Oxidative stress and antioxidative system in plants

Abstract

Free radicals and other active derivatives of oxygen are inevitable by-products of biological redox reactions. Reactive oxygen species inactivate enzymes and damage important cellular components. The increased production of toxic oxygen derivatives is considered to be a universal or common feature of stress conditions. Plant and other organisms have evolved a wide range of mechanisms to contend with this problem. The antioxidant defence system of the plant comprises a variety of antioxidant molecules and enzymes. The effects of the action of free radicals on membranes include the induction of lipid peroxidation and fatty acid de-esterification. Both ethylene biosynthesis and membrane breakdown, which appear to be closely linked, seem to involve free radicals, although the sequence of events generating these free radicals is still poorly understood. It is clear that the capacity and activity of the antioxidative defence system are important in limiting oxidative damage and in destroying active oxygen species that are produced in excess of those normally required for metabolism. Transgenic plants offered us a means by which to achieve complete understanding of the roles of the enzymes involved in protection against stress of many types, environmental and induced. Studies on transformed plants expressing increased activities of single enzymes of the antioxidative defence system indicate that it is possible to confer a degree of tolerance to stress by these means. The advent of plant transformation has placed within our grasp the possibility of engineering greater stress tolerance in plants by enhancements of the antioxidative defence system.