K/Na selectivity at the plasmalemma of cortical root cells and preferential release of sodium to the xylem vessels in roots of Atriplex hortensis |
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Authors: | Wilfried Stelter Wolf Dieter Jesehke |
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Institution: | Rovita GmbH, 8261 Engelsberg, West Germany;Lehrstuhl für Botanik I, Univ. Würzbttrg, Mittlerer Dallenbergweg 64, D-8700 Würzburg, West Germany. |
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Abstract: | Using excised roots of Atriplex hortensis L., cv. Gelbe Gartenmelde, the uptake, accumulation and xylem transport of K+ and Na+ have been measured. Influx as well as xylem transport proved to discriminate little between K+ and Na+, when considered in relation to the external solution. Both K+ and Na+ inhibited the uptake and xylem transport of each other to about the same degree. Measurements of intracel-lular Na+ fluxes by means of compartment analysis indicated that the low degree of K/Na discrimination during uptake was due to low influx selectivity. Moreover, K+/Na+ exchange at the plasmalemma was not very efficient in Atriplex roots. In order to establish the basis of the low K/Na discrimination in xylem transport, the rates of K+ and Na+ transport were related to the cytoplasmic K+ and Na+ concentrations to yield the selectivity ratio of transport, S(transport) = (φcx(K) × Na+]c)/(φcx(Na) × K+]c). Under all conditions this ratio was far below one indicating that Na+ was favoured during xylem release in excised roots of Atriplex at low external concentrations. The implications of this discrimination in favour of Na+ are discussed with respect to salt tolerance of A. hortensis . |
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Keywords: | Membrane transport potassium salt tolerance sodium unidirectional fluxes xylem transport |
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