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1.
Localization and Pattern of Graviresponse across the Pulvinus of Barley Hordeum vulgare 总被引:1,自引:1,他引:0 下载免费PDF全文
Pulvini of excised stem segments from barley (Hordeum vulgare cv `Larker') were pretreated with 1 millimolar coumarin before gravistimulation to reduce longitudinal cell expansion and exaggerate radial cell enlargement. The cellular localization and pattern of graviresponse across individual pulvini were then evaluated by cutting the organ in cross-section, photographing the cross-section, and then measuring pulvinus thickness and the radial width of cortical and epidermal cells in enlargements of the photomicrographs. With respect to orientation during gravistimulation, we designated the uppermost point of the cross-section 0° and the lowermost point 180°. A gravity-induced increase in pulvinus thickness was observable within 40° of the vertical in coumarin-treated pulvini. In upper halves of coumarin-treated gravistimulated pulvini, cells in the inner cortex and inner epidermis had increased radial widths, relative to untreated gravistimulated pulvini. In lower halves of coumarin-treated pulvini, cells in the central and outer cortex and in the outer epidermis showed the greatest increase in radial width. Cells comprising the vascular bundles also increased in radial width, with this pattern following that of the central cortex. These results indicate (a) that all cell types are capable of showing a graviresponse, (b) that the graviresponse occurs in both the top and the bottom of the responding organ, and (c) that the magnitude of the response increases approximately linearly from the uppermost point to the lowermost. These results are also consistent with models of gravitropism that link the pattern and magnitude of the graviresponse to graviperception via statolith sedimentation. 相似文献
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Characterization of gravitropic bending in the maize stem pulvinus, a tissue that functions specifically in gravity responses,
demonstrates that the pulvinus is an ideal system for studying gravitropism. Gravistimulation during the second of three developmental
phases of the pulvinus induces a gradient of cell elongation across the non-growing cells of the pulvinus, with the most elongation
occurring on the lower side. This cell elongation is spatially and temporally separated from normal internodal cell elongation.
The three characterized growth phases in the pulvinus correspond closely to a specialized developmental sequence in which
structural features typical of cells not fully matured are retained while cell maturation occurs in surrounding internodal
and nodal tissue. For example, the lignification of supporting tissue and rearrangement of transverse microtubules to oblique
that occur in the internode when cell elongation ceases are delayed for up to 10 d in the adjacent cells of the pulvinus,
and only occurs as a pulvinus loses its capacity to respond to gravistimulation. Gravistimulation does not modify this developmental
sequence. Neither wall lignification nor rearrangement of transverse microtubules occurs in the rapidly elongating lower side
or non-responsive upper side of the pulvinus until the pulvinus loses the capacity to bend further. Gravistimulation does,
however, lead to the formation of putative pit fields within the expanding cells of the pulvinus.
Received: 18 April 1998 / Accepted: 2 July 1998 相似文献
4.
The development of the leaf-sheath pulvinus of oat (Avena sativa L. cv. Victory) was studied in terms of its competency to respond to gravistimulation. Stages of onset of competency, maximum competency and loss of competency were identified, using the length of the supertending internode as a developmental marker. During the early phases in the onset of competency, the latency period between stimulus and graviresponse decreased and the steady state response rate increased significantly. When fully competent, the latency period remained constant as the plant continued to develop, suggesting that the latency period is relatively insensitive to quantitative changes (e.g., in carbohydrate or nutrient availability) at the cell level within the plant. In contrast, the response rate was found to increase with plant development, indicating that graviresponse rate is more strongly influenced by quantitative cellular changes. The total possible graviresponse of a single oat pulvinus was confirmed to be significantly less than the original presentation angle. This was shown to not result from a loss of competency, since the graviresponse could be reinitiated by increasing the presentation angle. As a result of the low overall graviresponse of individual pulvini, two or more pulvini are required to bring the plant apex to the vertical. This was determined to occur though the sequential, rather than simultaneous, action of successive pulvini, since a given pulvinus lost competency to gravirespond shortly after the next pulvinus became fully competent. 相似文献
5.
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. 相似文献
6.
