Studies on the Biochemical Formation Pathway of the Amino Acid l-Theanine in Tea (Camellia sinensis) and Other Plants

Tea ( Camellia sinensis ) is the most widely consumed beverage aside from water. The flavor of tea is conferred by certain metabolites, especially l -theanine, in C. sinensis . To determine why more l -theanine accumulates in C. sinensis than in other plants, we compare l -theanine contents between C. sinensis and other plant species ( Camellia nitidissima, Camellia japonica, Zea mays, Arabidopsis thaliana, and Solanum lycopersicum ) and use a stable isotope labeling approach to elucidate its biosynthetic route. We quantify relevant intermediates and metabolites by mass spectrometry. l -Glutamic acid, a precursor of l -theanine, is present in most plants, while ethylamine, another precursor of l -theanine, specifically accumulates in Camellia species, especially C. sinensis . Most plants contain the enzyme/gene catalyzing the conversion of ethylamine and l -glutamic acid to l -theanine. After supplementation with [ 2 H 5 ]ethylamine, all the plants produce [ 2 H 5 ] l -theanine, which suggests that ethylamine availability is the reason for the difference in l -theanine accumulation between C. sinensis and other plants.