ABSTRACT
A variety of environmental stresses (such as chilling, ozone, high light, drought, and heat) can severely damage crop plants with consequent high yield losses. A common factor in all these adverse conditions is the occurrence of oxidative stress. Oxidative stress can be defined as the enhanced accumulation of active oxygen species (AOS) within several subcellular compartments of the plant. The AOS can react very rapidly with DNA, lipids, and proteins, with cellular damage as a result. Under normal growth conditions, AOS are efficiently scavenged by both enzymatic and nonenzymatic detoxification mechanisms. Nevertheless, during prolonged stress conditions, this defense system becomes saturated and cellular damage is inevitable. The key players in the defense system are superoxide dismutases, ascorbate peroxidase, and catalases. These antioxidant enzymes directly eliminate AOS. This chapter gives an overview of transgenic plants with modulated antioxidant enzyme levels (focusing on superoxide dismutases, ascorbate peroxidase, and catalase) that are produced to test the potential use of antioxidant enzymes in improving stress tolerance during adverse environmental conditions.
