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1.
Water Relations in Pulvini from Samanea saman: I. Intact Pulvini   总被引:3,自引:3,他引:0       下载免费PDF全文
Gorton HL 《Plant physiology》1987,83(4):945-950
The movement of Samanea leaflets depends upon changes in the curvature of the pulvinus at the base of each leaflet. Pulvinar bending and straightening, in turn, are driven by the movement of water between opposing (extensor and flexor) sides of the pulvinus. Although water movement depends on water potential (Ψ) and thus on osmotic potential (π) and hydrostatic pressure (P), none of these parameters have been measured in Samanea. In this investigation, Ψ and π were measured and P was calculated for extensor and flexor tissues of excised, whole pulvini that were open in the light and closed in the dark. In fully open pulvini, π in the extensor was generally between 800 and 1000 milliosmol per kilogram and exceeded π in the flexor by 300 to 450 milliosmol per kilogram. In fully closed pulvini the reverse was true, with π in the flexor between 800 and 1000 milliosmol per kilogram, exceeding π in the extensor by 300 to 450 milliosmol per kilogram. To obtain approximate values of Ψ of pulvinar tissues, shallow cuts in extensor and flexor sides of oil-covered pulvini were filled with droplets of polyethylene glycol solutions of known Ψ. Droplets maintaining constant size were assumed to have the same Ψ as the tissue. Extensor and flexor halves of open pulvini had very different Ψ (extensor, about −1.4 MPa; flexor, about −0.3 MPa), but both sides of closed pulvini had similar Ψ (about −0.3 MPa). Measurements of Ψ and π and calculations of P indicate: (a) In open pulvini, P is about the same in extensor and flexor. The large Ψ gradient is caused by a large osmotic gradient. (b) In closed pulvini, P is approximately 50% higher in the flexor than in the extensor. This difference in P compensates for differences in π such that the Ψ gradient is small. (c) Pulvini close as P increases in the flexor and reopen as flexor P decreases; extensor P values are similar in open and closed pulvini.  相似文献   

2.
Protoplasts were isolated from extensor and flexor regions of open pulvini of the nyctinastic tree Samanea saman. Both types of protoplasts undergo many changes during isolation. Extensor protoplasts are univacuolate in vivo, but some become multivacuolate. All flexor protoplasts are univacuolate. In an open pulvinus, extensor cells have a higher osmotic pressure than flexor cells. However, both types of protoplasts can be isolated with optimal yield using the same osmoticum (0.5 molar sorbitol) in the digestion medium. This suggests that some leakage of osmoticum occurs during harvest or digestion, especially from extensor tissue. Despite these changes, both types of protoplasts extrude protons in response to 10 micromolar fusicoccin (1.6-1.8 nanoequivalent/106 protoplasts/minute), demonstrating that the protoplasts are metabolically active and that proton transport mechanisms must be at least partially functional. The changes in vacuolar structure and osmotic pressure are what one might expect if the protoplasts, which are isolated from open pulvini, take on characteristics of cells in a closed pulvinus.  相似文献   

3.
Concentrations of K, Cl, P, S, and Ca in extensor and flexor protoplasts from open pulvini of the nyctinastic tree Samanea saman were estimated using x-ray microanalysis. This technique is particularly suitable when absolute numbers of protoplasts are low, because less than 100 protoplasts are required to obtain statistically significant data. Flexor protoplasts contain similar concentrations of P and S but almost twice as much K and Cl as extensor protoplasts. Low levels of total measurable osmoticum suggest that extensive leakage has occurred during protoplast isolation. Both extensor and flexor protoplasts appear to contain some unidentified osmoticum not detectable by x-ray analysis. Extensor protoplasts must have more unidentified osmoticum to compensate for their lower levels of K and Cl.  相似文献   

4.
Samanea leaflets usually open in white light and fold together when darkened, but also open and dose with a circadian rhythm during prolonged darkness. Leaflet movement results from differential changes in the turgor and shape of motor cells on opposite sides of the pulvinus; extensor cells expand during opening and shrink during closure, while flexor cells shrink during opening and expand during closure but change shape more than size. Potassium in both open and closed pulvini is about 0.4 N. Flame photometric and electron microprobe analyses reveal that rhythmic and light-regulated postassium flux is the basis for pulvinar turgor movements. Rhythmic potassium flux during darkness in motor cells in the extensor region involves alternating predominance of inwardly directed ion pumps and leakage outward through diffusion channels, each lasting ca 12 h. White light affects the system by activating outwardly directed K+ pumps in motor cells in the flexor region.  相似文献   

