Effects of external Ca²⁺ on K⁺ permeability of the elongating region of mung bean roots under high KCl stress

Simultaneous measurements of the extracellular potential and the K⁺(⁸⁶Rb) efflux, and of the intracellular and extracellular potentials of the cortical cells were used to study the effects of external Ca²⁺ on the plasma membrane K⁺(⁸⁶Rb) permeability in two-day-old mung bean (Vigna mungo L. Hepper, 'Black matpe') roots under high KCl stress. The K⁺ efflux was enhanced by a high KCl solution (>7.5 mm), and addition of 0.5 mm Ca²⁺ could suppress this efflux. The removal of membrane-associated Ca⁺ from the root surface with EDTA led to a recovery of the K⁺ efflux along with a marked decrease in the extracellular potential.