Source Year: 1997

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 H. brasiliensis. Enhancement of in vitro organogenesis ability following somatic embryogenesis or repeated grafting onto juvenile rootstocks was accompanied by an increase of zeatin riboside levels in shoots used for in vitro micropropagation. Zeatin levels 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. It is concluded that endogenous zeatin-like cytokinin levels (free and ribosylated forms) can be considered as reliable markers for the recovery of in vitro shoot and root organogenesis, after rejuvenating treatments in rubber-tree clones.