Molecular Plant Breeding 2025, Vol.16, No.4, 221-230 http://genbreedpublisher.com/index.php/mpb 222 2.2 Key metabolic pathways involved in bud formation The formation and growth of buds rely on multiple metabolic pathways, among which plant hormones and secondary metabolism are the most important. Hormones such as auxin, gibberellin, abscisic acid, cytokinin and jasmonic acid jointly regulate the expression of related genes, thereby controlling the dormancy, activation and growth of buds (Hao et al., 2018). Among them, the regulatory genes of gibberellin and abscisic acid play a very important role in the process of bud transformation from dormant to active (Yue et al., 2018). Meanwhile, the synthesis of some secondary metabolites, such as gallic acid (GA) and tea polyphenols, is also regulated by hormones, and these substances can affect the quality and flavor of the buds (Shi et al., 2025). In addition, sugar metabolism, photosynthesis, and antioxidation-related metabolic activities also play a role in the growth of buds (Tong et al., 2018; Tang et al., 2023). 2.3 Environmental sensitivity of bud quality traits The quality of buds, such as the content of amino acids, tea polyphenols and caffeine, is particularly sensitive to the environment. Changes in conditions such as light, temperature and moisture can affect hormone signaling, expression of transcription factors and various metabolic pathways, thereby altering the growth rate of buds and accumulation of quality components (Chen et al., 2023b; Liu et al., 2023). For instance, different shading and watering frequencies can cause changes in amino acids and secondary metabolites in buds, thereby affecting the flavor and economic value of tea (Zhang et al., 2025a). In addition, the quality of buds is also influenced by genetic factors. There will be differences among different varieties, and it is also affected by seasonal changes. That is to say, the final quality of tea buds is determined by both genes and the environment. 3 Role of Light and Shading in Tea Plant Physiology 3.1 Effects of light intensity on photosynthesis and secondary metabolites The intensity of light directly affects the photosynthesis effect of tea plants and also influences the accumulation of various metabolites in tea leaves. Appropriate shading can increase the chlorophyll in the leaves, make the leaf color greener and improve the quality of tea (Figure 1) (Chen et al., 2021; Elango et al., 2023). Research has found that after shading, the content of amino acids (such as theanine) and caffeine in tea plants will increase, while polyphenols like epicatechin and epigallocatechin will decrease. This change is conducive to enhancing the freshness and flavor of tea (Liu et al., 2018; Kc et al., 2021; Kc et al., 2022). In addition, shading can also inhibit the synthesis of some substances such as flavonoids and lignin, thereby improving the taste of tea (Li et al., 2020; Teng et al., 2020; Zhang et al., 2020). Light changes can also affect many metabolic pathways and gene expressions, such as nitrogen metabolism, glucose metabolism and the synthesis of photosynthetic pigments. 3.2 Types of shading materials and their impacts Different shading materials have different effects on tea plants. For instance, black nets, blue nets, red nets, straw nets, etc. have all been used. Studies have found that using double-layer shading nets (such as those 50 cm high) can significantly increase the amino acid content in tea, reduce polyphenols, and also improve the environment of tea gardens, such as cooling and maintaining soil moisture (Ge et al., 2024). The blue net and the red net have better effects than the black net in promoting bud quantity and yield, but they have similar effects in reducing bitter substances (Fang et al., 2022). Different shading materials can also change the quality of light, such as the ratio of red light to far-red light, which can also affect the physiological activities of tea plants. 3.3 Adaptive responses of tea plants to light reduction Tea plants have many levels of responses to reduced light. Shading will increase the accumulation of chlorophyll and carotenoids, make the leaves greener and enhance the photosynthetic capacity (Chen et al., 2021; Yue et al., 2021). Shading also regulates the expression of some key genes, such as CsPOR, CsHY5, CPOX and SGR. These genes affect the synthesis and degradation of chlorophyll, and also change the distribution of amino acids and polyphenols (Chen et al., 2022; Han et al., 2023). In addition, shading can also cause changes in the structure of leaves, such as thinning of epidermal cells and reduction of downy hairs. At this time, the expression of some genes related to hair (such as CsCPCs) will increase, indicating that tea plants adapt to the weak light environment through both morphological and gene regulation (Jiang et al., 2020; Wang et al., 2023; Wakamatsu et al., 2024).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==