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1.
Escherichia coli accumulates K+ by means of multiple uptake systems of which Kup is the major transport system at acidic pH. In cells grown under fermentative conditions at pH 5.5, K+ influx by a wild-type strain upon hyper-osmotic stress at pH 5.5 was accompanied by a marked decrease in H+ efflux, with a 1:1 ratio of K+ to H+ fluxes. This was observed with cells treated with N,N'-dicyclohexylcarbodiimide. Similar results with a mutant defective in Kdp and TrkA but with a functional Kup system but not in a mutant defective in Kdp and Kup but having an active TrkA system suggest that Kup operates as a H+ -K+ -symporter. 相似文献
2.
Paul Jensén 《Physiologia plantarum》1982,56(3):259-265
Effects of interrupted K+ supply on different parameters of growth and mineral cation nutrition were evaluated for spring wheat (Triticum aestivum L. cv. Svenno). K+ (2.0 mM) was supplied to the plants during different periods in an otherwise complete nutrient solution. Shoot growth was reduced before root growth after interruption in K+ supply. Root structure was greatly affected by the length of the period in K+ -free nutrient solution. Root length was minimal, and root branching was maximal within a narrow range of K+ status of the roots. This range corresponded to cultivation for the last 1 to 3 days, of 11 in total, in K+ -free nutrient solution, or to continuous cultivation in solution containing 0.5 to 2 mM K+. In comparison, both higher and lower internal/external K+ concentrations had inhibitory effects on root branching. However, the differing root morphology probably had no significant influence on the magnitude of Ca2+, Mg2+ and Na+ uptake. Uptake of Ca2+ and especially Mg2+ significantly increased after K+ interruption, while Na+ uptake was constant in the roots and slowly increased in the shoots. The two divalent cations could replace K+ in the cells and maintain electroneutrality down to a certain minimal range of K+ concentrations. This range was significantly higher in the shoot [110 to 140 μmol (g fresh weight)?1] than in the root [20 to 30 μmol (g fresh weight)?1]. It is suggested that the critical K+ values are a measure of the minimal amount of K+ that must be present for physiological activity in the cells. At the critical levels, K+ (86Rb) influx and Ca2+ and Mg2+ concentrations were maximal. Below the critical K+ values, growth was reduced, and Ca2+ and Mg2+ could no longer substitute for K+ for electrostatic balance. In a short-term experiment, the ability of Ca2+ to compete with K+ in maintaining electroneutrality in the cells was studied in wheat seedlings with different K+ status. The results indicate that K+, which was taken up actively and fastest at the external K+ concentration used (2.0 mM), partly determines the size of Ca2+ influx. 相似文献
3.
Sune Pettersson 《Physiologia plantarum》1981,52(4):431-436
Passive fluxes of K+ (86 Rb) into roots of sunflower ( Helianthus annuus L. cv. Uniflorus) were determined at low K+ concentration (0.1 and 1.0 mM K+ ) in the ambient solution. Metabolic uptake of K+ was inhibited by 10−4 M 2,4-dinitrophenol (DNP). K+ (86 Rb) fluxes were studied both continuously and by time differentiation of uptake. In high K+ roots passive uptake was directly proportional to the K+ concentration of the uptake solution, indicating free diffusion. This assumption was supported by the fact that passive Rb+ uptake was not affected by high K+ concentrations. In low K+ roots the passive uptake of K+ was higher than in high K+ roots. The increase was possibly due to carrier-mediated K+ transport. As K+ effluxes were quantitatively similar to influxes, it is suggested that passive K+ fluxes represent exchange diffusion without relation to net K+ transport. 相似文献
4.
