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1.
The xylem vessels of excised adventitious roots of onion, Alliumcepa, were perfused with unbuffered nutrient solution adjustedinitially to either pH 9·3 or 3·9; the pH of thesolution after passage through the xylem, at rates not lessthan 2 xylem volume changes min1, was close to pH 6·5in both instances. The flux of H+ across the xylem/symplastboundary into mildly alkaline, phosphate-buffered solutionsperfusing the vessels could be increased greatly with increasingbuffer strength, up to a maximum value between 0·51·0pmol H+ mm2 s1. The apparent neutralization ofacidic malic acid buffers had a slightly lower maximum capacity,equivalent to 0·3 to 0·5 pmol H+mm2 s1. The addition of 5·0 pmol m3fusicoccin (FC) to the xylem perfusion solution stimulated theentry of H+ into the xylem; in unbuffered perfusion solutionsthe pH fell to pH 3·6 after a lag of 2535 min.FC additions to phosphate-buffered solutions also stimulatedthe H+ flux to an extent similar to that in unbuffered solution,viz. 0·20·4 pmol mm2 s1. The release of K+ (36Rb-labelled) into xylem sap transientlyincreased as the [K+] in weakly buffered perfusion solutionswas raised stepwise; a very marked increase being seen whenthe concentration was raised to 100 mol m3 from 40 molm3. The addition of 5·0 mmol m3 FC to theperfusing solution containing 100 mol m3 K+ rapidly decreasedthe K+ flux to the xylem as the H+ flux increased. Fusicoccinalso inhibited the flux of K+ into unbuffered perfusion solutionsbut the effect appeared reversible. Addition of 10 mmol m3abscisic acid (ABA) to the perfusion solution quickly producedtransient increases in both K+ and H+ fluxes into the xylem.In this and other experiments using weakly phosphate-bufferedperfusing solutions, H+ fluxes were comparable in size to thoseof K+ The results are consistent with the idea that the stele of onionroots contains a proton trarislocating ATPase whose activityresponds to the pH of the xylem sap. It is evident that theactivity of the proton secreting and proton neutralizing mechanismsin the xylem parenchyma control the movement of other ions acrossthe xylem/symplast boundary. Key words: Xylem perfusion, fusicoccin, abscisic acid, pH gradient 相似文献
2.
Chloride Transport in Chara corallina and the Electrochemical Potential Difference for Hydrogen Ions 总被引:6,自引:0,他引:6
The pH of the cytoplasm of Chara corallina cells has been measuredwith the weak acid 5,5-dimethyloxazolidine-2,4-dione (DM0).Over an external pH range 4·59·5 the resultsfit the regression equation pHcytoplasm=6·28+0·22pHout. Using measured values of the electric potential difference acrossthe plasmalemma we have calculated the electrochemical potentialdifference across this membrane for H+ and Cl. Thesedata are used to test the hypothesis that the inward transportof Cl is coupled to the inthix of H+ or, which comesto the same thing, efflux of OH. One-for-one couplingwill not give net Cl uptake from solutions with pH greaterthan about 7·2, unless the cytoplasmic Cl concentrationis lower than 10 mM, or the pH just outside the membrane islower than that in the bulk solution. It is shown that net Cluptake proceeds from solutions with pH up to 9. The alternative possibility is that Cl transport is broughtabout by co-transport of two H+ for each Cl; this isnot ruled out by the results reported. Such a mechanism mightbe detectable by its electrogenic effect: although such effectshave not been detected, it is shown that they would be smallunder most conditions. Other possible mechanisms are discussed. 相似文献
3.
Ammonium and methylammonium ions greatly increase the rate ofCl transport in Chara corallian. This effect is dependenton the pH of the bathing solution. The amine-stimulated Clinflux is small at pH 5·5, increases to a maximum atpH 6·57·5, and decreases again as the pHis raised to 8·5. Increased Cl influx is accompaniedby an increase in cytoplasmic pH, as calculated from the distributionof DMO. When the external pH lies between 5·5 and 7·3,cytoplasmic pH in the absence of amine is 7·657·70,with an increase of 0·150·25 in the presenceof amine. As external pH is increased above 7·3, cytoplasmicpH also increases, with progessively less effect of amine. Although the relationship between Cl influx and cytoplasmicpH is not simple, the results provide evidence in accord withthe hypothesis that Cl transport in Chara involves H+Clsymport, or the equivalent OHCl antiport.The possible role of cytoplasmic pH as a factor involved inthe regulation of membrane transport in Chara is discussed. 相似文献
4.
