Red light delays petal discoloration in Brunfelsia acuminata by regulating anthocyanin biosynthetic genes

Brunfelsia acuminata (Pohl) Benth. exhibits a distinctive post-anthesis transition in flower color from purple to white, which is closely associated with anthocyanin degradation. However, the photobiological mechanisms regulating pigment stability during petal senescence remain poorly understood. In this study, we investigated how different light qualities affect anthocyanin degradation, flavonoid and phenolic metabolism, and the expression of key anthocyanin biosynthetic genes in detached petals and flowers on intact plants. Among nine continuous light-quality treatments, red light most effectively delayed petal discoloration, whereas blue light accelerated anthocyanin loss. Further analyses under fluorescent, white, red, and blue light confirmed that red light consistently maintained higher anthocyanin levels, whereas blue light led to the most rapid decline in pigment levels. HPLC analysis identified malvidin 3-O-glucoside, petunidin 3-O-glucoside, and delphinidin 3-O-glucoside as the major anthocyanins, with malvidin 3-O-glucoside as the predominant pigment retained under red light. Quantitative real-time PCR analysis of key structural genes in the anthocyanin biosynthetic pathway indicated that CHS (chalcone synthase), CHI (chalcone isomerase), F3'5'H (flavonoid 3'5'-hydroxylase), DFR (dihydroflavonol 4-reductase), ANS (anthocyanidin synthase), and UGT (anthocyanidin 3-O-glucoside 2″'-O-xylosyltransferase) declined during petal senescence, but red light significantly sustained the expression of DFR, ANS, and UGT relative to blue and fluorescent light. These results suggest that red light, likely through phytochrome-mediated signaling, delays petal fading by maintaining anthocyanin biosynthetic and glycosylation capacity, thereby enhancing pigment stability, whereas blue light, likely associated with cryptochrome-related signaling and greater photochemical stress, fails to sustain these pathways and is associated with accelerated pigment degradation. This study provides mechanistic insight into light-quality regulation of anthocyanin stability and identifies red-light treatment as a non-chemical approach for preserving postharvest ornamental quality.