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1.
Abstract: Bovine chromaffin secretory vesicle ghosts loaded with Na+ were found to take up Ca2+ when incubated in K+ media or in sucrose media containing micromolar concentrations of free Ca2+. Li+- or choline+loaded ghosts did not take up Ca2+. The Ca2+ accumulated by Na+-loaded ghosts could be released by the Ca2+ ionophore A23187, but not by EGTA. Ca2+ uptake was inhibited by external Sr2+, Na +, Li +, or choline +. All the 45Ca2+ accumulated by Na+-dependent Ca2+ uptake could be released by external Na +, indicating that both Ca2+ influx and efflux occur in a Na+-dependent manner. Na + -dependent Ca2+ uptake and release were only slightly inhibited by Mg2+. In the presence of the Na+ ionophore Monensin the Ca2+ uptake by Na +-loaded ghosts was reduced. Ca2+ sequestered by the Na+-dependent mechanism could also be released by external Ca2+ or Sr2+ but not by Mg2+, indicating the presence of a Ca2+/Ca2+ exchange activity in secretory membrane vesicles. This Ca2+/Ca2+ exchange system is inhibited by Mg2+, but not by Sr2+. The Na + -dependent Ca2+ uptake system in the presence of Mg2+ is a saturable process with an apparent Km of 0.28 μM and a Vmax= 14.5 nmol min?1 mg protein?1. Ruthenium red inhibited neither the Na+/Ca2+ nor the Ca2+/Ca2+ exchange, even at high concentrations. 相似文献
2.
Abstract The comparative Na+ tolerance of Chora buckellii cultured in freshwater (FW) or artificial Waldsea water (AWW, which contains about 110 mol m?3 each Na +, Mg2+, Cl? and SO2-4 was tested with respect to the external Na+ to Ca2+ ratio (Na: Ca). Fifty per cent of FW cells subjected to 70 mol m?3 NaCl, which raised Na:Ca from 10: 1 to 700: 1 and the external osmotic pressure from 0.024 to 0.402 MPa, died within 6 d. Death was associated with the loss of Na/K selectivity, H+ -pump activity and turgor. Restoration of Na:Ca to 10:1 in high Na+ medium with CaCl2 ensured 100% survival and maintained H+-pump activity and Na/K selectivity of FW cells. Turgor was regulated within 3 d with net uptake of Na +, K+ and Cl? in the vacuolc. Mg2+ was not as effective as Ca2+ in enhancing survival or maintaining H+ -pump activity and Na/K selectivity of FW cells in the presence of elevated Na+. However, turgor was regulated within 3 d by accumulation of Cl? and an unknown cation in the vacuole. All AWW cells subjected to an increase of 70 mol m ?3 NaCl, which raised Na: Ca from 16:1 to 25: 1 and the external osmotic pressure from 0.915 to 1.22 MPa, survived and maintained H + -pump activity. Turgor was regulated within 6d by accumulating Na +, K+ and Cl? in the vacuole. All AWW cells subjected to 70molm?3 NaCl in a medium in which Na:Ca was equal to 700:1 survived and maintained H + -pump activity, but showed loss of Na/K selectivity. Turgor was regulated with an unknown osmoticum(a) within 6 d. 相似文献
3.
