Melatonin (N-acetyl-5-methoxytryptamine) is a small (232 daltons), nontoxic, indole molecule first isolated from the pineal gland of cows and later on found in
different tissues of plants and bacteria. Melatonin acts as a signaling
molecule/messenger, which plays an important role in coping with various biotic and
abiotic stress conditions. Biosynthesis of melatonin involves two key cellular
organelles viz. mitochondria and chloroplast. The endogenously produced melatonin
serves as an antioxidant signaling molecule during the generation of reactive oxygen
species (ROS) and reactive nitrogen species (RNS). The exogenous melatonin also
functions in the same way during critical conditions by repairing mitochondria and deal
with various stresses. The plants regulate the production of melatonin depending upon
the conditions and regulate salt, drought, cold, heat, oxidative, and heavy metalsrelated stresses. Besides that, melatonin acts as a plant hormone and regulates
numerous functions in plants, including growth, development, photoperiod, clearing
oxygen species, rhizogenesis, photosynthesis, and enhances antioxidase activity. It acts
as a multi regulatory molecule by regulating gene expressions as well as by cross-talks
with phytohormones (auxin, cytokinin, salicylic acid, and abscisic acid) involved in
plant growth and development. Therefore, understanding the mechanism of action of
melatonin as a signaling molecule may serve as a novel strategy to combat various
stresses in plants and animals. An attempt has been made in this chapter to discuss the
important role of melatonin in modulating oxidative stress in plants during stressful
conditions.
Keywords: Chloroplast, Cytoplasm, Drought, Hormones, Melatonin,
Mitochondria, N-acetyl serotonin methyltransferase, N-acetylserotonin, Oxidative
stress, Plants, RNS, ROS, Salinity, Serotonin N-acetyl transferase, Serotonin,
Stress, Tryptamine 5- hydroxylase, Tryptamine, Tryptophan decarboxylase,
Tryptophan.
