Comparative metabolomic analysis reveals the involvement of catechins in adaptation mechanism to cold stress in tea plant (Camellia sinensis var. sinensis)

Cold stress is a major environmental factor that affects tea production and quality. In this study, the global profiles of metabolites in response to cold acclimation (CA) of three tea plant cultivars with contrasting cold tolerances were investigated using UPLC/MS and GC/MS analyses. A total of 167 and 68 metabolites, which were CA responsive and showed differential accumulation in the susceptible and resistant cultivars under CA, were found from UPLC/MS and GC/MS analyses, respectively. The analysis revealed that higher levels of primary metabolites (amino acids, ascorbic acid, intermediates of the tricarboxylic acid cycle, and carbohydrates) were present in the resistant cultivar. Flavonoids (kaempferol, quercetin, myricetin, and catechin), which are secondary metabolites, also showed high accumulation in the cold-resistant cultivar. Accordingly, under CA, catechin component content in the four cold-resistant accessions was higher than that in the three cold-susceptible accessions, indicating that catechins play important roles in the cold response. Moreover, exogenous epigallocatechin gallate (EGCG) application conferred tolerance to freezing stress in tea plants. Tea leaves treated with EGCG exhibited decreased levels of relative electrolyte leakage and malondialdehyde content and increased reactive oxygen species scavenging activity and Fv/Fm under freezing conditions. Expression analysis of cold-regulated genes indicated that EGCG facilitated the transcriptional activation of CsICE1-CsCBF-CsCOR pathway to improve the freezing tolerance of tea plants. Taken together, the induction of stress tolerance-related metabolites was greater in the cold-resistant cultivar than in susceptible cultivars. This study highlights the important roles of catechins, especially EGCG, in cold tolerance.