The effect of exogenous nitric oxide on benzo[a]pyrene stress in ryegrass (Lolium perenne L.)

The pot experiment investigated the role of exogenous nitric oxide (NO) in mitigating benzo[a]pyrene (B[a]P) stress and regulating mineral element dynamics in ryegrass. Exposure to 30 µmol/dm³ B[a]P significantly suppressed seed germination, root vitality, nitrate reductase (NR) activity, and dry weight, while altering mineral distribution, copper (Cu) and manganese (Mn) accumulated in roots, whereas nitrogen (N), phosphorus (P), lead (Pb), and cadmium (Cd) were translocated to leaves. Seed germination, plant height, root vitality, and NR activity initially increased at 100-300 µmol/dm³ sodium nitroprusside (SNP, NO donor) but declined at 400 µmol/dm³. SNP treatments enhanced root retention of N, P, Mn, Cu, and Pb, reducing toxic metal mobility. PCA, cluster, and correlation analyses identified 200-300 µmol/dm³ SNP as optimal for alleviating B[a]P stress, with N and P dynamics most strongly correlated with growth recovery. Exogenous NO counteracts B[a]P-induced phytotoxicity by regulating root-to-leaf translocation of N and P to sustain metabolic activity, restricting Pb/Cd mobility and redistributing essential minerals (Cu, Mn) to minimize aerial tissue exposure, optimizing SNP concentration to enhance stress tolerance without overburdening detoxification pathways. This study underscores NO’s dual role as a nutrient coordinator and detoxification agent, offering strategies to enhance plant resilience in B[a]P-contaminated environments.