Cell wall and enzyme changes during the graviresponse of the leaf-sheath pulvinus of oat (Avena sativa) 下载免费PDF全文
Gibeaut DM Karuppiah N Chang S-R Brock TG Vadlamudi B Kim D Ghosheh NS Rayle DL Carpita NC Kaufman PB 《Plant physiology》1990,94(2):411-416
The graviresponse of the leaf-sheath pulvinus of oat (Avena sativa) involves an asymmetric growth response accompanied by several asymmetric processes, including degradation of starch and cell wall synthesis. To understand further the cellular and biochemical events associated with the graviresponse, changes in cell walls and their constituents and the activities of related enzymes were investigated in excised pulvini. Asymmetric increases in dry weight with relatively symmetric increases in wall weight accompanied the graviresponse. Starch degradation could not account for increases in wall weight. However, a strong asymmetry in invertase activity indicated that hydrolysis of exogenous sucrose could contribute significantly to the increases in wall and dry weights. Most cell wall components increased proportionately during the graviresponse. However, beta-D-glucan did not increase symmetrically, but rather increased in proportion in lower halves of gravistimulated pulvini. This change resulted from an increase in glucan synthase activity in lower halves. The asymmetry of beta-D-glucan content arose too slowly to account for initiation of the graviresponse. A similar pattern in change in wall extensibility was also observed. Since beta-D-glucan was the only wall component to change, it is hypothesized that this change is the basis for the change in wall extensibility. Since wall extensibility changed too slowly to account for growth initiation, it is postulated that asymmetric changes in osmotic solutes act as the driving factor for growth promotion in the graviresponse, while wall extensibility acts as a limiting factor during growth. 相似文献
7.
In higher plants, stems and roots show negative and positive gravitropism, respectively. However, current knowledge on the graviresponse of leaves is lacking. In this study, we analyzed the positioning and movement of rosette leaves of Arabidopsis thaliana under light and dark conditions. We found that the radial positioning of rosette leaves was not affected by the direction of gravity under continuous white light. In contrast, when plants were shifted to darkness, the leaves moved upwards, suggesting negative gravitropism. Analysis of the phosphoglucomutase and shoot gravitropism 2-1 mutants revealed that the sedimenting amyloplasts in the leaf petiole are important for gravity perception, as is the case in stems and roots. In addition, our detailed physiological analyses revealed a unique feature of leaf movement after the shift to darkness, i.e. movement could be divided into negative gravitropism and nastic movement. The orientation of rosette leaves is ascribed to a combination of these movements. 相似文献
8.
Determinations of pectin methylesterase in abscission zonesand surrounding parts of Phaseolus leaves have shown a relativelyhigh activity in young tissues, which decreases as the leafgrows older. The greatest fall occurs in the pulvinus. In non-senescent leaves, the enzyme activity is higher in pulvinithan elsewhere and there is a gradient of activity across theline of abscission from the pulvinus to the petiole or stem.During senescence this gradient falls, and is generally reversedat abscission. Data suggest that the advent of abscission maybe linked to the steepness of this gradient. If abscission of leaves or isolated abscission zones is acceleratedby appropriate treatments there is a more rapid decrease inpectin methylesterase activity than in the controls, and a morerapid fall in the gradient across the line of abscission. Ifabscission is retarded the enzyme activity is sustained andthe gradient is maintained or increased. The results are discussed in relation to the changes that mayoccur in the pectic constituents of cell walls during senescenceand abscission, and in relation to some of the known effectsof auxins on pectin metabolism. 相似文献
9.
The microtubule cytoskeleton does not integrate auxin transport and gravitropism in maize roots 总被引:5,自引:0,他引:5
The Cholodny-Went hypothesis of gravitropism suggests that the graviresponse is controlled by the distribution of auxin. However, the mechanism of auxin transport during the graviresponse of roots is still unresolved. To determine whether the microtubule (MT) cytoskeleton is participating in auxin transport, the cytoskeleton was examined and the movement of 3 H-IAA measured in intact and excised taxol, oryzalin, and naphthylphthalamic acid (NPA)-treated roots of Zea mays cv. Merit. Taxol and oryzalin did not inhibit the graviresponse of roots but the auxin transport inhibitor NPA greatly inhibited both auxin transport and graviresponse. NPA had no effect on MT organization in vertical roots, but caused MT reorientation in horizontally placed roots. Regardless of treatment, the organization of MTs in intact roots differed from that in root segments. The MT inhibitors, taxol and oryzalin had opposite effects on the MTs, namely, depolymerization (oryzalin) and stabilization and thickening (taxol), but both treatments caused swelling of the roots. The data indicate that the MT cytoskeleton does not directly interfere with auxin transport or auxin-mediated growth responses in maize roots. 相似文献
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Phototropism and gravitropism in lateral roots of Arabidopsis 总被引:4,自引:0,他引:4
Gravitropism and, to a lesser extent, phototropism have been characterized in primary roots, but little is known about structural/functional aspects of these tropisms in lateral roots. Therefore, in this study, we report on tropistic responses in lateral roots of Arabidopsis thaliana. Lateral roots initially are plagiogravitropic, but when they reach a length of approximately 10 mm, these roots grow downward and exhibit positive orthogravitropism. Light and electron microscopic studies demonstrate a correlation between positive gravitropism and development of columella cells with large, sedimented amyloplasts in wild-type plants. Lateral roots display negative phototropism in response to white and blue light and positive phototropism in response to red light. As is the case with primary roots, the photoresponse is weak relative to the graviresponse, but phototropism is readily apparent in starchless mutant plants, which are impaired in gravitropism. To our knowledge, this is the first report of phototropism of lateral roots in any plant species. 相似文献
12.
