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 = EK). 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.
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Selected References
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