Effects of the cyanobacterial toxin microcystin-LR on detoxication enzymes in aquatic plants

The enrichment of water bodies with plant nutrients often results in mass growths of cyanobacteria which can produce a range of toxins. Cyanobacterial toxins have adverse effects on fish, birds, and mammals, and are being increasingly recognized as animal and human health hazards. The effects of cyanobacterial toxins on plants, particularly aquatic macrophytes, are little understood. The uptake of microcystin-LR (MC-LR) by Ceratophyllum demersum was detected with approximately 11.2% of the applied C-14-labelled microcystin being taken up after 7 days of exposure. The effects of various concentrations of this toxin on the detoxication enzyme glutathione S-transferase (microsomal and soluble forms) were investigated. Microsomal glutathione S-transferase activity was increased in C. demersum exposed to concentrations of MC-LR above 0.12 mu g/L, but reduced at concentrations above 1.0 mu g/L, whereas soluble glutathione S-transferase activity was increased by exposure to MC-LR concentrations above 0.5 mu g/L. No reduction of soluble GST activity was observed. The activity of both microsomal and soluble GST systems, freshly prepared from a range of plants, was inhibited in the presence of 0.5 mu g/L MC-LR. The results indicate a detoxication pathway for MC-LR in aquatic plants. (C) 1999 by John Wiley & Sons, Inc.