ENDOGENOUS CYTOKININS AS BIOCHEMICAL MARKERS OF RUBBER-TREE (HEVEA-BRASILIENSIS) CLONE REJUVENATION

The endogenous levels of isopentenyladenine, isopentenyladenosine, zea tin and zeatin riboside and the ability for in vitro axillary shoot or ganogenesis and rhizogenesis were compared between mature and rejuvena ted clones of Hevea brasiliensis (Mull. Arg.). Enhancement of the in v itro organogenesis ability of rubber-tree clones following somatic emb ryogenesis or repeated grafting onto juvenile rootstocks was accompani ed by an increase of zeatin riboside levels in shoots used as starting material for in vitro micropropagation. Furthermore, the zeatin level , in in vitro shoots of clones treated by in vitro micrografting, and consequently capable of axillary shoot and root organogenesis, was hig her than in in vitro shoots of non treated mature material incapable o f in vitro organogenesis. We conclude that the endogenous zeatin-like cytokinin level (free and ribosylated forms) can be considered as a re liable marker for the recovery of in vitro shoot and root organogenesi s after rejuvenating treatments in rubber-tree clones.