The effect of low concentrations of sodium on potassium uptake and growth of wheat

Abstract

Sodium is a beneficial mineral for some plant species when external concentrations are low. The role of Na⁺ in energising K⁺ acquisition in terrestrial plants has recently been suggested because of evidence demonstrating that wheat root cells express a high-affinity Na⁺-energised K⁺ symporter. To determine whether low concentrations of Na⁺ improve the K⁺ nutrition and growth of wheat, long-term growth and short-term tracer flux experiments were conducted. Long-term growth experiments were conducted over a range of K⁺ concentrations, at acidic and alkaline pH, with and without 500 µM NaCl. Plant biomass and tissue Na⁺ and K⁺ content was measured. Short-term experi-ments were conducted using tracers to determine whether low concentrations of Na⁺ or K⁺ stimulate Rb⁺ or Na⁺ uptake, respectively. Sodium stimulated the growth of wheat only at low (20 µM) external K⁺ in one of the long-term experiments, but not in two other experiments. Na⁺ did not stimulate Rb⁺ uptake, but K⁺ stimulated Na⁺ uptake in short-term tracer flux experiments. The results suggest that low concentrations of Na⁺ do not increase K⁺ uptake to a large extent, and only when light levels are low does Na⁺ have a beneficial effect on the growth of wheat.