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1.
Uptake of l-[1- 14C]ascorbate by intact ascorbate-free spinach ( Spinacia oleracea L. cv Vital r) chloroplasts has been investigated using the technique of silicone oil filtering. Rates greater than 100 micromoles per milligram chlorophyll per hour (external concentration, 10 millimolar) of ascorbate transport were observed. Ascorbate uptake into the sorbitol-impermeable space (stroma) followed the Michaelis-Menten-type characteristic for substrate saturation. A Km of 18 to 40 millimolar was determined. Transport of ascorbate across the chloroplast envelope resulted in an equilibrium of the ascorbate concentrations between stroma and medium. A pH optimum of 7.0 to 7.5 and the lack of alkalization of the medium upon ascorbate uptake suggest that only the monovalent ascorbate anion is able to cross the chloroplast envelope. The activation energy of ascorbate uptake was determined to be 65.8 kilojoules (16 kilocalories) per mole (8 to 20°C). Interference of ascorbate transport with substrates of the phosphate or dicarboxylate translocator could not be detected, but didehydroascorbate was a competitive inhibitor. Preloading of chloroplasts with didehydroascorbate resulted in an increase of Vmax but did not change the Km for ascorbate. Millimolar concentrations of the sulfhydryl reagent p-chloromercuriphenyl sulfonate inhibited ascorbate uptake. The data are interpreted in terms of ascorbate uptake into chloroplasts by the mechanism of facilitated diffusion mediated by a specific translocator. 相似文献
2.
Spinach leaf chloroplasts isolated in isotonic media (330 millimolar sorbitol, −1.0 megapascals osmotic potential) had optimum rates of photosynthesis when assayed at −1.0 megapascals. When chloroplasts were isolated in hypertonic media (720 millimolar sorbitol, −2.0 megapascals osmotic potential) the optimum osmotic potential for photosynthesis was shifted to −1.8 megapascals and the chloroplasts had higher rates of CO 2-dependent O 2 evolution than chloroplasts isolated in 330 millimolar sorbitol when both were assayed at high solute concentrations. Transfer of chloroplasts isolated in 330 millimolar sorbitol to 720 millimolar sorbitol resulted in decreased chloroplast volume but this shrinkage was only transient and the chloroplasts subsequently swelled so that within 2 to 3 minutes at 20°C the chloroplast volume had returned to near the original value. Thus, actual steady state chloroplast volume was not decreased in hypertonic media. In isotonic media, there was a slow but significant uptake of sorbitol by chloroplasts (10 to 20 micromoles per milligram chlorophyll per hour at 20°C). Transfer of chloroplasts from 330 millimolar sorbitol to 720 millimolar sorbitol resulted in rapid uptake of sorbitol (up to 280 micromoles per milligram chlorophyll per hour at 20°C) and after 5 minutes the concentration of sorbitol inside the chloroplasts exceeded 500 millimolar. This uptake of sorbitol resulted in a significant underestimation of chloroplast volume unless [14C]sorbitol was added just prior to centrifuging the chloroplasts through silicone oil. Sudden exposure to osmotic stress apparently induced a transient change in the permeability of the chloroplast envelope since addition of [14C]sorbitol 3 minutes after transfer to hypertonic media (when chloroplast volume had returned to normal) did not result in rapid uptake of labeled sorbitol. It is concluded that chloroplasts can osmotically adjust in vitro by uptake of solutes which do not normally penetrate the chloroplast envelope, resulting in a restoration of normal chloroplast volume and partially preventing the inhibition of photosynthesis by high solute concentrations. The results indicate the importance of matching the osmotic potential of isolation media to that of the tissue, particularly in studies of stress physiology. 相似文献
3.
Chloroplasts, isolated from protoplasts of the green alga, Chlorella ellipsoidea, were estimated to be 99% intact by the ferricyanide-reduction assay, and gave CO 2 and PGA-dependent rates of O 2 evolution of 64.5 to 150 micromoles per milligram of chlorophyll per hour, that is 30 to 70% of the photosynthetic activity of the parent cells. Intact chloroplasts showed no carbonic anhydrase activity, but it was detected in preparations of ruptured organelles. Rates of photosynthesis, measured in a closed system at pH 7.5, were twice the calculated rate of CO 2 supply from the uncatalyzed dehydration of HCO 3− indicating a direct uptake of bicarbonate by the intact chloroplasts. Mass spectrometric measurements of CO 2 depletion from the medium on the illumination of chloroplasts indicate the lack of an active CO 2 transport across the chloroplast envelope. 相似文献
4.
