| Summary: | Tea (<i>Camellia sinensis</i>) is one of the most important cash crops in the world. Theanine, as an important amino acid component in tea, is a key quality index for excellent tea quality and high economic value. People increase theanine accumulation in tea mainly through the application of nitrogen fertilizer, shading and pruning. However, these methods are not effective. In this study, we treated tea buds with a 100 μM solution of GA<sub>3</sub> containing 1‰ tween-20, investigated the effects of GA<sub>3</sub> on theanine accumulation, bud yield, chlorophyll fluorescence parameters and expression level of theanine biosynthesis pathway genes in tea plant by qPCR, LC-MS/MS etc. Results showed that change trends of theanine and GA<sub>3</sub> was extremely positively correlated with each other. Exogenous GA<sub>3</sub> upregulated the expression level of theanine biosynthesis pathway genes, caused an increase of theanine content (mg·g<sup>-1</sup>) by 27% in tea leaves compared with Mock, and accelerated the germination of buds and elongation of shoots, which lead to a significant increase of tea yield by 56% (<i>w</i>/<i>w</i>). Moreover, the decrease of chlorophyll contents, photochemical quenching coefficient (<i>qP</i>) and relative electron transport rate (<i>rETR</i>) under GA<sub>3</sub> treatment suggested that GA<sub>3</sub> reduced photosynthesis in the tender tea leaves, indicating that the decline of carbon assimilation in tea plants was conducive to the nitrogen metabolism, and it was beneficial to the accumulation of theanine. This study provided a new technical and theoretical support for the precise control of tea quality components and phenophase.
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