Promotion of Lettuce Seed Germination by Gibberellin

Abstract

Gibberellin promotes dark germination of lettuce (Lactuca sativa. var. Grand Rapids) seeds which ordinarily would not germinate in the absence of a promoter because of: (1) low supra-optimal germination temperature, (2) inhibition induced by a high temperature pretreatment, (3) inhibition produced by a brief far red irradiance, and (4) dark-osmotic inhibition. Thus, gibberellin can substitute for red light in every case examined in which light stimulates lettuce seed germination. However, the effect of gibberellin could not be negated by far red irradiation of seeds as can the action of red light. When red light is administered briefly 4 hours after seeds begin to imbibe on gibberellin solution, the combined promotive effects of red light and gibberellin are additive or less than additive as reflected by per cent germination. The combined effects of red light and gibberellin, however, are greater than can be predicted by simple addition of the 2 single effects, when red light is given 20 hours or longer after the seeds are sown on gibberellin solution. No close relationship between the actions of gibberellin and red light was established.