Department of Plant Sciences

Concentration of free amino acids (AA) and polyphenols (PP) represent important components of green tea quality. As the accumulation of AA and PP, representing primary and secondary metabolites in tea plants, respectively, is governed interactively by the nitrogen (N) supply and carbon (C) status, providing an ideal system for studying the impact of C/N allocation on green tea quality. Saplings were cultivated hydroponically with 0.3, 0.75, 1.5 or 4.5 mmol L-1 N. Activities of glutamine synthetase (GS), phenylalanine ammonia lyase (PAL), and phosphoenolpyruvate carboxylase (PEPC) were determined, as were the concentrations of AA, PP and soluble sugars. Concentrations of free amino acids increased with enhancing N supply, but the AA profile was shifted towards AA characterised by low C/N ratios (arginine, glutamine) instead of theanine, a unique non-protein AA dominating in C. sinensis. High N supply significantly reduced the concentrations of PP in young shoots, which was accompanied by decreasing availability of carbohydrates (soluble sugars). Analysis of the C and N status and selected enzyme activities, combined with path coefficient analysis of variables associated with C and N metabolism, demonstrated increasing deviation of C flux to AA under abundant N supply. Accumulation of AA and PP strongly depended on the N status and the balance was shifted toward increasing synthesis of AA associated with enhanced growth, while investment of C in secondary metabolites is not changing proportionally under the condition of ample N supply. While the resulting higher AA/PP ratio is principally associated with improved green tea quality, the increasing fraction of AA of low C/N ratio, namely arginine, is counterproductive in this respect.