METABOLISM OF ADENINE AND HYPOXANTHINE IN A HORMONE AUTONOMOUS GENETIC TUMOR LINE OF TOBACCO

Genetic tumour tissues of Nicotiana glauca (Grah.) x N. langsdorffii ( Weinm.), which grow on auxin and cytokinin-free medium, were incubated with [C-14]-/[H-3]-adenine or [H-3]-hypoxanthine to investigate cytok inin biosynthesis. Adenine was supplied to tissues of two different ag es (2- and 3.5-week-old) for 8, 24 or 30 h, The uptake was over 91.0 % (of ''supplied radioactivity'') by 2-week-old tissues as compared to around 50.0 % uptake by 3.5-week-old tissues. Incorporation into cytok inins could not be detected. While unmetabolized adenine accounted for only about 24.0 and 13.4 % of ''extracted radioactivity'' (following 8 and 30 h incubation, respectively) in 2-week-old tissues, relatively higher levels, i.e. 36.0 and 34.5 % (following 8 and 24 h incubation, respectively) were present in 3.5-week-old tissues. The metabolites f ormed were adenosine and its nucleotides (4.5 - 16.5 % and 37.4 - 60.2 % of the extracted radioactivity, respectively). Hypoxanthine was sup plied to 3.5-week-old tissues for 8 and 24 h, While the uptake was low (< 28.0 % of supplied radioactivity), the major proportion of extract ed radioactivity was due to unmetabolized hypoxanthine (79.8 % and 85. 9 % after 8 and 24 h incubation periods, respectively); the minor meta bolites were inosine and adenosine (both < 0.5 %) and their nucleotide s (< 3.5 %). Radioactivity incorporation into cytokinins from hypoxant hine was not detected. Thus in the present investigations precursor in corporation from either adenine or hypoxanthine into cytokinins could not be demonstrated. It is possible that this may be due to slow rate of cytokinin turnover in these tissues.