Gibberellic acid and indole acetic acid compete in ethylene promoted abscission.

Abscission of cotton cotyledonary explant petioles is promoted by gibberellic acid (GA) in room air and, to a lesser extent, in 1 μl ethylene liter(-1) air. GA3 consistently reduced the abscission-retarding effect of indole-acetic acid (IAA) (promoted abscission in the presence of IAA), and exogenous ethylene further promoted abscission. It is proposed that GA's promotion of ethylene-induced abscission is achieved by reducing the abscission retarding action of auxin.