Review: the effect of light on the key pigment compounds of photosensitive etiolated tea plant

Abstract

Background Light is the ultimate energy source of plant photosynthesis, which has an important impact on the growth, development, physiology and biochemistry of tea plant. Photosensitive etiolated tea plant belongs to a kind of colored leaf plant, which is a physiological response to light intensity. Compared with conventional green bud and leaf of tea plant, the accumulation of pigment compounds (chlorophyll and carotenoids, etc.) closely related to a series of reactions of photosynthesis in photosensitive etiolated tea plant is reduced, resulting in the difference of leaf color of tea. This specific tea resource has high application value, among which high amino acid is one of its advantages. It can be used to process high-quality green tea with delicious taste and attractive aroma, which has been widely attention. The mechanism of the color presentation of the etiolated mutant tea leaves has been given a high topic and attention, especially, what changes have taken place in the pigment compounds of tea leaves caused by light, which makes the leaves so yellow. At present, there have been a lot of research and reports. Purpose of the review We describe the metabolism and differential accumulation of key pigment compounds affecting the leaf color of photosensitive etiolated tea that are triggered by light, and discuss the different metabolism and key regulatory sites of these pigments in different light environments in order to understand the “discoloration” matrix and mechanism of etiolated tea resources, answer the scientific question between leaf color and light. It provides an important strategy for artificial intervention of discoloration of colored tea plant. Conclusion The differential accumulation of pigment compounds in tea plant can be induced phytochrome in response to the change of light signal. The synthesis of chlorophyll in photoetiolated tea plants is hindered by strong light, among which, the sites regulated by coproporphyrinogen III oxidase and chlorophyllide a oxidase is sensitive to light and can be inhibited by strong light, resulting in the aggravation of leaf etiolation. The phenomenon can be disappeared or weakened by shading or reducing light intensity, and the leaf color is greenish, but the increase of chlorophyll-b accumulation is more than that of chlorophyll-a. The synthesis of carotenoids is inhibited strong light, and high the accumulation of carotenoids is reduced by shading. Most of the genes regulating carotenoids are up-regulated by moderate shading and down-regulated by excessive shading. Therefore, the accumulation of these two types of pigments in photosensitive etiolated tea plants is closely related to the light environment, and the leaf color phenotype shape of photosensitive etiolated tea plants can be changed by different light conditions, which provides an important strategy for the production and management of tea plant.

Untargeted Metabolomics and Transcriptomics Reveal the Mechanism of Metabolite Differences in Spring Tender Shoots of Tea Plants of Different Ages

“…As an important raw material for tea processing, the content and composition of the metabolites in the tender shoots are the decisive factors of tea quality [ 11 ]. The quality-related metabolites in the tender shoots of tea plants mainly include catechins, flavonoids and their glycosides, amino acids, alkaloids, nucleotides, saccharides, and organic acids [ 12 , 13 ]. Catechins, flavonoids and their glycosides, and alkaloids are mainly bitter and astringent, while amino acids, nucleotides, and saccharides are mainly umami and sweet [ 14 ].…”

“…In addition, the plant’s age changes the metabolism of the phenols and amino acids in the tea leaves, which is regulated by key genes in their biosynthesis pathways [ 20 ]. Although some effects of plant age on tea quality have been reported, in contrast to the depth of research regarding relevant factors, such as environment and processing [ 13 , 21 , 22 ], research on the influence mechanism of plant age on the metabolites of the tender shoots of tea is seriously lagging. The main reason is that the sample materials from the same tea cultivar but with plants of different ages planted in the same environment and under the same management mode are very difficult to find, which has restricted the exploration of its mechanism.…”

Mechanism underlying the carotenoid accumulation in shaded tea leaves

“…There have been relatively few studies on the regulation of carotenoids in tea leaves. Similar to the carotenoid regulation in other plants ( Fu et al, 2019 ), it was demonstrated that light also influences the synthesis and accumulation of tea pigments ( Yue, Wang, & Yang, 2021 ). The shading of commonly grown green tea varieties will lead to the increased intensity of green coloration on leaves ( Chen et al, 2021 ).…”

“…Previous studies revealed that shading can promote the accumulation of carotenoids in tea leaves ( Sonobe et al, 2018 , Yue et al, 2021 ), but the underlying regulatory mechanism is still unclear. In this study, shading treatment in tea gardens and dark treatment indoors was applied.…”

Effects of light intensity on the growth of Polygala fallax Hemsl. (Polygalaceae)

“…plants prefer weaker light intensity and thus may accumulate more chlorophyll under shaded conditions. In tea plants, chlorophyll and carotenoid synthesis-related genes were downregulated in response to strong light but were upregulated in response to shade or reduced light intensity (Yue et al, 2021). Genes involved in the biosynthesis of chlorophyll in P. fallax Hemsl.…”