METHODS AND RESULTS:
We examined the distribution of Ethylamine, glutamic acid and alanine, which are utilized in theanine biosynthesis, and other major amino acids in leaves, stems, cotyledons and roots of 6-week-old tea seedlings. Ethylamine and glutamic acid, which are substrates of theanine synthetase, were distributed almost uniformly in all parts of the seedlings; the contents in micromol/g fresh wt varied from 0.44-0.88 (Ethylamine) and 1.6-2.4 (glutamic acid). The content of alanine, a possible precursor of Ethylamine synthesis, was significantly higher in roots (3.1 micromol/g fresh wt) than in other parts. Incorporation of radioactivity from [U-14C]-alanine into theanine was also higher in roots than in other organs. In 10-week-old seedlings, [1-14C]Ethylamine was converted to theanine in young and developed leaves, stems, main and lateral roots; the highest rates of conversion were detected in the main and lateral roots.
CONCLUSIONS:
These results suggest that the theanine synthesis preferentially takes place in roots but is not restricted to them; substrates and the enzymatic machinery for theanine synthesis are available in all parts of tea seedlings. |
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