Comparison of endogenous ABA and IAA contents in somatic and zygotic embryos of Hevea brasiliensis (Müll. Arg.) during ontogenesis

Abstract

IAA and ABA contents were measured in somatic embryos and in zygotic embryos and the surrounding endosperm in Hevea brasiliensis. Two successive phases development and maturation, were defined during ontogenesis using morphological phological growth and water status criteria. Endosperm contained high amounts of IAA (10–25 nmol/g dry wt.) throughout development and high ABA (40 nmol/g dry wt.) at the end of the development phase. Zygotic embryos contained high IAA concentrations at the start of the development phase; the maximum was observed in early torpedo stage (when length was 5 mm) and the level then decreased progressively until 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 dropped during maturation. It would therefore appear firstly that the IAA and ABA contents were always higher in the endosperm than in the embryo and secondly that the very low IAA and ABA contents characterize maturity in these two types of tissue. The results support the hypothesis of a major role of IAA in embryo development and of ABA in causing and controlling maturation. In comparison, IAA and ABA contents of somatic embryos were low (0.6–2 nmol/g dry wt.) and varied little during ontogenesis. Their variation was very different to that observed in ovulo and might be related to the abnormal development and low germination percentages observed.