Red Light Induction of Gibberellin Synthesis in Leaves

GIBBERELLIC acid is known to mimic the morphogenetic effects of red light1 on certain plants. Brian2 has suggested that gibberellins are synthesized in plants after the absorption of red light and Kohler3 has shown that there is a significant increase in the content of gibberellic acid in etiolated peas after 24 h of irradiation with red light. This and other work4 suggests that phytochrome in the Pfr form (after irradiation with red light) initiates synthesis, or at least brings about increases in the content of gibberellin in plants and seeds. Many responses of phytochrome, however, can be observed a few hours (or in some cases in less than 1 h (ref. 5)) after illumination with red light. Thus to explain effects of phytochrome in terms of the action of gibberellin, it is necessary to show that gibberellins are synthesized during or very soon after the end of a period of red irradiation. This is what we have tried to do.