Abstract: As the main characteristic metabolite in tea plants, caffeine contributes to tea quality and flavor formation and is a natural functional component. Its function, distribution, biosynthetic pathway and related key genes in tea plants have been basically identified, but its synthetic site at subcellular level needs to be further clarified. In this study, ‘Baijiguan’ and its half-sib offsprings with different etiolated leaves were used as materials. The results of transmission electron microscopy show that the chloroplast structures in etiolated leaves were damaged or destroyed, which was closely related to the SPAD value and leaf phenotype. High performance liquid chromatography (HPLC) was used to determine the caffeine content. It was found that there was still a large amount of caffeine accumulation in etiolated leaves, even more than in normal green leaves. Then, the expression and location of CsTCS1, a key gene involved in caffeine synthesis, were studied by real-time PCR, in-situ hybridization and subcellular localization. It was shown that the expression level of CsTCS1 in different etiolated leaves varied obviously. But the expression site was basically consistent, mainly distributed in the nucleus and cytoplasm of palisade tissues. These results reveal that the synthetic site of caffeine at subcellular level in tea leaves were mainly nucleus and cytoplasm, but not chloroplasts.

Key words: tea plants, etiolated leaf, caffeine, synthetic site, subcellular level