Objective To study the characteristics of sugar accumulation in various source-sink organs during the growth and development of Camellia drupifera and its relationship with the enzymatic activities related to sugar metabolism for providing a basis for further improving the theory of sugar accumulation in characteristic oil tea camellia varieties in the South China region.

Method The ¹³C isotope pulse labeling method was employed to mesure the ¹³C content in various source and sink organs at different developmental stages of C. drupifera. Concurrently, the non-structural carbohydrate (NSC) content, sugar component characteristics, and related enzyme activities in the respective organs during the corresponding periods.

Result 1) After the stabilization of the transport of ¹³C-labeled photosynthates, during the early developmental stages, these products were primarily accumulated in the eaves, while in the later stages, the seed kernels gradually became the central location for assimilate distribution and accumulation. 2) The soluble sugar content in various organs was mainly observed in the order of peels > seeds > leaves, while starch content showed the order of leaves > seeds > peels. 3) The activities of SPS and SS-II were positively correlated with the soluble sugar content in leaves, peels, and seeds. B-AI primarily played a role during the later stages of development, with peak activities in seed kernels occurring in August and October. In leaves, NI served as the primary sugar-converting enzyme, with activity ranging between 50 and 60 U·g⁻¹. In seed kernels, the activities of S-AI and NI were roughly similar, with S-AI primarily acting during the early developmental stages, while NI was more active during the later stages of development.

Conclusion In C. drupifera , during the early stages of development, photosynthates primarily accumulate leaves of the source organ,. As fruit grows, the seed kernels gradually becomes the central location for assimilate distribution. Regarding sugar accumulation, during the early developmental stages, seed kernels primarily accumulates fructose and glucose, while in the later stages of development, they mainly accumulate sucrose. In the later stages of development, the sucrose transported to the peels will be decomposed into fructose and glucose, and the peels continues to thicken and extend, and continue to complete lignification. At this stage, there is intense competition for nutrients between the peels and seeds, resulting in the phenomenon of thick peels and large fruit size. The functions of SPS and SS-II complement each other and simultaneously influence sugar accumulation in C. drupifera , with SS-II being the key enzyme for sugar accumulation. This may be the primary reason for differences in sugar content among various source-sink organs. Sugar accumulation in C. drupifera is regulated comprehensively by sugar metabolism-related enzymes. NI serves as the primary conversion enzyme in the leaves, while S-AI and NI play roles in seed kernels during the early and late developmental stages, respectively. In peels, sucrose conversion primarily depends on S-AI. B-AI primarily functions in the later stages of development but with relatively low activity and limited conversion capacity.