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1.
Calcium Inhibits Ion-Stimulated Stomatal Opening in Epidermal Strips of Commelina communis L. 总被引:2,自引:0,他引:2
Inoue, H. and Katoh, Y. 1987. Calcium inhibitsion-stimulatedstomatal opening in epidermal strips of Commelina communis L.J.exp. Bot. 38: 142149. Ca2+ suppressed both the ion-stimulated stomatal opening andH+ extrusion of pre-illuminated epidermal strips isolated fromCommelina communis L. In the absence of Ca2+, the rate of H+release was 18 nmol H+ cm2 h1 per epidermal stripunit area in 150 mol m3 KCL at pH 7?4. Half-maximum inhibitionof stomatal opening was observed with 220 mmol m3 ofCa2+. The hexavalent dye, ruthenium red, showed concentration-dependentprevention of the inhibition by Ca2+ of the ion-stimulated stomatalopening. The effect of ruthenium red was non-competitive, andthe K1 for the calcium inhibition was found to be 3?6 mmol m3.The calcium inhibition of H+ extrusion was also prevented byruthenium red. These results suggest that Ca2+ inhibits theactivity of electrogenic H+ translocating ATPase of the guardcell plasma membrane and leads to the suppression of stomatalopening. Key words: Calcium, Commelina communis, ruthenium red, stomata 相似文献
2.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.J.exp. Bot. 38: 10551068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m3. Mg2+ was also very effectiveat less than 50 mol m3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m3, Vmax(HCO3) 0·26µmol O2 mg1 chl min1), but use of citratesalts above 500 mol m2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m3, Vmax(HCO3)0·68 µmol O2 mg1 chl min1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity 相似文献
3.
Effects of Cations on the Cytoplasmic pH of Chara corallina 总被引:1,自引:0,他引:1
Smith, F. A. and Gibson, J.L. 1985. Effects of cationson the cytoplasmic pH of Chara corallina.J.exp. Bot.36: 13311340 Removal of external Ca2+ from cells of Chara corallina lowersthe cytoplasmic pH, as determined by the intracellular distributionof the weak acid 5,5dimethyloxazolidine2,4dione(DM0), when the external pH is below about 60. This effect isreversed, at least partially, by addition of the following cationsto Ca2+-free solutions: tetraethylammonium (TEA+) and Na+ at5 or 10 mol m-3, Li+ and Cs+ (10 mol m-3), or Mg2+, Mn2+ andLa3+ (02 or 05 mol m-3). Under the same conditions, increasesin pH sometimes, but not always, occur in the presence of 10mol m-3 K+ or Rb+ The results are discussed in relation to the major transportprocesses that determine pH and the electric potential differenceacross the plasma membrane, namely fluxes of H+ and of K+. Thesimplest explanation of the effects of the various cations testedin this study is that they primarily affect pHic via changesin influx of H+ but direct effects on the H+ pump or on K+ fluxesmay also be involved Key words: Chara corallina, cytoplasmic pH, cations, H+transport 相似文献
4.
Effects of removal of external Ca2+ on the cytoplasmic pH (pHc)of Chara corallina have been measured with the weak acid 5,5-dimethyl-oxazolidine-2,4-dione(DMO) as a function of external pH (pH0) and of the externalconcentration of K+. Removal of Ca2+ always decreased pHc whenpH0 was below about 6.0; the decrease was about 0.20.4units at pH0 5.0, increasing to about 0.5 units at pH0 4.3.When pH0 was 6.0 or higher the removal of Ca2+ had little orno effect on pHc. This situation was not altered by changingthe concentration of K+, though in some experiments at pH0 5.05.2there was a slight decrease in pH0 (about 0.2 units) when K+was increased from 0.2 to 2.0 mol m3, an effect apparentlyreversed when K+ was higher (5.0 or 10.0 mol m3). Theresults suggest that H+ transport continues in the absence ofexternal Ca2+, despite previous suggestions to the contrary,and that the H+ pump does not necessarily run near thermodynamicequilibrium with its chemical driving reaction. They indicate,rather, that the H+ pump is under kinetic control and providefurther evidence for the inadequacy of present models for theoperation of the H+ pump in charophyte cells, especially inrelation to its proposed role in regulating pHc. Key words: Chara corallina, Cytoplasmic pH, Calcium 相似文献
5.
