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1.
Entry of the divalent cations Ni2+ , Co2+ and Zn2+ into cells of maize ( Zea mays L. cv. Dekalb XL 85) root tissue is accompanied by an acidification of the incubation medium, a decrease in both the pH of the cell sap and the level of malate in the cells, and by an inhibition of dark fixation of CO2 . K+ , on the contrary, induces only a very low acidification of the incubation medium, does not change either the pH of the cell sap or the malate level in the cells, and induces an increase in CO2 dark fixation. Different mechanisms are postulated for the stimulation of proton extrusion by divalent cations and K+ . 相似文献
2.
The effects of K+ concentration, light intensity and CO2 levels on the volume of Commelina communis L. guard cell protoplasts were studied. Two degrees of swelling response were observed, both dependent on an external supply of K+ , but not necessarily on the supply of a permeant anion. The presence of K+ itself, independent of light or CO2 level, stimulated swelling at a relatively slow rate. When K+ , light and low CO2 conditions were supplied together, the swelling was relatively rapid and of high magnitude. The rapid swelling was specific for K+ and Rb+ giving a half maximal effect after 2 h at a KCl concentration of about 18 mmol m−3 . The addition of CaCl2 at 1 mol m−3 inhibited K+ -dependent swelling under all conditions tested. The response to light and low CO2 levels by Commelina guard cell protoplasts is thought to reflect a high degree of physiological integrity. 相似文献
3.
J. Hernández-Nistal J. Aldasoro D. Rodriguez A. Matilla G. Nicolás 《Physiologia plantarum》1983,57(2):273-278
During the first 12 h of germination of Cicer arietinum L. (cv. Castellans) seeds, K+ is first lost into the surrounding medium and is later reabsorbed. Thiourea accelerates this reabsorption. Since there is an increase in the mobilization of K+ in response to thiourea, a greater accumulation of malate due to the carboxylation of phosphoenolpyruvic acid takes place as compared with that occurring in water. The subapical zone of the radicle accumulates the greatest amounts of water, K+ and malate. The variation in the "in vitro" activity of phosphoenolpyruvate carboxylase does not explain the difference in malate in response to the different treatments, consequently there must be chemical changes in the cytoplasm which favour this carboxylation "in vivo". These results show that thiourea accelerates the mobilization of K+ and stimulates the dark fixation of CO2 in embryonic axes of Cicer arietinum. 相似文献
4.
The responses of individual stomata to CO2 concentrations ranging from 0 to 900 μmol mol−1 air were analysed in Ipomoea pes-caprae L. Sweet (Convolvulaceae). The stomata were directly observed using a measurement system that permitted continuous observation of stomatal movement under controlled light and CO2 conditions. A CO2 concentration of 350 μmol mol−1 or higher induced stomatal closure, whereas concentrations below 350 μmol mol−1 did not. The time lag before stomatal closure decreased with increasing CO2 concentration, as did the steady-state aperture of the stomata after a change in CO2 concentration. However, the rate of stomatal closure increased with increasing CO2 concentration. Therefore, not only the stomatal closure rate but also the time from the CO2 concentration change to the beginning of stomatal closure changed with increasing CO2 concentration. These results suggest that atmospheric CO2 may be the stimulus for the closure of guard cells. No significant differences were observed between adaxial and abaxial stomata in terms of their responses to CO2 . However, heterogeneous responses were detected between neighbouring stomata on each leaf surface. 相似文献
5.
The cellular basis of guard cell sensing of rising CO2 总被引:5,自引:1,他引:4
S. M. ASSMANN 《Plant, cell & environment》1999,22(6):629-637
Numerous studies conducted on both whole plants and isolated epidermes have documented stomatal sensitivity to CO2 . In general, CO2 concentrations below ambient stimulate stomatal opening, or an inhibition of stomatal closure, while CO2 concentrations above ambient have the opposite effect. The rise in atmospheric CO2 concentrations which has occurred since the industrial revolution, and which is predicted to continue, will therefore alter rates of transpirational water loss and CO2 uptake in terrestrial plants. An understanding of the cellular basis for guard cell CO2 sensing could allow us to better predict, and perhaps ultimately to manipulate, such vegetation responses to climate change. However, the mechanisms by which guard cells sense and respond to the CO2 signal remain unknown. It has been hypothesized that cytosolic pH and malate levels, cytosolic Ca2+ levels, chloroplastic zeaxanthin levels, or plasma-membrane anion channel regulation by apoplastic malate are involved in guard cell perception and response to CO2 . In this review, these hypotheses are discussed, and the evidence for guard cell acclimation to prevailing CO2 concentrations is also considered. 相似文献
6.
