Plant Superoxide Dismutases: Function Under Abiotic Stress Conditions

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Superoxide dismutases (SODs) are a family of metalloenzymes that catalyze the dismutation or disproportionation of superoxide radicals (\( {{\text{O}}_{2}}^{ \cdot - } \)) into molecular oxygen (O2) and hydrogen peroxide (H2O2). In plants, essentially, there are three groups of SODs depending on the prosthetic metals in their active sites, either: copper and zinc (Cu,Zn-SODs); manganese (Mn-SODs); or iron (Fe-SODs). Different plant SODs have been isolated and characterized, and many cDNAs and genes for SODs have been identified and characterized. SODs have an important function in plant physiology as a result of the double role of reactive oxygen species (ROS), as signals in important transduction pathways and as inducers of cellular damage when overproduced at high concentrations. In metabolic reactions, superoxide radicals are modulated by SODs but in their enzymatic reaction the key metabolite and signaling molecule H2O2 is produced, an important transduction signal in response to abiotic and biotic stresses and in diverse physiological processes. In general, abiotic stresses in plants induce the generation of ROS that can produce cellular oxidative damage when overproduced in high amounts. After abiotic stress treatment, those cultivars more resistant/tolerant usually show an enhanced activity of antioxidative enzymes, including SODs. Different reports are described on the response of SODs to abiotic stress produced in plants by heavy metals, salinity and drought, xenobiotics, low and high temperature, high light intensity, ozone and atmospheric contaminants, and mechanical stress. The genetic manipulation of plants with altered SOD activity to produce more oxidative stress-tolerant phenotypes that could be used to improve the stress tolerance of economically important plants are briefly examined. Finally, the effect of nitric oxide-mediated post-translational modifications of SODs on their enzymatic activity is discussed.