instruments. There was no significant difference in the remaining dentin thickness or any of the parameters after preparation. Conclusions Ultrasonic tips with microprojections would be an option to substitute for the conventional ultrasonic tips with a diamond coating with the same clinical efficiency. PMID:25383346

Calcium and protein phosphorylation in the transduction of gravity signal in corn roots

NASA Technical Reports Server (NTRS)

Friedmann, M.; Poovaiah, B. W.

1991-01-01

The involvement of calcium and protein phosphorylation in the transduction of gravity signal was studied using corn roots of a light-insensitive variety (Zea mays L., cv. Patriot). The gravitropic response was calcium-dependent. Horizontal placement of roots preloaded with 32P for three minutes resulted in changes in protein phosphorylation of polypeptides of 32 and 35 kD. Calcium depletion resulted in decreased phosphorylation of these phosphoproteins and replenishment of calcium restored the phosphorylation.

Identification and analysis of novel genes involved in gravitropism of Arabidopsis thaliana.

NASA Astrophysics Data System (ADS)

Morita, Miyo T.; Tasaka, Masao; Masatoshi Taniguchi, .

2012-07-01

Gravitropism is a continuous control with regard to the orientation and juxtaposition of the various parts of the plant body in response to gravity. In higher plants, the relative directional change of gravity is mainly suscepted in specialized cells called statocytes, followed by signal conversion from physical information into physiological information within the statocytes. We have studied the early process of shoot gravitropism, gravity sensing and signaling process, mainly by molecular genetic approach. In Arabidopsis shoot, statocytes are the endodermal cells. sgr1/scarcrow (scr) and sgr7/short-root (shr) mutants fail to form the endodermis and to respond to gravity in their inflorescence stems. Since both SGR1/SCR and SGR7/SHR are transcriptional factors, at least a subset of their downstream genes can be expected to be involved in gravitropism. In addition, eal1 (endodermal-amyloplast less 1), which exhibits no gravitropism in inflorescence stem but retains ability to form endodermis, is a hypomorphic allele of sgr7/shr. Take advantage of these mutants, we performed DNA microarray analysis and compared gene expression profiles between wild type and the mutants. We found that approx. 40 genes were commonly down-regulated in these mutants and termed them DGE (DOWN-REGULATED GENE IN EAL1) genes. DGE1 has sequence similarity to Oryza sativa LAZY1 that is involved in shoot gravitropism of rice. DGE2 has a short region homologous to DGE1. DTL (DGE TWO-LIKE}) that has 54% identity to DGE2 is found in Arabidopsis genome. All three genes are conserved in angiosperm but have no known functional domains or motifs. We analyzed T-DNA insertion for these genes in single or multiple combinations. In dge1 dge2 dtl triple mutant, gravitropic response of shoot, hypocotyl and root dramatically reduced. Now we are carrying out further physiological and molecular genetic analysis of the triple mutant.

Automatic fixation facility for plant seedlings in the TEXUS Sounding Rocket Programme.

PubMed

Tewinkel, M; Burfeindt, J; Rank, P; Volkmann, D

1991-10-01

Automatic chemical fixation of plant seedlings within a 6 min period of reduced gravity (10(-4)g) was performed on three ballistic rocket flights provided by the German Sounding Rocket Programme TEXUS (Technologische Experimente unter Schwerelosigkeit = Technological Experiments in Microgravity). The described TEXUS experiment module consists of a standard experiment housing with batteries, cooling and heating systems, timer, and a data recording unit. Typically, 60 min before launch an experiment plug-in unit containing chambers with the plant material, the fixation system, and the temperature sensors is installed into the module which is already integrated in the payload section of the sounding rocket (late access). During the ballistic flight plant chambers are rapidly filled at pre-selected instants to preserve the cell structure of gravity sensing cells. After landing the plant material is processed for transmission electron microscopy. Up to now three experiments were successfully performed with cress roots (Lepidium sativum L.). Detailed improvements resulted in an automatic fixation facility which in principle can be used in unmanned missions.

Bone condition of the maxillary zygomatic process prior to orthodontic anchorage plate fixation.

PubMed

Präger, T M; Brochhagen, H G; Mischkowski, R; Jost-Brinkmann, P G; Müller-Hartwich, R

2015-01-01

The clinical success of orthodontic miniplates depends on the stability of the miniscrews used for fixation. For good stability, it is essential that the application site provides enough bone of good quality. This study was performed to analyze the amount of bone available for orthodontic miniplates in the zygomatic process of the maxilla. We examined 51 dental CT scans (Somatom Plus 4; Siemens, Erlangen, Germany) obtained from 51 fully dentate adult patients (mean age 24.0 ± 8.1 years; 27 male and 24 female) prior to third molar surgery. The amount of bone in the zygomatic process region at the level of the first molar root tips and at several other cranial levels as far as 15 mm from the root tips was measured Bone thickness at the root tip level averaged 4.1 ± 1.0 mm; the lowest value measured at this level in any of the patients was 2.7 mm. Bone thickness averaged 8.3 ± 1.0 mm at 15 mm cranial to the root tips; 6.9 mm was the lowest value. The zygomatic process appears to provide sufficient bone to accommodate screws for miniplate fixation. While some patients may possess a borderline amount of bone at more caudal levels, lack of volume is not a problem near the zygomatic bone.

The Darfur Swell, Africa: Gravity constraints on its isostatic compensation

NASA Astrophysics Data System (ADS)

Crough, S. Thomas

The free-air gravity anomaly observed over the Darfur Swell is explainable by local isostatic balance with a root approximately 50 km deep on average. This root depth is similar to that inferred beneath other African domes and beneath oceanic midplate swells, suggesting that the Darfur Swell is a hotspot uplift created by lithospheric reheating.

Gravitropism of Arabidopsis thaliana roots requires the polarization of PIN2 toward the root tip in meristematic cortical cells.

PubMed

Rahman, Abidur; Takahashi, Maho; Shibasaki, Kyohei; Wu, Shuang; Inaba, Takehito; Tsurumi, Seiji; Baskin, Tobias I

2010-06-01

In the root, the transport of auxin from the tip to the elongation zone, referred to here as shootward, governs gravitropic bending. Shootward polar auxin transport, and hence gravitropism, depends on the polar deployment of the PIN-FORMED auxin efflux carrier PIN2. In Arabidopsis thaliana, PIN2 has the expected shootward localization in epidermis and lateral root cap; however, this carrier is localized toward the root tip (rootward) in cortical cells of the meristem, a deployment whose function is enigmatic. We use pharmacological and genetic tools to cause a shootward relocation of PIN2 in meristematic cortical cells without detectably altering PIN2 polarization in other cell types or PIN1 polarization. This relocation of cortical PIN2 was negatively regulated by the membrane trafficking factor GNOM and by the regulatory A1 subunit of type 2-A protein phosphatase (PP2AA1) but did not require the PINOID protein kinase. When GNOM was inhibited, PINOID abundance increased and PP2AA1 was partially immobilized, indicating both proteins are subject to GNOM-dependent regulation. Shootward PIN2 specifically in the cortex was accompanied by enhanced shootward polar auxin transport and by diminished gravitropism. These results demonstrate that auxin flow in the root cortex is important for optimal gravitropic response.

Gravitropic mechanisms derived from space experiments and magnetic gradients.

NASA Astrophysics Data System (ADS)

Hasenstein, Karl H.; Park, Myoung Ryoul

2016-07-01

Gravitropism is the result of a complex sequence of events that begins with the movement of dense particles, typically starch-filled amyloplasts in response to reorientation. Although these organelles change positions, it is not clear whether the critical signal is derived from sedimentation or dynamic interactions of amyloplasts with relevant membranes. Substituting gravity by high-gradient magnetic fields (HGMF) provides a localized stimulus for diamagnetic starch that is specific for amyloplasts and comparable to gravity without affecting other organelles. Experiments with Brassica rapa showed induction of root curvature by HGMF when roots moved sufficiently close to the magnetic gradient-inducing foci. The focused and short-range effectiveness of HGMFs provided a gravity-like stimulus and affected related gene expression. Root curvature was sensitive to the mutual alignment between roots and HGMF direction. Unrelated to any HGMF effects, the size of amyloplasts in space-grown roots increased by 30% compared to ground controls and suggests enhanced sensitivity in a gravity-reduced environment. Accompanying gene transcription studies showed greater differences between HGMF-exposed and space controls than between space and ground controls. This observation may lead to the identification of gravitropism-relevant genes. However, space grown roots showed stronger transcription of common reference genes such as actin and ubiquitin in magnetic fields than in non-magnetic conditions. In contrast, α-amylase, glucokinase and PIN encoding genes were transcribed stronger under non-magnetic conditions than under HGMF. The large number of comparisons between space, ground, and HGMF prompted the assessment of transcription differences between root segments, root-shoot junction, and seeds. Because presumed transcription of reference genes varied more than genes of interest, changes in gene expression cannot be based on reference genes. The data provide an example of complex and different responses to microgravity conditions, induced curvature, ground controls, clinorotation, and magnetic field exposure.

Progressive Inhibition by Water Deficit of Cell Wall Extensibility and Growth along the Elongation Zone of Maize Roots Is Related to Increased Lignin Metabolism and Progressive Stelar Accumulation of Wall Phenolics1

PubMed Central

Fan, Ling; Linker, Raphael; Gepstein, Shimon; Tanimoto, Eiichi; Yamamoto, Ryoichi; Neumann, Peter M.

2006-01-01

Water deficit caused by addition of polyethylene glycol 6000 at −0.5 MPa water potential to well-aerated nutrient solution for 48 h inhibited the elongation of maize (Zea mays) seedling primary roots. Segmental growth rates in the root elongation zone were maintained 0 to 3 mm behind the tip, but in comparison with well-watered control roots, progressive growth inhibition was initiated by water deficit as expanding cells crossed the region 3 to 9 mm behind the tip. The mechanical extensibility of the cell walls was also progressively inhibited. We investigated the possible involvement in root growth inhibition by water deficit of alterations in metabolism and accumulation of wall-linked phenolic substances. Water deficit increased expression in the root elongation zone of transcripts of two genes involved in lignin biosynthesis, cinnamoyl-CoA reductase 1 and 2, after only 1 h, i.e. before decreases in wall extensibility. Further increases in transcript expression and increased lignin staining were detected after 48 h. Progressive stress-induced increases in wall-linked phenolics at 3 to 6 and 6 to 9 mm behind the root tip were detected by comparing Fourier transform infrared spectra and UV-fluorescence images of isolated cell walls from water deficit and control roots. Increased UV fluorescence and lignin staining colocated to vascular tissues in the stele. Longitudinal bisection of the elongation zone resulted in inward curvature, suggesting that inner, stelar tissues were also rate limiting for root growth. We suggest that spatially localized changes in wall-phenolic metabolism are involved in the progressive inhibition of wall extensibility and root growth and may facilitate root acclimation to drying environments. PMID:16384904

Sugars en route to the roots. Transport, metabolism and storage within plant roots and towards microorganisms of the rhizosphere.

PubMed

Hennion, Nils; Durand, Mickael; Vriet, Cécile; Doidy, Joan; Maurousset, Laurence; Lemoine, Rémi; Pourtau, Nathalie

2018-04-28

In plants, root is a typical sink organ that relies exclusively on the import of sugar from the aerial parts. Sucrose is delivered by the phloem to the most distant root tips and, en route to the tip, is used by the different root tissues for metabolism and storage. Besides, a certain portion of this carbon is exuded in the rhizosphere, supplied to beneficial microorganisms and diverted by parasitic microbes. The transport of sugars towards these numerous sinks either occurs symplastically through cell connections (plasmodesmata) or is apoplastically mediated through membrane transporters (MST, SUT/SUC and SWEET) that control monosaccharide and sucrose fluxes. Here, we review recent progresses on carbon partitioning within and outside roots, discussing membrane transporters involved in plant responses to biotic and abiotic factors. This article is protected by copyright. All rights reserved.

Rejection of atrial sensing artifacts by a pacing lead with short tip-to-ring spacing.

PubMed

Nash, A; Fröhlig, G; Taborsky, M; Stammwitz, E; Maru, F; Bouwens, L H M; Celiker, C

2005-01-01

The ability of a new pacing lead design, with a 10 mm tip-to-ring spacing, to facilitate rejection of sensed far field R-waves and myopotentials was evaluated. Measurements were performed in 66 patients. The occurrence of far field R-wave sensing and myopotential sensing was determined by means of the surface ECG and the ECG markers provided by the pacemaker. At an atrial sensitivity of 0.25 mV and an atrial blanking of 50 ms far field R-wave sensing was observed in 12 patients (18.2%) and at an atrial sensitivity of 1.0 mV no far-field R-wave sensing was observed. Myopotentials were sensed in 3 patients. In all patients the measured P-wave amplitude was at least twice the estimated amplitude of the far field R-wave at an atrial blanking of 50 ms. The results from this study show that a small tip-to-ring spacing allows for programming of a high atrial sensitivity and short atrial blanking with an acceptably low risk for atrial artifact sensing.

Curvature induced by amyloplast magnetophoresis in protonemata of the moss Ceratodon purpureus

NASA Technical Reports Server (NTRS)

Kuznetsov, O. A.; Schwuchow, J.; Sack, F. D.; Hasenstein, K. H.

1999-01-01

After gravistimulation of Ceratodon purpureus (Hedw.) Brid. protonemata in the dark, amyloplast sedimentation was followed by upward curvature in the wild-type (WT) and downward curvature in the wwr mutant (wrong way response). We used ponderomotive forces induced by high-gradient magnetic fields (HGMF) to simulate the effect of gravity and displace the presumptive statoliths. The field was applied by placing protonemata either between two permanent magnets at the edge of the gap, close to the edge of a magnetized ferromagnetic wedge, or close to a small (<1 mm) permanent magnet. Continuous application of an HGMF in all three configurations resulted in plastid displacement and induced curvature in tip cells of WT and wwr protonemata. WT cells curved toward the HGMF, and wwr cells curved away from the HGMF, comparable to gravitropism. Plastids isolated from protonemal cultures had densities ranging from 1.24 to 1.38 g cm-3. Plastid density was similar for both genotypes, but the mutant contained larger plastids than the WT. The size difference might explain the stronger response of the wwr protonemata to the HGMF. Our data support the plastid-based theory of gravitropic sensing and suggest that HGMF-induced ponderomotive forces can substitute for gravity.

The type III secretion system needle tip complex mediates host cell sensing and translocon insertion.

PubMed

Veenendaal, Andreas K J; Hodgkinson, Julie L; Schwarzer, Lynn; Stabat, David; Zenk, Sebastian F; Blocker, Ariel J

2007-03-01

Type III secretion systems (T3SSs) are essential virulence determinants of many Gram-negative bacterial pathogens. The Shigella T3SS consists of a cytoplasmic bulb, a transmembrane region and a hollow 'needle' protruding from the bacterial surface. Physical contact with host cells initiates secretion and leads to assembly of a pore, formed by IpaB and IpaC, in the host cell membrane, through which proteins that facilitate host cell invasion are translocated. As the needle is implicated in host cell sensing and secretion regulation, its tip should contain components that initiate host cell contact. Through biochemical and immunological studies of wild-type and mutant Shigella T3SS needles, we reveal tip complexes of differing compositions and functional states, which appear to represent the molecular events surrounding host cell sensing and pore formation. Our studies indicate that the interaction between IpaB and IpaD at needle tips is key to host cell sensing, orchestration of IpaC secretion and its subsequent assembly at needle tips. This allows insertion into the host cell membrane of a translocation pore that is continuous with the needle.

Gravitropism in Arabidopsis thaliana: violation of the sine- and resultant-law

NASA Astrophysics Data System (ADS)

Galland, Paul

We investigated the gravitropic bending of hypocotyls and roots of seedlings of Arabidopsis tha-liana in response to long-term centrifugal accelerations in a range of 5 x 10-3 to 4 x g. The so-cal-led resultant law of gravitropism, a corollary of the so called sine law, claims that during centri-fugation a gravitropic organ aligns itself parallel to the resultant stimulus vector. We show here that neither of the two empirical “laws” is apt to describe the complex gravitropic behaviour of seedlings of Arabidopsis. Hypocotyls obey reasonably well the resultant law while roots display a complex behaviour that is clearly at variance with it. Horizontally centrifuged seedlings sense minute accelerations acting parallel to the longitudinal axis. If the centrifugal vector points to-ward the cotyledons, then the bending of hypocotyls and roots is greatly enhanced. If the centri-fugal vector points, however, toward the root tip, then only the bending of roots is enhanced by accelerations as low as 5 x 10-3 x g (positive tonic effect). The absolute gravitropic thresholds were determined for hypocotyls and roots in a clinostat-centrifuge and found to be near 1.5 x 10-2 x g. A behavioural mutant, ehb1-2 (Knauer et al. 2011), displays a lower gravitropic threshold for roots, not however, for hypocotyls. The complex gravitropic behaviour of seedlings of Arabi-dopsis is at odds with the classical sine- as well as the resultant law and can indicates the eminent role that is played by the acceleration vector operating longitudinally to the seedling axis.

Conservation of the plastid sedimentation zone in all moss genera with known gravitropic protonemata

NASA Technical Reports Server (NTRS)

Schwuchow, J. M.; Kern, V. D.; White, N. J.; Sack, F. D.

2002-01-01

Moss protonemata from several species are known to be gravitropic. The characterization of additional gravitropic species would be valuable to identify conserved traits that may relate to the mechanism of gravitropism. In this study, four new species were found to have gravitropic protonemata, Fissidens adianthoides, Fissidens cristatus, Physcomitrium pyriforme, and Barbula unguiculata. Comparison of upright and inverted apical cells of P. pyriforme and Fissidens species showed clear axial sedimentation. This sedimentation is highly regulated and not solely dependent on amyloplast size. Additionally, the protonemal tip cells of these species contained broad subapical zones that displayed lateral amyloplast sedimentation. The conservation of a zone of lateral sedimentation in a total of nine gravitropic moss species from five different orders supports the idea that this sedimentation serves a specialized and conserved function in gravitropism, probably in gravity sensing.

Morphology of Er:YAG-laser-treated root surfaces

NASA Astrophysics Data System (ADS)

Keller, Ulrich; Stock, Karl; Hibst, Raimund

1997-12-01

From previous studies it could be demonstrated that an efficient ablation of dental calculus is possible using an Er:YAG laser with a special contact fiber tip. After improving of the design and the efficiency of light transmission of the contact tip laser treated tooth root surfaces were investigated due to morphological changes in comparison to conventional root scaling and planing. Surface modifications were observed histologically under the light microscope and by means of a Scanning Electron Microscope. During laser treatment the intrapulpal temperature increase was measured. The results show that the improved contact tip a microstructured surface can be generated, which shows no signs of thermal effects even when a laser pulse repetition rate of 15 Hz was used. Temperature increase was limited to 4 K at a repetition rate of 10 Hz and to 5.5 K at a repetition rate of 15 Hz.

Soil compaction and organic matter affect conifer seedling nonmycorrhizal and ectomycorrhizal root tip abundance and diversity. Forest Service research paper

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

Amaranthus, M.P.; Page-Dumroese, D.; Harvey, A.

1996-05-01

Three levels of organic matter removal (bole only; bole and crowns; and bole, crowns, and forest floor) and three levels of mechanical soil compaction (no compaction, moderate compaction, and severe soil compaction) were studied as they influence Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and western white pine (Pinus monticola Dougl. ex D. Don) seedlings following outplanting. Moderate and severe soil compaction significantly reduced nonmycorrhizal root tip abundance on both Douglas-fir and western white pine seedlings (p less than or equal to 0.05). Ectomycorrhizal root tip abundance was significantly reduced on Douglas-fir seedlings in severely compacted areas with bole andmore » crowns and bole, crowns, and forest floor removed. Ectomycorrhizal diversity also was significantly reduced on Douglas-fir seedlings in all severely compacted areas.« less

Actin Cytoskeleton-Based Plant Synapse as Gravitransducer in the Transition Zone of the Root Apex

NASA Astrophysics Data System (ADS)

Baluska, Frantisek; Barlow, Peter; Volkmann, Dieter; Mancuso, Stefano

The actin cytoskeleton was originally proposed to act as the signal transducer in the plant gravity sensory-motoric circuit. Surprisingly, however, several studies have documented that roots perfom gravisensing and gravitropism more effectively if exposed to diverse anti-F-actin drugs. Our study, using decapped maize root apices, has revealed that depolymerization of F-actin stimulates gravity perception in cells of the transition zone where root gravitropism is initiated (Mancuso et al. 2006). It has been proposed (Balǔka et al. 2005, 2009a) that s the non-growing adhesive end-poles, enriched with F-actin and myosin VIII, and active in endocytic recycling of both PIN transporters and cell wall pectins cross-linked with calcium and boron, act as the gravisensing domains, and that these impinge directly upon the root motoric responses via control of polar auxin transport. This model suggests that mechanical asymmetry at these plant synapses determines vectorial gravity-controlled auxin transport. Due to the gravity-imposed mechanical load upon the protoplast, a tensional stress is also imposed upon the plasma membrane of the physically lower synaptic cell pole. This stress is then relieved by shifting the endocytosis-exocytosis balance towards exocytosis (Balǔka et al. s 2005, 2009a,b). This `Synaptic Auxin Secretion' hypothesis does not conflict with the `Starch Statolith' hypothesis, which is based on amyloplast sedimentation. In fact, the `Synaptic Auxin Secretion' hypothesis has many elements which allow its unification with the Starch-Statolith model (Balǔka et al. 2005, 2009a,b). s References Balǔka F, Volkmann D, Menzel D (2005) Plant synapses: actin-based adhesion s domains for cell-to-cell communication. Trends Plant Sci 10: 106-111 Balǔka F, Schlicht M, s Wan Y-L, Burbach C, Volkmann D (2009a) Intracellular domains and polarity in root apices: from synaptic domains to plant neurobiology. Nova Acta Leopoldina 96: 103-122 Balǔka s F, Mancuso S, Volkmann D, Barlow PW (2009b) The 'root-brain' hypothesis of Charles and Francis Darwin: Revival after more than 125 years. Plant Signal Behav 4: 1121-1127 Mancuso S, Barlow PW, Volkmann D, Balǔka F (2006). Actin turnover-mediated gravity response in s maize root apices: gravitropism of decapped roots implicates gravisensing outside of the root cap. Plant Signal Behav 1: 52-58

Graviresponsiveness and the Development of Columella Tissue in Primary and Lateral Roots of Ricinus communis1

PubMed Central

Moore, Randy; Pasieniuk, John

1984-01-01

Half-tipped primary and lateral roots of Ricinus communis cv Hale bend toward the side of the root on which the intact half-tip remains. Therefore, the minimal graviresponsiveness of lateral roots is not due to the inability of their caps to produce growth effectors (presumably inhibitors). The columella tissues of primary (i.e. graviresponsive) roots are (a) 4.30 times longer, (b) 2.95 times wider, (c) 37.4 times more voluminous, and (d) composed of 17.2 times more cells than those of lateral roots. The onset of positive gravitropism by lateral roots is positively correlated with a (a) 2.99-fold increase in length, (b) 2.63-fold increase in width, and (c) 20.7-fold increase in volume of their columella tissues. We propose that the minimal graviresponsiveness of lateral roots is due to the small size of their columella tissues, which results in their caps being unable to (a) establish a concentration gradient of the effector sufficient to induce gravicurvature and (b) produce as much of the effector as caps of graviresponsive roots. Images Fig. 1 PMID:11540818

Superconducting gravity gradiometer for space and terrestrial applications

NASA Technical Reports Server (NTRS)

Moody, M. V.; Chan, H. A.; Paik, H. J.

1986-01-01

A three-axis superconducting gravity gradiometer with a potential sensitivity better than Eotvos per sq root Hz is currently under development for applications in space. Although such a high sensitivity may be needed for only a limited number of terrestrial applications, superconductivity offers many extraordinary effects which can be used to obtain a gravity gradiometer with other characteristics necessary for operation in a hostile moving-base environment. Utilizing a number of recently devised techniques which rely on certain properties of superconductors, a design for a sensitive yet rugged gravity gradiometer with a high degree of stability and a common-mode rejection ratio greater than 10 to the 9th is produced. With a base line of 0.11 m, a sensitivity of 0.1 Eotvos per sq root Hz is expected in an environment monitored to a level of 0.01 m/sq sec sq root Hz for linear vibration and 7 x 10 to the -6th rad/s sq root Hz for angular vibration. A conventional stabilized platform can be used at this level. The intrinsic noise level, which is two orders of magnitude lower, could be achieved by monitoring the attitude with a superconducting angular accelerometer which is under development. In addition, the new gradiometer design has the versatility of adapting the instrument to different gravity biases by adjusting stored dc currents.

A class I ADP-ribosylation factor GTPase-activating protein is critical for maintaining directional root hair growth in Arabidopsis.

PubMed

Yoo, Cheol-Min; Wen, Jiangqi; Motes, Christy M; Sparks, J Alan; Blancaflor, Elison B

2008-08-01

Membrane trafficking and cytoskeletal dynamics are important cellular processes that drive tip growth in root hairs. These processes interact with a multitude of signaling pathways that allow for the efficient transfer of information to specify the direction in which tip growth occurs. Here, we show that AGD1, a class I ADP ribosylation factor GTPase-activating protein, is important for maintaining straight growth in Arabidopsis (Arabidopsis thaliana) root hairs, since mutations in the AGD1 gene resulted in wavy root hair growth. Live cell imaging of growing agd1 root hairs revealed bundles of endoplasmic microtubules and actin filaments extending into the extreme tip. The wavy phenotype and pattern of cytoskeletal distribution in root hairs of agd1 partially resembled that of mutants in an armadillo repeat-containing kinesin (ARK1). Root hairs of double agd1 ark1 mutants were more severely deformed compared with single mutants. Organelle trafficking as revealed by a fluorescent Golgi marker was slightly inhibited, and Golgi stacks frequently protruded into the extreme root hair apex of agd1 mutants. Transient expression of green fluorescent protein-AGD1 in tobacco (Nicotiana tabacum) epidermal cells labeled punctate bodies that partially colocalized with the endocytic marker FM4-64, while ARK1-yellow fluorescent protein associated with microtubules. Brefeldin A rescued the phenotype of agd1, indicating that the altered activity of an AGD1-dependent ADP ribosylation factor contributes to the defective growth, organelle trafficking, and cytoskeletal organization of agd1 root hairs. We propose that AGD1, a regulator of membrane trafficking, and ARK1, a microtubule motor, are components of converging signaling pathways that affect cytoskeletal organization to specify growth orientation in Arabidopsis root hairs.

