Requirement of cotyledons for gibberellic acid-induced hypocotyl elongation in lettuce seedlings. Isolation of the cotyledon factor active in enhancing the effect of gibberellic acid

Abstract

The role of cotyledons in hypocotyl elongation caused by gibberellic acid was studied using young seedlings of lettuce, Lactuca saliva, var. ‘Grand Rapids’. Removal of cotyledons from intact seedlings resulted in a depression of hypocotyl elongation caused by gibberellic acid. Gibberellic acid-induced hypocotyl elongation in decotylized seedlings, was however, substantially enhanced by incubating the seedlings together with excised cotyledons. The exudate from excised cotyledons also enhanced the effect of gibberellic acid on hypocotyl elongation in decotylized seedlings. This active principle (named the cotyledon factor) in the cotyledon exudate was stable against heating at 100°C for 15 min, permeated the dialysis membrane, and was extractable with ethyl acetate. Biological activity of the cotyledon factor was not replaced by indole-3-acetic acid, kinetin, cyclic AMP, vitamins, sucrose or inorganic nutrients. The biological significance of the cotyledon factor is discussed in relation to the action of gibberellic acid.