Promotion of Lettuce Seed Germination by Gibberellin

Abstract

Lettuce seeds do not germinate in darkness under certain conditions, and their germination can then be promoted by many factors. Kahn et al (9, 10) have presented preliminary reports on the promotion of dark germination of Grand Rapids lettuce seeds by gibberellin. Some details of their work and more recent results of the study will be given here. Some of the previously reported findings have been con-firmed and amplified by researchers at The Hebrew University of Jerusalem (7, 15). Also, Lona (14) has found that gibberellic acid promotes dark germi-nation of a wild lettuce species, Lactuica scariola L. Among the factors which may inhibit dark germi-nation of lettuce seeds are: supra-optimal germination temperature (3, 5); pretreatment of imbibed seeds with high temperature (1, 2); and a process called "dark-osmotic inhibition" (8). Dark-osmotic in-hibition is the reduction of germination in darkness by the incorporation of appropriate amounts of os-nmotically active solute in the germination solution. The above inhibitory factors may all induce the same ultimate block in the germination pathway. Often lettuce see(ls whose germination is inhibited by one of these factors will germinate if they are irradiated briefly with red light. Such seeds may be termed "red-light responsive". When a red irradiation is followed by a far red irradiation, the action of red light is reversed (1, 2). Following the far red ir-radiation, the promotion of germination can again be potentiated by a red irradiation, and such a promotion and reversal can be accomplished many times. The effect of gibberellin upon germination was determined on seeds that were made red-light respon-sive by supra-optimal germination temperature, dark-osmotic inhibition, pretreatment with high tempera-ture, or irradiation with red light followed by irradia-tion with far red light. Gibberellin causes bolting and flowering of long day plants in short days (12, 13). Because the light action spectra for the control of flowering and seed germination are similar (2), a part of this