The presence of Ni2+ in the incubation medium of maize root segments ( Zen mays L. cv. Dekalb XL 640) induces an early and significant enhancement of the rate of proton extrusion both in the absence and presence of fusicoccin; with time, an inhibition of proton extrusion and a leakage of K+ appear. The inhibition of proton extrusion is accompanied by a decrease in the dark CO2 fixation and by a decrease in the level of malate in the cells. Ni2+ inhibits in vitro phosphoenolpyruvale carboxylase activity of maize roots. The data indicate a correlation between the operativity of the proton pump and that of the malate-pH stat mechanism for the homeostasis of cytoplasmic pH. 相似文献
7.
Z. CHEN I. NEWMAN M. ZHOU N. MENDHAM G. ZHANG & S. SHABALA 《Plant, cell & environment》2005,28(10):1230-1246
Development of salt-tolerant genotypes is central both to remediation of salinity-affected land and to meet increasing global food demand, which has been driving expansion of cropping into marginal areas. The bottleneck of any breeding programme is the lack of a reliable screening technique. This study tested the hypothesis that the ability of plants to retain K+ under saline conditions is central to their salt tolerance. Using seven barley cultivars contrasting in salt tolerance (CM72, Numar, ZUG293, ZUG95, Franklin, Gairdner, ZUG403), a comprehensive study was undertaken of whole-plant (growth rate, biomass, net CO2 assimilation, chlorophyll fluorescence, root and leaf elemental and water content) and cellular (net fluxes of H+ , K+ , Na+ and Ca2+ ) responses to various concentrations of NaCl (20–320 m m ). Na+ selective microelectrodes were found to be unsuitable for screening purposes because of non-ideal selectivity of the commercially available Na+ LIX. At the same time, our results show very strong negative correlation between the magnitude of K+ efflux from the root and salt tolerance of a particular cultivar. K+ efflux from the mature root zone of intact 3-day-old seedlings following 40 min pretreatment with 80 m m NaCl was found to be a reliable screening indicator for salinity tolerance in barley. As a faster and more cost-effective alternative to microelectrode measurements, a procedure was developed enabling rapid screening of large numbers of seedlings, based on amount of K+ leaked from plant roots after exposure to NaCl. 相似文献
8.
Seedlings of spring wheat ( Triticum aestivum L. cv. Svenno) were cultivated at 20°C in continuous light or darkness with the roots in nutrient solutions for six days. The plants were starved for K+ during different periods of time to produce plants with various K+ status. In one cultivation light-grown plants were pretreated in darkness, and vice versa, before the uptake experiment. In all experiments, roots were put in a complete nutrient medium containing 2.0 m M K+ radiolabelled with 86 Rb. The uptake time was varied (5, 60 or 120 min).
The K+ concentration in the roots, [K+ ]root , increased during the course of the uptake experiments, especially in light and at initially low [K+ ]root , At the same time K+ (86 Rb) influx in the roots decreased. The simoidal relationship obtained between K+ (86 Rb) influx and [K+ ]root was affected by these changes, and Hill plots gave various Hill coefficients, nH , depending on the duration of the uptake experiments. nH from three apparently straight line segments of the same plot, in different [K+ ]root - intervals, indicated a falling degree of interaction between the binding sites as [K+ ]root increased. For the dark-grown plants negative cooperativity could not be demonstrated. 相似文献
The K
9.
Vittoria Di Martino Rigano Vincenza Vona Catello Di Martino Carmelo Rigano 《Physiologia plantarum》1986,68(1):34-38
Cyanidium caldarium (Tilden) Geitler, a non-vacuolate unicellular alga, resuspended in medium flushed with air enriched with 5% CO2 , assimilated NH4 + at high rates both in the light and in the dark. The assimilation of NO3 − , by contrast, was inhibited by 63% in the dark. In cell suspensions flushed with CO2 -free air, NH4 + assimilation decreased with time both in the light and in the dark and ceased almost completely after 90 min. The addition of CO2 completely restored the capacity of the alga to assimilate NH4 + . NO3 − assimilation, by contrast, was 33% higher in the absence of CO2 and was linear with time. It is suggested that NO3 − and NH4 + metabolism in C. caldarium are differently controlled in response to the light and carbon conditions of the cell. 相似文献
10.
