Ameliorating heavy metal-induced oxidative stress in valerian: The role of melatonin

Heavy metals ubiquitously found in soil and water, as a serious environmental problem, are disrupting plant mineral nutrition homeostasis, osmotic balance, and metabolism. Application of some biostimulants can alleviate the disruption. Melatonin as a signal molecule, and antioxidant plays an important role in plant growth and stress tolerance due to its ability to directly neutralize reactive oxygen and nitrogen species. The reduction or mitigation of heavy metals adverse effects in valerian plants grown in open field conditions using melatonin was investigated in this paper. HPLC-FLD technique was used to identify and quantify melatonin concentration in valerian root extracts. Also, physiological, and biochemical plant status under abiotic stress was examined, especially in 100 ?M melatonin pre-treated plants. Higher concentrations of endogenous melatonin were measured in roots of Cd and Zn treated plants. Melatonin application alleviated the negative effect of Cd, particularly evident in Cd-Melatonin treatment which restored or enhanced bioactive compound levels. Melatonin effectively mitigates Cd and Zn-induced stress in valerian by enhancing both non-enzymatic and enzymatic antioxidant systems and promoting the synthesis of protective compounds. These findings highlight melatonin potential as a sustainable biostimulant to support plant resilience and productivity in heavy metal-stressed environments.