Effluxes of K+ and Ca2+ from root segments of both wheat, Triticunaestivum L. cv. Capelle and mung bean, Vigna radiata (L.) Wilczek,were measured in the presence or absence of 20 mol m3para-fluorophenylalanine (p-FPA). The results were used to estimatethe compartment contents and transmembrane K+ and Ca2+ fluxesin root cortex cells. Using the Ussing-Teorell flux equationas the criterion, it was concluded that entry of K+ from theoutside solution to the cytoplasm, and from the cytoplasm tothe vacuole were active in both wheat and mung bean. Also, inboth species, Ca2+ entered the cytoplasm passively across theplasmalemma and was actively pumped back to the external solution.However, interpretation of the direction of active transportacross the tonoplast depends upon an assumption about Ca2+ activityin the cytoplasm. The only qualitative effect of p-FPA was to alter the drivingforce for K+ influx, across the plasmalemma in wheat, from anactive to a passive one. Quantitative effects of the analoguewere seen for K+ fluxes in both wheat and mung bean and forCa2+ fluxes in wheat. The p-FPA reduced transport of K+ in bothspecies, while transport of Ca2+ was unaffected. The implicationsof these results for the two pump hypothesis arediscussed. Key words: Triticum aestivum, Vigna radiata, Two pump hypothesis 相似文献
6.
Concentrations and Transport of Solutes in Xylem and Phloem along the Leaf Axis of NaCl-treated Hordeum vulgare 总被引:5,自引:0,他引:5
WOLF OLAF; MUNNS RANA; TONNET M. LORRAINE; JESCHKE W. DIETER 《Journal of experimental botany》1990,41(9):1133-1141
Hordeum vulgare cv. California Mariout was established in sandculture at two different NaCl concentrations (0.5 mol m3control and 100 mol m3) in the presenceof 6.5 mol m3 K +. Between 16 and 31 d after germination,before stem elongation started, xylem sap was collected by useof a pressure chamber. Collections were made at three differentsites on leaves 1 and 3: at the base of the sheath, at the baseof the blade, i.e. above the ligule, and at the tip of the blade.Phloem sap was collected from leaf 3 at similar sites throughaphid stylets. The concentrations of K +, Na+, Mg2+ and Ca2+were measured. Ion concentrations in xylem sap collected at the base of leaves1 and 3 were identical, indicating there was no preferentialdelivery of specific ions to older leaves. All ion concentrationsin the xylem decreased from the base of the leaf towards thetip; these gradients were remarkably steep for young leaves,indicating high rates of ion uptake from the xylem. The gradientsdecreased with leaf age, but did not disappear completely. In phloem sap, concentrations of K+ and total osmolality declinedslightly from the tip to the base of leaves of both controland salt-treated plants. By contrast, Na+ concentrations inphloem sap collected from salt-treated plants decreased drasticallyfrom 21 mol m3 at the tip to 7.5 mol m3 at thebase. Data of K/Na ratios in xylem and phloem sap were used to constructan empirical model of Na+ and K+ flows within xylem and phloemduring the life cycle of a leaf, indicating recirculation ofNa+ within the leaf. Key words: Hordeum vulgare, xylem transport, phloem transport, NaCl-stress 相似文献
7.
