Abstract
Light, as a crucial environmental determinant, profoundly influences the synthesis of secondary metabolites in plant metabolism. This study investigated the impacts of the red light combined with ultraviolet-A (UV-A) and ultraviolet-B (UV-B) treatments on phenolic acid biosynthesis in black wheat seedlings. The results demonstrate that the red light combined with UV-A and UV-B treatments significantly enhanced the levels of phenolic acids in black wheat seedlings, at 220.4 μg/seedling and 241.5 μg/seedling, respectively. The content of bound phenolic acids in black wheat seedlings increased by 36.0% under the UV-B treatment. The application of the UV-A/UV-B treatments markedly enhanced the activities of phenylalanine ammonia-lyase, 4-coumarate CoA ligase, and cinnamate 4-hydroxylase in black wheat seedlings while also promoting the expression levels of genes related to phenolic acid synthesis. The expression levels of fructose-1,6-bisphosphate aldolase and NADP-malic enzyme related to photosynthesis were significantly upregulated. This resulted in an augmentation in the chlorophyll content, thereby enhancing photosynthesis in black wheat seedlings. Nevertheless, the UV-A and UV-B treatments also had a significant constraining effect on the growth and development of black wheat seedlings. In addition, the UV-A and UV-B treatments increased the activity and gene expression levels of antioxidant enzymes while significantly increasing the contents of total flavonoids and anthocyanins, activating the antioxidant system. The findings reveal that light-source radiation serves as an effective method for promoting the biosynthesis of phenolic acids in black wheat seedlings.