Transient Cytoplasmic pH Changes in Correlation with Opening of Potassium Channels in Eremosphaera 总被引:1,自引:0,他引:1
Steigner, W. Khler, K., Simonis, W. and Urbach, W. 1988. Transientcytoplasmic pH changes in correlation with opening of potassiumchannels in Eremosphaera.J. exp. Bot. 39: 2336. The role of the cytoplasmic pH (pHc) of Eremosphaera viridisin the signal transduction chain after light-off from the chloroplaststo the K+ channels in the plasmalemma of this unicellular algawas investigated. The temporary opening of K+ channels is indicatedby a transient hypcrpolarization (TP). To record rapid changesof pHc, continuous measurements with pH sensitive micro-electrodeswere carried out. (i) Under normal conditions pHc in the light(7·56 ±0·2) did not differ from pHc inthe dark (7·62 ±0·2). (ii) The vacuolepH ranged between 4·8 and 5·2. (iii) After light-offa rapid transient acidification of pHc O19±0·07occurred and a TP was released, (iv) In every case, the startof the transient acidification after light-off preceded thehyperpolarization by about 3s. (v) Light-on caused a rapid transientalkalinization but never a TP. (vi) Change to acid externalmedium (3.2) transiently acidified the cytoplasm and was ableto release a TP. (vii) After addition of NH4Cl, pHc again showeda rapid transient acidification and the release of a TP. The origin of the protons appearing in the cytoplasm after light-offis discussed critically with respect to the buffer capacity.Either direct or indirect translocation is a possible mechanismfor the movement of H+ from the chloroplasts into the cytoplasm.The intracellular acidification and its relation to the openingof potassium channels in the plasmalemma leads us to suggestthat a sudden change of pHc is a potent internal signal factorin Eremosphaera viridis. Key words: Cytoplasmic pH, transient potential, K+channels, Eremosphaera viridis 相似文献
5.
Effects of Two Plasmalemma ATPase Inhibitors on H+ Extrusion and Intracellular pH in Elodea densa Leaves 总被引:2,自引:0,他引:2
Beffagna, N. and Romani, G. 1988. Effects of two plasmalemmaATPase inhibitors on H+ extrusion and intracellular pH in Elodeadensa leaves.J. exp. Bot. 39: 10331043. Elodea leaves in the dark show very little exchange of H+ withthe medium in the external pH range between 5.0 and 6.0. Thepresence of fusicoccin and potassium in the medium markedlystimulates H+ extrusion. Fusicoccin- and K+ -induced H+ extrusionis inhibited by either erythrosin B (EB) or Na-orthovanadate,two inhibitors of H+ transporting plasma membrane ATPase. EBcompletely inhibits it from the first 30 min of treatment, whensupplied at pH 5.5 at a concentration of 30 mmol m3.Vanadate also inhibits H+ extrusion, this effect becoming evidentonly after 45 min of treatment. After this time inhibition iscomplete with 250 mmol m3 vanadate but only partial forlower concentrations. In the presence of either inhibitor the intracellular pH, measuredas cell sap pH, is significantly lowered. When the intracellularpH changes are determined on vacuole and, separately, on cytoplasmby the weak acid and base distribution method, acidificationof both compartments is found to accompany the blocking of H+extrusion by either of the inhibitors. Key words: Intracellular pH, vanadate, erythrosin B, H+pumping 相似文献
6.
