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1.
A new method has been devised in order to allow the rapid determinationof the physiological extensibility () of the cell wall togetherwith the apparent effective turgor (P — Y'). The methodconsists of determining the elongation growth rate of a segmentof pea hypocotyl with an auxanometer and applying a very smallincrease (around 10 kPa) in xylem pressure (jumps) by the xylemperfusion method. The cell turgor pressure is increased by thewater surge from the xylem that is due to the pressure jumpand reaches a new level within a short time. The elongationrate is also increased asymptotically to a new steady-statelevel within a short time. is estimated by simply dividingthe increase in the steady-state growth rate by the increasein perfusion pressure, which is monitored by a pressure transduceror by the increase in turgor pressure measured by a pressureprobe. Minimal length of the time period required to get a newsteady elongation rate is 1.5 min. Therefore, it is possibleto scan continuously the change in by the intermittent applicationof the brief, small pulses of xylem pressure during any experimentaltreatment. The apparent effective turgor P — Y' can becalculated by dividing the initial elongation growth rate by Using this method, we have demonstrated experimentally thenon-linearity of the relationship between elongation rate andturgor (Lockhart mechanical equation). (Received April 26, 1989; Accepted July 17, 1989)  相似文献   

2.
Green PB 《Plant physiology》1968,43(8):1169-1184
The view that the plant cell grows by the yielding of the cell wall to turgor pressure can be expressed in the equation: rate = cell extensibility × turgor. All growth rate responses can in principle be resolved into changes in the 2 latter variables. Extensibility will relate primarily to the yielding properties of the cell wall, turgor primarily to solute uptake or production. Use of this simple relationship in vivo requires that at least 2 of the 3 variables be measured in a growing cell. Extensibility is not amenable to direct measurement. Data on rate and turgor for single Nitella cells can, however, be continuously gathered to permit calculation of extensibility (rate/turgor). Rate is accurately obtained from measurements on time-lapse film. Turgor is estimated in the same cell, to within 0.1 atm or less, by measurement of the ability of the cell to compress gas trapped in the closed end of a capillary the open end of which is in the cell vacuole. The method is independent of osmotic equilibrium. It operates continuously for several days, over a several fold increase in cell length, and has response time of less than one minute. Rapid changes in turgor brought on by changes in tonicity of the medium, show that extensibility, as defined above, is not constant but has a value of zero unless the cell has about 80% of normal turgor. Because elastic changes are small, extensibility relates to growth. Over long periods of treatment in a variety of osmotica the threshold value for extensibility and growth is seen to fall to lower values to permit resumption of growth at reduced turgor. A brief period of rapid growth (5× normal) follows the return to normal turgor. All variables then become normal and the cycle can be repeated. The cell remains essentially at osmotic equilibrium, even while growing at 5× the normal rate. The method has potential for detailed in vivo analyses of “wall softening.”  相似文献   

3.
Treatment of bean (Phaseolus vulgaris L.) seedlings with low levels of salinity (50 or 100 millimolar NaCl) decreased the rate of light-induced leaf cell expansion in the primary leaves over a 3 day period. This decrease could be due to a reduction in one or both of the primary cellular growth parameters: wall extensibility and cell turgor. Wall extensibility was assessed by the Instron technique. Salinity did not decrease extensibility and caused small increases relative to the controls after 72 hours. On the other hand, 50 millimolar NaCl caused a significant reduction in leaf bulk turgor at 24 hours; adaptive decreases in leaf osmotic potential (osmotic adjustment) were more than compensated by parallel decreases in the xylem tension potential and the leaf apoplastic solute potential, resulting in a decreased leaf water potential. It is concluded that in bean seedlings, mild salinity initially affects leaf growth rate by a decrease in turgor rather than by a reduction in wall extensibility. Moreover, longterm salinization (10 days) resulted in an apparent mechanical adjustment, i.e. an increase in wall extensibility, which may help counteract reductions in turgor and maintain leaf growth rates.  相似文献   

