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1.
Stahlberg R  Cosgrove DJ 《Planta》1992,187(4):523-531
Excision of the epicotyl base of pea (Pisum sativum L.) seedlings in air results in a fast drop in the growth rate and rapid transient membrane depolarization of the surface cells near the cut. Subsequent immersion of the cut end into solution leads to a rapid, transient rise in the epicotyl growth rate and an acropetally propagating depolarization with an amplitude of about 35 mV and a speed of approx. 1 mm · s–1. The same result can be achieved directly by excision of the pea epicotyl under water. Shape, amplitude and velocity of the depolarization characterize it as a slow-wave potential. These results indicate that the propagating depolarization is caused by a surge in water uptake. Neither a second surge in water uptake (measured as a rapid increase in growth rate when the cut end was placed in air and then back into solution) nor another cut can produce the depolarization a second time. Cyanide suppresses the electrical signal at the treated position without inhibiting its transmission through this area and its development in untreated parts of the epicotyl. The large depolarization and repolarization which occur in the epidermal and subepidermal cells are not associated with changes in cell input resistance. Both results indicate that it is a transient shut-down of the plasma-membrane proton pump rather than large ion fluxes which is causing the depolarization. We conclude that the slow wave potential is spread in the stem via a hydraulic surge occurring upon relief of the negative xylem pressure after the hydraulic resistance of the root has been removed by excision.Abbreviations and Symbols GR growth rate - Px xylem pressure - Rin cell input resistance - SWP slow wave potential - Vm membrane potential - Vs surface potential This work was supported by grants to D.J.C. from the National Science Foundation and the U.S. Department of Energy.  相似文献   

2.
Jorge J. Casal  Harry Smith 《Planta》1988,176(2):277-282
Under continuous white light (WL), extension growth of the first internode in Sinapis alba L. was promoted by low red (R): far-red (FR) ratios reaching the stem and-or the leaves. Conversely, the growth promotion by end-of-day light treatments was only triggered by FR perceived by the leaves and cotyledons, while FR given to the growning internode alone was tatally ineffective. Continuous WL+FR given to the internode was also in-effective if the rest of the shoot remained in darkness. Both the background stem growth, and the growth promotion caused by either an end-of-day FR pulse or continuous WL+FR given to the internode, increased with increasing fluence rates of WL given to the rest of the shoot. The increase by WL of the growth-stimulatory effect of low phytochrome photoequilibria in the internode appears to be mediated by a specific blue-light-absorbing photoreceptor, as blue-deficient light from sodium-discharge lamps, or from filtered fluorescent tubes, promoted background stem growth similarly to WL but did not amplify the response to the R:FR ratio in the internode. Supplementing the blue-deficient light (94 mol·m-2·s-1) with low fluence rates of blue (<9 mol·m-2·s-1) restored the promotive effect of low R:FR reaching the internode.Abbreviations BL blue light - FR far-red light - PAR photosynthetically active radiation - Pfr/P ratio between the FR-absorbing form and total phytochrome - R red light - SOX low-pressure sodium lamp - WL white light Supported by the Consejo Nacional de Investigaciones Cientificas y Técnicas (República Argentina) and the ORS scheme (UK)  相似文献   

