In relation to changes in GPx activities, no differences have been found in root and leaves of plants exposed in the third experiment. Recently, Pichardo and Pflugmacher (2011) reported increases of peroxidases (POD) in roots and leaves in several bean variants irrigated with water containing MC-LR and exposed to a cyanobacterial crude extract. Again, in the case of CYN, no data has been published so far. This experiment demonstrates the sensitivity of GST for the cyanobacterial cell extracts employed and thereby the importance of this enzyme as a biomarker to assess the toxicity of cyanobacteria and their secondary metabolites