Heavy metal toxicity is one of the most devastating abiotic stresses. Heavy metals cause serious damage to plant growth and productivity, which is a major problem for sustainable agriculture. It adversely affects plant molecular physiology and biochemistry by generating osmotic stress, ionic imbalance, oxidative stress, membrane disorganization, cellular toxicity, and metabolic homeostasis. To improve and stimulate plant tolerance to heavy metal stress, the application of biostimulants can be an effective approach without threatening the ecosystem. Melatonin (N-acetyl-5-methoxytryptamine), a biostimulator, plant growth regulator, and antioxidant, promotes plant tolerance to heavy metal stress by improving redox and nutrient homeostasis, osmotic balance, and primary and secondary metabolism. It is important to perceive the complete and detailed regulatory mechanisms of exogenous and endogenous melatonin-mediated heavy metal-toxicity mitigation in plants to identify potential research gaps that should be addressed in the future. This review provides a novel insight to understand the multifunctional role of melatonin in reducing heavy metal stress and the underlying molecular mechanisms.

Department of Agronomy and Haor Agriculture Sylhet Agricultural University Sylhet 3100 Bangladesh

Department of Agronomy Bangladesh Agricultural University Mymensingh 2202 Bangladesh

Department of Biochemistry and Molecular Biology Bangladesh Agricultural University Mymensingh 2202 Bangladesh

Department of Biochemistry and Molecular Biology Hajee Mohammad Danesh Science and Technology Dinajpur 5200 Bangladesh

Department of Biochemistry and Molecular Biology Khulna Agricultural University Khulna 9100 Bangladesh

Department of Biotechnology Bangladesh Agricultural University Mymensingh 2202 Bangladesh

Department of Botany and Plant Physiology Faculty of Agrobiology Food and Natural Resources Czech University of Life Sciences Prague Kamycka 129 165 00 Prague Czech Republic

Department of Genetics and Plant Breeding Bangladesh Agricultural University Mymensingh 2202 Bangladesh

Faculty of Agriculture Bangladesh Agricultural University Mymensingh 2202 Bangladesh

Institute of Plant and Environmental Sciences Faculty of Agrobiology and Food Resources Slovak University of Agriculture 94976 Nitra Slovakia

Northeast Institute of Geography and Agroecology Chinese Academy of Sciences Changchun 130102 China

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