Abstract

The abscission-promoting activities of abscisic acid (ABA) and 5 ABA analogs were examined in cotton (Gossypium hirsutum L. cv LG102) seedlings and cotyledonary node explants. The analogs tested included a series of acetylenic derivatives that differ in the oxidation state of the C-1 atom, a 2′,3′ dihydro-derivative of ABA and a 2′,3′ dihydro-derivative of an acetylenic analog with a C-1 carboxyl moiety. ABA and all five analogs were active in stimulating petiole abscission in explants. Following treatment with 100,µM ABA or analog, 50% abscission of explants was observed after 29 h and complete abscission occurred within 40 h. With one exception, none of the treatments resulted in an increase in explant ethylene production. Pretreatment of the explants with the ethylene antagonist silver thiosulfate completely abolished the abscission-promoting activities of ABA and all of the analogs. Daily application of ABA or any of the analogs had no effect on cotyledon abscission in intact seedlings. The implications of the results with respect to the development of a commercial ABA-like regulator as well as to ABA structure-activity studies are discussed.

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