Effect of Monovalent Cations on Na+ /Ca2+ Exchange and ATP-Dependent Ca2+ Transport in Synaptic Plasma Membranes 总被引:1,自引:0,他引:1
Two Ca2+ transport systems were investigated in plasma membrane vesicles isolated from sheep brain cortex synaptosomes by hypotonic lysis and partial purification. Synaptic plasma membrane vesicles loaded with Na+ (Na+i) accumulate Ca2+ in exchange for Na+, provided that a Na+ gradient (in leads to out) is present. Agents that dissipate the Na+ gradient (monensin) prevent the Na+/Ca2+ exchange completely. Ca2+ accumulated by Na+/Ca2+ exchange can be released by A 23187, indicating that Ca2+ is accumulated intravesicularly. In the absence of any Na+ gradient (K+i-loaded vesicles), the membrane vesicles also accumulate Ca2+ owing to ATP hydrolysis. Monovalent cations stimulate Na+/Ca2+ exchange as well as the ATP-dependent Ca2+ uptake activity. Taking the value for Na+/Ca2+ exchange in the presence of choline chloride (external cation) as reference, other monovalent cations in the external media have the following effects: K+ or NH4+ stimulates Na+/Ca2+ exchange; Li+ or Cs+ inhibits Na+/Ca2+ exchange. The ATP-dependent Ca2+ transport system is stimulated by increasing K+ concentrations in the external medium (Km for K+ is 15 mM). Replacing K+ by Na+ in the external medium inhibits the ATP-dependent Ca2+ uptake, and this effect is due more to the reduction of K+ than to the elevation of Na+. The results suggest that synaptic membrane vesicles isolated from sheep brain cortex synaptosomes possess mechanisms for Na+/Ca2+ exchange and ATP-dependent Ca2+ uptake, whose activity may be regulated by monovalent cations, specifically K+, at physiological concentrations. 相似文献
4.
Abstract: The activities of certain properties of sodium, potassium-activated adenosine triphosphatase (Na +, K+- ATPase; EC 3.6.1.3) were examined in cultures and peri- karya fractions enriched in rat cerebellar nerve cells or astrocytes, in comparison with preparations from whole immature and adult rat cerebellum and derived synapto- somal fractions, as well as nonneural tissue such as the kidney. The specific activity of Na +, K+-ATPase was markedly higher in the freshly isolated astrocytes than in the nerve cells (3–15-fold greater depending on neuronal cell type). In contrast, the specific activity of the enzyme was about twice as high in the primary neuronal as in the a'strocytic cultures after 14 days in vitro. In membrane preparations from the whole cerebellum, synaptosomal fractions, and total perikarya suspensions the inhibition of enzyme activity by ouabain indicated complex kinetics, which were consistent with the presence of two forms of the Na +, K+-ATPase (apparent Aj values of about 10–7M and 10–4-10–5M, respectively), the high- affinity form accounting for 60–75% of the total activity. The interaction of the enzyme with ouabain was apparently similar in perikarya preparations of granule neurones, Purkinje cells, and astrocytes. Differences were, however, observed in the properties of the Na +,K + - ATPase of cultured neurones and astrocytes. The latter contained predominantly, but not exclusively, an Na+,K+-ATPase with low affinity for ouabain (73% of the total) that is similar to the single enzyme form in the kidney. This form constituted a significantly smaller proportion of the Na +, K+-ATPase in the cultured neuronal preparations (55%). It would appear, therefore, that in membrane fractions from preparations enriched in different separated and cultured neural cell types both the high- and the low-affinity forms of the enzyme, in terms of interaction with ouabain, are expressed. Depending on the class of cells these enzyme forms constituted a different proportion of the total activity, but both forms seemed to be present in every type of cell examined, even after taking into acc.ount the contribution in the enriched preparations of the contaminating cell types. In contrast with the results on the Na+, K+-ATPase activity determined under optimal conditions in preparations derived from disrupted cells, differences could not be detected between the cultured cell types when the effect of ouabain on the uptake of 86Rb into “live cells” was estimated as a measure of in situ ion pump activity. Besides the interaction with ouabain, the K+ dependence of the Na+, K+-ATPase activity was also investigated in crude particulate preparations from cultured cerebellar neurones and astrocytes. Differences were observed as nearly maximal enzyme activity was obtained in the as- trocyte preparations at 1 mM KCl, when only about one- third of the maximal activity was displayed by the cultured nerve cells. 相似文献
5.
