A pharmacological analysis of high-affinity sodium transport in barley (Hordeum vulgareL.): a24Na⁺/42K⁺ study

Soil sodium, while toxic to most plants at high concentrations, can be beneficial at low concentrations, particularly when potassium is limiting. However, little is known about Na⁺ uptake in this ‘high-affinity’ range. New information is provided here with an insight into the transport characteristics, mechanism, and ecological significance of this phenomenon. High-affinity Na⁺ and K⁺ fluxes were investigated using the short-lived radiotracers24Na and42K, under an extensive range of measuring conditions (variations in external sodium, and in nutritional and pharmacological agents). This work was supported by electrophysiological, compartmental, and growth analyses. Na⁺ uptake was extremely sensitive to all treatments, displaying properties of high-affinity K⁺ transporters, K⁺ channels, animal Na⁺ channels, and non-selective cation channels. K⁺, NH 4 + , and Ca²⁺ suppressed Na⁺ transport biphasically, yielding IC50values of 30, 10, and