Effect of UV-B and UV-C radiation on some physiological and biochemical parameters of Melissa officinalis and influence of salicylic acid in UV-stress ameliorations

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 Melissa Officinalis L plants were treated with 28_+2 ºC temperature for about 60 days. The light intensity was 150 µ E mˉ² Sˉ¹ and the lightness-darkness condition was8-16 hours. UV treatment was applied after the six-leaf stage and UV-B radiation was applied for a period of 15 days in every other day the time for each application was 20 minutes. But UV-C radiation was applied for 15 days in every other day and 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 in dry and wet weight، root elongation and shoots. The radiations also reduced the photosynthetic pigments (chlorophyll a، chlorophyll b and carotenoid) and sugar rate and total soluble proteins amount. The Malondialdehyde and phenylalanine ammonialyase compounds rate and UV- absorbing compounds were increased under the effect of UV-B and UV-C radiations. Surveying results showed that treatment with salicylic acid caused a reduced damage to the plant which had been created due to UV-B and UV-C radiations and was able compensate for changed factors that had been changed because of ultra violet radiations.