Endogenous cytokinins as biochemical markers of rubber-tree (Hevea brasiliensis) clone rejuvenation

The endogenous levels of isopentenyladenine, isopentenyladenosine, zeatin and zeatin riboside and the ability for in vitro axillary shoot organogenesis and rhizogenesis were compared between mature and rejuvenated clones of Hevea brasiliensis (Mull. Arg.). Enhancement of the in vitro organogenesis ability of rubber-tree clones following somatic embryogenesis or repeated grafting onto juvenile rootstocks was accompanied 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 higher than in in vitro shoots of non treated mature material incapable of in vitro organogenesis. We conclude that the endogenous zeatin-like cytokinin level (free and ribosylated forms) can be considered as a reliable marker for the recovery of in vitro shoot and root organogenesis after rejuvenating treatments in rubber-tree clones.