3.
Phototropism of Avena sativa L. has been characterized using a clinostat to negate the gravitropic response. The kinetics for development of curvature was measured following induction by a single pulse of blue light (BL), five pulses of BL at 20-min intervals, and this same pulsed-light regime following a 2-h red light (RL) pre-irradiation. A final curvature of about 14° is expressed within 180 min following the single pulse; a final curvature of about 62° in about 240 min following five pulses without pre-irradiation; and a curvature of over 125° in 360 min following five pulses after the RL pre-irradiation. For seedlings not pre-irradiated, the final curvature to five pulses of BL at a total fluence of 9.4 pmol·cm-2 increases with time of darkness between pulses up to 15 min; with seedlings pre-irradiated with RL, curvature increased more slowly with time of darkness between pulses to a maximum at 35 min. The final curvature induced by a constant fluence of 9.4 pmol·cm-2 increases linearly with time between the first pulse and last pulse of a five-pulse sequence. The curvature induced by a single BL pulse with a 5-min RL co-irradiation increases with fluence to a maximum of about 60° at about 10 pmol·cm-2, and then decreases to 0° at about 200 pmol·cm-2. Curvature induced by five BL pulses following a 2-h RL pre-irradiation increased with fluence from a threshold of about 0.05 pmol·cm-2 to a maximum of 90° at about 10 pmol·cm-2, and then gradually decreased with fluence to 50° at 1 000 pmol·cm-2. Based on these data, it is concluded that the initial photoproduct formed by a BL pulse has a limited lifetime, that there is a kinetic limitation downstream of the photoreceptor pigment for phototropism, and that the additivive effect of pulsed BL is distinct from the potentiating effect of RL on phototropism. Thus, any degree of curvature from 0° to over 90° may be induced by a fluence in the ascending arm of what is traditionally called the first positive phototropic response.Abbreviations BL blue light - RL red light  相似文献   

4.
Spalding EP  Cosgrove DJ 《Planta》1992,188(2):199-205
A large, transient depolarization of the plasma membrane precedes the rapid blue-light (BL)-induced growth suppression in etiolated seedlings of Cucumis sativus L. The mechanism of this voltage transient was investigated by applying inhibitors of ion channels and the plasma-membrane H+-ATPase, by manipulating extracellular ion concentrations, and by measuring cell input resistance and ATP levels. The depolarizing phase was not affected by Ca2+-channel blockers (verapamil, La3+) or by reducing extracellular free Ca2+ by treatment with ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA). However, these treatments did reduce the rate of repolarization, indicating an inward movement of Ca2+ is involved. No effects of the K+-channel blocker tetraethylammonium (TEA+) were detected. Vanadate and KCN, used to inhibit the H+-ATPase, reduced or completely inhibited the BL-induced depolarization. Levels of ATP increased by 11–26% after 1–2 min of BL. Input resistance of trichome cells, measured with double-barreled microelectrodes, remained constant during the onset of the depolarization but decreased as the membrane voltage became more positive than -90 mV. The results indicate that the depolarization mechanism initially involves inactivation of the H+-ATPase with subsequent transient activation of one or more types of ion channels.Abbreviations and Symbols BL blue light - CI current injection - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - TEA+ tetraethylammonium - Vm membrane voltage We wish to thank Drs. Adam Bertl and Clifford L. Slayman, Yale School of Medicine, New Haven, Conn., USA, for helpful discussions. This work was supported by a Natural Sciences and Engineering Research Council of Canada Scholarship (E.P.S.) and National Science Foundation Grant DMB-8351030 (D.J.C.).  相似文献   

5.
T. I. Baskin 《Planta》1986,169(3):406-414
First positive phototropism of the third internode of intact, 5-d-old pea (Pisum sativum L.) seedlings, grown under continuous, dim red light, showed maximal response following a photon fluence of 3 mol·m-2 blue light. Greater or lesser fluences (with irradiation time 100 s or less) caused less bending, no response being detectable above 300 or below 0.03 mol·m-2. Bilateral irradiation with blue light caused no detectable inhibition of growth rate over that range of fluences. The linear nutation of the pea third internode was shown to be driven by a balanced oscillation of growth rate such that the overall growth rate was little changed during the oscillation. Phototropic stimulation changed neither the amplitude nor the period of nutation. Nutation and phototropism probably regulate growth independently. Phototropism in response to the optimal blue light fluence was caused by concomitant depressed growth on the irradiated side and stimulated growth on the shaded side of the bending internode. These results are consistent with the Cholodny-Went hypothesis which states that unilateral blue light induces a lateral redistribution of a growth regulator.Abbreviations R red light - BL blue light Carnegie Institution, Department of Plant Biology paper No. 921  相似文献   