A Class I ADP-Ribosylation Factor GTPase-Activating Protein Is Critical for Maintaining Directional Root Hair Growth in Arabidopsis1[W][OA

PubMed Central

Yoo, Cheol-Min; Wen, Jiangqi; Motes, Christy M.; Sparks, J. Alan; Blancaflor, Elison B.

2008-01-01

Membrane trafficking and cytoskeletal dynamics are important cellular processes that drive tip growth in root hairs. These processes interact with a multitude of signaling pathways that allow for the efficient transfer of information to specify the direction in which tip growth occurs. Here, we show that AGD1, a class I ADP ribosylation factor GTPase-activating protein, is important for maintaining straight growth in Arabidopsis (Arabidopsis thaliana) root hairs, since mutations in the AGD1 gene resulted in wavy root hair growth. Live cell imaging of growing agd1 root hairs revealed bundles of endoplasmic microtubules and actin filaments extending into the extreme tip. The wavy phenotype and pattern of cytoskeletal distribution in root hairs of agd1 partially resembled that of mutants in an armadillo repeat-containing kinesin (ARK1). Root hairs of double agd1 ark1 mutants were more severely deformed compared with single mutants. Organelle trafficking as revealed by a fluorescent Golgi marker was slightly inhibited, and Golgi stacks frequently protruded into the extreme root hair apex of agd1 mutants. Transient expression of green fluorescent protein-AGD1 in tobacco (Nicotiana tabacum) epidermal cells labeled punctate bodies that partially colocalized with the endocytic marker FM4-64, while ARK1-yellow fluorescent protein associated with microtubules. Brefeldin A rescued the phenotype of agd1, indicating that the altered activity of an AGD1-dependent ADP ribosylation factor contributes to the defective growth, organelle trafficking, and cytoskeletal organization of agd1 root hairs. We propose that AGD1, a regulator of membrane trafficking, and ARK1, a microtubule motor, are components of converging signaling pathways that affect cytoskeletal organization to specify growth orientation in Arabidopsis root hairs. PMID:18539780

Antisense expression of an Arabidopsis ran binding protein renders transgenic roots hypersensitive to auxin and alters auxin-induced root growth and development by arresting mitotic progress

NASA Technical Reports Server (NTRS)

Kim, S. H.; Arnold, D.; Lloyd, A.; Roux, S. J.

2001-01-01

We cloned a cDNA encoding an Arabidopsis Ran binding protein, AtRanBP1c, and generated transgenic Arabidopsis expressing the antisense strand of the AtRanBP1c gene to understand the in vivo functions of the Ran/RanBP signal pathway. The transgenic plants showed enhanced primary root growth but suppressed growth of lateral roots. Auxin significantly increased lateral root initiation and inhibited primary root growth in the transformants at 10 pM, several orders of magnitude lower than required to induce these responses in wild-type roots. This induction was followed by a blockage of mitosis in both newly emerged lateral roots and in the primary root, ultimately resulting in the selective death of cells in the tips of both lateral and primary roots. Given the established role of Ran binding proteins in the transport of proteins into the nucleus, these findings are consistent with a model in which AtRanBP1c plays a key role in the nuclear delivery of proteins that suppress auxin action and that regulate mitotic progress in root tips.

Early Effects of Salinity on Water Transport in Arabidopsis Roots. Molecular and Cellular Features of Aquaporin Expression1

PubMed Central

Boursiac, Yann; Chen, Sheng; Luu, Doan-Trung; Sorieul, Mathias; van den Dries, Niels; Maurel, Christophe

2005-01-01

Aquaporins facilitate the uptake of soil water and mediate the regulation of root hydraulic conductivity (Lpr) in response to a large variety of environmental stresses. Here, we use Arabidopsis (Arabidopsis thaliana) plants to dissect the effects of salt on both Lpr and aquaporin expression and investigate possible molecular and cellular mechanisms of aquaporin regulation in plant roots under stress. Treatment of plants by 100 mm NaCl was perceived as an osmotic stimulus and induced a rapid (half-time, 45 min) and significant (70%) decrease in Lpr, which was maintained for at least 24 h. Macroarray experiments with gene-specific tags were performed to investigate the expression of all 35 genes of the Arabidopsis aquaporin family. Transcripts from 20 individual aquaporin genes, most of which encoded members of the plasma membrane intrinsic protein (PIP) and tonoplast intrinsic protein (TIP) subfamilies, were detected in nontreated roots. All PIP and TIP aquaporin transcripts with a strong expression signal showed a 60% to 75% decrease in their abundance between 2 and 4 h following exposure to salt. The use of antipeptide antibodies that cross-reacted with isoforms of specific aquaporin subclasses revealed that the abundance of PIP1s decreased by 40% as early as 30 min after salt exposure, whereas PIP2 and TIP1 homologs showed a 20% to 40% decrease in abundance after 6 h of treatment. Expression in transgenic plants of aquaporins fused to the green fluorescent protein revealed that the subcellular localization of TIP2;1 and PIP1 and PIP2 homologs was unchanged after 45 min of exposure to salt, whereas a TIP1;1-green fluorescent protein fusion was relocalized into intracellular spherical structures tentatively identified as intravacuolar invaginations. The appearance of intracellular structures containing PIP1 and PIP2 homologs was occasionally observed after 2 h of salt treatment. In conclusion, this work shows that exposure of roots to salt induces changes in aquaporin expression at multiple levels. These changes include a coordinated transcriptional down-regulation and subcellular relocalization of both PIPs and TIPs. These mechanisms may act in concert to regulate root water transport, mostly in the long term (≥6 h). PMID:16183846

A scanning electron microscopic study to evaluate the efficacy of NaviTip FX in removing the canal debris during root canal preparation: an in vitro study.

PubMed

Chandra, Vinay; Gandi, Padma; Shivanna, Anil Kumar; Srinivas, Siva; Himgiri, S; Nischith, K G

2013-07-01

To evaluate the efficacy of NaviTip FX in removing the canal debris during root canal preparation using scanning electron microscopic study. Thirty single rooted teeth with completely formed apices were used in this study. Standard endodontic access cavity preparations were performed. Then the teeth were randomly divided into two groups: groups 1 and 2 of 15 teeth each group. For group 1, NaviTip FX (brush covered needle) was used to irrigate the canal with 5.25% sodium hypochlorite after each instrument use. For group 2, NaviTip (brushless needle) was used for irrigation following each instrument use. ProTaper rotary files were used for the canal preparation. The teeth were then cleaned and dried before splitting them into two halves. The half with most visible part of the apex was used for scanning electron microscopic evaluation. The results were statistically analyzed using the Mann-Whitney U-test at significance level p < 0.005. The mean values for coronal and middle third of group 1 showed lower debris scores than group 2 and this difference was statistically significant at a p-value 0.01 and 0.05 respectively, but no significance difference between them at the apical third at a p-value of < 0.05. The NaviTip FX (brush covered needle) showed effectively better canal wall debris removal than the NaviTip (brushless needle).

ß-Cyanoalanine Synthase Action in Root Hair Elongation is Exerted at Early Steps of the Root Hair Elongation Pathway and is Independent of Direct Cyanide Inactivation of NADPH Oxidase.

PubMed

Arenas-Alfonseca, Lucía; Gotor, Cecilia; Romero, Luis C; García, Irene

2018-05-01

In Arabidopsis thaliana, cyanide is produced concomitantly with ethylene biosynthesis and is mainly detoxified by the ß-cyanoalanine synthase CAS-C1. In roots, CAS-C1 activity is essential to maintain a low level of cyanide for proper root hair development. Root hair elongation relies on polarized cell expansion at the growing tip, and we have observed that CAS-C1 locates in mitochondria and accumulates in root hair tips during root hair elongation, as shown by observing the fluorescence in plants transformed with the translational construct ProC1:CASC1-GFP, containing the complete CAS-C1 gene fused to green fluorescent protein (GFP). Mutants in the SUPERCENTIPEDE (SCN1) gene, that regulate the NADPH oxidase gene ROOT HAIR DEFECTIVE 2 (RHD2)/AtrbohC, are affected at the very early steps of the development of root hair that do not elongate and do not show a preferential localization of the GFP accumulation in the tips of the root hair primordia. Root hairs of mutants in CAS-C1 or RHD2/AtrbohC, whose protein product catalyzes the generation of ROS and the Ca2+ gradient, start to grow out correctly, but they do not elongate. Genetic crosses between the cas-c1 mutant and scn1 or rhd2 mutants were performed, and the detailed phenotypic and molecular characterization of the double mutants demonstrates that scn1 mutation is epistatic to cas-c1 and cas-c1 is epistatic to rhd2 mutation, indicating that CAS-C1 acts in early steps of the root hair development process. Moreover, our results show that the role of CAS-C1 in root hair elongation is independent of H2O2 production and of a direct NADPH oxidase inhibition by cyanide.

The importance of valve alignment in determining the pressure/flow characteristics of differential pressure shunt valves with anti-gravity devices.

PubMed

Francel, P C; Stevens, F A; Tompkins, P; Pollay, M

2001-02-01

The proper functioning of shunt valves in vivo is dependent on many factors, including the valve itself, the anti-siphon device or ASD (if included), patency of inlet and outlet tubing, and location of the valve. One important, but sometimes overlooked, consideration in valve function is the valve location relative to the tip of the ventricular inlet catheter. As with any pressure measurement, the zero or reference position is an important concept. In the case of shunt valves, the position of the proximal inlet catheter tip is fixed and therefore serves as the reference point for all pressure measurements. This study was conducted to document the importance of this relationship for the pressure/flow characteristics of the shunt valve. We bench-tested differential pressure valves (with integral anti-gravity devices; AGDs) from three manufacturers. Valves were connected to an "infinite" reservoir, and the starting head pressure for each was determined from product inserts. The inlet catheter tip was fixed at this position, and the valve body was moved in relation to the inlet catheter tip. Outflow rates were determined gravimetrically for positions varying between 4 cm above and 8 cm below the inlet catheter tip. All differential pressure valves utilized in this study that contained AGDs showed significant increases in outflow rate as the valve body was moved incrementally below the level of the inlet catheter tip. To allow functioning as a zero-hydrostatic pressure differential pressure valve, the AGD and the inlet catheter tip should be aligned at the same horizontal level.

Analysis of Cell Biomechanics Response to Gravity:A Fluids for Biology Study Utilizing NASA Glenns Zero Gravity Research Facility

NASA Technical Reports Server (NTRS)

Bomani, Bilal M. M.; Kassemi, Mohammad; Neumann, Eric S.

2016-01-01

It remains unclear how biological cells sense and respond to gravitational forces. Leading scientists state that a large gap exists in the understanding of physiological and molecular adaptation that occurs as biology enters the spaceflight realm. We are seeking a method to fully understand how cells sense microgravity/gravity and what triggers their response.

In Vivo potassium-39 NMR spectra by the burg maximum-entropy method

NASA Astrophysics Data System (ADS)

Uchiyama, Takanori; Minamitani, Haruyuki

The Burg maximum-entropy method was applied to estimate 39K NMR spectra of mung bean root tips. The maximum-entropy spectra have as good a linearity between peak areas and potassium concentrations as those obtained by fast Fourier transform and give a better estimation of intracellular potassium concentrations. Therefore potassium uptake and loss processes of mung bean root tips are shown to be more clearly traced by the maximum-entropy method.

Testing the link between community structure and function for ectomycorrhizal fungi involved in a global tripartite symbiosis.

PubMed

Walker, Jennifer K M; Cohen, Hannah; Higgins, Logan M; Kennedy, Peter G

2014-04-01

Alnus trees associate with ectomycorrhizal (ECM) fungi and nitrogen-fixing Frankia bacteria and, although their ECM fungal communities are uncommonly host specific and species poor, it is unclear whether the functioning of Alnus ECM fungal symbionts differs from that of other ECM hosts. We used exoenzyme root tip assays and molecular identification to test whether ECM fungi on Alnus rubra differed in their ability to access organic phosphorus (P) and nitrogen (N) when compared with ECM fungi on the non-Frankia host Pseudotsuga menziesii. At the community level, potential acid phosphatase (AP) activity of ECM fungal root tips from A. rubra was significantly higher than that from P. menziesii, whereas potential leucine aminopeptidase (LA) activity was significantly lower for A. rubra root tips at one of the two sites. At the individual species level, there was no clear relationship between ECM fungal relative root tip abundance and relative AP or LA enzyme activities on either host. Our results are consistent with the hypothesis that ECM fungal communities associated with Alnus trees have enhanced organic P acquisition abilities relative to non-Frankia ECM hosts. This shift, in combination with the chemical conditions present in Alnus forest soils, may drive the atypical structure of Alnus ECM fungal communities. © 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.

Genotoxicity of fenpropathrin and fenitrothion on root tip cells of Vicia faba.

PubMed

Bu, N; Wang, S H; Yu, C M; Zhang, Y; Ma, C Y; Li, X M; Ma, L J

2011-11-01

The genotoxicity of fenpropathrin and fenitrothion on root tip cells of Vicia faba was studied. The symptoms were investigated about the mitotic index, the micronucleus frequency and chromosomal aberration frequency of root tip cells of Vicia faba which were induced by different concentrations of fenpropathrin and fenitrothion (1 × 10(-10)-1 × 10(-2) g L(-1)). Results showed that fenpropathrin and fenitrothion could induce the micronucleus of root tip cells of Vicia faba. It occurred in a dose-dependent manner. Peaks were observed at 1 × 10( -6) g L(-1) fenpropathrin and 1 × 10(-4) g L(-1) fenitrothion, and micronucleus frequency reached 14.587 ± 1.511‰ and 14.164 ± 1.623‰, respectively. From 1 × 10(-10) g L(-1) to 1 × 10( -6) g L(-1) fenpropathrin and 1 × 10(-4) g L(-1) fenitrothion, the micronucleus frequency increased with the increase of the concentrations, but beyond this range, the micronucleus frequency decreased with the further increase of the concentrations. A similar trend was observed for mitotic index. Moreover, fenpropathrin and fenitrothion could induce various types of chromosome aberration, such as lagging chromosomes, chromosome fragment, chromosome bridge, multipolar, nuclear buds, karyorrhexis, etc.

Calcium- and potassium-permeable plasma membrane transporters are activated by copper in Arabidopsis root tips: linking copper transport with cytosolic hydroxyl radical production.

PubMed

Rodrigo-Moreno, Ana; Andrés-Colás, Nuria; Poschenrieder, Charlotte; Gunsé, Benet; Peñarrubia, Lola; Shabala, Sergey

2013-04-01

Transition metals such as copper can interact with ascorbate or hydrogen peroxide to form highly reactive hydroxyl radicals (OH(•) ), with numerous implications to membrane transport activity and cell metabolism. So far, such interaction was described for extracellular (apoplastic) space but not cytosol. Here, a range of advanced electrophysiological and imaging techniques were applied to Arabidopsis thaliana plants differing in their copper-transport activity: Col-0, high-affinity copper transporter COPT1-overexpressing (C1(OE) ) seedlings, and T-DNA COPT1 insertion mutant (copt1). Low Cu concentrations (10 µm) stimulated a dose-dependent Gd(3+) and verapamil sensitive net Ca(2+) influx in the root apex but not in mature zone. C1(OE) also showed a fivefold higher Cu-induced K(+) efflux at the root tip level compared with Col-0, and a reduction in basal peroxide accumulation at the root tip after copper exposure. Copper caused membrane disruptions of the root apex in C1(OE) seedlings but not in copt1 plants; this damage was prevented by pretreatment with Gd(3+) . Our results suggest that copper transport into cytosol in root apex results in hydroxyl radical generation at the cytosolic side, with a consequent regulation of plasma membrane OH(•) -sensitive Ca(2+) and K(+) transport systems. © 2012 Blackwell Publishing Ltd.

Gravitropism of Arabidopsis thaliana Roots Requires the Polarization of PIN2 toward the Root Tip in Meristematic Cortical Cells[C][W

PubMed Central

Rahman, Abidur; Takahashi, Maho; Shibasaki, Kyohei; Wu, Shuang; Inaba, Takehito; Tsurumi, Seiji; Baskin, Tobias I.

2010-01-01

In the root, the transport of auxin from the tip to the elongation zone, referred to here as shootward, governs gravitropic bending. Shootward polar auxin transport, and hence gravitropism, depends on the polar deployment of the PIN-FORMED auxin efflux carrier PIN2. In Arabidopsis thaliana, PIN2 has the expected shootward localization in epidermis and lateral root cap; however, this carrier is localized toward the root tip (rootward) in cortical cells of the meristem, a deployment whose function is enigmatic. We use pharmacological and genetic tools to cause a shootward relocation of PIN2 in meristematic cortical cells without detectably altering PIN2 polarization in other cell types or PIN1 polarization. This relocation of cortical PIN2 was negatively regulated by the membrane trafficking factor GNOM and by the regulatory A1 subunit of type 2-A protein phosphatase (PP2AA1) but did not require the PINOID protein kinase. When GNOM was inhibited, PINOID abundance increased and PP2AA1 was partially immobilized, indicating both proteins are subject to GNOM-dependent regulation. Shootward PIN2 specifically in the cortex was accompanied by enhanced shootward polar auxin transport and by diminished gravitropism. These results demonstrate that auxin flow in the root cortex is important for optimal gravitropic response. PMID:20562236

[Effects nutrients on the seedlings root hair development and root growth of Poncirus trifoliata under hydroponics condition].

PubMed

Cao, Xiu; Xia, Ren-Xue; Zhang, De-Jian; Shu, Bo

2013-06-01

Ahydroponics experiment was conducted to study the effects of nutrients (N, P, K, Ca, Mg, Fe, and Mn) deficiency on the length of primary root, the number of lateral roots, and the root hair density, length, and diameter on the primary root and lateral roots of Poncirus trifoliata seedlings. Under the deficiency of each test nutrient, root hair could generate, but was mainly concentrated on the root base and fewer on the root tip. The root hair density on lateral roots was significantly larger than that on primary root, but the root hair length was in adverse. The deficiency of each test nutrient had greater effects on the growth and development of root hairs, with the root hair density on primary root varied from 55.0 to 174.3 mm(-2). As compared with the control, Ca deficiency induced the significant increase of root hair density and length on primary root, P deficiency promoted the root hair density and length on the base and middle part of primary root and on the lateral roots significantly, Fe deficiency increased the root hair density but decreased the root hair length on the tip of primary root significantly, K deficiency significantly decreased the root hair density, length, and diameter on primary root and lateral roots, whereas Mg deficiency increased the root hair length of primary root significantly. In all treatments of nutrient deficiency, the primary root had the similar growth rate, but, with the exceptions of N and Mg deficiency, the lateral roots exhibited shedding and regeneration.

Superconducting gravity gradiometer and a test of inverse square law

NASA Technical Reports Server (NTRS)

Moody, M. V.; Paik, Ho Jung

1989-01-01

The equivalence principle prohibits the distinction of gravity from acceleration by a local measurement. However, by making a differential measurement of acceleration over a baseline, platform accelerations can be cancelled and gravity gradients detected. In an in-line superconducting gravity gradiometer, this differencing is accomplished with two spring-mass accelerometers in which the proof masses are confined to motion in a single degree of freedom and are coupled together by superconducting circuits. Platform motions appear as common mode accelerations and are cancelled by adjusting the ratio of two persistent currents in the sensing circuit. The sensing circuit is connected to a commercial SQUID amplifier to sense changes in the persistent currents generated by differential accelerations, i.e., gravity gradients. A three-axis gravity gradiometer is formed by mounting six accelerometers on the faces of a precision cube, with the accelerometers on opposite faces of the cube forming one of three in-line gradiometers. A dedicated satellite mission for mapping the earth's gravity field is an important one. Additional scientific goals are a test of the inverse square law to a part in 10(exp 10) at 100 km, and a test of the Lense-Thirring effect by detecting the relativistic gravity magnetic terms in the gravity gradient tensor for the earth.

Phytotoxic cyanamide affects maize (Zea mays) root growth and root tip function: from structure to gene expression.

PubMed

Soltys, Dorota; Rudzińska-Langwald, Anna; Kurek, Wojciech; Szajko, Katarzyna; Sliwinska, Elwira; Bogatek, Renata; Gniazdowska, Agnieszka

2014-05-01

Cyanamide (CA) is a phytotoxic compound produced by four Fabaceae species: hairy vetch, bird vetch, purple vetch and black locust. Its toxicity is due to complex activity that involves the modification of both cellular structures and physiological processes. To date, CA has been investigated mainly in dicot plants. The goal of this study was to investigate the effects of CA in the restriction of the root growth of maize (Zea mays), representing the monocot species. CA (3mM) reduced the number of border cells in the root tips of maize seedlings and degraded their protoplasts. However, CA did not induce any significant changes in the organelle structure of other root cells, apart from increased vacuolization. CA toxicity was also demonstrated by its effect on cell cycle activity, endoreduplication intensity, and modifications of cyclins CycA2, CycD2, and histone HisH3 gene expression. In contrast, the arrangement of microtubules was not altered by CA. Treatment of maize seedlings with CA did not completely arrest mitotic activity, although the frequency of dividing cells was reduced. Furthermore, prolonged CA treatment increased the proportion of endopolyploid cells in the root tip. Cytological malformations were accompanied by an induction of oxidative stress in root cells, which manifested as enhanced accumulation of H2O2. Exposure of maize seedlings to CA resulted in an increased concentration of auxin and stimulated ethylene emission. Taken together, these findings suggested that the inhibition of root growth by CA may be a consequence of stress-induced morphogenic responses. Copyright © 2014. Published by Elsevier GmbH.

Integrated Metabolomics and Transcriptomics Reveal Enhanced Specialized Metabolism in Medicago truncatula Root Border Cells1[OPEN

PubMed Central

Watson, Bonnie S.; Bedair, Mohamed F.; Urbanczyk-Wochniak, Ewa; Huhman, David V.; Yang, Dong Sik; Allen, Stacy N.; Li, Wensheng; Tang, Yuhong; Sumner, Lloyd W.

2015-01-01

Integrated metabolomics and transcriptomics of Medicago truncatula seedling border cells and root tips revealed substantial metabolic differences between these distinct and spatially segregated root regions. Large differential increases in oxylipin-pathway lipoxygenases and auxin-responsive transcript levels in border cells corresponded to differences in phytohormone and volatile levels compared with adjacent root tips. Morphological examinations of border cells revealed the presence of significant starch deposits that serve as critical energy and carbon reserves, as documented through increased β-amylase transcript levels and associated starch hydrolysis metabolites. A substantial proportion of primary metabolism transcripts were decreased in border cells, while many flavonoid- and triterpenoid-related metabolite and transcript levels were increased dramatically. The cumulative data provide compounding evidence that primary and secondary metabolism are differentially programmed in border cells relative to root tips. Metabolic resources normally destined for growth and development are redirected toward elevated accumulation of specialized metabolites in border cells, resulting in constitutively elevated defense and signaling compounds needed to protect the delicate root cap and signal motile rhizobia required for symbiotic nitrogen fixation. Elevated levels of 7,4′-dihydroxyflavone were further increased in border cells of roots exposed to cotton root rot (Phymatotrichopsis omnivora), and the value of 7,4′-dihydroxyflavone as an antimicrobial compound was demonstrated using in vitro growth inhibition assays. The cumulative and pathway-specific data provide key insights into the metabolic programming of border cells that strongly implicate a more prominent mechanistic role for border cells in plant-microbe signaling, defense, and interactions than envisioned previously. PMID:25667316

The Effect of Low Oxygen Stress on Phytophthora cinnamomi Infection and Disease of Cork Oak Roots

Treesearch

Karel A. Jacobs; James D. MacDonald; Alison M. Berry; Laurence R. Costello

1997-01-01

The incidence and severity of Phytophthora cinnamomi Rands root disease was quantified in cork oak (Quercus suber L.) roots subjected to low oxygen (hypoxia) stress. Seedling root tips were inoculated with mycelial plugs of the fungus and incubated in ≤1, 3-4, or 21 percent oxygen for 5 days. Ninety-four percent of roots...

Gravity-induced changes in intracellular potentials in elongating cortical cells of mung bean roots

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Evans, M. L.

1990-01-01

Gravity-induced changes in intracellular potentials in primary roots of 2-day-old mung bean (Vigna mungo L. cv. black matpe) seedlings were investigated using glass microelectrodes held by 3-dimensional hydraulic micro-drives. The electrodes were inserted into outer cortical cells within the elongation zone. Intracellular potentials, angle of root orientation with respect to gravity, and position within the root of the impaled cortical cell were measured simultaneously. Gravistimulation caused intracellular potential changes in cortical cells of the elongation zone. When the roots were oriented vertically, the intracellular potentials of the outer cortical cells (2 mm behind the root apex) were approximately - 115 mV. When the roots were placed horizontally cortical cells on the upper side hyperpolarized to - 154 mV within 30 s while cortical cells on the lower side depolarized to about - 62 mV. This electrical asymmetry did not occur in cells of the maturation zone. Because attempts to insert the electrode into cells of the root cap were unsuccessful, these cells were not measured. The hyperpolarization of cortical cells on the upper side was greatly reduced upon application of N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of respiratory energy coupling. When stimulated roots were returned to the vertical, the degree of hyperpolarization of cortical cells on the previous upper side decreased within 30 s and approached that of cortical cells in non-stimulated roots. This cycle of hyperpolarization/loss of hyperpolarization was repeatable at least ten times by alternately turning the root from the vertical to the horizontal and back again. The very short (<30 s) lag period of these electrical changes indicates that they may result from stimulus-perception and transduction within the elongation zone rather than from transmission of a signal from the root cap.

Tomato root growth, gravitropism, and lateral development: correlation with auxin transport

NASA Technical Reports Server (NTRS)

Muday, G. K.; Haworth, P.

1994-01-01

Tomato (Lycopersicon esculentum, Mill.) roots were analyzed during growth on agar plates. Growth of these roots was inhibited by the auxin transport inhibitors naphthylphthalamic acid (NPA) and semicarbazone derivative I (SCB-1). The effect of auxin transport inhibitors on root gravitropism was analyzed by measurement of the angle of gravitropic curvature after the roots were reoriented 90 degrees from the vertical. NPA and SCB-1 abolished both the response of these roots to gravity and the formation of lateral roots, with SCB-1 being the more effective at inhibition. Auxins also inhibited root growth. Both auxins tested has a slight effect on the gravity response, but this effect is probably indirect, since auxins reduced the growth rate. Auxins also stimulated lateral root growth at concentration where primary root growth was inhibited. When roots were treated with both IAA and NPA simultaneously, a cumulative inhibition of root growth was found. When both compounds were applied together, analysis of gravitropism and lateral root formation indicated that the dominant effect was exerted by auxin transport inhibitors. Together, these data suggest a model for the role of auxin transport in controlling both primary and lateral root growth.