Proton Transport and pH Control in Sinapis alba Root Hairs: A Study carried out with Double-Barrelled pH Micro-electrodes 总被引:3,自引:0,他引:3
Continuous measurements of cytoplasmic pH (pHc) in Sinapis roothairs have been carried out with double-barrelled pH-micro-electrodesin order to gain information on translocation of protons acrossthe plasmalemma and cytoplasmic pH control. (i) The cytoplasmicpH of Sinapis (733 ? 012, standard conditions)changes no more than 0.1 pHc, per pHo-unit, regardless of whethercyanide is present or not. (ii) Weak acids rapidly acidify pHcand hyperpolarize, while weak bases alkalize pHc and depolarizethe cells, (iii) 1.0 mol M,3 NaCN acidifies the cytoplasm by0.4 to 0.7 pH-units, but alkalizes the vacuole. (iv) 20 mmolm3 CCCP has no significant effect on pHc, if added atpH 9.6 or 7.2, but acidifies pHc by 1.3 units at pH 4.3. Inthe presence of CCCP, cyanide acidifies the cytoplasm, (v) Chloridetransiently acidifies pHc, while K+, Na+, and have no significant effects, (vi) Cytoplasmic buffer capacityforms a bell-shaped curve versus pHc with an optimum of about50 mol m3 H+pHc-unit. The modes of proton re-entry and the effects of active and passiveproton transport on cellular pH control are critically discussed.It is suggested that the proton leak, consisting of H+-cotransport(e.g. H+/Cl) rather than H+-uniport, is no threat topHc. The proton export pump, although itself reacting to changesin pHc, influences pHc only to a minor extent. It is concludedthat buffer capacity and membrane transport play moderate rolesin pHc control in Sinapis, while the interlocked H+-producingand -consuming reactions of cellular metabolism are the mainregulating factors. This makes pH control in Sinapis quite differentfrom bacterial and animal cells. Key words: Cytoplasmic pH, double-barrelled pH micro-electrode, pH control, proton transport, Sinapis 相似文献
7.
Potassium transport has been studied in the marine euryhalinealga, Enteromorpha intestimlis cultured in seawater and in low-salinitymedium (Artificial Cape Banks Spring Water, ACBSW; 25·5mol m3 Cl, 20·4 mol m3 Na+, 0·5mol m3 K+). K+ fluxes were measured using 42K+ and 86Rb+although 86Rb+ does not act as an efficient K+ analogue in thisplant. 42K+ experiments on seawater plants typically exhibiteda single protoplasmic exchange phase whereas 86Rb+ exhibitedtwo exchange phases. Compartmental analysis of 86Rb+ effluxexperiments on seawater-grown Enteromorpha plants were usedto deduce the intracellular partition of K+ between the cytoplasm(279±38 mMolal) and vacuole (405±68 mMolal). Theplasmalemma K+ flux in plants in seawater was greater in thelight than in the dark (563±108 nmol m2 s1versus 389±66·7 nmol m2 s1). Inlow-salinity plants, separate cytoplasmic and vacuolar exchangephases were apparent. Analysis of 42K+ efflux experiments onlow-salinity plants yielded a cytoplasmic K+ of 222±38mMolal and a vacuolar K+ of 82±11 mMolal. The plasmalemmaand tonoplast flux was 23±4·5 nmol m2 s1. The Nernst equation showed that, although K+ was close to electrochemicalequilibrium, active accumulation of K+ across the plasmalemmaoccurred in plants in seawater and ACBSW both in the light anddark. K+ was also actively transported inwards across the tonoplastin low-salinity plants. The electrochemical potential for K+across the plasmalemma ranged from 2·41±0·60kJ mol1 in plants grown in seawater in the light to 5·79±0·87kJ mol1 for plants in ACBSW in the light. Although K+is close to electrochemical equilibrium, the flux of K+ in plantsin both seawater and ACBSW media is high, hence the power consumptionof K+ transport is high. The permeability of K+ (PK+) was significantlyhigher in the light than in the dark in plants in seawater (about7·0 versus 2·5 nm s1) but in plants inlow-salinity (ACBSW) medium the permeability was independentof light (about 12 nm s1). The energy requirements ofactive K+ transport by ATP-dependent pumps is discussed. Key words: Enteromorpha, Potassium transport, Ionic relations, Saltwater, Low salinity, Thermodynamics 相似文献
8.
