Metabolomics Reveals the Dynamic Characteristics of Flavonoids During the Different Developmental Stages of Citrus reticulata 'Shiyue Ju' and Its Mutant C. reticulata 'Denglong Ju'.

Flavonoids, prominent bioactive compounds in citrus fruits, exhibit diverse health-promoting properties. However, the dynamic compositional changes in flavonoids during fruit development remain insufficiently characterized in Citrus reticulata 'Shiyue Ju' (STJ) and C. reticulata 'Denglong Ju' (DLJ). In this study, a comprehensive untargeted metabolomics approach was employed to systematically analyze the flavonoid profiles in both peel and flesh tissues across six key developmental stages, leading to the putative annotation of 205 flavonoids. Heatmap analysis revealed higher flavonoid levels in SP-4 (STJ peel in stage 4) compared to DP-4 (DLJ peel in stage 4), potentially resulting from the substantial upregulation of genes involved in flavonoid biosynthesis during this period. Furthermore, S-plot analysis identified salvigenin, demethylnobiletin, and nobiletin as key discriminators in the peel of STJ (SP), whereas sinensetin, tangeretin, and 3',4',5,7-tetramethoxyflavone were predominant in the peel of DLJ (DP). These compounds could represent potential biochemical markers for varietal differentiation. Notably, SP exhibited higher levels of neohesperidin, hesperidin, naringin, and naringenin, suggesting enhanced health-promoting properties. The results enhance our understanding of flavonoid dynamics during citrus development and provide valuable implications for quality-oriented cultivation and genetic improvement.