Gravitropism in plants: Hydraulics and wall growth properties of responding cells

NASA Technical Reports Server (NTRS)

Cosgrove, Daniel J.

1989-01-01

Gravitropism is the asymmetrical alteration of plant growth in response to a change in the gravity vector, with the typical result that stems grow up and roots grow down. The gravity response is important for plants because it enables them to grow their aerial parts in a mechanically stable (upright) position and to develop their roots and leaves to make efficient use of soil nutrients and sunlight. The elucidation of gravitropic responses will tell much about how gravity exerts its morphogenetic effects on plants and how plants regulate their growth at the cellular and molecular levels.

Exploration of plant growth and development using the European Modular Cultivation System facility on the International Space Station.

PubMed

Kittang, A-I; Iversen, T-H; Fossum, K R; Mazars, C; Carnero-Diaz, E; Boucheron-Dubuisson, E; Le Disquet, I; Legué, V; Herranz, R; Pereda-Loth, V; Medina, F J

2014-05-01

Space experiments provide a unique opportunity to advance our knowledge of how plants respond to the space environment, and specifically to the absence of gravity. The European Modular Cultivation System (EMCS) has been designed as a dedicated facility to improve and standardise plant growth in the International Space Station (ISS). The EMCS is equipped with two centrifuges to perform experiments in microgravity and with variable gravity levels up to 2.0 g. Seven experiments have been performed since the EMCS was operational on the ISS. The objectives of these experiments aimed to elucidate phototropic responses (experiments TROPI-1 and -2), root gravitropic sensing (GRAVI-1), circumnutation (MULTIGEN-1), cell wall dynamics and gravity resistance (Cell wall/Resist wall), proteomic identification of signalling players (GENARA-A) and mechanism of InsP3 signalling (Plant signalling). The role of light in cell proliferation and plant development in the absence of gravity is being analysed in an on-going experiment (Seedling growth). Based on the lessons learned from the acquired experience, three preselected ISS experiments have been merged and implemented as a single project (Plant development) to study early phases of seedling development. A Topical Team initiated by European Space Agency (ESA), involving experienced scientists on Arabidopsis space research experiments, aims at establishing a coordinated, long-term scientific strategy to understand the role of gravity in Arabidopsis growth and development using already existing or planned new hardware. © 2014 German Botanical Society and The Royal Botanical Society of the Netherlands.

Analysis of gene expression profiles for cell wall modifying proteins and ACC synthases in soybean cyst nematode colonized roots, adventitious rooting hypocotyls, root tips, flooded roots, and IBA and ACC treatment roots

USDA-ARS?s Scientific Manuscript database

We hypothesized that soybean cyst nematode (SCN) co-opts a part or all of one or more innate developmental process in soybean to establish its feeding structure, syncytium, in soybean roots. The syncytium in soybean roots is formed in a predominantly lateral direction within the vascular bundle by ...

Early root cap development and graviresponse in white clover (Trifolium repens) grown in space and on a two-axis clinostat

NASA Technical Reports Server (NTRS)

Smith, J. D.; Staehelin, L. A.; Todd, P.

1999-01-01

White clover (Trifolium repens) was germinated and grown in microgravity aboard the Space Shuttle (STS-60, 1994; STS-63, 1995), on Earth in stationary racks and in a slow-rotating two-axis clinostat. The objective of this study was to determine if normal root cap development and early plant gravity responses were dependent on gravitational cues. Seedlings were germinated in space and chemically fixed in orbit after 21, 40, and 72 h. Seedlings 96 h old were returned viable to earth. Germination and total seedling length were not dependent on gravity treatment. In space-flown seedlings, the number of cell stories in the root cap and the geometry of central columella cells did not differ from those of the Earth-grown seedlings. The root cap structure of clinorotated plants appeared similar to that of seedlings from microgravity, with the exception of three-day rotated plants, which displayed significant cellular damage in the columella region. Nuclear polarity did not depend on gravity; however, the positions of amyloplasts in the central columella cells were dependent on both the gravity treatment and the age of the seedlings. Seedlings from space, returned viable to earth, responded to horizontal stimulation as did 1 g controls, but seedlings rotated on the clinostat for the same duration had a reduced curvature response. This study demonstrates that initial root cap development is insensitive to either chronic clinorotation or microgravity. Soon after differentiation, however, clinorotation leads to loss of normal root cap structure and plant graviresponse while microgravity does not.

The RPG gene of Medicago truncatula controls Rhizobium-directed polar growth during infection

PubMed Central

Arrighi, Jean-François; Godfroy, Olivier; de Billy, Françoise; Saurat, Olivier; Jauneau, Alain; Gough, Clare

2008-01-01

Rhizobia can infect roots of host legume plants and induce new organs called nodules, in which they fix atmospheric nitrogen. Infection generally starts with root hair curling, then proceeds inside newly formed, intracellular tubular structures called infection threads. A successful symbiotic interaction relies on infection threads advancing rapidly at their tips by polar growth through successive cell layers of the root toward developing nodule primordia. To identify a plant component that controls this tip growth process, we characterized a symbiotic mutant of Medicago truncatula, called rpg for rhizobium-directed polar growth. In this mutant, nitrogen-fixing nodules were rarely formed due to abnormally thick and slowly progressing infection threads. Root hair curling was also abnormal, indicating that the RPG gene fulfils an essential function in the process whereby rhizobia manage to dominate the process of induced tip growth for root hair infection. Map-based cloning of RPG revealed a member of a previously unknown plant-specific gene family encoding putative long coiled-coil proteins we have called RRPs (RPG-related proteins) and characterized by an “RRP domain” specific to this family. RPG expression was strongly associated with rhizobial infection, and the RPG protein showed a nuclear localization, indicating that this symbiotic gene constitutes an important component of symbiotic signaling. PMID:18621693

The RPG gene of Medicago truncatula controls Rhizobium-directed polar growth during infection.

PubMed

Arrighi, Jean-François; Godfroy, Olivier; de Billy, Françoise; Saurat, Olivier; Jauneau, Alain; Gough, Clare

2008-07-15

Rhizobia can infect roots of host legume plants and induce new organs called nodules, in which they fix atmospheric nitrogen. Infection generally starts with root hair curling, then proceeds inside newly formed, intracellular tubular structures called infection threads. A successful symbiotic interaction relies on infection threads advancing rapidly at their tips by polar growth through successive cell layers of the root toward developing nodule primordia. To identify a plant component that controls this tip growth process, we characterized a symbiotic mutant of Medicago truncatula, called rpg for rhizobium-directed polar growth. In this mutant, nitrogen-fixing nodules were rarely formed due to abnormally thick and slowly progressing infection threads. Root hair curling was also abnormal, indicating that the RPG gene fulfils an essential function in the process whereby rhizobia manage to dominate the process of induced tip growth for root hair infection. Map-based cloning of RPG revealed a member of a previously unknown plant-specific gene family encoding putative long coiled-coil proteins we have called RRPs (RPG-related proteins) and characterized by an "RRP domain" specific to this family. RPG expression was strongly associated with rhizobial infection, and the RPG protein showed a nuclear localization, indicating that this symbiotic gene constitutes an important component of symbiotic signaling.

Root gravitropism in maize and Arabidopsis

NASA Technical Reports Server (NTRS)

Evans, Michael L.

1993-01-01

Research during the period 1 March 1992 to 30 November 1993 focused on improvements in a video digitizer system designed to automate the recording of surface extension in plants responding to gravistimulation. The improvements included modification of software to allow detailed analysis of localized extension patterns in roots of Arabidopsis. We used the system to analyze the role of the postmitotic isodiametric growth zone (a region between the meristem and the elongation zone) in the response of maize roots to auxin, calcium, touch and gravity. We also used the system to analyze short-term auxin and gravitropic responses in mutants of Arabidopsis with reduced auxin sensitivity. In a related project, we studied the relationship between growth rate and surface electrical currents in roots by examining the effects of gravity and thigmostimulation on surface potentials in maize roots.

An attempt to localize and identify the gravity sensing mechanism of plants

NASA Technical Reports Server (NTRS)

Bandurski, R. S.

1984-01-01

Gravistimulation causes an asymmetric distribution of the plant growth hormone, indole-3-acetic acid (IAA). In what tissue of the plant the IAA asymmetry arises will be determined so as to better localize the gravity sensing device.

[Influence of Four Kinds of PPCPs on Micronucleus Rate of the Root-Tip Cells of Vicia-faba and Garlic].

PubMed

Wang, Lan-jun; Wang, Jin-hua; Zhu, Lu-sheng; Wang, Jun; Zhao, Xiang

2016-04-15

In order to determine the degree of biological genetic injury induced by PPCPs, the genotoxic effects of the doxycycline (DOX), ciprofloxacin (CIP), triclocarban (TCC) and carbamazepine (CBZ) in the concentration range of 12.5-100 mg · L⁻¹ were studied using micronucleus rate and micronucleus index of Vicia-fabe and garlic. The results showed that: (1) When the Vicia-faba root- tip cells were exposed to DOX, CIP, TCC and CBZ, micronucleus rates were higher than 1.67 ‰ (CK₁), it was significantly different from that of the control group (P < 0.05), and the micronucleus index was even greater than 3.5; With the increasing concentrations of the PPCPs, the micronucleus rates first increased and then decreased. (2) When the garlic root tip cells were exposed to DOX, CIP, TCC and CBZ respectively, the micronucleus rates were less than those of the Vicia-faba, while in most treatments significantly higher than that of the control group (0.67‰). The micronucleus index was higher than 3.5 in the groups exposed to CIP with concentrations of 25, 50, 100 mg · L⁻¹ and TCC and CBZ with concentrations of 25 mg · L⁻¹; With the increase of exposure concentrations, the micronucleus rate showed a trend of first increasing and then decreasing as well. (3) Under the same experimental conditions, the cells micronucleus rates of the garlic cells caused by the four tested compounds were significantly lower than those of Vicia-faba. (4) The micronucleus index of the root tip cells of Vicia-faba and garlic treated with the four kinds of compounds followed the order of CIP > CBZ > TCC > DOX. These results demonstrated that the four compounds caused biological genetic injury to root-tip cells of Vicia-faba and garlic, and the genetic damage caused to garlic was significantly lower than that to Vicia-faba. The damages caused by the four kinds of different compounds were also different.

Characterization of LeMir, a Root-Knot Nematode-Induced Gene in Tomato with an Encoded Product Secreted from the Root1

PubMed Central

Brenner, Eric D.; Lambert, Kris N.; Kaloshian, Isgouhi; Williamson, Valerie M.

1998-01-01

A tomato gene that is induced early after infection of tomato (Lycopersicon esculentum Mill.) with root-knot nematodes (Meloidogyne javanica) encodes a protein with 54% amino acid identity to miraculin, a flavorless protein that causes sour substances to be perceived as sweet. This gene was therefore named LeMir (L. esculentum miraculin). Sequence similarity places the encoded protein in the soybean trypsin-inhibitor family (Kunitz). LeMir mRNA is found in root, hypocotyl, and flower tissues, with the highest expression in the root. Rapid induction of expression upon nematode infection is localized to root tips. In situ hybridization shows that LeMir is expressed constitutively in the root-cap and root-tip epidermis. The LeMir protein product (LeMir) was produced in the yeast Pichia pastoris for generation of antibodies. Western-blot analysis showed that LeMir expression is up-regulated by nematode infection and by wounding. LeMir is also expressed in tomato callus tissue. Immunoprint analysis revealed that LeMir is expressed throughout the seedling root, but that levels are highest at the root/shoot junction. Analysis of seedling root exudates revealed that LeMir is secreted from the root into the surrounding environment, suggesting that it may interact with soil-borne microorganisms. PMID:9733543

How grow-and-switch gravitropism generates root coiling and root waving growth responses in Medicago truncatula.

PubMed

Tan, Tzer Han; Silverberg, Jesse L; Floss, Daniela S; Harrison, Maria J; Henley, Christopher L; Cohen, Itai

2015-10-20

Experimental studies show that plant root morphologies can vary widely from straight gravity-aligned primary roots to fractal-like root architectures. However, the opaqueness of soil makes it difficult to observe how environmental factors modulate these patterns. Here, we combine a transparent hydrogel growth medium with a custom built 3D laser scanner to directly image the morphology of Medicago truncatula primary roots. In our experiments, root growth is obstructed by an inclined plane in the growth medium. As the tilt of this rigid barrier is varied, we find Medicago transitions between randomly directed root coiling, sinusoidal root waving, and normal gravity-aligned morphologies. Although these root phenotypes appear morphologically distinct, our analysis demonstrates the divisions are less well defined, and instead, can be viewed as a 2D biased random walk that seeks the path of steepest decent along the inclined plane. Features of this growth response are remarkably similar to the widely known run-and-tumble chemotactic behavior of Escherichia coli bacteria, where biased random walks are used as optimal strategies for nutrient uptake.

Tip Vortices of Isolated Wings and Helicopter Rotor Blades.

DTIC Science & Technology

1987-12-01

root to tip, as expected due to the induced downwash of the tip vor- tex and wake vortex sheet. Although the three different tip-caps produce very...the inherent limitation of not being able to model the vortex wake with these equations, although the Euler formulation has in it the necessary...physics to model vorticity transport correctly. These equations basically lack the physical mecha- nism needed to generate the vortex wake . However, in

Light Sheet Fluorescence Microscopy Quantifies Calcium Oscillations in Root Hairs of Arabidopsis thaliana.

PubMed

Candeo, Alessia; Doccula, Fabrizio G; Valentini, Gianluca; Bassi, Andrea; Costa, Alex

2017-07-01

Calcium oscillations play a role in the regulation of the development of tip-growing plant cells. Using optical microscopy, calcium oscillations have been observed in a few systems (e.g. pollen tubes, fungal hyphae and algal rhizoids). High-resolution, non-phototoxic and rapid imaging methods are required to study the calcium oscillation in root hairs. We show that light sheet fluorescence microscopy is optimal to image growing root hairs of Arabidopsis thaliana and to follow their oscillatory tip-focused calcium gradient. We describe a protocol for performing live imaging of root hairs in seedlings expressing the cytosol-localized ratiometric calcium indicator Yellow Cameleon 3.6. Using this protocol, we measured the calcium gradient in a large number of root hairs. We characterized their calcium oscillations and correlated them with the rate of hair growth. The method was then used to screen the effect of auxin on the properties of the growing root hairs. © The Author 2017. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.

Effects of the ionic liquid 1-hexyl-3-methylimidazolium bromide on root gravitropism in Arabidopsis seedlings.

PubMed

Zhang, Liang; Wang, Tianqi; Zheng, Fengxia; Ma, Lingyu; Li, Jingyuan

2016-03-01

The toxic effects of ionic liquids (ILs) have attracted increasing attention in recent years. However, the knowledge about the toxic effects of ILs on tropism in organisms remains quite limited. In this study, the effects of 1-hexyl-3-methylimidazolium bromide [C6mim]Br on root gravitropism were evaluated using Arabidopsis seedlings. Our results showed that the root growth and gravity response were significantly inhibited with increasing IL concentration. [C6mim]Br treatment affected the amount and distribution pattern of amyloplasts in root cap compared with controls. The auxin distribution marked with DR5rev::VENUS was altered in IL-treated seedlings. The signal intensity and gene expression of auxin efflux carriers PIN2 and PIN3 were obviously decreased by IL stress. Moreover, as consequences in response to gravity stimulus, the asymmetric DR5 signals in control root apex were impaired by IL treatment. The predominant PIN2 signals along the lower flank of root and PIN3 polarization in columella cells were also significantly reduced in seedlings exposed to IL. Our results suggest that the ionic liquid [C6mim]Br affects the amount and distribution of amyloplasts and disturbs the deployment of PIN2 and PIN3, thus impairing auxin flows in response to gravity stimulus and causing deficient root gravitropism in Arabidopsis seedlings. Copyright © 2015 Elsevier Inc. All rights reserved.

Enhanced Labeling Techniques to Study the Cytoskeleton During Root Growth and Gravitropism

NASA Technical Reports Server (NTRS)

Blancaflor, Elison B.

2005-01-01

Gravity effects the growth and development of all living organisms. One of the most obvious manifestations of gravity's effects on biological systems lies in the ability of plants to direct their growth along a path that is dictated by the gravity vector (called gravitropism). When positioned horizontally, in florescence stems and hypocotyls in dicots, and pulvini in monocots, respond by bending upward whereas roots typically bend downward. Gravitropism allows plants to readjust their growth to maximize light absorption for photosynthesis and to more efficiently acquire water and nutrients form the soil. Despite its significance for plant survival, there are still major gaps in understanding the cellular and molecular processes by which plants respond to gravity. The major aim of this proposal was to develop improved fluorescence labeling techniques to aid in understanding how the cytoskeleton modulated plant responses to gravity.

Gravity perception requires statoliths settled on specific plasma membrane areas in characean rhizoids and protonemata.

PubMed

Braun, Markus

2002-05-01

The noninvasive infrared laser micromanipulation technique (optical tweezers, optical trapping) and centrifugation were used to study susception and perception, the early events in the gravitropic pathway of tip-growing characean rhizoids and protonemata. Reorientation of the growth direction in both cell types was only initiated when at least 2-3 statoliths settled on specific areas of the plasma membrane. This statolith-sensitive plasma membrane area is confined to the statolith region (10-35 microns behind the tip) in positively gravitropic rhizoids, whereas in negatively gravitropic protonemata, this area is limited to the apical plasma membrane (0-10 microns). Statolith sedimentation towards the sensitive plasma membrane areas is mediated by the concerted action of actin and gravity. The process of sedimentation, the pure physical movement, of statoliths is not sufficient to initiate graviresponses in both cell types. It is concluded that specific statolith-sensitive plasma membrane areas play a crucial role in the signal transduction pathway of gravitropism. These areas may represent the primary sites for gravity perception and may transform the information derived from the gravity-induced statolith sedimentation into physiological signals which trigger the molecular mechanisms of the opposite graviresponses in characean rhizoids and protonemata.

Fate of oxygen losses from Typha domingensis (Typhaceae) and Cladium jamaicense (Cyperaceae) and consequences for root metabolism

USGS Publications Warehouse

Chabbi, A.; McKee, K.L.; Mendelssohn, I.A.

2000-01-01

The objective of this work was to determine whether radial oxygen loss (ROL) from roots of Typha domingensis and Cladium jamaicense creates an internal oxygen deficiency or, conversely, indicates adequate internal aeration and leakage of excess oxygen to the rhizosphere. Methylene blue in agar was used to quantify oxygen leakage. Typha's roots had a higher porosity than Cladium's and responded to flooding treatment by increasing cortical air space, particularly near the root tips. A greater oxygen release, which occurred along the subapical root axis, and an increase in rhizosphere redox potential (Eh) over time were associated with the well-developed aerenchyma system in Typha. Typha roots, regardless of oxygen release pattern, showed low or undetectable alcohol dehydrogenage (ADH) activity or ethanol concentrations, indicating that ROL did not cause internal deficiencies. Cladium roots also releases oxygen, but this loss primarily occurred at the root tips and was accompanied by increased root ADH activity and ethanol concentrations. These results support the hypothesis that oxygen release by Cladium is accompanied by internal deficiencies of oxygen sufficient to stimulate alcoholic fermentation and helps explain Cladium's lesser flood tolerance in comparison with Typha.

Phenotypic variation of Pseudomonas brassicacearum as a plant root-colonization strategy.

PubMed

Achouak, Wafa; Conrod, Sandrine; Cohen, Valérie; Heulin, Thierry

2004-08-01

Pseudomonas brassicacearum was isolated as a major root-colonizing population from Arabidopsis thaliana. The strain NFM421 of P. brassicacearum undergoes phenotypic variation during A. thaliana and Brassica napus root colonization in vitro as well as in soil, resulting in different colony appearance on agar surfaces. Bacteria forming translucent colonies (phase II cells) essentially were localized at the surface of young roots and root tips, whereas wild-type cells (phase I cells) were localized at the basal part of roots. The ability of phase II cells to spread and colonize new sites on root surface correlates with over-production of flagellin as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of surface proteins and microsequencing. Moreover, phase II cells showed a higher ability to swim and to swarm on semisolid agar medium. Phase I and phase II cells of P. brassicacearum NFM421 were tagged genetically with green fluorescent protein and red fluorescent protein. Confocal scanning laser microscopy was used to localize phase II cells on secondary roots and root tips of A. thaliana, whereas phase I cells essentially were localized at the basal part of roots. These experiments were conducted in vitro and in soil. Phenotypic variation on plant roots is likely to be a colonization strategy that may explain the high colonization power of P. brassicacearum.

Root hair-specific disruption of cellulose and xyloglucan in AtCSLD3 mutants, and factors affecting the post-rupture resumption of mutant root hair growth.

PubMed

Galway, Moira E; Eng, Ryan C; Schiefelbein, John W; Wasteneys, Geoffrey O

2011-05-01

The glycosyl transferase encoded by the cellulose synthase-like gene CSLD3/KJK/RHD7 (At3g03050) is required for cell wall integrity during root hair formation in Arabidopsis thaliana but it remains unclear whether it contributes to the synthesis of cellulose or hemicellulose. We identified two new alleles, root hair-defective (rhd) 7-1 and rhd7-4, which affect the C-terminal end of the encoded protein. Like root hairs in the previously characterized kjk-2 putative null mutant, rhd7-1 and rhd7-4 hairs rupture before tip growth but, depending on the growth medium and temperature, hairs are able to survive rupture and initiate tip growth, indicating that these alleles retain some function. At 21°C, the rhd7 tip-growing root hairs continued to rupture but at 5ºC, rupture was inhibited, resulting in long, wild type-like root hairs. At both temperatures, the expression of another root hair-specific CSLD gene, CSLD2, was increased in the rhd7-4 mutant but reduced in the kjk-2 mutant, suggesting that CSLD2 expression is CSLD3-dependent, and that CSLD2 could partially compensate for CSLD3 defects to prevent rupture at 5°C. Using a fluorescent brightener (FB 28) to detect cell wall (1 → 4)-β-glucans (primarily cellulose) and CCRC-M1 antibody to detect fucosylated xyloglucans revealed a patchy distribution of both in the mutant root hair cell walls. Cell wall thickness varied, and immunogold electron microscopy indicated that xyloglucan distribution was altered throughout the root hair cell walls. These cell wall defects indicate that CSLD3 is required for the normal organization of both cellulose and xyloglucan in root hair cell walls.

A Role for the TOC Complex in Arabidopsis Root Gravitropism1[W][OA

PubMed Central

Stanga, John P.; Boonsirichai, Kanokporn; Sedbrook, John C.; Otegui, Marisa S.; Masson, Patrick H.

2009-01-01

Arabidopsis (Arabidopsis thaliana) roots perceive gravity and reorient their growth accordingly. Starch-dense amyloplasts within the columella cells of the root cap are important for gravitropism, and starchless mutants such as pgm1 display an attenuated response to gravistimulation. The altered response to gravity1 (arg1) mutant is known to be involved with the early phases of gravity signal transduction. arg1 responds slowly to gravistimulation and is in a genetically distinct pathway from pgm1, as pgm1 mutants enhance the gravitropic defect of arg1. arg1 seeds were mutagenized with ethylmethane sulfonate to identify new mutants that enhance the gravitropic defect of arg1. Two modifier of arg1 mutants (mar1 and mar2) grow in random directions only when arg1 is present, do not affect phototropism, and respond like the wild type to application of phytohormones. Both have mutations affecting different components of the Translocon of Outer Membrane of Chloroplasts (TOC) complex. mar1 possesses a mutation in the TOC75-III gene; mar2 possesses a mutation in the TOC132 gene. Overexpression of TOC132 rescues the random growth phenotype of mar2 arg1 roots. Root cap amyloplasts in mar2 arg1 appear ultrastructurally normal. They saltate like the wild type and sediment at wild-type rates upon gravistimulation. These data point to a role for the plastidic TOC complex in gravity signal transduction within the statocytes. PMID:19211693

A role for the TOC complex in Arabidopsis root gravitropism.

PubMed

Stanga, John P; Boonsirichai, Kanokporn; Sedbrook, John C; Otegui, Marisa S; Masson, Patrick H

2009-04-01

Arabidopsis (Arabidopsis thaliana) roots perceive gravity and reorient their growth accordingly. Starch-dense amyloplasts within the columella cells of the root cap are important for gravitropism, and starchless mutants such as pgm1 display an attenuated response to gravistimulation. The altered response to gravity1 (arg1) mutant is known to be involved with the early phases of gravity signal transduction. arg1 responds slowly to gravistimulation and is in a genetically distinct pathway from pgm1, as pgm1 mutants enhance the gravitropic defect of arg1. arg1 seeds were mutagenized with ethylmethane sulfonate to identify new mutants that enhance the gravitropic defect of arg1. Two modifier of arg1 mutants (mar1 and mar2) grow in random directions only when arg1 is present, do not affect phototropism, and respond like the wild type to application of phytohormones. Both have mutations affecting different components of the Translocon of Outer Membrane of Chloroplasts (TOC) complex. mar1 possesses a mutation in the TOC75-III gene; mar2 possesses a mutation in the TOC132 gene. Overexpression of TOC132 rescues the random growth phenotype of mar2 arg1 roots. Root cap amyloplasts in mar2 arg1 appear ultrastructurally normal. They saltate like the wild type and sediment at wild-type rates upon gravistimulation. These data point to a role for the plastidic TOC complex in gravity signal transduction within the statocytes.

Induction of curvature in maize roots by calcium or by thigmostimulation: role of the postmitotic isodiametric growth zone

NASA Technical Reports Server (NTRS)

Ishikawa, H.; Evans, M. L.

1992-01-01

We examined the response of primary roots of maize (Zea mays L. cv Merit) to unilateral application of calcium with particular attention to the site of application, the dependence on growth rate, and possible contributions of thigmotropic stimulation during application. Unilateral application of agar to the root cap induced negative curvature whether or not the agar contained calcium. This apparent thigmotropic response was enhanced by including calcium in the agar. Curvature away from objects applied unilaterally to the extreme root tip occurred both in intact and detipped roots. When agar containing calcium chloride was applied to one side of the postmitotic isodiametric growth zone ( a region between the apical meristem and the elongation zone), the root curved toward the side of application. This response could not be induced by plain agar. We conclude that curvature away from calcium applied to the root tip results from a thigmotropic response to stimulation during application. In contrast, curvature toward the calcium applied to the postmitotic isodiametric growth zone results from direct calcium-induced inhibition of growth.

Lanthanum resulted in unbalance of nutrient elements and disturbance of cell proliferation cycles in V. faba L. seedlings.