6.
Data for the maximum carboxylation velocity of ribulose-1,5-biosphosphate carboxylase, Vm, and the maximum rate of whole-chain electron transport, Jm, were calculated according to a photosynthesis model from the CO2 response and the light response of CO2 uptake measured on ears of wheat (Triticum aestivum L. cv. Arkas), oat (Avena sativa L. cv. Lorenz), and barley (Hordeum vulgare L. cv. Aramir). The ratio Jm/Vm is lower in glumes of oat and awns of barley than it is in the bracts of wheat and in the lemmas and paleae of oat and barley. Light-microscopy studies revealed, in glumes and lemmas of wheat and in the lemmas of oat and barley, a second type of photosynthesizing cell which, in analogy to the Kranz anatomy of C4 plants, can be designated as a bundle-sheath cell. In wheat ears, the CO2-compensation point (in the absence of dissimilative respiration) is between those that are typical for C3 and C4 plants.A model of the CO2 uptake in C3–C4 intermediate plants proposed by Peisker (1986, Plant Cell Environ. 9, 627–635) is applied to recalculate the initial slopes of the A(pc) curves (net photosynthesis rate versus intercellular partial pressure of CO2) under the assumptions that the Jm/Vm ratio for all organs investigated equals the value found in glumes of oat and awns of barley, and that ribulose-1,5-bisphosphate carboxylase is redistributed from mesophyll to bundle-sheath cells. The results closely match the measured values. As a consequence, all bracts of wheat ears and the inner bracts of oat and barley ears are likely to represent a C3–C4 intermediate type, while glumes of oat and awns of barley represent the C3 type.Abbreviations A net photosynthesis rate (mol·m-2·s-1) - Jm maximum rate of whole-chain electron transport (mol·e-·m-2·s-1) - pc (bar) intercellular partial pressure of CO2 - PEP phosphoenolpyruvate - PPFD photosynthetic photon flux density (mol quanta·m-2·s-1) - RuBPCase ribulose bisphosphate carboxylase/oxygenase - RuBP ribulose bisphosphate - Vm maximum carboxylation velocity of RuBPCase (mol·m-2·s-1) - T* CO2 compensation point in the absence of dissimilative respiration (bar)  相似文献   

7.
The nature of subthreshold changes in excitable plasma membranes has been investigated in stem parenchyma cells of Cucurbita pepo L. during action-potential generation induced by gradual cooling (from 23 to 10 ° C). The character of the subthreshold depolarization of excitable cells is shown to be mainly defined by a decrease in the activity of the plasma-membrane electrogenie pump (H+-ATPase). In its turn, the pump activity is controlled by thermal changes in the structure of the membrane lipid matrix. Based on the results obtained, a sequence of subthreshold changes has been suggested in which thermally induced structural rearrangements of membrane lipids play the role of trigger.Abbreviations AP action potential - DCCD N,N-dicyclohexil-carbodiimide - Em membrane potential - Ie/Im ratio of pyrene excimer/monomer fluorescence intensities  相似文献   

