Purple Light Steers Metabolic Flux Towards Sulforaphane in Flowering Chinese Cabbage Sprouts by Activating a BcHY5 ‐Mediated “Push‐Pull” Mechanism

Light quality is a powerful tool to modulate the chemistry of functional foods, yet the underlying molecular regulatory networks are poorly understood. This study reveals that purple light-emitting diode illumination engineers the metabolic flux in flowering Chinese cabbage sprouts to maximize the production of the anti-cancer agent sulforaphane. Compared to dark and white light controls, purple light treatment (center wavelength: 398 nm, half-width: 13 nm) resulted in a significant (6.84-fold) increase in sulforaphane content. Integrated metabolomic and transcriptomic analyses uncovered a "push-pull" mechanism: purple light "pushed" glucosinolate biosynthesis while "pulling" the metabolic stream towards sulforaphane by enhancing hydrolysis and suppressing the competing nitrile-forming pathway. We identified the transcription factor BcHY5 as the master regulator. Yeast one-hybrid and dual-luciferase assays confirmed BcHY5 directly binds to and activates promoters of key GSL biosynthetic genes (GSTU11, SUR1). These findings establish a novel light-regulatory framework, offering a practical strategy for the precision production of high-value phytochemicals in functional foods.