PubMed

Wang, Chengrun; Lu, Xianwen; Tian, Yuan; Cheng, Tao; Hu, Lingling; Chen, Fenfen; Jiang, Chuanjun; Wang, Xiaorong

2011-11-01

Effects of lanthanum (La) on mineral nutrients, cell cycles, and root lengthening have been little reported. The present work investigated these physiological responses in roots of Vicia faba seedlings cultivated in La3+-contained solutions for 15 days. The results showed that the increasing contents of La in the roots and leaves contributed to disbalances of contents of Ca, Fe, Cu, Zn, Mg, Mn, P, and K elements, and potential redistributions of some elements in the roots and leaves. These disbalances might be involved in the subsequent alteration of cell cycle phases in the root tips. Low-dose promotion and high-dose inhibition (Hormetic effects) were demonstrated as the dose responses of G0/G1-, S- or G2/M-phase ratios. The cell cycles were most probably arrested at G1/S interphase by La3+ in the root tips. The fact that the root lengths were not consistent with the changes of cell cycle phases suggested that the cell proliferation activities might be masked by other factors (e.g., cell expansion) under long-time exposure to La3+.

Growth regulation in tip-growing cells that develop on the epidermis.

PubMed

Honkanen, Suvi; Dolan, Liam

2016-12-01

Plants develop tip-growing extensions-root hairs and rhizoids-that initiate as swellings on the outer surface of individual epidermal cells. A conserved genetic mechanism controls the earliest stages in the initiation of these swellings. The same mechanism controls the formation of multicellular structures that develop from swellings on epidermal cells in early diverging land plants. Details of the molecular events that regulate the positioning of the swellings involve sterols and phosphatidylinositol phosphates. The final length of root hairs is determined by the intensity of a pulse of transcription factor synthesis. Genes encoding similar transcription factors control root hair development in cereals and are potential targets for crop improvement. Copyright © 2016. Published by Elsevier Ltd.

Effects of ginsenosides Rg1 and Rb1 of Panax ginseng on mitosis in root tip cells of Allium cepa.

PubMed

Ng, W Y; Chao, C Y

1981-01-01

The effects of ginsenosides Rg1 and Rb1 of Panax ginseng on mitosis in the onion root tip cells as well as on the rate of DNA synthesis in onion seedlings were studied. Results obtained from the concentration and time course study in bulb and seeding root tip cells indicate that Rg1 promotes and Rb1 inhibits mitosis, both being dose-dependent. The promoting effect of Rg1 on the rate of DNA synthesis was observed at the peak hour which occurs at the same time as that of the control. Rb1 was found to shift the peak hour of DNA synthesis to a later period of the experiment. These results are in agreement with the results obtained from the study of the cell cycle by pulse labeling and autoradiography, which show that Rg1 shortens the mitotic cell cycle and S period while Rb1 lengthens them. They in turn increase and decrease the mitotic indices respectively.

Introduction: an overview of gravity sensing, perception, and signal transduction in animals and plants

NASA Technical Reports Server (NTRS)

Halstead, T. W.

1994-01-01

The antiquity of biological sensitivity and response to gravity can be traced through the ubiquity of morphology, mechanisms, and cellular events in gravity sensing biological systems in the most diverse species of both plants and animals. Further, when we examine organisms at the cellular level to elucidate the molecular mechanism by which a gravitational signal is transduced into a biochemical response, the distinction between plants and animals becomes blurred.

[Study on Chemical Constituents of Fat-soluble Extraction from Lepidium meyenii].

PubMed

Fan, Cai-hong; Ge, Fa-huan

2015-02-01

To study the chemical constituents of the fat-soluble extraction from Lepidium meyenii root. Different extraction methods were studied, including supercritical carbon dioxide extraction, circumfluence extraction and steam distillation. Chemical constituents of the fat-soluble extraction from Lepidium meyenii were analyzed by GC/MS. The number of compounds isolated by the above four methods were 38, 31, 14, 21 (specific gravity less than 1 in steam distillation) , and 25 (specific gravity greater than 1 in steam distillation), accounting for 85.79%, 81.18%, 62.08%, 98.36% (specific gravity less than 1 in steam distillation) and 81.54% (specific gravity greater than 1 in steam distillation) of each total peak area, respectively. This study lays a certain foundation for further study and development of functional factors in Lepidium meyenii root.

How Roots Perceive and Respond to Gravity.

ERIC Educational Resources Information Center

Moore, Randy

1984-01-01

Discusses graviperception and gravitropism by plant roots. Indicates that graviperception occurs via sedimentation of amyloplasts in columella cells of the root cap and that the minimal graviresponsiveness of lateral roots may be due to the intensity of their caps to establish a concentration gradient of inhibitor(s) sufficient to affect…

Cellular polarity and interactions in plant graviperception

NASA Technical Reports Server (NTRS)

Sack, Fred D.

1993-01-01

Presented are results of studies on the mechanisms of gravitropic sensing in higher and lower plants. Gravitropic roots of the aquatic angiosperm, Limnobium, were found to have sedimented amyloplasts in their elongation zone but not in their rootcap; nuclei were found to sediment in the elongation zone as well. Another study attempted to understand how plastid sedimentation occurs in vertical Ceratodon cells and how this sedimentation is regulated. To determine whether the cytoskeleton restricts plastid sedimentation, the effects of amiprophos-methyl (APM) and cytochalasin (CD) on plastid position were qualified. Results suggest that microtubules restrict the sedimentation of plastids along the length of the cell and that microtubules are load-bearing for all the plastids in the apical cell, demonstrating the importance of the cytoskeleton in maintaining organelle position and cell organization against the force of gravity. Physcomitrella and Funaria were also studied. Results suggest that gravitropism may be relatively common in moss protonemata and reinforce the idea that amyloplast mass functions in gravitropic sensing.

Three major nucleolar proteins migrate from nucleolus to nucleoplasm and cytoplasm in root tip cells of Vicia faba L. exposed to aluminum.

PubMed

Qin, Rong; Zhang, Huaning; Li, Shaoshan; Jiang, Wusheng; Liu, Donghua

2014-09-01

Results from our previous investigation indicated that Al could affect the nucleolus and induce extrusion of silver-staining nucleolar particles containing argyrophilic proteins from the nucleolus into the cytoplasm in root tip cells of Vicia faba L. So far, the nucleolar proteins involved have not been identified. It is well known that nucleophosmin (B23), nucleolin (C23), and fibrillarin are three major and multifunctional nucleolar proteins. Therefore, effects of Al on B23, C23, and fibrillarin in root tip cells of V. faba exposed to 100 μM Al for 48 h were observed and analyzed using indirect immunofluorescence microscopy and Western blotting. The results from this work demonstrated that after 100 μM of Al treatment for 48 h, B23 and C23 migrated from the nucleolus to the cytoplasm and fibrillarin from the nucleolus to the nucleoplasm. In some cells, fibrillarin was present only in the cytoplasm. Western blotting data revealed higher expression of the three major nucleolar proteins in Al-treated roots compared with the control and that the B23 content increased markedly. These findings confirmed our previous observations.

Analysis of growth patterns during gravitropic curvature in roots of Zea mays by use of a computer-based video digitizer

NASA Technical Reports Server (NTRS)

Nelson, A. J.; Evans, M. L.

1986-01-01

A computer-based video digitizer system is described which allows automated tracking of markers placed on a plant surface. The system uses customized software to calculate relative growth rates at selected positions along the plant surface and to determine rates of gravitropic curvature based on the changing pattern of distribution of the surface markers. The system was used to study the time course of gravitropic curvature and changes in relative growth rate along the upper and lower surface of horizontally-oriented roots of maize (Zea mays L.). The growing region of the root was found to extend from about 1 mm behind the tip to approximately 6 mm behind the tip. In vertically-oriented roots the relative growth rate was maximal at about 2.5 mm behind the tip and declined smoothly on either side of the maximum. Curvature was initiated approximately 30 min after horizontal orientation with maximal (50 degrees) curvature being attained in 3 h. Analysis of surface extension patterns during the response indicated that curvature results from a reduction in growth rate along both the upper and lower surfaces with stronger reduction along the lower surface.

Effect of ultrasonic tip designs on intraradicular post removal.

PubMed

Aguiar, Anny Carine Barros; de Meireles, Daniely Amorim; Marques, André Augusto Franco; Sponchiado Júnior, Emílio Carlos; Garrido, Angela Delfina Bitencourt; Garcia, Lucas da Fonseca Roberti

2014-11-01

To evaluate the effect of different ultrasonic tip designs on intraradicular post removal. The crowns of forty human canine teeth were removed, and after biomechanical preparation and filling, the roots were embedded in acrylic resin blocks. The post spaces were made, and root canal molding was performed with self-cured acrylic resin. After casting (Cu-Al), the posts were cemented with zinc phosphate cement. The specimens were randomly separated into 4 groups (n = 10), as follows: G1 - no ultrasonic vibration (control); G2 - ultrasonic vibration using an elongated cylindrical-shaped and active rounded tip; G3 - ultrasonic vibration with a flattened convex and linear active tip; G4 - ultrasonic vibration with active semicircular tapered tip. Ultrasonic vibration was applied for 15 seconds on each post surface and tensile test was performed in a Universal Testing Machine (Instron 4444 - 1 mm/min). G4 presented the highest mean values, however, with no statistically significant difference in comparison to G3 (P > 0.05). G2 presented the lowest mean values with statistically significant difference to G3 and G4 (P < 0.05). Ultrasonic vibration with elongated cylindrical-shaped and active rounded tip was most effective in reducing force required for intraradicular post removal.

Early root growth and architecture of fast- and slow-growing Norway spruce (Picea abies) families differ-potential for functional adaptation.

PubMed

Hamberg, Leena; Velmala, Sannakajsa M; Sievänen, Risto; Kalliokoski, Tuomo; Pennanen, Taina

2018-06-01

The relationship between the growth rate of aboveground parts of trees and fine root development is largely unknown. We investigated the early root development of fast- and slow-growing Norway spruce (Picea abies (L.) H. Karst.) families at a developmental stage when the difference in size is not yet observed. Seedling root architecture data, describing root branching, were collected with the WinRHIZO™ image analysis system, and mixed models were used to determine possible differences between the two growth phenotypes. A new approach was used to investigate the spatial extent of root properties along the whole sample root from the base of 1-year-old seedlings to the most distal part of a root. The root architecture of seedlings representing fast-growing phenotypes showed ~30% higher numbers of root branches and tips, which resulted in larger root extensions and potentially a better ability to acquire nutrients. Seedlings of fast-growing phenotypes oriented and allocated root tips and biomass further away from the base of the seedling than those growing slowly, a possible advantage in nutrient-limited and heterogeneous boreal forest soils. We conclude that a higher long-term growth rate of the aboveground parts in Norway spruce may relate to greater allocation of resources to explorative roots that confers a competitive edge during early growth phases in forest ecosystems.

Hydrotropism Interacts with Gravitropism by Degrading Amyloplasts in Seedling Roots of Arabidopsis and Radish1

PubMed Central

Takahashi, Nobuyuki; Yamazaki, Yutaka; Kobayashi, Akie; Higashitani, Atsushi; Takahashi, Hideyuki

2003-01-01

In response to a moisture gradient, roots exhibit hydrotropism to control the orientation of their growth. To exhibit hydrotropism, however, they must overcome the gravitropism that is dominant on Earth. We found that moisture gradient or water stress caused immediate degradation of the starch anchors, amyloplasts, in root columella cells of Arabidopsis and radish (Raphanus sativus). Namely, development of hydrotropic response was accompanied by a simultaneous reduction in starch content in columella cells. Rapid degradation of amyloplasts in columella cells also occurred in the water-stressed roots with sorbitol or mannitol. Both hydrotropically stimulated and water-stressed roots showed a reduced responsiveness to gravity. Roots of a starchless mutant, pgm1-1, showed an enhanced hydrotropism compared with that of the wild type. These results suggest that the reduced responsiveness to gravity is, at least in part, attributable to the degradation of amyloplasts in columella cells. Thus, the reduction in gravitropism allows the roots to exhibit hydrotropism. PMID:12805610

Phosphoproteomics reveals the effect of ethylene in soybean root under flooding stress.

PubMed

Yin, Xiaojian; Sakata, Katsumi; Komatsu, Setsuko

2014-12-05

Flooding has severe negative effects on soybean growth. To explore the flooding-responsive mechanisms in early-stage soybean, a phosphoproteomic approach was used. Two-day-old soybean plants were treated without or with flooding for 3, 6, 12, and 24 h, and root tip proteins were then extracted and analyzed at each time point. After 3 h of flooding exposure, the fresh weight of soybeans increased, whereas the ATP content of soybean root tips decreased. Using a gel-free proteomic technique, a total of 114 phosphoproteins were identified in the root tip samples, and 34 of the phosphoproteins were significantly changed with respect to phosphorylation status after 3 h of flooding stress. Among these phosphoproteins, eukaryotic translation initiation factors were dephosphorylated, whereas several protein synthesis-related proteins were phosphorylated. The mRNA expression levels of sucrose phosphate synthase 1F and eukaryotic translation initiation factor 4 G were down-regulated, whereas UDP-glucose 6-dehydrogenase mRNA expression was up-regulated during growth but down-regulated under flooding stress. Furthermore, bioinformatic protein interaction analysis of flooding-responsive proteins based on temporal phosphorylation patterns indicated that eukaryotic translation initiation factor 4 G was located in the center of the network during flooding. Soybean eukaryotic translation initiation factor 4 G has homology to programmed cell death 4 protein and is implicated in ethylene signaling. The weight of soybeans was increased with treatment by an ethylene-releasing agent under flooding condition, but it was decreased when plants were exposed to an ethylene receptor antagonist. These results suggest that the ethylene signaling pathway plays an important role, via the protein phosphorylation, in mechanisms of plant tolerance to the initial stages of flooding stress in soybean root tips.

Propidium iodide competes with Ca(2+) to label pectin in pollen tubes and Arabidopsis root hairs.

PubMed

Rounds, Caleb M; Lubeck, Eric; Hepler, Peter K; Winship, Lawrence J

2011-09-01

We have used propidium iodide (PI) to investigate the dynamic properties of the primary cell wall at the apex of Arabidopsis (Arabidopsis thaliana) root hairs and pollen tubes and in lily (Lilium formosanum) pollen tubes. Our results show that in root hairs, as in pollen tubes, oscillatory peaks in PI fluorescence precede growth rate oscillations. Pectin forms the primary component of the cell wall at the tip of both root hairs and pollen tubes. Given the electronic structure of PI, we investigated whether PI binds to pectins in a manner analogous to Ca(2+) binding. We first show that Ca(2+) is able to abrogate PI growth inhibition in a dose-dependent manner. PI fluorescence itself also relies directly on the amount of Ca(2+) in the growth solution. Exogenous pectin methyl esterase treatment of pollen tubes, which demethoxylates pectins, freeing more Ca(2+)-binding sites, leads to a dramatic increase in PI fluorescence. Treatment with pectinase leads to a corresponding decrease in fluorescence. These results are consistent with the hypothesis that PI binds to demethoxylated pectins. Unlike other pectin stains, PI at low yet useful concentration is vital and specifically does not alter the tip-focused Ca(2+) gradient or growth oscillations. These data suggest that pectin secretion at the apex of tip-growing plant cells plays a critical role in regulating growth, and PI represents an excellent tool for examining the role of pectin and of Ca(2+) in tip growth.

The use of optical fiber in endodontic photodynamic therapy. Is it really relevant?

PubMed

Garcez, Aguinaldo S; Fregnani, Eduardo R; Rodriguez, Helena M; Nunez, Silvia C; Sabino, Caetano P; Suzuki, Hideo; Ribeiro, Martha S

2013-01-01

This study analyzed the necessity of use of an optical fiber/diffusor when performing antimicrobial photodynamic therapy (PDT) associated with endodontic therapy. Fifty freshly extracted human single-rooted teeth were used. Conventional endodontic treatment was performed using a sequence of ProTaper (Dentsply Maillefer Instruments), the teeth were sterilized, and the canals were contaminated with Enterococcus faecalis 3 days' biofilm. The samples were divided into five groups: group 1--ten roots irradiated with a laser tip (area of 0.04 cm(2)), group 2--ten roots irradiated with a smaller laser tip (area of 0.028 cm(2)), and group 3--ten teeth with the crown, irradiate with the laser tip with 0.04 cm(2) of area. The forth group (G4) followed the same methodology as group 3, but the irradiation was performed with smaller tip (area of 0.028 cm(2)) and G5 ten teeth with crown were irradiated using a 200-mm-diameter fiber/diffusor coupled to diode laser. Microbiological samples were taken after accessing the canal, after endodontic therapy, and after PDT. Groups 1 and 2 showed a reduction of two logs (99%), groups 3 and 4 of one log (85% and 97%, respectively), and group 5 of four logs (99.99%). Results suggest that the use of PDT added to endodontic treatment in roots canals infected with E. faecalis with the optical fiber/diffusor is better than when the laser light is used directed at the access of cavity.

Dark conditions enhance aluminum tolerance in several rice cultivars via multiple modulations of membrane sterols.

PubMed

Wagatsuma, Tadao; Maejima, Eriko; Watanabe, Toshihiro; Toyomasu, Tomonobu; Kuroda, Masaharu; Muranaka, Toshiya; Ohyama, Kiyoshi; Ishikawa, Akifumi; Usui, Masami; Hossain Khan, Shahadat; Maruyama, Hayato; Tawaraya, Keitaro; Kobayashi, Yuriko; Koyama, Hiroyuki

2018-01-23

Aluminum-sensitive rice (Oryza sativa L.) cultivars showed increased Al tolerance under dark conditions, because less Al accumulated in the root tips (1 cm) under dark than under light conditions. Under dark conditions, the root tip concentration of total sterols, which generally reduce plasma membrane permeabilization, was higher in the most Al-sensitive japonica cultivar, Koshihikari (Ko), than in the most Al-tolerant cultivar, Rikuu-132 (R132), but the phospholipid content did not differ between the two. The Al treatment increased the proportion of stigmasterol (which has no ability to reduce membrane permeabilization) out of total sterols similarly in both cultivars under light conditions, but it decreased more in Ko under dark conditions. The carotenoid content in the root tip of Al-treated Ko was significantly lower under dark than under light conditions, indicating that isopentenyl diphosphate transport from the cytosol to plastids was decreased under dark conditions. HMG2 and HMG3 (encoding the key sterol biosynthetic enzyme 3-hydroxy-3-methylglutaryl CoA reductase) transcript levels in the root tips were enhanced under dark conditions. We suggest that the following mechanisms contribute to the increase in Al tolerance under dark conditions: inhibition of stigmasterol formation to retain membrane integrity; greater partitioning of isopentenyl diphosphate for sterol biosynthesis; and enhanced expression of HMGs to increase sterol biosynthesis. © The Author(s) 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Somatic embryogenesis and plant regeneration in Carica papaya L. tissue culture derived from root explants.

PubMed

Chen, M H; Wang, P J; Maeda, E

1987-10-01

The regeneration potential of shoot tip, stem, leaf, cotyledon and root explants of two papaya cultivars (Carica papaya cv. 'Solo' and cv. 'Sunrise') were studed. Callus induction of these two cultivars of papaya showed that the shoot tips and stems are most suitable for forming callus, while leaves, cotyledons and roots are comparatively difficult to induce callus. Callus induction also varied with the varities. Somatic embryogenesis was obtained from 3-month-old root cultures. A medium containing half strength of MS inorganic salts, 160 mg/l adenine sulfate, 1.0 mg/1 NAA, 0.5 mg/1 kinetin and 1.0 mg/1 GA3 was optimal for embryogenesis. The callus maintained high regenerative capacity after two years of culture on this medium. Plants derived from somatic embryos were obtained under green-house conditions.

Impact of post-mining subsidence on nitrogen transformation in southern tropical dry deciduous forest, India

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

Tripathi, N.; Singh, R.S.; Singh, J.S.

The goal of our research was to assess the impact of post-mining land subsidence, caused due to underground coal mining operations, on fine root biomass and root tips count; plant available nutrient status, microbial biomass N (MBN) and N-mineralization rates of a Southern tropical dry deciduous forest of Singareni Coalfields of India. The changes were quantified in all the three (rainy, winter and summer) seasons, in slope and depression microsites of the subsided land and an adjacent undamaged forest microsite. Physico-chemical characteristics were found to be altered after subsidence, showing a positive impact of subsidence on soil moisture, bulk density,more » water holding capacity, organic carbon content, total N and total P. The increase in all the parameters was found in depression microsites, while in slope microsites, the values were lower. Fine root biomass and root tips count increased in the subsided depression microsites, as demonstrated by increases of 62% and 45%, respectively. Soil nitrate-N and phosphate-P concentrations were also found to be higher in depression microsite, showing an increase of 35.68% and 24.74%, respectively. Depression microsite has also shown the higher MBN value with an increase over control. Net nitrification, net N-mineralization and MBN were increased in depression microsite by 29.77%, 25.72% and 34%, respectively. There was a positive relation of microbial N with organic C, fine root biomass and root tips.« less

Gravity-dependent differentiation and root coils in Arabidopsis thaliana wild type and phospholipase-A-I knockdown mutant grown on the International Space Station.

PubMed

Scherer, G F E; Pietrzyk, P

2014-01-01

Arabidopsis roots on 45° tilted agar in 1-g grow in wave-like figures. In addition to waves, formation of root coils is observed in several mutants compromised in gravitropism and/or auxin transport. The knockdown mutant ppla-I-1 of patatin-related phospholipase-A-I is delayed in root gravitropism and forms increased numbers of root coils. Three known factors contribute to waving: circumnutation, gravisensing and negative thigmotropism. In microgravity, deprivation of wild type (WT) and mutant roots of gravisensing and thigmotropism and circumnutation (known to slow down in microgravity, and could potentially lead to fewer waves or increased coiling in both WT and mutant). To resolve this, mutant ppla-I-1 and WT were grown in the BIOLAB facility in the International Space Station. In 1-g, roots of both types only showed waving. In the first experiment in microgravity, the mutant after 9 days formed far more coils than in 1-g but the WT also formed several coils. After 24 days in microgravity, in both types the coils were numerous with slightly more in the mutant. In the second experiment, after 9 days in microgravity only the mutant formed coils and the WT grew arcuated roots. Cell file rotation (CFR) on the mutant root surface in microgravity decreased in comparison to WT, and thus was not important for coiling. Several additional developmental responses (hypocotyl elongation, lateral root formation, cotyledon expansion) were found to be gravity-influenced. We tentatively discuss these in the context of disturbances in auxin transport, which are known to decrease through lack of gravity. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.

Negative gravitropism in plant roots.

PubMed

Ge, Liangfa; Chen, Rujin

2016-10-17

Plants are capable of orienting their root growth towards gravity in a process termed gravitropism, which is necessary for roots to grow into soil, for water and nutrient acquisition and to anchor plants. Here we show that root gravitropism depends on the novel protein, NEGATIVE GRAVITROPIC RESPONSE OF ROOTS (NGR). In both Medicago truncatula and Arabidopsis thaliana, loss of NGR reverses the direction of root gravitropism, resulting in roots growing upward.

The Automated Root Exudate System (ARES): a method to apply solutes at regular intervals to soils in the field.

PubMed

Lopez-Sangil, Luis; George, Charles; Medina-Barcenas, Eduardo; Birkett, Ali J; Baxendale, Catherine; Bréchet, Laëtitia M; Estradera-Gumbau, Eduard; Sayer, Emma J

2017-09-01

Root exudation is a key component of nutrient and carbon dynamics in terrestrial ecosystems. Exudation rates vary widely by plant species and environmental conditions, but our understanding of how root exudates affect soil functioning is incomplete, in part because there are few viable methods to manipulate root exudates in situ . To address this, we devised the Automated Root Exudate System (ARES), which simulates increased root exudation by applying small amounts of labile solutes at regular intervals in the field.The ARES is a gravity-fed drip irrigation system comprising a reservoir bottle connected via a timer to a micro-hose irrigation grid covering c . 1 m 2 ; 24 drip-tips are inserted into the soil to 4-cm depth to apply solutions into the rooting zone. We installed two ARES subplots within existing litter removal and control plots in a temperate deciduous woodland. We applied either an artificial root exudate solution (RE) or a procedural control solution (CP) to each subplot for 1 min day -1 during two growing seasons. To investigate the influence of root exudation on soil carbon dynamics, we measured soil respiration monthly and soil microbial biomass at the end of each growing season.The ARES applied the solutions at a rate of c . 2 L m -2  week -1 without significantly increasing soil water content. The application of RE solution had a clear effect on soil carbon dynamics, but the response varied by litter treatment. Across two growing seasons, soil respiration was 25% higher in RE compared to CP subplots in the litter removal treatment, but not in the control plots. By contrast, we observed a significant increase in microbial biomass carbon (33%) and nitrogen (26%) in RE subplots in the control litter treatment.The ARES is an effective, low-cost method to apply experimental solutions directly into the rooting zone in the field. The installation of the systems entails minimal disturbance to the soil and little maintenance is required. Although we used ARES to apply root exudate solution, the method can be used to apply many other treatments involving solute inputs at regular intervals in a wide range of ecosystems.

Silicon enhances suberization and lignification in roots of rice (Oryza sativa).

PubMed

Fleck, Alexander T; Nye, Thandar; Repenning, Cornelia; Stahl, Frank; Zahn, Marc; Schenk, Manfred K

2011-03-01

The beneficial element silicon (Si) may affect radial oxygen loss (ROL) of rice roots depending on suberization of the exodermis and lignification of sclerenchyma. Thus, the effect of Si nutrition on the oxidation power of rice roots, suberization and lignification was examined. In addition, Si-induced alterations of the transcript levels of 265 genes related to suberin and lignin synthesis were studied by custom-made microarray and quantitative Real Time-PCR. Without Si supply, the oxidation zone of 12 cm long adventitious roots extended along the entire root length but with Si supply the oxidation zone was restricted to 5 cm behind the root tip. This pattern coincided with enhanced suberization of the exodermis and lignification of sclerenchyma by Si supply. Suberization of the exodermis started, with and without Si supply, at 4-5 cm and 8-9 cm distance from the root tip (drt), respectively. Si significantly increased transcript abundance of 12 genes, while two genes had a reduced transcript level. A gene coding for a leucine-rich repeat protein exhibited a 25-fold higher transcript level with Si nutrition. Physiological, histochemical, and molecular-biological data showing that Si has an active impact on rice root anatomy and gene transcription is presented here.

The promotive effect of latrunculin B on maize root gravitropism is concentration dependent

NASA Technical Reports Server (NTRS)

Blancaflor, E. B.; Hou, G-C; Mohamalawari, D. R.

