Relations between exogenous growth regulators and endogenous indole-3-acetic acid and abscisic acid in the expression of somatic embryogenesis in Hevea brasiliensis (Müll. Arg.)

Abstract

Endogenous IAA (indole-3-acetic acid) and ABA contents were measured during the somatic embryogenesis process from Hevea brasiliensis (Müll. Arg.) callus. The decrease in 3,4-D (3,4-dichlorophenoxyacetic acid) and BAP (6-benzylaminopurine) supply in the culture medium and the addition of ABA both stimulated embryogenic induction. But only exogenous ABA sustained embryogenic expression of the callus. The two operations resulted in a decrease in endogenous ABA and an increase in IAA in callus. Low endogenous ABA levels (2–4 nmol/g dry wt.) appear to be necessary for the acquisition and conservation of a embryogenic state. Non-embryogenic calli accumulated high levels of ABA (25–40 pmol/g dry wt.). This accumulation confirm the hypothesis that non-embryogenic Hevea calli were water stressed.