The role of gibberellin in hypocotyl extension of dark-growing Lupinus albus seedlings.

Six authentic gibberellins marginally promoted hypocotyl lengthening of etiolated lupin seedlings whereas extracted lupin "gibberellin-like" compounds were ineffective. However, dwarfing by AMO-1618 [2'-isopropyl-4'-(trimethyl-ammonium chloride)-5'-methylphenyl piperidine carboxylate] was totally counteracted by co-application with GA3 and partially overcome by extracted lupin "gibberellins". Meaningful quantities of free extractable and diffusible gibberellins were detected; "bound" gibberellin activity was not found. The time-course of the decline in extractable gibberellin levels during the process of dwarfing showed a significant difference from 6 h after applying AMO-1618. It is suggested that axis growth is dependent on gibberellin in a system normally close to saturation for endogenous growth.