Detrimental effects of salinity on plants are known to be partially alleviated by external Ca2+. Previous work demonstrated that the Arabidopsis SOS3 locus encodes a Ca2+‐binding protein with similarities to CnB, the regulatory subunit of protein phosphatase 2B (calcineurin). In this study, we further characterized the role of SOS3 in salt tolerance. We found that reduced root elongation of sos3 mutants in the presence of high concentrations of either NaCl or LiCl is specifically rescued by Ca2+ and not Mg2+, whereas root growth is rescued by both Ca2+ and Mg2+ in the presence of high concentrations of KCl. Phenocopies of sos3 mutants were obtained in wild‐type plants by the application of calmodulin and calcineurin inhibitors. These data provide further evidence that SOS3 is a calcineurin‐like protein and that calmodulin plays an important role in the signalling pathways involved in plant salt tolerance. The origin of the elevated Na : K ratio in sos3 mutants was investigated by comparing Na+ efflux and influx in both mutant and wild type. No difference in Na+ influx was recorded between wild type and sos3; however, sos3 plants showed a markedly lower Na+ efflux, a property that would contribute to the salt‐oversensitive phenotype of sos3 plants. 相似文献
6.
Joseph D. Robinson 《Journal of neurochemistry》1981,37(1):140-146
Abstract: With a partially purified, membrane-bound (Ca + Mg)-activated ATPase preparation from rat brain, the K0.5 for activation by Ca2+ was 0.8 p μm in the presence of 3 mm -ATP, 6 mm -MgCl2, 100 mM-KCI, and a calcium EGTA buffer system. Optimal ATPase activity under these circumstances was with 6-100 μm -Ca2+, but marked inhibition occurred at higher concentrations. Free Mg2+ increased ATPase activity, with an estimated K0.5, in the presence of 100 μm -CaCl2, of 2.5 mm ; raising the MgCl2 concentration diminished the inhibition due to millimolar concentrations of CaCl2, but antagonized activation by submicromolar concentrations of Ca2+. Dimethylsulfoxide (10%, v/v) had no effect on the K0.5 for activation by Ca2+, but decreased activation by free Mg2+ and increased the inhibition by millimolar CaCl2. The monovalent cations K+, Na+, and TI+ stimulated ATPase activity; for K+ the K0.5 was 8 mm , which was increased to 15 mm in the presence of dimethylsulfoxide. KCI did not affect the apparent affinity for Ca2+ as either activator or inhibitor. The preparation can be phosphorylated at 0°C by [γ-32P]-ATP; on subsequent addition of a large excess of unlabeled ATP the calcium dependent level of phosphorylation declined, with a first-order rate constant of 0.12 s?1. Adding 10 mm -KCI with the unlabeled ATP increased the rate constant to 0.20 s?1, whereas adding 10 mm -NaCl did not affect it measurably. On the other hand, adding dimethyl-sulfoxide slowed the rate of loss, the constant decreasing to 0.06 s?1. Orthovanadate was a potent inhibitor of this enzyme, and inhibition with 1 μm -vanadate was increased by both KCI and dimethylsulfoxide. Properties of the enzyme are thus reminiscent of the plasma membrane (Na + K)-ATPase and the sarcoplasmic reticulum (Ca + Mg)-ATPase, most notably in the K+ stimulation of both dephosphorylation and inhibition by vanadate. 相似文献
7.
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
8.
Long-term effects of 1-naphtaleneacetic acid (NAA), benzyladenine (BA), gibberellic acid (GA3), abscisic acid (ABA) and ethylene on K+ levels, K+ uptake and translocation to the shoot were studied in young wheat plants (Triticum aesticum L. cv. Martonvásári-8) grown at different K+ supplies. Na+ levels and K+/Na+ selectivity were also investigated. Both in shoots and roots, NAA, BA and ABA decreased K+ and Na+ levels more effectively in high-K+ plants than in low-K+ plants. GA, and ethylene did not influence K+ and Na+ levels. K+/Na+ selectivity in roots of low-K+ plants was increased in favour of K+ by BA, NAA and to a lesser extent by ABA. In high-K+ plants only BA increased the K+/Na+ ratio, whereas the effects of the other hormones were the opposite (NAA) or less pronounced (ABA). K+(86Rb) uptake was inhibited by NAA and BA in low-K+ plants but not in high-K+ plants. K+(86Rb) uptake was inhibited throughout by 10 μM ABA. K+(86Rb) translocation to the shoot was influenced by the hormones similarly to the uptake patterns, with the exception of ABA, which inhibited translocation in low-K+ plants but not in high-K+ plants. The results show that hormonal effects may quantitatively and qualitatively be modified by K+ levels in the plant and that internal K+ concentration may play a role in the mechanisms regulating the effects of NAA, BA and ABA but probably not in those of GA3 or ethylene. 相似文献
9.