GYENES M.; ANDRIANOV V. K.; BULYCHEV A. A.; KURELLA G. A. 《Journal of experimental botany》1978,29(5):1185-1195
The effects of light on the pH in the vacuole and the electricpotential difference across the plasmalemma and the tonoplastof Nitellopsis obtusa were investigated by means of conventionaland H+-specific glass or antimony microelectrodes. Illuminationis found to bring about a decrease in the pH of the vacuolarsap by 0.10.5 units concomitant with a depolarizationof the cell. The light-induced changes of the potential differenceand the vacuolar pH depend in different ways on the pH of theexternal medium (pHo). At pHo 9.0 cells exhibit great light-inducedpotential changes (up to 100 mV), but only small pH changesof the vacuolar sap. At neutral or slightly acidic pHo valuesthe amplitude of the light-induced pH changes in the vacuoleincreases up to 0.30.5 pH units, but the amplitudes ofthe potential changes at the plasmalemma are relatively small.At pHo 9.0 a transient acidification of the medium is observedupon illumination whereas at lower pH values light-induced alkalinizationwas only seen. Transfer of the cells from pHo 9.0 to pHo 7.5results in a cell hyperpolarization by 6080 mV and adecrease of the vacuolar pH by 0.40.5 units under lightconditions but has no significant effect on the potential andthe vacuolar pH in the darkness. It is proposed that mechanismsof active H+ extrusion from the cytoplasm are located both inthe plasmalemma and the tonoplast. The observed acidificationin the vacuole appears to be determined by a light-induced increaseof the concentration of H+ in the cytoplasm. The H+ conductionof the plasmalemma seems to increase on illumination. The patternof the light-induced H+ fluxes across the tonoplast and theplasmalemma depends crucially on the extent of the light-inducedchanges in the H+ conductance and on the electrochemical gradientfor H+ at the plasmalemma. 相似文献
9.
Bean plants (Phaseolus vulgaris L. cv. Fardenlosa Shiny) werelabelled with carbon-11 via their first trifoliate leaves when3-weeks-old and the transient inhibitions of translocation causedby the application of ammonium chloride solutions (10 mol m3)to a peeled region of stem were studied. At pH 6·5 theammonium was without effect. At pH 11·0 even a briefapplication inhibited translocation for many minutes, whilelonger applications inhibited translocation for considerablylonger. Solutions of 10 mol m3 sodium chloride were withouteffect at either pH. At pH 6·5 ammonium chloride solution contains predominantlyammonium ions (NH4+) and at pH 11·0 predominantly dissolvedammonia gas (NH3). Hence we conclude that phloem transport withinbean stems is inhibited by dissolved ammonia gas but not ammoniumions. Key words: Phloem translocation, transient inhibition, ammonia, ammonium ion 相似文献
10.
Ion Composition of the Chara Internode 总被引:2,自引:0,他引:2
Ion compositions of the cytoplasm and the vacuole of Chara australiswere analyzed according to Kishimoto and Tazawa (1964) and Kiyosawa(1979a). The ions in the cytoplasm and the vacuole analyzedwere K+, Na+, Ca2+, Mg2+, Cl, NO3 and H2PO4.Assuming that the volume of the cytoplasm Vp is 10% of thatof the whole cell V, the concentrations of K+, Na+, Ca2+, Mg2+,Cl, NO3 and H2PO4 in the cytoplasm averaged70, 15, 13, 4.6, 31, 2.2 and 16 mM, respectively. If the volumeof the cytoplasm was assumed to be 5% of that of the whole cell,their averaged concentrations were 139, 31, 25, 9.2, 62, 4.4and 33 mM, respectively. The averaged ion compositions of thecell sap were K+, 111; Na+, 47; Ca2+, 4.4; Mg2+, 8.9; Cl,91; NO3, 3.3 and H2PO4, 6.0 mM. These values,taking the concentrations and the charges of the protein (Kiyosawa1979b) and amino acids (Sakano and Tazawa 1984) into accountand assuming the presence of some uni- or oligovalent anionsand/or small nonelectrolyte molecules, could explain fairlywell both the electroneutrality and the osmotic pressure ofthe cell, except when Vp/V = 5%. (Received May 18, 1987; Accepted September 29, 1987) 相似文献
11.