Altered Growth Response to Exogenous Auxin and Gibberellic Acid by Gravistimulation in Pulvini of Avena sativa 总被引:3,自引:3,他引:0 下载免费PDF全文
Pulvini of excised segments from oats (Avena sativa L. cv Victory) were treated unilaterally with indoleacetic acid (IAA) or gibberellic acid (GA3) with or without gravistimulation to assess the effect of gravistimulation on hormone action. Optimum pulvinus elongation growth (millimeters) and segment curvature (degrees) over 24 hours were produced by 100 micromolar IAA in vertical segments. The curvature response to IAA at levels greater than 100 micromolar, applied to the lower sides of gravistimulated (90°) pulvini, was significantly less than the response to identical levels in vertical segments. Furthermore, the bending response of pulvini to 100 micromolar IAA did not vary significantly over a range of presentation angles between 0 and 90°. In contrast, the response to IAA at levels less than 10 micromolar, with gravistimulation, was approximately the sum of the responses to gravistimulation alone and to IAA without gravistimulation. This was observed over a range of presentation angles. Also, GA3 (0.3-30 micromolar) applied to the lower sides of horizontal segments significantly enhanced pulvinus growth and segment curvature, although exogenous GA3 over a range of concentrations had no effect on pulvinus elongation growth or segment curvature in vertical segments. The response to GA3 (10 micromolar) plus IAA (1.0 or 100 micromolar) was additive for either vertical or horizontal segments. These results indicate that gravistimulation produces changes in pulvinus responsiveness to both IAA and GA3 and that the changes are unique for each growth regulator. It is suggested that the changes in responsiveness may result from processes at the cellular level other than changes in hormonal sensitivity. 相似文献
13.
Gravitropism is explained by the Cholodny–Went hypothesis: the basipetal flow of auxin is diverted laterally. The resulting
lateral auxin gradient triggers asymmetric growth. However, the Cholodny–Went hypothesis has been questioned repeatedly because
the internal auxin gradient is too small to account for the observed growth asymmetry. Therefore, an additional gradient in
indolyl-3-acetic acid (IAA) sensitivity has been suggested (Brauner and Hager in Planta 51:115–147, 1958). We challenged the
Cholodny–Went hypothesis for gravitropism of rice coleoptiles (Oryza sativa L.) and found it to be essentially true. However, we observed, additionally, that the two halves of gravitropically stimulated
coleoptiles responded differentially to the same amount of exogenous auxin: the auxin response is reduced in the upper flank
but normal in the lower flank. This indicates that the auxin-gradient is amplified by a gradient of auxin responsiveness.
Hormone contents were measured across the coleoptile by a GC-MS/MS technique and a gradient of jasmonate was detected opposing
the auxin gradient. Furthermore, the total content of jasmonate increased during the gravitropic response. Jasmonate gradient
and increase persist even when the lateral IAA gradient is inhibited by 1-N-naphtylphtalamic acid. Flooding with jasmonate delays the onset of gravitropic bending. Moreover, a jasmonate-deficient rice
mutant bends more slowly and later than the wild type. We discuss a role of jasmonate as modulator of auxin responsiveness
in gravitropism. 相似文献
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The role of hormones in mediating tropic responses has been a central question in plant biology. Another key issue concerns how interactions between hormones regulate plant responses. In the September 2007 issue of Physiologia Plantarum, we published a paper relevant to both these questions.1 This paper focuses on gravitropism in the barley leaf sheath pulvinus. The results support the Cholodny-Went theory on hormones and tropic responses, and highlight how an environmental factor (gravity) appears to first affect auxin content and consequently that of bioactive gibberellins (GAs). It appears that while GAs do not actually trigger the gravitropic bending of barley pulvini, they do act to magnify the bending response.Key words: auxin, gibberellin, Cholodny-Went theory, barley, pulvinus, gravitropism, mutant 相似文献
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Jonathan D. B. Weyers Neil W. Paterson Richard A'Brook Zhi-Yong Peng 《Physiologia plantarum》1995,95(3):486-494
We highlight the need to combine information about hormone concentrations and tissue sensitivity when assessing control of physiological phenomena by plant hormones. A quantitative approach to this problem is suggested and the method illustrated using data for stomatal closure induced by abscisic acid. The technique requires accurate estimates of hormone concentration at the putative site of action and information about the kinetics of responses in the form of dose-response curves obtained under relevant conditions. Extending this approach, hormonal control is seen as relative, in that it must be considered against a background of other controlling influences. Possible means of evaluating this 'control potential' from dose-response curves are discussed. Finally, we draw together the above in an analytical framework for assessing hormonal control. This involves (1) matching observed and predicted responses; (2) studying effects of manipulating hormone concentration or sensitivity; and (3) assessing the relative control potential of the compound of interest. 相似文献
18.
