Seasonal Dynamics of Polymethoxyflavones and Their Relationship with Peel Color Indices in ‘Ponkan’ (Citrus reticulata Blanco) Under Plant Growth Regulator Treatments
摘要
Polymethoxyflavones (PMFs), including nobiletin and tangeretin, are characteristic bioactive compounds accumulated in the flavedo of ‘Ponkan’ (Citrus reticulata Blanco). This study investigated seasonal changes in PMF concentration (mg g⁻1 FW) and total content per fruit (mg per peel) under gibberellic acid (GA), prohydrojasmon (DPJ), and combined treatments, and evaluated their relationships with fruit physical traits and peel color parameters (CIELAB L*, a*, b*, C*, h°). The GA-treated fruits exhibited higher nobiletin and tangeretin contents than other treatments, whereas PDJ-treated fruits tended to show reduced PMF levels. The PMF concentrations increased from September to October and declined thereafter. Importantly, changes in PMF levels occurred earlier than visible peel color development, indicating a temporal lag between PMF metabolism and peel coloration. Pearson correlation analyses revealed significant negative correlations between ∆PMF concentration and ∆L*, ∆a*, ∆b*, and ∆C*, and positive correlations with ∆h°, suggesting that higher PMF levels are associated with greener peel characteristics. These findings show that GA and PDJ differentially regulate PMF metabolism and that PMF decline appears to precede carotenoid-related peel coloration. The associations between PMFs and color indices suggest the feasibility of indirectly estimating PMF levels using nondestructive color measurements. These findings provide new insight into hormonal regulation of PMF metabolism and suggest the potential use of peel color parameters as practical indicators for estimating functional compound levels in citrus peel.