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1.
Abstract. Rates of proton extrusion and potassium (86 Rb) influx by intact roots of barley ( Hordeum vulgare cvs . Fergus, Conquest and Betzes) plants were simultaneously measured in short-term (15min) experiments. The nature and extent of apparent coupling between these ion fluxes was explored by manipulating conditions of temperature, pH and cation composition and concentration during flux determinations. In addition, the influence of salt status upon these fluxes was examined. At low K+ concentrations (0.01 to 1 mol m−3 ), H+ efflux and K+ influx were strongly correlated in both low- and high-K+ roots, although K+ : H+ exchange stoichiometries were almost consistently greater than 2:1. At higher concentrations (1 to 5 mol m−3 ), H+ efflux was either reduced or remained unchanged while K+ influxes increased. In the presence of Na2 SO4 , rates of H+ extrusion demonstrated similar cation dependence, although below 10 mol m−3 Na2 SO4 , H+ fluxes were generally 50% lower than in equivalent concentrations of K2 SO4 . These observations are considered in the context of current hypotheses regarding the mechanisms of k+ /H+ exchange. 相似文献
2.
Although temperature-induced changes in membrane structure and activity seem to be central to chilling stress perception, the specific details of temperature effects on plant nutrient acquisition remain obscure. In this study, we have undertaken a comparative study of low temperature effects on the activity of plasma membrane transporters of different ions in corn ( Zea mays L.) leaf and root tissues by non-invasive measurements of net ion fluxes using ion-selective microelectrode (the MIFE) technique. Kinetics of net H+ , Ca2+ , K+ , Na+ , and Cl– fluxes were measured as plant tissues recovered after short-term (3 h) chilling stress. The major findings can be summarized as follows: (1) The critical temperatures, under which the recovery of the activity of plasma membrane transporters took place, were found to be the same for all ions measured and are likely to be associated with the phase transition of membrane lipids. (2) The most pronounced was the reduction in net uptake of K+ and (3) Chilling treatment caused a significant net influx of Cl– and Na+ in the leaf tissue. (4) For the same species, the critical temperatures for membrane-transport processes in roots were 2–2.5°C lower than in leaves. Possible physiological significance of these findings is discussed. 相似文献
3.
Potassium ion channels in the plasmalemma 总被引:2,自引:0,他引:2
Friedrich-Wilhelm Bentrup 《Physiologia plantarum》1990,79(4):705-711
The potassium ion is an indispensible cytosolic component of living cells and a key osmolyte of plant cells, crossing the plasmalemma to drive physiological processes like cell growth and motor cell activity. K+ transport across the plasmalemma may be passive through channels, driven by the electrochemical gradient, K+ equilibrium potential (EK ) – membrane potential (Vm ), or secondary active by coupling through a carrier to the inward driving force of H+ or Na+ . Known K+ channels are permeable to monovalent cations, a permeability order being K+ > Rb+ > NH4 + > Na+ ≥ Li+ > Cs+ . The macroscopic K+ currents across a cell or protoplast surface commonly show rectification, i.e. a Vm -dependent conductance which in turn, may be controlled by the cytosolic activity of Ca2+ , of K+ , of H+ , or by the K+ driving force. Analysis by the patch clamp technique reveals that plant K+ channels are similar to animal channels in their single channel conductance (4 to 100 pS), but different in that a given channel population slowly activates and may not inactivate at all. Single-channel kinetics reveal a broad range of open times (ms to s) and closed times (up to 100 s). Further progress in elucidating plant K+ channels will critically depend on molecular cloning, and the availability of channel-specific (phyto)toxins. 相似文献
4.
