Changes in Endogenous Hormone Concentrations during Berry Development in Relation to the Ripening of Delaware Grapes

Changes in concentrations of endogenous hormones during berry development were investigated in relation to the ripening of Delaware grapes. The concentration of ethylene was low before and during ripening. Gibberellin and cytokinin activities were high in the early stage, but then declined to lower levels before initiation of ripening. The concentration of IAA in seedless berries was high before veraison, then decreased rapidly, while that in seeded ones decreased gradually from 3 weeks after anthesis to veraison. The time of disappearance of absorbed 2, 4-D in the 2, 4-D treated berries coincided closely with the time of initiation of ripening. ABA contents of seeded, seedless and 2, 4-D treated berries increased remarkably as they ripened. The data indicate that an auxin-ABA relationship may be involved in the natural regulation of grape ripening.