4.
The physical mechanism of seed germination and its inhibition by abscisic acid (ABA) in Brassica napus L. was investigated, using volumetric growth (= water uptake) rate (dV/dt), water conductance (L), cell wall extensibility coefficient (m), osmotic pressure (i), water potential (Ψi), turgor pressure (P), and minimum turgor for cell expansion (Y) of the intact embryo as experimental parameters. dV/dt, i, and Ψi were measured directly, while m, P, and Y were derived by calculation. Based on the general equation of hydraulic cell growth [dV/dt = Lm/(L + m) (Δ - Y), where Δ = i - of the external medium], the terms (Lm/(L + m) and i - Y were defined as growth coefficient (kG) and growth potential (GP), respectively. Both kG and GP were estimated from curves relating dV/dt (steady state) to of osmotic test solutions (polyethylene glycol 6000).

During the imbibition phase (0-12 hours after sowing), kG remains very small while GP approaches a stable level of about 10 bar. During the subsequent growth phase of the embryo, kG increases about 10-fold. ABA, added before the onset of the growth phase, prevents the rise of kG and lowers GP. These effects are rapidly abolished when germination is induced by removal of ABA. Neither L (as judged from the kinetics of osmotic water efflux) nor the amount of extractable solutes are affected by these changes. i and Ψi remain at a high level in the ABA-treated seed but drop upon induction of germination, and this adds up to a large decrease of P, indicating that water uptake of the germinating embryo is controlled by cell wall loosening rather than by changes of i or L. ABA inhibits water uptake by preventing cell wall loosening. By calculating Y and m from the growth equation, it is further shown that cell wall loosening during germination comprises both a decrease of Y from about 10 to 0 bar and an at least 10-fold increase of m. ABA-mediated embryo dormancy is caused by a reversible inhibition of both of these changes in cell wall stability.

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5.
HAINES  F. M. 《Annals of botany》1953,17(4):629-639
Turgor depends on the excess pressure inside a cell, not upona reaction between the wall and contents. It is independentof the environmental pressure whereas the total reaction isnot. Turgor pressure is not identical with the reaction, or,unless the effects of the protoplasmic membranes be ignored,with the wall pressure. Changes in turgor pressure can be saidto cause changes in volume, but only when both are actuallysimultaneous results of differential diffusion. The effectsof environmental pressures are considered. Some misconceptionsare discussed and some terms more fully defined.  相似文献   

6.
The sporangiophore of Phycomyces responds to a temporary increase in light intensity with a transient increase in growth rate that begins 2 to 3 minutes after the initiation of the stimulus and continues until approximately the 12th minute. Tensile tests conducted on the stage IVb sporangiophore demonstrate that an increase in mechanical extensibility of the cell wall occurs 2 minutes after the initiation of a light stimulus and continues until approximately the 15th minute. This finding supports the theory that light-stimulated plant cell expansion and rate of expansion is a function of the mechanical extensibility of the cell wall.  相似文献   

7.
The growth rate of hydroponically grown wheat roots was reducedby mannitol solutions of various osmotic pressures. For example,following 24 h exposure to 0·96 MPa mannitol root elongationwas reduced from 1· mm h–1 to 0·1 mm h–1 Mature cell length was reduced from 290 µm in unstressedroots to 100 µm in 0·96 MPa mannitol. This indicatesa reduction in cell production rate from about 4 per h in theunstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4·5 mm in unstressedroots but became shorter as growth ceased in the proximal regionsat higher levels of osmotic stress. The turgor pressure along the apical 5·0 mm of unstressedroots was between 0·5 and 0·6 MPa but declinedto 0·41 MPa over the next 50 mm. Following 24 h in 0·48(200 mol m–3) or 0·72 MPa (300 mol m) mannitol,turgor along the apical 50 mm was indistinguishable from thatof unstressed roots but turgor declined more steeply in theregion 5·10 mm from the tip. At the highest level ofstress (0·96 MPa or 400 mol m–3 mannitol) turgordeclined steeply within the apical 20 mm. Key words: Growth, turgor pressure, wall rheology, osmotic stress, osmotic adjustment  相似文献   

