Metabolic profiling reveal changes in shoots and roots of nitrogen-deficient tea plants (Camellia sinensis cv. Jinxuan)

Abstract

Tea plants require high levels of nitrogen for optimal growth. However, delayed or insufficient nitrogen supply often induces nitrogen deficiency stress. This stress can adversely affect the plant's growth, development, and metabolic processes. Therefore, studying how tea plants respond to nitrogen deficiency conditions is crucial for enhancing our understanding and management of their growth environment. In this study, we utilized High-Performance Liquid Chromatography (HPLC), Gas Chromatography-Mass Spectrometry (GC–MS), and Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS) techniques to analyze the non-volatile and volatile components of both shoots and roots of the 'Jing Xuan (JX)' tea variety under nitrogen deprivation for 30 days (Nd). The results revealed that nitrogen deprivation led to a deceleration in shoot growth of 'JX', accompanied by reduced chlorophyll and water-soluble extract contents, with nitrogen accumulating predominantly in the roots. Significant decreases were observed in caffeine content in shoots and in the total amounts of theanine and catechins in both shoots and roots, while epigallocatechin gallate (EGCG) accumulation increased in shoots. Moreover, we identified 65 volatile components in shoots, including a notable decrease in floral and fruity compounds such as trans-β-Ionone, Geranylacetone, and α-Ionone. The biosynthesis of amino acids and phenylpropane metabolism are more active pathways under nitrogen stress. Nitrogen deficiency led to reduced levels of amino acids, carboxylic acids, flavonoids, steroids, and their derivatives in roots, with the most notable decline observed in carboxylic acids, typified by Leucine, l-Aspartate, and l-histidine. In contrast, shoots accumulate carbohydrates and phenolic compounds, mainly sucrose. Additionally, metabolites such as Myristic acid and 3-Dehydroshikimate could be a critical indicator of stress levels. These findings enhance our understanding of tea plant growth and metabolism under nitrogen deficiency, providing valuable insights for breeding nitrogen-efficient tea varieties.