Evidence is presented for low rates of carriermediated uptake of sulphate, thiosulphate and sulphite into the stroma of the C3 plant Spinacia oleracea. Uptake of sulphate in the dark was followed using two techniques (1) uptake of sulphate [ 35S] as determined by silicon oil centrifugal filtration and (2) uptake as indicated by inhibition of CO 2-dependant O 2 evolution rates after addition of sulphate.Sulphate, thiosulphate and sulphite were transported across the envelope leading to an accumulation in the chloroplasts. Sulphate transport had saturation kinetics of the Michaelis-Menten type (Vmax : 25 μmoles . mg −1 chl . h −1 at 22°C ; Km : 2.5 mM). The rate of transport for sulphate was not influenced either by illumination or pH change in the external medium. Phosphate was a competitive inhibitor of sulphate uptake by chloroplasts (Ki : 0.7 mM, fig. 1). The rate of transport for phosphate appeared to be much higher than for sulphate. When the chloroplasts were pre-loaded with labelled sulphate, radioactivity was rapidly released after addition of phosphate into the external medium. Consequently, the transport of sulphate occurs by a strict counter-exchange : for each molecule of sulphate entering the chloroplast, one molecule of phosphate leaves the stroma, and vice-versa.The uptake of sulphate by isolated intact chloroplasts exchanging for internal free phosphate induced a lower rate of photophosphorylation, which in turn inhibited CO 2-dependent O 2 evolution.The presence, on the inner membrane of the chloroplast envelope, of a specific sulphate carrier, distinct from the phosphate translocator, is discussed. 相似文献
5.
Photosynthesis, stroma-pH, and internal K + and Cl − concentrations of isolated intact chloroplasts from Spinacia oleracea, as well as ion (K +, H +, Cl −) movements across the envelope, were measured over a wide range of external KCl concentrations (1-100 millimolar). Isolated intact chloroplasts are a Donnan system which accumulates cations (K+ or added Tetraphenylphosphonium+) and excludes anions (Cl−) at low ionic strength of the medium. The internally negative dark potential becomes still more negative in the light as estimated by Tetraphenylphosphonium+ distribution. At 100 millimolar external KCl, potentials both in the light and in the dark and also the light-induced uptake of K+ or Na+ and the release of protons all become very small. Light-induced K+ uptake is not abolished by valinomycin suggesting that the K+ uptake is not primarily active. Intact chloroplasts contain higher K+ concentrations (112-157 millimolar) than chloroplasts isolated in standard media. Photosynthetic activity of intact chloroplasts is higher at 100 millimolar external KCl than at 5 to 25 millimolar. The pH optimum of CO2 fixation at high K+ concentrations is broadened towards low pH values. This can be correlated with the observation that high external KCl concentrations at a constant pH of the suspending medium produce an increase of stroma-pH both in the light and in the dark. These results demonstrate a requirement of high external concentrations of monovalent cations for CO2 fixation in intact chloroplasts. 相似文献
6.
Mass-spectrometric disequilibrium analysis was applied to investigate CO 2 uptake and HCO 3− transport in cells and chloroplasts of the microalgae Dunaliella tertiolecta and Chlamydomonas reinhardtii, which were grown in air enriched with 5% (v/v) CO 2 (high-Ci cells) or in ambient air (low-Ci cells). High- and low-Ci cells of both species had the capacity to transport CO 2 and HCO 3−, with maximum rates being largely unaffected by the growth conditions. In high- and low-Ci cells of D. tertiolecta, HCO 3− was the dominant inorganic C species taken up, whereas HCO 3− and CO 2 were used at similar rates by C. reinhardtii. The apparent affinities of HCO 3− transport and CO 2 uptake increased 3- to 9-fold in both species upon acclimation to air. Photosynthetically active chloroplasts isolated from both species were able to transport CO 2 and HCO 3−. For chloroplasts from C. reinhardtii, the concentrations of HCO 3− and CO 2 required for half-maximal activity declined from 446 to 33 μm and 6.8 to 0.6 μm, respectively, after acclimation of the parent cells to air; the corresponding values for chloroplasts from D. tertiolecta decreased from 203 to 58 μm and 5.8 to 0.5 μm, respectively. These results indicate the presence of inducible high-affinity HCO 3− and CO 2 transporters at the chloroplast envelope membrane. 相似文献
7.
