Melatonin: Awakening the Defense Mechanisms during Plant Oxidative Stress

Abstract

Melatonin is a multifunctional signaling molecule that is ubiquitously distributed in different parts of a plant and responsible for stimulating several physio-chemical responses to adverse environmental conditions. In this review, we show that, although plants are able to biosynthesize melatonin, the exogenous application of melatonin to various crops can improve plant growth and development in response to various abiotic and biotic stresses (e.g., drought, unfavorable temperatures, high salinity, heavy metal contamination, acid rain, and combined stresses) by regulating antioxidant machinery of plants. Current knowledge suggests that exogenously applied melatonin can enhance the stress tolerance of plants by regulating both the enzymatic and non-enzymatic antioxidant defense systems. Enzymic antioxidants upregulated by exogenous melatonin include superoxide dismutase, catalase, glutathione peroxidase, and enzymes involved in the ascorbate–glutathione cycle (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase), whereas levels of non-enzymatic antioxidants such as ascorbate, reduced glutathione, carotenoids, tocopherols, and phenolics are also higher under stress conditions. The enhanced antioxidant system consequently exhibits lower lipid peroxidation and greater plasma membrane integrity when under stress. However, these responses vary greatly from crop to crop and depend on the intensity and type of stress, and most studies to date have been conducted under controlled conditions. This means that a wider range of crop field trials and detailed transcriptomic analysis are required to reveal the gene regulatory networks involved in the between melatonin, antioxidants, and abiotic stress.

Pure Organic Active Compounds Against Abiotic Stress: A Biostimulant Overview

“…This compound is a multifunctional molecule distributed in different parts of plants and involved in several physiological processes: the circadian rhythm, photosynthesis, biomass production, root development, seed germination, fruit ripening, foliar senescence, membrane integrity, redox network, osmoregulation and response to abiotic stress ( Khan et al, 2020 ). Several works have shown that exogenous application of melatonin can increase plant growth and resistance to stress.…”

“…It was suggested that the protective role of melatonin is due to the regulation of the antioxidant defence system, from direct ROS scavenging by reaction with H 2 O 2 , O 2 – , and OH ⋅ , to an increase in the activity of antioxidant enzymes (CAT, SOD, and GPX), as well as enzymes of the ascorbate-glutathione cycle (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase). It is also involved in the effects of non-enzymatic antioxidants (carotenoids, tocopherols, ascorbate, reduced glutathione, and phenolic compounds) ( Khan et al, 2020 ).…”

“…Although the positive effects of melatonin application are well established, most studies have been conducted under controlled conditions. Therefore, Khan et al (2020) highlighted the need for more field trials and transcriptomics analysis. On the other hand, Wang S.-Y.…”

Role of melatonin in UV‐B signaling pathway and UV‐B stress resistance in Arabidopsis thaliana

“…Removal of excessive accumulated ROS within cells through increased antioxidant system activity is a crucial protective mechanism in stress‐exposed plants. Previous researches demonstrated that under stress condition, melatonin acts as an antioxidant at cellular level to alleviate ROS and indirectly activates the gene expression of antioxidant enzymes (Arnao & Hernández‐Ruiz, 2019a, 2019b; Khan et al, 2020; Moustafa‐Farag et al, 2019). We also hypothesized that melatonin functions at the gene level to enhance expression of antioxidant enzymes, and their protective effect.…”

Mechanisms of Plant Antioxidants Action

“…I have received many excellent manuscripts that try to shed some light on the potential mechanism of action of antioxidants and also described the identification of new compounds, bringing to the collection nine articles [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ] and two reviews [ 16 , 17 ].…”