Plant superoxide dismutases: Important players in abiotic stress tolerance

Abstract

Abiotic stresses affect plant growth and development, and significantly reduce crop productivity by causing the alteration in cell biochemistry. Common for all abiotic stresses is that they cause an imbalance between production and scavenging of reactive oxygen species (ROS) in cells, resulting in elevation of ROS concentrations to cytotoxic level. Superoxide dismutases (SODs) are enzymes that play an important role of primary ROS scavengers by catalyzing the conversion of superoxide anion radical to hydrogen peroxide and oxygen. Most plant species contain numerous SOD isoforms which are classified according to the active site metal into three major types: FeSOD, MnSOD and Cu/ZnSOD. All plant SODs are nuclear-encoded, synthesized on cytosolic ribosomes and transported into various cell compartments, such as cytosol, plastids, mitochondria, peroxisomes and cell wall. Expression of SODs genes might be modulated by developmental and environmental cues, including nutrition and abiotic stresses. So far, enhanced expression and/or activity of SODs have been reported in response to various abiotic stressors, such as water deficit, high salinity, heavy metals, hypoxia, high and low temperatures. This chapter summarizes the current knowledge of plant SODs, their abiotic-stress modulated expression and activity, and analyses results on genetic engineering of plant SODs. The significance of superoxide dismutases in the crop improvement for stress tolerance is also discussed.