Plasmalemma abscisic acid perception leads to RAB18 expression via phospholipase D activation in Arabidopsis suspension cells.

Abscisic acid (ABA) plays a key role in the control of stomatal aperture by regulating ion channel activities and water exchanges across the plasma membrane of guard cells. Changes in cytoplasmic calcium content and activation of anion and outward-rectifying K(+) channels are among the earliest cellular responses to ABA in guard cells. In Arabidopsis suspension cells, we have demonstrated that outer plasmalemma perception of ABA triggered similar early events.

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.

Abscissic acid specific expression of RAB18 involves activation of anion channels in Arabidopsis thaliana suspension cells.

The abscissic acid (ABA) transduction cascade following the plasmalemma perception was analyzed in intact Arabidopsis thaliana suspension cells. In response to impermeant ABA, anion currents were activated and K(+) inward rectifying currents were inhibited. Anion current activation was required for the ABA specific expression of RAB18.

Induction of RAB18 gene expression and activation of K+ outward rectifying channels depend on an extracellular perception of ABA in Arabidopsis thaliana suspension cells.

Important progress has been made regarding the characterization of the ABA signalling components using genetic and molecular approaches (Leung and Giraudat, 1998). However, we do not yet know the mechanism of ABA perception. Conflicting results concerning the site of ABA perception have been published.