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-(trichloromethy]thio)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 (mu)M). 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 Stransferase 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.