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

Abstract The early response of K + and Na + net fluxes to different external NaCl and KCl levels has been studied in wheat ( 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 86 Rb and 22 Na showed that K + ( 86 Rb) and Na + influxes were not involved in genotypic differences in K + ( 86 Rb) and Na + net uptake observed after 6 h of exposure to salt stress. Differences in K + ( 86 Rb) net uptake could be attributed to differences in K + ( 86 Rb) efflux and/or to K + ( 86 Rb) 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 Na + 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.