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 radiation on Melissa officinalis L. and to study the impact of salicylic acid and magnetic fields in reducing the harmful effects of radiation on plants. The Melissa officinalis L. plants were treated with 28_+2 Celsius 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, the time for each application was 20 minutes. Salicylic acid was sprayed on the plants after the six-leaf stage with a concentration of 1 mmol. Magnetic field treatment was applied for an hour with intensities of 0, 40 and 85 mT. The results indicated that the UV-B radiation led to reduction in dry and fresh weight, root elongation and shoots. The radiations also reduced the photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoid) and sugar rate and soluble proteins amount. The phenylalanine ammonia-lyase compounds rate and UV-absorbing compounds were increased under the effect of UV-B radiation. The results showed that treatment with salicylic acid and magnetic fields caused a reduced damage to the plant which had been created due to UV-B radiation and were able compensate for changed factors that had been changed because of UV radiation.

Keywords: UV radiation, Melissa officinalis L, magnetic field, salicylic acid