Determination of apoplastic K+ in intact leaves by ratio imaging of PBFI fluorescence 总被引:2,自引:0,他引:2
The tetraammonium salt of the K+ binding fluorescent dye benzofuranisophthalate (PBFI) was used to investigate the influence ofpotassium nutrition (0.12.1 mol m3) on apoplasticK+ inVicia faba leaves by means of ratio imaging. As a referencethe infiltration-centrifugation method was used. Both methodsreflected the influence of K+ supply on apoplastic K+ concentration.The abaxial leaf side revealed significantly higher K+ concentrations(20-25 mol m3) than the adaxial side (58 mol m3).Application of CCCP led to an immediate increase in apoplasticK+ demonstrating the reliability of the PBFI method. Key words: Vicia faba, leaf, apoplast, K+, PBFI, ratio imaging, ratiometric fluorescence microscopy 相似文献
8.
Growth and ion accumulation were measured in callus culturesof Cicer arietinum L. cv. BG-203, grown on media supplementedwith 0200 mol m3 NaCl. Fresh and dry weights decreasedat concentrations ranging from 100200 mol m3,the reduction being greater during the third and fourth weeksof culture. Slight stimulation of growth was observed at 25and 50 mol m3 NaCl. There was also a decrease in tissuewater content (fresh weight: dry weight) at 100200 molm3 NaCl. The concentration of Na+ and Cl in thetissue increased with increasing salinity of the medium. Mostof the accumulation of these ions occurred by the first weekwhile significant growth inhibition became apparent by onlythe third week of culture. Tissue K+ and Mg2+ decreased withincreasing salinization, the decrease being greater in K+ levels.Levels of Ca2+, however, were maintained throughout the experimentalrange. Key words: Cicer arietinum, NaCl stress, Callus cultures, Ion accumulation 相似文献
9.
Ricinus communis L. (castor bean) plants were grown in the absence(control) and in the presence of 100molm3NaCl with areciprocal split-root system, in which K+ was supplied to oneand NO3 to the other part of the root system. In theseplants shoot and, to a lesser extent, total root growth wereinhibited compared to plants with non-split roots. Without andwith NaCl, growth of roots receiving NO3 but noK+ (minusK/plus N-roots) was substantially more vigorous thanunder the reverse conditions (plus K/minus N-roots1).100mol m3 NaCl inhibited growth of minus K/plus N-roots1to the same extent as that of non-split roots, indicating thatexternally supplied K+ was not required for root growth undersaline conditions. In growth media without added K+ the rootdepleted the external low K + levels resulting from chemicalsdown to a minimum value Cmln (1.0 to 1.4 mmol m3); inthe presence of 100 mol m3 NaCl, Cmin, was higher (1018mmol m3) and resulted from an initial net loss of K +.Cmin, was pH-dependent The distribution of K+, Na+ and Mg2+along the root was measured. In meristematic root tissues, K+ concentrations were scarcely affected by external K+ or byNaCl, where Na + concentrations were low, but somewhat elevatedat low external K+ and/or high NaCl. In differentiated, vacuolatedtissues K + concentrations were low and Na+ concentrations high,if K + was not supplied externally and/or NaCl was present.The longitudinal distribution of ions within the root was usedto estimate cytoplasmic and vacuolar ion concentrations. Thesedata showed a narrow homoeostasis of cytoplasmic K+ concentrations(100140 mol m3) independent of external K + supplyeven in the presence of 100 mol m 3 NaCl. CytoplasmicNa + concentrations were maintained at remarkably low levels.Hence, external K+ concentrations above Cmin, were not requiredfor maintaining K/Na selectivity, i.e. for controlling Na+ entry.The results are discussed with regard to mechanisms of K/Naselectivity and to the importance of phloem import of K+ forsalt tolerance of roots and for cytoplasmic K+ homoeostasis. Key words: Ricinus communis, nitrate, potassium, root (split-root), salt tolerance, phloem transport 相似文献
10.
