Melatonin in Plants

Abstract

Once thought to be exclusively a molecule of the animal kingdom, melatonin has now been found to exist in plants as well. Among a number of actions, melatonin is a direct free radical scavenger and an indirect antioxidant. Melatonin directly detoxifies the hydroxyl radical (*OH), hydrogen peroxide, nitric oxide, peroxynitrite anion, peroxynitrous acid, and hypochlorous acid. The products from each of these reactions have been identified in pure chemical systems and in at least one case in vivo; the interaction product of melatonin with the OH, i.e., cyclic 3‐hydroxymelatonin, is found in the urine of humans and rats. Some of the products that are produced when melatonin detoxifies reactive species are also highly efficient scavengers. As a result, a cascade of scavenging reactions may enhance the antioxidant capacity of melatonin. Additionally, melatonin increases the activity of several antioxidative enzymes, thereby improving its ability to protect macromolecules from oxidative stress. Melatonin is endogenously produced and is also consumed in edible plants. In animal experiments, feeding melatonin‐containing foods raised blood levels of the indole. Because physiologic concentrations of melatonin in the blood are known to correlate with the total antioxidant capacity of the serum, consuming foodstuffs containing melatonin may be helpful in lowering oxidative stress.

Effects of Melatonin-Soaked Seeds on Photosynthetic Pigment Contents and Antioxidant Enzyme Activities of Broadbean (Vicia faba) Seedlings

“…The different concentrations of MT increased the CAT activity level and the soluble protein content of broadbean seedlings. These results were similar to those of previous studies [17][18], which might be related to MT's role as an antioxidant [19][20]. Thus, MT could improve the resistance of broadbean seedlings to Cd stress by increasing the antioxidant enzyme activity levels.…”

International Union of Basic and Clinical Pharmacology. LXXV. Nomenclature, Classification, and Pharmacology of G Protein-Coupled Melatonin Receptors

“…Melatonin decreased cancer cell growth by affecting cell proliferation and cytokine secretion, reducing tumor number and size, increasing tumor latency, and lowering tumor incidence (for review, see Pawlikowski et al, 2002;Sá nchez-Barceló et al, 2003). Melatonin inhibits cell proliferation through receptor-mediated effects on the cell cycle (Shiu et al, 1999), interaction with sex steroid-responsive pathways (Sá nchez- Barceló et al, 2003), and/or perhaps in part via its free radical scavenging potential (Reiter et al, 2001).…”

Regulatory roles of serotonin and melatonin in abiotic stress tolerance in plants

“…It thus limits O 2 ¡ formation. 43 Melatonin helps in improving the redox state of cells by scavenging ROS and RNS. 44 Majority of stress factors may alter the endogenous levels of melatonin.…”