Molecular Regulation of Flavonoid Biosynthesis in Onion (Allium cepa L.) During Developmental Progression and Its Cytotoxic Implications

Abstract This study investigated the expression of key flavonoid biosynthetic genes (CHS, CHI, ANS, and FLS) across developmental stages and organs in three onion (Allium cepa L.) genotypes (PRO-6, Rec-1404, and D-97-B). Gene expression exhibited stage-dependent variation, with maximum activity in bulb organs at stages S3 and S4, particularly in the PRO-6 genotype. Elevated transcript levels corresponded with increased total phenolic, quercetin, and anthocyanin contents, signifying enhanced flavonoid biosynthesis during bulb maturation. Cytotoxicity assays on HeLa and HCT-15 cell lines indicated dose- and time-dependent declines in cell viability, with HeLa cells showing greater susceptibility. PRO-6 onion extracts displayed the highest cytotoxic potential, consistent with their enriched flavonoid profiles. The study highlights genotype-, organ-, and stage-specific regulation of flavonoid metabolism in onions and establishes a link between pigment biosynthesis and cytotoxic activity. These results suggest that colored onion genotypes possess significant nutraceutical and therapeutic potential due to their superior bioactive compound composition.