UV Radiation Induced Changes of Phenolic Compounds and Antioxidant Enzymes in Okra (Hibiscus esculents L.) Seedlings

The influences of different ultraviolet (UV-A, UV-B and UV-C) radiation treatments on phenolic compounds (total phenol, anthocyanin and flavonoid), lipid peroxidation content and behavior of the some enzymes such as polyphenoloxidase (PPO), phenylalanin ammonia–lyase (PAL), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT) and glutathione reductase (GR) were studied in okra (Hibiscus esculents L.) seedlings. results showed that UV-B and UV-C treatments increased UV absorbing compounds and lipid peroxidation contents as compared with the control and UV-A treatment plants. UV-A treatment did not significantly affect the activity of antioxidant enzymes (APX, GPX, CAT, GR), but in plants treated with UV-B and UV-C, APX, GPX, CAT and GR activity were significantly increased when compared with the control plants. Also activity level of PPO and PAL in the shoots of okra plants increased significantly in response to UV-B and UV-C treatments. These results suggest that the increased phenolic compounds and antioxidant system activity in the UV-B and UV-C treatments may be considered as biomarkers of intensity of UV radiation stress. However, more research is necessary to elucidate the precise role that the antioxidant system plays under ultraviolet radiation stress.