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Abscisic Acid and Apple Seed Dormancy1


c,t-Abscisic acid (ABA) was identified in methanol extracts of mature apple (Malus domestica Borkh.) seeds by gas chromatography-mass spectrometry, and concentrations of both free and base-hydrolyzable (bound) ABA in immature and mature seeds were quantified by electron capture gas chromatography. Immature embryos failed to germinate regardless of time of sampling unless seed coats were removed. Germination of excised embryos reached a maximum in early August, then gradually declined to nil in mid-September. Although ABA content of the embryonic axes rose sharply at maturity, the rise occurred only after germination capacity declined. Premature defoliation reduced ABA content of the axes, but did not prevent the induction of embryo dormancy. ABA content of mature seeds declined during stratification at both 5° and 20°C, with maximum differences occurring in the embryonic axis, but dormancy was broken only at 5°. Induction of secondary dormancy by high temperature (27°) was accompanied by a slight decline in ABA content of whole seeds.