COMPARISON OF ENDOGENOUS ABA AND IAA CONTENTS IN SOMATIC AND ZYGOTIC EMBRYOS OF HEVEA-BRASILIENSIS (MULL ARG) DURING ONTOGENY

IAA and ABA contents were measured in somatic embryos and in zygotic e mbryos and the surrounding endosperm in Hevea brasiliensis. Two succes sive phases, development and maturation, were defined during ontogenes is using morphological growth and water status criteria. Endosperm con tained high amounts of IAA (10-25 nmol/g dry wt.) throughout developme nt and high ABA (40 nmol/g dry wt.) at the end of the development phas e. Zygotic embryos contained high IAA concentrations at the start of t he development phase; the maximum was observed in early torpedo stage (when length was 5 mm) and the level then decreased progressively unti l the end of the maturation phase. ABA accumulated (26 nmol/g dry wt.) in zygotic embryos at the end of growth and then its concentration dr opped during maturation. It would therefore appear firstly that the IA A and ABA contents were always higher in the endosperm than in the emb ryo and secondly that the very low IAA and ABA contents characterize m aturity in these two types of tissue. The results support the hypothes is of a major role of IAA in embryo development and of ABA in causing and controlling maturation. In comparison, IAA and ABA contents of som atic embryos were low (0.6-2 nmol/g dry wt.) and varied little during ontogenesis. Their variation was very different to that observed in ov ulo and might be related to the abnormal development and low germinati on percentages observed.