The effects of external K+ , H+ and Ca2+ concentrations on the intracellular K+ concentration, [K+ ]i, and the K+ -ATPase activity in 2-day-old mung bean roots [ Vigna mungo (L.) Hepper] were investigated. [K+ ]i, in mung bean roots was markedly decreased by external K+ or H+ stress and did not recover the initial value even after the stress was removed. This decrease in [K+ ]i, gradually disappeared with the addition of (Ca2+ . Ca2+ may offset the harmful effects of ion stress. Ca2+ seems to have two effects on K+ transport; control of K+ permeability and activation of K+ uptake, although K+ -ATPase activity was inhibited by Ca2+ concentrations higher than 10–4 M. We suggest that Ca2+ activates K+ uptake indirectly through the acidification of the cytoplasm. 相似文献
5.
The effects of cadmium and lead on the internal concentrations of Ca2+ and K+, as well as on the uptake and translocation of K(86Rb+) were studied in winter wheat (Triticum aestivum L. a. MV-8) grown hydroponically at 2 levels of K+ (100 uM and 10 mM). Cd2+ and Pb2+ were applied in the nutrient solution in the range of 0.3 to 1000 u.M. Growth was more severely inhibited by Cd2+ and in the high-K+ plants as compared to Pbz+ and low-K+ plants. Ions of both heavy metals accumulated in the roots and shoots, but the K+ status influenced their levels. Ca2+ accumulation was increased by low concentrations of Cd2+ mainly in low-K+ shoots, whereas it was less influenced by Pb2+. The distribution of Cd2+ and Ca2+ in the plant and in the growth media indicated high selectivity for Cd2+ in the root uptake, while Ca2+ was preferred in the radial and/or xylem transport. Cd2+ strongly inhibited net K+ accumulation in high-K+ plants but caused stimulation at low K+ supply. In contrast, the metabolis-dependent influx of K+(86Rb+) was inhibited in low-K+ plants, while the passive influx in high-K+ plants was stimulated. Translocation of K+ from the roots to the shoots was inhibited by Cd2+ but less influenced in Pb2+-treated plants. It is concluded that the effects of heavy metals depend upon the K+-status of the plants. 相似文献
6.
R. H. Jongbloed J. M. A. M. Clement G. W. F. H. Borst-Pauwels 《Physiologia plantarum》1991,83(3):427-432
NH4+ and K+ uptake experiments have been conducted with 3 ectomycorrhizal fungi, originating from Douglas fir (Pseudotsuga menziesii (Mirb.] Franco) stands. At concentrations up to 250 μM, uptake of both NH4+ and K+ follow Michaelis-Menten kinetics. Laccaria bicolor (Maire) P. D. Orton, Lactarius rufus (Scop.) Fr. and Lactarius hepaticus Plowr. ap. Boud. exhibit Km values for NH4+ uptake of 6, 35, and 55 μM, respectively, and Km values for K+ uptake of 24, 18, and 96 μM, respectively. Addition of 100 μM NH4+ raises the Km of K+ uptake by L. bicolor to 35 μM, while the Vmax remains unchanged. It is argued that the increase of Km is possibly caused by depolarization of the plasma membrane. It is not due to a competitive inhibition of K+ by NH4+ since the apparent inhibitor constant is much higher than the Km, for NH4+ uptake. The possibility that NH4+ and K+ are taken up by the same carrier can be excluded. The Km, values for K+ uptake in the two other fungi are not significantly affected by 100 μM NH4+. Except for a direct effect of NH4+ on influx of K+ into the cells, there may also be an indirect effect after prolonged incubation of the cells in the presence of 100 μM NH4+. 相似文献
7.
Two monovalent ion porters, the putative Na+/H+ antiporter (NapA) of Enterococcus hirae and the putative K+/H+ antiporter (KefC) of Escherichia coli, are similar in sequence throughout their hydrophobic domains. These two proteins, which comprise a novel family of transporters unrelated to the previously characterized Na+/H+ exchangers of E. coli (NhaA and NhaB) are proposed to function by essentially the same mechanism. 相似文献
8.