2003-01-01

The cytoskeleton has been proposed to be a key player in the gravitropic response of higher plants. A major approach to determine the role of the cytoskeleton in gravitropism has been to use inhibitors to disrupt the cytoskeleton and then to observe the effect that such disruption has on organ bending. Several investigators have reported that actin or microtubule inhibitors do not prevent root gravitropism, leading to the conclusion that the cytoskeleton is not involved in this process. However, there are recent reports showing that disruption of the actin cytoskeleton with the actin inhibitor, latrunculin B, promotes the gravitropic response of both roots and shoots. In roots, curvature is sustained during prolonged periods of clinorotation despite short periods of gravistimulation. These results indicate that an early gravity-induced signal continues to persist despite withdrawal of the constant gravity stimulus. To investigate further the mechanisms underlying the promotive effect of actin disruption on root gravitropism, we treated maize roots with varying concentrations of latrunculin B in order to determine the lowest concentration of latrunculin B that has an effect on root bending. After a 10-minute gravistimulus, treated roots were axially rotated on a one rpm clinostat and curvature was measured after 15 hours. Our results show that 100 nM latrunculin B induced the strongest promotive effect on the curvature of maize roots grown on a clinostat. Moreover, continuously gravistimulated roots treated with 100 nM latrunculin B exhibited stronger curvature responses while decapped roots treated with this concentration of latrunculin B did not bend during continuous gravistimulation. The stronger promotive effect of low concentrations of latrunculin B on the curvature of both clinorotated and continuously gravistimulated roots suggests that disruption of the finer, more dynamic component of the actin cytoskeleton could be the cause of the enhanced tropic responses of roots to gravity. c2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

The promotive effect of latrunculin B on maize root gravitropism is concentration dependent

NASA Astrophysics Data System (ADS)

Blancaflor, E. B.; Hou, G.-c.; Mohamalawari, D. R.

2003-05-01

The cytoskeleton has been proposed to be a key player in the gravitropic response of higher plants. A major approach to determine the role of the cytoskeleton in gravitropism has been to use inhibitors to disrupt the cytoskeleton and then to observe the effect that such disruption has on organ bending. Several investigators have reported that actin or microtubule inhibitors do not prevent root gravitropism, leading to the conclusion that the cytoskeleton is not involved in this process. However, there are recent reports showing that disruption of the actin cytoskeleton with the actin inhibitor, latrunculin B, promotes the gravitropic response of both roots and shoots. In roots, curvature is sustained during prolonged periods of clinorotation despite short periods of gravistimulation. These results indicate that an early gravity-induced signal continues to persist despite withdrawal of the constant gravity stimulus. To investigate further the mechanisms underlying the promotive effect of actin disruption on root gravitropism, we treated maize roots with varying concentrations of latrunculin B in order to determine the lowest concentration of latrunculin B that has an effect on root bending. After a 10-minute gravistimulus, treated roots were axially rotated on a one rpm clinostat and curvature was measured after 15 hours. Our results show that 100 nM latrunculin B induced the strongest promotive effect on the curvature of maize roots grown on a clinostat. Moreover, continuously gravistimulated roots treated with 100 nM latrunculin B exhibited stronger curvature responses while decapped roots treated with this concentration of latrunculin B did not bend during continuous gravistimulation. The stronger promotive effect of low concentrations of latrunculin B on the curvature of both clinorotated and continuously gravistimulated roots suggests that disruption of the fmer, more dynamic component of the actin cytoskeleton could be the cause of the enhanced tropic responses of roots to gravity.

Expanding torque possibilities: A skeletally anchored torqued cantilever for uprighting "kissing molars".

PubMed

Barros, Sérgio Estelita; Janson, Guilherme; Chiqueto, Kelly; Ferreira, Eduardo; Rösing, Cassiano

2018-04-01

Several uprighting mechanics and devices have been used for repositioning tipped molars. "Kissing molars" (KMs) are an uncommon tooth impaction involving 2 severely tipped mandibular molars with their occlusal surfaces positioned crown to crown, with the roots pointing in opposite directions. Orthodontic uprighting of KMs has not been a usual treatment protocol, and it can be a challenging task due to the severe tipping and double impaction, requiring efficient and well-controlled uprighting mechanics. An innovative skeletally anchored cantilever, which uses the torque principle for uprighting tipped molars, is suggested. This torqued cantilever is easy to manufacture, install, and activate; it is a well-known torque that is effective for producing root movement. A successful treatment of symptomatic KMs, involving the first and second molars, was achieved with this cantilever. Thus, clinicians should consider the suggested uprighting mechanics and orthodontic device as a more conservative alternative to extraction of KMs, depending on the patient's age, involved teeth in KMs, tipping severity, and impaction positions. Copyright © 2018 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.

Diode laser for endodontic treatment: investigations of light distribution and disinfection efficiency

NASA Astrophysics Data System (ADS)

Stock, Karl; Graser, Rainer; Udart, Martin; Kienle, Alwin; Hibst, Raimund

2011-03-01

Diode lasers are used in dentistry mainly for oral surgery and disinfection of root canals in endodontic treatment. The purpose of this study was to investigate and to improve the laser induced bacteria inactivation in endodontic treatment. An essential prerequisite of the optimization of the irradiation process and device is the knowledge about the determinative factors of bacteria killing: light intensity? light dosis? temperature? In order to find out whether high power NIR laser bacterial killing is caused by a photochemical or a photothermal process we heated bacteria suspensions of E. coli K12 by a water bath and by a diode laser (940 nm) with the same temporal temperature course. Furthermore, bacteria suspensions were irradiated while the temperature was fixed by ice water. Killing of bacteria was measured via fluorescence labeling. In order to optimize the irradiation of the root canal, we designed special fiber tips with radial light emission characteristic by optical ray tracing simulations. Also, we calculated the resulting light distribution in dentin by voxelbased Monte Carlo simulations. Furthermore, we irradiated root canals of extracted human teeth using different fiber tip geometries and measured the resulting light and heat distribution by CCD-camera and thermography. Comparison of killing rates between laser and water based heating shows no significant differences, and irradiation of ice cooled suspensions has no substantial killing effect. Thus, the most important parameter for bacterial killing is the maximum temperature. Irradiation of root canals using fiber tips with radial light emission results in a more defined irradiated area with minor irradiation of the apex and higher intensity and therefore higher temperature increase on root canal surface. In conclusion, our experiments show that at least for E. coli bacteria inactivation by NIR laser irradiation is solely based on a thermal process and that heat distribution in root canal can be significantly improved by specially designed fiber tips.

The improved Allium/Vicia root tip micronucleus assay for clastogenicity of environmental pollutants.

PubMed

Ma, T H; Xu, Z; Xu, C; McConnell, H; Rabago, E V; Arreola, G A; Zhang, H

1995-04-01

The meristematic mitotic cells of plant roots are appropriate and efficient cytogenetic materials for the detection of clastogenicity of environmental pollutants, especially for in situ monitoring of water contaminants. Among several cytological endpoints in these fast dividing cells, such as chromosome/chromatid aberrations, sister-chromatid exchanges and micronuclei, the most effective and simplest indicator of cytological damage is micronucleus formation. Although the Allium cepa and Vicia faba root meristem micronucleus assays (Allium/Vicia root MCN) have been used in clastogenicity studies about 12 times by various authors in the last 25 years, there is no report on the comparison of the efficiency of these two plant systems and in different cell populations (meristem and F1) of the root tip as well as under adequate recovery duration. In order to maximize the efficiency of these bioassays, the current study was designed to compare the Allium and the Vicia root MCN assays on the basis of chromosome length, peak sensitivity of the mitotic cells, and the regions of the root tip where the MCN are formed. The total length of the 2n complement of Allium chromosomes is 14.4 microns and the total length of the 2n complement of Vicia is 9.32 microns. The peak sensitivity determined by serial fixation at 12-h intervals after 100 R of X-irradiation is 44 h. The slope of the X-ray dose-response curve of Allium roots derived from the meristematic regions was lower than that derived from cells in the F1 region. Higher efficiency was also demonstrated when the MCN frequencies were scored from the F1 cells in both Allium and Vicia treated with formaldehyde (FA), mitomycin C (MMC), and maleic hydrazide (MH). The results indicated that scoring of MCN frequencies from the F1 cell region of the root tip was more efficient than scoring from the meristematic region. The X-ray linear regression dose-response curves were established in both Allium and Vicia cell systems and the coefficients of correlations, slope values were used to verify the reliability and efficiency of these two plant cell systems. Based on the dose-response slope value of 0.894 for Allium and 0.643 for Vicia, the Allium root MCN was a more efficient test system. The greater sensitivity of the Allium roots is probably due to the greater total length of the diploid complement and the higher number of metacentric chromosomes.(ABSTRACT TRUNCATED AT 400 WORDS)

The Rice E3-Ubiquitin Ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 Modulates the Expression of ROOT MEANDER CURLING, a Gene Involved in Root Mechanosensing, through the Interaction with Two ETHYLENE-RESPONSE FACTOR Transcription Factors1

PubMed Central

Lourenço, Tiago F.; Serra, Tânia S.; Cordeiro, André M.; Swanson, Sarah J.; Gilroy, Simon; Saibo, Nelson J.M.; Oliveira, M. Margarida

2015-01-01

Plant roots can sense and respond to a wide diversity of mechanical stimuli, including touch and gravity. However, little is known about the signal transduction pathways involved in mechanical stimuli responses in rice (Oryza sativa). This work shows that rice root responses to mechanical stimuli involve the E3-ubiquitin ligase rice HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 (OsHOS1), which mediates protein degradation through the proteasome complex. The morphological analysis of the roots in transgenic RNA interference::OsHOS1 and wild-type plants, exposed to a mechanical barrier, revealed that the OsHOS1 silencing plants keep a straight root in contrast to wild-type plants that exhibit root curling. Moreover, it was observed that the absence of root curling in response to touch can be reverted by jasmonic acid. The straight root phenotype of the RNA interference::OsHOS1 plants was correlated with a higher expression rice ROOT MEANDER CURLING (OsRMC), which encodes a receptor-like kinase characterized as a negative regulator of rice root curling mediated by jasmonic acid. Using the yeast two-hybrid system and bimolecular fluorescence complementation assays, we showed that OsHOS1 interacts with two ETHYLENE-RESPONSE FACTOR transcription factors, rice ETHYLENE-RESPONSIVE ELEMENT BINDING PROTEIN1 (OsEREBP1) and rice OsEREBP2, known to regulate OsRMC gene expression. In addition, we showed that OsHOS1 affects the stability of both transcription factors in a proteasome-dependent way, suggesting that this E3-ubiquitin ligase targets OsEREBP1 and OsEREBP2 for degradation. Our results highlight the function of the proteasome in rice response to mechanical stimuli and in the integration of these signals, through hormonal regulation, into plant growth and developmental programs. PMID:26381316

Demonstration of prominent actin filaments in the root columella

NASA Technical Reports Server (NTRS)

Collings, D. A.; Zsuppan, G.; Allen, N. S.; Blancaflor, E. B.; Brown, C. S. (Principal Investigator)

2001-01-01

The distribution of actin filaments within the gravity-sensing columella cells of plant roots remains poorly understood, with studies over numerous years providing inconsistent descriptions of actin organization in these cells. This uncertainty in actin organization, and thus in actin's role in graviperception and gravisignaling, has led us to investigate actin arrangements in the columella cells of Zea mays L., Medicago truncatula Gaertn., Linum usitatissiilium L. and Nicotianla benthamiana Domin. Actin organization was examined using a combination of optimized immunofluorescence techniques, and an improved fluorochrome-conjugated phalloidin labeling method reliant on 3-maleimidobenzoyl-N-hydroxy-succinimide ester (MBS) cross-linking combined with glycerol permeabilization. Confocal microscopy of root sections labeled with anti-actin antibodies revealed patterns suggestive of actin throughout the columella region. These patterns included short and fragmented actin bundles, fluorescent rings around amyloplasts and intense fluorescence originating from the nucleus. Additionally, confocal microscopy of MBS-stabilized and Alexa Fluor-phalloidin-labeled root sections revealed a previously undetected state of actin organization in the columella. Discrete actin structures surrounded the amyloplasts and prominent actin cables radiated from the nuclear surface toward the cell periphery. Furthermore, the cortex of the columella cells contained fine actin bundles (or single filaments) that had a predominant transverse orientation. We also used confocal microscopy of plant roots expressing endoplasmic reticulum (ER)-targeted green fluorescent protein to demonstrate rapid ER movements within the columella cells, suggesting that the imaged actin network is functional. The successful identification of discrete actin structures in the root columella cells forms the perception and signaling.

Curvature Induced by Amyloplast Magnetophoresis in Protonemata of the Moss Ceratodon purpureus1

PubMed Central

Kuznetsov, Oleg A.; Schwuchow, Jochen; Sack, Fred D.; Hasenstein, Karl H.

1999-01-01

After gravistimulation of Ceratodon purpureus (Hedw.) Brid. protonemata in the dark, amyloplast sedimentation was followed by upward curvature in the wild-type (WT) and downward curvature in the wwr mutant (wrong way response). We used ponderomotive forces induced by high-gradient magnetic fields (HGMF) to simulate the effect of gravity and displace the presumptive statoliths. The field was applied by placing protonemata either between two permanent magnets at the edge of the gap, close to the edge of a magnetized ferromagnetic wedge, or close to a small (<1 mm) permanent magnet. Continuous application of an HGMF in all three configurations resulted in plastid displacement and induced curvature in tip cells of WT and wwr protonemata. WT cells curved toward the HGMF, and wwr cells curved away from the HGMF, comparable to gravitropism. Plastids isolated from protonemal cultures had densities ranging from 1.24 to 1.38 g cm−3. Plastid density was similar for both genotypes, but the mutant contained larger plastids than the WT. The size difference might explain the stronger response of the wwr protonemata to the HGMF. Our data support the plastid-based theory of gravitropic sensing and suggest that HGMF-induced ponderomotive forces can substitute for gravity. PMID:9952461

The 'root-brain' hypothesis of Charles and Francis Darwin: Revival after more than 125 years.

PubMed

Baluska, Frantisek; Mancuso, Stefano; Volkmann, Dieter; Barlow, Peter W

2009-12-01

This year celebrates the 200(th) aniversary of the birth of Charles Darwin, best known for his theory of evolution summarized in On the Origin of Species. Less well known is that, in the second half of his life, Darwin's major scientific focus turned towards plants. He wrote several books on plants, the next-to-last of which, The Power of Movement of Plants, published together with his son Francis, opened plants to a new view. Here we amplify the final sentence of this book in which the Darwins proposed that: "It is hardly an exaggeration to say that the tip of the radicle thus endowed [with sensitivity] and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements." This sentence conveys two important messages: first, that the root apex may be considered to be a 'brain-like' organ endowed with a sensitivity which controls its navigation through soil; second, that the root apex represents the anterior end of the plant body. In this article, we discuss both these statements.

endodermal-amyloplast less 1 is a novel allele of SHORT-ROOT

NASA Astrophysics Data System (ADS)

Morita, Miyo T.; Saito, Chieko; Nakano, Akihiko; Tasaka, Masao

Plants can sense the direction of gravity and change the growth orientation of their organs. Arabidopsis mutants have been isolated and characterized in order to elucidate the molecular mechanisms of gravitropism. endodermal-amyloplast less 1 ( eal1) is a unique mutant that completely lacks gravitropism in inflorescence stems and exhibits reduced gravitropism in hypocotyls, whereas its roots showed normal gravitropism. Previously, it was suggested that differentiation or development of amyloplasts in shoot statocytes (endodermal cells) is affected by the eal1 mutation. Here, we have identified EAL1 as a SHORT-ROOT ( SHR) allele based on map position. Three nucleotides in the SHR coding region were deleted in the eal1 mutant, resulting in the deletion of just one amino acid. The protein encoded by the novel allele of SHR appears to have retained its function as a transcription factor since the endodermal cell layer was formed both in roots and in shoots of eal1. SCARECROW (SCR) promoter activity monitored by reporter protein expression was significantly decreased in eal1, suggesting that the activity of SHR lacking one amino acid is reduced. In addition, transcription levels of SHOOT GRAVITROPISM 5 (SGR5), which is mainly expressed in the endodermis of inflorescence stems, was markedly decreased. Together with the presence of abnormal endodermal amyloplasts in eal1, these results strongly suggest that the endodermis observed in eal1 is not sufficiently differentiated to execute shoot gravitropism.

Ontogeny of mouse vestibulo-ocular reflex following genetic or environmental alteration of gravity sensing.

PubMed

Beraneck, Mathieu; Bojados, Mickael; Le Séac'h, Anne; Jamon, Marc; Vidal, Pierre-Paul

2012-01-01

The vestibular organs consist of complementary sensors: the semicircular canals detect rotations while the otoliths detect linear accelerations, including the constant pull of gravity. Several fundamental questions remain on how the vestibular system would develop and/or adapt to prolonged changes in gravity such as during long-term space journey. How do vestibular reflexes develop if the appropriate assembly of otoliths and semi-circular canals is perturbed? The aim of present work was to evaluate the role of gravity sensing during ontogeny of the vestibular system. In otoconia-deficient mice (ied), gravity cannot be sensed and therefore maculo-ocular reflexes (MOR) were absent. While canals-related reflexes were present, the ied deficit also led to the abnormal spatial tuning of the horizontal angular canal-related VOR. To identify putative otolith-related critical periods, normal C57Bl/6J mice were subjected to 2G hypergravity by chronic centrifugation during different periods of development or adulthood (Adult-HG) and compared to non-centrifuged (control) C57Bl/6J mice. Mice exposed to hypergravity during development had completely normal vestibulo-ocular reflexes 6 months after end of centrifugation. Adult-HG mice all displayed major abnormalities in maculo-ocular reflexe one month after return to normal gravity. During the next 5 months, adaptation to normal gravity occurred in half of the individuals. In summary, genetic suppression of gravity sensing indicated that otolith-related signals might be necessary to ensure proper functioning of canal-related vestibular reflexes. On the other hand, exposure to hypergravity during development was not sufficient to modify durably motor behaviour. Hence, 2G centrifugation during development revealed no otolith-specific critical period.

Ontogeny of Mouse Vestibulo-Ocular Reflex Following Genetic or Environmental Alteration of Gravity Sensing

PubMed Central

Beraneck, Mathieu; Bojados, Mickael; Le Séac’h, Anne; Jamon, Marc; Vidal, Pierre-Paul

2012-01-01

The vestibular organs consist of complementary sensors: the semicircular canals detect rotations while the otoliths detect linear accelerations, including the constant pull of gravity. Several fundamental questions remain on how the vestibular system would develop and/or adapt to prolonged changes in gravity such as during long-term space journey. How do vestibular reflexes develop if the appropriate assembly of otoliths and semi-circular canals is perturbed? The aim of present work was to evaluate the role of gravity sensing during ontogeny of the vestibular system. In otoconia-deficient mice (ied), gravity cannot be sensed and therefore maculo-ocular reflexes (MOR) were absent. While canals-related reflexes were present, the ied deficit also led to the abnormal spatial tuning of the horizontal angular canal-related VOR. To identify putative otolith-related critical periods, normal C57Bl/6J mice were subjected to 2G hypergravity by chronic centrifugation during different periods of development or adulthood (Adult-HG) and compared to non-centrifuged (control) C57Bl/6J mice. Mice exposed to hypergravity during development had completely normal vestibulo-ocular reflexes 6 months after end of centrifugation. Adult-HG mice all displayed major abnormalities in maculo-ocular reflexe one month after return to normal gravity. During the next 5 months, adaptation to normal gravity occurred in half of the individuals. In summary, genetic suppression of gravity sensing indicated that otolith-related signals might be necessary to ensure proper functioning of canal-related vestibular reflexes. On the other hand, exposure to hypergravity during development was not sufficient to modify durably motor behaviour. Hence, 2G centrifugation during development revealed no otolith-specific critical period. PMID:22808156

Turbine blade squealer tip rail with fence members

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

Little, David A

2012-11-20

A turbine blade includes an airfoil, a blade tip section, a squealer tip rail, and a plurality of chordally spaced fence members. The blade tip section includes a blade tip floor located at an end of the airfoil distal from the root. The blade tip floor includes a pressure side and a suction side joined together at chordally spaced apart leading and trailing edges of the airfoil. The squealer tip rail extends radially outwardly from the blade tip floor adjacent to the suction side and extends from a first location adjacent to the airfoil trailing edge to a second locationmore » adjacent to the airfoil leading edge. The fence members are located between the airfoil leading and trailing edges and extend radially outwardly from the blade tip floor and axially from the squealer tip rail toward the pressure side.« less

Genotoxic effects and induction of phytochelatins in the presence of cadmium in Vicia faba roots.

PubMed

Béraud, Eric; Cotelle, Sylvie; Leroy, Pierre; Férard, Jean-François

2007-10-04

This study investigates different effects in roots of Vicia faba (broad bean) after exposure to cadmium. Genotoxic effects were assessed by use of the well-known Vicia root tip micronucleus assay. Cytotoxic effects were evaluated by determining the mitotic index in root tip cells. Finally, molecular induction mechanisms were evaluated by measuring phytochelatins with HPLC. After hydroponical exposure of V. faba roots to a range of cadmium concentrations and during different exposure times, the results of this approach showed large variations, according to the endpoint measured: after 48 h of exposure, genotoxic effects were found between 7.5 x 10(-8) and 5 x 10(-7)M CdCl(2), and cytotoxic effects were observed between 2.5 x 10(-7) and 5 x 10(-7)M CdCl(2). Statistically significant phytochelatin (PC) concentrations were measured at >or=10(-6)M CdCl(2) for PC(2), and at >or=10(-5)M CdCl(2) for PC3 and PC4.

Hydraulic resistance of a plant root to water-uptake: A slender-body theory.

PubMed

Chen, Kang Ping

2016-05-07

A slender-body theory for calculating the hydraulic resistance of a single plant root is developed. The work provides an in-depth discussion on the procedure and the assumptions involved in calculating a root׳s internal hydraulic resistance as well as the physical and the mathematical aspects of the external three-dimensional flow around the tip of a root in a saturated soil and how this flow pattern enhances uptake and reduces hydraulic resistance. Analytical solutions for the flux density distribution on the stele-cortex interface, local water-uptake profile inside the stele core, the overall water-uptake at the base of the stele, and the total hydraulic resistance of a root are obtained in the slender-body limit. It is shown that a key parameter controlling a root's hydraulic resistance is the dimensionless axial conductivity in the stele, which depends on the permeabilities of the stele and the cortex as well as the root's radial and axial dimensions. Three-dimensional tip effect reduces a root's hydraulic resistance by as much as 36% when compared to the radial flow theory of Landsberg and Fowkes. In addition, the total hydraulic resistance cannot be generally decomposed into the direct sum of a radial resistance and an axial resistance. Copyright © 2016 Elsevier Ltd. All rights reserved.

Water Uptake along the Length of Grapevine Fine Roots: Developmental anatomy, tissue specific aquaporin expression, and pathways of water transport

USDA-ARS?s Scientific Manuscript database

To better understand water uptake patterns in root systems of woody perennial crops, we detailed the developmental anatomy and hydraulic physiology along the length of grapevine fine roots- from the tip to secondary growth zones. Our characterization included localization of suberized structures an...

Nitric oxide-cytokinin interplay influences selenite sensitivity in Arabidopsis.

PubMed

Lehotai, Nóra; Feigl, Gábor; Koós, Ágnes; Molnár, Árpád; Ördög, Attila; Pető, Andrea; Erdei, László; Kolbert, Zsuzsanna

2016-10-01

Selenite oppositely modifies cytokinin and nitric oxide metabolism in Arabidopsis organs. A mutually negative interplay between the molecules exists in selenite-exposed roots; and their overproduction causes selenite insensitivity. Selenium-induced phytotoxicity is accompanied by developmental alterations such as primary root (PR) shortening. Growth changes are provoked by the modulation of hormone status and signalling. Cytokinin (CK) cooperates with the nitric oxide (NO) in many aspects of plant development; however, their interaction under abiotic stress has not been examined. Selenite inhibited the growth of Arabidopsis seedlings and reduced root meristem size through cell division arrest. The CK-dependent pARR5::GUS activity revealed the intensification of CK signalling in the PR tip, which may be partly responsible for the root meristem shortening. The selenite-induced alterations in the in situ expressions of cytokinin oxidases (AtCKX4::GUS, AtCKX5::GUS) are associated with selenite-triggered changes of CK signalling. In wild-type (WT) and NO-deficient nia1nia2 root, selenite led to the diminution of NO content, but CK overproducer ipt-161 and -deficient 35S:CKX2 roots did not show NO decrease. Exogenous NO (S-nitroso-N-acetyl-DL-penicillamine, SNAP) reduced the pARR5::GFP and pTCS::GFP expressions. Roots of the 35S:CKX and cyr1 plants suffered more severe selenite-triggered viability loss than the WT, while in ipt-161 and gsnor1-3 no obvious viability decrease was observed. Exogenous NO ameliorated viability loss, but benzyladenine intensified it. Based on the results, selenite impacts development by oppositely modifying CK signalling and NO level. In the root system, CK signalling intensifies which possibly contributes to the nitrate reductase-independent NO diminution. A mutually negative CK-NO interplay exists in selenite-exposed roots; however, overproduction of both molecules worsens selenite sensing. Hereby, we suggest novel regulatory interplay and role for NO and CK in abiotic stress signalling.

Probing the surface profile and friction behavior of heterogeneous polymers: a molecular dynamics study

NASA Astrophysics Data System (ADS)

Dai, L.; Sorkin, V.; Zhang, Y. W.

2017-04-01

We perform molecular dynamics simulations to investigate molecular structure alternation and friction behavior of heterogeneous polymer (perfluoropolyether) surfaces using a nanoscale probing tip (tetrahedral amorphous carbon). It is found that depending on the magnitude of the applied normal force, three regimes exist: the shallow depth-sensing (SDS), deep depth-sensing (DDS), and transitional depth-sensing (TDS) regimes; TDS is between SDS and DDS. In SDS, the tip is floating on the polymer surface and there is insignificant permanent alternation in the polymer structure due to largely recoverable atomic deformations, and the surface roughness profile can be accurately measured. In DDS, the tip is plowing through the polymer surface and there is significant permanent alternation in the molecular structure. In this regime, the lateral friction force rises sharply and fluctuates violently when overcoming surface pile-ups. In SDS, the friction can be described by a modified Amonton’s law including the adhesion effect; meanwhile, in DDS, the adhesion effect is negligible but the friction coefficient is significantly higher. The underlying reason for the difference in these regimes rests upon different contributions by the repulsion and attraction forces between the tip and polymer surfaces to the friction force. Our findings here reveal important insights into lateral depth-sensing on heterogeneous polymer surfaces and may help improve the precision of depth-sensing devices.

Spaceflight exposure effects on transcription, activity, and localization of alcohol dehydrogenase in the roots of Arabidopsis thaliana.

