Stimulation of caffeine biosynthesis in suspension-cultured coffee cells and the in situ existence of 7-methylxanthosine
1995
Schulthess, B.H. | Baumann, T.W.
Suspension-cultured cells of coffee were subjected to various conditions such as photoperiod, 1 mM adenine, 0.1-10 mM ethephon, or to the combination of both adenine and ethephon. Concentrations of purine bases, nucleosides, nucleotides as well as of purine alkaloids (PA; i.e. 7-methylxanthine, theobromine and caffeine) were measured by HPLC. In the dark, both adenine and ethephon drastically stimulated overall PA formation by a factor of 4 and 7, respectively. Their simultaneous application resulted in an additional increase yielding a stimulation factor of 11. In photoperiod, caffeine formation was, as compared to the control in the dark, enhanced by a factor of 21 without affecting theobromine and 7-methylxanthine pools: additional stimulation by ethephon was not possible. Conversely to light and ethephon, which had no effect on the accumulation of primary purine metabolites. adenine feeding resulted in persistently enlarged pools of nucleosides (xanthosine, guanosine, inosine) and 7-glucopyranosyladenine, 7-methylxanthosine, the postulated precursor of 7-methylxanthine in caffeine biosynthesis could not be detected under any conditions at any time. Since no other methylated purine was found, it is not yet feasible to discard the '7-methylxanthosine hypothesis'. However, the present investigation provides a suitable system to study the early steps of caffeine biosynthesis by means of radiolabelling kinetics.
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