Water stress enhances ethylene-mediated leaf abscission in cotton

Abscission of cotyledonary leaves from cotton (Gossypium hirsutum L. cv. Stoneville 213) seedlings occurred following relief from water stress. The amount of abscission was related to the magnitude of the plant water deficit. Leaf abscission promoted by exogenous ethylene was enhanced in seedlings subjected to water stress. Treatment with ethylene (2.0 to 3.2 microliters of ethylene per liter of air for 24 hours) raised the threshold plant water potential required to induce abscission from -17 to -7 bar, indicating that the stress caused the tissue to become predisposed to ethylene action. Based on the abscission response curve for seedlings treated with ethylene while under water stress, this apparent predisposition was developed as the plant water potentials reached the -7 to -10 bar range. The abscission-promoting effects of ethylene in combination with water stress were reversed with 15% CO2 at plant water potentials above -12 bar, but the CO2 reversal was lost at lower water potentials. These results are compatible with the concept that ethylene plays a regulatory role in leaf abscission induced by water stress.