Abstract. Two experiments are described which test the normal correlations that arise between stomatal conductance, net CO2 assimilation rate, and intercellular CO2 concentration (Ci ), using whole shoots of Commelina communis L. In the first, conductance increased with decreasing Ci , at four different quantum flux densities, such that there was no unique relationship between conductance and quantum flux density or Ci , In the second, conductance increased hyperbolically with increasing quantum flux density while Ci was held constant at 466, 302, and 46 μmiolmol−1 , and the response differed at each Ci . In neither experiment was conductance consistently related to net CO2 assimilation rate in the mesophyll. In both experiments high Ci suppressed the response of conductance to light, while there was a large response of conductance to light at low Ci , indicating an interaction between the effects of light and CO2 on stomata. The results show that the parallel responses of assimilation and conductance to light result in constant intercellular CO2 concentrations, and not that stomata maintain a 'constant Ci '. 相似文献
11.
YUKIO FUJINO KEIKO MITSUNAGA IKUO YASUMASU 《Development, growth & differentiation》1987,29(6):591-597
Embryos kept with omeprazole, a specific H+ , K+ -ATPase inhibitor, in a period of development between the mesenchyme blastula and the pluteus corresponding stage became abnormal plutei having quite small spicules, somewhat poor pluteus arms and apparently normal archenterons. In micro-mere-derived cells, kept with omeprazole at pH 8.2 in a period between 15 and 40 hr of culture at 20°C, omeprazole strongly inhibited spicule formation but did not block the outgrowth of pseudopodial cables, in which spicule rods were to be formed. These indicate that omeprazole probably exerts no obvious inhibitory effects other than spicule rods formation. Omeprazole-sensitive H+ , K+ -ATPase, an H+ pump, seems to be indispensable for CaCO3 deposition (formation of spicule rod) in these spicule forming cells. H+ , produced in overall reaction for CaCO3 formation: Ca2+ + CO2 +H2 O°CaCO3 +2H+ , is probably released from the cells by this H+ pump and hence, this reaction tends to go to CaCO3 production to form spicule rods. Omeprazole, known to become effective following its conversion to a specific inhibitor of H+ , K+ -ATPase at acidic pH, is able to inhibit formation of spicule rod at alkaline pH in sea water. This is probably due to an acidification of sea water near the cell surface by H+ ejection in H+ , K+ -ATPase reaction. 相似文献
12.
Valentino Casolo Enrico Braidot Elisa Chiandussi Angelo Vianello Francesco Macrì 《Physiologia plantarum》2003,118(3):313-318
The role of a recently identified K+ ATP channel in preventing H2 O2 formation was examined in isolated pea stem mitochondria. The succinate-dependent H2 O2 formation was progressively inhibited, when mitochondria were resuspended in media containing increasing concentration of KCl (from 0.05 to 0.15 M ). This inhibition was linked to a partial dissipation of the transmembrane electrical potential (ΔΨ) induced by KCl. Conversely, the malate plus glutamate-dependent H2 O2 formation was not influenced. The succinate-sustained H2 O2 generation was also unaffected by nigericin (a H+ /K+ exchanger), but completely prevented by valinomycin (a K+ ionophore). In addition, cyclosporin A (a K+ ATP channel opener) inhibited this H2 O2 formation, while ATP (an inhibitor of the channel opening) slightly increased it. The inhibitory effect of ATP was strongly stimulated in the presence of atractylate (an inhibitor of the adenine nucleotide translocase), thus suggesting that the receptor for ATP on the K+ channel faces the intermembrane space. Finally, the succinate-dependent H2 O2 formation was partially prevented by phenylarsine oxide (a thiol oxidant). 相似文献
13.
Photosynthetic CO2 -fixation, chlorophyll content, growth rate and nitrate reductase activity were used to examine the influence of NH+ 4 -N and NO− 3 -N on Sphagnum magellanicum cultivated under defined conditions in phytotrons. NO− 3 -concentrations up to 322 μ M were found to be favourable. Increased NH+ 4 concentrations, however, resulted in growth inhibition and decreased chlorophyll content at concentrations ≧ 255 μ M ; e.g. 600 μ M NH+ 4 caused a 20% reduction of nitrate reductase activity and net photosynthesis. For raised bog Sphagna an improved standard nutrient solution is proposed with the following ion concentrations (μ M ): 55 Na+ ; 17 K+ ; 95 NH+ 4 ; 22 Ca2+ ; 22 Mg2+ ; 2 Fe3+ ; 20 Cl− ; 100 NO− 3 ; 57 SO2- 4 ; 7.4 H2 PO− 4 ; trace elements: A-Z solution (Hoagland) 50 μl 1000 ml−1 ; pH 5.8. 相似文献
14.