Bicarbonate uptake by isolated chloroplast envelope membranes and intact chloroplasts of spinach ( Spinacia oleracea L. var. Viroflay) in darkness exhibited a similar dependency upon temperature, pH, time, and concentrations of isolated or attached envelope membranes. This similarity in uptake properties demonstrates the usefulness of the envelope membranes for the study of chloroplast permeability. Maximal rates for dark HCO 3- uptake by isolated envelope membranes and intact chloroplasts were more than sufficient to account for the maximal rates of photosynthetic CO 2 fixation observed with intact chloroplasts. The active species involved in the uptake process was found to be HCO 3- and not CO 2. The significance of HCO 3- uptake and its relationship to carbonic anhydrase and ribulose diphosphate carboxylase is discussed. Conditions for maximal HCO 3- uptake in darkness by intact chloroplasts were found to be similar to those required for maximal photosynthetic CO 2 fixation, suggesting that HCO 3- uptake by the envelope membrane may regulate photosynthetic CO 2 fixation. 相似文献
8.
Neither Dunaliella cells grown with 5% CO 2 nor their isolated chloroplasts had a CO 2 concentrating mechanism. These cells primarily utilized CO 2 from the medium because the K(0.5) (HCO 3−) increase from 57 micromolar at pH 7.0 to 1489 micromolar at pH 8.5, where as the K(0.5) CO 2 was about 12 micromolar over the pH range. After air adaptation for 24 hours in light, a CO 2 concentrating mechanism was present that decreased the K0.5 (CO 2) to about 0.5 micromolar and K0.5 (HCO 3−) to 11 micromolar at pH 8. These K0.5 values suggest that air-adapted cells preferentially concentrated CO 2 but could also use HCO 3− from the medium. Chloroplasts isolated from air-adapted cells had a K(0.5) for total inorganic carbon of less than 10 micromolar compared to 130 micromolar for chloroplasts from cells grown on high CO 2. Chloroplasts from air-adapted cells, but not CO 2-grown cells, concentrate inorganic carbon internally to 1 millimolar in 60 seconds from 240 micromolar in the medium. Maximum uptake rates occurred after preillumination of 45 seconds to 3 minutes. The CO 2 concentrating mechanism by chloroplasts from air-adapted cells was light dependent and inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) or flurocarbonyl-cyamidephenylhydrazone (FCCP). Phenazine-methosulfate at 10 micromolar to provide cyclic phosphorylation partially reversed the inhibition by DCMU but not by FCCP. One to 0.1 millimolar vanadate, an inhibitor of plasma membrane ATPase, inhibited inorganic carbon accumulation by isolated chloroplasts. Vanadate had no effect on CO 2 concentration by whole cells, as it did not readily cross the cell plasmalemma. Addition of external ATP to the isolated chloroplast only slightly stimulated inorganic carbon uptake and did not reverse vanadate inhibition by more than 25%. These results are consistent with a CO 2 concentrating mechanism in Dunaliella cells which consists in part of an inorganic carbon transporter at the chloroplast envelope that is energized by ATP from photosynthetic electron transport. 相似文献
9.
Ricinus communis L. plants were grown in nutrient solutions in which N was supplied as NO 3− or NH 4+, the solutions being maintained at pH 5.5. In NO 3−-fed plants excess nutrient anion over cation uptake was equivalent to net OH − efflux, and the total charge from NO 3− and SO 42− reduction equated to the sum of organic anion accumulation plus net OH − efflux. In NH 4+-fed plants a large H + efflux was recorded in close agreement with excess cation over anion uptake. This H + efflux equated to the sum of net cation (NH 4+ minus SO 42−) assimilation plus organic anion accumulation. In vivo nitrate reductase assays revealed that the roots may have the capacity to reduce just under half of the total NO 3− that is taken up and reduced in NO 3−-fed plants. Organic anion concentration in these plants was much higher in the shoots than in the roots. In NH 4+-fed plants absorbed NH 4+ was almost exclusively assimilated in the roots. These plants were considerably lower in organic anions than NO 3−-fed plants, but had equal concentrations in shoots and roots. Xylem and phloem saps were collected from plants exposed to both N sources and analyzed for all major contributing ionic and nitrogenous compounds. The results obtained were used to assist in interpreting the ion uptake, assimilation, and accumulation data in terms of shoot/root pH regulation and cycling of nutrients. 相似文献
10.
