SIGNAL-TRANSDUCTION IN BARLEY ALEURONE PROTOPLASTS IS CALCIUM-DEPENDENT AND INDEPENDENT

Gibberellic acid (GA) increases Ca2+ and calmodulin (CaM) levels in ba rley aleurone cells, and abscisic acid (ABA) antagonizes the GA effect , These alterations in cytoplasmic Ca2+ and CaM have been suggested to be central regulators of the secretory response of the barley aleuron e, Using microinjection of caged Ca2+, Ca2+ chelators, and CaM, we mim icked or blocked these hormonally induced changes in Ca2+ and CaM and assessed their effects on GA and ABA action, Although mimicking GA-ind uced changes in Ca2+ and CaM did not mimic GA action, blocking these c hanges did prevent GA stimulation of secretion. The induction of the a mylase gene by CA was, however, unaffected. Similarly, blocking the de crease in Ca2+ normally caused by ABA in these cells blocked ABA actio n, except that induction of Em gene transcription by ABA was unaffecte d. These results suggest that GA and ABA signals are transduced by Ca2 +- and CaM-dependent and Ca2+- and CaM-independent systems in the aleu rone cell.