PubMed Central

Porterfield, D M; Matthews, S W; Daugherty, C J; Musgrave, M E

1997-01-01

Although considerable research and speculation have been directed toward understanding a plant's perception of gravity and the resulting gravitropic responses, little is known about the role of gravity-dependent physical processes in normal physiological function. These studies were conducted to determine whether the roots of plants exposed to spaceflight conditions may be experiencing hypoxia. Arabidopsis thaliana (L.) Heynh. plants were grown in agar medium during 6 or 11 d of spaceflight exposure on shuttle missions STS-54 (CHROMEX-03) and STS-68 (CHROMEX-05), respectively. The analysis included measurement of agar redox potential and root alcohol dehydrogenase (ADH) activity, localization, and expression. ADH activity increased by 89% as a result of spaceflight exposure for both CHROMEX-03 and -05 experiments, and ADH RNase protection assays revealed a 136% increase in ADH mRNA. The increase in ADH activity associated with the spaceflight roots was realized by a 28% decrease in oxygen availability in a ground-based study; however, no reduction in redox potential was observed in measurements of the spaceflight bulk agar. Spaceflight exposure appears to effect a hypoxic response in the roots of agar-grown plants that may be caused by changes in gravity-mediated fluid and/or gas behavior. PMID:9085569

Spaceflight exposure effects on transcription, activity, and localization of alcohol dehydrogenase in the roots of Arabidopsis thaliana

NASA Technical Reports Server (NTRS)

Porterfield, D. M.; Matthews, S. W.; Daugherty, C. J.; Musgrave, M. E.

1997-01-01

Although considerable research and speculation have been directed toward understanding a plant's perception of gravity and the resulting gravitropic responses, little is known about the role of gravity-dependent physical processes in normal physiological function. These studies were conducted to determine whether the roots of plants exposed to spaceflight conditions may be experiencing hypoxia. Arabidopsis thaliana (L.) Heynh. plants were grown in agar medium during 6 or 11 d of spaceflight exposure on shuttle missions STS-54 (CHROMEX-03) and STS-68 (CHROMEX-05), respectively. The analysis included measurement of agar redox potential and root alcohol dehydrogenase (ADH) activity, localization, and expression. ADH activity increased by 89% as a result of spaceflight exposure for both CHROMEX-03 and -05 experiments, and ADH RNase protection assays revealed a 136% increase in ADH mRNA. The increase in ADH activity associated with the spaceflight roots was realized by a 28% decrease in oxygen availability in a ground-based study; however, no reduction in redox potential was observed in measurements of the spaceflight bulk agar. Spaceflight exposure appears to effect a hypoxic response in the roots of agar-grown plants that may be caused by changes in gravity-mediated fluid and/or gas behavior.

Inclination not force is sensed by plants during shoot gravitropism.

PubMed

Chauvet, Hugo; Pouliquen, Olivier; Forterre, Yoël; Legué, Valérie; Moulia, Bruno

2016-10-14

Gravity perception plays a key role in how plants develop and adapt to environmental changes. However, more than a century after the pioneering work of Darwin, little is known on the sensing mechanism. Using a centrifugal device combined with growth kinematics imaging, we show that shoot gravitropic responses to steady levels of gravity in four representative angiosperm species is independent of gravity intensity. All gravitropic responses tested are dependent only on the angle of inclination from the direction of gravity. We thus demonstrate that shoot gravitropism is stimulated by sensing inclination not gravitational force or acceleration as previously believed. This contrasts with the otolith system in the internal ear of vertebrates and explains the robustness of the control of growth direction by plants despite perturbations like wind shaking. Our results will help retarget the search for the molecular mechanism linking shifting statoliths to signal transduction.

Inclination not force is sensed by plants during shoot gravitropism

NASA Astrophysics Data System (ADS)

Chauvet, Hugo; Pouliquen, Olivier; Forterre, Yoël; Legué, Valérie; Moulia, Bruno

2016-10-01

Gravity perception plays a key role in how plants develop and adapt to environmental changes. However, more than a century after the pioneering work of Darwin, little is known on the sensing mechanism. Using a centrifugal device combined with growth kinematics imaging, we show that shoot gravitropic responses to steady levels of gravity in four representative angiosperm species is independent of gravity intensity. All gravitropic responses tested are dependent only on the angle of inclination from the direction of gravity. We thus demonstrate that shoot gravitropism is stimulated by sensing inclination not gravitational force or acceleration as previously believed. This contrasts with the otolith system in the internal ear of vertebrates and explains the robustness of the control of growth direction by plants despite perturbations like wind shaking. Our results will help retarget the search for the molecular mechanism linking shifting statoliths to signal transduction.

Sealing ability of three root-end filling materials prepared using an erbium: Yttrium aluminium garnet laser and endosonic tip evaluated by confocal laser scanning microscopy

PubMed Central

Nanjappa, A Salin; Ponnappa, KC; Nanjamma, KK; Ponappa, MC; Girish, Sabari; Nitin, Anita

2015-01-01

Aims: (1) To compare the sealing ability of mineral trioxide aggregate (MTA), Biodentine, and Chitra-calcium phosphate cement (CPC) when used as root-end filling, evaluated under confocal laser scanning microscope using Rhodamine B dye. (2) To evaluate effect of ultrasonic retroprep tip and an erbium:yttrium aluminium garnet (Er:YAG) laser on the integrity of three different root-end filling materials. Materials and Methods: The root canals of 80 extracted teeth were instrumented and obturated with gutta-percha. The apical 3 mm of each tooth was resected and 3 mm root-end preparation was made using ultrasonic tip (n = 30) and Er:YAG laser (n = 30). MTA, Biodentine, and Chitra-CPC were used to restore 10 teeth each. The samples were coated with varnish and after drying, they were immersed in Rhodamine B dye for 24 h. The teeth were then rinsed, sectioned longitudinally, and observed under confocal laser scanning microscope. Statistical Analysis Used: Data were analyzed using one-way analysis of variance (ANOVA) and a post-hoc Tukey's test at P < 0.05 (R software version 3.1.0). Results: Comparison of microleakage showed maximum peak value of 0.45 mm for Biodentine, 0.85 mm for MTA, and 1.05 mm for Chitra-CPC. The amount of dye penetration was found to be lesser in root ends prepared using Er:YAG laser when compared with ultrasonics, the difference was found to be statistically significant (P < 0.05). Conclusions: Root-end cavities prepared with Er:YAG laser and restored with Biodentine showed superior sealing ability compared to those prepared with ultrasonics. PMID:26180420

A study on plant root apex morphology as a model for soft robots moving in soil

PubMed Central

Pugno, Nicola Maria; Mazzolai, Barbara

2018-01-01

Plants use many strategies to move efficiently in soil, such as growth from the tip, tropic movements, and morphological changes. In this paper, we propose a method to translate morphological features of Zea mays roots into a new design of soft robots that will be able to move in soil. The method relies on image processing and curve fitting techniques to extract the profile of Z. mays primary root. We implemented an analytic translation of the root profile in a 3D model (CAD) to fabricate root-like probes by means of 3D printing technology. Then, we carried out a comparative analysis among the artificial root-like probe and probes with different tip shapes (cylindrical, conical, elliptical, and parabolic) and diameters (11, 9, 7, 5, and 3 mm). The results showed that the energy consumption and the penetration force of the bioinspired probe are better with respect to the other shapes for all the diameters of the developed probes. For 100 mm of penetration depth and 7 mm of probe diameter, the energy consumption of the bioinspired probe is 89% lesser with respect to the cylindrical probe and 26% lesser with respect to the conical probe. The penetration performance of the considered tip shapes was evaluated also by means of numerical simulations, obtaining a good agreement with the experimental results. Additional investigations on plant root morphology, movement strategies, and material properties can allow the development of innovative bioinspired solutions exploitable in challenging environments. This research can bring to breakthrough scenarios in different fields, such as exploration tasks, environmental monitoring, geotechnical studies, and medical applications. PMID:29874267

Quantification of root gravitropic response using a constant stimulus feedback system.

PubMed

Wolverton, Chris

2015-01-01

Numerous software packages now exist for quantifying root growth responses, most of which analyze a time resolved sequence of images ex post facto. However, few allow for the real-time analysis of growth responses. The system in routine use in our lab allows for real-time growth analysis and couples this to positional feedback to control the stimulus experienced by the responding root. This combination allows us to overcome one of the confounding variables in studies of root gravity response. Seedlings are grown on standard petri plates attached to a vertical rotating stage and imaged using infrared illumination. The angle of a particular region of the root is determined by image analysis, compared to the prescribed angle, and any corrections in positioning are made by controlling a stepper motor. The system allows for the long-term stimulation of a root at a constant angle and yields insights into the gravity perception and transduction machinery not possible with other approaches.

Growth of cress seedlings and morphogenesis of root Gravisensors under clino-rotation and in unidirectional red or blue light

NASA Astrophysics Data System (ADS)

Rakleviciene, D.; Svegzdiene, D.; Tamulaitis, G.; Zukauskas, A.

2005-08-01

The growth rate and orientation of cress seedlings in response to the direction of illumination under clino- rotation were investigated at the initial stage of intensive hypocotyl elongation. Roots and hypocotyls growing in normal gravity conditions (1 g) and under clino-rotation at 3 rpm were illuminated with red (660 nm) or blue (450 nm) light from light-emitting diodes (LEDs). Unidirectional illumination in the direction opposite to the gravity vector promoted the growth rate of roots. Inhibition of gravitropism by clino-rotation reduced the growth of roots and stimulated the elongation of hypocotyls in both red and blue light. Illumination of roots invoked changes in the formation of gravisensing cells in the columella. Illumination under clino-rotation stimulated root statocyte growth and increased the number of amyloplasts in cells of the 3rd-6th columella rows. Also, an increase in the columella cell area, mainly caused by cell elongation in blue light and by enhanced radial growth in red light, was observed.

Protein synthesis in geostimulated root caps

NASA Technical Reports Server (NTRS)

Feldman, L. J.

1982-01-01

A study is presented of the processes occurring in the root cap of corn which are requisite for the formation of root cap inhibitor and which can be triggered or modulated by both light and gravity. The results of this study indicate the importance of protein synthesis for light-induced gravitropic bending in roots. Root caps in which protein synthesis is prevented are unable to induce downward bending. This suggests that light acts by stimulating proteins which are necessary for the translation of the gravitropic stimulus into a growth response (downward bending). The turnover of protein with time was also examined in order to determine whether light acts by stimulating the synthesis of unique proteins required for downward growth. It is found that auxin in combination with light allows for the translation of the gravitropic stimulus into a growth response at least in part through the modification of protein synthesis. It is concluded that unique proteins are stimulated by light and are involved in promoting the downward growth in roots which are responding to gravity.

Selective progressive response of soil microbial community to wild oat roots.

PubMed

DeAngelis, Kristen M; Brodie, Eoin L; DeSantis, Todd Z; Andersen, Gary L; Lindow, Steven E; Firestone, Mary K

2009-02-01

Roots moving through soil induce physical and chemical changes that differentiate rhizosphere from bulk soil, and the effects of these changes on soil microorganisms have long been a topic of interest. The use of a high-density 16S rRNA microarray (PhyloChip) for bacterial and archaeal community analysis has allowed definition of the populations that respond to the root within the complex grassland soil community; this research accompanies compositional changes reported earlier, including increases in chitinase- and protease-specific activity, cell numbers and quorum sensing signal. PhyloChip results showed a significant change compared with bulk soil in relative abundance for 7% of the total rhizosphere microbial community (147 of 1917 taxa); the 7% response value was confirmed by16S rRNA terminal restriction fragment length polymorphism analysis. This PhyloChip-defined dynamic subset was comprised of taxa in 17 of the 44 phyla detected in all soil samples. Expected rhizosphere-competent phyla, such as Proteobacteria and Firmicutes, were well represented, as were less-well-documented rhizosphere colonizers including Actinobacteria, Verrucomicrobia and Nitrospira. Richness of Bacteroidetes and Actinobacteria decreased in soil near the root tip compared with bulk soil, but then increased in older root zones. Quantitative PCR revealed rhizosphere abundance of beta-Proteobacteria and Actinobacteria at about 10(8) copies of 16S rRNA genes per g soil, with Nitrospira having about 10(5) copies per g soil. This report demonstrates that changes in a relatively small subset of the soil microbial community are sufficient to produce substantial changes in functions observed earlier in progressively more mature rhizosphere zones.

Plant-mediated Sediment Oxygenation in Coastal Wetlands

NASA Astrophysics Data System (ADS)

Koop-Jakobsen, K.

2016-02-01

Belowground sediment oxygenation by wetland plants is an important mechanism controlling many microbial processes and chemical fluxes in coastal wetlands. Although transport of oxygen via the arenthyma tissue and subsequent oxygen loss across root surfaces is well-documented for Spartina grasses, only few studies have measured the oxygenation of sediment surrounding roots and rhizomes. In this study, the degree of sediment oxygenation in Spartina anglica rhizospheres was assessed in situ using a novel multifiber optode system inserting 100 oxygen sensing fiber optodes directly into the rhizosphere. Two closely located, but morphologically different, S. anglica populations growing in permeable sandy sediment and tidal flat deposit, respectively, were investigated. No oxygen was detected inside the rhizospheres at any depth in either location indicating that plant-mediated sediment oxygenation in S. anglica had a limited impact on the bulk anoxic sediment. This was substantiated by planar optode studies showing that sediment oxygenation was confined to the immediate vicinity of the root tips of adventitious root and root hairs stretching only up to 1.5mm away from the roots surface in permeable sandy sediment and 0.4mm in tidal flat deposit, which had a substantially higher oxygen demand. This contrasts previous studies estimating that more than half of the S. anglica rhizosphere volume may be oxygenated, and thereby suggests a high variability in the degree of sediment oxygenation among different S. anglica populations. Furthermore, there may be a significant difference in the degree of sediment oxygenation among different Spartina species; our recent in situ investigation of oxygen profiles in a Spartina alterniflora-dominated marsh suggested that oxygen leakage here may keep the bulk sediment at low oxygen concentration ranging from 0.5-4μM.

Statolith sedimentation kinetics and force transduction to the cortical endoplasmic reticulum in gravity-sensing Arabidopsis columella cells.

PubMed

Leitz, Guenther; Kang, Byung-Ho; Schoenwaelder, Monica E A; Staehelin, L Andrew

2009-03-01

The starch statolith hypothesis of gravity sensing in plants postulates that the sedimentation of statoliths in specialized statocytes (columella cells) provides the means for converting the gravitational potential energy into a biochemical signal. We have analyzed the sedimentation kinetics of statoliths in the central S2 columella cells of Arabidopsis thaliana. The statoliths can form compact aggregates with gap sizes between statoliths approaching <30 nm. Significant intra-aggregate sliding motions of individual statoliths suggest a contribution of hydrodynamic forces to the motion of statoliths. The reorientation of the columella cells accelerates the statoliths toward the central cytoplasm within <1 s of reorientation. During the subsequent sedimentation phase, the statoliths tend to move at a distance to the cortical endoplasmic reticulum (ER) boundary and interact only transiently with the ER. Statoliths moved by laser tweezers against the ER boundary experience an elastic lift force upon release from the optical trap. High-resolution electron tomography analysis of statolith-to-ER contact sites indicate that the weight of statoliths is sufficient to locally deform the ER membranes that can potentially activate mechanosensitive ion channels. We suggest that in root columella cells, the transduction of the kinetic energy of sedimenting statoliths into a biochemical signal involves a combination of statolith-driven motion of the cytosol, statolith-induced deformation of the ER membranes, and a rapid release of kinetic energy from the ER during reorientation to activate mechanosensitive sites within the central columella cells.

Statolith Sedimentation Kinetics and Force Transduction to the Cortical Endoplasmic Reticulum in Gravity-Sensing Arabidopsis Columella Cells[W][OA

PubMed Central

Leitz, Guenther; Kang, Byung-Ho; Schoenwaelder, Monica E.A.; Staehelin, L. Andrew

2009-01-01

The starch statolith hypothesis of gravity sensing in plants postulates that the sedimentation of statoliths in specialized statocytes (columella cells) provides the means for converting the gravitational potential energy into a biochemical signal. We have analyzed the sedimentation kinetics of statoliths in the central S2 columella cells of Arabidopsis thaliana. The statoliths can form compact aggregates with gap sizes between statoliths approaching <30 nm. Significant intra-aggregate sliding motions of individual statoliths suggest a contribution of hydrodynamic forces to the motion of statoliths. The reorientation of the columella cells accelerates the statoliths toward the central cytoplasm within <1 s of reorientation. During the subsequent sedimentation phase, the statoliths tend to move at a distance to the cortical endoplasmic reticulum (ER) boundary and interact only transiently with the ER. Statoliths moved by laser tweezers against the ER boundary experience an elastic lift force upon release from the optical trap. High-resolution electron tomography analysis of statolith-to-ER contact sites indicate that the weight of statoliths is sufficient to locally deform the ER membranes that can potentially activate mechanosensitive ion channels. We suggest that in root columella cells, the transduction of the kinetic energy of sedimenting statoliths into a biochemical signal involves a combination of statolith-driven motion of the cytosol, statolith-induced deformation of the ER membranes, and a rapid release of kinetic energy from the ER during reorientation to activate mechanosensitive sites within the central columella cells. PMID:19276442

A Bird's-Eye View of Molecular Changes in Plant Gravitropism Using Omics Techniques.

PubMed

Schüler, Oliver; Hemmersbach, Ruth; Böhmer, Maik

2015-01-01

During evolution, plants have developed mechanisms to adapt to a variety of environmental stresses, including drought, high salinity, changes in carbon dioxide levels and pathogens. Central signaling hubs and pathways that are regulated in response to these stimuli have been identified. In contrast to these well studied environmental stimuli, changes in transcript, protein and metabolite levels in response to a gravitational stimulus are less well understood. Amyloplasts, localized in statocytes of the root tip, in mesophyll cells of coleoptiles and in the elongation zone of the growing internodes comprise statoliths in higher plants. Deviations of the statocytes with respect to the earthly gravity vector lead to a displacement of statoliths relative to the cell due to their inertia and thus to gravity perception. Downstream signaling events, including the conversion from the biophysical signal of sedimentation of distinct heavy mass to a biochemical signal, however, remain elusive. More recently, technical advances, including clinostats, drop towers, parabolic flights, satellites, and the International Space Station, allowed researchers to study the effect of altered gravity conditions - real and simulated micro- as well as hypergravity on plants. This allows for a unique opportunity to study plant responses to a purely anthropogenic stress for which no evolutionary program exists. Furthermore, the requirement for plants as food and oxygen sources during prolonged manned space explorations led to an increased interest in the identi-fication of genes involved in the adaptation of plants to microgravity. Transcriptomic, proteomic, phosphoproteomic, and metabolomic profiling strategies provide a sensitive high-throughput approach to identify biochemical alterations in response to changes with respect to the influence of the gravitational vector and thus the acting gravitational force on the transcript, protein and metabolite level. This review aims at summarizing recent experimental approaches and discusses major observations.

A Bird’s-Eye View of Molecular Changes in Plant Gravitropism Using Omics Techniques

PubMed Central

Schüler, Oliver; Hemmersbach, Ruth; Böhmer, Maik

2015-01-01

During evolution, plants have developed mechanisms to adapt to a variety of environmental stresses, including drought, high salinity, changes in carbon dioxide levels and pathogens. Central signaling hubs and pathways that are regulated in response to these stimuli have been identified. In contrast to these well studied environmental stimuli, changes in transcript, protein and metabolite levels in response to a gravitational stimulus are less well understood. Amyloplasts, localized in statocytes of the root tip, in mesophyll cells of coleoptiles and in the elongation zone of the growing internodes comprise statoliths in higher plants. Deviations of the statocytes with respect to the earthly gravity vector lead to a displacement of statoliths relative to the cell due to their inertia and thus to gravity perception. Downstream signaling events, including the conversion from the biophysical signal of sedimentation of distinct heavy mass to a biochemical signal, however, remain elusive. More recently, technical advances, including clinostats, drop towers, parabolic flights, satellites, and the International Space Station, allowed researchers to study the effect of altered gravity conditions – real and simulated micro- as well as hypergravity on plants. This allows for a unique opportunity to study plant responses to a purely anthropogenic stress for which no evolutionary program exists. Furthermore, the requirement for plants as food and oxygen sources during prolonged manned space explorations led to an increased interest in the identi-fication of genes involved in the adaptation of plants to microgravity. Transcriptomic, proteomic, phosphoproteomic, and metabolomic profiling strategies provide a sensitive high-throughput approach to identify biochemical alterations in response to changes with respect to the influence of the gravitational vector and thus the acting gravitational force on the transcript, protein and metabolite level. This review aims at summarizing recent experimental approaches and discusses major observations. PMID:26734055

EMCS Experiment Container for the Plant Gravity Perception Experiment

NASA Image and Video Library

2018-02-08

iss054e037079 (Feb. 8, 2018) --- Plant Gravity Perception experiment in a centrifuge on a European Modular Cultivation System (EMCS) Experiment Container (EC) to test the gravity-sensing ability of plants in microgravity.

Proteomic and phosphoproteomic analysis of polyethylene glycol-induced osmotic stress in root tips of common bean (Phaseolus vulgaris L.)

PubMed Central

Horst, Walter Johannes

2013-01-01

Previous studies have shown that polyethylene glycol (PEG)-induced osmotic stress (OS) reduces cell-wall (CW) porosity and limits aluminium (Al) uptake by root tips of common bean (Phaseolus vulgaris L.). A subsequent transcriptomic study suggested that genes related to CW processes are involved in adjustment to OS. In this study, a proteomic and phosphoproteomic approach was applied to identify OS-induced protein regulation to further improve our understanding of how OS affects Al accumulation. Analysis of total soluble proteins in root tips indicated that, in total, 22 proteins were differentially regulated by OS; these proteins were functionally categorized. Seventy-seven per- cent of the total expressed proteins were involved in metabolic pathways, particularly of carbohydrate and amino acid metabolism. An analysis of the apoplastic proteome revealed that OS reduced the level of five proteins and increased that of seven proteins. Investigation of the total soluble phosphoproteome suggested that dehydrin responded to OS with an enhanced phosphorylation state without a change in abundance. A cellular immunolocalization analysis indicated that dehydrin was localized mainly in the CW. This suggests that dehydrin may play a major protective role in the OS-induced physical breakdown of the CW structure and thus maintenance of the reversibility of CW extensibility during recovery from OS. The proteomic and phosphoproteomic analyses provided novel insights into the complex mechanisms of OS-induced reduction of Al accumulation in the root tips of common bean and highlight a key role for modification of CW structure. PMID:24123251

Propidium Iodide Competes with Ca2+ to Label Pectin in Pollen Tubes and Arabidopsis Root Hairs1[W][OA

PubMed Central

Rounds, Caleb M.; Lubeck, Eric; Hepler, Peter K.; Winship, Lawrence J.

2011-01-01

We have used propidium iodide (PI) to investigate the dynamic properties of the primary cell wall at the apex of Arabidopsis (Arabidopsis thaliana) root hairs and pollen tubes and in lily (Lilium formosanum) pollen tubes. Our results show that in root hairs, as in pollen tubes, oscillatory peaks in PI fluorescence precede growth rate oscillations. Pectin forms the primary component of the cell wall at the tip of both root hairs and pollen tubes. Given the electronic structure of PI, we investigated whether PI binds to pectins in a manner analogous to Ca2+ binding. We first show that Ca2+ is able to abrogate PI growth inhibition in a dose-dependent manner. PI fluorescence itself also relies directly on the amount of Ca2+ in the growth solution. Exogenous pectin methyl esterase treatment of pollen tubes, which demethoxylates pectins, freeing more Ca2+-binding sites, leads to a dramatic increase in PI fluorescence. Treatment with pectinase leads to a corresponding decrease in fluorescence. These results are consistent with the hypothesis that PI binds to demethoxylated pectins. Unlike other pectin stains, PI at low yet useful concentration is vital and specifically does not alter the tip-focused Ca2+ gradient or growth oscillations. These data suggest that pectin secretion at the apex of tip-growing plant cells plays a critical role in regulating growth, and PI represents an excellent tool for examining the role of pectin and of Ca2+ in tip growth. PMID:21768649

Gravity response mechanisms of lateral organs and the control of plant architecture in Arabidopsis

NASA Astrophysics Data System (ADS)

Mullen, J.; Hangarter, R.

Most research on gravity responses in plants has focused on primary roots and shoots, which typically grow in a vertical orientation. However, the patterns of lateral organ formation and their growth orientation, which typically are not vertical, govern plant architecture. For example, in Arabidopsis, when lateral roots emerge from the primary root, they grow at a nearly horizontal orientation. As they elongate, the roots slowly curve until they eventually reach a vertical orientation. The regulation of this lateral root orientation is an important component affecting the overall root system architecture. We have found that this change in orientation is not simply due to the onset of gravitropic competence, as non-vertical lateral roots are capable of both positive and negative gravitropism. Thus, the horizontal growth of the new lateral roots is determined by what is called the gravitropic set-point angle (GSA). In Arabidopsis shoots, rosette leaves and inflorescence branches also display GSA-dependent developmental changes in their orientation. The developmental control of the GSA of lateral organs in Arabidopsis provides us with a useful system for investigating the components involved in regulating directionality of tropistic responses. We have identified several Arabidopsis mutants that have either altered lateral root orientations, altered orientation of lateral organs in the shoot, or both, but maintain normal primary organ orientation. The mgsa ({m}odified {g}ravitropic {s}et-point {a}ngle) mutants with both altered lateral root and shoot orientation show that there are common components in the regulation of growth orientation in the different organs. Rosette leaves and lateral roots also have in common a regulation of positioning by red light. Further molecular and physiological analyses of the GSA mutants will provide insight into the basis of GSA regulation and, thus, a better understanding of how gravity controls plant architecture. [This work was supported by the National Aeronautics and Space Administration through grant no. NCC 2-1200.

The Allium Test--A Simple, Eukaryote Genotoxicity Assay.

ERIC Educational Resources Information Center

Babich, H.; Segall, M. A.; Fox, K. D.

1997-01-01

Explains the allium test in which roots are excised from onion bulblets grown in aqueous solutions of a test agent. Root tips are then isolated and stained with aceto-orcein, and chromosomal aberrations are microscopically observed. (Author/AIM)

Vitality and chemistry of roots of red spruce in forest floors of stands with a gradient of soil Al/Ca ratios in the northeastern United States

Treesearch

Philip M. Wargo; Kristiina Vogt; Daniel Vogt; Quintaniay Holifield; Joel Tilley; Gregory Lawrence; Mark David

2003-01-01

Number of living root tips per branch, percent dead roots, percent mycorrhizae and mycorrhizal morphotype, response of woody roots to wounding and colonization by fungi, and concentrations of starch, soluble sugars, phenols, percent C and N and C/N ratio, and Al, Ca, Fe, K, Mg, Mn, and P were measured for 2 consecutive years in roots of red spruce (Picea...