The light-dependent accumulation of radioactively labeled inorganic carbon in isolated spinach ( Spinacia oleracea L.) chloroplasts was determined by silicone oil filtering centrifugation. Intact chloroplasts, dark-incubated 60 seconds at pH 7.6 and 23°C with 0.5 millimolar sodium bicarbonate, contained 0.5 to 1.0 millimolar internal inorganic carbon. The stromal pool of inorganic carbon increased 5- to 7-fold after 2 to 3 minutes of light. The saturated internal bicarbonate concentration of illuminated spinach chloroplasts was 10- to 20-fold greater than that of the external medium. This ratio decreased at lower temperatures and with increasing external bicarbonate. Over one-half the inorganic carbon found in intact spinach chloroplasts after 2 minutes of light was retained during a subsequent 3-minute dark incubation at 5°C. Calculations of light-induced stromal alkalization based on the uptake of radioactively labeled bicarbonate were 0.4 to 0.5 pH units less than measurements performed with [ 14C]dimethyloxazolidine-dione. About one-third of the binding sites on the enzyme ribulose 1,5-bisphosphate carboxylase were radiolabeled when the enzyme was activated in situ and 14CO 2 bound to the activator site was trapped in the presence of carboxypentitol bisphosphates. Deleting orthophosphate from the incubation medium eliminated inorganic carbon accumulation in the stroma. Thus, bicarbonate ion distribution across the chloroplast envelope was not strictly pH dependent as predicted by the Henderson-Hasselbach formula. This finding is potentially explained by the presence of bound CO 2 in the chloroplast. 相似文献
11.
Pea chloroplasts isolated in salt media show decreased rates of 2:6 dichlorophenolindophenol (DCPIP) and ferricyanide reduction when depleted of CO 2 at pH values below 7.5. The greatest effect of CO 2 was on uncoupled systems. The incorporation of 10 −2, 2 × 10 −2 and 4 × 10 −2 m sodium acetate into the reaction mixtures progressively increased the bicarbonate concentration required for half maximal rates of reduction of DCPIP. The reaction was saturated by bicarbonate concentrations of 1 to 4 × 10 −2 m. With both DCPIP and ferricyanide, the addition of bicarbonate to illuminated chloroplast systems depleted of CO 2 gave very rapid increases in the rates of reduction. Bicarbonate also stimulated oxygen uptake by the illuminated chloroplasts when added hydrogen acceptors had been reduced. There was no effect of bicarbonate on ferricyanide reduction at low light intensities, but with DCPIP reduction, the apparent magnitude of the effect was independent of light intensity. This suggests that DCPIP reacts with the chloroplast electron transport chain at a site nearer to a photochemical stage than does ferricyanide. It also suggests that CO 2 has at least 2 sites of action. 相似文献
12.
The effects of several amino-reactive disulfonic stilbene derivatives and N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate on Cl −, SO 42−, and inorganic phosphate (Pi) uptake in protoplasts isolated from corn root tissue were studied. 4-Acetamido-4′-isothiocyano-2,2′-stilbenedisulfonic acid, 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid, 4,4′-diamino-2,2′-stilbenedisulfonic acid, and NAP-taurine inhibited Cl − and SO 42− but not Pi and K + uptake in corn root protoplasts; whereas mersalyl inhibited Pi but not Cl − or SO 42− uptake. The rate of uptake of all anions decreased with increasing external pH. In addition, these reagents markedly inhibited plasmalemma ATPase activity isolated from corn root tissue. Excised root segments were less sensitive to Cl − and SO 42− transport inhibitors. 相似文献
13.
Ricinus communis L. was used to test the Dijkshoorn-Ben Zioni hypothesis that NO 3− uptake by roots is regulated by NO 3− assimilation in the shoot. The fate of the electronegative charge arising from total assimilated NO 3− (and SO 42−) was followed in its distribution between organic anion accumulation and HCO 3− excretion into the nutrient solution. In plants adequately supplied with NO 3−, HCO 3− excretion accounted for about 47% of the anion charge, reflecting an excess nutrient anion over cation uptake. In vivo nitrate reductase assays revealed that the roots represented the site of about 44% of the total NO 3− reduction in the plants. To trace vascular transport of ionic and nitrogenous constituents within the plant, the composition of both xylem and phloem saps was thoroughly investigated. Detailed dry tissue and sap analyses revealed that only between 19 and 24% of the HCO 3− excretion could be accounted for from oxidative decarboxylation of shoot-borne organic anions produced in the NO 3− reduction process. The results obtained in this investigation may be interpreted as providing direct evidence for a minor importance of phloem transport of cation-organate for the regulation of intracellular pH and electroneutrality, thus practically eliminating the necessity for the Dijkshoorn-Ben Zioni recycling process. 相似文献
14.
