O dano por oxidação causado por cobre e a resposta antioxidante das plantas

Industrial and agricultural wastes are the main source of copper accumulation in the soil. Copper is an essential micronutrient for plants, required for their growth, and participates in oxidation-reduction reactions. However, copper becomes a toxic metal when it is in tissues at concentrations higher than those needed for plant growth (>30mg·kg-1). Copper promotes the generation of reactive oxygen species (ROS), in enzymatic and non-enzymatic form (through the Fenton reaction), which may cause oxidation of proteins and lipids, alter membrane integrity, photosynthesis and growth, and induce cell death. Among the biochemical mechanisms that are induced in response to the oxidative damage caused by copper is the in crease in the activities of antioxidant enzymes such as catalase, superoxide dismutase, glutathione reductase, ascorbate and guaiacol peroxidases. Some studies indicate that antioxidant secondary metabolites such as phenolic acids, polyamines and flavonols could also be involved in counteracting the oxidative damage generated by copper. Due to the relevance of the damage that causes in plants the exposure to toxic levels of copper, in this article we review the studies performed from 2000 to 2012, showing the biochemical and physiological processes affected in plants by the oxidative stress induced by the metal and the antioxidant mechanisms that participate in the defense to copper excess.