Effects of UV-B and UV-C radiation on antioxidative enzymes activity of Melissa officinalis and influences of salicylic acid in UV-stress ameliorations

The effects of decreased ozone and increased UV radiation have been studied by many researchers. The aim of this study was to investigate the effects of UV-B and UV-C radiations on Melissa officinalis L. and to study the impact of salicylic acid in reducing the harmful effects of radiation on plants. The M. officinalis L. plants were grown at 28±2 ºC temperature for about 60 days. The light intensity was 150 µEmˉ²Sˉ¹ and the light-dark condition was 8-16 hours. UV treatment was applied after the six-leaf stage and UV-B radiation was applied for a period of 15 days on alternative dys and the time for each application was 20 minutes. But UV-C radiation was applied for 15 days and the time of each application was 8 minutes. Salicylic acid was sprayed on the plants after the six-leaf stage with a concentration of 1 mM. The results indicated that the UV-B and UV-C radiations led to reduction of the dry and fresh weight، root elongation and shoots. The radiations increased activity of antioxidant enzymes ascorbate peroxides، and catalase activity reduction was also observed. The Malondialdehyde and H2O2 content were increased under the effect of UV-B and UV-C radiations. The results showed that treatment with salicylic acid reduced damage to the plants resulting from UV-B and UV-C radiations and were able to compensate for changed factors that had been changed because of ultra violet radiations.