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 calci um chelator EGTA inhibited the ABA-induced RAB18 gene expression. However, extracellular calcium alone, up to 10 mM, did not trigger RAB18 expression, Spectrofluorimetric extracellular Ca2+ measurement with Fluo-3 showed a fa st, within 1 min, Ca2+ influx associated with outer plasmalemma ABA percept ion. In the presence of the Ca2+ blockers Cd2+ and Ni2+, RAB18 expression s as suppressed. Pimozide and fluspirilene Inhibited Ca2+ influx and ABA-indu ced RAB18 expression. Thus we demonstrated the involvement of specific Ca2 influx in the ABA signaling sequence leading to RAB18 expression. (C) 2000 Federation of European Biochemical Societies, Published by Elsevier Scienc e B,V, All rights reserved.