The acidophilic alga Dunaliella acidophila exhibits optimalgrowth at pH 1. We have investigated the regulation of phosphateuptake by this alga using tracer techniques and by performingintracellular phosphate measurements under different growthconditions including phosphate limitation. In batch culturewith 2·2 mol m3 phosphate in the medium the uptakeof phosphate at micromolar phosphate concentrations followeda linear time dependence in the range of minutes and rates werein the range of 1 µmol phosphate mg1 chl h1,only. However, under discontinuous phosphate-limited growthconditions, tracer influx revealed a biphasic pattern at micromolarphosphate concentrations: An initial burst phase resulted ina 104-fold internal phosphate accumulation and levelled offafter about 10 s. A double reciprocal plot of the initial influxrates obtained for phosphate-limited and unlimited algae exhibitedMichaelis-Menten kinetics. Phosphate limitation caused a significantactivation of the maximum velocity of uptake, yielding Vmaxup to 1 mmol mg1 chl h1 as compared to valuesin the order of 50 µmol phosphate mg1 chl h1for the second phase (this magnitude is also representativefor non-limited batch cultures). Concomitantly the Michaelisconstant was altered from 4 mmol m3 to 0·7 mmolm3. The rapid uptake of phosphate was inhibited by arsenateand FCCP and was not stimulated by Na+. The pH dependence oftracer accumulation and measurements of the intracellular phosphatepool under different growth conditions indicate that at lowpH and low external phosphate concentrations the high protongradient present under these conditions is utilized for a H3PO4uptake or a H+/H2PO4 cotransport. However, when the externalphosphate concentration was increased to levels sufficientlyhigh for transport to be driven by the positive membrane potential(10 mol m3 phosphate), the pH dependence of phosphateuptake was more complex, but could be explained by the uptakeof H3PO4 or a H+/H2PO4-cotransport at low pH and a differenttype H2PO4-transport (with unknown type of ion coupling)at high pH-values. It is suggested that this flexible couplingof phosphate transport is of essential importance for the acidresistance of Dunaliella acidophila. Key words: Acid resistance, Dunaliella acidophila, phosphate cotransport, phosphate limitation, plasma membrane, sodium 相似文献
12.
The Ionic Relations of Acetabularia mediterranea 总被引:3,自引:0,他引:3
The concentrations of K+, Na+, and Cl in the cytoplasmand the vacuole of Acetabularia mediterranea have been measured,as have the vacuolar concentrations of SO4 andoxalate. The electrical potential difference between externalsolution, and vacuole and cytoplasm has been measured. The resultsindicate that Cl and SO4 are probably transportedactively into the cell, and that active transport of Na+ isoutwards. The results for K+ are equivocal. The fluxes of K+,Na+, Cl, and S04 into the cell and theeffluxes of Na+ and Cl have been determined. The Clfluxes are extremely large. In all cases the plasmalemma isthe rate-limiting membrane for ion movement. A technique isdescribed for the preparation of large, completely viable cellfragments containing only cytoplasm, with no vacuole. 相似文献
13.
At high external pH, the Chara membrane is known to switch toa new state in which the membrane potential is highly negative;it has been characterized as a passive diffusion potential forH+ (or 0H). DCCD is shown to inhibit the increased conductanceand the highly negative membrane potential associated with thisstate. DCCD also inhibits the plasmalemma H+-ATPase, as wellas cytoplasmic streaming. The alkaline state of the membraneis shown to involve a decreased permeability to K+; this enhancesthe selectivity for H+ (or OH) which results from theincreased permeability to H+ (or OH). Altering the cytoplasmicpH affects the membrane potential at both neutral and alkalinepH. It can also affect the ability of the cell to make the transitionto the alkaline state. 相似文献
14.