8.
The effect of repeated exposure to high light (1200 mol · m–2 · s–1 photosynthetic photon flux density, PPFD) at 5° C was examined in attached leaves of cold-grown spring (cv. Katepwa) and winter (cv. Kharkov) wheat (Triticum aestivum L.) over an eight-week period. Under these conditions, Kharkov winter wheat exhibited a daily reduction of 24% in FV/FM (the ratio of variable to maximal fluorescence in the dark-adapted state), in contrast to 41% for cold-grown Katepwa spring wheat. Both cultivars were able to recover from this daily suppression of FV/FM such that the leaves exhibited an average morning FV/FM of 0.651 ± 0.004. Fluorescence measurements made under steady-state conditions as a function of irradiance from 60 to 2000 mol · m–2 · s–1 indicated that the yield of photosystem II (PSII) electron transport under light-saturating conditions was the same for photoinhibited and control cold-grown plants, regardless of cultivar. Repeated daily exposure to high light at low temperature did not increase resistance to short-term photoinhibition, although zeaxanthin levels increased by three- to fourfold. In addition, both cultivars increased the rate of dry-matter accumulation, relative to control plants maintained at 5° C and 250 mol · m–2 · s–1 PPFD (10% and 28% for Katepwa and Kharkov, respectively), despite exhibiting suppressed fv/fm and reduced photon yields for O2 evolution following daily high-light treatments. Thus, although photosynthetic efficiency is suppressed by a longterm, photoinhibitory treatment, light-saturated rates of photosynthesis are sufficiently high during the high-light treatment to offset any reduction in photochemical efficiency of PSII. We suggest that in these cold-tolerant plants, photoinhibition of PSII may represent a longterm, stable, down-regulation of photochemistry to match the overall photosynthetic demand for ATP and reducing equivalents.Abbreviations and Symbols Chl chlorophyll - HL high light - PPFD photosynthetic photon flux density - FO minimum fluorescence in the dark-adapted state - FM maximum fluorescence in the dark-adapted state - FV maximum variable fluorescence in the dark-adapted state (FM-FO) - FV/FV photosynthetic efficiency of the dark-adapted state - fV/fM photosynthetic efficiency of the light-adapted steady state - qP photochemical quenching parameter - qN non-photochemical quenching parameter - e yield of electron transport and equals qP · fV/fM - 1-qO FO quenching parameter - app apparent photon yield. The assistance of Amy So is gratefully acknowledged. This research was supported by a Natural Sciences and Engineering Research Council of Canada (NSERCC) Operating Grant to N.P.A.H. G.Ö. was supported by an NSERCC International Exchange Award and the Swedish Natural Sciences Research Council.  相似文献   

9.
Temperature-dependent feedback inhibition of photosynthesis in peanut   总被引:7,自引:0,他引:7  
Arachis hypogaea L. is a tropical crop that is slow-growing at temperatures below 25°C. Unadapted CO2-assimilation rate (A) showed insufficient variation between 15 and 30°C in the short term (hours) to explain this marked reduction in growth. However, at longer periods (12 d), A was depressed as were growth rate and leafproduction rate. To examine the possible relationship between growth, A and sink demand plants were transferred from 30°C, which is near the optimum for growth, to a suboptimal temperature (19°C). In the first 2 d of cooling, A decreased by 50–70%, the stomata stayed open, and the intercellular CO2 concentration (ci) rose, i.e. the decrease in A of the cooled plants was the result of non-stomatal factors. Changes in dark respiration did not account for the decline in A.Clear evidence was obtained of sink control of A by independently manipulating the temperature of different leaves on the plant. Cooling (to 19°C) most of the plant (the sink) led to a 70% decline in A of the remaining leaves at 30°C after 3 d, whereas the converse treatments (30°C sink, 19°C source) resulted in small changes (17%). In plants at 19°C which were exposed to low CO2 concentration to prevent photosynthesis, A was not reduced when measured at normal CO2 concentrations, indicating that carbohydrate accumulation was responsible for the decline in A. Dry-matter build-up at suboptimal temperature was also consistent with end-product inhibition of photosynthesis.Abbreviations and symbols A (mol·m-2·s-1) rate of net CO2 assimilation - Ci (l·l-1) substomatal CO2 concentration - DW (g) dry weight - g (mol·m-2·s-1) stomatal conductance to diffusion of water vapour - PFD (mol·m-2·s-1) photon flux density  相似文献   

