Abstract: The shade can effectively improve the quality of tea(Camellia sinensis) by causing an increase in the concentration of theanine, the main compound that contributes to the fresh and brisk taste of tea leaves. We analyzed the influence of shade on theanine biosynthesis in relation to the expression of genes related to theanine synthesis in tea leaves during summer. Our data reveal that shade has a notable effect on the level of both theanine and total free amino acids in young leaves. The results of qPCR and western blot analysis suggest that these effects are mainly brought about via an increase in the mRNA expression of TS and promotion of TS protein synthesis. The qPCR results also suggest that the mRNA expression of all the genes related to the theanine pathway in the leaves, including glutamine synthetase(GS), glutamate dehydrogenase(GDH), glutamine 2-oxoglutarate amino-transferase(GOGAT), nitrite reductase(NiR), arginine decarboxylase(ADC), are significantly affected by shade. However, from two different expression patterns, the GS/GOGAT pathway is triggered by shade and members of this pathway show higher expression in old leaves, which reassimilate more NH⁺₄ to supply more amides to young leaves. The gene expression of NiR and ADC was markedly lower in both the old and young leaves from the shaded plants, which suggests that nitric nitrogen metabolism might be inhibited by shade treatment. Thus, shade treatment can increase the content of free amino acids especially theanine in tea leaves and improve the effective utilization of summer tea.

Key words: Camellia sinensis, theanine synthetase, theanine metabolism pathway, shading, comparative expression