Potassium Transport in Corn Roots

Abstract

Plasmalemma electron transport may be involved in the generation of H+ gradients and the uptake of ions into root tissue. The influence of extracellular NADH and ferricyanide on K+ (86Rb+) influx, K+ (86Rb+) efflux, net apparent H+ efflux and O2 consumption in 2 cm corn (Z. mays [A632 .times. Oh43]) root segments and intact corn roots is reported. In freshly excised root segments, NADH had no effect on O2 consumption and K+ uptake. After the root segments were given a 4 h wash in aerated salt solution, NADH elicited a moderate stimulation in O2 consumption but caused a dramatic inhibition of K+ influx. Net apparent H+ efflux was significantly inhibited following NADH exposure in 4 h washed root segments. Exogenous ferricyanide inhibited K+ influx in a similar fashion to that caused by NADH, but caused a moderate stimulation of net H+ efflux. Both reagents substantially altered K+ efflux at both the plasmalemma and tonoplast. These complex results do not lend themselves to straightforward interpretation and are in contradiction with previously published results. The interaction between cell surface redox reactions and membrane transport are apparently more complex than previously considered. Indeed, > 1 electron transport system may operate in the plasmalemma to influence, or regulate, a number of transport functions and other cellular processes. Plasmalemma redox reactions may be involved in the regulation of ion uptake and the wound response exhibited by corn roots.