Dormancy breaking in Fagus sylvatica seeds is linked to formation of abscisic acid-glucosyl ester

Seed dormancy is an adaptive mechanism that allows seed germination under suitable environmental conditions. Germination of stored dormant seeds proceeds after dormancy breaking induced by stratification. To improve understanding of dormancy breaking in beechnuts, we: investigated effects of moisture content and temperature during storage; analysed contents of abscisic acid, abscisic acid metabolites and indole-3-acetic acid in embryonic axes during storage and stratification; and histochemically localized storage proteins in embryogenic axes and cotyledons of beechnut embryos. The results show that storage conditions can affect the nuts’ abscisic acid contents, but not the stratification process. In addition, dormancy breaking is linked to a reduction in abscisic acid contents and depth of dormancy is not influenced by either of these storage factors. Detected changes that correlated most strongly with dormancy breaking were a big increase in abscisic acid-glucosyl ester levels and accompanying reduction in the abscisic acid-glucosyl ester to abscisic acid ratio. We detected extremely low concentrations of other abscisic acid metabolites-neophaseic, phaseic and dihydrophaseic acids—in non-dormant stored beechnuts, but somewhat higher concentrations during dormancy. No relationships between changes in indole-3-acetic acid levels with either storage conditions or dormancy breaking were detected. Changes in distributions of storage proteins were related to the seeds’ moisture content during storage and stratification rather than seed dormancy. We conclude that increases in endogenous abscisic acid-glucosyl ester levels and abscisic acid-glucosyl ester to abscisic acid ratios are good markers of depth of dormancy and/or effectiveness of stratification in beechnuts.