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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 20–50% 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   

2.
The effect of elevated Na+ concentration on Na+ permeability(PNa) and Na+ influx in the presence of two levels of externaldivalent cations was determined in Chara corallina and freshwater-culturedChara buckellii. When Na+ in the medium was increased from 1.0to 70 mol m–3, Na+ influx increased in both species ifCa2+ was low (0.1 mol m–3). If Ca2+ was increased to 7.0mol m–3 when Na+ was increased, Na+ influx remained atthe low control level in C. corallina, and showed only a temporaryincrease in C. buckellii. Mg2+ was a better substitute for Ca2+in C. buckellii than in C. corallina. Na+ permeability data suggest that when the external Ca2+ concentrationis low, PNa does not increase in the presence of elevated NaCl;the increase in Na+ influx appears to be due to the increasein external Na+ concentration alone. Ca2 + supplementation appearsto decrease PNa whereas supplemental Mg2+ has no effect. Na+ effluxes were computed from previously determined net fluxesand the influxes. It was found that for both species, fluxesin both directions were stimulated in response to all experimentaltreatments, but Na+ influx always exceeded efflux. This resultedin net Na+ accumulation in the vacuoles of both species. The results are discussed with reference to net flux and electrophysiologicaldata obtained previously under identical conditions, as wellas the comparative salinity tolerance of both species and theNa+/divalent cation ratio. Key words: Na+ influx, Na+ tolerance, membrane potential, permeability, Chara  相似文献   

3.
Sodium efflux from 22Na+-loaded root tips root tips of Hordeumvulgare L. was markedly increased by replacing 10mM Na2SO4 inthe washing solution by K2SO4 with the same electrical conductivity.This increase was inhibited by both an uncoupler and an inhibitorof oxidative phosphorylation but not by ouabain. Potassium ionsdid not enhance Na+ efflux in the presence of a rapidly absorbedcounter anion, such as Cl, instead of . Efflux of 22Na+ could also be enhanced by a low pH in theabsence of K+; this was prevented by uncouplers, but not byan inhibitor of the mitochondrial ATPase. It seems that K+ indirectly enhances Na+ efflux. It is suggestedthat metabolic K+ uptake in excess of the counter anion resultsin a proton gradient across the plasmalemma (acid outside) inducingH+/Na+ antiport.  相似文献   

4.
PATRICK  J. W. 《Annals of botany》1987,59(2):181-190
Rates of 14C-photosynthate unloading from excised seed-coathalves of Phaseolus vulgaris L. plants were stimulated by externalKCI concentrations in excess of 10 mM with an optimal responseat 100–150 mM KCI. The cellular pattern of 14C-photosynthatemetabolism was not altered by KCI but the treatment preferentiallystimulated the release of sucrose from the seed-coats. Photosynthateunloading was insensitive to Cl and was stimulated bya range of membrane-permeable cations (Na+, Mg2+ and tetraphenylphosphoniumion) in addition to K+. The K+ ionophore, valinomycin, abolishedthe K+ stimulation of 14C-photosynthate unloading. A switchto a wash solution containing K+ elicited a rapid burst of 14C-photosynthateunloading; the rate constant for the final phase of 14C-efflux(probably across the tonoplast) was unaffected by K+. The KCItreatment did not change the passive permeability of eitherthe plasmalemma or tonoplast. While sucrose influx across theplasmalemma was insensitive to K+, sucrose transfer to the vacuolewas slowed. The results obtained support the postulate thatK+ (and other membrane permeable cations) preferentially stimulatesucrose efflux across the plasmalemma of the unloading cellsby serving to carry positive charge in the opposite direction. Phaseolus vulgaris, bean, photosynthate unloading, potassium stimulation, seed-coat  相似文献   

5.
In springwater (25.5 mol m–3 Cl, 20.4 mol m–3Na+, 0.14 mol m–3 K+) Enteromorpha intestinalis couldnot survive for more than a few weeks unless provided with 0.5mol m–3 K+ in the medium or alternatively exposed to seawaterfor 1 day per week. Maintenance of a cytoplasmic K+ level ofabout 200 mol m–3 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   