In order to identify physiological components that contribute to salinity tolerance, we compared the effects of Na+, Mg2+ and K+ salts (NaCl, Na2SO4, MgCl2, MgSO4, KCl and K2SO4), Ca2+ (CaSO4), mannitol and melibiose on the wild type and the single-gene NaCl-tolerant mutants stl1 and stl2 of Ceratopteris richardii. Compared with gametophytic growth of the wild type, stl2 showed a low level of tolerance that was restricted to Na+ salts and osmotic stress. stl2 exhibited high tolerance to both Na+ and Mg2+ salts, as well as to osmotic stress. In response to short-term exposure (3 d) to NaCl, accumulation of K+ and Na+ was similar in the wild type and stl1. In contrast, stl2 accumulated higher levels of K+ and lower levels of Na+. Ca2+ supplementation (1.0 mol m?3) ameliorated growth inhibition by Na+ and Mg2+ stress in wild type and stll, but not in stl2. In addition, under Na+ stress (175 mol m?3) wild-type, stll and stl2 gametopbytes maintained higher tissue levels of K+ and lower levels of Na+ when supplemented with Ca2+ (1.0 mol m?3). stl2 gametophytes were extremely sensitive to K+ supplementation. Growth of stl2 was greater than or equal to that of the wild type at trace concentrations of K+ but decreased substantially with increasing K+ concentration. Supplementation with K+ from 0 to 1.85 mol m?3 alleviated some of the inhibition by 75 mol m?3 NaCl in the wild type and in stl1. In stl2, growth at 75 mol m?3 NaCl was similar at 0 and 1.85 mol m?3 K+ supplementation. Although K+ supplementation above 1.85 mol m?3 did not alleviate inhibition of growth by Na+ in any genotype, stl2 maintained greater relative tolerance to NaCl at all K+ concentrations tested. 相似文献
10.
Emilia Ballesteros Eduardo Blumwald Juan Pedro Donaire rés Belver 《Physiologia plantarum》1997,99(2):328-334
Na+ transport across the tonoplast and its accumulation in the vacuoles is of crucial importance for plant adaptation to salinity. Mild and severe salt stress increased both ATP- and PPi-dependent H+ transport in tonoplast vesicles from sunflower seedling roots, suggesting the possibility that a Na+/H+ antiport system could be operating in such vesicles under salt conditions (E. Ballesteros et al. 1996. Physiol. Plant. 97: 259–268). During a mild salt stress, Na+ was mainly accumulated in the roots. Under a more severe salt treatment, Na+ was equally distributed in shoots and roots. In contrast to what was observed with Na+, all the salt treatments reduced the shoot K+ content. Dissipation by Na+ of the H+ gradient generated by the tonoplast H+-ATPase, monitored as fluorescence quenching of acridine orange, was used to measure Na+/H+ exchange across tonoplast-enriched vesicles isolated by sucrose gradient centrifugation from sunflower (Helianthus annuus L.) roots treated for 3 days with different NaCl regimes. Salt treatments induced a Na+/H+ exchange activity, which displayed saturation kinetics for Na+ added to the assay medium. This activity was partially inhibited by 125 μM amiloride, a competitive inhibitor of Na+/H+ antiports. No Na+/H+ exchange was detected in vesicles from control roots. The activity was specific for Na+. since K+ added to the assay medium slightly dissipated H+ gradients and displayed non-saturating kinetics for all salt treatments. Apparent Km for Na+/H+ exchange in tonoplast vesicles from 150 mM NaCl-treated roots was lower than that of 75 mM NaCl-treated roots, Vmax remaining unchanged. The results suggest that the existence of a specific Na+/H+ exchange activity in tonoplast-enriched vesicle fractions, induced by salt stress, could represent an adaptative response in sunflower plants, moderately tolerant to salinity. 相似文献
11.
