Patterns of adenine metabolism and caffeine biosynthesis in different parts of tea seedlings

Contents of purine alkaloids in different parts of tea ( Camellia sinensis L. cv. Yabukita ) seedlings, seeds and tissue cultures were determined with high-performance liquid chromatography. More than 99% of the caffeine detected was in the leaves of the 4-month-old seedlings. The amount expressed per g fresh weight was higher in older leaves. Theobromine, a precursor of caffeine biosynthesis, was found only in younger leaves. Zero or only trace amounts of theophylline, a degradation product of caffeine, were found in the seedlings. Almost all the caffeine in tea seeds was found in the seed coats. Theobromine and theophilline could not be detected in any part of the seeds.
Tracer experiments using [8-¹⁴C]-adenine indicate that (i) caffeine biosynthesis from [8-¹⁴C]-adenine occurs only in younger leaves,(ii) salvage of [8-¹⁴C]-adenine for nucleic acid synthesis takes place in all parts of the seedlings, (iii) considerable degradation of [8-¹⁴C]-adenine by conventional purine degradation pathway via uric acid takes place in roots and lower parts of stem tissue.
The results strongly suggest that caffeine is synthesized in younger leaves and accumulated within the leaves. Both caffeine contents and its synthetic activity from adenine were extremely low in tissue culture of tea.