Studies in seed dormancy

Abstract

When dormant hazel seeds were subjected to six weeks chilling at 5° C their subsequent transfer to 20° C resulted in the accumulation of gibberellin (GA) followed by germination. In the presence of either phosphon D or β-chlorethyltrimethylammonium chloride (CCC) at 20° C there was inhibition of both GA accumulation and germination, a finding consistent with the hypothesis that GA biosynthesis is a necessary prerequisite for the germination of chilled hazel seeds. As abscisic acid showed a strong inhibition of germination but had little effect on GA accumulation it is presumed not to have affected GA biosynthesis but to have inhibited GA action. These conclusions were supported by experiments in which the interaction of exogenous GA3 with growth retardants and ABA was tested on the germination of chilled hazel seeds. Experiments in which the embryonic axes and cotyledons of chilled seeds were incubated separately at 20° C established that GA biosynthesis de novo occurred in the embryonic axis and indicated that in the intact seed some of the GA would have been translocated to the cotyledons. The isolated cytoledons showed no GA biosynthesis de novo but gave some release of GA from one or more bound forms.