Puccinellia tenuiflora maintains a low Na+ level under salinity by limiting unidirectional Na+ influx resulting in a high selectivity for K+ over Na+

Puccinellia tenuiflora is a useful monocotyledonous halophyte that might be used for improving salt tolerance of cereals. This current work has shown that P. tenuiflora has stronger selectivity for K⁺ over Na⁺ allowing it to maintain significantly lower tissue Na⁺ and higher K⁺ concentration than that of wheat under short- or long-term NaCl treatments. To assess the relative contribution of Na⁺ efflux and influx to net Na⁺ accumulation, unidirectional ²²Na⁺ fluxes in roots were carried out. It was firstly found that unidirectional ²²Na⁺ influx into root of P. tenuiflora was significantly lower (by 31–37%) than in wheat under 100 and 150 m m NaCl. P. tenuiflora had lower unidirectional Na⁺ efflux than wheat; the ratio of efflux to influx was similar between the two species. Leaf secretion of P. tenuiflora was also estimated, and found the loss of Na⁺ content from leaves to account for only 0.0006% of the whole plant Na⁺ content over 33 d of NaCl treatments. Therefore, it is proposed that neither unidirectional Na⁺ efflux of roots nor salt secretion by leaves, but restricting unidirectional Na⁺ influx into roots with a strong selectivity for K⁺ over Na⁺ seems likely to contribute to the salt tolerance of P. tenuiflora .     

An effect of Na+ on K+ uptake in intact seedlings of Zea mays

Models for the regulation of K⁺ uptake in higher plant roots have become more complex as studies have moved from the level of excised low-salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.
The uptake of K⁺ by low-salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na⁺ concentration over a wide range. However, independence of Na⁺ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na⁺ in the uptake medium enhanced K⁺ uptake. In the presence of Na⁺, K⁺ uptake rates were similar in whole plants with high root K⁺ contents to rates in excised or intact, low-salt roots.     

Control of Na+ and K+ transport in Spergularia marina I. Transpiration effects

In this paper we begin our study of factors controlling Na⁺ and K⁺ uptake in the halophyte Spergularia marina (L.) Griseb., with emphasis on plants growing at moderate salinity (0.2x sea water). The involvement of transpiration was considered first because of its potential to account for much or all of the transport of ions, and particularly of Na⁺, to the shoot under these growth conditions. Transpiration was constant with time through most of the light period, quickly dropping to 6% of the day time rate at night. ²²Na⁺ uptake, on the other hand, showed much less day/night variation, and relative transport to the shoot was constant. After establishing that transpiration was linearly related to leaf weight, possible transpiration effects were further considered as correlations between leaf weight and transport to the shoot. Under constant, day-time conditions, with linear effects of time and plant size removed, total transport of ²²Na⁺ to the shoot (per plant) was not correlated to leaf weight. A similar result was found when transport was expressed per gram of root, and when partitioning of total label to the shoot was considered. Finally, the correlation was considered between leaf weight and a Na⁺/K⁺ enrichment factor defined as the Na⁺/K⁺ ratio in the leaves divided by that in the roots. This correlation was also insignificant. The results indicate that analysis of control of Na⁺ and K⁺ uptake and transport in this experimental system need not consider effects of transpiration.     

Possible Involvement of K^＋/Na^＋ in Assessing the Seed Vigor Index

More substances leaked from a higher-vigor seed sample than from a lower-vigor sample. This indicates that, in some cases, electric conductivity does not represent seed vigor level very well, especially for high-vigor seeds. Results from germination, germination index, leachate conductivity, and the ratio of K^＋/Na^＋ from three-seed lots of Chinese cabbage （Brassica pekinensis （Louv.） Rupr） showed that K^＋/Na^＋ correlated well with germination and germination index. The ability of K^＋/Na^＋ to indicate well changes in vigor was further supported by investigation in soybean （Glycine max （L.） Merr.） seeds and another cultivar of Chinese cabbage seeds. Thus, seed leakage of K^＋/Na^＋ can accurately indicate seed vigor, whereas the conductivity test failed to do so. Furthermore, K^＋/Na^＋ showed up bigger quantitative differences in vigor level than did the conductivity test. This findings provide a more sensitive and accurate index for the assessment of seed vigor. The mechanisms of Na^＋ and K^＋ ion transport are also discussed.     

