Melatonin as a Chemical Substance or as Phytomelatonin Rich-Extracts for Use as Plant Protector and/or Biostimulant in Accordance with EC Legislation

Abstract

Melatonin (N-acetyl-5-methoxytryptamine) is a ubiquitous molecule present in animals and plants, and also in bacteria and fungi. In plants, it has an important regulatory and protective role in the face of different stress situations in which it can be involved, mainly due to its immobility. Both in the presence of biotic and abiotic stressors, melatonin exerts protective action in which, through significant changes in gene expression, it activates a stress tolerance response. Its anti-stress role, along with other outstanding functions, suggests its possible use in active agricultural management. This review establishes considerations that are necessary for its possible authorization. The particular characteristics of this substance and its categorization as plant biostimulant are discussed, and also the different legal aspects within the framework of the European Community. The advantages and disadvantages are also described of two of its possible applications, as a plant protector or biostimulant, in accordance with legal provisions.

Melatonin and Its Protective Role against Biotic Stress Impacts on Plants

“…Recently, exogenous melatonin treatment was found to activate ETI-and PTI-associated genes in watermelon and Arabidopsis according to transcriptomic data [40,41]. In addition, melatonin plays a key role in the regulation of ROS and reactive nitrogen species (RNS) rates in plants, which act as a signal in many cellular and physiologic responses to both abiotic and biotic stresses, both directly (as scavengers of ROS/RNS) and indirectly (as gene regulators of the redox network) [25,49]. Other melatonin defense mechanisms are elaborated in Table 3 and Figure 1.…”

“…Recently, this knowledge gap was partially bridged when AtPMTR1, the first receptor for phytomelatonin, was discovered in Arabidopsis [75]. This finding has created new expectations for melatonin's function as a plant hormone [49]. Although this important discovery has elucidated the upstream pathway regarding stomata closure phenotype, there is still the need to explore the crucial role of other melatonin receptor-mediated signaling pathways during biotic/abiotic stress in plants [25,76], although interesting transcriptome approaches have already been made [41].…”

Effects of Light Quality and Phytochrome Form on Melatonin Biosynthesis in Rice

“…Melatonin acts as a hormone in plants, and as a signaling molecule in a wide range of biological activities [5]. For example, melatonin treatment enhances plant tolerance against many stresses, including salt [6,7], drought [8,9], viruses [10], pathogens [11,12], waterlogging [13], and senescence [14], among others [15][16][17]. Melatonin is also involved in plant development processes such as growth [18,19], seed viability [20], flowering [21,22], endoplasmic reticulum (ER) quality control [23,24], secondary metabolite synthesis [25], and others [26].…”

Melatonin Positively Influences the Photosynthetic Machinery and Antioxidant System of Avena sativa during Salinity Stress

“…Recent studies suggest that exogenous application of melatonin in plants under salt stress leads to an increase in endogenous melatonin levels, partly via the phyto-melatonin receptor CAND2/PMTR1. Elevated melatonin levels then improve photosynthesis, ion homeostasis, and initiate a signaling cascade to boost the biosynthesis of hormones, nitric oxide, and polyamine (reviewed in [19,20]). Though the ability of melatonin to increase the tolerance of plants to different stresses is well documented, the precise mechanisms by which melatonin confers stress resistance are poorly characterized.…”