10.
Lemna gibba L., grown in the presence or absence of Fe, reduced extracellular ferricyanide with a V max of 3.09 mol · g-1 fresh weight · h-1 and a K m of 115 M. However, Fe3+-ethylenediaminetetraacetic acid (EDTA) was reduced only after Fe-starvation. External electron acceptors such as ferricyanide, Fe3+-EDTA, 2,6-dichlorophenol indophenol or methylene blue induced a membrane depolarization of up to 100 mV, but electron donors such as ferrocyanide or NADH had no effect. Light or glucose enhanced ferricyanide reduction while the concomitant membrane depolarization was much smaller. Under anaerobic conditions, ferricyanide had no effect on electrical membrane potential difference (Em). Ferricyanide reduction induced H+ and K+ release in a ratio of 1.16 H++1 K+/2 e- (in +Fe plants) and 1.28 H++0.8 K+/2 e- (in -Fe plants). Anion uptake was inhibited by ferricyanide reduction. It is concluded that the steady-state transfer of electrons and protons proceeds by separate mechanisms, by a redox system and by a H+-ATPase.Abbreviations E m electrical membrane potential difference - EDTA ethylenediaminetetraacetic acid - DCPIP dichlorophenol indophenol - +Fe control plant - -Fe iron-deficient plant - FW fresh weight - H+ electrochemical proton gradient  相似文献   

11.
E. Steudle  J. S. Boyer 《Planta》1985,164(2):189-200
Hydraulic resistances to water flow have been determined in the cortex of hypocotyls of growing seedlings of soybean (Glycine max L. Merr. cv. Wayne). Data at the cell level (hydraulic conductivity, Lp; half-time of water exchange, T 1/2; elastic modulus, ; diffusivity for the cell-to-cell pathway, D c) were obtained by the pressure probe, diffusivities for the tissue (D t) by sorption experiments and the hydraulic conductivity of the entire cortex (Lpr) by a new pressure-perfusion technique. For cortical cells in the elongating and mature regions of the hypocotyls T 1/2=0.4–15.1 s, Lp=0.2·10-5–10.0·10-5 cm s-1 bar-1 and D c=0.1·10-6–5.5·10-6 cm2 s-1. Sorption kinetics yielded a tissue diffusivity D t=0.2·10-6–0.8·10-6 cm2 s-1. The sorption kinetics include both cell-wall and cell-to-cell pathways for water transport. By comparing D c and D t, it was concluded that during swelling or shrinking of the tissue and during growth a substantial amount of water moves from cell to cell. The pressure-perfusion technique imposed hydrostatic gradients across the cortex either by manipulating the hydrostatic pressure in the xylem of hypocotyl segments or by forcing water from outside into the xylem. In segments with intact cuticle, the hydraulic conductance of the radial path (Lpr) was a function of the rate of water flow and also of flow direction. In segments without cuticle, Lpr was large (Lpr=2·10-5–20·10-5 cm s-1 bar-1) and exceeded the corticla cell Lp. The results of the pressure-perfusion experiments are not compatible with a cell-to-cell transport and can only the explained by a preferred apoplasmic water movement. A tentative explanation for the differences found in the different types of experiments is that during hydrostatic perfusion the apoplasmic path dominates because of the high hydraulic conductivity of the cell wall or a preferred water movement by film flow in the intercellular space system. For shrinking and swelling experiments and during growth, the films are small and the cell-to-cell path dominates. This could lead to larger gradients in water potential in the tissue than expected from Lpr. It is suggested that the reason for the preference of the cell-to-cell path during swelling and growth is that the solute contribution to the driving force in the apoplast is small, and tensions normally present in the wall prevent sufficiently thick water films from forming. The solute contribution is not very effective because the reflection coefficient of the cell-wall material should be very small for small solutes. The results demonstrate that in plant tissues the relative magnitude of cell-wall versus cell-to-cell transport could dependent on the physical nature of the driving forces (hydrostatic, osmotic) involved.Abbreviations and symbols D c diffusivity of the cell-to-cell pathway - D t diffusivity of the tissue - radial flow rate per cm2 of segment surface - Lp hydraulic conductivity of plasma-membrane - Lpr radial hydraulic conductance of the cortex - T 1/2 half-time of water exchange between cell and surroundings - volumetric elastic modulus  相似文献   

