The Effect of Inhibitors on the K⁺-Dependent Na⁺ Efflux and the K⁺-Na⁺ Selectivity of Barley Roots

Abstract

The K⁺-Na⁺ selectivity of ion uptake by higher plants has been attributed to the presence of a Na⁺ efflux pump at the plasmalemma of their root cells (PITMAN and SADDLER, 1967; ETHERTON, 1967; JESCHKE, 1970). Recently, a transient Independent Na⁺ efflux at the plasmalemma of the cortical cells of barley roots, induced by an addition of K⁺ to the external medium, has been measured quantitatively (JESCHKE, 1972, 1973). This Na⁺ efflux was followed by a substantial drop in the Na⁺ transport and the beginning of K⁺ transport through the xylem of these roots. I proposed that the efflux was due to a K⁺-dependent Na⁺ pump in the cortical cells and that this was the basis of the K⁺-Na⁺ selectivity of transport in barley roots.