The mechanisms mediating CO2 sensing and light–CO2 interactions in guard cells are unknown. In growth chamber-grown Vicia faba leaves kept under constant light (500 μ mol m–2 s–1 ) and temperature, guard cell zeaxanthin content tracked ambient [CO2 ] and stomatal apertures. Increases in [CO2 ] from 400 to 1200 cm3 m–3 decreased zeaxanthin content from 180 to 80 mmol mol–1 Chl and decreased stomatal apertures by 7·0 μ m. Changes in zeaxanthin and aperture were reversed when [CO2 ] was lowered. Guard cell zeaxanthin content was linearly correlated with stomatal apertures. In the dark, the CO2 -induced changes in stomatal aperture were much smaller, and guard cell zeaxanthin content did not change with chamber [CO2 ]. Guard cell zeaxanthin also tracked [CO2 ] and stomatal aperture in illuminated stomata from epidermal peels. Dithiothreitol (DTT), an inhibitor of zeaxanthin formation, eliminated CO2 -induced zeaxanthin changes in guard cells from illuminated epidermal peels and reduced the stomatal CO2 response to the level observed in the dark. These data suggest that CO2 -dependent changes in the zeaxanthin content of guard cells could modulate CO2 -dependent changes of stomatal apertures in the light while a zeaxanthin-independent CO2 sensing mechanism would modulate the CO2 response in the dark. 相似文献
15.
N. N. ARTUS MSU-DOE 《Plant, cell & environment》1990,13(6):575-580
Abstract. Two nonallelic, nuclear recessive mutants of Arabidopsis thaliana (L.) Heynh. which become chlorotic when grown in an atmosphere enriched to 20000 cm3 CO2 m-3 have been isolated. For one of the mutants, chlorosis begins at the veins and gradually spreads to the interveinal regions. A minimum photon flux density of ca 50 μmol m-2 s-1 is required for this response. For the other mutant, the yellowing is independent of the light intensity and begins at the basal regions of the leaves and spreads to the tips. The injurious effects of CO2 seem to be restricted to photosynthetic tissues, since root elongation and callus growth were not inhibited by a high atmospheric CO2 concentration for either mutant. Neither mutant became chlorotic in a low O2 atmosphere that suppressed photorespiration as effectively as the elevated CO2 does. Thus, the mutations do not impose a requirement for photorespiration. The possibilities that the high CO2 -sensitive phenotypes are caused by an effect of CO2 in stomata, on ethylene synthesis, or on mineral uptake are discussed but are considered unlikely. 相似文献
16.
Effect of sink size on photosynthesis and carbohydrate content of leaves of three spring wheat varieties 总被引:3,自引:0,他引:3
R. Martínez-Carraseo E. Cervantes P. Pérez R. Morcuende I. M. Martín del Molino 《Physiologia plantarum》1993,89(3):453-459
Effects of CO2 on stomatal movements of Commelina communis L. were studied with plants, epidermal strips and guard cell protoplasts. With plants, the stomatal response induced by a blue light pulse was studied for different ambient CO2 concentration ranging from CO2 -deprived air to 100 Pa in darkness or under red light. It was observed that the blue light response could be obtained not only under a red light background but also in darkness and CO2 -free air, the two responses being quite similar.
With epidermal strips, the effect of CO2 on ferricyanide reductase activity at the guard cell plasmalemma was studied by transmission electron microscopy. In the presence of ferric ions, reduced ferricyanide gives an electron dense precipitate of Prussian Blue. In darkness and air, no precipitate was observed. In darkness and CO2 -free air as well as under light and normal air, a precipitate was found along the plasmalemma of the guard cells, indicating a ferricyanide reductase activity. With guard cell protoplasts suspended in a medium either in equilibrium with air or in a CO2 -free medium the H+ extrusion induced by a blue light pulse added to a red light background was measured. A low CO2 content was obtained by adding photosynthetic algae to the suspension of guard cell protoplasts. In a CO2 -free medium the rate of H+ extrusion was enhanced.