12.
The effects of preirradiation with blue light on the shift of the fluence-response curve for the first and the second positive curvatures were examined in Pilobolus crystallinus (Wiggers) Tode sporangiophores. A 1-min preirradiation with blue light at 47 or 960 nmol·m-2 lowered the fluence-response curve for the first positive curvature and shifted the peak to a higher fluence. The fluence-response curve was shifted back to a lower fluence when a dark period was inserted between the preirradiation and the curvature-inducing light. This shift back to lower fluence was biphasic when the fluence was high (960 nmol · m-2), indicating the participation of two components in the phototropic reaction for the first positive curvature.The fluence-response curve for the second positive curvature did not seem to be shifted to a higher fluence region when fluence was varied by varying exposure time. However, the fluence-response curve obtained by varying the fluence rate of a 20-min irradiation period indicated that the second positive curvature was also shifted to a higher-fluence region by preirradiation with blue light. A small shoulder appeared on the fluence-response curve when preirradiation at a high fluence rate was given.Abbreviations BL blue light - CIL curvature-inducing light  相似文献   

13.
The influence of far-red (FR; 700–800 nm) radiation on steady-state stomatal conductance and net photosynthesis in P. vulgaris has been studied. Whereas FR radiation alone was relatively ineffective, addition of FR to a background of white light (WL; predominantly 400–700 nm) resulted in increased stomatal conductance. Stomata exhibited a marked diurnal sensitivity to FR. The action maximum for enhancing stomatal conductance was near 714 nm. A combination of FR and infra-red (IR; >800 nm) enhanced net photosynthesis when added to a background of WL. When IR alone was added to WL, there was a net decrease in photosynthesis, indicating that it is the FR waveband which is responsible for the observed photosynthetic effects. Naturally occurring levels of FR radiation (235 mol·m-2·s-1) in vegetation-canopy shade enhanced net photosynthetic CO2 gain by 28% when added to a background of 55 mol·m-2·s-1 WL.Abbreviations BL blue - FR far-red - IR infra-red - PAR photosynthetically active radiation - R red - WL white light  相似文献   

14.
Sulfate uptake into duckweed (Lemna gibba G1) was studied by means of [35S]sulfate influx and measurements of electrical membrane potential. Uptake was strongly regulated by the intracellular content of soluble sulfate. At the onset of sulfate uptake the membrane potential was transiently depolarized. Fusicoccin stimulated uptake up to 165% of the control even at pH 8. It is suggested that sulfate uptake is energized in the whole pH range by a 3H+/sulfate cotransport mechanism. Kinetics of sulfate uptake and sulfate-induced membrane depolarization in the concentration range of 5 M to 1 mM sulfate at pH 5.7 was best described by two Michaelis-Menten terms without any linear component. The second system had a lower affinity for sulfate and was fully active only at sufficiently high proton concentrations.Abbreviations c o extracellular sulfate concentration - c i intracellular sulfate concentration - E m electrical membrane potential difference - E m sulfate-induced, maximal membrane depolarization - electrochemical proton gradient - FW fresh weight  相似文献   

