Varietal Differences in the Environmental Behavior of 14C-Caffeine in Tea Plants: Accumulation, Subcellular Distribution, and Metabolism

Caffeine contamination in water sources raises concerns about its transfer to agricultural products and potential risks to human health through the food chain. Despite these concerns, limited research has focused on the accumulation and distribution of exogenous caffeine in tea plants. This study explored the uptake, translocation, targeted accumulation, subcellular distribution, and preliminary metabolism of ¹⁴C-labeled caffeine in a hydroponic tea seedling system. After 192 h of cultivation, more than 83.8% of the caffeine had been removed from the nutrient solution. Within the plants, ¹⁴C-caffeine and its metabolites predominantly accumulated in the roots. Subcellular analysis indicates that in root cells, ¹⁴C was mainly distributed in the soluble fraction, cell walls, and plastids, while in shoot cells, it was concentrated in the soluble fraction and cell walls. Metabolic profiling reveals distinct varietal differences: in Longjing 43 tea seedlings, ¹⁴C was predominantly present as the caffeine parent compound, whereas in Jiaming No. 1 tea seedlings, ¹⁴C was found both as the parent compound and as its metabolite, xanthine. This study revealed differences in the uptake, translocation, and metabolism of exogenous caffeine among different tea plant varieties, providing broader insights into the impact of caffeine pollution on agricultural ecosystems.