6.
Ammonia (pKa 9.25) and methylamine (pKa, 10.65) increase cytoplasmicpH and stimulate Cl influx in Chara corallina, theseeffects being associated with influx of the amine cations ona specific porter. The weak base imidazole (pKa 6.96) has similareffects but diffuses passively into the cell both as an unionizedbase and as a cation. When the external pH is greater than 6.0influx of the unionized species predominates. Imidazole accumulates to high concentrations in the vacuole,where it is protonated. Cytoplasmic pH and vacuolar pH riseby only 0.2–0.3 units, suggesting a large balancing protoninflux across the plasma membrane. Balance of electric chargeis partially maintained by net efflux of K+ and net influx ofCl. Calculation of vacuolar concentrations of imidazole(from (14C] imidazole uptake, assuming that there is no metabolism)plus K+ and Na+ indicates an excess of cations over inorganicanions (Cl). However, although the osmotic potentialof the cells increases, also indicating increased solute concentrations,the increase is less than that predicted by the calculated ionicconcentrations. This discrepancy remains to be resolved. Becausethe osmotic potential also increases when imidazole is absorbedfrom Cl-free solutions it is likely that maintenanceof charge-balance can also involve synthesis and vacuolar storageof organic or amino acids. Key words: Imidazole, potassium, intracellular pH, membrane transport, Chara  相似文献   

7.
JUNG  K.-D.; LUTTGE  U. 《Annals of botany》1980,45(3):339-349
Fusicoccin (FC) inhibited net excretion of Cl by theglands of the pitchers of the carnivorous plant Nepenthes hookeriana;of Na+ and Cl by the salt glands of the halophytes Limoniumvulgare and L. pectinatum and of K+ in the nectar of Acer platanoidesflowers. It had no effect on K+ elimination with nectar of Impatienswalleriana (extrafloral nectaries) and Abutilon striatum. Abscisicacid (ABA) stimulated net excretion of K+ and Cl in Nepenthesand of Na+ and Cl in Limonium but had no effects on K+in nectar. Thus, FC and ABA had opposing effects on ion excretionby the salt eliminating glands of Limonium and Nepenthes. Bothcompounds, however, had similar effects on sugar secretion ofnectary glands which was either inhibited or unaffected by FCand ABA. It is suggested that the effects of FC and ABA on ion excretionby gland cells could be reconciled with literature showing FC-stimulationand possible ABA-inhibition of proton pumps at the plasmalemmaof plant cells. Nepenthes hookeriana, Limonium vulgare, Limonium pectinatum, Acer platanoides, salt-glands, nectaries, excretion, fusicoccin, abscisic acid, proton pump  相似文献   

8.
Using the compartmental analysis the unidirectional Na+ fluxesin cortical cells of barley roots, the cytoplasmic and vacuolarNa+ contents Qc and Qv, and the trans-root Na+ transport R'have been studied as a function of the external Na+ concentration.Using the re-elution technique the effect of low K+ concentrationson the plasmalemma efflux co of Na+ (K+-Na+ exchange) and onR' was investigated at different Na+ concentrations and correspondinglydifferent values of the cytoplasmic sodium content Qc. The relationof the K+-dependent Na+ efflux coK+-dep to Qc or to the cytoplasmicNa+ concentration obeyed Michaelis-Menten kinetics. This isconsistent with a linkage of co, K+-dep to K+ influx by a K+-Na+exchange system. The apparent Km corresponded to a cytoplasmicNa+ concentration of 28 mM at 0·2 mM K+ and about 0·2mM Na+ in the external solution. 0·2 mM K+ stimulatedthe plasma-lemma efflux of Na+ and inhibited Na+ transport selectivelyeven in the presence of 10 mM Na+ in the external medium showingthe high efficiency of the K+-Na+ exchange system. However,co, K+-dep was inhibited at 10 mM Na1 compared to lower Na1concentrations suggesting some competition of Na1 with K1 atthe external site of the exchange system. The effect of theNa+ concentration on Na1 influx oc is discussed with respectto kinetic models of uuptake.  相似文献   

