Relation between permeability to potassium and sodium ions and fusicoccin-stimulated hydrogen-ion efflux in barley roots.

Measurements are described of fusicoccin (FC)-stimulated H(+) efflux in barley (Hordeum vulgare L.) roots when K(+) and Na(+) concentrations were varied. In low-salt roots H(+) efflux was stimulated in both 5 mM KCl and NaCl. In salt-saturated roots H(+) efflux was stimulated more effectively in KCl than in NaCl solution. The stimulation of H(+) efflux thus is parallel with the selectivity of these different root preparations for K(+) and Na(+) and with estimates of permeability ratios (P Na/P K) determined from electrical measurements. It is suggested that the results support electrogenic coupling between FC-stimulated H(+) efflux and cation uptake.