Germination, establishment and growth of Melica ciliata L.,an 'acidifuge' species of rocky habitats in Europe, were studiedexperimentally and related to chemical properties of the soilsolution, including pH, base cation composition, Al concentrationand speciation, and Mn concentration. M. ciliata failed to establishin acid leptite soil. However, it was able to grow in solutionat pH 3·6 and exhibited vigorous growth at pH 3·9,a typical soil solution pH of leptite sites, which Melica isunable to colonize. Higher concentrations of Mn than those measuredin any leptite soil solutions did not influence growth. Exposureto 0·037 mmol l-1 (1 mg l-1) of Al3+, a concentrationusually exceeded in the soil solution of leptite sites, severelyretarded root growth. Speciation technique applied to Al insoil solutions obtained by centrifugation demonstrated a closerelationship between H+ and Al concentrations and, in particular,between H+ and free ionic (quickly reacting) Al species. Soilsolution concentrations of free ionic Al proved to be < 0·002mmol l-1 in sites lacking Melica , but often > 0·10mmol l-1 in site lacking Metalica . It is concluded that theinability of M. ciliata to establish in acid soils is not primarilydue to the high H+ concentration but to the high soil solutionconcentrations of Al, especially free Al ionic species at lowsoil pH.Copyright 1993, 1999 Academic Press Melica ciliata, distribution, soil solution, pH, aluminium speciation, manganese, base cations, iron 相似文献
15.
Biophysical and Biochemical Regulation of Cytoplasmic pH in Chara corallina during Acid Loads 总被引:1,自引:0,他引:1
The contribution of membrane transport to regulation of cytoplasmicpH in Chara corallina has been measured during proton-loadingby uptake of butyric acid. In the short-term (i.e. up to 20min) uptake of butyric acid is not affected by removal of externalK+, Na+ or Cl but over longer periods uptake is decreased(by 2050% in different experiments) in the absence ofexternal Na+ or, sometimes, K+. Influxes of both Na+ and K+increase temporarily after addition of butyrate, Na+ immediatelyand K+ after a lag. Effects on Cl influx are small butCl efflux increases enormously after a short lag. Anapproximate comparison of internal butyrate with changes inthe concentration of K+, Na+, and Cl suggests that initially(i.e. for a few min) cytoplasmic pH is determined by bufferingand possibly by some decarboxylation of organic acids (biochemicalpH regulation), and that biophysical pH regulation involvingefflux of H+ balanced by influxes of K+, Na+ and especiallyefflux of Cl progressively becomes dominant. When butyric acid is washed out of the cells, cytoplasmic pHis restored completely or partially (depending on the butyrateconcentration used) and this is independent of the presenceor absence of external Cl. Where Cl is present,its influx is relatively small. It is suggested that cytoplasmicpH is then controlled biochemically, involving the synthesisof an (unidentified) organic acid and the accumulation of acidicanions in place of butyurate lost from the cell. During thesecond application of butyrate, net Cl efflux is small:it is suggested that control of cytoplasmic pH then involvesdecarboxylation of the organic acid anions. The questions of the source of Cl lost from the cell(cytoplasm or vacuole) and of possible cytoplasmic swellingassociated with the accumulation of butyrate are discussed. Key words: Chara corallina, butyric acid, cytoplasmic pH, membrane transport 相似文献
16.
In semicells of the unicellular green alga Closterium that areundergoing elongation, transcellular ion currents enter theelongating region of the cell and leave via the non-elongatingregion of the cell, as in the case of many other tip-growingorganisms. The density of the inwardly and outwardly directedcurrents was 142.5±63.7 nA cm2 (n=42) and 109.3±46.5nA cm2 (n=33), respectively, at the respective regionsof the cells. Both currents clearly decreased with decreasesin the external concentration of Ca2+ ions, and they were completelyblocked by addition of Ca2+-channel blockers, such as 20 µMLaCl3, to the external medium. Increases in pH up to 10.2 hadno effect on the currents, but a decrease in pH from 7.5 to5.7 or 4.5 resulted in an explosive increase in the currents.Removal of external K+ and Cl ions induced some increasesin the currents, but removal of external Na+ Mg2+ plus and ions had little effect on the currents. A major part of thecurrents may be carried by Ca2+ ions, while H+, K+ and Clions may play a minor role as members of the group of ions thatcarry the currents. Thus, there is a clear relationship betweenCa2+ ion currents and elongation in Closterium. (Received April 30, 1992; Accepted July 13, 1992) 相似文献
17.
