Effect of Melatonin on Some Morphophysiological Characteristics of Phaseolus vulgaris cv. Sadri under Salinity Stress

Melatonin (N-acetyle-5-methoxy tryptamine) has recently been considered as a phytohormone in raising the resistance of plants against environmental stresses. The present study aims to assess the effect of melatonin treatment on the tolerance of salt by Phaseolus vulgaris cv. Sadri which was conducted in completely randomized design, repeated three times. In this study, salinity stress was introduced in three levels of 0, 100 and 200 mM of NaCl to bean plants treated by melatonin with respective concentrations of 0, 100 and 200 µM. It was found that salinity stress decreased the dry weight of shoot, the root and the photosynthetic pigments while it increased proline, soluble sugars, malondialdehyde and H2O2 as it increased the activity of antioxidant enzymes of catalase, peroxidase and ascorbate peroxidase. Applying melatonin improved plant growth, the concentration of photosynthetic pigments, proline, soluble sugars and the activity of antioxidant enzymes while it reduced H2O2 and malondialdehyde concentration. Results showed that melatonin had a significant effect on raising the resistance of phaseolus vulgaris cv. Sadri against salt and that lower concentrations of melatonin worked better.