Molecular mechanisms of exogenous quercetin in enhancing cold resistance in tea plants

Extreme weather events, such as spring cold spells, pose a serious threat to tea production by reducing both yield and quality. Quercetin is a flavonoid widely distributed in plants and plays important antioxidant and signaling roles in responses to abiotic stresses. To evaluate the effects of quercetin on cold resistance in tea shoots and to elucidate the underlying mechanisms, <italic>Camellia sinensis</italic> cv. “Longjing 43” plants were foliar-sprayed with exogenous quercetin at different concentrations (0.1 μg mL^-1 and 0.5 μg mL^-1). Physiological traits and gene expression in tea shoots under cold stress were subsequently assessed. Cold stress markedly induced quercetin accumulation in young shoots, and exogenous quercetin significantly enhanced the cold resistance of young shoots. Compared with the control, quercetin-treated shoots showed higher maximum photochemical efficiency (<italic>F</italic>_v/<italic>F</italic>_m), lower relative electrolyte leakage, malondialdehyde, and hydrogen peroxide contents, and increased antioxidant enzyme activities under cold stress. Transcriptome analysis further indicated that quercetin significantly upregulated genes involved in hormone signaling, calcium signaling, and MAPK signaling pathways under cold stress. Collectively, these results suggest that quercetin enhances cold resistance in tea shoots by activating cold signal transduction and inducing downstream stress-responsive genes.