ABSTRACT
The ozone level variation in the stratosphere and its depletion by anthropogenic activities has given rise to global concern during the last few decades. Concomitantly, unabsorbed and dangerous ultraviolet-B (UV-B) radiation exerts adverse influences on biotic components reaching the earth’s surface. Since plants are sessile, they have evolved mechanisms to avoid and protect themselves from UV-B radiation. Continuous exposure of UV-B radiation influences the plants indirectly by inducing the formation of reactive oxygen species enormously inside the cell, leading to oxygen toxicity and thereby causing oxidative damage to lipids and proteins. This damage can also directly affect the membrane and nucleic acids and ultimately leads to a decline in plant productivity, disturbing the ecological balance in turn. In general, UV radiation tends to increase the activity of enzymatic and non-enzymatic antioxidants. The key enzymatic antioxidants of the defense mechanism are superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione-S-transferase (GST), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR). The non-enzymatic antioxidants are ascorbate (AsA), glutathione (GSH), non-protein thiols (NP-SH), cysteine and proline, which maintain the production of reactive oxygen species (ROS) and exert roles at multiple levels. They help to detoxify H2O2 to induce transcription of defense related genes leading to enhancement in protective mechanisms against oxidative stress under UV-B stress conditions. Therefore, it is reported that these biochemical changes often reflect the acclimatization response of plants, but they may either have positive or negative consequences that need deeper insight.