The results are discussed on the basis of a possible competition for reducing power between CO2 fixation and a putative blue light dependent redox chain located on the plasma membrane. 相似文献
With epidermal strips, the effect of CO
The results are discussed on the basis of a possible competition for reducing power between CO
17.
To investigate the diurnal variation of stomatal sensitivity to CO2 , stomatal response to a 30 min pulse of low CO2 was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata , which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in p CO2 in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low p CO2 . Stomata did not respond to a decreased p CO2 in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO2 was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal p CO2 , and suggest that in CAM species the diurnal variability in the responsiveness of stomata to p CO2 could be explained by hypothesizing the existence of a single CO2 sensor which interacts with other signalling pathways. When not perturbed by low p CO2 , CO2 assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species. 相似文献
18.
Net Glutamate Release from Astrocytes Is Not Induced by Extracellular Potassium Concentrations Attainable in Brain 总被引:2,自引:0,他引:2
Abstract: Elevated extracellular potassium concentration ([K+ ]e ) has been shown to induce reversal of glial Na+ -dependent glutamate uptake in whole-cell patch clamp preparations. It is uncertain, however, whether elevated [K+ ]e similarly induces a net glutamate efflux from intact cells with a physiological intracellular milieu. To answer this question, astrocyte cultures prepared from rat and mouse cortices were incubated in medium with elevated [K+ ]e (by equimolar substitution of K+ for Na+ ), and glutamate accumulation was measured by HPLC. With [K+ ]e elevations to 60 m M , medium glutamate concentrations did not increase during incubation periods of 5–120 min. By contrast, 45 min of combined inhibition of glycolytic and oxidative ATP production increased medium glutamate concentrations 50–100-fold. Similar results were obtained in both rat and mouse cultures. Studies were also performed using astrocytes loaded with the nonmetabolized glutamate tracer d -aspartate, and parallel results were obtained; no increase in medium d -aspartate content resulted from [K+ ]e elevation up to 90 m M , whereas a large increase occurred during inhibition of energy metabolism. These results suggest that a net efflux of glutamate from intact astrocytes is not induced by any [K+ ]e attainable in brain. 相似文献
19.
José M. Quintero José M. Fournier José Ramos Manuel Benlloch 《Physiologia plantarum》1998,102(2):279-284
Twenty‐day‐old sunflower plants ( Helianthus annuus L. cv. Sun‐Gro 380) grown in nutrient solutions with different KCl levels were used to study the effects of K+ status of the root and of abcisic acid (ABA) on the exudation rate (Jv ), the hydraulic conductivity of the root (Lp ), the fluxes of exuded K+ and Na+ (JK and JNa ), and the gradient of osmotic pressure between the xylem and the external medium. Jv and Lp increased in direct proportion to the K+ starvation of the root. Also addition of ABA (4 µ M ) at the onset of exudation in the external medium made Jv and Lp rise, and this effect also increased with the degree of K+ starvation. Similarly, K+ starvation and ABA promoted both the flux of exuded Na+ and the accumulation of Na+ in the root. We suggest that ABA acts as a regulating signal for the radial transport of water across the root, and that potassium may be an effector of this mechanism. 相似文献
20.
In embryos of the sea urchin, Hemicentrotus pulcherrimus , as well as in cultured cells derived from isolated micromeres, spicule formation was inhibited by allylisothiocyanate, an inhibitor of H+ , K+ -ATPase, at above 0.5 μM and was almost completely blocked at above 10 μM. Amiloride, an inhibitor of Na+ , H+ antiporter, at above 100 μM exerted only slight inhibitory effect, if any, on spicule formation. Intravesicular acidification, determined using [ dimethylamine -14 C]-aminopyrine as a pH probe, was observed in the presence of ATP and 200 mM KCl in microsome fraction obtained from embryos at the post gastrula stage, at which embryos underwent spicule calcification. Intravesicular acidification and K+ -dependent ATPase activity were almost completely inhibited by allylisothiocyanate at 10 μM. Allylisothiocyanate-sensitive ATPase activity was found mainly in the mesenchyme cells with spicules isolated from prisms. H+ , K+ -ATPase, an H+ pump, probably mediates H+ release to accelerate CaCO3 deposition from Ca2+ , CO2 and H2 O in the primary mesenchyme cells. Intravesicular acidification was stimulated by valinomycin at the late gastrula and the prism stages but not at the pluteus stage. K+ permeability probably increases after the prism stage to activate H+ release. 相似文献