Endogenous Ethylene and Abscisic Acid Relative to Phytogerontology

Endogenous production of ethylene and endogenous levels of abscisic acid were measured from Hibiscus rosa-sinensis L. abscission zone explants at six stages of development: tight bud, open flower, closed flower, petal abscission, calyx abscission, and peduncle abscission.Explants acropetal and basipetal to the abscission zone produced less ethylene than the abscission zone explants. Ethylene production increased with time both prior to and during abscission, reaching a peak in the later stages of senescence after abscission was complete.Bound abscisic acid was greatest in segments acropetal to the abscission zone at the closed flower stage. Free abscisic acid was double that of bound abscisic acid in the tight bud stage with the basipetal level exceeding that of the acropetal level until flower closure. Acropetal-free abscisic acid began to rise at petal abscission increasing sharply to a peak at calyx abscission. Both free and bound abscisic acid were greatly reduced at peduncle abscission. A relationship of ethylene and abscisic acid to abscission and senescence appears to exist.