ABSTRACT
Melatonin is assumed to have originated in bacteria, as it has been discovered in both proteobacteria and photosynthetic cyanobacteria. Melatonin promotes the immune system in plants, altering circadian cycles and leaf stomatal closure. Melatonin is a multifunctional chemical found in plants and microalgae. It primarily functions as an antioxidant. Melatonin scavenges reactive oxygen species and reactive nitrogen in plants and microalgae, protecting them from cellular damages. Melatonin is also involved in the germination, growth, rooting, photosynthesis, respiration, and nitrogen assimilation of plant seeds. Melatonin influences lipid synthesis in microalgae under nitrogen stress. Abiotic stress produced by the activation of antioxidant enzymes has been overcome by the exogenous melatonin treatment in microalgae, which eradicates the reactive oxygen species produced, thus playing a role as an effector molecule. Due to the presence of circadian rhythms endogenously in some species of plants, melatonin played a central role in the regulation of the day-night cycle. This chapter deals with understanding the regulatory role of melatonin in photosynthesis, respiration, and nitrogen assimilation in plants and microalgae in detail. More specifically, our knowledge escalates towards the role of melatonin in physiological studies in plants and microalgae and their future prospects.
