Energy-linked Potassium Influx as Related to Cell Potential in Corn Roots

Abstract

Cell potentials and K⁺ (⁸⁶Rb) influx were determined for corn roots over a wide range of external K⁺ activity (K°) under control, anoxic, and uncoupled conditions. The data were analyzed using Goldman theory for the contribution of passive influx to total influx. For anoxic and uncoupled roots the K⁺ influx shows the functional relationship with K° predicted with constant passive permeability, although K⁺ permeability in uncoupled roots is about twice that of anoxic roots. In control roots the equation fails to describe K⁺ influx at low K°, but does so at high K°, with a gradual transition over the region where the electrical potential becomes equal to the equilibrium potential for K⁺ (ψ = E_K). In the low K° range, where net K⁺ influx is energetically uphill, participation of an energy-linked K⁺ carrier is indicated. In the high K° range, K⁺ influx becomes passive down the electrical gradient established by the cell potential. Since the cell potential includes a substantial electrogenic component, anoxia or uncoupling reduces passive influx.