Activities of antioxidants in plants under environmental stress.

Abstract

There is growing evidence that in plants subjected to environmental stress. It causes significant crop losses. The stresses are numerous and often cropor location-specific. They include increased UV-B radiation, water, high salinity, metal toxicity, herbicides, fungicides, air pollutants, light, temperatue, topography and hypoxia (restricted oxygen supply in waterlogged and compacted soil),. Research in this area is driven by the hope of improving crop yield in afflicted areas. The balance between the production of activated oxygen species and the quenching activity of antioxidant is upset which often results in oxidative damage. Many metabolic processes produce active oxygen species. Among the four major active oxygen species [superoxide radical O2, hydrogen peroxide H2O2, hydroxyl radical OH and singlet oxygen O2] H2O2 and the hydroxyl radical are most active, toxic and destructive. High salt concentrations normally impair the cellular electron transport within the different subcellular compartments and lead to the generation of reactive oxygen species (ROS) such as singlet oxygen superoxide, hydrogen peroxide and hydroxyl radicals. Excess of ROS triggers phytotoxic reactions such as lipid peroxidation, protein degradation and DNA mutation. Since higher plants are immobile they cannot escape environmental stresses. The ability of higher plants to scavenge the toxic active oxygen seems to be a very important determinant of their tolerance to environmental stress. Many enzymes and secondary compounds of higher plants have been demonstrated in vitro experiments to protect against oxidative damage by inhibition or quenching free radicals and reactive oxygen species. The roles of many other compounds as potential antioxidants can be inferred by similarity to synthetic antioxidants of related structure. The evidence supports at least a partial antioxidant role in vivo for many classes of plant metabolite.