Enzymatic antioxidant defense in resistant plant: Pennisetum americanum (L.) K. Schum during long-term atrazine exposure.

Plants belonging to the genus Pennisetum have been reported to be resistant to atrazine, a widely used herbicide that also can cause serious pollution of soil and water. To evaluate the enzymatic antioxidant defense mechanism to the oxidative stress of atrazine, experiments focusing on the malondialdehyde (MDA) content and antioxidant enzyme in the leaf and root of Pennisetum americanum (L.) K. Schum (P. americanum) during long-term (68days) atrazine exposure were carried out. The test plant had not suffered obvious lipid membrane peroxidation, which was further confirmed by the result that the MDA content in the root and the leaf of the test plant did not significantly increase when treated with various concentrations of atrazine. The activity of the well-known antioxidases, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD), was increased when the plants were exposed to atrazine, especially at moderate concentrations (20mgkg(-1) or below). These results revealed that antioxidant enzymes played important roles in protecting P. americanum from the oxidative damage induced by atrazine. The increased and more stable SOD activity in the leaf compared to in the root portion of the plant under increasing atrazine concentrations and increasing exposure time indicated that the leaf exhibited more pronounced superoxide radical scavenging ability than the root. Furthermore, correlation analysis showed that the studied antioxidases were positively correlated with the exposure time, suggesting that the antioxidant defense in P. americanum seedlings might become stronger as the plant matures. In conclusion, the increasing antioxidant enzyme activities enable P. americanum seedlings to cope with the oxidative stress induced by moderate concentrations (20mgkg(-1) or below) of atrazine.