The effects of combined treatment of light quality and sodium selenite on the growth and quality of mustard sprouts were clarified, which provided a theoretical basis and technical support for the optimization of light environment and quality improvement in facility cultivation of mustard sprouts.

This study focused on mustard sprouts, investigating the impacts of different light qualities (white light, red light, blue light) alone and in combination with sodium selenite on key quality indicators such as morphogenesis, photosynthetic characteristics, antioxidant capacity, and accumulation of secondary metabolites, and combined with transcriptome analysis to reveal its regulatory mechanism.

Compared with white light, red light treatment significantly increased the edible fresh weight, plant height, and soluble sugar content of mustard sprouts by 1.19-, 1.07-, and 1.06-fold, respectively. Blue light promoted photosynthetic pigment accumulation by upregulating the expression of photosynthetic pigment-related genes (chlE, por, crtISO, crtZ). The content of total chlorophylls and total carotenoids under blue light were 1.09- and 1.08-fold higher than those under white light, and 1.10- and 1.04-fold higher than those under red light, respectively. Additionally, blue light enhanced the accumulation of flavonoids and total phenolics in mustard sprouts by upregulating the genes involved in phenylpropanoid biosynthesis (PAL, C4H, 4CL, CCR, COMT, POD), with their content increasing by 1.20- and 1.44-fold relative to white light, and by 1.05- and 1.10-fold relative to red light, respectively. Furthermore, blue light treatment significantly increased total glucosinolates content by 1.28-fold and 1.23-fold compared with white light and red light treatments, respectively. The combination of white or blue light with sodium selenite further promoted the accumulation of total chlorophylls and total carotenoids, with the respective content significantly increased by 1.15- and 1.15-fold, and 1.07- and 1.07-fold. The synergistic interaction between blue light and sodium selenite regulated carbon and nitrogen metabolism to facilitate the accumulation of soluble sugar and soluble protein, whose content were significantly enhanced by 1.07-fold and 1.08-fold, respectively. This synergistic effect also improved the antioxidant capacity of mustard sprouts, with the content of ascorbic acid, flavonoids, and total phenolics being 1.13-, 1.16-, and 1.05-fold higher than those under single blue light treatment. Principal component analysis (PCA) showed that PC1 and PC2 accounted for 66.1% and 14.0% of the total variance, respectively. The combined treatment of red light and sodium selenite was strongly correlated with plant height, edible fresh weight, and soluble sugar content; single blue light treatment was closely associated with total glucosinolates content; and the combined treatment of blue light and sodium selenite exhibited significant positive correlations with total chlorophylls, total carotenoids, ascorbic acid, and phenolic compounds. Correlation analysis further demonstrated that soluble protein content was significantly and positively correlated with flavonoids, total phenolics, total chlorophylls, and total carotenoids.

Light quality and sodium selenite have significant regulation and synergistic interaction effects on the nutritional quality of mustard sprouts. In particular, the synergistic effect of blue light and sodium selenite can promote the photosynthetic pigments, antioxidant activity and secondary metabolites accumulation of mustard sprouts in an all-round way.