Biosynthesis of theanine (γ-ethylamino-l-glutamic acid) in seedlings of Camellia sinensis

Theanine (γ-glutamylethylamide) is the most abundant free amino acid in tea seedlings, and is distributed in cotyledons, shoots and roots. Theanine was synthesised from 15 N-labelled (NH 4 ) 2 SO 4 , glutamic acid and alanine and from 14 C-labelled ethylamine in all parts of seedlings. When ( 15 NH 4 ) 2 SO 4 was supplied to intact seedlings in liquid culture, incorporation of 15 N into theanine in roots was greater than in shoots. Incorporation into theanine was negligible in cotyledons, but theanine synthesis in roots and shoots was reduced in seedlings with cotyledons detached. Expression of theanine synthetase genes ( TS1 and TS2 ) was found in all organs, but the transcript level was significantly lower in cotyledons. These results suggest that theanine can be synthesised from glutamic acid and ethylamine derived from alanine in all parts of tea seedlings. However, supplied NH 3 exogenously to intact seedlings was converted to theanine mainly in roots. Amino acids stored in cotyledons may also be utilised for theanine synthesis in all parts of seedlings.