Melatonin is known to delay postharvest nutrient loss. However, its specific roles in regulating cell wall and sugar metabolism to maintain postharvest quality in flowering Chinese cabbage remain unclear. In this study, postharvest flowering Chinese cabbage was treated with melatonin (100 µmol L^− 1) to investigate the cell wall and sugar metabolisms. Our research found that melatonin supplementation increased levels of important nutrients like ascorbic acid, sugars, soluble protein, carotenoid, and glucosinolates. It also enhanced various cell wall components (cellulose, hemicellulose, lignin, and protopectin) while reducing water-soluble pectin accumulation. Melatonin helped stabilize cell wall by reducing the expression of genes related to cell wall degradation (BrBGAL4, BrPG, BrCEL3, and BrPME3), inhibiting activities of cell wall-degrading enzymes like pectin methylesterase and cellulase, and improving expressions of cellulose biosynthesis-related genes (BrCesA1, BrCesA3.1, and BrCesA3.2). Additionally, it boosted sugar accumulation by increasing activities of sucrose synthetase and sucrose phosphate synthetase, upregulating expressions of BrSUS1, BrSUS5, BrSPS1F, BrSPS3F, BrSPS4F, and suppressing activities of neutral invertase and acidic invertase and expressions of genes involved in sugar metabolism (BrSUS3, BrINV, BrSWEET2, BrSWEET4, and BrSWEET17). This study highlights melatonin’s vital roles in maintaining postharvest quality and offers practical insights for improving market performance of flowering Chinese cabbage.

Low light caused by industrial development and environment change has become a limitation in crop production. This condition inhibits the petiole anthocyanin synthesis and even its tastes in purple cai-tai (Brassicarapa L. var. purpurea); however, the molecular basis of the inhibitory effects by low light on anthocyanin synthesis in purple cai-tai petiole is less reported. In this study, we performed an integrated analysis of transcriptomes and metabolisms to decipher key genes and/or metabolites that responsible for low light acclimation in a purple cai-tai cultivar, XH1. Results shows that anthocyanin is obviously repressed by low light treatment, and consistently the structural genes related to the anthocyanin biosynthesis pathway is significantly enriched in the list of differentially expressed genes according to both GO and KEGG analysis. Furthermore, the amounts of some metabolites related to anthocyanin are dramatically decreased under low light treatment, such as cyanindin 3-O-glucoside chloride, cyanindin O-syringic acid, and cyanidin 3-O-rutinoside. In addition, we found that five transcription factors in TCP gene family especially BrTCP15 is substantially downregulated by low light treatments. The expression pattern of BrTCP15 in response to low light treatment was further confirmed by qPCR. This study reports the inhibitory effects of the anthocyanin biosynthesis pathway and BrTCP15 by low light treatments, and extends our knowledge on regulatory mechanism of the anthocyanin biosynthetic pathway in response to low light in B. rapa L.

Low light caused by industrial development and environment change has become a limitation in crop production. This condition inhibits the stalk anthocyanin synthesis and even its tastes in brassica rapa L; however, the molecular basis on the inhibitory effects by low light on anthocyanin synthesis in brassica stalk is less reported. In this study, we combined transcriptomes and metabolisms to decipher key genes and /or metabolites that responsible for shading acclimation in a brassica cultivar, XH1. Results shows that anthocyanin is obviously repressed in low light condition, and consistently the structural genes related to anthocyanin biosynthesis pathway is significantly enriched in the list of differentially expressed genes according to both GO and KEGG analysis. Furthermore, amounts of some metabolites related to anthocyanin are dramatically decreased under shading treatment, such as cyanindin 3-O-glucoside chloride, cyanindin O-syringic acid, and cyanidin 3-O-rutinoside. In addition, we found that some transcription factors of interest such as TCP15 is stimulated by shading treatments, while acts as a negative regulator anthocyanin biosynthesis by low light. The mechanistic explanation of inhibitory effects of anthocyanin by low light condition through TCP15 was proposed. This study extend our knowledge on transcriptional regulation mechanism for anthocyanin biosynthesis in response to shading condition, and provides an evidence that a potential role of TCP15 in low light inhibitory effects in anthocyanin synthesis in brassica.