Changes in targeted metabolites, enzyme activities and transcripts at different developmental stages of tea leaves: a study for understanding the biochemical basis of tea shoot plucking

Abstract

Standard plucking of fresh tea leaves is one of the major factors in determining tea quality, apart from processing conditions. Tea quality is a function of metabolite content and declines with leaf maturity. In this work, we studied the metabolic consequences of leaf maturity on tea leaf quality by metabolite profiling. Significant variation in metabolite levels was observed during tea leaf maturation. The concentration of catechin, epicatechin gallate, epigallocatechin gallate and total catechins decreased with leaf maturity while epicatechin and epigallocatechin showed reverse trend. A concentration dependent increase with leaf maturity was noted for cell wall-bound phenolics, which was predominated by gallic acid followed by trans p-coumaric acid. The relative abundance of monoterpenoids declined with leaf age while fatty acid derivative volatiles showed inverse trend. Activities of shikimate dehydrogenase and phenylalanine ammonia-lyase also decreased with leaf age. The transcript levels of flavone-3-hydroxylase and anthocyanidin synthase showed a significant positive correlation with total catechins content. Interestingly, accumulation of total catechin showed significant negative correlation with total fatty acid derivative volatiles, total wall-bound phenolics, chlorophyll and volatile benzenoids during leaf development. This suggests a possible alteration of carbon pool in tea leaf during maturation. We hypothesize that the declination of flavan-3-ols biosynthesis in mature leaves might lead to a shifting of carbon flow in the direction of linked metabolic pathway related to chlorophyll, wall-bound phenolics, benzenoids and fatty acids biosynthesis.