‘Ziyan’ is a novel anthocyanin-rich tea cultivar with dark purple young shoots. However, how its anthocyanin accumulation is affected by environmental factors, such as ultraviolet (UV), remains unclear. In this study, we observed that UV light treatments stimulated anthocyanin accumulation in ‘Ziyan’ leaves, and we further analyzed the underlying mechanisms at gene expression and enzyme activity levels. In addition, the catechins and chlorophyll contents of young shoots under different light treatments were also changed. The results showed that the contents of total anthocyanins and three major anthocyanin molecules, i.e., delphinidin, cyanidin, and pelargonidin, were significantly higher in leaves under UV-A, UV-B, and UV-AB treatments than those under white light treatment alone. However, the total catechins and chlorophyll contents in these purple tea plant leaves displayed the opposite trends. The anthocyanin content was the highest under UV-A treatment, which was higher by about 66% than control. Compared with the white light treatment alone, the enzyme activities of chalcone synthase (CHS), flavonoid 3′,5′-hydroxylase (F3′5′H), and anthocyanidin synthase (ANS) under UV treatments increased significantly, whereas the leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) activities reduced. There was no significant difference in dihydroflavonol 4-reductase (DFR) activity under all treatments. Comparative transcriptome analyses unveiled that there were 565 differentially expressed genes (DEGs) of 29,648 genes in three pair-wise comparisons (white light versus UV-A, W vs. UV-A; white light versus UV-B, W vs. UV-A; white light versus UV-AB, W vs. UV-AB). The structural genes in anthocyanin pathway such as flavanone 3-hydroxylase (F3H), F3′5′H, DFR, and ANS, and regulatory gene TT8 were upregulated under UV-A treatment; F3′5′H, DFR, ANS, and UFGT and regulatory genes EGL1 and TT2 were upregulated under UV-AB treatment. However, most structural genes involved in phenylpropanoid and flavonoid pathways were downregulated under UV-B treatment compared with control. The expression of LAR and ANR were repressed in all UV treatments. Our results indicated that UV-A and UV-B radiations can induce anthocyanin accumulation in tea plant ‘Ziyan’ by upregulating the structural and regulatory genes involved in anthocyanin biosynthesis. In addition, UV radiation repressed the expression levels of LAR, ANR, and FLS, resulting in reduced ANR activity and a metabolic flux shift toward anthocyanin biosynthesis.

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.

Cadmium (Cd) is highly toxic and not easily degradable. It damages plant growth and results in large-scale economic losses. The present study explored the feasibility of using melatonin to alleviate Cd toxicity, and to reduce Cd accumulation in tea seedlings cultivated in Cd-contaminated soil. Exogenous melatonin, especially at 150 μM, promoted tea seedling growth under Cd stress, and increased the photosynthetic pigment by 16% and soluble protein content by 5%. Furthermore, melatonin effectively increased the activities of superoxide dismutase (SOD), and peroxidase (POD) by 21 and 31%, respectively, contributed to a decrease of the malondialdehyde (MDA) by 2% and the Cd content in leaves by 52%. Furthermore, soil enzyme activities were enhanced, including acid phosphatase (ACP), urease (UE), soil sucrase (SC), and soil catalase (CAT), by 11, 70, 1, and 18%, respectively, along with a pH reduction and available Cd content increase, after melatonin application. Taken together, our results provide evidence that melatonin lessens the adverse Cd effects on tea seedlings’ physiology, mainly through enhancing the antioxidant capacity of the plants and soils to scavenge reactive oxygen species (ROS) upon Cd exposure. Therefore, melatonin may be used as a modulator to alleviate Cd-induced toxicity in tea seedlings, thereby resulting in healthier tea plant growth.

(1) Background: Anthocyanins, the main pigments in plants, are influenced by both temperature and photoperiod. However, the specific mechanisms underlying anthocyanin accumulation in tea plants in response to these two environmental factors remain unclear. (2) Methods: This study subjected potted ‘Ziyan’ tea plants to four types of day-length and temperature treatments (HL (28 °C, 16 h), HS (28 °C, 8 h), LL (18 °C, 16 h), and LS (18 °C, 8 h)), and then conducted targeted metabolomic and transcriptomic analyses of the samples. (3) Results: Long photoperiods and low temperatures both promoted anthocyanin accumulation in the new shoots of the tea plants. Furthermore, the enhancing effects of these two environmental factors on anthocyanin accumulation are additive and exhibit interactive effects. Through a combined analysis of metabolomics and transcriptomics, five key differentially accumulated metabolites (DAMs) and twenty-two key differentially expressed genes (DEGs) were identified, the latter being found to participate in the regulation of anthocyanin biosynthesis pathways under varying light and temperature conditions. In summary, extended photoperiods primarily increase the content levels of ten metabolites, including cyanidin and naringenin-7-O-glucoside, by upregulating CHS, F3H, and ANS genes. In contrast, low temperatures primarily enhance the synthesis of seven anthocyanins, including cyanidin and cyanidin-3-O-rutinoside, by upregulating the ANS and UFGT genes. (4) Conclusions: Collectively, the differences in the expression levels of CHS, F3H, ANS, and UFGT might be responsible for ‘Ziyan’ tea plants’ purple shoot coloration, providing important data towards the discovery of candidate genes and molecular bases controlling the purple leaves of these tea plants under varied photoperiods and temperatures.

Nitrogen (N) is a key regulator in the growth of tea plants and the synthesis of amino acids (AAs) and related secondary metabolites, thus affecting the yield and quality of tea leaves. Increased N fertilization significantly improves the yield and quality of tea plants, but applying excess nitrogen wastes resources and causes pollution problems. Herein, we employed morphological, physiological, metabolomic, and RNA-seq methods to study the response of ‘Ziyan’ roots to high N. High N supply induced an increase in arginine (Arg), asparagine (Asn), and glutamine (Gln) in roots and simultaneously decreased sucrose, polyphenols, and caffeine contents. High N reduced the length, volume, number, and activity of the roots by 10.63%, 25.00%, 26.95%, and 14.50%, respectively, which inhibited ‘Ziyan’ root growth, probably by disturbing the regulation of carbon and nitrogen metabolism in the tea plant. According to the Kyoto Encyclopedia of Genes and Genome (KEGG) enrichment analysis, AAs, flavonoids, and flavonol-related pathways were relatively active after supplying high N. In addition, the transcriptome analysis identified NRT1/PTR and GOGAT as key genes, and the transcription factors (e.g., AP2/ERF, MYB, and WRKY) and auxins were actively involved in the high N stress response of ‘Ziyan’ roots. These findings will help us understand the adaptive mechanism of high N supply in tea tree roots and provide a reference for guiding the fertilization of ‘Ziyan’ 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.