Seed Dormancy in Acer: CHANGES IN ENDOGENOUS CYTOKININS, GIBBERELLINS AND GERMINATION INHIBITORS DURING THE BREAKING OF DORMANCY IN ACER SACCHARUM MARSH

The present studies on changes in the levels of cytokinins,gibberellins, and germination inhibitors during stratificationof Acer saccharum sceds suggest that the breaking of dormancyis a phasic process. Stratification at 5°C led to a markedincrease in the butanol-soluble cytokinins after 20 d. Furtherchilling resulted in a loss of cytokinin. The majority of thedetectable cytokinin activity co-chromatographed with zoatin.Similarly, at day 40, acidic gibberellin-like substances increasedand declined with further chilling. A loss of acidic germinationinhibitors was also detected during stratification. The acidicfraction was shown to contain abscisic acid (ABA) by its behaviouron GLC and isomerization with ultra-violet light. Determinationsof endogenous levels of ABA by combined GLC and isotope dilutionmethods indicated a loss of 97.9 per cent ABA during stratification.The data suggest that the breaking of seed dormancy at low temperatureinvolves the initiation of an ordered sequence of events thatinclude the changes in growth hormones necessary to determinethe course of development for the removal of dormancy.