Photosynthetic machinery and antioxidant enzymes system regulation confers cadmium stress tolerance to tomato seedlings pretreated with melatonin

Cadmium (Cd), a significant heavy metal, is widely distributed in the Earth's crust. However, little is known about its effects on plants and management measured. Melatonin (MEL) is a well-known multifunctional biomolecule; it is a powerful antioxidant molecule that increases a plant's abiotic stress tolerance. MEL enhances nickel, vanadium, and chromium tolerance in plants. This research aimed to examine the impact of Cd-stress on tomato plants and explore the possible contribution of MEL in improving the resistance of tomato plants towards Cd-stress. The current findings exhibited that MEL application significantly enhanced leaf photosynthesis, root structure, osmolytes accumulation, and seedling growth compared with only Cd treatment. MEL application decreased Cd transport from root to shoot, lowering Cd concentrations in leaves. In addition, MEL treatment increased catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) activity and decreased the level of hydrogen peroxide (H2O2), superoxide ion (O-2(center dot-)) and malondialdehyde (MDA) in tomato plants. Considering findings, MEL may be used to increase plant growth and Cd stress tolerance while lowering the availability of Cd to plants.