Plant glutathione peroxidases: Antioxidant enzymes in plant stress responses and tolerance

Abstract

In contrast to other eukaryotic organisms, plants are unable to run away from unfavourable conditions; they must cope with different abiotic and biotic stress factors. Under abiotic and biotic stresses, the production of reactive oxygen and reactive nitrogen species (ROS and RNS) can damage the biological membranes, proteins and nucleic acids. However, plants have developed complex defence systems including different non-enzymatic and enzymatic antioxidants as shields to prevent the toxic effects of an increased amount of ROS and RNS. Glutathione peroxidases (GPXs) are important antioxidant enzymes in animals, but plants contain GPX-like (GPXLs) enzymes. In contrast to animal GPXs, plant GPXLs contain cysteine in their active site instead of selenocysteine, and most of them prefer thioredoxin as the electron donor rather than glutathione. In the last 25 years, many researches proved that plant GPXLs also are essential elements of plant stress responses and are important ROS scavengers. Overexpression of GPXLs in different plant species led to increased tolerance against drought, salt, osmotic, heavy metal and particularly oxidative stresses; however, in some cases, it caused decreased tolerance against biotic stresses. In this chapter, we focus on the importance of plant GPXLs in stress responses, highlighting the significance of distinct genes as possible candidates for genetic engineering to improve the yield of agricultural plants under unfavourable environment.