Effects of LED illumination spectra on glucosinolate and sulforaphane accumulation in broccoli seedlings

Glucosinolates (GSLs) are well known for plant defense and human nutrition. In this study, broccoli seedlings were illuminated under different LED light, including white, red, blue, and 75% red + 25% blue (200 mmol·m^-2·s^-1) for 4 weeks to investigate the effects of LED light on GSLs and sulforaphane biosynthesis. Results showed that red light promoted GSL biosynthesis and sulforaphane accumulation because red light could induce SOT18 expression to advance aliphatic GSLs biosynthesis, whereas the high tryptophan content and the upregulation of CYP79B2, CYP79B3, and CYP83B1 were attributed to indole GSL biosynthesis. Low-level methionine content and downregulated SOT18 were the main factors inhibiting GSLs and sulforaphane accumulation under blue LED illumination. BoHY5 gene expression was induced significantly and the yeast one-hybrid assay demonstrated BoHY5 could bind to SOT18 promoter. Consequently, BoHY5 inhibited SOT18 expression, and played a negative role in the GSL biosynthetic network.