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
12.
ZxAKT1 is essential for K+ uptake and K+/Na+ homeostasis in the succulent xerophyte Zygophyllum xanthoxylum
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Qing Ma Jing Hu Xiang‐Rui Zhou Hui‐Jun Yuan Tanweer Kumar Sheng Luan Suo‐Min Wang 《The Plant journal : for cell and molecular biology》2017,90(1):48-60
The inward‐rectifying K+ channel AKT1 constitutes an important pathway for K+ acquisition in plant roots. In glycophytes, excessive accumulation of Na+ is accompanied by K+ deficiency under salt stress. However, in the succulent xerophyte Zygophyllum xanthoxylum, which exhibits excellent adaptability to adverse environments, K+ concentration remains at a relatively constant level despite increased levels of Na+ under salinity and drought conditions. In this study, the contribution of ZxAKT1 to maintaining K+ and Na+ homeostasis in Z. xanthoxylum was investigated. Expression of ZxAKT1 rescued the K+‐uptake‐defective phenotype of yeast strain CY162, suppressed the salt‐sensitive phenotype of yeast strain G19, and complemented the low‐K+‐sensitive phenotype of Arabidopsis akt1 mutant, indicating that ZxAKT1 functions as an inward‐rectifying K+ channel. ZxAKT1 was predominantly expressed in roots, and was induced under high concentrations of either KCl or NaCl. By using RNA interference technique, we found that ZxAKT1‐silenced plants exhibited stunted growth compared to wild‐type Z. xanthoxylum. Further experiments showed that ZxAKT1‐silenced plants exhibited a significant decline in net uptake of K+ and Na+, resulting in decreased concentrations of K+ and Na+, as compared to wild‐type Z. xanthoxylum grown under 50 mm NaCl. Compared with wild‐type, the expression levels of genes encoding several transporters/channels related to K+/Na+ homeostasis, including ZxSKOR, ZxNHX, ZxSOS1 and ZxHKT1;1, were reduced in various tissues of a ZxAKT1‐silenced line. These findings suggest that ZxAKT1 not only plays a crucial role in K+ uptake but also functions in modulating Na+ uptake and transport systems in Z. xanthoxylum, thereby affecting its normal growth. 相似文献
13.
E. García-Martín F. J. Martín-Romero C. Gutiérrez-Merino 《Journal of neurochemistry》1995,65(6):2757-2764
Abstract: Synaptosomes can be loaded with mag-fura-2 without significant perturbation of their ATP content by incubation for 10 min at 37°C with 10 µM mag-fura-2 acetoxymethyl ester in Hanks'-HEPES buffer (pH 7.45). The intrasynaptosomal free Mg2+ concentration ([Mg2+]i) was found to be dependent on external Mg2+ concentration, increasing from 0.8 to 1.25 mM when the concentration of Mg2+ in the incubation medium increased from 1 to 8 mM. Dissipation of the Na+ gradient across the plasma membrane of synaptosomes by treatment with the Na+ ionophore monensin (0.2 mM) or with veratridine (0.2 mM) and ouabain (0.6 mM) produced a moderate increase of [Mg2+]i, from 1.0 to 1.2–1.3 mM in an incubation medium containing 5 mM Mg2+. Plasma membrane depolarization by incubation of synaptosomes in a medium containing 68 mM KCl and 68 mM NaCl had no effect on [Mg2+]i. Reversal of the Na+ gradient by incubation of synaptosomes in a medium in which external Na+ was replaced by choline increased [Mg2+]i up to 1.6 and 2.2 mM for extrasynaptosomal Mg2+ concentrations of 1 and 8 mM, respectively. We conclude that a Na+/Mg2+ exchange operates in the plasma membrane of synaptosomes. In the presence of Mg2+ in the incubation medium, extrasynaptosomal ATP, but not ADP or adenosine, increased [Mg2+]i from 1.1 ± 0.1 up to 1.6 ± 0.1 mM. The nonhydrolyzable ATP analogue adenosine 5′-(βγ-imido)triphosphate antagonized the effect of ATP, but had no effect by itself on [Mg2+]i. It is concluded that Mg2+ transport across the plasma membrane of synaptosomes is modulated by the activity of an ecto-ATPase or an ecto-protein kinase. 相似文献
14.
