The Metabolism of Hormones during Seed Germination and Dormancy

Embryos from dormant and stratified Fraxinus americana seed were incubated with (S)-2-(14)C-abscisic acid (ABA) under a variety of conditions. Both dormant and stratified embryos rapidly metabolize abscisic acid to phaseic acid, dihydrophaseic acid, and an unidentified polar metabolite apparently derived from dihydrophaseic acid. Although the stratified embryos may have an increased capacity to metabolize abscisic acid, our calculations suggest that such an increased capacity would probably not be physiologically significant.Dormant intact seeds also metabolize (S)-2-(14)C-abscisic acid during stratification at 5 C or incubation at 25 C. The metabolites appear to be similar to those observed in excised embryos although by 12 days of stratification a fourth metabolite is observed. More than 90% of the (14)C-abscisic acid was metabolized after 26 days of stratification at 5 C or after 12 days of incubation at 25 C. Stratification at 5 C leads to the breaking of dormancy while incubation at 25 C does not.