Stable Isotope-Labeled Precursor Tracing Reveals that L-Alanine is Converted to L-Theanine via L-Glutamate not Ethylamine in Tea Plants In Vivo

Tea plants (Camellia sinensis) specifically produce L-theanine, which contributes to tea function and taste. Ethylamine is a limiting factor differentiating L-theanine accumulation between tea and other plants. Ethylamine has long been assumed to be derived from L-alanine in tea. In this study, the L-alanine content in tea root cells was mainly located in vacuoles and mitochondria using a nonaqueous fractionation technique, while alanine decarboxylase in tea (CsADC) was located in the cytoplasm. Although CsADC was able to catalyze L-alanine decarboxylation to produce ethylamine in vitro, it may not provide the same enzyme activity in tea plants. Stable isotope-labeled precursor tracing in tea plants discovered that L-alanine is not a direct precursor of ethylamine but a precursor of L-glutamate, which is involved in L-theanine biosynthesis in tea. Cortex with epidermis from root tissue was the main location of ethylamine. In summary, L-alanine is converted to L-theanine via L-glutamate not ethylamine in tea plants in vivo.

Automated summary

In tea plants, L-alanine is mainly located in vacuoles and mitochondria of root cells, while ethylamine is mainly found in the cortex with epidermis. Research discovered that in tea plants, L-alanine is converted to L-theanine via L-glutamate instead of ethylamine.