Mode of action of gibberellic Acid and light on lettuce seed germination

The seeds of lettuce (Lactuca sativa L. cv. Grand Rapids) germinate in darkness at 25 C when treated by gibberellic acid (GA(3)) for 1 hour following 2 hours of imbibition. The time of GA(3) application influences the rate and the final percentage of seeds that germinate. In contrast, red light illumination given at different times affects only the rate and not the final germination percentage. The early process(es) of germination initiated by GA(3) or light treatment can be arrested by subjecting the treated seeds to a nongerminative temperature of 35 C. The results suggest differences in the mode of action of light and GA(3) during germination. They indicate that different kinds of processes are involved in the biochemical control of germination.