Flower Bud Dormancy in Coffea Arabica L. I. Studies of Gibberellin in Flower Buds and Xylem Sap and of Abscisic Acid in Flower Buds in Relation to Dormancy Release

Abstract

Changes were studied in gibberellin and abscisic acid in coffee flower buds and gibberellin in xylem sap when bud dormancy was released by rainfall or irrigation. Gibberellin leveis in the buds increased rapidly, while those in the xylem sap remained unchanged. Bud gibberellin stopped rising when rapid expansion began and then decreased as this proceeded. The absolute amount of abscisic acid in buds remained steady prior to increasing just before anthesis. On a fresh weight basis levels declined during rapid water uptake but recovered as anthesis approached. The resumption of active growth leading to blossoming may be regulated by the liberation of free gibrrellin from a bound form in the buds, but, second, xylem-transported, stimulus could also be involved.