Potassium Transport in Enteromorpha intestinalis (L.) Link: II. EFFECTS OF MEDIUM COMPOSITION AND METABOLIC INHIBITORS 总被引:2,自引:0,他引:2
In springwater (25.5 mol m3 Cl, 20.4 mol m3Na+, 0.14 mol m3 K+) Enteromorpha intestinalis couldnot survive for more than a few weeks unless provided with 0.5mol m3 K+ in the medium or alternatively exposed to seawaterfor 1 day per week. Maintenance of a cytoplasmic K+ level ofabout 200 mol m3 is critical for the maintenance of normalmetabolic activity. Net gains of intracellular K+ occurred whenthe plants were transferred from low-salinity to seawater; converselylarge net losses occurred when plants were transferred fromseawater to springwater. These two processes were not simplythe reverse of one another; net gain of K+ involved a largeincrease in the tracer flux both into and out of the cell butnet loss of K+ virtually halted the tracer flux into the cell.Any injury incurred by rapid salinity changes was short-lived;plants were rapidly able to adjust intracellular [K1.K+). K+(orto some extent Rb+) was found to be necessary in the effluxmedium for 42K+ exchange to occur. The osmotic concentrationof the medium was also important but extracellular Na+ and Clconcentrationswere not critical. K+ influx and efflux in both springwaterand seawater were largely independent of light and were sensitivein varying degrees to a range of common metabolic inhibitorsand uncouplers. The results are best explained by the presenceof an active K+ influx, generated by an ATP-dependent K+ pumpat the plasmalemma. Key words: Enteromorpha, Potassium transport, Salinity changes, Uncouplers, Inhibitors 相似文献
11.
This paper reports the effects of low O2 concentration (001,0055, and 0.115mol m3) in nutrient solutions onK+/Na+ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O2 uptake,K+ uptake and K+/Na+ selectivity were all more pronounced and/oroccurred at higher external O2 concentrations in the apex (02mm) than in the expanding tissues (24 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (412 mm). Selectivity for K+ over Na+ in roots and shoots was particularlysensitive to O2 deficiency. For example, in apical tissues (02mm) K + /Na+ selectivity was already reduced at 0.115 mol m3O2, yet at this O2 concentration there was no effect on eithergrowth or (K+/Na+) uptake. Upon transfer from 0.01 to 0.26 mol m3 O2, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K+ + Na+) concentrations and K+/Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K+ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K+/Na+ selectivity, expanded and expanding tissues 相似文献
12.
MEMON ABDUL RAZAQUE; SIDDIQI M. YAEESH; CLASS ANTHONY D. M. 《Journal of experimental botany》1985,36(1):79-90
Barley (Hordeum vulgare L.) varieties differed in their raponseto [K+]0, in terms of their utilization efficiencies (UE = freshweight. concentration of [K+]11). At low [K+]0, Compana,an efficient-non-responder demonstrated superior utilizationof absorbed K+. On the other hand, at high [K+]0, Fergus (anefficient responder) and BT 334 (an inefficient responder) hadhigher UE values for K+ than Compana which performed poorlyat this [K+]0. Kinetic parameters for K+ activation of the enzyme pyruvatekinase from 12 barley varieties, representing a range of UEvalues, were determined. Varieties showed substantial differencesin their Vmax values (P<0·01). Compana, an efficientvariety, had the highest Vmax (31 µmol g1 freshwt. h1) which was about 50% higher than that of Mingo,an inefficient variety. By contrast, Km values for the enzymeswere not significantly different among varieties The mean valuesfor all varieties (3·9±0·15 mol m3K+) is far below the estimated cytoplasmic [K+] (100-200 molm3). It is, therefore, unlikely that differences in theutilization of K+ by these varieties can be explained on thebasis of differential requirements for (K+) activation of theseenzymes. Alternative possibilities for differences in the utilizationof K+ are discussed. Key words: K+ utilization efficiency, Pyruvate kinase, Barley varieties 相似文献
13.