Enhanced formation of aerenchyma and induction of a barrier to radial oxygen loss in adventitious roots of Zea nicaraguensis contribute to its waterlogging tolerance as compared with maize (Zea mays ssp. mays).

PubMed

Abiko, Tomomi; Kotula, Lukasz; Shiono, Katsuhiro; Malik, Al Imran; Colmer, Timothy David; Nakazono, Mikio

2012-09-01

Enhancement of oxygen transport from shoot to root tip by the formation of aerenchyma and also a barrier to radial oxygen loss (ROL) in roots is common in waterlogging-tolerant plants. Zea nicaraguensis (teosinte), a wild relative of maize (Zea mays ssp. mays), grows in waterlogged soils. We investigated the formation of aerenchyma and ROL barrier induction in roots of Z. nicaraguensis, in comparison with roots of maize (inbred line Mi29), in a pot soil system and in hydroponics. Furthermore, depositions of suberin in the exodermis/hypodermis and lignin in the epidermis of adventitious roots of Z. nicaraguensis and maize grown in aerated or stagnant deoxygenated nutrient solution were studied. Growth of maize was more adversely affected by low oxygen in the root zone (waterlogged soil or stagnant deoxygenated nutrient solution) compared with Z. nicaraguensis. In stagnant deoxygenated solution, Z. nicaraguensis was superior to maize in transporting oxygen from shoot base to root tip due to formation of larger aerenchyma and a stronger barrier to ROL in adventitious roots. The relationships between the ROL barrier formation and suberin and lignin depositions in roots are discussed. The ROL barrier, in addition to aerenchyma, would contribute to the waterlogging tolerance of Z. nicaraguensis. © 2012 Blackwell Publishing Ltd.

Gravitropism and Autotropism in Cress Roots

NASA Technical Reports Server (NTRS)

Sack, Fred D.

1998-01-01

The overall purpose of this experiment was to study how cress roots respond to a withdrawal of a gravity stimulus i.e. when and how much the roots straighten (autotropism) after curving (gravitropism). This question was studied both in extensive ground-based research and in microgravity on BioRack.

Spatial Distributions of Potassium, Solutes, and Their Deposition Rates in the Growth Zone of the Primary Corn Root 1

PubMed Central

Silk, Wendy Kuhn; Hsiao, Theodore C.; Diedenhofen, Ulrike; Matson, Christina

1986-01-01

Densities of osmoticum and potassium were measured as a function of distance from the tip of the primary root of Zea mays L. (cv WF9 × mo17). Millimeter segments were excised and analyzed for osmotic potential by a miniaturized freezing point depression technique, and for potassium by flame spectrophotometry. Local deposition rates were estimated from the continuity equation with values for density and growth velocity. Osmotic potential was uniform, −0.73 ± 0.05 megapascals, throughout the growth zone of well-watered roots. Osmoticum deposition rate was 260 μosmoles per gram fresh weight per hour. Potassium density fell from 117 micromoles per gram in the first mm region to 48 micromoles per gram at the base of the growth zone. Potassium deposition rates had a maximum of 29 micromoles per gram per hour at 3.5 millimeters from the tip and were positive (i.e. potassium was being added to the tissue) until 8 millimeters from the tip. The results are discussed in terms of ion relations of the growing zone and growth physics. PMID:16665121

Cytotoxicity of aluminum oxide nanoparticles on Allium cepa root tip--effects of oxidative stress generation and biouptake.

PubMed

Rajeshwari, A; Kavitha, S; Alex, Sruthi Ann; Kumar, Deepak; Mukherjee, Anita; Chandrasekaran, Natarajan; Mukherjee, Amitava

2015-07-01

The commercial usage of Al2O3 nanoparticles (Al2O3 NPs) has gone up significantly in the recent times, enhancing the risk of environmental contamination with these agents and their consequent adverse effects on living systems. The current study has been designed to evaluate the cytogenetic potential of Al2O3 NPs in Allium cepa (root tip cells) at a range of exposure concentrations (0.01, 0.1, 1, 10, and 100 μg/mL), their uptake/internalization profile, and the oxidative stress generated. We noted a dose-dependent decrease in the mitotic index (42 to 28 %) and an increase in the number of chromosomal aberrations. Various chromosomal aberrations, e.g. sticky, multipolar and laggard chromosomes, chromosomal breaks, and the formation of binucleate cells, were observed by optical, fluorescence, and confocal laser scanning microscopy. FT-IR analysis demonstrated the surface chemical interaction between the nanoparticles and root tip cells. The biouptake of Al2O3 in particulate form led to reactive oxygen species generation, which in turn probably contributed to the induction of chromosomal aberrations.

The "Gravity-Powered Calculator," a Galilean Exhibit

ERIC Educational Resources Information Center

Cerreta, Pietro

2014-01-01

The Gravity-Powered Calculator is an exhibit of the Exploratorium in San Francisco. It is presented by its American creators as an amazing device that extracts the square roots of numbers, using only the force of gravity. But if you analyze his concept construction one can not help but recall the research of Galileo on falling bodies, the inclined…

The change in spatial distribution of upper trapezius muscle activity is correlated to contraction duration.

PubMed

Farina, Dario; Leclerc, Frédéric; Arendt-Nielsen, Lars; Buttelli, Olivier; Madeleine, Pascal

2008-02-01

The aim of the study was to confirm the hypothesis that the longer a contraction is sustained, the larger are the changes in the spatial distribution of muscle activity. For this purpose, surface electromyographic (EMG) signals were recorded with a 13 x 5 grid of electrodes from the upper trapezius muscle of 11 healthy male subjects during static contractions with shoulders 90 degrees abducted until endurance. The entropy (degree of uniformity) and center of gravity of the EMG root mean square map were computed to assess spatial inhomogeneity in muscle activation and changes over time in EMG amplitude spatial distribution. At the endurance time, entropy decreased (mean+/-SD, percent change 2.0+/-1.6%; P<0.0001) and the center of gravity moved in the cranial direction (shift 11.2+/-6.1mm; P<0.0001) with respect to the beginning of the contraction. The shift in the center of gravity was positively correlated with endurance time (R(2)=0.46, P<0.05), thus subjects with larger shift in the activity map showed longer endurance time. The percent variation in average (over the grid) root mean square was positively correlated with the shift in the center of gravity (R(2)=0.51, P<0.05). Moreover, the shift in the center of gravity was negatively correlated to both initial and final (at the endurance) entropy (R(2)=0.54 and R(2)=0.56, respectively; P<0.01 in both cases), indicating that subjects with less uniform root mean square maps had larger shift of the center of gravity over time. The spatial changes in root mean square EMG were likely due to spatially-dependent changes in motor unit activation during the sustained contraction. It was concluded that the changes in spatial muscle activity distribution play a role in the ability to maintain a static contraction.

Gravitropism and development of wild-type and starch-deficient mutants of Arabidopsis during spaceflight

NASA Technical Reports Server (NTRS)

Kiss, J. Z.; Katembe, W. J.; Edelmann, R. E.

1998-01-01

The "starch-statolith" hypothesis has been used by plant physiologists to explain the gravity perception mechanism in higher plants. In order to help resolve some of the controversy associated with ground-based research that has supported this theory, we performed a spaceflight experiment during the January 1997 mission of the Space Shuttle STS-81. Seedlings of wild-type (WT) Arabidopsis, two reduced-starch strains, and a starchless mutant were grown in microgravity and then given a gravity stimulus on a centrifuge. In terms of development in space, germination was greater than 90% for seeds in microgravity, and flight seedlings were smaller (60% in total length) compared to control plants grown on the ground and to control plants on a rotating clinostat. Seedlings grown in space had two structural features that distinguished them from the controls: a greater density of root hairs and an anomalous hypocotyl hook structure. However, the slower growth and morphological changes observed in the flight seedlings may be due to the effects of ethylene present in the spacecraft. Nevertheless, during the flight hypocotyls of WT seedlings responded to a unilateral 60 min stimulus provided by a 1-g centrifuge while those of the starch-deficient strains did not. Thus the strain with the greatest amount of starch responded to the stimulus given in flight and therefore, these data support the starch-statolith model for gravity sensing.

Role of inositol 1,4,5-triphosphate signalling in gravitropic and phototropic gene expression.

PubMed

Salinas-Mondragon, Raul E; Kajla, Jyoti D; Perera, Imara Y; Brown, Christopher S; Sederoff, Heike Winter

2010-12-01

Plants sense light and gravity to orient their direction of growth. One common component in the early events of both phototropic and gravitropic signal transduction is activation of phospholipase C (PLC), which leads to an increase in inositol 1,4,5-triphosphate (InsP(3)) levels. The InsP(3) signal is terminated by hydrolysis of InsP(3) through inositolpolyphosphate-5-phosphatases (InsP 5-ptases). Arabidopsis plants expressing a heterologous InsP 5-ptase have low basal InsP(3) levels and exhibit reduced gravitropic and phototropic bending. Downstream effects of InsP(3)-mediated signalling are not understood. We used comparative transcript profiling to characterize gene expression changes in gravity- or light-stimulated Arabidopsis root apices that were manipulated in their InsP(3) metabolism either through inhibition of PLC activity or expression of InsP 5-ptase. We identified InsP(3)-dependent and InsP(3)-independent co-regulated gene sets in response to gravity or light stimulation. Inhibition of PLC activity in wild-type plants caused similar changes in transcript abundance in response to gravitropic and phototropic stimulation as in the transgenic lines. Therefore, we conclude that changes in gene expression in response to gravitropic and phototropic stimulation are mediated by two signal transduction pathways that vary in their dependence on changes in InsP(3). © 2010 Blackwell Publishing Ltd.

L-Cysteine inhibits root elongation through auxin/PLETHORA and SCR/SHR pathway in Arabidopsis thaliana.

PubMed

Wang, Zhen; Mao, Jie-Li; Zhao, Ying-Jun; Li, Chuan-You; Xiang, Cheng-Bin

2015-02-01

L-Cysteine plays a prominent role in sulfur metabolism of plants. However, its role in root development is largely unknown. Here, we report that L-cysteine reduces primary root growth in a dosage-dependent manner. Elevating cellular L-cysteine level by exposing Arabidopsis thaliana seedlings to high L-cysteine, buthionine sulphoximine, or O-acetylserine leads to altered auxin maximum in root tips, the expression of quiescent center cell marker as well as the decrease of the auxin carriers PIN1, PIN2, PIN3, and PIN7 of primary roots. We also show that high L-cysteine significantly reduces the protein level of two sets of stem cell specific transcription factors PLETHORA1/2 and SCR/SHR. However, L-cysteine does not downregulate the transcript level of PINs, PLTs, or SCR/SHR, suggesting that an uncharacterized post-transcriptional mechanism may regulate the accumulation of PIN, PLT, and SCR/SHR proteins and auxin transport in the root tips. These results suggest that endogenous L-cysteine level acts to maintain root stem cell niche by regulating basal- and auxin-induced expression of PLT1/2 and SCR/SHR. L-Cysteine may serve as a link between sulfate assimilation and auxin in regulating root growth. © 2014 Institute of Botany, Chinese Academy of Sciences.

Global expression pattern comparison between low phosphorus insensitive 4 and WT Arabidopsis reveals an important role of reactive oxygen species and jasmonic acid in the root tip response to phosphate starvation

PubMed Central

Chacón-López, Alejandra; Ibarra-Laclette, Enrique; Sánchez-Calderón, Lenin; Gutiérrez-Alanís, Dolores

2011-01-01

Plants are exposed to several biotic and abiotic stresses. A common environmental stress that plants have to face both in natural and agricultural ecosystems that impacts both its growth and development is low phosphate (Pi) availability. There has been an important progress in the knowledge of the molecular mechanisms by which plants cope with Pi deficiency. However, the mechanisms that mediate alterations in the architecture of the Arabidopsis root system responses to Pi starvation are still largely unknown. One of the most conspicuous developmental effects of low Pi on the Arabidopsis root system is the inhibition of primary root growth that is accompanied by loss of root meristematic activity. To identify signalling pathways potentially involved in the Arabidpsis root meristem response to Pi-deprivation, here we report the global gene expression analysis of the root tip of wild type and low phosphorus insensitive4 (lpi4) mutant grown under Pi limiting conditions. Differential gene expression analysis and physiological experiments show that changes in the redox status, probably mediated by jasmonic acid and ethylene, play an important role in the primary root meristem exhaustion process triggered by Pi-starvation. PMID:21368582

An evaluation of root resorption after orthodontic treatment.

PubMed

Thomas, E; Evans, W G; Becker, P

2012-08-01

Root resorption is commonly seen, albeit in varying degrees, in cases that have been treated orthodontically. In this retrospective study the objective was to compare the amount of root resorption observed after active orthodontic treatment had been completed with one of three different appliance systems, namely, Tip Edge, Modified Edgewise and Damon. The sample consisted of pre and post-treatment cephalograms of sixty eight orthodontic cases. Root resorption of the maxillary central incisor was assessed from pre- and post- treatment lateral ce phalograms using two methods. In the first, overall tooth length from the incisal edge to the apex was measured on both pre and post-treatment lateral cephalograms and root resorption was recorded as an actual millimetre loss of tooth length. There was a significant upward linear trend (p = 0.052) for root resorption from the Tip Edge Group to the Damon Group. In the second method root resorption was visually evaluated by using the five grade ordinal scale of Levander and Malmgren (1988). It was found that the majorty of cases in the sample came under Grade 1 and Grade 2 category of root resorption. Statistical evaluation tested the extent of agree ment in this study between visual measurements and actual measurements and demonstrated a significant association (p = 0.018) between the methods.

Determination of zinc oxide nanoparticles toxicity in root growth in wheat (Triticum aestivum L.) seedlings.

PubMed

Prakash, Meppaloor G; Chung, Ill Min

2016-09-01

The effect of zinc oxide nanoparticles (ZnONPs) was studied in wheat (Triticum aestivum L.) seedlings under in vitro exposure conditions. To avoid precipitation of nanoparticles, the seedlings were grown in half strength semisolid Murashige and Skoog medium containing 0, 50, 100, 200, 400 and 500 mg L(-1) of ZnONPs. Analysis of zinc (Zn) content showed significant increase in roots. In vivo detection using fluorescent probe Zynpyr-1 indicated accumulation of Zn in primary and lateral root tips. All concentrations of ZnONPs significantly reduced root growth. However, significant decrease in shoot growth was observed only after exposure to 400 and 500 mg L(-1) of ZnONPs. The reactive oxygen species and lipid peroxidation levels significantly increased in roots. Significant increase in cell-wall bound peroxidase activity was observed after exposure to 500 mg L(-1) of ZnONPs. Histochemical staining with phloroglucinol-HCl showed lignification of root cells upon exposure to 500 mg L(-1) of ZnONPs. Treatment with propidium iodide indicated loss of cell viability in root tips of wheat seedlings. These results suggest that redox imbalances, lignification and cell death has resulted in reduction of root growth in wheat seedlings exposed to ZnONPs nanoparticles.

Nose Surgery

MedlinePlus

... because of gravity, causing the sides of the nose to collapse inward, obstructing air flow. Mouth breathing or noisy and restricted breathing are common. Try lifting the tip of your nose to see if you breathe better. If so, ...

Influence of minor geometric features on Stirling pulse tube cryocooler performance

NASA Astrophysics Data System (ADS)

Fang, T.; Spoor, P. S.; Ghiaasiaan, S. M.; Perrella, M.

2017-12-01

Minor geometric features and imperfections are commonly introduced into the basic design of multi-component systems to simplify or reduce the manufacturing expense. In this work, the cooling performance of a Stirling type cryocooler was tested in different driving powers, cold-end temperatures and inclination angles. A series of Computational Fluid Dynamics (CFD) simulations based on a prototypical cold tip was carried out. Detailed CFD model predictions were compared with the experiment and were used to investigate the impact of such apparently minor geometric imperfections on the performance of Stirling type pulse tube cryocoolers. Predictions of cooling performance and gravity orientation sensitivity were compared with experimental results obtained with the cryocooler prototypes. The results indicate that minor geometry features in the cold tip assembly can have considerable negative effects on the gravity orientation sensitivity of a pulse tube cryocooler.

A new insight into root responses to external cues: Paradigm shift in nutrient sensing

PubMed Central

Bhardwaj, Deepak; Medici, Anna; Gojon, Alain; Lacombe, Benoît; Tuteja, Narendra

2015-01-01

Higher plants are sessile and their growth relies on nutrients present in the soil. The acquisition of nutrients is challenging for plants. Phosphate and nitrate sensing and signaling cascades play significant role during adverse conditions of nutrient unavailability. Therefore, it is important to dissect the mechanism by which plant roots acquire nutrients from the soil. Root system architecture (RSA) exhibits extensive developmental flexibility and changes during nutrient stress conditions. Growth of root system in response to external concentration of nutrients is a joint operation of sensor or receptor proteins along with several other cytoplasmic accessory proteins. After nutrient sensing, sensor proteins start the cellular relay involving transcription factors, kinases, ubiquitin ligases and miRNA. The complexity of nutrient sensing is still nebulous and many new players need to be better studied. This review presents a survey of recent paradigm shift in the advancements in nutrient sensing in relation to plant roots. PMID:26146897

ARG1 (altered response to gravity) encodes a DnaJ-like protein that potentially interacts with the cytoskeleton

NASA Technical Reports Server (NTRS)

Sedbrook, J. C.; Chen, R.; Masson, P. H.

1999-01-01

Gravitropism allows plant organs to direct their growth at a specific angle from the gravity vector, promoting upward growth for shoots and downward growth for roots. Little is known about the mechanisms underlying gravitropic signal transduction. We found that mutations in the ARG1 locus of Arabidopsis thaliana alter root and hypocotyl gravitropism without affecting phototropism, root growth responses to phytohormones or inhibitors of auxin transport, or starch accumulation. The positional cloning of ARG1 revealed a DnaJ-like protein containing a coiled-coil region homologous to coiled coils found in cytoskeleton-interacting proteins. These data suggest that ARG1 participates in a gravity-signaling process involving the cytoskeleton. A combination of Northern blot studies and analysis of ARG1-GUS fusion-reporter expression in transgenic plants demonstrated that ARG1 is expressed in all organs. Ubiquitous ARG1 expression in Arabidopsis and the identification of an ortholog in Caenorhabditis elegans suggest that ARG1 is involved in other essential processes.

Ontogeny of plants under various gravity condition

NASA Astrophysics Data System (ADS)

Laurinavičius, R.; Švegždienṡ, D.; Raklevičienė, D.; Kenstavičienė, P.

2001-01-01

The results of experiments performed under conditions of microgravity (MG) or under its simulation on the horizontal clinostat (HC) with the callus, seedlings of various species and embryogenic structures have revealed a definite role of gravity as an ecological factor in the processes of cytomorphogenesis, growth, and development. The transformation of differentiated somatic cells of arabidopsis seed into undifferentiated callus was not inhibited under MG, though modifications of the whole callus morphology and of mean cell and nucleus size were observed. The morphogenesis of polar structures such as root-hair bearing cells of Lactuca primary root has been shown to be modified in the course of differentiation under mass acceleration diminished below 0.1 g. Seed germination and seedling morphogenesis under MG follow their normal course, but a significant stimulation of shoot growth with no effect on primary root growth has been determined. A successful in vitro regeneration of Nicotiana tabacum plantlets from leaf cells and subsequent formation of shoots and roots on a continuously rotating HC as well as the formation of viable seeds during seed-to-seed growth of Arabidopsis plants under MG have indicated that gravity plays but a limited role in the processes of embryogenesis and organogenesis.

Rejuvenation of Sequoia sempervirens by Repeated Grafting of Shoot Tips onto Juvenile Rootstocks in Vitro 1

PubMed Central

Huang, Li-Chun; Lius, Suwenza; Huang, Bau-Lian; Murashige, Toshio; Mahdi, El Fatih M.; Van Gundy, Richard

1992-01-01

Repeated grafting of 1.5-centimeter long shoot tips from an adult Sequoia sempervirens tree onto fresh, rooted juvenile stem cuttings in vitro resulted in progressive restoration of juvenile traits. After four successive grafts, stem cuttings of previously adult shoots rooted as well, branched as profusely, and grew with as much or more vigor as those of seedling shoots. Reassays disclosed retention for 3 years of rooting competence at similar levels as originally restored. Adventitious shoot formation was remanifested and callus development was depressed in stem segments from the repeatedly grafted adult. The reversion was associated with appearance and disappearance of distinctive leaf proteins. Neither gibberellic acid nor N6-beneyladenine as nutrient supplements duplicated the graft effects. ImagesFigure 2Figure 5Figure 8 PMID:16668609

Protocol for Removal of Third Molar Root Tips from the Inferior Alveolar Canal-Crossing the line.

PubMed

Punga, Rohit; Keswani, Kiran

2014-12-01

The safe removal of third molars involved with the inferior alveolar canal (IAC) has been an area of concern since long. Many times we hesitate for the removal of third molars, fearing injury to the inferior alveolar nerve. The authors here describe a simple technique which can be used to remove third molars showing evidence of proximity to IAC on presurgical radiographic evaluation, as well as those root tips which, during removal, accidentally enter the IAC space. A step-by-step protocol is presented along with necessary precautions during the operative procedure.

Control of Adventitious Root Architecture in Rice by Darkness, Light, and Gravity1[OPEN

PubMed Central

2018-01-01

Rice (Oryza sativa) is a semiaquatic plant that is well adapted to partial flooding. Rice stems develop adventitious root (AR) primordia at each node that slowly mature but emerge only when the plant gets flooded, leading to the formation of a whole new secondary root system upon flooding. AR growth is induced by ethylene that accumulates in submerged plant tissues due to its lowered diffusion rate in water. Here, we report that the architecture of the secondary root system in flooded rice plants is controlled not only by altered gas diffusion but also by gravity and light. While ethylene promotes the emergence and growth of ARs, gravity and light determine their gravitropic setpoint angle (i.e. the deviation of growth direction relative to vertical). ARs grow upward at about 120° in the dark and downward at 54° in the light. The upward growth direction is conserved in indica and japonica rice varieties, suggestive of a conserved trait in rice. Experiments with a klinostat and with inverted stem orientation revealed that gravity promotes upward growth by about 10°. Red, far-red, and blue light lead to negative phototropism in a dose-dependent manner, with blue light being most effective, indicating that phytochrome and blue light signaling control AR system architecture. The cpt1 (coleoptile phototropism1) mutant, which lacks one of the phototropin-interacting CPT proteins, shows reduced sensitivity to blue light. Hence, the gravitropic setpoint angle of rice ARs is controlled by genetic and environmental factors that likely balance the need for oxygen supply (upward growth) with avoidance of root desiccation (downward growth). PMID:29242375

Control of Adventitious Root Architecture in Rice by Darkness, Light, and Gravity.

PubMed

Lin, Chen; Sauter, Margret

2018-02-01

Rice ( Oryza sativa ) is a semiaquatic plant that is well adapted to partial flooding. Rice stems develop adventitious root (AR) primordia at each node that slowly mature but emerge only when the plant gets flooded, leading to the formation of a whole new secondary root system upon flooding. AR growth is induced by ethylene that accumulates in submerged plant tissues due to its lowered diffusion rate in water. Here, we report that the architecture of the secondary root system in flooded rice plants is controlled not only by altered gas diffusion but also by gravity and light. While ethylene promotes the emergence and growth of ARs, gravity and light determine their gravitropic setpoint angle (i.e. the deviation of growth direction relative to vertical). ARs grow upward at about 120° in the dark and downward at 54° in the light. The upward growth direction is conserved in indica and japonica rice varieties, suggestive of a conserved trait in rice. Experiments with a klinostat and with inverted stem orientation revealed that gravity promotes upward growth by about 10°. Red, far-red, and blue light lead to negative phototropism in a dose-dependent manner, with blue light being most effective, indicating that phytochrome and blue light signaling control AR system architecture. The cpt1 ( coleoptile phototropism1 ) mutant, which lacks one of the phototropin-interacting CPT proteins, shows reduced sensitivity to blue light. Hence, the gravitropic setpoint angle of rice ARs is controlled by genetic and environmental factors that likely balance the need for oxygen supply (upward growth) with avoidance of root desiccation (downward growth). © 2018 American Society of Plant Biologists. All Rights Reserved.

Plant Evo-Devo: How Tip Growth Evolved.

PubMed

Rensing, Stefan A

2016-12-05

Apical elongation of polarized plant cells (tip growth) occurs in root hairs of flowering plants and in rhizoids of bryophytes. A new report shows that the formation of these cells relies on genes already present in the first land plants. Copyright © 2016 Elsevier Ltd. All rights reserved.

Genetic Analysis of Mice Skin Exposed by Hyper-Gravity

NASA Astrophysics Data System (ADS)

Takahashi, Rika; Terada, Masahiro; Seki, Masaya; Higashibata, Akira; Majima, Hideyuki J.; Ohira, Yoshinobu; Mukai, Chiaki; Ishioka, Noriaki

2013-02-01

In the space environment, physiological alterations, such as low bone density, muscle weakness and decreased immunity, are caused by microgravity and cosmic radiation. On the other hand, it is known that the leg muscles are hypertrophy by 2G-gravity. An understanding of the effects on human body from microgravity to hyper-gravity is very important. Recently, the Japan Aerospace Exploration Agency (JAXA) has started a project to detect the changes on gene expression and mineral metabolism caused by microgravity by analyzing the hair of astronauts who stay in the international Space Station (ISS) for a long time. From these results of human hair’s research, the genetic effects of human hair roots by microgravity will become clear. However, it is unclear how the gene expression of hair roots was effected by hypergravity. Therefore, in this experiment, we analyzed the effect on mice skin contained hair roots by comparing microgravity or hypergravity exposed mice. The purpose of this experiment is to evaluate the genetic effects on mice skin by microgravity or 2G-gravity. The samples were taken from mice exposed to space flight (FL) or hypergravity environment (2G) for 3-months, respectively. The extracted and amplified RNA from these mice skin was used to DNA microarray analysis. in this experiment, we analyzed the effect of gravity by using mice skin contained hair roots, which exposed space (FL) and hyper-gravity (2G) for 3 months and each control. By DNA microarray analysis, we found the common 98 genes changed in both FL and 2G. Among these 98 genes, the functions and pathways were identified by Gene Ontology (GO) analysis and Ingenuity Pathways Analysis (IPA) software. Next, we focused the one of the identified pathways and compared the effects on each molecules in this pathways by the different environments, such as FL and 2G. As the results, we could detect some interesting molecules, which might be depended on the gravity levels. In addition, to investigate the relationships between genes and protein expression, the proteome analysis was performed. From the result of 2-dimentional electrophoresis, we could detect the some different spots between FL and 2G. These identifications are now in progress using by MALDI-TOF-MS/MS. These results suggested that many genes or proteins on the mice skin might be effected by the different gravity levels.