The stimulation of dicotyledonous leaf growth by light depends on increased H+ efflux, to acidify and loosen the cell walls, and is enhanced by K+ uptake. The role of K+ is generally considered to be osmotic for turgor maintenance. In coleoptiles, auxin‐induced cell elongation and wall acidification depend on K+ uptake through tetraethylammonium (TEA)‐sensitive channels (Claussen et al., Planta 201, 227–234, 1997), and auxin stimulates the expression of inward‐rectifying K+ channels ( Philippar et al. 1999) . The role of K+ in growing, leaf mesophyll cells has been investigated in the present study by measuring the consequences of blocking K+ uptake on several growth‐related processes, including solute accumulation, apoplast acidification, and membrane polarization. The results show that light‐stimulated growth and wall acidification of young tobacco leaves is dependent on K+ uptake. Light‐stimulated growth is enhanced three‐fold over dark levels with increasing external K+, and this effect is blocked by the K+ channel blockers, TEA, Ba++ and Cs+. Incubation in 10 mm TEA reduced light‐stimulated growth and K+ uptake by 85%, and completely inhibited light‐stimulated wall acidification and membrane polarization. Although K+ uptake is significantly reduced in the presence of TEA, solute accumulation is increased. We suggest that the primary role of K+ in light‐stimulated leaf growth is to provide electrical counterbalance to H+ efflux, rather than to contribute to solute accumulation and turgor maintenance. 相似文献
9.
PAUL JENSÉN 《Physiologia plantarum》1980,49(3):291-295
The influx of Rb+ into the roots of two barley varieties (Hordeum vulgare L. cv. Salve and cv. Ingrid) from a K+-free 86Rb-labelled nutrient solution with 2.0 mM Rb+, was checked at intervals from day 6 to day 18. The control plants were continuously grown in complete nutrient solution containing 5.0 mM K+, while two other groups of plants were grown in K+-free nutrient solution starting on day 6 and between day 6 and day 9, respectively. The pattern of Rb+ influx was similar for both varieties, although their efficiencies in absorbing Rb+ were different. The relationship between Rb+ influx and K+ concentration of the root could be interpreted in terms of negative feedback through allosteric control of uptake across the plasmalemma of the root cells. Hill plots were bimodal, but in the opposite direction. The Hill coefficients, reflecting the minimum number of interacting allosteric binding sites for K+ (Rb+), were low (≤–3.0). It is discussed whether the threshold value, that is the breaking point in the Hill plot, is indicative of a changed efficiency of transporting units for K+ (Rb+) transport to the xylem. Moreover, feedback regulation might be involved in transport of K+ between root and shoot. The variation in K+ concentrations in the roots and shoots of control plants were cyclic but in phase opposition despite an exponential growth. The average K+ concentration varied only slightly with age. 相似文献
10.
11.
Steady state kinetics were used to examine the influence of Cd2+ both on K+ stimulation of a membrane-bound ATPase from sugar beet roots (Beta vulgaris L. cv. Monohill) and on K+(86Rb+) uptake in intact or excised beet roots. The in vitro effect of Cd2+ was studied both on a 12000–25000 g root fraction of the (Na++K++Mg2+)ATPase and on the ATPase when further purified by an aqueous polymer two-phase system. The observed data can be summarized as follows: 1) Cd2+ at high concentrations (>100 μM) inhibits the MgATPase activity in a competitive way, probably by forming a complex with ATP. 2) Cd2+ at concentrations <100 μM inhibits the specific K+ activation at both high and low affinity sites for K+. The inhibition pattern appears to be the same in the two ATPase preparations of different purity. In the presence of the substrate MgATP, and at K+ <5 mM, the inhibition by Cd2+ with respect to K+ is uncompetitive. In the presence of MgATP and K+ >10 μM, the inhibition by Cd2+ is competitive. 3) At the low concentrations of K+, Cd2+ also inhibits the 2,4-dinitrophenol(DNP)-sensitive (metabolic) K+(86Rb+) uptake uncompetitively both in excised roots and in roots of intact plants. 4) The DNP-insensitive (non metabolic) K+(86Rb+) uptake is little influenced by Cd2+. As Cd2+ inhibits the metabolic uptake of K+(86Rb+) and the K+ activation of the ATPase in the same way at low concentrations of K+, the same binding site is probably involved. Therefore, under field conditions, when the concentration of K+ is low, the presence of Cd2+ could be disadvantageous. 相似文献
12.
