Blockage by Gibberellic Acid of Phytochrome Effects on Growth, Auxin Responses, and Flavonoid Synthesis in Etiolated Pea Internodes

Open Access
Publisher Website
Google Scholar
Abstract
Red light inhibits the growth of etiolated pea internodes, causes a shift toward higher indoleacetic acid (IAA) concentrations in the IAA dose-response curve of excised sections, and promotes the synthesis in intact internodes of kaempferol-3-triglucoside. Gibberellic acid (GA3) prevents all 3 effects, the first effect substantially and the last 2 completely. This suggests GA3 blockage of an early or basic event initiated by the active form of phytochrome. The red light-induced shift in the IAA dose-response curve of excised sections is consistent with a light-induced increase in the activity of an IAA destruction system, since the magnitude of the red light inhibition varied with IAA concentration. The red light and GA3 effects on growth and on flavonoid synthesis are consistent with the view that phytochrome may control growth by regulating the synthesis of phenolic compounds which act as cofactors in an IAA-oxidase system. GA3 reversal of the red light-induced shift in the IAA dose-response curve involves both growth promotion and inhibition by GA3 at different IAA concentrations and this, together with the GA3 reversal of light-induced flavonoid synthesis, supports the suggested regulatory role of phenolic compounds in growth.