%0 Journal Article
%T Phytomelatonin: Discovery, Content, and Role in Plants
%A Marino B. Arnao
%J Advances in Botany
%D 2014
%R 10.1155/2014/815769
%X Melatonin (N-acetyl-5-methoxytryptamine) is an indolic compound derived from tryptophan. Usually identified as a neurotransmitter or animal hormone, this compound was detected in plants in 1995. Interest in knowing the melatonin content of plants and its possible role therein is growing, as indicated by the increasing number of related publications. Melatonin is present in all plant species studied, with large variations in its level depending on the plant organ or tissue. It seems to be more abundant in aromatic plants and in leaves than in seeds. Regarding its physiological function in plants, melatonin shows auxin activity and is an excellent antioxidant, regulating the growth of roots, shoots, and explants, activating seed germination and rhizogenesis (lateral- and adventitious-roots), and delaying induced leaf senescence. Its ability to strengthen plants subjected to abiotic stress such as drought, cold, heat, salinity, chemical pollutants, herbicides, and UV radiation makes melatonin an interesting candidate for use as a natural biostimulating substance for treating field crops. 1. Introduction Melatonin is a molecule endowed with a multitude of functions, particularly in mammals. This indoleamine is a hormone that acts in many physiological aspects, influencing mood, sleep, body temperature, the retina, and sexual behavior, among others. Most of these aspects are regulated through or in conjunction with the circadian clock present in animals [1¨C7]. In addition, melatonin is involved in numerous cellular actions as an antioxidant, acting as an excellent in vitro and in vivo free radical scavenger [8¨C15]. Chemically, melatonin (N-acetyl-5-methoxytryptamine) is an indolic compound derived from serotonin (5-hydroxytryptamine) (Figure 1). Both biogenic amines are synthesized from the amino acid tryptophan in a well-characterized biosynthetic pathway in animals and with some particular characteristics in plants. In plants, the auxin, indolyl-3-acetic acid (IAA), bears some resemblance to melatonin since both are indole compounds and have a common biosynthetic pathway through the compound tryptamine in the tryptophan-dependent IAA biosynthetic pathway (Figure 1). Figure 1: Molecular structure of melatonin and its related compounds in the biosynthesis pathway: tryptophan, serotonin, and tryptamine. This last compound is a precursor of the auxin indolyl-3-acetic acid, IAA. 2. Discovery of Melatonin in Plants The presence of melatonin was described for the first time in the bovine pineal gland by Lerner and coworkers [16]. The isolated substance was able
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