Sucrose and ouabain effects on the kinetic properties of a membrane-bound (Na++ K++ Mg2+) ATPase in sugar beet roots

Kinetic studies of a microsomal (Na⁺+ K⁺+ Mg²⁺)ATPase from sugar beet roots ( Beta vulgaris L. cv. Monohill) show that sucrose influences the MgATPase in different ways depending on the presence of K⁺ and/or Na⁺ 1) In the presence of the substrate MgATP and Na⁺ the effect of sucrose follows simple Michaelis-Menten kinetics. 2) In the presence of substrate together with K⁺ or (K⁺+ Na⁺), sucrose has little effect on the ATPase activity. 3) In the presence of Na⁺, onabain acts as an uncompetitive inhibitor with respect to MgATP. 4) In the presence of K⁺ or (K⁺+ Na⁺), the inhibition by ouabain is somewhat depressed and shows non-linearity when 1/v is plotted versus 1/MgATP. 5) Sucrose and Na⁺ activate in a competitive way, so that a successive increase of the Na⁺ level decreases the activation by sucrose. Both K_m and V-values are thereby changed. 6) The sucrose activation in the presence of Na⁺ is also influenced by ouabain. It is, therefore, suggested that Na⁺ may regulate the interference between the Na⁺/K⁺ pump and a sucrose sensitive system.     

The Na+ and K+ Content of Isolated Torpedo Synaptosomes and Its Effect on Choline Uptake

Abstract: The Na⁺ and K⁺ concentrations in isolated Torpedo marmorata synaptosomes were determined. Synaptosomes made according to the method of Israël et al. have high internal Na⁺ (290 MM) and low internal K⁺ (30 mM) concentrations. Modification of the homogenisation media permitted the isolation of synaptosomes which could maintain transmembrane ion gradients (internal Na⁺, 96 mM; K⁺, 81 mM); 0.1 mM-ouabain abolished these gradients. The trans-membrane Na⁺ gradient started to dissipate after 15 min at 20°C. Inclusion of ATP in the homogenisation medium enabled the synaptosomes to maintain the Na⁺ gradient for about 90 min. The presence of these transmembrane ion gradients stimulated choline uptake sevenfold. It is concluded that (a) by selecting the isolation media, Torpedo synaptosomes can be prepared with transmembrane ion gradients; (b) these gradients are ouabain-sensitive and stimulate choline uptake: (c) the synaptosomes require additional ATP to maintain the ion gradients.     

Heterogeneous Na+ Sensitivity of Na+,K+-ATPase Isoenzymes in Whole Brain Membranes

Abstract: The Na⁺ sensitivity of whole brain membrane Na⁺,K⁺-ATPase isoenzymes was studied using the differential inhibitory effect of ouabain (α1, low affinity for ouabain; α2, high affinity; and α3, very high affinity). At 100 m M Na⁺, we found that the proportion of isoforms with low, high, and very high ouabain affinity was 21, 38, and 41%, respectively. Using two ouabain concentrations (10⁻⁵ and 10⁻⁷ M ), we were able to discriminate Na⁺ sensitivity of Na⁺, K⁺-ATPase isoenzymes using nonlinear regression. The ouabain low-affinity isoform, α1, exhibited high Na⁺ sensitivity [ K _a of 3.88 ± 0.25 m M Na⁺ and a Hill coefficient ( n ) of 1.98 ± 0.13]; the ouabain high-affinity isoform, α2, had two Na⁺ sensitivities, a high ( K _a of 4.98 ± 0.2 m M Na⁺ and n of 1.34 ± 0.10) and a low ( K _a of 28 ± 0.5 m M Na⁺ and an n of 1.92 ± 0.18) Na⁺ sensitivity activated above a thresh old (22 ± 0.3 m M Na⁺); and the ouabain very-high-affinity isoform, α3, was resolved by two processes and appears to have two Na⁺ sensitivities (apparent K _a values of 3.5 and 20 m M Na⁺). We show that Na⁺ dependence in the absence of ouabain is the result of at least of five Na⁺ reactivities. This molecular functional characteristic of isoenzymes in membranes could explain the diversity of physiological roles attributed to isoenzymes.     

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.     

Glutamate Induces a Calcineurin-Mediated Dephosphorylation of Na+,K+-ATPase that Results in Its Activation in Cerebellar Neurons in Culture

