Heat stress induced changes in the activity of antioxidant enzymes in wheat

Abstract

Introduction The cellular changes induced by temperature stress result in the over-accumulation of toxic components in the cells. These extremely toxic compounds include reactive oxygen species (ROS), which are present to some extent in all plants as the product of the aerobic metabolism. Stress tolerance is thus based on antioxidant compounds and antioxidant enzyme systems which, when activated, are capable of neutralising the reactive oxygen species continuously produced in response to stress factors (Daood et al., 2006; El-Tayeb, 2006; Misan et al., 2006). If not removed, these compounds damage the cell tissues, eventually resulting in cell death (Bencze and Veisz, 2005). It was proved by Mittler (2002) that stress increases the production of ROS, the accumulation of which causes typical symptoms in stressed plants. High temperature also has a destructive effect on major physiological processes. The ROS accumulated as the result of heat stress lead to mitochondrial dysfunction, an increase in lipid peroxidation and the oxidative destruction of cell components (Fridovich, 1978). Many data have been presented proving the role of antioxidant enzymes (e.g. catalase, peroxidases, the enzymes of the ascorbate-glutathione cycle, etc.) and radical scavengers (e.g. glutathione, ascorbic acid, etc.) in the defence against various stress effects. A number of authors have reported a rise in the activity of the antioxidant enzymes responsible for eliminating ROS in the course of heat stress (Rainwater et al., 1996; Jiang and Huang, 2001; Vacca et al., 2004). Two antioxidant enzymes were examined in the present experiments: glutathione reductase (GR) and ascorbate peroxidase (APx).