Revealing Summer Leaf Purpling Phenotype of Camellia sinensis cv. 'Longrui 1' with Untargeted Metabolomics

To elucidate the molecular mechanism underlying the seasonal variation in leaf color of the unique tea plan germplasm 'Longrui 1' (Camellia sinensis cv. 'Longrui 1', Lr1), the dynamic patterns and underlying mechanisms of the seasonal purple phenotype in 'Longrui 1', particularly regarding leaf coloration, quality components, and metabolic profiles, were systematically investigated. A combined approach of biochemical assays, untargeted and targeted metabolomics was employed, using the constitutively green cultivar 'Zhongcha 108' and the constitutively purple cultivar 'Zijuan' as controls. The results indicated that the young shoots of Lr1 transitioned from purple-green in spring to purple in summer, a process accompanied by a significant decrease (P<0.05) in the content of free amino acids and a significant increase (P<0.05) in total polyphenols and catechins. Untargeted metabolomics identified 116 common differentially expressed metabolites (DEMs) between the purple and green phenotypes, with flavonoids being the most predominant class (31 metabolites). Notably, Lr1 exhibited a unique metabolic reprogramming during its seasonal transition, characterized by the specific activation of pathways such as monoterpenoid biosynthesis. Further targeted quantitative approach revealed that the seasonal purpling of Lr1 was driven by an explosive accumulation of cyanidin and delphinidin-O-galactoside in summer, an accumulation pattern that stood in stark contrast to that of 'Zijuan', whose levels decreased in summer. In conclusion, this study demonstrated that the seasonal purpling of Lr1 was a dynamic response process mediated by the massive de novo synthesis of specific anthocyanins (particularly cyanidin), induced by environmental factors. Its metabolic regulatory model was fundamentally different from that of constitutively purple cultivars. This unique germplasm provides a valuable genetic resource and a theoretical basis for understanding the environmental adaptability of tea plants and for breeding novel specialty cultivars.