Efficacy of exogenous GA(3) and herbicide safeners in protection of Zea mays from metolachlor toxicity

Contents of gibberellic acid (GA(3)), glutathione (gamma-L-glutamyl-L-cyste inyl glycine, GSH) and protein, activities of a-amylase (EC 3.2.1.1) and gl utathione S-transferase (GST, EC 2.5.1.18) as well as metolachlor residues, were investigated in shoots of 6-d old maize seedlings during an 8-d perio d following treatment with metolachlor, either alone or combined with GA(3) , naphthalic anhydride (NA) or flurazole (FL). Metolachlor provoked a signi ficant decrease in dry weight but had no effect when combined with GA(3), N A or FL. Metolachlor induced a significant decrease in GA(3) content and in alpha-amylase activity throughout the entire experiment. Externally applie d GA(3) relieved this effect while NA and FL relatively raised the enzyme a ctivity but still remained below control levels. Protein content was also r educed by metolachlor, an effect that was counterbalanced by NA or FL but n ot by GA(3). Metolachlor residues progressively accumulated in shoots up to the 4th day, and decreased gradually thereafter. Residues were appreciably lowered by NA or FL but not by GA(3). Significant increases of GSH content were induced by metolachlor or its combinations; the magnitude of the incr ease was more pronounced with FL. GST activity was significantly enhanced b y metolachlor; the effect was not influenced by GA(3), being augmented by t he presence of NA and multiplied by FL. The results indicate that GA(3) com pensates the loss of the endogenous GA(3) content and of alpha-amylase acti vity while FL, and to some extent NA, stimulated the detoxification rate of metolachlor by enhancing GSH content and GST activity. (C) Elsevier, Paris .