Effects of external KCl on electrical properties and K^$(⁸⁶Rb) transport in the elongating region of intact phaseolus mungo roots

Two simultaneous measurements, extracellular potential V and K^$(⁸⁶Rb) transport, and the intracellular potential of cortical cell E and potential V, were used to study the effects of external KCl on two-day-old bean roots. High, external KCl concentrations (>10 mm) markedly enhanced K^$ loss from tissues in the elongating region to the external solution and induced depolarization of the membrane potential difference (PD=V-E).When Phaseolus roots were returned to a solution with a lower concentration of K^$, the K^$ loss and the potential difference, PD, were restored to their previous values. K^$ transport from other parts of the root to the elongating region, however, did not recover, and the potential, E, increased. These results clearly demonstrate that treatment of Phaseolus roots with a high external K^$ concentration inhibits K^$ translocation through the stele to the elongating cortical cells and is dependent on depolarization of the intracellular potential.