Ethylene-induced Leaf Abscission Is Promoted by Gibberellic Acid.

Gibberellic acid (GA(3)) promoted leaf abscission from cotton (Gossypium hirsutum L.) plants exposed to ethylene. With mature plants, only the rate of abscission was increased, but when vegetative plants were exposed to ethylene for 4 days or less, the amount of abscission was increased markedly. Promotion of abscission occurred at near saturating ethylene levels (10 mul/liter), over a wide range of GA(3) concentrations, and with both GA(3) and GA(7).GA(3) promoted abscission when Ethephon was substituted for ethylene and at locations not receiving direct application of GA(3). The magnitude of the abscission promotion by GA(3) was greater than that resulting from auxin transport inhibitors or abscisic acid. The characteristic inhibition of abscission by auxin occurred. The responses suggest that endogenous gibberellins may be involved in rapid abscission of apical leaves from vegetative cotton plants exposed to ethylene. Application of GA(3) may offer an additional option in agricultural manipulation of abscission and dehiscence.