The effects of abscisic acid (ABA) on growth, uptake and translocation of potassium ions, K+ ,Mg2+ -ATPase activity and transpiration were investigated in young wheat ( Triticum aestivum L. cv. Martonvásári-8) plants grown at different K+ supplies. Long-term treatment with ABA (10 μ M ) reduced growth in high-K+ plants, but had less effect under low-K+ conditions. K+ (86 Rb) uptake was inhibited by about 70 and 40% in low- and high-K+ plants, respectively. The stimulation by K+ of the Mg2+ -ATPase activity in the root microsomal fraction was lost with ABA treatment. It is suggested that the inhibitory effect of ABA on K+ uptake may be related to this effects on the K+ ,Mg2+ -ATPase. Translocation of K+ to the shoot was inhibited in low-K+ plants only, and it was not affected in high-K+ plants. In parallel to this, ABA treatment reduced transpiration by about 50% in low-K+ plants, whereas a much smaller effect was seen in high-K+ plants. These observations suggest that the regulation by ABA of the stomatal movements is strongly counteracted by high-K+ status. 相似文献
13.
K+ and Na+ influxes into Nitella translucens Agardh in buffered artificial pond water have been measured in the pH range 5.7 to 8.1 with and without sub-threshold electric current. For pH levels below 7 the results confirm previous observations that neither ion is a major carrier of membrance current. At pH levels greater than 7 the effect of applied current is generally to depress cation influx. It is argued that this is evidence in favour of OH− being the principal charge carrier under these conditions. Observations of the effects of OH− gradients on K+ influx tend to support this hypothesis. 相似文献
14.
D. Guillaume†‡ T. Grisar†‡ A. V. Delgado-Escueta‡§ J. Laschet M. Bureau-Heeren‡ 《Journal of neurochemistry》1990,54(1):130-134
Analysis of purified Na+,K+-ATPase from cat and human cortex by sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals two large catalytic subunits called alpha (-) (lower molecular weight) and alpha (+) (higher molecular weight). Differences in K+ dephosphorylation of these two molecular forms have been investigated by measuring the phosphorylation level of each protein after their separation on sodium dodecyl sulfate gels. In the presence of Na+, Mg2+, and ATP, both subunits are phosphorylated. Increasing concentrations (from 0 to 3 mM) of K+ induce progressive dephosphorylation of both alpha-subunits, although the phosphoprotein content of alpha (-) is decreased significantly less than that of alpha (+). Ka values of alpha (-) for K+ are 40% and 50% greater in cat and human cortex, respectively, than values of alpha (+). alpha (-) and alpha (+) are thought to be localized in specific cell types of the brain: alpha (-) is the exclusive form of nonneuronal cells (astrocytes), whereas alpha (+) is the only form of axolemma. Our results support the hypothesis that glial and neuronal Na+,K+-ATPases are different molecular entities differing at least by their K+ sensitivity. Results are discussed in relation to the role of glial cells in the regulation of extracellular K+ in brain. 相似文献
15.
