The concentrations of free amino acids (AA) and polyphenols (PP) are important determinants of green tea quality. Levels of AA and PP are governed interactively by nitrogen (N) supply and carbon (C) status, so the impact of C/N allocation on green tea quality was investigated in saplings 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 concentrations of AA, PP and soluble sugars. Concentrations of AA increased with increasing N supply, and the AA profile was shifted towards AA characterised by low C/N ratios (arginine, glutamine) and away from theanine, the unique non-protein AA that is abundant in Camellia sinensis. High N supply significantly reduced the concentrations of PP in young shoots, and was accompanied by lower levels 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 depended strongly on N status, and the balance shifted toward increasing synthesis of AA associated with enhanced growth, while investment of C in secondary metabolites did not change proportionally under the condition of ample N supply.

The quality of green tea is highly dependent on the concentration of free amino acids, whose profile is dominated by the unique amino acid theanine (N 5 -ethyl-glutamine). A high quality is associated with a high amino acid-to-catechin ratio, but previous results indicated that excessive chloride (Cl -) supply is detrimental for amino acid accumulation. Several experiments were conducted to investigate the effect of chloride on growth and concentrations of free amino acids in young tea plants. Soil-grown tea plants supplied with different levels of potassium (K) as K 2 SO 4 or KCl exhibited increased concentrations of free amino acid in young shoots only when supplied with K 2 SO 4 , and the negative effect of KCl supply was mainly due to a reduced concentration of theanine. Concentrations of other nutrients in plant tissues were not influenced. The uptake of Cland its interaction with nitrogen (N) uptake were further investigated in a second experiment, in which soil-cultivated tea plants were supplied with varying amounts of Cl -. Chloride application reduced yield of young shoots, and severity of leaf damage was related to the con-centration of Clin leaves. Nitrogen uptake was reduced by Claddition. To verify whether the decrease of free amino acids was simply a result of inhibited NO À 3 assimilation, a third experiment was conducted, in which tea plants were NH 4 -fed in the absence or presence (equivalent to the NH 4 concentration) of Cl -. Again, concentrations of theanine and total free amino acids in young shoots were reduced by Clsupply, but changes of the free-amino acid pool did not contribute to the maintenance of charge balance. However, concentration of theanine in roots, where it is synthesized, was not influenced by Cl -. Total N concentrations of roots and mature leaves, uptake rate of NH 4 , and activity of glutamine synthetase in fibrous roots and young leaves were all unaffected by Clas well. It is suggested that translocation of theanine from root to shoot and its catabolism in young shoots might be influenced by Cl -.