Stimulation of Endomitotic DNA Synthesis and Cell Elongation by Gibberellic Acid in Epicotyls Grown from Gamma-irradiated Pea Seeds

Large doses of gamma-irradiation, given to air-dried pea seeds, inhibit the endomitotic DNA synthesis in pea epicotyls during germination in darkness. The cortex cells of the etiolated epicotyls reach only the 4 C DNA level, whereas cortex cells of unirradiated seeds reach the 8 C DNA level. Epicotyl elongation and cell elongation are also reduced.Application of gibberellic acid restores the endomitotic DNA synthesis and the cell elongation in epicotyls of irradiated seeds. The cortex cells reach again the 8 C DNA level in darkness.The results suggest that gamma-irradiation blocks endomitotic DNA synthesis and cell elongation by lowering the concentration of endogenous gibberellins.