Antioxidative defense under salt stress

Abstract

Salt tolerance is a complex trait involving the coordinated action of many gene families that perform a variety of functions such as control of water loss through stomata, ion sequestration, metabolic adjustment, osmotic adjustment and antioxidative defense. In spite of the large number of publications on the role of antioxidative defense under salt stress, the relative importance of this process to overall plant salt tolerance is still a matter of controversy. In this article, the generation and scavenging of reactive oxygen species (ROS) under normal and salt stress conditions in relation to the type of photosynthesis is discussed. The CO(2) concentrating mechanism in C4 and CAM plants is expected to contribute to decreasing ROS generation. However, the available data supports this hypothesis in CAM but not in C4 plants. We discuss the specific roles of enzymatic and non enzymatic antioxidants in relation to the oxidative load in the context of whole plant salt tolerance. The possible preventive antioxidative mechanisms are also discussed.

Figure 1

Main intracellular sites of ROS generation under salt stress. The possible preventive antioxidative mechanisms are shown in italic in each cell organelle. Question marks mean the mechanism needs more evidence. The generated ROS are regulated by the action of different enzymes as indicated. The ROS concentrations in excess of normal steady state level work as signal to induce the defense mechanisms. Other sites of ROS generation (cell wall, etc.) are not shown for the sake of simplicity.