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

Jianwei Liu,Hanhan Fang,Jianyun Ruan,Qunfeng Zhang,Meiya Liu

doi:10.3389/fpls.2021.756433

Abstract

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.

Highlights

MATERIALS AND METHODSThe growth and quality of tea are strongly influenced by the nitrogen supply, which influences metabolites, enzymes, and genes (Bryan, 2008)
We found that most genes involved in secondary metabolism correlated negatively with amino acids in young shoots (Supplementary Figure 2), which suggests that genes related to secondary metabolism could be inhibited as nitrogen metabolism increases under high nitrogen supply than under low nitrogen supply
We noted that the contents of some sugars increased in shoots but decreased in mature leaves and roots, which suggests that C is transported from the source to the sink (Figure 2). we find that several carbohydrates involved in plant cell wall biosynthesis, such as galactose, arabinose, and xylose, were significantly increased in young shoots under high nitrogen supply versus under low nitrogen (Figure 2 and Supplementary Table 1)

Summary

Introduction

MATERIALS AND METHODSThe growth and quality of tea are strongly influenced by the nitrogen supply, which influences metabolites, enzymes, and genes (Bryan, 2008). Quality green tea is characterized by high contents of free amino acids with appropriate concentrations of catechins and caffeine. Li et al (2017) investigated transcriptomes in two tea varieties using RNA-seq and the contents of amino acid under different N treatments They identified 196 and 29 differentially expressed genes in roots and leaves, respectively. We hypothesized the accumulation of quality-related compounds in young tea shoots was highly affected by the metabolism and the expression of key genes in mature tea leaves and roots, especially under different N supply conditions. We hope that this work will provide a framework for an improved understanding of the molecular and metabolite mechanisms of the accumulation of quality-related compounds in young shoots affected by N supply, as well as metabolism in roots and mature leaves

Results

Discussion

Conclusion