Changes of antioxidants and GSH-associated enzymes in isoproturon-treated maize

The recommended field dose ( RFD) of isoproturon induced significant accumulations of H2O2 in the leaves of 10-d-old maize seedlings throughout the following 20 d; the accumulation increased with time and also with herbicide dose. Meanwhile, low doses significantly increased ascorbic acid, glutathione and thiols while high doses caused diminutions. Superoxide dismutase ( SOD; EC 1.15.1.1) activity was significantly enhanced up to the 12th d whereas ascorbate peroxidase ( APX; EC 1.11.1.7) activity was significantly reduced after the fourth d onwards. Catalase ( CAT; EC 1.11.1.6) and guaiacol peroxidase ( GPX; EC 1.11.1.7) activities were similarly increased during the first 4 d but decreased from the 12th and the eighth d, respectively. Low doses increased SOD and GPX activities but high doses led to diminutions whereas CAT and APX were reduced by all doses. The activities of gamma-glutamyl-cysteine synthethase ( gamma-GCS; EC 6.3.2.2) and glutathione synthethase ( GSS; EC 6.3.2.3) were enhanced for 4 d; high doses caused general reductions. Isoproturon significantly reduced activities of glutathione S-transferase ( GST; EC 2.5.1.18) isoforms [ GST((CDNB)), GST((ALA)), or GST((MET))] after the fourth d, however, it had no effect on GST((ATR)). Similar reductions in activities of glutathione peroxidase ( GSPX; EC 1.15.1.1) and glutathione reductase ( GR; EC 1.6.4.2) were detected up to the 16th and the 12th d, respectively. The activities of GST isoforms, GSPX and GR were reduced by high doses. These changes seemed to be related and might point to an oxidative stress state that exacerbated with prolonged time and/or increased isoproturon dose.