SYLVIA LINDBERG 《Physiologia plantarum》1980,48(1):65-70
A microsomal (Na++ K++ Mg2+)ATPase preparation from sugar beet roots was used. The activation by simultaneous addition of Na+ and K+ at different levels was examined in terms of steady state kinetics. The observed data can be summarized in the following way: 1. The apparent affinity between the enzyme and the substrate MgATP depends on the ratio between Na+ and K+. At low Na+ concentration (below 5 mM), the apparent Km decreases with increasing concentrations of K+ (1–20 mM). At 5 mM Na+, the K+ level does not change the apparent Km, while at Na+ levels above 10 mM, the apparent Km between enzyme and substrate increases with increasing concentration of K+. 2. When the MgATP concentration is kept constant, homotropic cooperativity (concerning one type of ligand) and heterotropic cooperativity (concerning different types of ligands) exist in the activation by Na+ and K+. The Na+ binding is cooperative with different Km values and Hill coefficients (n) in the presence of low and high concentration of K+. At low Na+ level (< 5 mM). a negative cooperativity exists for Na+ (nNa < 1) which is more pronounced in the presence of high [K+]. When the concentration of Na+ is raised the negative cooperativity disappears and turns into a positive one (nNa > 1). Only K+ binding in the presence of low [Na+] shows cooperativity with a Hill coefficient that reflects changes from negative to positive homotropic cooperativity with increasing concentrations of K+ (nK < 1 → nK > 1). In the presence of [Na+] > 10 mM, the changes in nk are insignificant. 3. A model is proposed in which one or two different K sites and one or two Na sites control the catalytic activity, with multiple interactions between Na+, K+ and MgATP. 4. In the presence of Na+ (< 10 mM), K+ is probably bound to two K sites, one of which translocates K+ through the membrane by an antiport Na+/K+ mechanism. This could be connected with an elevated K+ uptake in the presence of Na+ and could therefore explain some field properties of sugar beets. 相似文献
16.
For determination of the effect of K+ on macro- and micronuclear differentiation Paramecium caudatum exconjugants were transferred to medium with various concentrations of Valinomycin and/or K+ at the critical stage of nuclear differentiation. The differentiation was not disturbed by transfer to medium containing 1.5 mM to 50 mM KCl. Injection of KCl solution at the critical stage also did not affect differentiation of the macronucleus appreciably. But change of the KCl concentration in the medium at the critical stage interrupted of normal development of the macronucleus.
Macro- and micronuclear differentiations after conjugation are known to be determined by the antero-posterior localization of postzygotic micronuclei. This nuclear localization is achieved by elongation of mitotic spindles and marked shortening of the cell length at the time of micronuclear division. Successive measurements of cell length at 25°C showed that cells began to shorten 1.5 hr after mating-pair separation, reaching to half the initial length about 2.5 hr after the separation, and then returning to recover their initial length within about 50 min. In a solution of K+ (50 mM) plus Valinomycin (1μg/ml or more), cell shortening was inhibited. It is not known whether elongation of mitotic spindles at the time of critical nuclear division was disordered by this treatment, but the macronuclear anlagen developed in the treated cells. Thus shortening in the cell length is not indispensable for nuclear differentiation. 相似文献
Macro- and micronuclear differentiations after conjugation are known to be determined by the antero-posterior localization of postzygotic micronuclei. This nuclear localization is achieved by elongation of mitotic spindles and marked shortening of the cell length at the time of micronuclear division. Successive measurements of cell length at 25°C showed that cells began to shorten 1.5 hr after mating-pair separation, reaching to half the initial length about 2.5 hr after the separation, and then returning to recover their initial length within about 50 min. In a solution of K
17.
Kinetic studies of a microsomal, dithiotreitol treated, homogenate from sugar beet roots led to the following conclusions about its ATPase activity: (1) MgATP in complex appears to be the primary substrate for the reaction. The reciprocal equilibrium constant for the binding to the enzyme is estimated to be approximately 0.2 × 10?3M. (2) Free ATP acts as a competitive inhibitor of the MgATP. The binding constant is about twice as high as for MgATP. Consequently the enzyme has less affinity for ATP than for MgATP. (3) Free Mg2+ has little influence on the velocity, as the binding affinity of the enzyme for Mg2+ is almost negligible. 相似文献
18.