8.
The aim of this work was to test the hypothesis that the reduced growth rate of wheat and barley that results when the roots are exposed to NaCl is due to inadequate turgor in the expanding cells of the leaves. The hypothesis was tested by exposing plants to 100 millimolar NaCl (which reduced their growth rates by about 20%), growing them for 7 to 10 days with their roots in pressure chambers, and applying sufficient pneumatic pressure in the chambers to offset the osmotic pressure of the NaCl, namely, 0.48 megapascals. The results showed that applying the pressure had no sustained effect (relative to unpressurized controls) on growth rates, transpiration rates, or osmotic pressures of the cell sap, in either the fully expanded or currently expanding leaf tissue, of both wheat and barley. The results indicate that the applied pressure correspondingly increased turgor in the shoot although this was not directly measured. We conclude that shoot turgor alone was not regulating the growth of these NaCl-affected plants, and, after discussing other possible influences, argue that a message arising in the roots may be regulating the growth of the shoot.  相似文献   

9.
Growth, Turgor, Water Potential, and Young's Modulus in Pea Internodes   总被引:1,自引:0,他引:1  
The relations between longitudinal growth, Young's modulus, turgor, water potential, and tissue tensions have been studied on growing internodes of etiolated pea seedlings in an attempt to apply some physical concepts to the growth of a well-known plant material. The modulus has been determined by the resonance frequency method and expressed as Etissue It increases nearly proportional to the turgor pressure and is at water saturation more than 50 times higher than at plasmolysis. Etissue is higher in the epidermis than in the ground parenchyma. Indoleacetic acid causes a decrease in Etissue Other properties have been studied on intact and split segments of internodes in solutions of graded mannitol additions. — The following tentative picture of the normal course of the growth has been obtained. Auxin induces growth both in the periphery (epidermis) and in the central core (parenchyma) under a decrease in Etissue This is followed by an increase of Etissue which is independent of auxin but depending upon the turgor pressure. It is assumed to involve internal structural changes of the cell walls of the type of creep. The rapid growth takes place in a dynamic system with a low water potential despite favourable water conditions. Epidermis and parenchyma grow equally rapid without tissue tensions. — Such can be produced artificially by splitting of segments and water uptake. The parenchyma thereby loses its sensitivity to auxin. This is the background of the split stem test for auxin. — Etissue increases when growth is slowing down, probably owing to both synthesis of wall substance and structural changes within the wall. The cells attain a more static condition with Etissue higher in epidermis than in parenchyma. This leads to the normal tissue tensions. — The result agrees with growth according to the multi-net-principle. The cause of the low water potential and low turgor is discussed with reference to the dynamic nature of both growth and water transport and a probably low matric potential of the streaming water. The decrease in Etissue following auxin addition is small but is the net difference between an auxin-induced decrease and an increase through the assumed creep.  相似文献   

10.
Ortega JK 《Plant physiology》1977,60(5):805-806
The sporangiophore of Phycomyces shows a transient response to a double barrier, the avoidance growth response. Tensile tests conducted on the stage IV sporangiophore demonstrate that an increase in mechanical extensibility occurs about a minute after a double barrier stimulus. This change in mechanical extensibility is similar to the one that occurs after a light stimulus. We have concluded that the avoidance stimulus occurs somewhere on the same pathway between the photoreceptor mechanism and the final growth response.  相似文献   

11.
Sai J  Johnson CH 《The Plant cell》2002,14(6):1279-1291
Using transgenic Nicotiana plumbaginifolia seedlings in which the calcium reporter aequorin is targeted to the chloroplast stroma, we found that darkness stimulates a considerable flux of Ca(2+) into the stroma. This Ca(2+) flux did not occur immediately after the light-to-dark transition but began approximately 5 min after lights off and increased to a peak at approximately 20 to 30 min after the onset of darkness. Imaging of aequorin emission confirmed that the dark-stimulated luminescence emanated from chloroplast-containing tissues of the seedling. The magnitude of the Ca(2+) flux was proportional to the duration of light exposure (24 to 120 h) before lights off; the longer the duration of light exposure, the larger the dark-stimulated Ca(2+) flux. On the other hand, the magnitude of the dark-stimulated Ca(2+) flux did not appear to vary as a function of circadian time. When seedlings were maintained on a 24-h light/dark cycle, there was a stromal Ca(2+) burst after lights off every day. Moreover, the waveform of the Ca(2+) spike was different during long-day versus short-day light/dark cycles. The dark-stimulated Ca(2+) flux into the chloroplastidic stroma appeared to affect transient changes in cytosolic Ca(2+) levels. DCMU, an inhibitor of photosynthetic electron transport, caused a significant increase in stromal Ca(2+) levels in the light but did not affect the magnitude of the dark-stimulated Ca(2+) flux. This robust Ca(2+) flux likely plays regulatory roles in the sensing of both light/dark transitions and photoperiod.  相似文献   