Darkening after illumination induces a transient hyperpolarizationof the plasma membrane of the unicellular green alga Eremosphaeraviridis de Bary. With electro-physiological methods, in particularthe two electrode voltage-clamp technique, we investigated theion fluxes involved in this transient potential change (TP).The question was whether other ion currents besides those carriedby the known Ca2+-dependent K+ channel take part in this actionpotential-like, but hyperpolarizing, response. At maximum hyperpolarizationvoltage-clamp measurements resulted in N-shapedI/V curves, known from other botanical systems. The differentinstantaneous current components of the N-shaped I/V curvesoccurred at different times during a single transient potentialchange (TP). Substitution of alkali metal cations in the bathingsolution by NMG/NO3 showed that the inward currents in the I/Vcurves were not carried by an influx of K+ into the cytoplasm.The voltage amplitude of the TP not only depended on the externalK+ concentration, but also on the Mg2+ concentration in thebathing solution. Increasing Mg2+ concentrations shifted themembrane potential in the top of the TP in the direction ofthe Nernst potential of Mg2+ and resulted in an increased inwardcurrent component of the N-shaped I/V curves. Another currentcomponent was found to be carried not by cations but by an effluxof anions. It was a voltage-dependent component with a maximumcurrent amplitude at voltages of about 220 to 240mV, and was blocked by the anion channel inhibitors anthracen-9-carboxylicacid (A9C), (5-nitro-2-3-phenylpropylamino) benzoic acid (NPPB)and ZnCI2. Based on these data a model is proposed which explainsthe N-shape of the I/V curves observed during the transientpotential change of the alga E. viridis by the combination ofan inward cation current with an inward anion current and theoutward cation current carried by the Ca2+-dependent K+ channels. Key words: Anion current, cation current, Eremosphaera viridis, potassium channel, voltage-clamp 相似文献
14.
Plants of Lupinus albus L., cv. Ultra, were grown hydroponicallywith NO3-nutrition for 51 d under control (0.05 mol m3Na+ and 10 mol m3 Cl) and saline (40 mol m3NaCI) conditions. Plants were harvested 41 and 51 d after germinationand analysed for content and net increment of C, N and the mineralcations K+, Na+, Mg2+, and Ca2+ and the anions Cl, NOJ,malate, phosphate, and SO42. Roots, stem interaodes,petioles and leaflets were analysed separately. During the studyperiod net photosynthesis, respiratory losses of CO2 from shootand root and the composition of the spontaneously bleeding phloemsap and the root pressure xylem exudate were also determined.Using molar ratios of C over N in the transport fluids, incrementsof C and N, and photosynthetic gains as well as respiratorylosses of C, the net flows of C and N in the xylem and phloemwere then calculated as in earlier studies (Pate, Layzell andMcNeill, 1979a). Knowing the carbon flows, the ratios of ionto carbon in the phloem sap, and ion increments in individualorgans, net flows of K+, Na+, and Cl over the study periodwere also calculated. Salt stress led to a general decrease of all partial componentsof C and N partitioning indicating that inhibitions were notdue to specific effects of NaCI salinity on photosynthesis oron NO3 uptake. However, there were differences between variouslyaged organs, and net phloem export of nitrogenous compoundsfrom ageing leaves was substantially enhanced under saline conditions.In addition, NO3reduction in the roots was specificallyinhibited. Uptake and xylem transport of K+ was more severelyinhibited than photosynthetic carbon gain or NO3 uptakeby the root. K+ transport in the phloem was even more severelyrestricted under saline conditions. Na+ and Cl flowsand uptake, on the other hand, were substantially increasedin the presence of salt and, in particular, there were thenmassive flows of Na in the phloem. The results are discussedin relation to the causes of salt sensitivity of Lupinus albus.The data suggest that both a restriction of K+ supply and astrongly increased phloem translocation of Na+ contribute tothe adverse effects of salt in this species. Restriction ofK+ supply occurs by diminished K+ uptake and even more by reducedK+ cycling within the plant. Key words: Lupinus albus, salt stress, phloem transport, xylem transport, partitioning, carbon, nitrogen, K+, Na+, CI 相似文献
15.
