Seasonal variations in biosynthetic capacity for the synthesis of caffeine in tea leaves

Seasonal variations in the metabolic fate of adenine nucleotides prelabelled with [8-14C]adenine were examined in leaf disks prepared at one-month intervals, over the course of one year, from the shoots of tea plants (Camellia sinensis L. cv Yabukita)which were growing under natural field conditions. Incorporation of radioactivity into nucleic acids and catabolites of purine nucleotides was found throughout the experimental period, but incorporation into theobromine and caffeine was found only in the young leaves harvested from April to June. Methylation of xanthosine, 7-methylxanthine and theobromine was catalysed by gel-filtered leaf extracts from young shoots (April to June), but the reactions could not be detected in extracts from leaves in which no synthesis of caffeine was observed in vivo. By contrast, the activity of 5-phosphoribosyl-1-pyrophosphate synthetase was still found in leaves harvested in July and August.