5.
Kim HY  Coté GG  Crain RC 《Plant physiology》1992,99(4):1532-1539
Rhythmic light-sensitive movements of the leaflets of Samanea saman depend upon ion fluxes across the plasma membrane of extensor and flexor cells in opposing regions of the leaf-movement organ (pulvinus). We have isolated protoplasts from the extensor and flexor regions of S. saman pulvini and have examined the effects of brief 30-second exposures to white, blue, or red light on the relative membrane potential using the fluorescent dye, 3,3′-dipropylthiadicarbocyanine iodide. White and blue light induced transient membrane hyperpolarization of both extensor and flexor protoplasts; red light had no effect. Following white or blue light-induced hyperpolarization, the addition of 200 millimolar K+ resulted in a rapid depolarization of extensor, but not of flexor protoplasts. In contrast, addition of K+ following red light or in darkness resulted in a rapid depolarization of flexor, but not of extensor protoplasts. In both flexor and extensor protoplasts, depolarization was completely inhibited by tetraethylammonium, implicating channel-mediated movement of K+ ions. These results suggest that K+ channels are closed in extensor plasma membranes and open in flexor plasma membranes in darkness and that white and blue light, but not red light, close the channels in flexor plasma membranes and open them in extensor plasma membranes. Vanadate treatment inhibited hyperpolarization in response to blue or white light, but did not affect K+ -induced depolarization. This suggests that white or blue light-induced hyperpolarization results from activation of the H+ -ATPase, but this hyperpolarization is not the sole factor controlling the opening of K+ channels.  相似文献   

6.
The structure of the secondary pulvinus of Robinia pseudoacacia has been examined together with ultrastructural features of motor cells both in open and closed pulvini, to identify ultrastructural changes associated with leaflet movement. Pulvini have a central vascular core bordered by thick-walled collenchyma cells, which in turn are surrounded by several layers of cortical parenchyma cells. Cortical motor cells exhibit ultrastructural features similar to those reported in homologous cells of other pulvini. The vacuolar compartment contains two kinds of vacuoles: nontannin vacuoles, which change both in number and size during leaflet movement, and tannin vacuoles, which may act as an ion reservoir. No differences in wall thickness were found between flexor and extensor motor cells. Thick walls of collenchyma cells show numerous pits with plasmodesmata through which the phloem parenchyma cells and the inner cortical motor cells are connected. Tannin vacuoles and calcium oxalate crystals are common inclusions of phloem parenchyma cells. The tissue arrangement and the occurrence of pits with plasmodesmata in the central cylinder cells provide evidence of symplastic continuity through the central cylinder between the extensor and flexor regions of the motor organs. The greater amplitude of Robinia leaflet movements may be related to the extension of motor regions, the scarcity of lignification in the central vascular core, and the thin flexor walls.  相似文献   

7.
Transverse sections of Albizzia pulvinules were examined with an electron microprobe to determine ion fluxes associated with turgorcontrolled leaflet movements. K+ and Cl concentrations are high in the flexor and low in the extensor region of closed pulvini. Both ions migrate out of the flexor and into the extensor during opening as previously described for K+. The distribution of these elements is significantly correlated in each phase of the rhythmic cycle examined, but only 50 to 60% of the ionic charge of potassium is balanced by chloride. This value increases to 65 to 85% if one considers only the mobile fraction of the potassium.  相似文献   

8.
The initiation of radicle growth during seed germination may be driven by solute accumulation and increased turgor pressure, by cell wall relaxation, or by weakening of tissues surrounding the embryo. To investigate these possibilities, imbibition kinetics, water contents, and water (Ψ) and solute (ψs) potentials of intact muskmelon (Cucumis melo L.) seeds, decoated seeds (testa removed, but a thin perisperm/endosperm envelope remains around the embryo), and isolated cotyledons and embryonic axes were measured. Cotyledons and embryonic axes excised and imbibed as isolated tissues attained water contents 25 and 50% greater, respectively, than the same tissues hydrated within intact seeds. The effect of the testa and perisperm on embryo water content was due to mechanical restriction of embryo swelling and not to impermeability to water. The Ψ and ψs of embryo tissues were measured by psychrometry after excision from imbibed intact seeds. For intact or decoated seeds and excised cotyledons, Ψ values were >−0.2 MPa just prior to radicle emergence. The Ψ of excised embryonic axes, however, averaged only −0.6 MPa over the same period. The embryonic axis apparently is mechanically constrained within the testa/perisperm, increasing its total pressure potential until axis Ψ is in equilibrium with cotyledon Ψ, but reducing its water content and resulting in a low Ψ when the constraint is removed. There was no evidence of decreasing ψs or increasing turgor pressure (Ψ-ψs) prior to radicle growth for either intact seeds or excised tissues. Given the low relative water content of the axes within intact seeds, cell wall relaxation would be ineffective in creating a Ψ gradient for water uptake. Rather, axis growth may be initiated by weakening of the perisperm, thus releasing the external pressure and creating a Ψ gradient for water uptake into the axis. The perisperm envelope contains a cap of small, thin-walled endosperm cells adjacent to the radicle tip. We hypothesize that weakening or separation of cells in this region could initiate radicle expansion.  相似文献   

