Responses to gibberellin of light-requiring seeds of lettuce & Lepidium virginicum

Abstract

The mode of action of gibberellin in the germination of light-requiring seeds of Lepidium virginicum and Grand Rapids lettuce was studied. The response to 4 forms of gibberellin, optimum concentration, effects of buffering the acid and the potassium salt of gibberellin, and the interaction with temperature and with the photo-chrome system were determined, Gibberellin had 3 separate effects: (1) It caused light-requiring seeds to germinate in total darkness, (2) it removed temperature blocks to the germination of light-promoted seeds and prevented the onset of dormancy imposed by high temperature, and (3) it caused a higher percentage of seeds to germinate at a given energy of red light. Seeds fully promoted by gibberellin were not inhibited by short exposures to far red but were retarded in rate of germination by continuous far red. Seeds partially promoted by gibberellin were inhibited to, or slightly below, the gibberellin dark controls by short exposures to far red, and much below the gibberellin dark controls by continuous far red. Gibberellin solutions buffered below the pKa value were more active than unbuffered solutions in promoting germination.