12.
Effects of ancymidol (Anc) and gibberellin A3 (GA3) on rootgrowth, osmotic concentration and cell-wall extensibility ofthe root were investigated in the gibberellin-sensitive cultivarof dwarf pea, Little Marvel. Anc strongly suppressed elongationof both shoots and roots in darkness. Although the elongationof shoots of this dwarf cultivar was severely retarded in thelight, it was repressed still further by Anc. GA3 promoted elongationof shoots both in the presence and in the absence of Anc, whereasit reversed suppression of root elongation by Anc. The concentrationof GA3 required for the recovery of root elongation was lowerthan that required for the promotion of shoot elongation. Treatmentwith Anc led to increased thickening of roots with increasednumbers of cells per cross section and lateral expansion ofcells in the cortex. GA3 had little effect on the osmotic concentration of cell sapobtained from root segments. Anc-treated roots did not respondto acid solutions by elongation, whereas GA3-treated roots respondednormally to such solutions. Anc suppressed but GA3 enhancedthe cell-wall extensibility of roots as measured in vivo andin vitro. These results indicate that a low concentration of gibberellinplays a role in normal elongation of roots by maintaining theextensibility of the cell wall in this gibberellin-sensitivedwarf pea. (Received January 17, 1994; Accepted July 15, 1994)  相似文献   

13.
14.
Turgor regulation in two saprophytic hyphal organisms was examined directly with the pressure probe technique. The ascomycete Neurospora crassa, a terrestrial fungi, regulates turgor after hyperosmotic treatments when growing in a minimal medium containing K(+), Mg(2+), Ca(2+), Cl(-), and sucrose. Turgor recovery by N. crassa after hyperosmotic treatment is concurrent with changes in ion transport: hyperpolarization of the plasma membrane potential and a decline in transmembrane ion conductance. In contrast the oomycete Achlya bisexualis, a freshwater hyphal organism, does not regulate turgor after hyperosmotic treatment, although small transient increases in turgor were occasionally observed. We also monitored turgor in both organisms during hypoosmotic treatment and did not observe a turgor increase, possibly due to turgor regulation. Both hyphal organisms grow with similar morphologies, cellular expansion rates and turgor (0.4-0.7 MPa), yet respond differently to osmotic stress. The results do not support the assumption of a universal mechanism of tip growth driven by cell turgor.  相似文献   

15.
Irradiation of white fluorescent light (5 W m2) inhibitedthe growth of Oryza coleoptiles. Light irradiation increasedstress-relaxation parameters of coleoptile cell walls, minimumstressrelaxationtime and relaxation rate, and decreased cellwall extensibility (strain/load). Under light conditions, thecontents of ferulic and diferulic acids ester-linked to thehemicellulosic arabinose residue in cell walls increased andcorrelated with the modification of the cell wall mechanicalproperties. These results suggest that light irradiation enhancesthe formation of diferulic acid bridges in hemicelluloses, makingcell walls mechanically rigid and thus inhibits cell elongationin rice coleoptiles. Also, irrespective of coleoptile age orthe presence of light, the ratio of diferulic acid to ferulicacid was almost constant, suggesting that the rate limitingstep in the formation of diferulic acid bridges in Oryza cellwalls is in the step of feruloylation. (Received September 24, 1991; Accepted December 3, 1991)  相似文献   

