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

Sodium is a beneficial mineral for some plant species when external concent rations are low. The role of Na+ in energising K+ acquisition in terrestria l plants has recently been suggested because of evidence demonstrating that wheat root cells express a high-affinity Na+-energised K+ symporter. To de termine whether low concentrations of Na+ improve the K+ nutrition and grow th of wheat, long-term growth and short-term tracer flux experiments were c onducted. Long-term growth experiments were conducted over a range of K+ co ncentrations, at acidic and alkaline pH, with and without 500 mu M NaCl. Pl ant biomass and tissue Na+ and K+ content was measured. Short-term experime nts 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 mu M) external K+ in one of the long-term experiments, but not in two other experiments. Na+ did not stimulate Rb+ up take, but K+ stimulated Na+ uptake in short-term tracer flux experiments. T he 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 bene ficial effect on the growth of wheat.