ABSTRACT
Application of signaling molecules has gained immense importance in improving the phytoremediative capacity of plants. This study investigated the possible role of melatonin (MEL) as a signaling molecule in ameliorating lead (Pb)-induced oxidative injury in safflower seedlings. Pot grown 10-day-old safflower seedlings were exposed to 50 µM Pb (NO3)2 alone and in combination with different MEL concentrations (0-300 µM). Exposure to Pb, resulted in a severe oxidative stress, which was indicated by reducing biomass production and enhancing the level of oxidative stress markers (e.g. MDA and H2O2). Addition of exogenous MEL considerably decreased Pb uptake and its root-to-shoot translocation while, biomass production of roots, stems and leaves increased significantly. With MEL application a marked increase in reduced glutathione (GSH) content in leaves and roots was noted as compared with Pb treatment alone. In leaves the activity of enzymes involved in glyoxalase system increased markedly by adding MEL to Pb-sressed plants. In response to increasing MEL treatments, the phytochelatin content of leaves increased substantially in comparison with Pb treatment alone. These findings confirmed that MEL can alleviate Pb toxicity by reducing Pb uptake and its root-to-shoot translocation along with modulating different antioxidant systems. The results also showed that despite the insignificant effect of melatonin on the improvement of Pb phytoremediation potential, the application of this signaling molecule can improve the survival of safflower in Pb-contaminated soils by stimulating antioxidant defense mechanisms.