Effect of ABA, GA3 and FC on the development of potassium uptake in germinating radish seeds

Germination of Rhaphanus sativus seeds is accompanied in its early phase by a consistent loss to the medium of the main cations. During the first ten hours there is a general efflux of K + , Na + , Mg 2+ and Ca 2+ , while in the following period K + is actively taken up so that after eighteen hours almost no K + is detected in the external medium. When seed germination is stimulated by fusicoccin (FC) the development of uptake capacity is markedly anticipated. Moreover, inhibition of seed germination by abscisic acid (ABA) inhibits the development of K + uptake. The ABA-induced inhibition is reversed by FC and also, even if to a lesser extent, by gibberellic acid (GA 3 ). Preliminary data suggest that a K + activated ATPase present in membrane preparation is involved in the mechanism of active K + uptake in the seeds.