9.
Internal Factors Regulating Nitrate and Chloride Influx in Plant Cells   总被引:14,自引:0,他引:14  
The primary factor determining the observed decrease in activeC1 influx during salt accumulation in carrot and barleyroot cells has been shown to be the concentration of C1+ NO3 in the vacuole. The relationship between C1 influx and the vacuolar concentrationsof various substances was examined after the tissues had accumulatedions from various salt solutions. After accumulating K+ malate,C1 influx was not reduced, but after accumulating C1or NO3 salts, C1 influx was reduced by up to 90per cent. Considering all treatments, C1 influx was notcorrelated with the vacuolar concentration of K+, Na+, (K++Na+),reducing sugars, malate, C1, or NO3, nor withthe cellular osmotic pressure. The correlation coefficient betweenCl influx and log (C1 + NO3 concentrationin the vacuole) was highly significant, and accounted for allthe variation in C1 influx in this experiment. Net NO3 influx is similarly reduced by a high C1concentration in the vacuole. External Cl and NO3have quantitatively different, apparently competitive, effectson C1 influx. These differ from the apparently negative-feedbackeffects of C1 and NO3 in the vacuole, which arequantitatively similar. Decreasing the internal hydrostatic pressure by raising theexternal osmotic pressure increased active K+ influx in Valoniaventricosa, but had no effect on C1 or K+ influx in carrotor maize root cells. Cl influx is not related to thereducing sugar concentration during ageing drifts in excisedcarrot root tissue. Acetazolamide did not inhibit C1 influx to carrot tissue. The implications of this type of negative feedback regulation,and the relationship between C1 and NO3 transportare discussed.  相似文献   

10.
We examined a role of Ca2+ in the activation of the two majorion channels, i.e., Cl and K+ channels at the excitationof the characean plasmalemma. The current-voltage relation (I-Vcurve) of the Chara membrane was compared under the ramp voltageclamp condition before and after external application of 20µMof La3+ (a Ca2+ channel blocker). The transient inward currentcomponent, which is carried mainly by the efflux of Cl,disappeared almost completely in about 30 min with La3+ treatment.On the other hand, no effect was observed on the late largeoutward current, which is mainly carried by the efflux of K+in a large depolarization region (less negative than –50mV). These results suggest that the Cl channel in theChara plasmalemma is activated by Ca2+ influx, while the K+channel is simply activated by depolarization. (Received April 7, 1986; Accepted June 6, 1986)  相似文献   

11.
Coupling of Proton Fluxes in the Polar Leaves of Potamogeton lucens L   总被引:1,自引:0,他引:1  
An attempt has been made to quantify the light-induced H+ effluxand influx observed in polar leaves of Potamogeton lucens.Theseproton fluxes are spatially separated. The H+ efflux, mediatedby a plasmalemma bound H+ –ATPase, occurs across theplasmamembrane at the morphological lower epidermis and is accompaniedby an H+ influx (or OH efflux) at the upper side oftheleaf. As a result, these leaves exhibit a remarkable pH–polarityin the light. The pH near the lower epidermis may drop to avalueas low as 3.5, while a pH of about 10.5 can be observed at theupper epidermis. Obviously this phenomenon requires theco–ordinationof transport processes in the different cell layers of the leaftissue. These observations led to quantitative studies oftherelation between the H+ fluxes at either plasmalemma. Thesefluxes were calculated from the pH values recorded at twodistancesfrom the leaf surface. Although the H+ influx always exceededthe efflux, a coupling between the transport processesacrosseither plasma membrane became evident from the time–coursesof the two fluxes. Key words: Potamogeton lucens, proton flux, flux coupling, pH–;polarity  相似文献   

12.
Measurements of Ion Concentrations and Fluxes in Dunaliella parva   总被引:2,自引:0,他引:2  
Measurements of K+, Na+, and Cl were made on a halotolerantstrain of Dunaliella growing at 500 mM NaCl, 25 ?C, and a relativelylow light intensity (6000 Lx). Much effort was spent in searchingfor a means of measuring the extracellular volume of fluid trappedbetween the cells of centrifuged pellets. All of the sugarstried as markers were rejected because they were found to bedigested in the cell suspension. The most suitable marker wasfound to be [14C]polyethylene glycol2 (mol. wt. 4000); althoughthis substance was apparently adsorbed to the cell exterior,it was found possible to correct for adsorption and then obtaina reasonable figure for the trapped fluid. The final concentrationsof cell K+ and Na+ were 128 ? 53 mM and 131 ? 117 mM respectively.Cl balanced the sum of K+ Na+. Influxes of 22Na+, 42K+,and 36C1 were measured in cells in which the ions werein the steady state. Averages of 610 and 6.6 nmol m–2s–1 were obtained for Na+ and K+ respectively. Clinflux was divided into 2 phases with values of 1540 and 178mmol m–2 s–1. The faster influx was considered tobe across the outer cell membrane. The membrane responsiblefor the slower influx has not been identified. By comparingvalues of the potential difference calculated from the Nernstand Goldman equations, it was concluded that Na+ and K+ areprobably controlled by active mechanisms, whereas cell Clis likely to be at thermodynamic equilibrium with the medium.  相似文献   

