Abscisic acid, abscisic acid-esters and phaseic acid in vegetative terminal buds of Acer pseudoplatanus during emergence from winter dormancy.

Levels of free-abscisic acid and "boundabscisic acid" (alkaline hydrolyzable abscisic acidesters) in replicated samples of terminal vegetative buds of sycamore trees were measured during natural emergence from winter dormancy by gas chromatographic methods together with isotope dilution estimation of recovery rates. Not until after the buds had been released from true dormancy in January by winter chilling did any clear change occur in either abscisic acid (ABA) fraction, or in total ABA, on any basis of comparison. The percentage of total ABA present as the free acid declined at the end of true dormancy to approximately two-thirds of its value in the earlier winter months. It is concluded that glucosylation of ABA is unlikely to play a major part in the mechanism of release from dormancy in vegetative sycamore buds. At the end of true dormancy there was a large transient increase in what appeared to be phaseic acid, but this was not accompanied by any marked decrease in either free- or bound-ABA.