Ricinus communis L. var. Gibsonii was grown in Long Ashton nutrientmedium with either 12mol m3 NO3 or 8.0 mol m3NH+4 as N source. Two plants from each N treatment were harvestedtwice a week and analysed for C, N, P, S, NO3, SO24ClK+Na+, Ca2+ Mg2+ and ash alkalinity. Statistical analysis of thedata showed that the effect of age and N source was differentfor the chemical variables analysed. Thus [Na+] was unaffectedby age or N source, and for both N sources [Mg2+] started atthe same level and decreased at the same rate as the plantsmatured. With NH+4 as N source, [SO24] was higher thanwith NO3, but did not alter with age. The concentrations,in mmol g1 dry wt, of C, organic N, K+ and Ca2+ weredifferent for the two N sources, but the levels of these variablesaltered with age in the same way for both N sources; i.e. therewas no age x N interaction. In the case of P, NO3, Cl and COO, however,age-related variations were different for the two N sources.It is concluded, inter alia, that [Na+] is determined by external[Na+] alone, and that K+, Ca2+ and Cl are the inorganicions actively involved in charge balance during ion uptake bythe roots. Key words: Ontogeny, Chemical composition, Plant nutrition 相似文献
16.
Potassium-Ammonium Uptake Interactions in Tobacco Seedlings 总被引:6,自引:0,他引:6
SCHERER HEINRICH W.; MACKOWN CHARLES T.; LEGGETT J. EVERETT 《Journal of experimental botany》1984,35(7):1060-1070
Short-term (< 12 h) uptake experiments were conducted with67-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K+ andNH4+. At equal solution concentrations (0.5 mol m3) netK+ uptake was inhibited 3035% by NH4+ and NH4+ uptakewas decreased 924%. Removal of NH4+ resulted in completerecovery in K+ uptake rate, but NH4+ uptake rate did not recoverwhen K+ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m3. The relative effectof K+-NH4+ interactions was not altered when Cl- was replacedwith SO42, but the magnitudes of the uptake rates wereless in the absence of Cl-. The Vmax for NH4+ uptake was reducedfrom 128 to 105 µmol g1 dry wt. h1 in thepresence of 0.5 mol m3 K+ and the Km for NH4+ doubledfrom 12 to 27 mmol m3 in the presence of K+. The resultsof these K+-NH4+ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K+ coupled to NH4+influx via an antiporter cannot be ruled out as contributingto the decrease in net K+ uptake. Key words: Nicotiana tabacum, K+, NH4+, Uptake interactions 相似文献
17.
Potassium Transport Across the Membranes of Chara: IV. INTERACTIONS WITH OTHER CATIONS 总被引:3,自引:0,他引:3
Smith, J. R. and Kerr, R. J. 1987. Potassium transport acrossthe membranes of Chara. IV. Interactions with other cations.J.exp. Bot. 38: 788799. The 42K influx () and the membrane electrical conductance (Gm were measured simultaneously forintemodal cells of Chara australis bathed in solutions containingdifferent concentrations of various cationic species. It wasfound that the potassium permeability (Pk,) of the membranewas reduced significantly when the bathing [CaSO4 exceeded 01mol m1. Concentrations of tetra-ethylammonium ions (TEA)exceeding 0?3 mol m3 were found to reduce significantlyboth and , but even high concentrations (10 mol m3)usually did not reduce the fluxes by more than a factor of 3.Na+ ions were found to be capable of reducing PK by a factorof 5?6 to a value of 4 nm s1. This appeared to be aminimum value for PK which was not reduced even if several inhibitorycations were present simultaneously. This suggests that possiblyonly one of two different modes of K+ transport can be inhibitedby cations. The possible geometry of the inhibitable K+ channelis briefly discussed and the implications of the presence ofNa+ and Ca2+ ions in many common bathing solutions are considered. Key words: Potassium, calcium, tetraethylammonium, inhibition 相似文献
18.
