Effect of exogenous melatonin on growth, electrolyte leakage and antioxidant enzyme activity in rosemary under salinity stress

Melatonin is a new plant hormone that plays an important role in stress tolerance. For investigation the effect of exogenous application of melatonin on salt tolerance in rosemary (Rosmarinus officinalis L.), a factorial experiment was conducted in a completely randomized design with three replications. The first factor was melatonin (50, 100 µM) and the second factor was salinity stress (6, 9, 12 ds m-1). Water was used for control treatment. In the treated plants with concentrations of 6, 9 and 12 dsm-1 NaCl, stem height decreased compared to the control. Melatonin treatment (100 μM) reduced the effects of NaCl stress. 100 μM melatonin increased leaf growth compared to the control. The highest activity of SOD and POD was recorded in pretreatment plants with 50 and 100 μM melatonin. Melatonin prevented the reduction of chlorophyll content due to salt stress. The lowest ion leakage was related to 100 μM melatonin in control, 6 and 9 dsm-1 NaCl. Also, the highest reduction of electrolyte leakage (with 28.5% reduction) was related to 100 μM MT at 12 dsm-1NaCl. According to the results, 100 μM melatonin was more effective in reducing the effects of salinity stress.