Objective In order to explore the defense mechanism of the antioxidant system of Salix viminalis , the dynamic changes of reactive oxygen and antioxidant substances under phenanthrene stress were observed which can provide new evidence for improving the resistance of plants to polycyclic aromatic hydrocarbon (PAHs) stress and enhancing the phytoremediation potential.

Method The cutting seedlings of S. viminalis were selected as experimental materials, and a 16-day hydroponic experiment with 0 and 1.0 mg·L^-1 phenanthrene concentrations were conducted to study the dynamic changes of reactive oxygen, antioxidant enzymes, antioxidants and malondialdehyde (MDA) contents.

Result The Results showed that: (1) Under phenanthrene treatment, the superoxide anion radical (O₂^·-) production and H₂O₂ content increased rapidly, then MDA content rose. Catalase (CAT) activity significantly increased on the 4th day, and the superoxide dismutase (SOD) and peroxidase (POD) activity increased on the 8th day. On the 16th day, no significant difference was found in H₂O₂ content between the samples treated with phenanthrene and that of the control. Meanwhile, the increment of O₂^·- and MDA also slowed down. (2) The contents of reduced glutathione (GSH) and glutathione reductase rose rapidly on the 4th day under phenanthrene treatment, and the activity of glutathione-s-transferase (GST) increased slowly. (3) Under phenanthrene treatment, the content of ascorbic acid was initially lower than the control group, but higher on the 16th day as the treatment time continued.

Conclusion Under phenanthrene stress, O₂^·- is the main reactive oxygen causing cell membrane lipid peroxidation. SOD activity is always higher than that of the control group, but not enough to eliminate the increased O₂^·-. The increase of CAT and POD could eliminate the excessive H₂O₂. GSH is an effective antioxidant to resist the stress of phenanthrene and participates in the detoxification of phenanthrene through the catalysis of GST.