Lioubov I. Tikhonova Igor I. Pottosin Karl-Josef Dietz Gerald Schönknecht 《The Plant journal : for cell and molecular biology》1997,11(5):1059-1070
In contrast to the vacuolar ion channels which are gated open by an increase of cytosolic Ca2+ the vacuolar ion currents at resting cytosolic Ca2+ are poorly explored. Therefore, this study was performed to investigate the properties of the so-called fast-activating vacuolar (FV) current which dominates the electrical characteristics of the tonoplast at physiological free Ca2+ concentrations. Patch—clamp measurements were performed on whole barley ( Hordeum vulgare ) mesophyll vacuoles and on excised tonoplast patches. Single ion channels were identified, which, based on their selectivity, activation kinetics, Ca2+ - and voltage-dependence, carry the whole-vacuole FV current. Reversal potential determinations indicated a K+ overs C− permeability ratio of about 30. Both inward and outward whole-vacuole currents as well as the activity of single FV channels were inhibited by an increase of cytosolic Ca2+ , with a Kd ≈ 6 µM. At physiological vacuolar Ca2+ activities, the FV channel is an outward-rectifying potassium channel. The FV channel was activated in less than a few milliseconds both by negative and positive potential steps, having a minimal activity that is 40 mV negative of the K+ equilibrium potential. It is proposed that transport of K+ through this cation channel controls the electrical potential difference across the tonoplast. 相似文献
5.
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
6.
Keiko Mitsunaga Akiko Fujiwara Yukio Fujino Ikuo Yasumasu 《Development, growth & differentiation》1989,31(2):171-178
In cultured cells derived from micromeres isolated at the 16-cell stage of sea urchin embryos, the activity of H+ , K+ -ATPase became detectable after 15 hr of culture, when the cells started to form spicules, and then increased reaching a plateau from 25 hr of culture. The Na+ , K+ -ATPase activity of isolated micromeres increased to a maximum at 20 hr of culture and thereafter decreased gradually. Allylisothiocyanate, an inhibitor of H+ , K+ -ATPase, caused a decrease in intracellular pH (pHi) accompanied by blockage of 45 Ca deposition in spicule rods in spicule-forming cells at 30 hr of culture. Ouabain and amiloride had scarcely any effect on the pHi or 45 , deposition. In cultured cells exposed to nifedipine, which blocked 45 Ca deposition in spicule rods, allylisothiocyanate did not cause any decrease in pHi. These results show that H+ , which is generated in the overall reaction to produce CaCO3 from Ca2+ and HCO3 − , is probably released from the cells mainly in the reaction catalyzed by H+ , K+ -ATPase to maintain successive production of CaCO3 . 相似文献
7.
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
8.
As water and nutrient uptake should be related in the response of plants to salinity, the aim of this paper is to establish whether or not aquaporin functionality is related to H+ -ATPase activity in root cells of pepper ( Capsicum annuum L.) plants. Thus, H+ -ATPase activity was measured in plasma membrane vesicles isolated from roots and aquaporin functionality was measured using a cell pressure probe in intact roots. Salinity was applied as 60 m M NaCl or 60 m M KCl, to determine which ion (Na+ , K+ or Cl− ) is producing the effects. We also investigated whether the effects of both salts were ameliorated by Ca2+ . Similar results were obtained for cell hydraulic conductivity, Lpc , and H+ -ATPase activity, large reductions in the presence at NaCl or KCl and an ameliorative effect of Ca2+ . However, fusicoccin (an activator of H+ -ATPase) did not alter osmotic water permeability of protoplasts isolated from roots. Addition of Hg2+ inhibited both ATPase and aquaporins, but ATPase also contains Hg-binding sites. Therefore, the results indicate that H+ -ATPase and aquaporin activities may not be related in pepper plants. 相似文献
9.
Uptake and distribution of calcium, magnesium and potassium in cucumber of different age 总被引:1,自引:0,他引:1
Uptake and distribution of Ca+ , Mg2+ and K2+ were investigated in plants of cucumber ( Cucumis sativus L. var. Cila) which had been cultivated for 12, 19, 32, or 53 days in complete nutrient solution with 1.0 m M Ca2+ , 2.0 m M Mg2+ and 2.0 m M K+ . The + concentration was about the same in roots and shoots, while the Ca2+ and Mg2+ concentrations were low in roots compared to shoots. The K+ concentration decreased with increasing leaf age, while the Ca2+ and Mg2+ concentrations increased, except in older plants with flowers and fruits, where an increased concentration was found in the youngest leaves. This is discussed in connection with increased indoleacetic acid (IAA) synthesis in the shoot. Excision of leaves at different levels from 21-day-old plants, followed by uptake for 24 h from the nutrient solution on days 22 and 23, resulted in no immediate reduction in Ca2+ (45 Ca) uptake. Transport of Ca2+ increased to leaves above and below the excision point and total Ca2+ uptake remained at the same level as for the intact plant. It is suggested that regulation of Ca2+ uptake is primarily achieved in the root while the distribution in the shoot is regulated by the accessability of negative binding sites. 相似文献
10.
