Phytochrome-mediated Germination Responses in gamma-Irradiated Lettuce Seeds

Sublethal doses of γ-radiation and far red light have some-what analogous, red light reversible, effects on the germination of lettuce seeds (Lactuca sativa L. var. Grand Rapids). However, the mechanism by which γ-radiation retards germination appears to differ from that of far red light. Compared to controls, γ-radiation retarded germination for the first 24 hours; but after 36 or 48 hours of imbibition gemination of treated seeds was higher than that of the controls, whether or not the γ-irradiated seeds received red or far red light. The effects of γ-radiation are more pronounced in seeds containing 15% water at the time of treatment than in those containing only 7% water. The promotive action of red light is operative in the presumed absence of cell division in γ-treated seeds.