Comparative study of flavonoid production in lycopene-accumulated and blonde-flesh sweet oranges (Citrus sinensis) during fruit development

Four main flavanone glycosides (FGs) and four main polymethoxylated flavones (PMFs) were determined in fruits of 'Cara Cara' navel orange, 'Seike' navel orange, 'Anliu' and 'Honganliu' sweet orange (Citrus sinensis). No bitter neohesperidosides were detected in the FG profiles, indicating the functional inability of 1,2-rhamnosyltransferase, though relatively high transcription levels were detected in the fruit tissues of 'Anliu' and 'Honganliu' sweet oranges. Different to the FGs, the PMFs only exist abundantly in the peel and decreased gradually throughout fruit development of sweet oranges, suggesting the expression of methylation-related genes accounting for PMF biosynthesis have tissue-specificity. Significant changes in production of the eight flavonoids were found between red-flesh and blonde-flesh sweet oranges, indicating that lycopene accumulation might have direct or indirect effects on the modification of flavonoid biosynthesis in these citrus fruits.