Exogenous Melatonin Treatment Research Articles

Exogenous Melatonin Application Accelerated the Healing Process of Oriental Melon Grafted onto Squash by Promoting Lignin Accumulation.

Melatonin (MT) is a vital hormone factor in plant growth and development, yet its potential to influence the graft union healing process has not been reported. In this study, we examined the effects of MT on the healing of oriental melon scion grafted onto squash rootstock. The studies indicate that the exogenous MT treatment promotes the lignin content of oriental melon and squash stems by increasing the enzyme activities of hydroxycinnamoyl CoA ligase (HCT), hydroxy cinnamaldehyde dehydrogenase (HCALDH), caffeic acid/5-hydroxy-conifer aldehyde O-methyltransferase (COMT), caffeoyl-CoA O-methyltransferase (CCoAOMT), phenylalanine ammonia-lyase (PAL), 4-hydroxycinnamate CoA ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD). Using the oriental melon and squash treated with the exogenous MT to graft, the connection of oriental melon scion and squash rootstock was more efficient and faster due to higher expression of wound-induced dedifferentiation 1 (WIND1), cyclin-dependent kinase (CDKB1;2), target of monopteros 6 (TMO6), and vascular-related NAC-domain 7 (VND7). Further research found that the exogenous MT increased the lignin content of the oriental melon scion stem by regulating CmCAD1 expression, and then accelerated the graft healing process. In addition, the root growth of grafted seedlings treated with the exogenous MT was more vigorous.

Metabolome and Transcriptome Analysis Revealed the Pivotal Role of Exogenous Melatonin in Enhancing Salt Tolerance in Vitis vinifera L.

Vitis vinifera L. possesses high economic value, but its growth and yield are seriously affected by salt stress. Though melatonin (MT) has been widely reported to enhance tolerance towards abiotic stresses in plants, the regulatory role melatonin plays in resisting salt tolerance in grapevines has scarcely been studied. Here, we observed the phenotypes under the treatment of different melatonin concentrations, and then transcriptome and metabolome analyses were performed. A total of 457 metabolites were detected in CK- and MT-treated cell cultures at 1 WAT (week after treatment) and 4 WATs. Exogenous melatonin treatment significantly increased the endogenous melatonin content while down-regulating the flavonoid content. To be specific, the melatonin content was obviously up-regulated, while the contents of more than a dozen flavonoids were down-regulated. Auxin response genes and melatonin synthesis-related genes were regulated by the exogenous melatonin treatment. WGCNA (weighted gene coexpression network analysis) identified key salt-responsive genes; they were directly or indirectly involved in melatonin synthesis and auxin response. The synergistic effect of salt and melatonin treatment was investigated by transcriptome analysis, providing additional evidence for the stress-alleviating properties of melatonin through auxin-related pathways. The present study explored the impact of exogenous melatonin on grapevines' ability to adapt to salt stress and provided novel insights into enhancing their tolerance to salt stress.

Melatonin induces acclimation to heat stress and pollen viability by enhancing antioxidative defense in rice (Oryza sativa L.)

Melatonin is a signalling molecule in plants which act as a growth regulator and stress buffering agent but little is known about its defensive role in heat stress tolerance in rice. In this study we analysed the acclimation response of two contrasting heat responsive rice genotypes NERICA-L-44 (NL-44, heat stress tolerant) and Pusa Basmati 1121 (PB-1121, heat stress susceptible) to exogenous melatonin treatment under heat stress. Heat stress induces melatonin biosynthesis in both the genotypes and maximum increase was observed in NL-44. Application of exogenous melatonin further increases melatonin biosynthesis and endogenous content significantly in PB-1121. To understand melatonin’s role in alleviating effects of heat stress, some of the heat stress associated traits such as membrane stability index, hydrogen peroxide content, malondialdehyde content, total antioxidant capacity and enzymatic antioxidants like superoxide dismutase, catalase, ascorbate peroxidase and peroxidase were analysed. We observed that melatonin significantly enhanced membrane stability by reducing hydrogen peroxide mediated membrane damage. Higher activity of antioxidative enzymes and increased total antioxidant capacity helped to maintain reactive oxygen species homeostasis by scavenging mechanism. Exogenous melatonin increased pollen viability, spikelet fertility and grain yield under heat stress treatment. The findings of this study indicates that heat stress induced increase in melatonin biosynthesis may be involved in heat stress tolerance in rice. Exogenous melatonin treatment can further improve heat stress tolerance in susceptible rice genotype (PB-1121) by activating antioxidative mechanism.