13.
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   

14.
Entry of Methylammonium and Ammonium Ions into Chara Internodal Cells   总被引:6,自引:0,他引:6  
Low concentrations of ammonia and methylamine greatly affectmembrane transport by, and the electrical properties of, cellsof Chara corallina (=C. australis). In the presence of theseamines, influx of Cl and efflux of K+ increase and alarge depolarizing current flows through the cell membrane. Measurements with [14C]methylamine show that methylamine isabsorbed rapidly over a wide pH range, and that the absorptionisotherm is complex. Methylamine influx is not affected by presenceor absence of Cl, K+, or Na+, but is decreased by additionof . The depolarizing current is associated with a small increase in membrane conductance, except at highpH, and both these effects are reversible. The current showssaturation with increasing amine concentration; when methylamineis 10–12 times more concentrated than ammonia, it producesa current of the same magnitude. The results show that the amines enter the cells as cations( or CH3) except where external pH is high, and that a specific, selective electrogenicporter is involved. There is no need to invoke active transport,as there is no evidence that internal amine concentrations exceedthe equilibrium (Nernst) concentrations.  相似文献   

15.
Na+, K+ and Cl- in Xylem Sap Flowing to Shoots of NaCl-Treated Barley   总被引:7,自引:0,他引:7  
Munns, R. 1985. Na+, K+ and Cl in xylem sap flowing toshoots of NaCl-treated barley.—J. exp. Bot. 36: 1032–1042. Na+, Cl and K+ concentrations were measured in xylemsap obtained by applying pressure to the roots of decapitatedbarley plants grown at external [NaCl] of 0, 25, 50, 100, 150and 200 mol m–3. For any given NaCl treatment, ion concentrationsin the xylem sap were hyperbolically related to the flux ofwater. Ion concentrations in sap collected at very low volumefluxes (without applied pressure) were 5–10 times higherthan in sap collected at moderate fluxes (under pressure). Fora given moderate volume flux, Na+ concentration in the xylemsap, [Na+]x, was only 4.0 mol m–3 at external [NaCl] of25–150 mol m–3, and increased to 7.0 mol m–3at 200 mol m–3. [Cl-]x showed a similar pattern. Thisshows there would be little difference in the rate of uptaketo the shoot of plants at 25–150 mol m–3 externalNaCl and indicates little change even at 200 mol m-3 NaCl becausetranspiration rates would be much lower. Thus the reduced growthof the shoot of plants at high NaCl concentrations is not dueto higher uptake rates of Na+ or Cl. The fluxes of Na+, Cl and K increased non-linearlywith increasing volume flux indicating little movement of saltin the apoplast. The flux of K+ increased even when [K+]x wasgreater than external [K+], indicating that membrane transportprocesses modify the K+ concentration in the transpiration streamas it flows through the root system. Key words: -Xylem sap, Na+, K+, Cl fluxes, salinity, barley  相似文献   

16.
A method has been developed to measure the cell volume of theunicellular green alga Dunaliella parva 19/9 using Li+ measurementsonly. Concentrations of internal solutes can also be calculatedif they are assayed in the same samples as Li+. We found thatD. parva cells grown in 0.4 kmol m–3 NaCl have an averageaqueous cell volume of 65.1 ?2.9 µm3, a K+ concentrationof 126?6 mol m–3, a Na+ concentration of 11?11 mol m–3and a glycerol concentration of 615?27 mol m–3 (n= 12).Algae grown in 1.5 kmol m–3 NaCl have an average aqueouscell volume of 131 ?7.5 µm3, a K+ concentration of 109?4mol m–3, a Na+ concentration of 10?39 mol m–3 anda glycerol concentration of 1 425?59 mol m–3 (n = 12).These results indicate that D. parva cells adapted to high salinitieshave larger cell volumes than those adapted to lower salinities.However, there is no evidence for a significant difference ininternal Na+ concentration, despite the almost 4-fold differencein the concentration of external NaCl. The intracellular glycerolconcentration alone accounts for 65% and 54%, respectively,of the osmotic balance in low and high salt grown cells. Key words: Dunaliella, cell volume, intracellular solutes  相似文献   