Genome duplication improves rice root resistance to salt stress

PubMed Central

2014-01-01

Background Salinity is a stressful environmental factor that limits the productivity of crop plants, and roots form the major interface between plants and various abiotic stresses. Rice is a salt-sensitive crop and its polyploid shows advantages in terms of stress resistance. The objective of this study was to investigate the effects of genome duplication on rice root resistance to salt stress. Results Both diploid rice (HN2026-2x and Nipponbare-2x) and their corresponding tetraploid rice (HN2026-4x and Nipponbare-4x) were cultured in half-strength Murashige and Skoog medium with 150 mM NaCl for 3 and 5 days. Accumulations of proline, soluble sugar, malondialdehyde (MDA), Na+ content, H+ (proton) flux at root tips, and the microstructure and ultrastructure in rice roots were examined. We found that tetraploid rice showed less root growth inhibition, accumulated higher proline content and lower MDA content, and exhibited a higher frequency of normal epidermal cells than diploid rice. In addition, a protective gap appeared between the cortex and pericycle cells in tetraploid rice. Next, ultrastructural analysis showed that genome duplication improved membrane, organelle, and nuclei stability. Furthermore, Na+ in tetraploid rice roots significantly decreased while root tip H+ efflux in tetraploid rice significantly increased. Conclusions Our results suggest that genome duplication improves root resistance to salt stress, and that enhanced proton transport to the root surface may play a role in reducing Na+ entrance into the roots. PMID:25184027

Dynamic Pressure Probes Developed for Supersonic Flow-Field Measurements

NASA Technical Reports Server (NTRS)

Porro, A. Robert

2001-01-01

A series of dynamic flow-field pressure probes were developed for use in large-scale supersonic wind tunnels at the NASA Glenn Research Center. These flow-field probes include pitot and static pressure probes that can capture fast-acting flow-field pressure transients occurring on a millisecond timescale. The pitot and static probes can be used to determine local Mach number time histories during a transient event. The flow-field pressure probe contains four major components: 1) Static pressure aerodynamic tip; 2) Pressure-sensing cartridge assembly; 3) Pitot pressure aerodynamic tip; 4) Mounting stem. This modular design allows for a variety of probe tips to be used for a specific application. Here, the focus is on flow-field pressure measurements in supersonic flows, so we developed a cone-cylinder static pressure tip and a pitot pressure tip. Alternatively, probe tips optimized for subsonic and transonic flows could be used with this design. The pressure-sensing cartridge assembly allows the simultaneous measurement of steady-state and transient pressure which allows continuous calibration of the dynamic pressure transducer.

Mitochondrial β-Cyanoalanine Synthase Is Essential for Root Hair Formation in Arabidopsis thaliana[W

PubMed Central

García, Irene; Castellano, José María; Vioque, Blanca; Solano, Roberto; Gotor, Cecilia; Romero, Luis C.

2010-01-01

Cyanide is stoichiometrically produced as a coproduct of the ethylene biosynthesis pathway and is detoxified by β-cyanoalanine synthase enzymes. The molecular and phenotypical analysis of T-DNA insertion mutants of the mitochondrial β-cyanoalanine synthase CYS-C1 suggests that discrete accumulation of cyanide is not toxic for the plant and does not alter mitochondrial respiration rates but does act as a strong inhibitor of root hair development. The cys-c1 null allele is defective in root hair formation and accumulates cyanide in root tissues. The root hair defect is phenocopied in wild-type plants by the exogenous addition of cyanide to the growth medium and is reversed by the addition of hydroxocobalamin or by genetic complementation with the CYS-C1 gene. Hydroxocobalamin not only recovers the root phenotype of the mutant but also the formation of reactive oxygen species at the initial step of root hair tip growth. Transcriptional profiling of the cys-c1 mutant reveals that cyanide accumulation acts as a repressive signal for several genes encoding enzymes involved in cell wall rebuilding and the formation of the root hair tip as well as genes involved in ethylene signaling and metabolism. Our results demonstrate that mitochondrial β-cyanoalanine synthase activity is essential to maintain a low level of cyanide for proper root hair development. PMID:20935247

A proposed role for selective autophagy in regulating auxin-dependent lateral root development under phosphate starvation in Arabidopsis.

PubMed

Sankaranarayanan, Subramanian; Samuel, Marcus A

2015-01-01

Plants respond to limited soil nutrient availability by inducing more lateral roots (LR) to increase the root surface area. At the cellular level, nutrient starvation triggers the process of autophagy through which bulk degradation of cellular materials is achieved to facilitate nutrient mobilization. Whether there is any link between the cellular autophagy and induction of LR had remained unknown. We recently showed that the S-Domain receptor Kinase (ARK2) and U Box/Armadillo Repeat-Containing E3 ligase (PUB9) module is required for lateral root formation under phosphate starvation in Arabidopsis thaliana.(1) We also showed that PUB9 localized to autophagic bodies following either activation by ARK2 or under phosphate starvation and ark2-1/pub9-1 plants displayed lateral root defects with inability to accumulate auxin in the root tips under phosphate starvation.(1) Supplementing exogenous auxin was sufficient to rescue the LR defects in ark2-1/pub9-1 mutant. Blocking of autophagic responses in wild-type Arabidopsis also resulted in inhibition of both lateral roots and auxin accumulation in the root tips indicating the importance of autophagy in mediating auxin accumulation under phosphate starved conditions.(1) Here, we propose a model for ARK2/AtPUB9 module in regulation of lateral root development via selective autophagy.

Ground penetrating radar for underground sensing in agriculture: a review

NASA Astrophysics Data System (ADS)

Liu, Xiuwei; Dong, Xuejun; Leskovar, Daniel I.

2016-10-01

Belowground properties strongly affect agricultural productivity. Traditional methods for quantifying belowground properties are destructive, labor-intensive and pointbased. Ground penetrating radar can provide non-invasive, areal, and repeatable underground measurements. This article reviews the application of ground penetrating radar for soil and root measurements and discusses potential approaches to overcome challenges facing ground penetrating radar-based sensing in agriculture, especially for soil physical characteristics and crop root measurements. Though advanced data-analysis has been developed for ground penetrating radar-based sensing of soil moisture and soil clay content in civil engineering and geosciences, it has not been used widely in agricultural research. Also, past studies using ground penetrating radar in root research have been focused mainly on coarse root measurement. Currently, it is difficult to measure individual crop roots directly using ground penetrating radar, but it is possible to sense root cohorts within a soil volume grid as a functional constituent modifying bulk soil dielectric permittivity. Alternatively, ground penetrating radarbased sensing of soil water content, soil nutrition and texture can be utilized to inversely estimate root development by coupling soil water flow modeling with the seasonality of plant root growth patterns. Further benefits of ground penetrating radar applications in agriculture rely on the knowledge, discovery, and integration among differing disciplines adapted to research in agricultural management.

X-ray computed tomography uncovers root-root interactions: quantifying spatial relationships between interacting root systems in three dimensions.

PubMed

Paya, Alexander M; Silverberg, Jesse L; Padgett, Jennifer; Bauerle, Taryn L

2015-01-01

Research in the field of plant biology has recently demonstrated that inter- and intra-specific interactions belowground can dramatically alter root growth. Our aim was to answer questions related to the effect of inter- vs. intra-specific interactions on the growth and utilization of undisturbed space by fine roots within three dimensions (3D) using micro X-ray computed tomography. To achieve this, Populus tremuloides (quaking aspen) and Picea mariana (black spruce) seedlings were planted into containers as either solitary individuals, or inter-/intra-specific pairs, allowed to grow for 2 months, and 3D metrics developed in order to quantify their use of belowground space. In both aspen and spruce, inter-specific root interactions produced a shift in the vertical distribution of the root system volume, and deepened the average position of root tips when compared to intra-specifically growing seedlings. Inter-specific interactions also increased the minimum distance between root tips belonging to the same root system. There was no effect of belowground interactions on the radial distribution of roots, or the directionality of lateral root growth for either species. In conclusion, we found that significant differences were observed more often when comparing controls (solitary individuals) and paired seedlings (inter- or intra-specific), than when comparing inter- and intra-specifically growing seedlings. This would indicate that competition between neighboring seedlings was more responsible for shifting fine root growth in both species than was neighbor identity. However, significant inter- vs. intra-specific differences were observed, which further emphasizes the importance of biological interactions in competition studies.

Chromosomal Fragmentation: A Possible Marker for the Selection of High Gymnemic Acid Yielding Accessions of Gymnema sylvestre R. Br.

PubMed

Verma, Ashutosh Kumar; Dhawan, Sunita Singh

2017-10-01

Gymnema sylvestre R. Br. a member of family Asclepiadaceae as mentioned in Indian Pharmacopoeia popular among the researchers because of stimulatory effect of its phytoconstituent on pancreatic cells and potential to treat Type I and II type of diabetes. Development of cost-effective marker system for the selection of high gymnemic acid yielding accessions of G. sylvestre . Presoaked seeds of Brassica campestris treated with different dilutions of gymnemagenin and 10% leaf extract of twenty different accessions of G. sylvestre . Root tips of germinated seeds were fixed, and chromosomal studies were made by root tip bioassay method. Exposure of seeds to treatment solutions promotes various types of chromosomal anomalies in root meristem, and surprisingly, direct correlation between the percentage of chromosomal fragmentation and the percentage of gymnemic acid shared by treatment solution were observed. Later finding may be explored for the development of a novel methodology or marker system for the selection of high active principle yielding accessions of G. sylvestre . An experiment was carried out using root tip bioassay method for the study of effect of different dilutions of standard gymnemic acid and 10% leaf extract of twenty different accessions of Gymnema sylvestre on root tip meristem of Brassica campestris . Various types of chromosomal anomalies were observed. Of which, percentage of chromosomal fragmentation was showed a direct (∞) relationship with the percentage of gymnemic acid shared by treatment solution. This interesting result after more and more exploration and revalidation could be utilized for the development of a novel methodology for the selection of high active principle yielding accessions of G. sylvestre . Abbreviations used: MI: Mitotic index; CP: Condensed prophase; CM: Clumped metaphase; MC: Metaphase cleft; FR: Fragmentation; AP: Anaphase with persistent nucleolous; LA: Laggard, BR: Bridge; BI: Bi-nucleated cell; DA: Disturbed anaphasic polarity.

Chromosomal Fragmentation: A Possible Marker for the Selection of High Gymnemic Acid Yielding Accessions of Gymnema sylvestre R. Br

PubMed Central

Verma, Ashutosh Kumar; Dhawan, Sunita Singh

2017-01-01

Background: Gymnema sylvestre R. Br. a member of family Asclepiadaceae as mentioned in Indian Pharmacopoeia popular among the researchers because of stimulatory effect of its phytoconstituent on pancreatic cells and potential to treat Type I and II type of diabetes. Objectives: Development of cost-effective marker system for the selection of high gymnemic acid yielding accessions of G. sylvestre. Materials and Methods: Presoaked seeds of Brassica campestris treated with different dilutions of gymnemagenin and 10% leaf extract of twenty different accessions of G. sylvestre. Root tips of germinated seeds were fixed, and chromosomal studies were made by root tip bioassay method. Results: Exposure of seeds to treatment solutions promotes various types of chromosomal anomalies in root meristem, and surprisingly, direct correlation between the percentage of chromosomal fragmentation and the percentage of gymnemic acid shared by treatment solution were observed. Conclusion: Later finding may be explored for the development of a novel methodology or marker system for the selection of high active principle yielding accessions of G. sylvestre. SUMMARY An experiment was carried out using root tip bioassay method for the study of effect of different dilutions of standard gymnemic acid and 10% leaf extract of twenty different accessions of Gymnema sylvestre on root tip meristem of Brassica campestris. Various types of chromosomal anomalies were observed. Of which, percentage of chromosomal fragmentation was showed a direct (∞) relationship with the percentage of gymnemic acid shared by treatment solution. This interesting result after more and more exploration and revalidation could be utilized for the development of a novel methodology for the selection of high active principle yielding accessions of G. sylvestre. Abbreviations used: MI: Mitotic index; CP: Condensed prophase; CM: Clumped metaphase; MC: Metaphase cleft; FR: Fragmentation; AP: Anaphase with persistent nucleolous; LA: Laggard, BR: Bridge; BI: Bi-nucleated cell; DA: Disturbed anaphasic polarity. PMID:29142402

Centrifugation causes adaptation of microfilaments: studies on the transport of statoliths in gravity sensing Chara rhizoids.

PubMed

Braun, M; Sievers, A

1993-01-01

The actin cytoskeleton is involved in the positioning of statoliths in tip growing Chara rhizoids. The balance between the acropetally acting gravity force and the basipetally acting net outcome of cytoskeletal force results in the dynamically stable position of the statoliths 10-30 micrometers above the cell tip. A change of the direction and/or the amount of one of these forces in a vertically growing rhizoid results in a dislocation of statoliths. Centrifugation was used as a tool to study the characteristics of the interaction between statoliths and microfilaments (MFs). Acropetal and basipetal accelerations up to 6.5 g were applied with the newly constructed slow-rotating-centrifuge-microscope (NIZEMI). Higher accelerations were applied by means of a conventional centrifuge, namely acropetally 10-200 g and basipetally 10-70 g. During acropetal accelerations (1.4-6g), statoliths were displaced to a new stable position nearer to the cell vertex (12-6.5 micrometers distance to the apical cell wall, respectively), but they did not sediment on the apical cell wall. The original position of the statoliths was reestablished within 30 s after centrifugation. Sedimentation of statoliths and reduction of the growth rates of the rhizoids were observed during acropetal accelerations higher than 50 g. When not only the amount but also the direction of the acceleration were changed in comparison to the natural condition, i.e., during basipetal accelerations (1.0-6.5 g), statoliths were displaced into the subapical zone (up to 90 micrometers distance to the apical cell wall); after 15-20 min the retransport of statoliths to the apex against the direction of acceleration started. Finally, the natural position in the tip was reestablished against the direction of continuous centrifugation. Retransport was observed during accelerations up to 70 g. Under the 1 g condition that followed the retransported statoliths showed an up to 5-fold increase in sedimentation time onto the lateral cell wall when placed horizontally. During basipetal centrifugations > or = 70 g all statoliths entered the basal vacuolar part of the rhizoid where they were cotransported in the streaming cytoplasm. It is concluded that the MF system is able to adapt to higher mass accelerations and that the MF system of the polarly growing rhizoid is polarly organized.

Stiffness Control of Surgical Continuum Manipulators

PubMed Central

Mahvash, Mohsen; Dupont, Pierre E.

2013-01-01

This paper introduces the first stiffness controller for continuum robots. The control law is based on an accurate approximation of a continuum robot’s coupled kinematic and static force model. To implement a desired tip stiffness, the controller drives the actuators to positions corresponding to a deflected robot configuration that produces the required tip force for the measured tip position. This approach provides several important advantages. First, it enables the use of robot deflection sensing as a means to both sense and control tip forces. Second, it enables stiffness control to be implemented by modification of existing continuum robot position controllers. The proposed controller is demonstrated experimentally in the context of a concentric tube robot. Results show that the stiffness controller achieves the desired stiffness in steady state, provides good dynamic performance, and exhibits stability during contact transitions. PMID:24273466

The ARG1-LIKE2 gene of Arabidopsis functions in a gravity signal transduction pathway that is genetically distinct from the PGM pathway

NASA Technical Reports Server (NTRS)

Guan, Changhui; Rosen, Elizabeth S.; Boonsirichai, Kanokporn; Poff, Kenneth L.; Masson, Patrick H.

2003-01-01

The arl2 mutants of Arabidopsis display altered root and hypocotyl gravitropism, whereas their inflorescence stems are fully gravitropic. Interestingly, mutant roots respond like the wild type to phytohormones and an inhibitor of polar auxin transport. Also, their cap columella cells accumulate starch similarly to wild-type cells, and mutant hypocotyls display strong phototropic responses to lateral light stimulation. The ARL2 gene encodes a DnaJ-like protein similar to ARG1, another protein previously implicated in gravity signal transduction in Arabidopsis seedlings. ARL2 is expressed at low levels in all organs of seedlings and plants. arl2-1 arg1-2 double mutant roots display kinetics of gravitropism similar to those of single mutants. However, double mutants carrying both arl2-1 and pgm-1 (a mutation in the starch-biosynthetic gene PHOSPHOGLUCOMUTASE) at the homozygous state display a more pronounced root gravitropic defect than the single mutants. On the other hand, seedlings with a null mutation in ARL1, a paralog of ARG1 and ARL2, behave similarly to the wild type in gravitropism and other related assays. Taken together, the results suggest that ARG1 and ARL2 function in the same gravity signal transduction pathway in the hypocotyl and root of Arabidopsis seedlings, distinct from the pathway involving PGM.

Occurrence of mycorrhizae after logging and slash burning in the Douglas-fir forest type.

Treesearch

Ernest Wright; Robert F. Tarrant

1958-01-01

The association of certain fungi with plant roots results in formation of an organ called a mycorrhiza. There are two principal types of mycorrhizae: those with the fungus confined internally in the root, or endotrophic mycorrhizae, and those with both internal fungus development and an external fungal mantle enveloping the root tips, or ectotrophic mycorrhizae....

Lanthanum Element Induced Imbalance of Mineral Nutrients, HSP 70 Production and DNA-Protein Crosslink, Leading to Hormetic Response of Cell Cycle Progression in Root Tips of Vicia faba L. seedlings.

PubMed

Wang, Chengrun; Shi, Cuie; Liu, Ling; Wang, Chen; Qiao, Wei; Gu, Zhimang; Wang, Xiaorong

2012-01-01

The effects and mechanisms of rare earth elements on plant growth have not been extensively characterized. In the current study, Vicia faba L. seedlings were cultivated in lanthanum (La)-containing solutions for 10 days to investigate the possible effects and mechanisms of La on cell proliferation and root lengthening in roots. The results showed that increasing La levels resulted in abnormal calcium (Ca), Ferrum (Fe) or Potassium (K) contents in the roots. Flow cytometry analysis revealed G1/S and S/G2 arrests in response to La treatments in the root tips. Heat shock protein 70 (HSP 70) production showed a U-shaped dose response to increasing La levels. Consistent with its role in cell cycle regulation, HSP 70 fluctuated in parallel with the S-phase ratios and proliferation index. Furthermore, DNA-protein crosslinks (DPCs) enhanced at higher La concentrations, perhaps involved in blocking cell progression. Taken together, these data provide important insights into the hormetic effects and mechanisms of REE(s) on plant cell proliferation and growth.

Correlation of toxicity with lead content in root tip cells (Allium cepa L.).

PubMed

Carruyo, Ingrid; Fernández, Yusmary; Marcano, Letty; Montiel, Xiomara; Torrealba, Zaida

2008-12-01

The present study determines lead content in onion root tip cells (Allium cepa L.), correlating it with its toxicity. The treatment was carried at 25 +/- 0.5 degrees C using aqueous solutions of lead chloride at 0.1, 0.25, 0.50, 0.75, and 1 ppm for 12, 24, 48, and 72 h. For each treatment, a control where the lead solution was substituted by distilled water was included. After treatment, the meristems were fixed with a mixture of alcohol-acetic acid (3:1) and colored according to the technique of Feulgen. Lead content was quantified by graphite furnace absorption atomic spectrometry. The lead content in the roots ranged from 3.25 to 244.72 microg/g dry weight, with a direct relation with the concentration and time of exposure. A significant negative correlation was presented (r = -0.3629; p < 0.01) among lead content and root growth increment, and a positive correlation (r = 0.7750; p < 0.01) with the induction of chromosomic aberrations. In conclusion, lead is able to induce a toxic effect in the exposed roots, correlated with its content.

Gravitropism interferes with hydrotropism via counteracting auxin dynamics in cucumber roots: clinorotation and spaceflight experiments.

PubMed

Morohashi, Keita; Okamoto, Miki; Yamazaki, Chiaki; Fujii, Nobuharu; Miyazawa, Yutaka; Kamada, Motoshi; Kasahara, Haruo; Osada, Ikuko; Shimazu, Toru; Fusejima, Yasuo; Higashibata, Akira; Yamazaki, Takashi; Ishioka, Noriaki; Kobayashi, Akie; Takahashi, Hideyuki

2017-09-01

Roots of land plants show gravitropism and hydrotropism in response to gravity and moisture gradients, respectively, for controlling their growth orientation. Gravitropism interferes with hydrotropism, although the mechanistic aspects are poorly understood. Here, we differentiated hydrotropism from gravitropism in cucumber roots by conducting clinorotation and spaceflight experiments. We also compared mechanisms regulating hydrotropism and auxin-regulated gravitropism. Clinorotated or microgravity (μG)-grown cucumber seedling roots hydrotropically bent toward wet substrate in the presence of moisture gradients, but they grew straight in the direction of normal gravitational force at the Earth's surface (1G) on the ground or centrifuge-generated 1G in space. The roots appeared to become hydrotropically more sensitive to moisture gradients under μG conditions in space. Auxin transport inhibitors significantly reduced the hydrotropic response of clinorotated seedling roots. The auxin efflux protein CsPIN5 was differentially expressed in roots of both clinorotated and μG-grown seedlings; with higher expression in the high-humidity (concave) side than the low-humidity (convex) side of hydrotropically responding roots. Our results suggest that roots become hydrotropically sensitive in μG, and CsPIN5-mediated auxin transport has an important role in inducing root hydrotropism. Thus, hydrotropic and gravitropic responses in cucumber roots may compete via differential auxin dynamics established in response to moisture gradients and gravity. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

Sunlight decreased genotoxicity of azadirachtin on root tip cells of Allium cepa and Eucrosia bicolor.

PubMed

Kwankua, W; Sengsai, S; Kuleung, C; Euawong, N

2010-07-01

Utilization of neem plant (Azadirachta indica A. Juss) extract for pest control in agriculture has raised concerns over contamination by the residues to the environment. Such residues, particularly azadirachtin (Aza), may cause deleterious effect to non-target organisms. This investigation was conducted to find out if Aza could be inactivated through exposures to sunlight. Activity of Aza was assessed as its ability to cause cytotoxic and genotoxic effects in the forms of nuclei abnormality and chromosome aberration as measured by mitotic index (MI) and mitotic aberration (MA). Varying concentrations of Aza were tested on Allium cepa and Eucrosia bicolor. It was found that the MI of all root tip meristematic cells of A. cepa and E. bicolor treated with 0.00005%, 0.00010%, 0.00015%, and 0.00020% (w/v) Aza-containing neem extract for 24h, were significantly lower than the controls. Complementary to the lower levels of MI, the Aza-treated groups showed higher MA levels in all cases investigated. Furthermore, the decreasing levels of MI and the increasing levels of MA related well with the increasing concentration of Aza. Microscopic examination of root tip meristematic cells revealed that the anomaly found most often were mitotic disturbances and chromosomal bridges. Exposures of 0.00020% (w/v) Aza to sunlight for 3 days and 7 days decreased Aza ability to induce cytotoxicity and genotoxicity, both in terms of MI and MA, to root tip meristematic cells in A. cepa and E. bicolor. Photodegradation of Aza upon exposure to direct sunlight was confirmed by HPLC. The study implicates that Aza would unlikely cause long term deleterious effects to the environment since it would be inactivated by sunlight. Copyright (c) 2010 Elsevier Inc. All rights reserved.

Plastic responses of native plant root systems to the presence of an invasive annual grass.

PubMed

Phillips, Allison J; Leger, Elizabeth A

2015-01-01

• The ability to respond to environmental change via phenotypic plasticity may be important for plants experiencing disturbances such as climate change and plant invasion. Responding to belowground competition through root plasticity may allow native plants to persist in highly invaded systems such as the cold deserts of the Intermountain West, USA.• We investigated whether Poa secunda, a native bunchgrass, could alter root morphology in response to nutrient availability and the presence of a competitive annual grass. Seeds from 20 families were grown with high and low nutrients and harvested after 50 d, and seeds from 48 families, grown with and without Bromus tectorum, were harvested after ∼2 or 6 mo. We measured total biomass, root mass fraction, specific root length (SRL), root tips, allocation to roots of varying diameter, and plasticity in allocation.• Plants had many parallel responses to low nutrients and competition, including increased root tip production, a trait associated with tolerance to reduced resources, though families differed in almost every trait and correlations among trait changes varied among experiments, indicating flexibility in plant responses. Seedlings actively increased SRL and fine root allocation under competition, while older seedlings also increased coarse root allocation, a trait associated with increased tolerance, and increased root mass fraction.• The high degree of genetic variation for root plasticity within natural populations could aid in the long-term persistence of P. secunda because phenotypic plasticity may allow native species to persist in invaded and fluctuating resource environments. © 2015 Botanical Society of America, Inc.

APSR1, a novel gene required for meristem maintenance, is negatively regulated by low phosphate availability.

PubMed

González-Mendoza, Víctor; Zurita-Silva, Andrés; Sánchez-Calderón, Lenin; Sánchez-Sandoval, María Eugenia; Oropeza-Aburto, Araceli; Gutiérrez-Alanís, Dolores; Alatorre-Cobos, Fulgencio; Herrera-Estrella, Luis

2013-05-01

Proper root growth is crucial for anchorage, exploration, and exploitation of the soil substrate. Root growth is highly sensitive to a variety of environmental cues, among them water and nutrient availability have a great impact on root development. Phosphorus (P) availability is one of the most limiting nutrients that affect plant growth and development under natural and agricultural environments. Root growth in the direction of the long axis proceeds from the root tip and requires the coordinated activities of cell proliferation, cell elongation and cell differentiation. Here we report a novel gene, APSR1 (Altered Phosphate Starvation Response1), involved in root meristem maintenance. The loss of function mutant apsr1-1 showed a reduction in primary root length and root apical meristem size, short differentiated epidermal cells and long root hairs. Expression of APSR1 gene decreases in response to phosphate starvation and apsr1-1 did not show the typical progressive decrease of undifferentiated cells at root tip when grown under P limiting conditions. Interestingly, APSR1 expression pattern overlaps with root zones of auxin accumulation. Furthermore, apsr1-1 showed a clear decrease in the level of the auxin transporter PIN7. These data suggest that APSR1 is required for the coordination of cell processes necessary for correct root growth in response to phosphate starvation conceivably by direct or indirect modulation of PIN7. We also propose, based on its nuclear localization and structure, that APSR1 may potentially be a member of a novel group of transcription factors. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.