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
15.
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
16.
Tonoplast, ion antiport activities are critical to ion homeostasis and sequestration in plants. The biochemical properties of these activities, and the enzymes that catalyse them, are little characterized. Here we applied biochemical approaches to study some characteristics and to distinguish between Ca2+/H+ and Cd2+/H+ antiporter activities of tonoplast vesicles from non‐transformed, wild‐type plants. Solubilization and reconstitution of oat‐seedling (Avena sativa L.) root tonoplast vesicles resulted in about a 6‐fold loss of protein, about a 6‐fold enhancement of Cd2+/H+ antiport specific activity (at 10 µM Cd2+), and almost complete loss of Ca2+/H+ antiport activity. Similar results were found for vesicles from mature tobacco (Nicotiana tabacum) roots. Cd2+ concentration‐dependent proton efflux was similar and linear with both oat vesicles and proteoliposomes. In contrast, Ca2+ concentration‐dependent proton efflux of oat vesicles was easily observed while that with proteoliposomes was minimal and non‐linear. Cd2+ pre‐treatment of oat vesicles reduced verapamil inhibition of Cd2+/H+ activity and verapamil binding to vesicles, while Ca2+ pre‐treatment was much less protective of Ca2+/H+ activity and verapamil binding. Results show the usefulness of reconstitution, and also inhibitor/ion interaction assays for distinguishing between transporter activities in vitro, but they do not resolve the question of whether there are separate enzymes for Cd2+/H+ and Ca2+/H+. Our observation that solubilization and reconstitution have similar effects on both Cd2+/H+ and Ca2+/H+ activities of root tonoplast vesicles from immature oat and mature tobacco roots suggests that the transporters involved are similar in young and mature roots, and in roots of different species. 相似文献
17.
Interactive effects of K+ and N (principally NH4+) on plant growth and ion uptake were investigated using hydroponically grown rice (Oryza sativa L. cv. M202) seedlings by varying the availability of NH4+ or NO3? and K+ during an 18d growth period, a 3d pretreatment period and during flux measurements. Plants grew best in media containing 100 mmol m?3 NH4+ and 200mmolm?3 K+ (N100/K200), followed by N2/K200 < N100/K2 < N2/K2. 86Rb+(K+) fluxes were increased by exposure to N during the 18 d growth period and the 3 d of pretreatment, but decreased by the presence of NH4+ during flux measurements. This inhibition was a function of prior N/K provision and the [NH4+]0 present during flux determinations. NH4+ was least inhibitory to 86Rb+(K+) influx in high-N/low-K plants. Pretreatments with K+ failed to stimulate NH4+ uptake, and the presence of K+ in the uptake solutions reduced NH4+ fluxes only in high-N/low-K plants. 相似文献
18.
Abstract. Slightly vacuolated cells, i.e. microalgae and meristematic cells of vascular plants, maintain low Cl? and Na+ concentrations even when exposed to a highly saline environment. The factors regulating the internal ion concentration are the relative rate of volume expansion, the membrane permeability to ions, the electrical potential, and the active ion fluxes. For ion species which are not actively transported, a formula is developed which relates the internal concentration to the rate of expansion of cell volume, the permeability of membranes to that ion, and the electrical potential. For example, when the external concentration of Cl? is high, and Cl? influx is probably mainly passive, the formula predicts that rapid growth keeps the internal Cl? concentration lower than that in a non-growing cell with the same electrical potential; this effect is substantial if the plasmalemma has a low permeability to Cl?. For ion species which are actively transported, the rate of pumping must be considered. For instance Na+ concentrations are kept low mainly by an efficient Na+ extrusion pump which works against the electric field across the membrane. The requirement for Na+ extrusion is related to the external Na+ concentration, the rate of expansion of cell volume, the membrane permeability, and the electrical potential. It is possible that microalgae have a more positive electrical potential than many other plant cells; if so, requirements for high rates of active Na+ extrusion will be lower. The required rates of Na+ extrusion are lower during rapid growth, provided that the permeability of the plasmalemma to Na+ is low. The energy required for the regulation of Cl? and Na+ concentrations is low, especially in rapidly expanding cells where Na+ extrusion requires only 1–2% of the energy normally produced in respiration. The exclusion of these ions, however, must be accompanied by the synthesis of enough organic compounds to provide adequate osmotic solutes for the increases in volume accompanying growth. This process reduces the substrates available for respiration and synthesis of cell constituents, but the reduction is not prohibitively large—even for cells growing in 750 mol m?3 NaCl, the carbohydrate accumulated as osmotic solute is only 10% of that consumed in respiration. 相似文献
19.