9.
Leaflet movements in Samanea saman (Jacq.) Merrill are driven by fluxes of K+, anions, and water through membranes of motor cells in the pulvinus (R.L. Satter et al., 1974, J. Gen. Physiol. 64, 413–430). Extensor cells take up K+ and swell in white light (WL) while flexor cells take up K+ and swell in darkness (D). Excised strips of extensor and flexor motor tissue acidify their bathing medium under conditions that normally promote increase in K+ in the intact tissue, and alkalize the medium under conditions that normally induce decrease in K+ (A. Iglesias and R.L. Satter, 1983, Plant Physiol. 72, 564). To obtain information on pH changes in the whole pulvinus, we measured effects of light on pH of the apoplast, using liquid membrane microelectrodes sensitive to H+. We report the following: (1) The pH of the extensor apoplast was higher than that of the flexor apoplast in WL and in D (pH gradient of 1.0 units in WL and 2.0 units in D). Apoplastic pH might affect K+ transport through the plasma membranes of Samanea motor cells, since the conductance, gating, and selectivity of ionic channels in other systems depend upon external pH. (2) Extensor cells acidified and flexor cells alkalized their environment in response to irradiation with WL, while the reverse changes occurred in response to D. These results are consistent with the results of Iglesias and Satter (1983), and support the physiological relevance of data obtained with excised tissue. (3) The pH changes in response to irradiation with red light were similar to those obtained with D; also, the pH changes in response to blue light were similar to those obtained with WL. The pulvinus closed in red light as in darkness and opened in WL, but failed to open in blue light. The advantages and limitations of apoplastic pH measurements for assaying H+ transport are discussed.Abbreviations BL blue light - D darkness - RL red light - WL white light  相似文献   

10.
Summary. We have analysed the incorporation of [3H]sucrose and [3H]mannitol in pulvinar motor cells of Robinia pseudoacacia L. during phytochrome-mediated nyctinastic closure. Pairs of leaflets, excised 2 h after the beginning of the photoperiod, were fed with 50 mM [3H]sucrose or [3H]mannitol, irradiated with red (15 min) or far-red (5 min) light and placed in the dark for 2–3 h. Label uptake was measured in whole pulvini by liquid scintillation counting. The distribution of labelling in pulvinar sections was assessed by both light and electron microautoradiography. [3H]Sucrose uptake was twice that of [3H]mannitol incorporation in both red- and far-red-irradiated pulvini. In the autoradiographs, [3H]sucrose and [3H]mannitol labelling was localised in the area from the vascular bundle to the epidermis, mainly in vacuoles, cytoplasm, and cell walls. Extensor and flexor protoplasts displayed a different distribution of [3H]sucrose after red and far-red irradiation. Far-red light drastically reduced the [3H]sucrose incorporation in extensor protoplasts and caused a slight increase in internal flexor protoplasts. After red light treatment, no differences in [3H]sucrose labelling were found between extensor and flexor protoplasts. Our results indicate a phytochrome control of sucrose distribution in cortical motor cells and seem to rule out the possibility of sucrose acting as an osmoticum. Correspondence and reprints: Unidad de Fisiología Vegetal, Facultad de Biología, Universidad de Barcelona, Avenida Diagonal 645, 08028 Barcelona, Spain.  相似文献   

11.
Leaflet movements in Samanea saman are driven by the shrinking and swelling of cells in opposing (extensor and flexor) regions of the motor organ (pulvinus). Changes in cell volume, in turn, depend upon large changes in motor cell content of K+, Cl and other ions. We performed patch-clamp experiments on extensor and flexor protoplasts, to determine whether their plasma membranes contain channels capable of carrying the large K+ currents that flow during leaflet movement. Recordings in the “whole-cell” mode reveal depolarization-activated K+ currents in extensor and flexor cells that increase slowly (t½ = ca. 2 seconds) and remain active for minutes. Recordings from excised patches reveal a single channel conductance of ca. 20 picosiemens in both cell types. The magnitude of the K+ currents is adequate to account quantitatively for K+ loss, previously measured in vivo during cell shrinkage. The K+ channel blockers tetraethylammonium (5 millimolar) or quinine (1 millimolar) blocked channel opening and decreased light- and dark-promoted movements of excised leaflets. These results provide evidence for the role of potassium channels in leaflet movement.  相似文献   