Effects of exogenous melatonin on the osmotic regulation and antioxidant capacity of Ginkgo biloba seedlings under salt stress.

We investigated the effects of exogenous melatonin on the osmotic regulation and antioxidant capacity of 4-year-old Ginkgo biloba seedlings under salt stress. There were three treatments, with low (50 mmol·L-1), medium (100 mmol·L-1), and high (200 mmol·L-1) NaCl stress. Leaves were sprayed and the soil was watered with melatonin solution (0, 0.02, 0.1, 0.5 mmol·L-1). The results showed that saline stress significantly inhibited the osmoregulation and antioxidant capacities of G. biloba seedlings. Application of exogenous melatonin at appropriate concentrations (0.02, 0.1 mmol·L-1) under salt stress could promote plant growth, reduce the rate of electrolyte leakage, decrease the content of flavonoids and malonic dialdehyde, and enhance peroxidase and superoxide dismutase activities in leaves. High concentration (0.5 mmol·L-1) of exogenous melatonin would aggravate the oxidative and osmotic stresses. The 0.02 and 0.1 mmol·L-1 exogenous melatonin alleviated osmotic stress and oxidative stress in G. biloba seedlings under salt stress, while the 0.02 mmol·L-1 exogenous melatonin treatment had the best effect on NaCl stress alleviation. Ground diameter, branch width, branch length, electrolyte leakage rate, superoxide dismutase activity, and flavonoids content could be used as the key indices for rapid identification of the degree of salt stress in G. biloba seedlings.

Exogenous melatonin delays programmed cell death in broccoli via maintenance of ROS homeostasis and reduction of mitochondrial dysfunction

Plant senescence is the final period of the plant life cycle and represents a programmed cell death (PCD) process. Melatonin, a versatile signaling molecule, exhibits potent free radical scavenging properties and actively participates in cellular antioxidant systems, effectively retarding plant senescence throughout its development. In order to illustrate the impact of melatonin on PCD during senescence, we examined the effects of exogenous melatonin at 80 μmol L−1 on PCD and mitochondrial function in broccoli bud cells at 25 ℃. The findings revealed that melatonin treatment not only maintained the morphological integrity of chloroplasts and mitochondria but also attenuated the decline in chlorophyll content by reducing the expression of genes that metabolize chlorophyll, including BoPPH, BoPAO, and BoSGR1. In comparison to the control group, the treatment decreased the content of H2O2 and the rate of O2- production in mitochondria and simultaneously enhanced the activities of ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD), resulting in effective maintenance of reactive oxygen species (ROS) homeostasis and reduction of the level of lipid peroxidation in broccoli buds during senescence. Meanwhile, exogenous melatonin treatment up-regulated alternative oxidase (AOX) activity and its gene expression while delayed the reduction of cytochrome oxidase (COX) activity and restrained the over-opening of mitochondrial permeability transition pores (MPTP). Additionally, exogenous melatonin decelerated the increase in membrane potential and prevented mitochondria from releasing excess cytochrome c (Cyt c) into the cytoplasm. Taken together, the results indicate that melatonin treatment delayed mitochondrial dysfunction, preserved mitochondrial ROS homeostasis, and consequently postponed the initiation of PCD, ultimately inhibiting senescence in broccoli.

Exogenous melatonin and interstock treatments confer chilling tolerance in citrus fruit during cold storage

Fruit quality can be improved using rootstocks and melatonin (MT) after harvest. However, the effects of the combined use of interstocks and MT on citrus fruit storage quality and physiological senescence are unknown. Hence, this study aimed to assess how MT treatment affects the organoleptic quality and antioxidant system of Kiyomi Tangor fruit obtained from trees growing on rootstocks with and without interstocks during the cold storage period. All treatments reduced fruit weight loss while increasing firmness, soluble sugars, total soluble solids, titratable acids, and skin color as compared with those of the control, indicating that MT and rootstocks slowed the deterioration of fruit quality during cold storage. Furthermore, the combined use of interstocks and MT prevented electrolyte leakage and malondialdehyde from accumulating, suggesting the potential hindrance of reactive oxygen species (ROS) generation and oxidative harm. This can be attributed to the improved efficacy of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase in removing ROS. Although both MT and rootstocks can improve the quality of Kiyomi Tangor fruit after harvest, the combination of MT and interstocks provided the highest quality during cold storage.

