Melatonin and plant growth-promoting rhizobacteria alleviate the cadmium and arsenic stresses and increase the growth of Spinacia oleracea L

Melatonin (N-acetyl-5-methoxytryptamine) is a recently discovered natural product that helps the plant to cope with environmental stresses. In the same way, plant growth-promoting rhizobacteria colonise plant roots and enhance plant stress tolerance. To study the impact of exogenous melatonin and Bacillus licheniformis on the growth of Spinacia oleracea L. seedlings were treated with 100 µmol exogenous melatonin and B. licheniformis under cadmium (Cd) and arsenic (As) stresses by a pot experiment. Different plant growth parameters, antioxidant enzymes, and lipid peroxidation were studied. The results showed that melatonin application and B. licheniformis inoculation alleviated As and Cd toxicity by significantly reducing the negative impacts of stresses and increasing the fresh and dry weight as well as preventing the damage to the chlorophyll content of S. oleracea L. Moreover, supplementation of melatonin, and B. licheniformis, enhanced activities of antioxidant enzymes superoxide dismutase, peroxidase, catalase, thus acting as a line of defense against As and Cd stresses. Similarly, lipid peroxidation was also inhibited by exogenous melatonin and B. licheniformis inoculation. Exogenous application of melatonin and inoculating roots of S. oleracea L. with B. licheniformis found to ameliorate the harmful effects of As and Cd contamination.