Abstract: In primary cultures of cerebellar neurons glutamate neurotoxicity is mainly mediated by activation of the NMDA receptor, which allows the entry of Ca²⁺ and Na⁺ into the neuron. To maintain Na⁺ homeostasis, the excess Na⁺ entering through the ion channel should be removed by Na⁺,K⁺-ATPase. It is shown that incubation of primary cultured cerebellar neurons with glutamate resulted in activation of the Na⁺,K⁺-ATPase. The effect was rapid, peaking between 5 and 15 min (85% activation), and was maintained for at least 2 h. Glutamate-induced activation of Na⁺,K⁺-ATPase was dose dependent: It was appreciable (37%) at 0.1 µ M and peaked (85%) at 100 µ M . The increase in Na⁺,K⁺-ATPase activity by glutamate was prevented by MK-801, indicating that it is mediated by activation of the NMDA receptor. Activation of the ATPase was reversed by phorbol 12-myristate 13-acetate, an activator of protein kinase C, indicating that activation of Na⁺,K⁺-ATPase is due to decreased phosphorylation by protein kinase C. W-7 or cyclosporin, both inhibitors of calcineurin, prevented the activation of Na⁺,K⁺-ATPase by glutamate. These results suggest that activation of NMDA receptors leads to activation of calcineurin, which dephosphorylates an amino acid residue of the Na⁺,K⁺-ATPase that was previously phosphorylated by protein kinase C. This dephosphorylation leads to activation of Na⁺,K⁺-ATPase.     

Promoting effect of fusicoccin on Na+ efflux in barley roots: evidence for a Na+−H+ antiport

Abstract. The effect of fusicoccin (FC) on the K⁺stimulated Na⁺ efflux in root cells of Na⁺ loaded barley roots was studied. FC (0.02 mM) stimulated Na⁺ efflux in the presence of K⁺ and its effect was synergistic with that of K⁺, in a similar way as its effect on proton extrusion. Decreasing the pH of the elution medium promoted Na⁺ efflux and partially replaced the effect of FC. As FC is known to increase the electrochemical proton gradient at the plasmalemma level, these results are consistent with the hypothesis that Na⁺ is extruded in exchange for H⁺. A further support to this view came from the finding that Na⁺ efflux was also promoted by a lipophilic cation, tributylbenzylammonium (TBBA ⁺), which stimulates H ⁺ extrusion and is generally accepted not to enter the cells by means of the same carrier as K ⁺.     

Impairment of Na+,K+-ATPase activity following enterotoxigenic Campylobacter jejuni infection: changes in Na+, Cl− and 3-O-methyl-D-glucose transport in vitro, in rat ileum

Abstract Unidirectional fluxes of Na⁺, Cl⁻ and 3-O-methyl-D-glucose (3-MG) were measured in vitro across Campylobacter jejuni live culture-infected and control rat ileal short-circuited tissues by the Using Chamber technique. Net secretion of Na⁺ and enhanced secretion of Cl⁻ ions was observed in the infected animals ( P < 0.001, n =6) as compared to the net absorption of Na⁺ and marginal secretion of Cl⁻ ions in the control animals. There was a significant decrease in the mucosal-to-serosal fluxes of 3-MG in C. jejuni -infected rat ileum. The specific Na⁺,K⁺-ATPase activity when measured biochemically in the membrane-rich fraction of enterocytes was found to be significantly lower (58%) in the infected group as compared to the control group ( P < 0.001). Our results therefore suggest that infection with an enterotoxigenic C. jejuni inhibits the Na⁺,K⁺-ATPase activity in rat enterocytes. The impairment of Na⁺,K⁺-ATPase activity thus appears to induce a secondary change in Na⁺,Cl⁻ and 3-MG transport in vitro in rat ileum.     

Excretion of ions (Cd2+, Li+, Na+ and Cl−) by Tamarix aphylla

Excretion of minerals by the NaCl-resistant and comparatively cadmium-resistant tree Tamarix aphylla (L.) Karst, was investigated. Cd²⁺ was excreted by plants exposed for 1–10 days to 9 or 45 μ M Cd²⁺ solutions. Excretion of this toxic ion increased considerably with time but was less than 5% of the quantities that had been accumulated in the shoots. Excretion of Na⁺ and Cl⁻ was positively correlated with NaCl concentration (1.5, 10, 50 m M ) of the medium. The Na⁺/Cl⁻ ratios of the excrete were positively correlated with the concentration of the treatment solution. Ca²⁺ excretion decreased with increasing NaCl concentrations of the solution. Excretion of K⁺ and Mg²⁺ was only little affected by NaCl. Excretion of Li⁺ occurred whenever this element was supplied in the uptake solution; daily excretion rates of Li⁺ increased with time. The ecological significance of excretion is discussed in relation to the low selectivity of the mechanism in T. aphylla .     