Melatonin treatment induces DNA methylation to alleviate chilling induced-browning in cold stored peach fruit

Chilling injury (CI) often occurs in postharvest peach fruit during low-temperature storage, and exogenous melatonin (MT) treatment has been demonstrated to alleviate CI in cold-stored peach fruit. In this study, we further investigated the effect of MT treatment on DNA methylation in relation to the chilling-induced browning in cold stored peaches. The results revealed that MT treatment upregulated PpPAL expression while simultaneously suppressing the transcripts of PpPPO and PpPOD. This dual effect resulted in the increased accumulation of phenolics, effectively reducing the incidence of browning in peaches stored at 4 °C. In addition, MT treatment increased the activities of methylesterase and demethylase, affecting significant changes in the DNA methylation levels of the local genes PpPPO, PpPOD and PpPAL, which suggested that MT treatment could mediate DNA methylation of the browning-related genes such as PpPPO, PpPOD and PpPAL, and consequently increased the phenolic contents and alleviated browning symptoms in cold-stored peaches.

Identification of rice melatonin receptor OsPMTR and its comparative in silico analysis with arabidopsis AtCAND2 receptor

Melatonin (N-acetyl-5-methoxytryptamine) is a signaling molecule having crucial role in plant growth, development and stress responses. Melatonin receptor has been identified in Arabidopsis, maize, tobacco and cassava. However no bona fide receptor has been identified in rice. Here we have identified a homolog of Arabidopsis melatonin receptor (AtCAND2/PMTR1) in rice OsPMTR. It is predicted to be a plasma membrane localized, seven transmembrane domain containing protein resembling G-protein coupled receptor. The comparative in silico analysis revealed that OsPMTR has similar gene structure and physiochemical properties as that of AtCAND2/PMTR1. Molecular docking analysis of OsPMTR and melatonin revealed pKi and ligand efficiency that were comparable to that of AtCAD2 which indicates strong possible interaction between OsPMTR and melatonin. To further elucidate melatonin signaling, we identified 24 potential interacting partners of OsPMTR using in silico protein-protein interaction, and also identified co-expression network of OsPMTR. OsRGA1, a known downstream signaling protein in G-protein mediated pathway, was identified as one of the interacting partners. We confirmed the interaction of OsPMTR with OsRGA1 through molecular docking. The quantitative expression analysis revealed that OsPMTR, two interacting partners (OsRGA1, OsCOLD1) and four co-expressed genes (OsTGA2.1, OsWRKY90, OsDREB6/OsERF60 and OsTCP5) were significantly induced by exogenous melatonin treatment in rice. This further suggests a potential role of OsPMTR interacting partners and coexpressed genes in OsPMTR signaling pathway. Our study shows that OsPMTR may act as a G-protein coupled receptor (GPCR) which activates the G-protein signaling through the downstream α subunit (OsRGA1) and may transcriptionally regulate many transcription factors and genes related to plant growth, development, biotic and abiotic stress tolerance. Our findings lay the foundation for the future experimental investigation in plant system to bring out the functional role of OsPMTR as a melatonin receptor and its signaling pathway in rice. This will further help develop cheap agonists and orthogonal receptors for management of abiotic stress tolerance and yield of crops. © 2017 Elsevier Inc. All rights reserved.

Evaluation of the Effect of Preharvest Melatonin Spraying on Fruit Quality of 'Yuluxiang' Pear Based on Principal Component Analysis.

Melatonin (MT), an indoleamine compound, has a pleiotropic effect on plant growth and development and can regulate the quality of tree fruit. Systematic research on the effect of preharvest MT spraying on pear fruit quality and technical solutions for MT application to regulate pear fruit quality are still lacking. Thus, here we aimed to evaluate the effects of different spraying times, concentrations, and exogenous MT application times on 'Yuluxiang' pear fruit quality. Our results showed that the single fruit weight and vertical and horizontal diameters of pear fruit sprayed with MT twice at 30 and 90 d after full bloom were the largest, and the red and green values of the treatment were the highest. MT-treated pears had higher contents of total soluble solids, soluble sugar, sucrose, sorbitol, fructose, and glucose and lower contents of titratable acid, malic acid, and citric acid. Moreover, exogenous MT treatment increased the pear peel strength. Based on the principal component analysis of 10 fruit quality indices, the suitable periods for MT spraying on 'Yuluxiang' pears were 30 and 90 d after full bloom, the suitable concentration was 100 μmol/L, and the suitable number of times was two. This study provides a theoretical reference for optimizing MT application and improving pear fruit quality.

Biosynthesis of neuroprotective melatonin is dysregulated in Huntington's disease.