This paper examines the ionic composition of wound-induced electricalcurrents in higher plant tissue, using two non-injurious electrophysiologicaltechniques. By simultaneous recording of K+, H+ , and Ca2+ ionfluxes with extracellular ion-selective microelectrodes, wehave determined that a Ca2+ influx (2.4 µA cm2),a small H+ influx (0.17 µA cm2) and a large K+efflux (16 µA cm2) occur immediately after woundingin roots of Pisum sativum L. var. Greenfeast. Using an extracellularvibrating probe at the wound site, net ion currents of 26 µAcm2 were measured 5 min after wounding. In a more concentratedbathing medium (1/4 rather than 1/16 strength Hoagland's solution),net ion currents of 59 µA cm2 were measured, andthese would appear to be the largest extracellular currentsthat have been measured in plants. We made a quantitative comparisonof the summed ion fluxes with the net ion currents and thisrevealed that ion fluxes, in addition to those measured here,occur after wounding. Key words: Wounding, ion flux, electric current, calcium, potassium 相似文献
19.
Smith, J. R., Smith, F. A. and Walker, N. A. 1987. Potassiumtransport across the membrane of Chara. I. The relationshipbetween radioactive tracer influx and electrical conductance.J.exp. Bot. 38:731751. The 42K influx () and the electrical conductance (Gm) were measured simultaneously for the membraneof internodal cells of Chara australis as a function of theexternal [KCl] (K?. In bathing solutions of pH = 5?0, progressively increased from 20?5to 430?60 nmol m2 s1 and Gm increased from 0?36?0?02to 3?8?0?8 S m2 when K? was increased from 0?1 to 10mol m3. The resting membrane potential difference (p.d.)was approximately -135 mV for low K? and approached the expectedNernst equilibrium p.d. for K+ ions when K? > 1?0 mol m3.Measurements of 36Cl influx suggested that the 42K influx waspredominantly electrogenic. The equivalent Goldman permeabilityto K+ ions (Pk) was approximately 2030 nm s1 anddid not vary significantly with increasing K?. The equivalentconductance attributable to the electrogenic transport of K+ ions was calculated from assuming passive, independent diffusionof K+ ions and the ratio was found to be typically close to one. It was also found that themagnitudes of and Gm measuredsimultaneously for each individual cell were also well correlatedfor K? 1?0 mol m3, and that the slope of the line ofbest fit was close to one. For each K? it was found that theconductance not attributable to K+ translocation and presumablyassociated primarily with the transport of protons or theirequivalents was typically 0?20?5 Sm2. For K? >1?0 mol m3 the results indicated that the transport ofK+ ions was essentially independent, i.e. there was no evidencefor flux interactions. The results also indicated that the equivalentconductance derived from the measured 42K influx could usefullyindicate the fraction of the electrical conductance attributableto the translocation of K+ ions. Key words: Potassium, conductance, influx 相似文献
20.
The activity of plasma membrane H+-ATPase was measured withmembrane fragments of guard-cell protoplasts isolated from Viciafaba L. ATP hydrolytic activity was slightly inhibited by oligomycinand ammonium molybdate, and markedly inhibited by NO3and vanadate. In the presence of oligomycin, ammonium molybdateand NO3, the ATP-hydrolyzing activity was strongly inhibitedby vanadate. It was also inhibited by diethylstilbestrol (DES),p-chloromercuribenzoic acid (PCMB) and Ca2+, but slightly stimulatedby carbonyl cyanide m-chlorophenylhydrazone (CCCP). The acitivityhad higher specificity for ATP as a substrate than other phosphoricesters such as ADP, AMP, GTP and p-nitrophenylphosphate; theKm was 0.5 mM for ATP. The activity required Mg2+ but was notaffected by K+, and it was maximal around pH 6.8. When guard-cellprotoplasts were used instead of membrane fragments, the ATPaseactivity reached up to 800µmol Pi.(mg Chl)1.h1in the presence of lysolecithin. These results indicate thatthe guard cell has a high plasma membrane H+-ATPase activity. (Received December 23, 1986; Accepted April 28, 1987) 相似文献