Effects of red and blue light on photosynthetic carbon assimilation and growth-development in plants: A review.

Red and blue light are the primary spectra absorbed by photosynthetic pigments in plants. Through the signal pathways mediated by phytochromes (PHY) and cryptochromes (CRY)/phototropins (PHOT), they coope-ratively regulate photosynthetic carbon assimilation, and plant growth and development. We reviewed the regulatory mechanisms of red and blue light on photosynthetic characteristics and plant growth and development. Red light activates chlorophyll synthesis genes (HEMA1, CHLH) through phytochrome B (PHYB), increases chlorophyll b content but inhibits carotenoid accumulation. Blue light upregulates genes such as PSY and PDS through cryptochromes1/2 (CRY1/2), and promotes carotenoid synthesis. The combination of red and blue light significantly enhances photosynthetic rate and electron transfer efficiency by optimizing the thickness of palisade/spongy tissue and stomatal conductance. Blue light can alleviate the photoinhibition of PSⅡinduced by red light, increasing the maximum photochemical efficiency (Fv/Fm) and actual photochemical efficiency (ΦPSⅡ) of PSⅡ. In terms of growth and development, red light promotes stem elongation through the PHY-auxin pathway but inhibits root activity, while blue light enhances root absorption area and inhibits hypocotyl elongation through the CRY-PIN3 signaling pathway. Red and blue light cooperatively regulate flowering time. Red light delays flowering through the PHYB-PHYL-CO protein complex, while blue light promotes flowering through the CRY2/CO-FT protein pathway. Combined blue and red light can extend the flowering period and improve the quality of floral organs. We reviewed the applications of red and blue light in multiple fields such as plant factories, accelerated breeding, factory seedling cultivation, and space breeding. Currently, it is necessary to analyze the molecular networks of cross-regulation of photoreceptors, establish multi-factor coupling models, and develop crop-specific light requirement databases. In the future, combined with gene editing and intelligent light control technologies, the photosynthesis-morphogenesis coordination mechanism should be optimized directionally to promote the development of facility agriculture towards high efficiency and intelligence, and to provide theoretical support and technical references for high light efficiency, high-quality cultivation, and high-yield breeding practices in modern agriculture.