Joao B. T. Rocha Herman Wolosker †Diogo O. Souza Leopoldo de Meis 《Journal of neurochemistry》1996,66(2):772-778
Abstract: Rat brain microsomes accumulate Ca2+ at the expense of ATP hydrolysis. The rate of transport is not modulated by the monovalent cations K+, Na+, or Li+. Both the Ca2+ uptake and the Ca2+-dependent ATPase activity of microsomes are inhibited by the sulfated polysaccharides heparin, fucosylated chondroitin sulfate, and dextran sulfate. Half-maximal inhibition is observed with sulfated polysaccharide concentrations ranging from 0.5 to 8.0 µg/ml. The inhibition is antagonized by KCl and NaCl but not by LiCl. As a result, Ca2+ transport by the native vesicles, which in the absence of polysaccharides is not modulated by monovalent cations, becomes highly sensitive to these ions. Trifluoperazine has a dual effect on the Ca2+ pump of brain microsomes. At low concentrations (20–80 µM) it stimulates the rate of Ca2+ influx, and at concentrations >100 µM it inhibits both the Ca2+ uptake and the ATPase activity. The activation observed at low trifluoperazine concentrations is specific for the brain Ca2+-ATPase; for the Ca2+-ATPases found in blood platelets and in the sarcoplasmic reticulum of skeletal muscle, trifluoperazine causes only a concentration-dependent inhibition of Ca2+ uptake. Passive Ca2+ efflux from brain microsomes preloaded with Ca2+ is increased by trifluoperazine (50–150 µM), and this effect is potentiated by heparin (10 µg/ml), even in the presence of KCl. It is proposed that the Ca2+-ATPase isoform from brain microsomes is modulated differently by polysaccharides and trifluoperazine when compared with skeletal muscle and platelet isoforms. 相似文献
20.
Effects of salinity and replacement of K+ by Na+ on lipid composition in two sugar beet inbred lines
The effects of NaCl and replacement of K+ by Na+ on the lipid composition of the two sugar beet inbred lines FIA and ADA were studied (a) with increasing additions of NaCl to the basal medium, and (b) with increasing replacement of K+ by Na+ at the same total concentration as in the basal medium. Direct relations were noted between NaCl concentration of the nutrient solution and the phospholipid concentration in the roots of FIA, the genotype characterized by a low K+ /Na+ ratio, as well as between NaCl in the medium and the phospholipid concentration in the shoots of ADA, the genotype with a high K + /Na + ratio. The sulfolipid level in the roots of FIA was maintained at higher NaCl concentrations, while it was decreased in ADA. The glycolipid concentration in the shoots of ADA and the degree of unsaturation of the fatty acids of the total lipid fraction were decreased by salinity, indicating reduced biosynthesis of chloroplast glycolipids and/or accelerated oxidation of these lipids in the presence of NaCl.
In the Na+ for K+ replacement experiment a low content of K+ in the medium resulted in decreased levels of total lipids, phospholipids and sulfolipid in the roots of both genotypes, which did not relate to root growth. K+ -leakage from the roots at low K+ -level in the medium may be reduced by the increase in saturation of the lipids. In the shoots of ADA increased levels of total lipids, phospholipids and Sulfolipid were noted at a low K+ -concentration of the nutrient solution. 相似文献
In the Na