15.
D. H. Greer  W. A. Laing 《Planta》1988,175(3):355-363
Photoinhibition of photosynthesis was induced in intact kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson) leaves grown at two photon flux densities (PFDs) of 700 and 1300 mol·m-2·s-1 in a controlled environment, by exposing the leaves to PFD between 1000 and 2000 mol·m-2·s-1 at temperatures between 10 and 25°C; recovery from photoinhibition was followed at the same range of temperatures and at a PFD between 0 and 500 mol·m-2·s-1. In either case the time-courses of photoinhibition and recovery were followed by measuring chlorophyll fluorescence at 692 nm and 77K and by measuring the photon yield of photosynthetic O2 evolution. The initial rate of photoinhibition was lower in the high-light-grown plants but the long-term extent of photoinhibition was not different from that in low-light-grown plants. The rate constants for recovery after photoinhibition for the plants grown at 700 and 1300 mol·m-2·s-1 or for those grown in shade were similar, indicating that differences between sun and shade leaves in their susceptibility to photoinhibition could not be accounted for by differences in capacity for recovery during photoinhibition. Recovery following photoinhibition was increasingly suppressed by an increasing PFD above 20 mol·m-2·s-1, indicating that recovery in photoinhibitory conditions would, in any case, be very slow. Differences in photosynthetic capacity and in the capacity for dissipation of non-radiative energy seemed more likely to contribute to differences in susceptibility to photoinhibition between sun and shade leaves of kiwifruit.Abbreviations and symbols F o , F m , F v instantaneous, maximum, variable fluorescence - F v /F m fluorescence ratio - F i =F v at t=0 - F F v at t= - K D rate constant for photochemistry - k(F p ) first-order rate constant for photoinhibition - k(F r ) first-order rate constant for recovery - PFD photon flux density - PSII photosystem II - i photon yield of O2 evolution (incident light)  相似文献   

16.
Phosphate uptake inLemna gibba G1: energetics and kinetics   总被引:2,自引:0,他引:2  
Phosphate uptake was studied by determining [32P]phosphate influx and by measurements of the electrical membrane potential in duckweed (Lemna gibba L.). Phosphate-induced membrane depolarization (E m ) was controlled by the intracellular phosphate content, thus maximal E m by 1 mM H2PO 4 - was up to 133 mV after 15d of phosphate starvation. The E m was strongly dependent on the extracellular pH, with a sharp optimum at pH 5.7. It is suggested that phosphate uptake is energized by the electrochemical proton gradient, proceeding by a 2H+/H2PO 4 - contransport mechanism. This is supported also by the fusicoccin stimulation of phosphate influx. Kinetics of phosphate influx and of E m , which represent mere plasmalemma transport, are best described by two Michaelis-Menten terms without any linear components.Abbreviations E m electrical membrane potential difference - E m phosphate-induced, maximal membrane depolarization - FW fresh weight  相似文献   

17.
S. Somersalo  G. H. Krause 《Planta》1989,177(3):409-416
The effects of moderate light at chilling temperature on the photosynthesis of unhardened (acclimated to +18° C) and hardened (cold-acclimated) spinach (Spinacea oleracea L.) leaves were studied by means of fluorescence-induction measurements at 20° C and 77K and by determination of quantum yield of O2 evolution. Exposure to 550 mol photons·m-2·s-1 at +4° C induced a strong photoinhibition in the unhardened leaves within a few hours. Photoinhibition manifested by a decline in quantum yield was characterized by an increase in initial fluorescence (F o) and a decrease in variable fluorescence (F v) and in the ratio of variable to maximum fluorescence (F V/F M), both at 77K and 20° C. The decline in quantum yield was more closely related to the decrease in the F V/F M ratio measured at 20° C, as compared with F V/F M at 77K. Quenching of the variable fluorescence of photosystem II was accompanied by a decline in photosystem-I fluorescence at 77K, indicating increased thermal de-excitation of pigments as the main consequence of the light treatment. All these changes detected in fluorescence parameters as well as in the quantum yield of O2 evolution were fully reversible within 1–3 h at a higher temperature in low light. The fast recovery led us to the view that this photoinhibition represents a regulatory mechanism protecting the photosynthetic apparatus from the adverse effects of excess light by increasing thermal energy dissipation. Long-term cold acclimation probably enforces other protective mechanisms, as the hardened leaves were insensitive to the same light treatment that induced strong inhibition of photosynthesis in unhardened leaves.Abbreviations F 0 initial fluorescence - F M maximum fluorescence - F V variable fluorescence (F M-F 0 - PFD photon flux density - PS photosystem  相似文献   

