Potassium Transport in Corn Roots

Abstract

Influx isotherms were obtained for ⁸⁶Rb⁺ uptake into 2-cm corn (Zea mays [A632 × (C3640 × Oh43)] root segments for both low- (0.2 millimolar CaSO₄) and high-salt (0.2 millimolar CaSO₄ + 5 millimolar KCl) grown roots. Unlike the discontinuous curves usually presented for K⁺ influx, our isotherms were smooth, nonsaturating curves that approached linearity at K⁺ (Rb⁺) concentrations above 1 millimolar. The kinetics for K⁺ transport could be resolved into saturable and linear components. The saturable components yielded K_m values of 16 and 86 micromolar for low- and high-salt roots, respectively, while V_max values were 5.62 and 1.85 moles per gram fresh weight per hour. Results of experiments with the penetrating sulfhydryl reagent, N-ethyl maleimide (NEM), and the impermeant reagent, p-chloromercuribenzene sulfonic acid (PCMBS) indicated that the saturable and linear components were independent mechanisms of K⁺ transport.