Dynamic changes of main carbon and nitrogen metabolites in tea plants (Camellia sinensis L.) shoots under shading and re-lighting

【Objective】To explorethe dynamic changes of the quality biochemical components and main carbon and nitrogen metabolites of tea plants under shading and relighting,so as to provide a theoretical basis for the selection of the suitability of fresh leaves in process of shading and relighting.【Method】A field experiment was carried out with Huangjincha-1,Xiangfeicui and Jinxuan Camellia sinensis L. cultivar as test materials under 80% and 95% shading treatments. And one bud and two leaves were taken before shading,on the 12^nd day of shading,and on the 1^st, 3^rd,and 5^th days after relighting todetectsoluble sugar,flavonoids,caffeine,amino acid components and catechin components to analyze the carbon and nitrogen metabolites and quality changes of fresh leaves under shading and re-lighting.【Result】Under shading treatment,the content of tea polyphenols of the three tea plant cultivars decreased significantly(P<0.05,the same be-low). The ratio of tea polyphenol to amino acid of Huangjincha-1 and Xiangfeicui decreased to 4-5,and the ratio of epicatechins or ester catechins decreased to 0.23-0.42. The tea polyphenol/amino acid ratio and chlorophyll a/b values of Huangjincha-1 under 80% shading treatment(HJC-80%) were significantly lower than those under 95% shading treatment;Xiangfeicui and Jinxuan under 95% shading treatment (XFC-95% and JX-95%),compared with 80% shading treatment(XFC-80% and JX-80%),their tea polyphenol/amino acid ratio and chlorophyll a/b were significantly decreased, and the contents of water extract and soluble sugar were increased,moreover,the catechin quality index of JX-95% was significantly higher than that of JX-80%. After re-lighting,the coefficient of variation of free amino acids is greater than that of tea polyphenols;the ratio of polyphenol to amino acid of Xiangfeicui and Jinxuan was greater than 7,and the quality index of catechins was higher than that before shading. During the process of shading and re-lighting,the content of water extracts,flavonoids and EGCG of the three cultivars reached the peak value on the 5^th re-lighting day. Under shading and re-lighting,the coefficients of tea polyphenols and free amino acids of Jinxuan werelower than those of Huangjin and Xiangfeicui. On the 12^nd day of shading,Xiangfeicui under the 95% shading treatment(XFC-95%) and Huangjincha under 80% shading treatment(HJC-80%) had the lowest content of main carbon metabolites and the highest content of main nitrogen metabolites.【Conclusion】Tea plants adjust carbon and nitrogen metabolism to adapt to environmental changes,there by chan-ging the suitability of fresh leaves. The fresh leaves of tea plants are more suitable for making famous and high-quality green tea under shading and in the early stage of relighting. In the later period of re-lighting,the fresh leaves of tea plants are more suitable for making high-quality black tea.