Glyoxalase System and Reactive Oxygen Species Detoxification System in Plant Abiotic Stress Response and Tolerance: An Intimate Relationship

Plants are sessile and sensitive organisms that inevitably encounter a variety of abiotic stresses in nature. Abiotic stresses such as salinity, drought, heavy metal toxicity and extreme temperatures are critical factors that reduce crop yields by more than 50% worldwide (Wang et al., 2003). The scenario is even more aggravated by the predicted forthcoming global changes in climate, foreseen extremization of environmental conditions, continuous increase of world population, ever-increasing deterioration of arable land, and scarcity of fresh water, all underscoring the importance of developing stress-resistant crops that are able to sustain growth and productivity in stressful environments. Plants tolerate abiotic stresses by modulating multiple genes and by coordinating the action of various genes from different pathways or systems (Sasaki-Sekimoto et al., 2005; Ahuja et al., 2010). During the past few years, the complex interrelationship of biochemical pathways that changes during stress has become appreciated, although we are far from understanding this complexity. A thorough understanding of biochemical and molecular responses of plants to various abiotic stresses and the interaction of different molecular pathways is, therefore, essential for a holistic perception of plant resistance mechanisms under stressful conditions. The regulatory roles of the glyoxalase system and reactive oxygen species (ROS) detoxification systems in plant abiotic stress tolerance have increasingly attracted much interest because excessive production of ROS and methylglyoxal (MG) is a common consequence of both abiotic and biotic stresses in plants (Veena et al., 1999; Chen et al., 2004; Yadav et al., 2005a, 2005b; Singla-Pareek et al., 2006; Hossain & Fujita, 2009, 2010; Banu et al., 2010; El-Shabrawi et al., 2010; Hossain et al., 2009, 2010, 2011). ROS and MG are highly toxic to plant cells, and in the absence of adequate protective mechanisms, they can react with proteins, lipids and nucleic acids and inactivate the vital defense system leading to irreparable metabolic dysfunction and death. Plants have a complex network of enzymatic