Melatonin and Its Protective Role against Biotic Stress Impacts on Plants

Abstract

A.A.); shaoyingai@21cn.com (S.A.); Tel.: +86-186-8050-4072 (M.M.-F.); +967-777766831 (A.A); +86-020-3288-5970 (S.A.) † These authors contributed equally to this work.Abstract: Biotic stress causes immense damage to agricultural products worldwide and raises the risk of hunger in many areas. Plants themselves tolerate biotic stresses via several pathways, including pathogen-associated molecular patterns (PAMPs), which trigger immunity and plant resistance (R) proteins. On the other hand, humans use several non-ecofriendly methods to control biotic stresses, such as chemical applications. Compared with chemical control, melatonin is an ecofriendly compound that is an economical alternative strategy which can be used to protect animals and plants from attacks via pathogens. In plants, the bactericidal capacity of melatonin was verified against Mycobacterium tuberculosis, as well as multidrug-resistant Gram-negative and -positive bacteria under in vitro conditions. Regarding plant-bacteria interaction, melatonin has presented effective antibacterial activities against phytobacterial pathogens. In plant-fungi interaction models, melatonin was found to play a key role in plant resistance to Botrytis cinerea, to increase fungicide susceptibility, and to reduce the stress tolerance of Phytophthora infestans. In plant-virus interaction models, melatonin not only efficiently eradicated apple stem grooving virus (ASGV) from apple shoots in vitro (making it useful for the production of virus-free plants) but also reduced tobacco mosaic virus (TMV) viral RNA and virus concentration in infected Nicotiana glutinosa and Solanum lycopersicum seedlings. Indeed, melatonin has unique advantages in plant growth regulation and increasing plant resistance effectiveness against different forms of biotic and abiotic stress. Although considerable work has been done regarding the role of melatonin in plant tolerance to abiotic stresses, its role in biotic stress remains unclear and requires clarification. In our review, we summarize the work that has been accomplished so far; highlight melatonin's function in plant tolerance to pathogens such as bacteria, viruses, and fungi; and determine the direction required for future studies on this topic.

Chitosan Induces Plant Hormones and Defenses in Tomato Root Exudates

“…Phytomelatonin has been recently considered a plant master regulator involved in abiotic and biotic stress responses. In our work, exposure of tomato roots to increasing chitosan doses accumulates phytomelatonin and hormones in roots and root exudates in a typical biotic stress response ( Arnao and Hernández-Ruiz, 2019 ; Moustafa-Farag et al, 2019 ). The decrease in levels of some plant hormones at toxic chitosan doses has also been found for phenolics ( Park et al, 2019 ).…”

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].…”

Role of Melatonin in Plant Tolerance to Soil Stressors: Salinity, pH and Heavy Metals

“…Melatonin acts as an effective antioxidant against both of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Moreover, melatonin is a protective agent against different abiotic stresses [3,11,12]. Although each stressful agent provides concrete details in the induced physiological responses, MT, in general, reinforces physiological processes such as stomatic uptake, growth, rooting, germination, photosynthesis, osmoregulation, anti-senescence, primary and secondary metabolism, and plant hormone regulation [3,13].…”