Transcriptomic analysis reveals Brassica rapa ssp. chinensis (pakchoi) responses to different UV filters

Common broad-spectrum ultraviolet (UV) filters—oxybenzone (OBZ), avobenzone (AVB), octocrylene (OCR), and octinoxate (OMC)—can accumulate in natural environment at concentrations toxic to plants, yet their mechanisms of toxicity remain unclear. In this study, pakchoi ( Brassica rapa ssp. chinensis ) was individually exposed to these UV filters, and transcriptomic analysis revealed that approximately 8,500 genes were differentially expressed, especially those related to photosynthesis, antioxidant defense, nitrogen use, and amino acid biosynthesis. All four UV filters inhibited plant growth through multiple pathways, but their toxicological profiles differed. AVB, OCR, and OMC primarily suppressed genes involved in photosynthesis, reducing light capture and carbon fixation. In contrast, OBZ exposure upregulated photosynthetic genes, likely as a compensatory mechanism. All treatments triggered oxidative stress, indicated by increased reactive oxygen species (ROS) and expression of damage biomarkers, which activated antioxidant defenses; notably, OMC markedly increased peroxidase activity, possibly reinforcing cell wall resilience. UV filter treatments also impaired nitrogen assimilation by downregulating key enzymes, leading to increased nitrate uptake, and disrupted amino acid balance, with selective increases and decreases among amino acids. These combined physiological changes resulted in pronounced growth inhibition in pakchoi. The findings advance understanding of UV filter phytotoxicity and inform strategies for mitigating their environmental impact.