Terrestrial plants have evolved remarkable morphological plasticity that enables them to adapt to their surroundings. One
of the most important traits that plants have acquired is the ability to sense environmental cues and use them as a basis
for governing their growth orientation. The directional growth of plant organs relative to the direction of environmental
stimuli is a tropism. The Cholodny–Went theory proposes that auxin plays a key role in several tropisms. Recent molecular
genetic studies have strongly supported this hypothesis for gravitropism. However, the molecular mechanisms of other tropisms
are far less clear. Hydrotropism is the response of roots to a moisture gradient. Since its re-discovery in 1985, root hydrotropism
has been shown to be common among higher plant species. Additionally, in some species, gravitropism interferes with hydrotropism,
suggesting that both shared and divergent mechanisms mediating the two tropisms exist. This hypothesis has been supported
by recent studies, which provide an understanding of how roots sense multiple environmental cues and exhibit different tropic
responses. In this review, we focus on the overlapping and unique mechanisms of the hormonal regulation underlying gravitropism
and hydrotropism in roots. 相似文献
19.
The growth direction of the Arabidopsis (Arabidopsis thaliana) etiolated-seedling hypocotyl is a complex trait that is controlled by extrinsic signals such as gravity and touch as well as intrinsic signals such as hormones (brassinosteroid [BR], auxin, cytokinin, ethylene) and nutrient status (glucose [Glc], sucrose). We used a genetic approach to identify the signaling elements and their relationship underlying hypocotyl growth direction. BR randomizes etiolated-seedling growth by inhibiting negative gravitropism of the hypocotyls via modulating auxin homeostasis for which we designate as reset, not to be confused with the gravity set point angle. Cytokinin signaling antagonizes this BR reset of gravity sensing and/or tropism by affecting ethylene biosynthesis/signaling. Glc also antagonizes BR reset but acts independently of cytokinin and ethylene signaling pathways via inhibiting BR-regulated gene expression quantitatively and spatially, by altering protein degradation, and by antagonizing BR-induced changes in microtubule organization and cell patterning associated with hypocotyl agravitropism. This BR reset is reduced in the presence of the microtubule organization inhibitor oryzalin, suggesting a central role for cytoskeleton reorganization. A unifying and hierarchical model of Glc and hormone signaling interplay is proposed. The biological significance of BR-mediated changes in hypocotyl graviresponse lies in the fact that BR signaling sensitizes the dark-grown seedling hypocotyl to the presence of obstacles, overriding gravitropism, to enable efficient circumnavigation through soil. 相似文献
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On the Nature and Origin of the Calcium Asymmetry Arising during Gravitropic Response in Etiolated Pea Epicotyls 总被引:2,自引:0,他引:2 下载免费PDF全文
Seven day old etiolated pea epicotyls were loaded symmetrically with 3H-indole 3-acetic acid (IAA) or 45Ca2+, then subjected to 1.5 hours of 1g gravistimulation. Epidermal peels taken from top and bottom surfaces after 90 minutes showed an increase in IAA on the lower side and of Ca2+ on the upper side. Inhibitors of IAA movement (TIBA, 9-hydroxyfluorene carboxylic acid) block the development of both IAA and Ca2+ asymmetries, but substances known to interfere with normal Ca2+ transport (nitrendipine, nisoldipine, Bay K 8644, A 23187) do not significantly alter either IAA or Ca2+ asymmetries. These substances, however, are active in modifying both Ca2+ uptake and efflux through oat and pea leaf protoplast membranes. We conclude that the 45Ca2+ fed to pea epicotyls occurs largely in the cell wall, and that auxin movement is primary and Ca2+ movement secondary in gravitropism. We hypothesize that apoplastic Ca2+ changes during graviresponse because it is displaced by H+ secreted through auxin-induced proton release. This proposed mechanism is supported by localized pH experiments, in which filter paper soaked in various buffers was applied to one side of a carborundum-abraded epicotyls. Buffer at pH 3 increases calcium loss from the side to which it is applied, whereas pH 7 buffer decreases it. Moreover, 10 micromolar IAA and 1 micromolar fusicoccin, which promote H+ efflux, increase Ca2+ release from pea epicotyl segments, whereas cycloheximide, which inhibits H+ efflux, has the reverse effect. We suggest that Ca2+ does not redistribute actively during gravitropism: the asymmetry arises because of its release from the wall adjacent to the region of high IAA concentration, proton secretion, and growth. Thus, the asymmetric distribution of Ca2+ appears to be a consequence of growth stimulation, not a critical step in the early phase of the graviresponse. 相似文献