Investigating the effects of magnetic field and salicylic acid on Melissa officinalis (Lamiaceae) under UV-B stress

Effects of ozone depletion and increase of 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. as well as the impact of salicylic acid and magnetic fields in the reduction of harmful effects of radiation on plants. The Melissa officinalis L. plants were treated with 28 ± 2 Cº for approximately 60 days. The light intensity was 150 µ E mˉ² Sˉ¹ and the light/dark regime was 16/8 h. UV-B treatment was applied after the six-leaf stage for a period of 15 days and 20 min every day. Salicylic acid (1mM) was daily sprayed on the plants after the six-leaf stage for one week. 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 of root and shoot dry and fresh weights, and root and shoot elongation. The radiations also reduced the content of photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoid), sugar and soluble proteins. The phenylalanine ammonia-lyase activity and UV-absorbing content compounds increased under the effect of UV-B radiation. The results showed that treatment with salicylic acid and magnetic fields reduced damages to the plant due to UV-B radiation.