Effects of monochromatic red and blue light on photosynthetic efficiency and nutritional quality in Chinese kale microgreens

Microgreens, a type of rapidly grown and consumed vegetable, are rich in secondary metabolites. Chlorophyll serves as a crucial component contributing to their visual quality and is also recognized as a key nutritional constituent in Chinese kale microgreens. This study employed an integrated physiology-transcriptomics approach to investigate how preharvest light quality modulates metabolic pathways in microgreens. Our findings demonstrate that blue light (450 nm) preferentially enhances chlorophyll b content (1.72-fold) while improving photosynthetic efficiency through upregulation of photosystem I/II subunits and light-harvesting complex genes. This spectral treatment significantly promoted chlorophyll biosynthesis, increased soluble sugar accumulation by 154.85%, and activated cryptochrome-mediated signaling pathways. Conversely, red light (660 nm) induced morphological expansion but suppressed chlorophyll accumulation through phytochrome signaling-mediated repression of key biosynthetic enzymes (POR/CAO) and Mg-chelatase components. Transcriptomic analysis further revealed blue light's stabilization of chlorophyll biosynthetic enzymes and suppression of degradation pathways via GLK2. These findings provide molecular insights into spectral regulation of plant metabolism and propose practical LED lighting strategies for optimizing nutritional quality and visual characteristics of microgreens in controlled environment agriculture.