INVOLVEMENT OF THE PROTON PUMP AND PROTON CONDUCTANCE CHANGE IN THE WAVE OF DEPOLARIZATION INDUCED BY WOUNDING IN BIDENS-PILOSA

The role of protons in the slow wave of depolarization induced by wounding in Bidens pilosa L. was studied by means of voltage measurements performed under differing extracellular conditions. The degree of depolarization caused by an extracellular pH acidification from 7 to 4 was different when performed either in the resting conditions or 20 min after eliciting the slow wave. In the presence of cyanide, a heat stimulation still induced a slow wave, the amplitude of which was reduced to 42% of the control. While cyanide remained in the perfusing medium, the membrane did not repolarize. An extracellular pH change from 7 to 4 in the presence of cyanide induced a higher depolarization in the resting conditions than 20 min after eliciting a slow wave. Furthermore, when pumps were previously stimulated either by acid loading or by fusicoccin, the amplitude of the slow wave was increased. We thus propose that the slow wave was largely dominated by a transient "switch off" of the proton pump and we discuss the possible involvement of proton conductance change during the slow wave.