1. dl-Cysteine decreases the uptake of 35SO 42− by Euglena gracilis but does not decrease the relative incorporation of the isotope into sulpholipid; cysteic acid, on the other hand, does not affect the uptake of 35SO 42− but does dilute out its incorporation into the sulpholipid. 2. Both l-[ 35S]cysteic acid and dl-+ meso-[3- 14C]cysteic acid appear almost exclusively in 6-sulphoquinovose. 3. Molybdate inhibits the incorporation of 35SO 42− into sulpholipid but not its uptake into the cells; this suggests that adenosine 3′-phosphate 5′-sulphatophosphate may be concerned with the biosynthesis of sulpholipid, and it was shown to be formed by chloroplast fragments. 4. An outline scheme for sulpholipid biosynthesis based on these observations is discussed. 相似文献
15.
Evidence is presented for high rates of carrier-mediated dicarboxylate anion transport in maize mesophyll chloroplasts. Radioactively labeled malate is transported across the chloroplast envelope leading to accumulation in the stroma. Malate in the stroma will exchange for external malate, oxaloacetate, glutamate, aspartate, and oxoglutarate. At 4 °C the V of malate uptake is 50 μmol·h ?1·mg Chl ?1 and the Km for malate is 0.5 mm. Oxaloacetate competitively inhibits malate uptake with a Ki estimated to be 0.3 mm. The temperature dependence of malate uptake indicates an activation energy of 12 kcal/mol, and extrapolation using this value gives a rate of transport at 30 °C of approximately 300 μmol·h ?1·mg Chl ?1. This rate approximates the rates of photosynthetic malate production by these chloroplasts. 相似文献
16.
Tomato plants ( Lycopersicon esculentum L. var. Ailsa Craig) were grown in water culture in nutrient solution in a series of 10 increasing levels of nitrate nutrition. Using whole plant data derived from analytical and yield data of individual plant parts, the fate of anion charge arising from increased NO 3 assimilation was followed in its distribution between organic anion accumulation in the plant and OH − efflux into the nutrient solution as calculated by excess anion over cation uptake. With increasing NO 3 nutrition the bulk of the anion charge appeared as organic anion accumulation in the plants. OH − efflux at a maximum accounted for only 20% of the anion charge shift. The major organic anion accumulated in response to nitrate assimilation was malate. The increase in organic anion accumulation was paralleled by an increase in cation concentration (K +, Ca 2+, Mg 2+, Na +). Total inorganic anion levels (NO 3−, SO 42−, H 2PO 4−, Cl −) were relatively constant. The effect of increasing NO 3 nutrition in stimulating organic anion accumulation was much more pronounced in the tops than in the roots. 相似文献
17.
The influence of NO 3− uptake and reduction on ionic balance in barley seedlings ( Hordeum vulgare, cv. Compana) was studied. KNO 3 and KCl treatment solutions were used for comparison of cation and anion uptake. The rate of Cl − uptake was more rapid than the rate of NO 3− uptake during the first 2 to 4 hours of treatment. There was an acceleration in rate of NO 3− uptake after 4 hours resulting in a sustained rate of NO 3− uptake which exceeded the rate of Cl − uptake. The initial (2 to 4 hours) rate of K + uptake appeared to be independent of the rate of anion uptake. After 4 hours the rate of K + uptake was greater with the KNO 3 treatment than with the KCl treatment, and the solution pH, cell sap pH, and organic acid levels with KNO 3 increased, relative to those with the KCl treatment. When absorption experiments were conducted in darkness, K + uptake from KNO 3 did not exceed K + uptake from KCl. We suggest that the greater uptake and accumulation of K + in NO 3−-treated plants resulted from ( a) a more rapid, sustained uptake and transport of NO 3− providing a mobile counteranion for K + transport, and ( b) the synthesis of organic acids in response to NO 3− reduction increasing the capacity for K + accumulation by providing a source of nondiffusible organic anions. 相似文献
18.
