Currently, the effects of the differences between day and night temperatures (DIFs) on tea plant are poorly understood. In order to investigate the influence of DIFs on the growth, photosynthesis, and metabolite accumulation of tea plants, the plants were cultivated under 5 °C (25/20 °C, light/dark), 10 °C (25/15 °C, light/dark), and 15 °C (25/10 °C, light/dark). The results showed that the growth rate of the new shoots decreased with an increase in the DIFs. There was a downward trend in the photosynthesis among the treatments, as evidenced by the lowest net photosynthetic rate and total chlorophyll at a DIF of 15 °C. In addition, the DIFs significantly affected the primary and secondary metabolites. In particular, the 10 °C DIF treatment contained the lowest levels of soluble sugars, tea polyphenols, and catechins but was abundant in caffeine and amino acids, along with high expression levels of theanine synthetase (TS3) and glutamate synthase (GOGAT). Furthermore, the transcriptome data revealed that the differentially expressed genes were enriched in valine, leucine, and isoleucine degradation, flavone/flavonol biosyntheses, flavonoid biosynthesis, etc. Therefore, we concluded that a DIF of 10 °C was suitable for the protected cultivation of tea plants in terms of the growth and the quality of a favorable flavor of tea, which provided a scientific basis for the protected cultivation of tea seedlings.

Nitrogen (N) and selenium (Se) are beneficial for tea growth and tea quality; however, it is unknown how the combined application of N and Se affects tea quality and N uptake and utilization in tea plants. In the present study, a hydroponic experiment with three N levels (0, 2 and 4.5 mmol/L) and three Se levels (0, 0.3 and 3 mg/L) was carried out with ‘Chuancha No.2’ as the material, and the contents of tea polyphenols, amino acids and caffeine as well as the expression levels of genes related to N uptake and utilization in tea plants were tracked. The findings reveal that the contents of tea polyphenols, AAs and caffeine in new shoots were the highest when supplied with 0.3 mg/L Se and 4.5 mmol/L N, while the contents of total N, AAs and tea polyphenols in mature leaves were the highest at the concentrations of 3 mg/L Se and 2 mmol/L N. Se supply (0.3 and 3 mg/L) induced an increase in amino acid and tea polyphenol contents in tea shoots under N deficiency conditions, whereas total N content, tea polyphenols and AAs in mature leaves and total N content in tea roots decreased significantly. When supplied with N (2 mmol/L and 4.5 mmol/L), the contents of tea polyphenols and caffeine in new shoots first increased and then decreased with the increase in Se concentration, while the total N content in mature leaves and roots increased. In leaves, CsAMT1.1, CsAMT1.2 and CsAMT3.1 had similar trends, and their expression levels were remarkably upregulated when supplied with 0.3 mg/L Se or 2 mmol/L N, respectively; the expression level of CsGS1.1 was significantly induced by N and Se, while CsGS1.2 and CsTS1 were mainly induced by N. In roots, CsAMT1.1 could play a major role in N uptake under the combined application of N and Se; CsGS1.2 expression was significantly induced compared to CsGS1.1 under the combined application of N and Se. This study explored the potential of the interaction of Se and N to promote tea quality and N uptake and utilization in tea plants.

The purple-leaf tea cultivar ‘Ziyan’ is characterized by its high anthocyanin levels, which confer unique visual traits and health benefits. However, the effects of light quality on anthocyanin production remain poorly understood. This study explored the effects of red and blue light on anthocyanin biosynthesis in ‘Ziyan’, with white light as the control, using transcriptomic analysis, enzyme assays, and anthocyanin content measurements. The results showed that anthocyanin content increased under blue and red light, with blue light being the most effective, as the total anthocyanin content reached 81.79 mg/100 g FW, a 29.64% increase compared with white light. Delphinidin, cyanidin, and pelargonidin increased by 27.52%, 42.58%, and 102.72%, respectively. Transcriptome analysis showed red and blue light influenced photoreceptors and light signaling components, with decreased COP1 and increased SPA1 expression. Blue light upregulated key anthocyanin structural genes despite downregulating their transcription factors; it enhanced CHS, F3′H, F3′5′H, and ANS activities but decreased LAR and ANR activities, similar to the effect of red light. This research showed that the underlying mechanism may be achieved by coordinating light perception, gene expression, and enzyme activity. This study provides a theoretical basis for optimizing the light quality in purple tea plant cultivation.

