Protection against oxygen radicals: an important defence mechanism studied in transgenic plants

Abstract

Free radicals and other active derivatives of oxygen are inevitable by‐products of biological redox reactions. Reduced oxygen species, such as hydrogen peroxide, the superoxide radical anion and hydroxyl radicals, inactivate enzymes and damage important cellular components. In addition, singlet oxygen, produced via formation of triplet state chlorophyll, is highly destructive. This oxygen species initiates lipid peroxidation, and produces lipid peroxy radicals and lipid hydroperoxides that are also very reactive. The increased production of toxic oxygen derivatives is considered to be a universal or common feature of stress conditions. Plants 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. Considerable interest has been focused on the ascorbate‐glutathione cycle because it has a central role in protecting the chloroplasts and other cellular compartments from oxidative damage. It is clear that the capacity and activity of the antioxidative defence systems are important in limiting photo‐oxidative damage and in destroying active oxygen species that are produced in excess of those normally required for signal transduction or metabolism. In our studies on this system, we became aware that the answers to many unresolved questions concerning the nature and regulation of the antioxidative defence system could not be obtained easily by either a purely physiological or purely biochemical approach. Transgenic plants offered us a means by which to achieve a more complete understanding of the roles of the enzymes involved in protection against stress of many types: environmental and man‐made. The ability to engineer plants which express introduced genes at high levels provides an opportunity to manipulate the levels of these enzymes, and hence metabolism in vivo. 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 tolerence to stress by this means. However, attempts to increase stress resistance by simply increasing the activity of one of the antioxidant enzymes have not always been successful presumably because of the need for a balanced interaction of protective enzymes. The study of these transformed plants has allowed a more complete understanding of the roles of individual enzymes in metabolism. Protection against oxidative stress has become a feasible objective through the application of molecular genetic techniques in conjunction with a biochemical and physiological approach.

RETRACTED ARTICLE: Antioxidants and ROS scavenging ability in ten Darjeeling tea clones may serve as markers for selection of potentially adapted clones against abiotic stress

“…for protection against damaging effect of ROS (Asada 1992;Procházková and Wilhelmova 2007). Foyer et al (1994) also opined that plants possess efficient system of scavenging ROS, thus protecting them from destructive oxidative reaction and antioxidant enzymes play a pivotal role in defense mechanisms in stressful environment. Successful stress management can be attributed to a plant to withstand the imposed stress and this probably happens by…”

Induction of Oxidative Stress by Sunflower Phytotoxins in Germinating Mustard Seeds

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Modification of reactive oxygen species scavenging capacity of chloroplasts through plastid transformation

“…Inevitably, therefore, ROS scavenging capacity has been long recognised as a target for genetic engineering (Foyer et al 1994;Allen 1995;Bhatnagar-Mathur et al 2008), and over-expression of genes encoding enzymic components of these defences has been explored in a number of studies. The most intensively studied has been the over-expression of SOD.…”