Evidence for a K+-stimulated Na+ efflux at the plasmalemma of barley root cells

Jeschke, W. Dieter

doi:10.1007/bf00386136

Cited by 32 publications

(5 citation statements)

References 9 publications

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“…3). By contrast, application of high (5 mM) K + in the same manner did produce a small but detectable increase in Na + efflux (not shown), a phenomenon previously observed by Jeschke (1970). Compartmental analysis of 24 Na + -efflux and -retention data yielded key flux and pool-size parameters (Fig.…”

Section: Resultssupporting

confidence: 72%

A pharmacological analysis of high-affinity sodium transport in barley (Hordeum vulgare L.): a 24Na+/42K+ study

Schulze

Britto

et al. 2012

Journal of Experimental Botany

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Soil sodium, while toxic to most plants at high concentrations, can be beneficial at low concentrations, particularly when potassium is limiting. However, little is known about Na+ uptake in this ‘high-affinity’ range. New information is provided here with an insight into the transport characteristics, mechanism, and ecological significance of this phenomenon. High-affinity Na+ and K+ fluxes were investigated using the short-lived radiotracers 24Na and 42K, under an extensive range of measuring conditions (variations in external sodium, and in nutritional and pharmacological agents). This work was supported by electrophysiological, compartmental, and growth analyses. Na+ uptake was extremely sensitive to all treatments, displaying properties of high-affinity K+ transporters, K+ channels, animal Na+ channels, and non-selective cation channels. K+, NH4+NH4+, and Ca2+ suppressed Na+ transport biphasically, yielding IC50 values of 30, 10, and <5 μM, respectively. Reciprocal experiments showed that K+ influx is neither inhibited nor stimulated by Na+. Sodium efflux constituted 65% of influx, indicating a futile cycle. The thermodynamic feasibility of passive channel mediation is supported by compartmentation and electrophysiological data. Our study complements recent advances in the molecular biology of high-affinity Na+ transport by uncovering new physiological foundations for this transport phenomenon, while questioning its ecological relevance.

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Section: Resultssupporting

confidence: 72%

A pharmacological analysis of high-affinity sodium transport in barley (Hordeum vulgare L.): a 24Na+/42K+ study

Schulze

Britto

et al. 2012

Journal of Experimental Botany

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“…1) and the addition of ouabain (Table I) had little effect on the plasma membrane ATPase of oat roots. This is not too surprising, however, since the existence and magnitude of a tightly coupled Na+ -K+ transport in roots that is inhibited by ouabain is uncertain (4,23). There is one report for barley roots that seems to demonstrate a coupled Na+ -K+ transport at the plasma membrane; however, the possibility of an equally active Na+ -Na+ exchange was not ruled out, and there was little effect of ouabain on the K+-induced Nae efflux (23).…”

Section: Discussionmentioning

confidence: 99%

“…This is not too surprising, however, since the existence and magnitude of a tightly coupled Na+ -K+ transport in roots that is inhibited by ouabain is uncertain (4,23). There is one report for barley roots that seems to demonstrate a coupled Na+ -K+ transport at the plasma membrane; however, the possibility of an equally active Na+ -Na+ exchange was not ruled out, and there was little effect of ouabain on the K+-induced Nae efflux (23). Synergistic effects of Na+ and K+ in activating membrane-bound ATPase have been reported for halophytic plants (14,25) and only after treating the membrane fraction with deoxycholate.…”

Section: Discussionmentioning

confidence: 99%

Characterization of Plasma Membrane-associated Adenosine Triphosphase Activity of Oat Roots

Leonard¹,

Hodges²

1973

Plant Physiol.

