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

The enrichment of water bodies with plant nutrients often results in mass g rowths of cyanobacteria which can produce a range of toxins. Cyanobacterial toxins have adverse effects on fish, birds, and mammals, and are being inc reasingly recognized as animal and human health hazards. The effects of cya nobacterial 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 microcys tin being taken up after 7 days of exposure. The effects of various concent rations 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 expos ure to MC-LR concentrations above 0.5 mu g/L. No reduction of soluble GST a ctivity was observed. The activity of both microsomal and soluble GST syste ms, 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.