METABOLISM OF ZEATIN RIBOSIDE IN A HORMONE AUTONOMOUS GENETIC TUMOR LINE OF TOBACCO

The metabolic fate of externally applied [H-3]-zeatin riboside ([9R]Z) was studied in a cultured genetic tumour line of Nicotiana glauca (Gr ah.) x N. langsdorffii (Weinm.), which grows on auxin and cytokinin fr ee medium. Metabolism by 3.5-week-old tissues showed enhanced stabilit y of supplied [9R]Z; unmetabolized [9R]Z accounted for 48.7 and 37.5% of extracted radioactivity following 8 and 24 h incubation, respective ly; tissues of different ages (1-10 weeks following subculture) also i ndicated high cytokinin stability following 8 h incubation (unmetaboli zed [9R]Z accounted for 32.5-53.0% of extracted radioactivity). All an alyses were performed by thin layer chromatography (TLC) and the resul ts subsequently confirmed by high performance liquid chromatography (H PLC). Side-chain cleavage and modification of the purine ring were the major forms of metabolism; metabolites with an intact cytokinin moiet y included zeatin (Z), [9R]Z nucleotides and glucosyl derivatives. Det ailed analysis of metabolites carried out in the experiments using 3.5 -week-old tissues indicated that both dihydro-derivatives as well as c is isomers of Z and [9R]Z were not formed. Adenine, adenosine and its nucleotide(s) were the main degradative metabolites; in 3.5-week-old t issues these metabolites accounted for about 5.9 and 7.8% (of H-3 extr acted) following 8 and 24 h incubation, respectively. In tissues of di fferent ages (1-10 weeks following subculture), these metabolites acco unted for about 7.6-22.9% of the extracted H-3. Some metabolites (zeat in, adenine and adenosine) were also detected in the staled incubation media. The observed high [9R]Z stability in this tissue may reflect l ow levels of cytokinin oxidase activity and/or some form of compartmen tation.