Exogenous brassinolide promotes the synthesis and enrichment of polyphenols during the germination of brown rice

Brown rice is a nutrient-dense whole grain with beneficial bioactive compounds that could be enriched by germination. Brassinolide is a plant growth regulator that promotes germination and modulate secondary metabolism but its role in brown rice germination remains unexplored. This study investigated the effects of brassinolide pretreatment on the polyphenol metabolism and antioxidant capacity of brown rice seeds during germination. Brassinolide exposure demonstrated concentration-dependent effects, with optimal concentrations increasing germination rates by 24.51% while supraoptimal levels suppressed germination. Treated samples exhibited 19.97%–86.05% elevation in polyphenolic content and improved antioxidant capacity. Untargeted metabolomics showed brassinolide-induced metabolic reprogramming, particularly in phenylpropanoid derivatives (phenylalanine, ferulic acid, caffeic acid). KEGG analysis revealed enrichment in phenylpropanoid and flavonoid biosynthesis pathways, while suggesting sucrose metabolism may provide precursor support for polyphenol accumulation. Enzymatic assays confirmed significant upregulation of phenylpropanoid biosynthetic enzymes, with PAL activity 2.1 times higher than the controls. These findings provide insights into brassinolide's dual-phase mechanism: enhancing germination kinetics while activating secondary metabolite synthesis. Moreover, the results indicate that optimized brassinolide treatment effectively modulates metabolic networks to improve phenolic content and antioxidant capacity in germinated brown rice, providing a biochemical basis for functional food development.