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 wheat (Triticum aestivum L.) and the amphiploid cross wheat X Lophopyrum elongatum (Host) Löve 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 86Rb and 22Na showed that K(+)(86Rb) and Na(+) influxes were not involved in genotypic differences in K(+)(86Rb) and Na(+) net uptake observed after 6 h of exposure to salt stress. Differences in K(+)(86Rb) net uptake could be attributed to differences in K(+)(86Rb) efflux and/or to K(+)(86Rb) 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.