FUNCTIONAL ANALYSIS OF ANTIOXIDANT GENES AND THEIR ROLE IN PLANT STRESS

Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409-3131 USA

Reactive oxygen species (ROS) such as superoxide anions, hydroxyl radicals and hydrogen peroxide are produced in plant cells and their levels increase during stress. These molecules can react with most cellular macromolecules and are responsible for much of the damage associated with abiotic stress. Plant cells contain efficient mechanisms for the removal of ROS and experimental analysis of the role of these systems in protecting plant cells from stress-induced damage has been evaluated primarily in transgenic plants. Functional analyses of plants that over-express ROS-scavenging enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, glutathione S-transferase, and glutathione peroxidase have been carried out. In addition, genes that encode enzymes, such as glutathione reductase and monodehydroascorbate reductase, which are involved in maintenance of low molecular weight antioxidants have also been characterized. Several of these genes have been found to contribute relatively small but significant increases in stress tolerance and additive effects have been detected when these genes are expressed in combinations. In some cases, suppression of the expression of endogenous antioxidant genes leads to increased sensitivity to stress. These results clearly indicate that antioxidant genes play a critical role in protecting plants from stress-induced damage and these genes provide attractive research targets to increase our understanding of basic plant stress tolerance mechanisms and for potential improvement of crop plants.