Calcium transport and ATPase activity in a microsomal vesicle fraction from corn roots 总被引:2,自引:2,他引:0
Abstract. An investigation has been made of methods for isolating membrane vesicles from corn ( Zea mays L.) roots active in calcium transport and K+ -stimulated ATPase. Pretreating and grinding the roots at room temperature with EGTA and fusicoccin increases basal ATPase activity. Improvement in Ca2+ uptake requires isolation of a scaled vesicle fraction by the method of Sze(1980). Sorbitol is superior to sucrose as an osmoticant. The pH optimum for Ca2+ uptake is 7.5. whereas that for associated ATPase activity is 6.5. Calmodulin strongly stimulates Ca2+ uptake in a process little affected by uncouplers and ATPase inhibitors, but blocked by chlorpromazine. Fusicoccin gives less stimulation of Ca2+ uptake which is sensitive to uncouplers, and is dependent upon isolation with fusicoccin present. It appears that the sealed vesicle fraction may possess two Ca2+ transport systems: a calmodulin-activated Ca2+ -transporting ATPase, and a Ca2+ /H+ antiport coupled through the protonmotive force to a fusicoccin-stimulated H+ -ATPase. 相似文献
11.
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
12.
The effects of external K+ , H+ and Ca2+ concentrations on the intracellular K+ concentration, [K+ ]i, and the K+ -ATPase activity in 2-day-old mung bean roots [ Vigna mungo (L.) Hepper] were investigated. [K+ ]i, in mung bean roots was markedly decreased by external K+ or H+ stress and did not recover the initial value even after the stress was removed. This decrease in [K+ ]i, gradually disappeared with the addition of (Ca2+ . Ca2+ may offset the harmful effects of ion stress. Ca2+ seems to have two effects on K+ transport; control of K+ permeability and activation of K+ uptake, although K+ -ATPase activity was inhibited by Ca2+ concentrations higher than 10–4 M. We suggest that Ca2+ activates K+ uptake indirectly through the acidification of the cytoplasm. 相似文献
13.
François Bouteau Ulrike Bousquet Anne-Marie Pennarun Monique Convert Olivier Dellis Daniel Cornel Jean-Pierre Rona 《Physiologia plantarum》1996,98(1):97-104
The purpose of our work was to investigate the functioning of K+ channels in protoplasts of laticifers of Hevea brasiliensis Muell. Arg., anastomosed into a network devoid of large central vacuoles, after tapping stress. Physiological functions such as proton pump activity and uptake of sucrose (a rubber precursor) were maintained, when the voltage-clamp method was used in vivo to record the whole-cell K+ current during the stress response.
A time-dependent inward current was induced in 50 m M KCl and rapidly inactivated (about 100 ms). The activation potential of this inward K+ channel was not closely dependent on Ek . This would be coherent with the 'valve model' of Schroeder and Fang (1991, Proc. Natl. Acad. Sci. USA 88: 11583–11587) involving the activation of a H+ -pump accounting for the K+ uptake observed in laticiferous cells under stress. The activation half-time of outward currents was clearly voltage dependent: from about 350 to 60 ms for 125 and 155 mV, respectively. Time-dependent outward current sensitivity to 5 m M BaCl2 or CaCl2 or to 5 μ M Erythrosin B showed that the K+ channels could be Ca2+ -dependent. Because of the positive values of the activation potential of the outward current, the possibility opens that an action potential exists, these cells being specialized for stress response. 相似文献
A time-dependent inward current was induced in 50 m M KCl and rapidly inactivated (about 100 ms). The activation potential of this inward K
14.
