Potassium/sodium selectivity in wheat and the amphiploid cross wheat X Lophopyrum elongatum

The early response of K+ and Na+ net fluxes to different external NaCl and KCl levels has been studied in wheal (Triticum aestivum L.) and the amphiploid cross wheat X Lophopyrum elongatum (Host) Love in culture solution experiments. We found that during the first 24 h of exposure to 100 or 200 mM NaCl, at low K+ levels, the amphiploid absorbed, translocated and allocated to the youngest leaf less Na+ than the wheat parental line. During that period, the amphiploid retained more K+ than wheat. Short-term uptake studies with Rb-86 and Na-22 showed that K+(Rb-86) and Na+ influxes were not involved in genotypic differences in K+(Rb-86) and Na+ net uptake observed after 6 h of exposure to salt stress. Differences in K+(Rb-86) net uptake could be attributed to differences in K+(Rb-86)efflux and/or to K+(Rb-86) accumulation by root vacuoles. The possibility that differential shrinkage of protoplast volume plays a role in the genotypic difference in K+ retention cannot be ruled out. On the other hand, Na+ efflux did not contribute significantly to differences in Na+ net uptake between these genotypes. Hence, differences in Na+ net uptake were attributed to differences in the transport of Nai to the shoot. The presence in the amphiploid of fast acting mechanisms able to enhance Na+/K+ selectivity at different plant levels minimizes the early build-up of Na+ concentration, and K+ substitution by Na+, in the growing tissue of the leaf. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.