Since environmental pollution by potentially acidic gases such as SO 2 causes proton release inside leaf tissues, homogenates of needles of spruce ( Picea abies) and fir ( Abies alba) and of leaves of spinach ( Spinacia oleracea) and barley ( Hordeum vulgare) were titrated and buffer capacities were determined as a function of pH. Titration curves of barley leaves were compared with titration curves of barley mesophyll protoplasts. From the protoplasts, chloroplasts and vacuoles were isolated and subjected to titration experiments. From the titration curves, the intracellular distribution of buffering capacities could be deduced. Buffering was strongly pH-dependent. It was high at the extremes of pH but still significant close to neutrality. Owing to its large size, the vacuole was mainly responsible for cellular buffering. However, on a unit volume basis, the cytoplasm was much more strongly buffered than the vacuole. Potentially acidic gases are trapped in the anionic form. They release protons when trapped. The magnitude of diffusion gradients from the atmosphere into the cells, which determines flux, depends on intracellular pH. In the light, the chloroplast stroma, as the most alkaline leaf compartment, has the highest trapping potential. Acidification of the chloroplast stroma inhibits photosynthesis. The trapping potential of the chloroplast is followed by that of the cytosol. Compared with the cytoplasm, the vacuole possesses little trapping potential in spite of its large size. It is particularly small in the acidic vacuoles of conifer needles. In the physiological pH range (slightly above neutrality), chloroplast buffering was about 1 microequivalents H + per milligram chlorophyll per pH unit or 35 microequivalents H + per milliliter per pH unit in barley or spinach chloroplasts. This compares with SO 2-generated H + production of somewhat more than 1 microequivalent H + per milligram chlorophyll per hour, which results from observed SO 2 uptake of leaves when stomata were open and the atmospheric SO 2 concentration was 0.4 microliters per liter (GE Taylor Jr, DT Tingey 1983 Plant Physiol 72: 237-244). At lower SO 2 concentrations, similar H + generation inside the cells requires correspondingly longer exposure times. 相似文献
19.
Uptake and release of abscisic acid (AbA) by isolated mesophyll cells of Papaver somniferum is characterized by the following observations: (a) Uptake rate is a linear function of the external AbA concentration in the range from 10 −6 to 5 × 10 −5 molar, and decreases with increasing pH. At any pH, uptake rate is linearly related to the concentration of undissociated abscisic acid, calculated from the pK = 4.7 according to the Henderson-Hasselbalch equation. At low external pH (5.0), AbA accumulation in the cells is about 10-fold. (b) Uptake of AbA is completely inhibited by salts such as KNO 2 or sodium acetate, which decrease the pH gradient between medium and cells. KCN or m-chlorocarbonylcyanide phenylhydrazone inhibits AbA uptake only after longer incubation periods (20-40 minutes). (c) Uptake rate as well as equilibrium concentration is significantly higher in light than in darkness. (d) At low external pH, release of AbA from preloaded cells is strongly stimulated by KNO 2. It is concluded that AbA is distributed between leaf cells and free space according to pH gradients, with the undissociated abscisic acid being the main penetrating species. Uptake and release occur via diffusion, without participation of a carrier. 相似文献
20.
The ATP-dependent proton-pumping activity of soybean ( Glycine max L.) root microsomes is predominantly nitrate sensitive and presumably derived from the tonoplast. We used microsomes to characterize anion effects on proton pumping of the tonoplast vesicles using two distinctly different techniques. Preincubation of the vesicles with nitrate caused inhibition of proton pumping and ATPase activity, with similar concentration dependence. Fluoride, which preferentially inhibits the plasma membrane ATPase, inhibited ATPase activity strongly at concentrations which did not affect proton pumping activity. Addition of potassium salts, after a steady-state pH gradient is established in the absence of such salts, caused an increased pH gradient which was due to alleviation of Δ Ψ and subsequent increased influx of H+ into these vesicles. This anion-induced increase in the pH gradient could be used as a measure of the relative anion permeabilities, which were of the order Br− = NO3− > Cl− SO42−. Phosphate and fluoride caused no increase in the pH gradient. Since the concentration dependence of KCl- and KNO3-induced quenching exhibited a saturable component, and since H+ uptake was increased by only certain anions, the data suggest that there may be a relatively specific anion channel associated with tonoplast-derived vesicles. 相似文献
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