18.
There has been persisting controversy over the role of photosynthesis in the stimulation of the plasma membrane H+-ATPase and growth of dicotyledonous leaves by light. To investigate this, we compared the effects of light on growth, H+ net efflux and membrane potential (Vm) of strips which contained either only chlorophyll-free (white) mesophyll cells or chlorophyll-containing (green) cells cut from variegated Coleus leaves. White mesophyll cells responded to white, blue and red light with a hyperpolarization of Vm, an acidification of the apoplast and a promotion of growth, all of which began after a lag of 2–7 min. In contrast, green mesophyll cells showed a biphasic light response in which the hyperpolarization and the acidification were preceded by a rapid depolarization of Vm and an alkalinization of the apoplast. Nevertheless, green and white tissues showed comparable growth promotions in response to light. The light response of the leaf mesophyll is a composite of two separate photosystems. The initial depolarization and alkalinization are mediated by photosynthesis and blocked by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The slower hyperpolarization, acidification and growth response, on the other hand, are clearly in response to light absorption by pigments other than chlorophyll. Received: 11 February 2000 / Accepted: 2 May 2000  相似文献   

19.
Red light (R) and gibberellins (GA) each induce a water potential decrease in the axes of lettuce (Lactuca sativa L.) embryos resulting in germination of intact seeds (achenes) or an increase in growth of the axes of isolated embryos. The fruit coat and endosperm are a substantial barrier to the penetration of exogeneous GA. Isolated embryos take up 35 times as much [3H]GA1 as the embryos of intact seeds and respond to less than 1·10-10 M GA3 or GA4+7. We calculated that only 1·10-8 M of either GA3 or GA4+7 would result in 50% germination if the GA were able freely to penetrate the fruit coat. Exogenous GA3 or GA4+7, at concentrations insufficient to cause germination, result in an apparent synergistic promotion of germination when suboptimal R is applied. Yet suboptimal concentrations of exogenous GA3 or GA4+7 and suboptimal R result in only additive increases in the growth response in axes of isolated embryos. Dose-response curves demonstrate quantitative increases in the growth response of the isolated axes after R or GA treatments insufficient to induce germination in intact seeds, indicating that a threshold potential must be achieved by the embryonic axes before germination can occur.Abbreviations FR far=red light - GA gibberellin - PEG poly-ethylene glycol 4000 - Pfr far-red-absorbing phytochrome - R red light III.=Carpita et al. 1979b; IV.=Carpita et al. 1979c  相似文献   

20.
Electrophysiological investigations of intercellular communication and membrane resistance in higher plants have been hampered by the difficulty in measuring these quantities independently. Uncertainty about the position of an electrode inserted into vacuolate tissue has further complicated such measurement. To overcome these problems sister cell pairs of a Zea mays L. Black Mexican Sweet suspension culture were used and dye was injected from the current-injecting electrode to determine the location of the electrode tip in each experiment. Of the impalements, 72% were cytoplasmic. The presence of plasmodesmata was fully incorporated into the electriccircuit model for the cell, and the resistance of the membrane of the current-injected cell was calculated, separate from the plasmodesmata resistance. This avoided some of the confusion resulting from work on multicellular tissue in which the position of the electrode and the extent of intercellular coupling is not determined. Using this technique, plasma-membrane resistivity was measured as 0.65 ·m2, the resistivity of the tonoplast and plasma membrane in series was 1.35 ·m2, and the resistance of a single plasmodesma was calculated to be 53 ± 11 G.Abbreviations BMS Black Mexican Sweet - PD potential difference - Rj resistance of the plasmodesmata in the junction between cells - Rm resistance of the plasma membrane of the current-injected cell - Rt resistance of the tonoplast - V1, V2 membrane PDs of sister cells This work was funded by an Australian Research Council grant to R.L.O. We are grateful to Dr. Maret Vesk (Electron Microscope Unit, The University of Sydney) for assistance with the preparation of EM sections, and to Dr. Richard Brettell (C.S.I.R.O. Division of Plant Industry) for assistance with the BMS culture.  相似文献   

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