17.
The processes of NO3 uptake and transport and the effectsof NH4+ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO3 net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentKm of 9.2 µM and a Vmax of 366 nmol g–1 FW h–1.NH4+, when present in excess to NO3, or 10 mM L-glutamateinhibited the net uptake of NO3 Apparently, part of NO3taken up was loaded into the xylem. Relative xylem loading ofNO3 ranged from 3.21.6 to 6.45.1% of NO3 netuptake. It was not affected by treatment with NH4+ or L-glutamate.16N/13N double labelling experiments showed that NO3efflux from roots increased with increasing influx of NO3and, therefore, declined if influx was reduced by NH4+ or L-glutamateexposure. From these results it is concluded that NO3net uptake by non-mycorrhizal beech roots is reduced by NH4+or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae  相似文献   

18.
Using beetroot, Beta vulgaris L. var. Avon Early, grown in radioactivelylabelled nutrient solutions, concentrations and fluxes of Na+and Cl were estimated for cells of freshly cut storageroot disks, by compartmental analysis of radioisotope elutionmeasurements. These values were compared with results obtainedin a similar manner from beetroot grown in non-labelled nutrientsolution and loaded instead during an aging period in 22Na-or 36Cl- labelled 1 mM NaCl solution. In accord with the generallyaccepted, but never properly tested, view, it was found thatnet Na+ influx followed from a reduction in efflux with agingand net Cl uptake depended on a marked increase in influx.However, both these important changes took place at the tonoplast,and, although aging led to a reduction of plasmalemma fluxes,at no time was entry of Cl into the cytoplasm, or lossof Na+ from the cytoplasm, significantly restricted.  相似文献   

19.
Salinity-induced Malate Accumulation in Chara   总被引:3,自引:0,他引:3  
Ion absorption by Chara corallina from solutions containingpredominantly KC1 or RbCl at up to 100 mol m–3 resultedin accumulation of salts and turgor regulation. Turgor regulationdid not occur in solutions containing Na+ or Li+salts. Duringion absorption from various salts of K+ and Rb+ vacuolar cationconcentration exceeded Cl concentration. This differencewas shown to be balanced by the synthesis and accumulation ofmalate. Vacuolar malate concentration reached 48 mol m3,with accumulation occurring at rates of up to 0.45 mol m–3h–1. Malate accumulation was inhibited by low externalpH and was dependent upon external HCO3 concentration.The synthesis of malic acid and its subsequent dissociationimposed a severe acid load on the cell. Biophysical regulationof cellular pH was achieved by a H+efflux at a rate of about40 nmol m–2 s–1from the cell. The results presentedargue against cytoplasmic Cl, HCO3 or pH regulatingmalate accumulation in Chara and it is suggested that malatetransport across the tonoplast may regulate malate accumulation. Key words: Malate, Chara corallina, pH regulation, salinity  相似文献   

20.
The ion contents and membrane potentials of the cells of young,hydroponically cultured seedlings of Atriplex hastata L. var.salina, Wallr. have been measured at several different NaClconcentrations. The total tissue concentrations of Na+ and Clincrease as external NaCl increases, but there is always a markedexcess of internal Na+ over Cl; this is balanced by endogenousorganic anion formation with a concomitant extrusion of H+ tothe bathing solution. Membrane potentials of the root cells remain essentially invariantwith changes in external NaCl at approx. –130 mV; thereis no evidence of a radial gradient of potential across theroot. The potential seems to contain a cyanide-sensitive electrogeniccomponent, also invariant with NaCl concentration, of about–70 mV, and a diffusion component. The electrogenic componentseems likely to be a H+ efflux, probably through a H+ uniportATPase.  相似文献   

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