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
18.
The primary leaves of kidney bean (Phaseolus vulgaris L.) openunder light and close in the dark by the deformation of thepulvinus resulting from diurnal distribution changes of K+,Cl, organic acid (or H+) and NO3. When Rb+ was added as a tracer of K+ to the seedlings throughtheir roots, it was transported to the pulvinus cells duringthe light period but not during the dark period. Transpirationoccurred vigorously in the light but almost stopped in the dark.We concluded that Rb+ absorbed by the roots was carried to thepulvinus by the transpiration stream. Phaseolus vulgaris L., pulvinus, Rb+, diurnal transport transpiration stream 相似文献
19.
Effects of Ions and Membrane Potential on the Elongation of the Unicellular Green Alga Closterium 总被引:1,自引:0,他引:1
Cells of the unicellular green alga Closterium ehrenbergii elongatedexclusively at septa and for 45 hours after cell division.Cell elongation was strongly inhibited by a decrease in eitherthe external concentration of Ca2+ or pH, and was also inhibitedby several competitive Ca2+ channel blockers. Changes in concentrationsof other external ions had no effect on the elongation. Theaverage concentrations of ions in the intracellular fluid ofthe interphase cell before cell division was as follows (inmM): K+=56.5, Na+=4.8, Ca2+=2.4, Mg2+=1.3, Cl=59.5; thepH was 7.4. The levels of K+, Na+ and Cl ions decreasedsignificantly with cell elongation, suggesting that this process,which proceeds with water uptake, surpasses ion absorption.The plasma membrane potential (Vm) in both the interphase cellsand in the elongating cells was in the range of 90 to105 mV (interior negative). The Vm was entirely determinedby the simple diffusion of K+. A decrease in the external concentrationof Ca2+ caused depolarization, probably by an indirect effectof low Ca2+. Changes in the extracellular level of H+ and othercations barely affected Vm. Thus, external Ca2+ and H+ are concludedto affect cell elongation but not via a change in the Vm acrossthe plasma membrane. (Received February 29, 1988; Accepted June 8, 1988) 相似文献
20.
Rates of Hydrogen Ion Efflux by Nodulated Legumes Grown in Flowing Solution Culture with Continuous pH Monitoring and Adjustment 总被引:6,自引:1,他引:5
The net efflux of H+ from lucerne (Medicago saliva L.), redclover (Trifolium pratense L.) and white clover (Trifolium repensL.) growing in flowing solution culture and dependent upon symbioticfixation of atmospheric N, was measured over a 75 d experimentalperiod. Considerable and rapid increases in acidity of the nutrientsolution of up to 1.45 pH units were recorded when the pH wasriot held constant over a 30 h period. There was little differencein H+ efflux when solution pH was held constant at 4.75, 5.75or 6.75, but there was an immediate cessation when it was adjustedto 3.75. Differences in the daily net efflux of H+ closely followedthe pattern of daily differences in incoming radiation, andthere was also evidence of a diurnal pattern of H+ efflux. Althoughthere were initially distinct differences between the speciesin the calculated rate of net H+ efflux (µg H+ g1dry shoot d), by day 75 these had diminished. In allspecies, however, the maximum rate of efflux per unit of shootsoccurred during the earlier rapid phases of growth. The measuredefflux of H+ was well equated with the plant content of excesscations (as measured by ash alkalinity) and, on average, theratio of acidity produced to N assimilated (expressed as anequivalent) was 0-24. Medicago sativa L., Trifolium pratense L., Trifolium repens L., lucerne, red clover, white clover, acidification, cation/anion balance, flowing solution culture, H+ efflux, nitrogen fixation 相似文献