Table_2_Accumulation of Amino Acids and Flavonoids in Young Tea Shoots Is Highly Correlated With Carbon and Nitrogen Metabolism in Roots and Mature Leaves.DOCX

The quality of tea product and the metabolism of quality-related compounds in young shoots are significantly affected by the nitrogen(N) supply. However, little is known of the metabolic changes that take place in tea roots and mature leaves under different supplies, which has a large effect on the accumulation of quality-related compounds in young shoots. In this study, young shoots, mature leaves, and roots under different N conditions were subjected to metabolite profiling using gas chromatography and ultraperformance liquid chromatography, coupled with quadrupole time-of-flight mass spectrometry. The contents of free amino acids (e.g., theanine and glutamate) involved in N metabolism were significantly greater under high N than under low N, while a high N supply reduced soluble sugars (e.g., glucose) in all three tissues. Organic acids (e.g., malate, fumarate, α-ketoglutatare, and succinate) involved in tricarboxylic acid cycle remarkably increased as the nitrogen supply increased, which confirms that carbon (C) allocation was restricted by increasing the nitrogen supply, especially in mature leaves. RT-PCR results indicated that gene expression related to nitrogen assimilation significantly increased in roots with increasing nitrogen supply, which had a significant positive relationship with the level of free amino acids in young shoots. In addition, the expression of most genes involved in flavonoid synthesis was significantly upregulated under conditions of low nitrogen supply relative to high nitrogen supply in young shoot and roots. These data suggest that enhanced assimilation of N in tea roots and the coordinated regulation of C (sugars, organic acids, and flavonoids) and N(amino acids) in mature leaves can lead to a high accumulation of amino acids in young shoots. Furthermore, as the N supply increased, more C was partitioned into compounds containing N in mature leaves and roots, resulting in a decrease in flavonoids in young shoots. In conclusion, the accumulation of amino acids and flavonoids in young tea shoots is highly correlated with carbon and nitrogen metabolism in roots and mature leaves.

茶叶产品品质与新梢中品质相关化合物的代谢过程，显著受氮素（N）供给水平的影响。然而，目前对于不同氮素供给下茶树根系与成熟叶片中的代谢变化仍知之甚少，而这些代谢变化又会显著影响新梢中品质相关化合物的积累。本研究针对不同氮素条件下的新梢、成熟叶片及根系，采用气相色谱（gas chromatography, GC）-超高效液相色谱（ultraperformance liquid chromatography, UPLC）串联四极杆飞行时间质谱（quadrupole time-of-flight mass spectrometry, QTOF-MS）进行代谢组学分析。结果显示，参与氮代谢的游离氨基酸（如茶氨酸、谷氨酸）含量在高氮条件下显著高于低氮条件；而高氮供给则会降低三种组织中的可溶性糖（如葡萄糖）含量。参与三羧酸循环（tricarboxylic acid cycle, TCA循环）的有机酸（如苹果酸、延胡索酸、α-酮戊二酸及琥珀酸）含量随氮素供给增加而显著升高，这证实氮素供给提升会限制碳（C）的分配，尤其在成熟叶片中表现明显。逆转录PCR（RT-PCR）结果表明，随着氮素供给增加，茶树根系中与氮同化相关的基因表达量显著上调，且该表达水平与新梢内游离氨基酸含量呈显著正相关。此外，与类黄酮合成相关的多数基因，在新梢与根系的低氮条件下，其表达量显著高于高氮条件。上述数据表明，茶树根系中氮同化作用的增强，以及成熟叶片内碳（糖类、有机酸与类黄酮）与氮（氨基酸）代谢的协同调控，可促使新梢内氨基酸大量积累。此外，随着氮素供给提升，成熟叶片与根系中更多的碳会被分配至含氮化合物中，进而导致新梢内类黄酮含量下降。综上，茶树新梢中氨基酸与类黄酮的积累，与根系及成熟叶片的碳、氮代谢密切相关。