CALCIUM DEPENDENCE OF THE EFFECTS OF ABSCISIC-ACID ON RNA-SYNTHESIS DURING GERMINATION OF CICER-ARIETINUM SEEDS

The effect of abscisic acid (ABA) and CaCl2 in the medium on RNA synthesis in embryonic axes of seeds of chick-pea (Cicer arietinum L. cv. Castellana) during the first hours of germination has been studied. ABA decreases the incorporation of H-3-uridine in the embryonic axes and modifies the mRNA populations by preventing the disappearance of three polypeptides of 25, 22 and 21.6 kDa and inducing the appearance of two polypeptides of 35 and 27 kDa absent in the control. Calcium increases the effect of ABA on the synthesis of these mRNAs and seems to be involved in the synthesis of at least the polypeptide of 25 kDa, as this polypeptide disappears in the treatments with EGTA and Verapamil. Moreover, cytosolic calcium seems to be necessary for the accumulation of these messengers since treatment with TMB-8 (chelating agent for endogenous calcium) decreases the intensity of the bands corresponding to these 5 polypeptides. The possible synergistic action of ABA and calcium in this process is discussed.