Acide abscissique lié et dormance embryonnaire chez Pyrus malus

Bound abscisic acid and embryo dormancy in Pyrus malus. The first part of this work was devoted to the study of the behaviour of Pyrus malus L. cv. Golden Delicious embryos cultivated in vitro. At the beginning of the experiment, either the root (RM) or the distal part of the cotyledons (CM) was immersed in the medium. For embryos directly isolated from the fruits at harvest time, as well as for embryos submitted to a 3-month post-maturation treatment at 4°C, the dormancy was deeper in CM cultures than in RM. The use of gibberellins (GA₄ or GA₇) emphasized these differences. The second part of this work was devoted to the study of free and bound forms of ABA (cis and trans isomers) in embryos isolated from the fruits at harvest time and cultivated by the RM or CM procedure during 3 weeks. The biochemical data obtained indicated in both cases the existence of the following three processes: (A) Mobilization of the bound ABA with the consequent release of free ABA; this was particularly important in CM. (B) Metabolism of free ABA: the isomerization into trans-ABA only partly accounted for the decrease in the content of free ABA which was much greater in RM than in CM. (C) Transport of ABA towards the root, the result being an accumulation of free ABA in the root, much greater in CM than in RM; this would account for the deeper dormancy in CM than in RM.