Dexamethasone Increases Adrenalectomy-Depressed Na+,K+-ATPase mRNA and Ouabain Binding in Spinal Cord Ventral Horn

Abstract: The Na⁺,K⁺-ATPase plays a key role in the regulation of ion fluxes and membrane repolarization in the CNS. We have studied glucocorticoid effects on biosynthesis of the Na⁺,K⁺-ATPase and on ouabain binding in the ventral horn of the spinal cord using intact rats, adrenalectomized (ADX) rats, and ADX rats receiving dexamethasone (ADX + DEX) during 4 days. Cryostat sections from spinal cords were incubated with a ³⁵S-oligonucleotide coding for the α₃-subunit or a ³H-cDNA coding for the β₁-subunit of the Na⁺,K⁺-ATPase using in situ hybridization techniques. In ventral horn motoneurons, grain density per cell and grain density per area of some for both probes were slightly reduced in ADX rats but significantly increased in the ADX + DEX group, using ANOVA and the Bonferroni's test. Statistical analysis of frequency histograms of neuronal densities further indicated a significant shift to the right for intact rats compared with ADX rats for both probes. Concomitantly, [³H]ouabain binding to membrane preparations from ventral horns was reduced in ADX rats and restored to normal by DEX administration. No effect of adrenalectomy or DEX treatment was obtained in the dorsal horn. In conclusion, glucocorticoids positively modulate the mRNA for the α₃-subunit and the β₁-subunit of the Na⁺,K⁺-ATPase and recover ouabain binding to normal values. The increments of the synthesis and activity of an enzyme affecting membrane repolarization and synaptic neurotransmission are consistent with the alleged stimulatory effect of glucocorticoids on spinal cord function.     

Inhibition of Rat Brain Microsomal Na+,K+-ATPase by S-Adenosylmethionine

Abstract: Rat brain microsomes were preincubated with S -adenosylmethionine (SAM), MgCl₂, and CaCl₂, then re-isolated, and the activity of Na⁺,K⁺-ATPase determined. SAM inhibited the Na⁺,K⁺-ATPase activity compared with microsomes subjected to similar treatment in the absence of SAM. A biphasic inhibitory effect was observed with a 50% decrease at a SAM concentration range of 0.4 μ M -3.2 μ M and a 70% reduction at a concentration range above 100 μ M . Inclusion of either S- adenosylhomocysteine or 3-deazaadenosine in the preincubations prevented the SAM inhibition of Na⁺,K⁺-ATPase activity. The inhibition by SAM appeared to be Mg²⁺- or Ca²⁺-dependent.     

Plasma ionic regulation and gill Na+/K+-ATPase changes during rapid transfer to sea water of yearling rainbow trout, Salmo gairdneri: time course and seasonal variation

Danish rainbow trout, Salmo gairdneri Richardson, (40–65 g) were transferred to 28%o sea water at intervals throughout the early spring and summer. Gill Na⁺/K⁺-ATPase of fish kept in fresh water surged distinctly during May. Simultaneously, a body silvering occurred and plasma concentrations of Cl⁻, Na⁺ and total thyroxine (T4) decreased. The seawater transfer-induced adaptive response in plasma electrolytes comprised a biphasic change, i.e., an adjustive peak phase and a regulatory phase lasting for 2 days and 1 week after transfer, respectively. Further, gill Na⁺/K⁺-ATPase activity increased to a new level after an initial lag phase of 2–3 days, but electrolyte regulation was mostly initiated prior to the adaptive change in ATPase activity. In spite of increasing pre-transfer freshwater Na⁺/K⁺-ATPase activity during the spring, the electrolyte peak level, the degree of muscle dehydration and the mortality of fish transferred to sea water increased from April to July. The apparent uncoupling of freshwater Na⁺/K⁺-ATPase activity and plasma electrolyte regulation in sea water is discussed in relation to smelting and prediction of hypo-osmoregulatory performance.     

K+ and Na+ influxes in Nitella modified by pH and electric current

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.     

Brain (Na+, K+)-ATPase and Noradrenergic Activity: Effects of Hyperinnervation and Denervation on High-Affinity Ouabain Binding

Abstract: To examine the role of nerve-specific (Na⁺, K⁺)-ATPase in chronic changes in noradrenergic activity, we examined the effects of noradrenergic denervation and hyperinnervation on p -nitrophenylphosphatase activity and on total and nerve-specific ouabain binding. High-affinity and erythrosin B-sensitive binding were compared as measurements of nerve-specific binding. Hyperinnervation and denervation was produced in cerebellum and cerebral cortex, respectively, by 6-hydroxydopamine lesions of the dorsal noradrenergic bundle. Hyperinnervation increased, and denervation decreased, enzyme activity, high-affinity ouabain inhibition, and erythrosin B-sensitive ouabain binding. As (Nat⁺, K⁺)-ATPase has a major role in the regulation of neural excitability and energy metabolism, and the ouabain binding site has been shown to have endogenous ligands, these changes in (Na⁺, K⁺)-ATPase may be important in the long-term regulation of neuron function by norepinephrine.     

Effect of K+ and H+ stress and role of Ca2+ in the regulation of intracellular K+ concentration in mung bean roots

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.