夏季遮阴对茶树茶氨酸合成及其代谢相关基因表达的影响(英文)

Effect of Shade Treatment in Summer on the Expression of Genes Related to Theanine Biosynthesis in Tea Plants(Camellia sinensis)

为了研究夏季遮阴对茶树茶氨酸代谢途径的影响及对茶树内含物品质的改良作用,本研究以多年实生茶树为研究对象,利用Western blotting检测了夏季遮阴对茶树不同部位中茶氨酸合成酶(TS)、谷氨酰胺合成酶(GS)蛋白表达的影响,确定遮阴有利于嫩叶中TS的表达;随后利用实时荧光定量PCR检测方法探索了茶氨酸代谢途径中相关基因:TS、GS、谷氨酰胺α-酮戊二酸氨基转移酶(GOGAT)、谷氨酸脱氢酶(GDH)以及与氮素吸收和转化密切相关的亚硝酸还原酶(NiR)、精氨酸脱羧酶(ADC),在老、嫩叶中及不同遮阴时期的表达情况。结果表明遮阴有利于嫩叶中TS基因的表达,与叶部氨的再同化作用密切相关的GS、GOGAT和GDH基因均在老叶中有明显增加,而与硝基氮代谢相关的NiR、ADC基因表达在老叶与嫩叶中均明显下降。利用HPLC对遮阴后嫩叶中游离氨基酸含量的检测结果表明,遮阴明显促进茶叶部游离氨基酸总量的提高,其中贡献率最大是茶氨酸。本研究从分子水平上解析了遮阴促进茶叶部茶氨酸积累的调控机制,为今后夏秋茶栽培措施改良和品质改善提供理论基础。

The shade can effectively improve the quality of tea（ Camellia sinensis） by causing an increase in the concentration of theanine, the main compound that contributes to the fresh and brisk taste of tea leaves. We analyzed the influence of shade on theanine biosynthesis in relation to the expression of genes related to theanine synthesis in tea leaves during summer. Our data reveal that shade has a notable effect on the level of both theanine and total free amino acids in young leaves. The results of qPCR and western blot analysis suggest that these effects are mainly brought about via an increase in the mRNA expression of TS and promotion of TS protein synthesis. The qPCR results also suggest that the mRNA expression of all the genes related to the theanine pathway in the leaves, including glutamine synthetase （GS）, glutamate dehydrogenase （GDH）, glutamine 2- oxoglutarate amino-transferase （ GOGAT ）, nitrite reductase （ NiR ）, arginine decarboxylase （ ADC ）, are significantly affected by shade. However, from two different expression patterns, the GS/GOGAT pathway is triggered by shade and members of this pathway show higher expression in old leaves, which reassimilate more NH4＋ to supply more amides to young leaves. The gene expression of NiR and ADC was markedly lower in both the old and young leaves from the shaded plants, which suggests that nitric nitrogen metabolism might be inhibited by shade treatment. Thus, shade treatment can increase the content of free amino acids especially theanine in tea leaves and improve the effective utilization of summer tea.