SYLVIA LINDBERG 《Physiologia plantarum》1976,36(2):139-144
Kinetic studies of a dithiothreitol treated membrane ATPase fraction from sugar beet roots led to the following conclusions: 1) In the presence of MgATP, Na+ and K+ stimulate the ATPase activity in different ways following simple Michaelis-Menten kinetics. Thus separate sites for Na+ and K+ are suggested. 2) In the absence of K+, Na+ acts as an uncompetitive modifier raising the apparent Km and Vmax for MgATP. 3) In the absence of Na+, K+ activates non-competitively with respect to MgATP. Thus K+ increases Vmax but does not affect the apparent affinity constant. 4) K+ and Na+ double the rate constants. 5) In the presence of Na+ or K+, Mg2+ in excess acts as a weak inhibitor to Na+ and/or K+ activity. 6) The temperature-activity dependence in the 5–40°C interval shows biphasic Arrhenius plots with the transition point between 15–18°C. The activation energy is lowered at temperatures > 18°C. 相似文献
19.
Ouabain Binding, ATP Hydrolysis, and Na+ ,K+ -Pump Activity During Chemical Modification of Brain and Muscle Na+ ,K+ -ATPase 总被引:1,自引:0,他引:1
J. Teisinger H. Zemková P. Svoboda E. Amler F. Vyskoil 《Journal of neurochemistry》1992,58(3):1066-1072
The effects of 16 group-specific, amino acid-modifying agents were tested on ouabain binding, catalytical activity of membrane-bound (rat brain microsomal), sodium dodecyl sulfate-treated Na+,K(+)-ATPase, and Na+,K(+)-pump activity in intact muscle cells. With few exceptions, the potency of various tryptophan, tyrosine, histidine, amino, and carboxy group-oriented drugs to suppress ouabain binding and Na+,K(+)-ATPase activity correlated with inhibition of the Na+,K(+)-pump electrogenic effect. ATP hydrolysis was more sensitive to inhibition elicited by chemical modification than ouabain binding (membrane-bound or isolated enzyme) and than Na+,K(+)-pump activity. The efficiency of various drugs belonging to the same "specificity" group differed markedly. Tyrosine-oriented tetranitromethane was the only reagent that interfered directly with the cardiac receptor binding site as its inhibition of ouabain binding was completely protected by ouabagenin preincubation. The inhibition elicited by all other reagents was not, or only partially, protected by ouabagenin. It is surprising that agents like diethyl pyrocarbonate (histidine groups) or butanedione (arginine groups), whose action should be oriented to amino acids not involved in the putative ouabain binding site (represented by the -Glu-Tyr-Thr-Trp-Leu-Glu- sequence), are equally effective as agents acting on amino acids present directly in the ouabain binding site. These results support the proposal of long-distance regulation of Na+,K(+)-ATPase active sites. 相似文献
20.
Terence M. Murphy 《Physiologia plantarum》1988,74(3):537-543
A low fluence of ultraviolet radiation (UV) causes cultured cells of Rosa damascena Mill cv. Gloire de Guilan to lose intracellular K+ . This effect required the presence of Ca2+ in the medium. A reduction in the concentration of free Ca2+ to 10−5 M with ethyleneglycol-bis-(β-aminoethyl-ether)-N.N.N',N'-tetraacetic acid (EGTA) buffer inhibited the UV-stimulated efflux; this was correlated with a discharge of the membrane potential and a stimulation of the leakage of K+ from unirradiated cells. All the same effects were seen with La3+ at 0.2 m M. At 0.02 m M La3+ , the UV-stimulated efflux of K+ was blocked without concomitant effects on the membrane potential or K+ efflux from control cells. It is suggested that removal of Ca2+ blocks or masks the UV-induced leakage of K+ by destabilizing the plasma membrane. In addition, La3+ may specifically inhibit the UV-stimulated opening of K+ or anion channels. 相似文献