ROS and NO Phytomelatonin-Induced Signaling Mechanisms under Metal Toxicity in Plants: A Review

Abstract

Metal toxicity in soils, along with water runoff, are increasing environmental problems that affect agriculture directly and, in turn, human health. In light of finding a suitable and urgent solution, research on plant treatments with specific compounds that can help mitigate these effects has increased, and thus the exogenous application of melatonin (MET) and its role in alleviating the negative effects of metal toxicity in plants, have become more important in the last few years. MET is an important plant-related response molecule involved in growth, development, and reproduction, and in the induction of different stress-related key factors in plants. It has been shown that MET plays a protective role against the toxic effects induced by different metals (Pb, Cd, Cu, Zn, B, Al, V, Ni, La, As, and Cr) by regulating both the enzymatic and non-enzymatic antioxidant plant defense systems. In addition, MET interacts with many other signaling molecules, such as reactive oxygen species (ROS) and nitric oxide (NO) and participates in a wide variety of physiological reactions. Furthermore, MET treatment enhances osmoregulation and photosynthetic efficiency, and increases the concentration of other important antioxidants such as phenolic compounds, flavonoids, polyamines (PAs), and carotenoid compounds. Some recent studies have shown that MET appeared to be involved in the regulation of metal transport in plants, and lastly, various studies have confirmed that MET significantly upregulated stress tolerance-related genes. Despite all the knowledge acquired over the years, there is still more to know about how MET is involved in the metal toxicity tolerance of plants.

Interaction between Melatonin and NO: Action Mechanisms, Main Targets, and Putative Roles of the Emerging Molecule NOmela

“…Several other studies have also shown that both NO and MEL play a role during metals’ toxicity stress response, specifically under cadmium (Cd) toxicity [ 107 ]. In Catharanthus roseus , MEL and sodium nitroprusside (SNP, a NO donor) improved seedling growth under Cd toxicity via the increase in the concentration of photosynthetic pigments, Cd translocation, proline concentration, and antioxidant enzymes activity (SOD, POD, APX, and CAT), leading to a decrease in lipid peroxidation and H 2 O 2 content.…”

Melatonin in Plant Defense against Abiotic Stress

“…Melatonin promotes plant growth by developing antioxidant systems and alleviating heavy metal toxicity by employing its chelating property that helps in reducing their accumulation at the rhizospheric surface [155]. Lower concentrations of melatonin show apositive impact on Cd tolerance by promoting photosynthesis, growth, and maintaining relative water content and stomatal conductance through increasing proline metabolism in Malva parviflora (L.) [156], and preventing metal toxicity by inducing defense systems [157]. Melatonin decreases the methylation of upregulated genes RsAPX2, RsPOD52, and Rs-GST and scavenges lead-induced ROS in radish [158].…”

OsSGT1 promotes melatonin‐ameliorated seed tolerance to chromium stress by affecting the OsABI5–OsAPX1 transcriptional module in rice

“…With the intensification of anthropogenic activities, heavy metal pollution has become a growing global problem that threatens public health and ecosystems (Pardo‐Hernández et al., 2021). Although some metals, like copper and zinc, are essential for plant development and growth, many heavy metals, such as chromium (Cr), are hazardous elements contaminating agricultural lands and water, posing severe threats to human health through the food chain (Malik et al., 2022; Singh et al., 2013).…”