207

121

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Based on high correlations between membrane-bound ATPase activities and ion absorption rates of several plant species (9-11, 29), it was suggested that an ATPase mediates energy transfer to the ion transport system. This proposal was strengthened by the demonstration that the monovalent ionstimulated ATPase is associated with the plasma membrane of oat roots (19,20).The purified plasma membrane ATPase is specific for ATP, requires Mg" and is further activated by monovalent ions 'This research was supported by a grant from the National Science Foundation (GB-31052X (19,20,28). In this paper the enzyme is further characterized with respect to its requirements for ATP, Mg2+, and KCI. The kinetics of KCl stimulation of the plasma membrane ATPase of oat roots were virtually identical to the kinetics of K+ influx into oat roots, both of which are best described by a single isotherm with continually changing kinetic parameters. MATERIALS AND METHODSPlasma membranes were isolated from oat (Avena sativa L. cv. Goodfield) roots as previously described (19,20). Briefly, about 50 g of 6-day-old roots were excised, washed in cold deionized water, and ground (mortar and pestle) in 200 ml of a medium consisting of 0.25 M sucrose, 0.003 M EDTA, 2.5 mm dithiothreitol, and 0.025 M tris-MES, pH 7.2. The homogenate was strained through cheesecloth and successively centrifuged at 13,000g for 15 min and 80,000g for 30 min. The 13,000 to 80,000g pellet was suspended in 30 ml of fresh grinding medium, pelleted. suspended in 2.5 ml of 20% (w/w) sucrose containing 1 mM MgSO4 and 1 mm tris-MES, pH 7.2, and 2 ml were layered onto a 36-ml discontinuous gradient consisting of 28 ml of 45%4o (w/w) and 8 ml of 34% sucrose in 1 mM MgSO, and 1 mm tris-MES, pH 7.2 (Mg2+ was omitted from the gradient for experiments involving Mg2+ as a variable). The gradient was centrifuged for 2 hr at 95,000g in a Spinco SW 27 rotor. The membranes collecting at the 34 to 45% sucrose interface are more than 75% plasma membranes (20).ATPase activity was measured at 38 C in a 1-ml volume containing 3 mm ATP (tris salt) at desired pH, 33 mm tris-MES at desired pH and variable amounts of mono-and divalent ions

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“…Plants may exclude Na from shoots in various ways: (1) by controlling Na influx and/or efflux at the plasmalemma of root cells (Jacoby and Hanson, 1985;Jeschke, 1970;Nassery and Baker, 1972), (2) by removing Na from the xylem stream and sequestering Na in stelar parenchyma cells of roots and lower stems (Drew and Dikumwin, 1985;Jacoby, 1964;Johanson and Cheeseman, 1983;Kramer et al, 1977) and (3) by retranslocating Na from shoots to roots, via the phloem, for subsequent extrusion (Jacoby, 1979;Lessani and Marschner, 1978). It is possible that any or all of these exclusion mechanisms may be operating less efficiently in strains 576 and 571 than in the other strains, allowing these two strains to accumulate more Na.…”

Section: Discussionmentioning

confidence: 99%

The effect of increasing NaCl levels on the potassium utilization efficiency of tomatoes grown under low-K stress

1989

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Tomato strains were grown under low-K stress (71/tM K) over a wide range of external Na levels (from 0.014 to 27.8 mM Na) to measure strain response in Na substitution capacity in relation to Na concentration. Relative differences among strains for Na substitution capacity were similar at all Na levels except for the minus Na control treatment. Successive doubling of external Na concentration over the range of Na levels tested resulted in a positive linear response in plant dry weight, under low-K stress, with a similar slope for all five strains. The five strains also were grown at a toxic Na level (87 mM Na) under low K and adequate K conditions. Plant dry weight was not reduced at the toxic Na level relative to the minus Na control when the strains were grown under low-K stress; however, plant dry weight was reduced an average of fifty-five percent at the toxic Na level relative to the control when the strains were grown under adequate K conditions. There was no relationship between Na substitution capacity of strains grown under low-K stress and tolerance to toxic Na levels under adequate K conditions.

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Evidence for a K+-stimulated Na+ efflux at the plasmalemma of barley root cells

Cited by 32 publications

References 9 publications

A pharmacological analysis of high-affinity sodium transport in barley (Hordeum vulgare L.): a 24Na+/42K+ study

A pharmacological analysis of high-affinity sodium transport in barley (Hordeum vulgare L.): a 24Na+/42K+ study

Characterization of Plasma Membrane-associated Adenosine Triphosphase Activity of Oat Roots

The effect of increasing NaCl levels on the potassium utilization efficiency of tomatoes grown under low-K stress

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