Characteristics of the Wave of Depolarization Induced by Wounding in Bidens pilosa L.

Heating locally the hypocotyl of Bidens pilosa L. elicits awave of depolarization. The mechanism of the wave has been investigatedby means of microelectrophysiological techniques. The amplitudeof the transmembrane potential variation induced by an extracellularion concentration change (K⁺, Na⁺, Ca²⁺, Cl^–) was thesame in the resting conditions as during the slow wave. At pH4.0, the amplitude of the slow wave was reduced by 56% comparedwith the control performed at pH 7.0. In the presence of theuncoupler CCCP, the slow wave was not observed. The Ca²⁺ -chelatorEGTA and the Ca2²⁺ -channel blocker La³⁺ reduced, respectively,the amplitude of the slow wave by 78% and 68%. These resultsindicate the involvement of Ca²⁺ in triggering the slow wave.A transient modification of the electrogenic H⁺ pump activity(inactivation-activation) and of the transmembrane H⁺ flux inthe slow wave are discussed. Key words: Slow wave (of depolarization), wounding, electrogenic pump, calcium, Bidens pilosa L