Anatoxin-a elicits an increase in peroxidase and glutathione S-transferase activity in aquatic plants

Although the toxic effects of cyanotoxins on animals have been examined extensively, little research has focused on their effects on macrophytes and macroalgae. To date only microcystins have been found to be detrimental to aquatic plants. Peroxidase activity of the free floating aquatic plant Lemna minor and the filamentous macroalga Chladophora fracta was measured after exposure to several concentrations of the cyanotoxin, anatoxin-a. Peroxidase activity (POD) was significantly (P < 0.05) increased after 4 days of exposure to an anatoxin-a concentration of 25 microg mL(-1) for both L. minor and C. fracta. Peroxidase activity was not significantly increased at test concentrations of 15 microg mL(-1) or lower. In another experiment, the effects of various concentrations of anatoxin-a on the detoxication enzyme, glutathione S-transferase (GST) in L. minor were investigated. GST activity was significantly elevated at anatoxin-a concentrations of 5 and 20 microg mL(-1). Photosynthetic oxygen production by L. minor was also found to be reduced at these concentrations. This is the first report to our knowledge of the cyanotoxin anatoxin-a being harmful to aquatic plants.