Direct coupling of action potential generation in cells of a higher plant (Cucurbita pepo) with the operation of an electrogenic pump

Abstract

Changes in membrane potential (Em) were investigated during action potential (AP) generation by excitable cells in bundle parenchyma of 2-week-old pumpkin (Cucurbita pepo L.) seedlings. APs were evoked by gradual cooling from 21 to 6°C at a rate of 1.3–1.5°C/min. Changes in Em were measured with standard microelectrode technique. The plots of the function dEm/dt = f (Em) were obtained from experimental data by numerical differentiation of Em records. The depolarization proceeded as a one-stage process. Conversely, AP repolarization comprised two stages, distinguished by specific dynamics of dEm/dt. The second stage of repolarization occurred on a larger scale of Em and was more sensitive to temperature than the first one. It is supposed that the second stage of repolarization during AP is related to the operation of electrogenic H+-pump in the excitable membrane. The scheme of AP generation in higher plant cells is suggested; it foresees the involvement in AP generation of both passive and active mechanisms of electrogenesis.