Protective Mechanisms of Melatonin Against Vanadium Phytotoxicity in Tomato Seedlings: Insights into Nutritional Status, Photosynthesis, Root Architecture System, and Antioxidant Machinery

In recent decades, global crop production is being threatened by contamination of arable lands with vanadium (V). Among many stress-relief substances, melatonin (ME) is a widely studied biomolecule acting as an antioxidant under stress conditions. The current study was aimed to investigate the response of tomato seedlings towards vanadium stress, along with the circumventing role of ME by promoting V stress tolerance in tomato seedlings. Our results revealed that accentuated inhibition of growth and biomass were caused by V (40 mg/L) stress, mainly due to impairments of photosynthetic systems, root traits, and mineral homeostasis. Conversely, notable reinforcement of plant growth parameters was seen with ME (100 µM) application, with improved chlorophyll content, root morphology, mineral nutrient homeostasis, and gas exchange parameters, along with reduced V accumulation. Further, ME efficiently triggered the antioxidant enzymes activities, by restoring cellular integrity [reduced electrolyte leakage (EL) and malondialdehyde] and restricted production of superoxide (O 2 •− ) and hydrogen peroxide (H 2 O 2 ) radicals, mainly through regulation of antioxidant enzymes. The present study highlighted the potential role of ME in tomato, for circumventing V-induced phytotoxicity, mainly by boosting photosynthesis, biomass production, redox balance, nutrient uptake, and root traits. In conclusion, ME application restricted the V availability in plant, improved plant growth and, thus, provided an improved V stress tolerance.