Abscisic acid plasmalemma perception triggers a calcium influx essential for RAB18 gene expression in Arabidopsis thaliana suspension cells

Pretreatment of Arabidopsis thaliana suspension cells with impermeant calcium chelator EGTA inhibited the ABA-induced RAB18 gene expression. However, extracellular calcium alone, up to 10 mM, did not trigger RAB18 expression. Spectrofluorimetric extracellular Ca(2+) measurement with Fluo-3 showed a fast, within 1 min, Ca(2+) influx associated with outer plasmalemma ABA perception. In the presence of the Ca(2+) blockers Cd(2+) and Ni(2+), RAB18 expression was suppressed. Pimozide and fluspirilene inhibited Ca(2+) influx and ABA-induced RAB18 expression. Thus we demonstrated the involvement of specific Ca(2+) influx in the ABA signaling sequence leading to RAB18 expression.