Effect of Melatonin Premedication on Some Physiological Parameters and Reduction of Oxidative Stress in Tagetes etecta Seedlings under Salt Stress

Salinity is one of the most important environmental stresses which affect the growth of plants. Most of the plants are sensitive to salt stress at the seedling stage, so the growth of them in salt-water accompanies with problems. Various agronomic and physiological practices (treatments) are applied to minimize the adverse effects of salinity on plant growth and using of plant growth regulator is one of them. This study was conducted to investigate the effect of melatonin on the resistance of Tagetes erecta seedlings to salinity. In order to evaluate the effect of different levels of salinity on early growth of Tagetes erecta seedlings, a factorial experiment was conducted in a completely randomized design with three replications. Experimental treatments consisted of two levels of 0.25 and 0.5 μM of melatonin, and four different levels of saline solution containing pure sodium chloride at concentrations of 0, 50, 100 and 150 mM. In this research, the effect of pretreatment with two concentrations of Melatonin was investigated on the growth biochemical and antioxidant parameters of Tagetes erecta under salt stress. In some measured parameters, such as chlorophyll and protein content, pretreatment with 0.25 µM Melatonin 50, 100 and 150 mM NaCl was effective. Pretreatment with melatonin at both concentrations 0.25 and 0.5 µM in seedlings those were under salinity stress, reduced MDA and other aldehydes. Salinity stress increased activity of catalase in leaves, while had no effect on the ascorbate and guaiacol peroxidaes activity. Pretreatment of seedlings with melatonin at concentrations 0.25 µM increased the catalase activity under salinity condition. However, pretreatment with melatonin only at concentrations 0.25 µM increased ascorbate and guaiacol peroxidaes activity in salinity condition. The present results indicate that Tagetes erecta pretreatment by melatonin increased seedlings tolerance under salt stress.