SAXITOXIN TETRODOTOXIN AND THE METABOLISM AND CATION FLUXES IN ISOLATED CEREBRAL TISSUES 总被引:2,自引:0,他引:2
Abstract— Saxitoxin and tetrodotoxin at low concentrations (10−7 -10−8 M) exerted similar inhibitory effects on the increase in lactate production and the redistrjbution of Na+ and K+ that normally accompany electrical stimulation of rat cerebral cortical slices. In contrast, the toxins exerted dissimilar effects on the production of lactate in response to low concentrations of Ca2+ in the medium. Inhibition by tetrodotoxin occurred at a higher concentration of Ca2+ and was significantly greater than that produced by saxitoxin at concentrations of Ca2+ below 0.75 mM. These differences were not related to differential effects on the redistribution of Na+ and K+ under such conditions. The toxins had different effects on Ca2+ influx. Tetrodotoxin, but not saxitoxin, inhibited the influx of Ca2+ in the absence of electrical stimulation. The influx of Ca2+ increased when electrical pulses were applied and tetrodotoxin inhibited this increase, whereas saxitoxin potentiated influx of Ca2+ during stimulation. Our results suggest that metabolic responses to conditions that increase excitability are not governed solely by changes in the distribution of Na+ and K+ . The differential effects of the toxins on Ca2+ fluxes suggest that one site of Ca2+ entry during electrical stimulation may be functionally independent of Na+ entry. 相似文献
15.
Multiple signalling pathways and their messengers – entailing changes in cytosolic-free Ca2+ ([Ca2− ]). pH (pH) and protein phosphorylation – underpin K+ and anion channel control during stomatal movements. This redundancy is wholly consistent with the ability of the guard cells to integrate the wide range of environmental and hormonal stimuli that affect stomatal aperture. Signal redundancy effects a spectrum of graded responses by linking pathways to gate signal transmission, and so boosts or mutes the final 'integrated signal' that reaches each ion channel. All evidence supports a role for the AB11 protein phosphatase and protein kinase elements in gating K+ channel sensitivity to pH and ABA. Changes in [Ca2+ ] I . in turn, are demonstrably sensitive to pH1 . Because each of these signal elements modulate and, in turn, are influenced by the activity of different sets of ion channels, the additional couplings engender a remarkably complex network, layering positive and negative controls with the ion channels that facilitate ion fluxes for stomatal movement. 相似文献
16.
SERGEY SHABALA JIAYIN PANG MEIXUE ZHOU LANA SHABALA TRACEY A. CUIN PETER NICK & LARS H. WEGNER 《Plant, cell & environment》2009,32(2):194-207
Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1–2 min) effects on net K+ and H+ transport at the root surface. H+ efflux decreased (from −18 to −12 nmol m−2 s−1 ) and K+ uptake (∼2 nmol m−2 s−1 ) reverted to efflux (∼−3 nmol m−2 s−1 ). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a ∼3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H+ efflux and stopped K+ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 m m NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (−50 nmol m−2 s−1 ). Kinetin (2–4 µ m ), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed. 相似文献
17.
Maria Chiara Pugliarello Franca Rasi-Caldogno Maria Ida De Michelis Claudio Olivari 《Physiologia plantarum》1991,83(3):339-345
The activity of the H+ -pyrophosphatase (H+ -PPase) was characterized in microsomes from 24-h-old radish ( Raphanus sativus L., ev. Tondo Rosso Quarantino) seedlings, which are virtually devoid of the tonoplast H+ -ATPase. The H+ -PPase was localized to membranes which roughly comigrated with the plasma membrane in a sucrose density gradient, but clearly separated from plasma membrane when microsomes were partitioned in an aqueous dextran-polyethylene glycol two-phase system. The H+ -PPase activity was strictly dependent on Mg2+ and on the presence of a monovalent cation (K+ =Rb+ =NH3 + Cs+ ≫Na+ Li+ ) and was insensitive to anions such as Cl−, Br−, NO3 − and SO4 2- . It was inhibited by F−, imidodiphosphate and Ca2+ . It had a pH optimum between pH 7.5 and 8.5 and was saturated by low concentrations of pyrophosphate (half saturation at 30 μ M pyrophosphate). All of these characteristics are identical to those reported for the tonoplast H+ -PPase from various plant materials. The functional molecular weight of the H+ -PPase, measured with the radiation-inactivation technique was 96 kDa. 相似文献
18.