12.
Leaflet movements in the legume Samanea saman are dependent upon massive redistribution of potassium (K), chloride (Cl), and other solutes between opposing (extensor and flexor) halves of the motor organ (pulvinus). Solutes are known to diffuse through the apoplast during redistribution. To test the possibility that solute diffusion might be restricted by apoplastic barriers, we analyzed elements in the apoplast in freeze-dried cryosections of pulvini using scanning electron microscopy/x-ray microanalysis. Large discontinuities in apoplastic K and Cl at the extensor-flexor interface provide evidence for a barrier to solute diffusion. The barrier extends from the epidermis on upper and lower sides of the pulvinus to cambial cells in the central vascular core. It is completed by hydrophobic regions between phloem and cambium, and between xylem rays and surrounding vascular tissue, as deduced by discontinuities in apoplastic solutes and by staining of fresh sections with lipid-soluble Sudan dyes. Thus, symplastic pathways are necessary for ion redistribution in the Samanea pulvinus during leaflet movement. In pulvini from leaflets in the closed state, all cells on the flexor side of the barrier have high internal as well as external K and Cl, whereas cells on the extensor side have barely detectable internal or external K or Cl. Approximately 60% of these ions are known to migrate to the extensor during opening; all return to the flexor during subsequent closure. We propose that solutes lost from shrinking cells in the outer cortex diffuse through the apoplast to plasmodesmata-rich cells of the inner cortex, collenchyma, and phloem; and that solutes cross the barrier by moving through plasmodesmata.  相似文献   

13.
Lee Y  Satter RL 《Plant physiology》1987,83(4):856-862
We investigated H+ fluxes during circadian rhythmic movements of Samanea saman leaflets by monitoring the pH of a weakly buffered medium bathing extensor or flexor motor tissue excised at different times during 51 hours of darkness. Experiments were made in media of two different osmotic potentials: −0.3 megapascal (control medium) and −1.2 megapascals (control medium supplemented with 0.4 molar mannitol or sorbitol). Both extensor and flexor tissue took up H+ from the control medium at all times when the initial pH was 5.5. Rates of uptake by the extensor varied rhythmically in phase with the leaflet movement rhythm, whereas rates for the flexor were similar at all times. Addition of 0.4`molar mannitol (or sorbitol) to the medium magnified the amplitude of the rhythm in H+ uptake and release by extensor tissue and revealed a rhythm with flexor tissue. In the flexor, mannitol promoted H+ release (or reduced H+ uptake) at all times. We propose that mannitol reduces flexor cell turgor, and that low turgor activates the H+ pump. The magnitude and/or direction of pH changes varied with the initial pH of the medium. The pH values after 60 minutes converged to a narrow range, suggesting that cell wall pH might be regulated.  相似文献   

14.
We used quantitative histochemistry to investigate the tissue-specific compartmentation of potassium in the laminar pulvinus of Phaseolus coccineus L. at day and night positions of diurnal leaf movement. The assay was based on the potassium-dependent activation of pyruvate kinase. Total potassium levels of pulvini were higher in the light than in the dark [0.88 and 0.57mol (kg dry weight)?1, respectively]. Transverse compartmentation of potassium was studied on three tissue slices, representing the middle part, petiolar and laminar sides of individual pulvini. These were dissected further into 10 distinct subsamples (bundle; motor tissues: extensor, flexor; flanks). In the day position the amount of potassium in the extensor was higher than in the night position [1.92 and 1.50 mol (kg dry weight)?1, respectively]. Flexor changes were opposite [1.13 and 1.65 mol (kg dry weight)?1, respectively]. In the day position there was a steep and consistent increase in potassium content from the innermost to the outermost zones of the extensor. In the night position this was much more variable. Comparable gradients were not detected in flexor samples. Here highest amounts of potassium were recovered from the middle of the motor tissue. The data specify distinct tissue regions involved in osmotic adjustment during leaf movement in Phaseolus coccineus.  相似文献   

