Effects of the fungicide folpet on the activities of antioxidative enzymes in duckweed (Lemna minor)

In a previous paper we reported the phytotoxicity of the fungicide folpet [N-(trichloromethylthio)phtalimide] in the aquatic floating macrophyte Lemna minor. The objectives of this study were to investigate the modifications of several antioxidative enzymatic activities in fronds of L. minor during a 96-h exposure to a sublethal folpet concentration (33 muM). The specific activities of enzymes of the Halliwell-Asada pathway, namely, ascorbate peroxidase and glutathione reductase, increased after 24 h of exposure, reaching 155 and 273% of the control level at 96 h, respectively. A fast induction of glutathione S-transferase activity was observed after 6 h of folpet exposure. From data presented it cannot be concluded whether glutathione S-transferase was involved in folpet metabolization or in peroxide scavenging. The fungicide was also found to stimulate the activities of two H2O2-scavenging enzymes, catalase and pyrogallol peroxidase. Stimulation of catalase was very rapid (as soon as 12 h after exposure) and very strong since the activity was 252% of the control after 48 h of exposure. Induction of pyrogallol peroxidase was less important; nevertheless, it reached 66% at 96 h. No effect of the fungicide on guaiacol peroxidase was observed. As suggested by the simultaneous and important induction (55 to 173%) of antioxidative enzymatic defenses of L. minor, the generation of reactive oxygen species by the fungicide was proposed and the involvement of a possible oxidative stress in the phytotoxicity of folpet was discussed. (C) 2001 Academic Press.