Roles for Potassium and Calcium Channels in the Initiation of Sperm Motility in Rainbow Trout. 总被引:4,自引:0,他引:4
It is well known that the motility of spermatozoa in rainbow trout is suppressed by K+ . We showed here that although trout sperm are completely immotile in medium containing 5 mM K+ , motility was initiated by the subsequent addition of several mM Ca2+ , suggesting that both K+ and Ca2+ are related to the process of the initiation of sperm motility. It was further found that K+ channel blockers tetraethylammonium, nonyltriethylammonium, Ba2+ and Cs+ , as well as the Ca2+ channel blocker verapamil, inhibited the initiation of sperm motility at doses at which these reagents inhibit chnnel-related functions in other cells. However, Na+ channel blocker, tetrodotoxin and anion channel blocker 4, 4-diisothiocyatatostilbene-2, 2'-disulfonic acid inhibited the motility only at extremely high doses. These results suggest that transport of K+ and Ca2+ through ion channels at the plasma membrane of spermatozoa is the first event that triggers the initiation of sperm motility in rainbow trout. 相似文献
19.
Proton and calcium flux oscillations in the elongation region correlate with root nutation 总被引:7,自引:0,他引:7
The involvement of Ca2+ and H+ flux oscillations in root nutation was studied for decapped roots of corn ( Zea mays L. cv. Aussie Gold) placed horizontally. Net ion fluxes were measured around the elongation and meristematic regions using a microelectrode ion flux measuring system. High correlation between H+ flux oscillations and root nutations was found in the elongation region. Two oscillatory components of H+ flux, with periods of about 90 min and 7 min, correlated with root circumnutations and micronutations, respectively. The periods of H+ flux oscillations and rhythmical root movements in this region could be modified similarly by external factors including pH. In the meristematic region no association between ion flux behaviour and nutation was apparent. Ion flux oscillations and nutations both decreased in amplitude as the growth rate at the measured location decreased. Possible involvement of ion flux oscillations in root circumnutation is discussed. It is concluded that a model involving an internal oscillator must be developed to explain the H+ flux involvement in root nutations. 相似文献
20.
Temporal Characteristics of Potassium-Stimulated Acetylcholine Release and Inactivation of Calcium Influx in Rat Brain Synaptosomes 总被引:10,自引:9,他引:1
Abstract: The time course of Ca2+ -dependent [3 H]acetylcholine ([3 H]ACh) release and inactivation of 45 Ca2+ entry were examined in rat brain synaptosomes depolarized by 45 m M [K+ ]o . Under conditions where the intrasynaptosomal stores of releasable [3 H]ACh were neither exhausted nor replenished in the course of stimulation, the K+ -evoked release consisted of a major (40% of the releasable [3 H]ACh pool), rapidly terminating phase ( t 1/2 = 17.8 s), and a subsequent, slow efflux that could be detected only during a prolonged, maintained depolarization. The time course of inactivation of K+ -stimulated Ca2+ entry suggests the presence of fast-inactivating, slow-inactivating, and noninactivating, or very slowly inactivating, components. The fast-inactivating component of the K+ -stimulated Ca2+ entry into synaptosomes appears to be responsible for the rapidly terminating phase of transmitter release during the first 60 s of K+ stimulus. The noninactivating Ca2+ entry may account for the slow phase of transmitter release. These results indicate that under conditions of maintained depolarization of synaptosomes by high [K+ ]o the time course and the amount of transmitter released may be a function of the kinetics of inactivation of the voltage-dependent Ca channels. 相似文献