Consequences of metolachlor persistence of treated and safened Zea mays on gibberellins, glutathione, alpha-amylase, and glutathione S-transferase

Contents of GA(3), GSH and protein, activities of alpha-amylase (EC 3.2.1.1) and GST (EC 2.5.1.18) as well as met residues were investigated in shoots of six-d-old maize seedlings during 8-d period following treatment with metolachlor (met), either alone or combined with GA(3), NA or FL. Met provoked a significant decrease in dry weight but had no effect when combined with GA(3), NA or FL. Met induced a significant decrease in GA(3) content and in alpha-amylase activity throughout the entire experiment: Externally applied GA(3) relieved this effect while NA and FL seemed to lower this decrease. Protein content was also reduced by met; an effect that was counterbalanced by NA or FL but not by GA(3). Met residues progressively accumulated in shoots up to the 4th day, and decreased gradually thereafter. Residues were appreciably dropped by NA or FL but not by GA(3). Comparable and significant increaser of GSH content were induced by met or its combinations, particularly with FL which induced about 2.2-fold of untreated values. GST activity was significantly enhanced by met; the effect was not influenced by GA(3), whereas NA or FL respectively, induced 3.2- or 7.2-fold of control values. The results indicate that GA(3) compensates the loss of the endogenous GA(3) content and of alpha-amylase activity while FL, and to some extent NA, stimulated the detoxification rate of met by enhancing GSH content and GST activity.