15.
Summary Paired leaflets ofAlbizzia julibrissin spread apart (open) in the daytime and fold together (close) at night. We examined the structure of cells in open and closedAlbizzia motor organs (pulvini) to identify reversible changes in structure associated with motility. Pulvini were fixed in glutaraldehyde and stained using conventional methods. The pulvinus has a central vascular cylinder bordered by thick-walled collenchyma cells, in turn surrounded by an endodermis and many layers of cortical parenchyma. Cortical cells in the extensor undergo large changes in shape during leaflet closure linked with: formation of wall infoldings, development of a large periplasmic space filled with fibrils and membranes, development of lobes on the nucleus, evagination of the nuclear outer envelope membrane, break-up of the large central vacuole to form many small vacuoles, and linking of the plasmalemma to inner regions of the cytoplasm by microfilaments. Cortical cells in the flexor, by contrast, remain relatively stable during leaflet movement. Microtubules are present near the plasmalemma in both extensor and flexor cells; in the extensor, spherical coated vesicles are located near the microtubules. The possible function of these structures in regulating intracellular shuttling processes is discussed.  相似文献   

16.
Changes in shape and size of Robinia pulvinar cortical cellsin relation to leaflet movements have been investigated usingan image processing system applied to drawings of transverseand longitudinal pulvinar sections. Both the size and shapeof cell sections underwent change during movement. The dorsal-leftside region of the cortex has been characterized as the extensorregion which increases turgor during opening. Morphometric changesoccur throughout the cortical motor cells except in the threeor four inner layers. K, Cl, S, and Ca distribution in cellwalls and protoplasts of inner and outer motor cells have beenmeasured with X-ray microanalysis. The distribution patternof K and Cl shows that these ions are mainly responsible forturgor changes. K and Cl were simultaneously depleted in apoplastand protoplast, which suggests that cell walls do not possessa high enough ionic reservoir during Robinia leaflet movements.Ca was always higher in flexor cell walls than in extensor regionsof closed pulvini. This fact could be related to a lower abilityto extend of flexor cells which underwent fewer morphomerticchangrs during movement.  相似文献   

17.
18.
19.
Summary Mature leaves ofMimosa pudica L. or parts of them were exposed to14CO2, and translocation was recorded by macroautoradiography. It was observed that considerable amounts of labelled photoassimilates were accumulated in pulvini when the leaf was stimulated. In non-stimulated leaves, no such accumulation of label was observed.Microautoradiographs of pulvinar regions of the non-stimulated leaf showed14C- label restricted to the phloem. When stimulated, the14C- label was unloaded from the phloem of the pulvini. Labelled photoassimilates appeared most concentrated in the walls of the collenchymatous cells and beyond in the extensor region of the motor cortex. There, label was accumulated in the apoplastic compartments. Stimulation causes a sudden phloem unloading of sucrose, and its accumulation in the apoplast lowers the water potential which eventually exceeds the osmotic potential of the extensor cells of the motor cortex. By removal of cytoplasmic water the motor cells lose turgidity which results in the closing movement of the leaflets, and — some seconds later — in the bending down of the petiole. In late afternoon night-stimulation triggers sucrose unloading in secondary pulvini. During phases of relaxation, labelled material is taken up by motor cells of the extensor, which concomitantly gain turgor.Part of the doctoral dissertation of Jörg Fromm supported by the Deutsche Forschungsgemeinschaft  相似文献   

20.
Legume plants, due to their distinctive botanical characteristics, such as leaf movements, physiological characteristics, such as nitrogen fixation, and their abilities to endure environmental stresses, have important roles in sustainable pastures development. Leaf movement of legume plants is turgor regulated and osmotically active fluxes of ions between extensor and flexor of pulvinus cause this movement. To determine the role of calcium ions in circadian leaf movements of Phaseolus vulgaris L., a radiotracer technique experiment using 45Ca ions were employed. Measurements were taken during circadian leaf movements, and samples were taken from different parts of the leaflet. The 45Ca β-particle activity reduced from leaflet base pulvinus to leaf tip. The pulvinus had the highest activity, while the leaf tip had the lowest. By increase of the ratio of 45Ca β-particle activity within flexor to extensor (Fl/Ex) the midrib-petiole angle, as an indicator of leaf movement, increased linearly during circadian leaf movement (r = 0.86). The 45Ca β-particle activity of Flex/Ext ratio reduced linearly (r = −0.88) toward midnight. In conclusion, it was found that calcium ions accumulation is opposite to the fluxes of osmatically active ions and water movement. Calcium ions accumulate at less negative water potential side of the pulivnus.Key words: pulvinus, extensor, flexor, leaf movement, rhythm, circadian, calcium, Phaseolus vulgaris, radioactive  相似文献   

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