Tea is a vital economic crop in China, with many anthocyanin-rich cultivars having been bred. Photoperiod is an important environmental factor that regulates anthocyanin production in plants. Nonetheless, the precise mechanisms by which photoperiod affects anthocyanin biosynthesis in tea plants remain unclear. In this study, the purple-leaf cultivar Camellia sinensis ‘Ziyan’ was exposed to three different photoperiods: 8 h/16 h (light/dark, short-day, SD), 14 h/10 h (light/dark, medium-day, MD), and 20 h/4 h (light/dark, long-day, LD). A comprehensive analytical approach, including transcriptomics, enzymology, and quantitative anthocyanin analysis, was used to uncover the molecular and biochemical processes regulating anthocyanin synthesis in purple-leaf tea plants grown under varying photoperiods. The results showed that the delphinidin, cyanidin, pelargonidin, and total anthocyanin contents in the long-day treatment were 178.10%, 92.37%, 50.40%, and 148.76% higher, respectively, than those in the short-day treatment. Under long-day conditions, all structural genes associated with anthocyanin synthesis were upregulated, and enzymatic activities related to anthocyanin synthesis were significantly increased. Furthermore, the regulatory genes (MYB1, MYB73, MYB111, MYB48, MYB75, MYB113, MYB5, MYB12, MYB5a, MYB5b, and WRKY41) were differentially expressed under short- and long-day treatments. These findings suggest that extended photoperiods activate the expression of structural genes through gene regulation and enhancement of enzymatic activity, thereby facilitating anthocyanin biosynthesis. This study provides novel insights into the photoperiodic regulation of anthocyanin biosynthesis in tea plants.

Anthocyanins are water-soluble flavonoid pigments that contribute to leaf coloration, tea quality, and have potential health-promoting properties. Purple-leaf tea plants have attracted significant interest due to their high anthocyanin levels; however, cultivar-specific evidence linking light intensity with pigment accumulation, enzyme activity, and transcriptional regulation in purple-leaf tea remains limited. In this study, the purple-leaf tea cultivar ‘Ziyan’ was exposed to three light intensity treatments: low (LL, 100 μmol·m⁻²·s⁻¹), medium (ML, 200 μmol·m⁻²·s⁻¹), and high (HL, 400 μmol·m⁻²·s⁻¹). Increasing light intensity resulted in deeper purple coloration and significantly higher anthocyanin accumulation. The contents of delphinidin, cyanidin, pelargonidin, and total anthocyanins under HL increased by 124.2%, 63.4%, 57.2%, and 105.9%, respectively, compared to the control. Activities of major biosynthetic enzymes (CHS, CHI, F3H, F3′H, F3′5′H, DFR, ANS) were enhanced under ML and HL, whereas ANR activity decreased. Transcriptome sequencing identified 1349 differentially expressed genes (DEGs) (404 up-regulated, 945 down-regulated) in the LL vs. HL comparison. Notably, TFBS motif enrichment analysis revealed that up-regulated DEGs were dominated by a single cohesive SPL/SBP regulatory module, while down-regulated DEGs partitioned into independent NAC, HSF, and EIL modules, suggesting a multi-layered transcriptional regulatory network governing light-responsive anthocyanin biosynthesis. Several transcription factors, including MYB44, MYB75, bHLH162, and WRKY40, were also identified as candidate regulators. These results indicate that increasing light intensity is associated with enhanced anthocyanin accumulation, accompanied by coordinated changes in phenotype, flavonoid metabolism, enzyme activities, and gene expression, providing evidence for a possible regulatory mechanism of light-responsive pigmentation in purple-leaf tea and a basis for cultivation optimization and molecular breeding.