16.
Calcineurin is a calcium-activated phosphatase that controls morphogenesis and stress responses in eukaryotes. Fungal pathogens have adopted the calcineurin pathway to survive and effectively propagate within the host. The difficulty in treating fungal infections stems from similarities between pathogen and host eukaryotic cells. Using calcineurin inhibitors such as cyclosporin A or tacrolimus (FK506) in combination with antifungal drugs, including azoles or echinocandins, renders these drugs fungicidal, even towards drug-resistant species or strains, making calcineurin a promising drug target. This article summarizes the current understanding of the calcineurin pathway and its roles in governing the growth and virulence of pathogenic fungi, and compares and contrasts the roles of calcineurin in fungal pathogens that infect humans (Candida albicans and Cryptococcus neoformans) or plants (Magnaporthe oryzae and Ustilago maydis). Further investigation of calcineurin biology will advance opportunities to develop novel antifungal therapeutic approaches and provide insight into the evolution of virulence.  相似文献   

17.
The dependence of stem elongation on solute import was investigated in etiolated pea seedlings (Pisum sativum L. var Alaska) by excising the cotyledons. Stem elongation was inhibited by 60% within 5 hours of excision. Dry weight accumulation into the growing region stopped and osmotic pressure of the cell sap declined by 0.14 megapascal over 5 hours. Attempts to assay phloem transport via ethylenediaminetetraacetate-enhanced exudation from cut stems revealed no effect of cotyledon excision, indicating that the technique measured artifactual leakage from cells. Despite the drop in cell osmotic pressure, turgor pressure (measured directly via a pressure probe) did not decline. Turgor maintenance is postulated to occur via uptake of solutes from the free space, thereby maintaining the osmotic pressure difference across the cell membrane. Cell wall properties were measured by the pressure-block stress relaxation technique. Results indicate that growth inhibition after cotyledon excision was mediated primarily via an increase in the wall yield threshold.  相似文献   

18.
19.
When isometrically contracting muscles are subjected to a quick release followed by a shortening ramp of appropriate speed (V(o)), tension decays from its value at the isometric plateau (P(o)) to <0. 05 P(o) with the same time course as the quick part of the release; thereafter, tension remains at a negligible level for the duration of the shortening ramp. X-ray diffraction data obtained under these conditions provide evidence that 1) at V(o) very few heads form an actomyosin complex, while the number of heads doing so at P(o) is significant; 2) relative to rest the actin filament at V(o) is approximately 0.12% shorter and more twisted, while it is approximately 0.3% longer and less twisted at P(o); and 3) the myosin heads attaching to actin during force development do so against a thin filament compliance of at least 0.646 +/- 0.046% nm per P(o).  相似文献   

20.
Water loss from plants is determined by the aperture of stomatal pores in the leaf epidermis, set by the level of vacuolar accumulation of potassium salt, and hence volume and turgor, of a pair of guard cells. Regulation of ion fluxes across the tonoplast, the key to regulation of stomatal aperture, can only be studied by tracer flux measurements. There are two transport systems in the tonoplast. The first is a Ca2+-activated channel, inhibited by phenylarsine oxide (PAO), responsible for the release of vacuolar K+(Rb+) in response to the “drought” hormone, abscisic acid (ABA). This channel is sensitive to pressure, down-regulated at low turgor and up-regulated at high turgor, providing a system for turgor regulation. ABA induces a transient stimulation of vacuolar ion efflux, during which the flux tracks the ion content (volume, turgor), suggesting ABA reduces the set-point of a control system. The second system, which is PAO-insensitive, is responsible for an ion flux from vacuole to cytoplasm associated with inward water flow following a hypo-osmotic transfer. It is suggested that this involves an aquaporin as sensor, and perhaps also as responder; deformation of the aquaporin may render it ion-permeable, or, alternatively, the deformed aquaporin may signal to an associated ion channel, activating it. Treatment with inhibitors of aquaporins, HgCl2 or silver sulfadiazine, produces a large transient increase in ion release from the vacuole, also PAO-insensitive. It is suggested that this involves the same aquaporin, either rendered directly ion-permeable, or signalling to activate an associated ion channel.  相似文献   

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