One putative mechanism of cyanotoxin action in plants is the induction of oxidative stress. This has been suggested for MCs since the cyanotoxins are capable of physiological stress in plants concomitant with the alterations in low-molecular-weight anti-oxidants and anti-oxidative enzyme activities (Pflugmacher et al., 2007). Activities of enzymes from the anti-oxidative mechanism, such as glutathione-S-transferase (GST), peroxidases and glutathione reductase were subsequently measured to assess the effects of MC-LR and cyanobacterial cell extracts in different plant species (Pichardo and Pflugmacher, 2011). Recent studies suggest a relation between the toxicity of CYN and the production of reactive oxygen species (ROS), alterations in glutathione levels and activities of GST and glutathione peroxidase (GPx) in animal models (Gutie´ rrez-Praena et al. 2011; Puerto et al., 2011). Never-theless it is not known if CYN is able to induce oxidative stress in plants.