Huntington's disease (HD) is a progressive neurodegenerative brain disorder associated with uncontrolled body movements, cognitive decline, and reduced circulating melatonin levels. Melatonin is a potent antioxidant and exogenous melatonin treatment is neuroprotective in experimental HD models. In neurons, melatonin is exclusively synthesized in the mitochondrial matrix. Thus, we investigated the integrity of melatonin biosynthesis pathways in pineal and extrapineal brain areas in human HD brain samples, in the R6/2 mouse model of HD and in full-length mutant huntingtin knock-in cells. Aralkylamine N-acetyltransferase (AANAT) is the rate-limiting step enzyme in the melatonin biosynthetic pathway. We found that AANAT expression is significantly decreased in the pineal gland and the striatum of HD patients compared to normal controls. In the R6/2 mouse forebrain, AANAT protein expression was decreased in synaptosomal, but not nonsynaptosomal, mitochondria and was associated with decreased synaptosomal melatonin levels compared to wild type mice. We also demonstrate sequestration of AANAT in mutant-huntingtin protein aggregates likely resulting in decreased AANAT bioavailability. Paradoxically, AANAT mRNA expression is increased in tissues where AANAT protein expression is decreased, suggesting a potential feedback loop that is, ultimately unsuccessful. In conclusion, we demonstrate that pineal, extrapineal, and synaptosomal melatonin levels are compromised in the brains of HD patients and R6/2 mice due, at least in part, to protein aggregation.

Transcriptome Profiles Reveal the Promoting Effects of Exogenous Melatonin on Fruit Softening of Chinese Plum.

In this study, we investigated the effect of exogenous melatonin (MT) on cell wall metabolism leading to Chinese plum (Prunus salicina Lindl.) fruit softening. Exogenous MT treatment increased the endogenous MT content in plum fruits before fruit ripening. However, in mature plum fruits, exogenous MT treatment decreased the fruit hardness, pulp hardness, fruit elasticity, contents of ion-bound pectin, covalently-bound pectin, hemicellulose, and cellulose, and activities of xyloglucan endotransglycosylase/hydrolase and endo-β-1,4-glucanase, and increased the water-soluble pectin content, and activities of pectin methyl esterase, pectin lyase, polygalacturonase, β-galactopyranosidase, and α-L-arabinofuranosidase. Transcriptome analysis revealed that the differentially expressed genes (DEGs) associated with cell wall metabolism in the exogenous MT-treated plum fruits were mainly enriched in the pentose and glucuronate interconversions, phenylpropanoid biosynthesis, cyanoamino acid metabolism, and galactose metabolism pathways. Analysis of these DEGs revealed that exogenous MT treatment affected the expression of genes regulating the cell wall metabolism. Overall, exogenous MT treatment promotes the fruit softening of Chinese plum.

Uporaba egzogenog melatonina u Ouled Djellal ovaca i ovnova izvan sezone parenja

The study aimed to investigate the effect of exogenous melatonin treatment on the ewe’s and ram’s reproductive activity, out-of-season breeding, usually matching with spring. The eighty four adult ewes and 16 genitor rams of Ouled Djellal breed, taken randomly out of a 176 ovine flock were treated with respectively 1 or 3 melatonin subcutaneous ear implants (Melovine). The 76 non-treated remaining ewes served as the control group. The rams, kept separately from the females, had scrotal perimeters measured before (PS1) and 47 days after (PS2) melatonin treatment, before they were allowed to run with the ewes. The analysis of the lambing rates had not shown anysignificant difference (P>0.05) between the melatonin treated ewes and those of the control group (90.4% vs. 97.3%) which proves that their sexual activity is not under photoperiod control. However, the analysis by the t-test of the paired samples of the ram’s scrotal perimeters had shown a significant difference (P<0.05) between the measurements before and after melatonin treatment in rams which proves the potential effect of this hormone on daily sperm output. During the study period, no effect on female sexual activity has been noted. In Ouled Djellal sheep breed, melatonin use is not recommended in ewes but it can be useful in rams since it enhances sexual capacity during mating.

Potential application of melatonin in reducing boron toxicity in rice seedlings through improved growth, cell wall composition, proline, and defense mechanisms

Melatonin (MT) has been demonstrated to provide defense against both biotic and abiotic stressors. Boron toxicity (BT) can significantly limit the growth and production of plants. However, few studies have been conducted on whether MT is effective in attenuating B toxicity in different plants. In order to evaluate the efficacy of exogenous MT treatment in reducing the negative impact of BT on rice seedlings, this study examined the influence of MT on growth, antioxidant capacity, cell wall composition, and proline metabolism in rice seedlings under hydroponics. Four treatments were established: MT (50 μM), MT + BT (50 μM MT + 800 μM B), BT (800 μM), and CK (control) in a completely randomized design. The results indicate that BT had a significant detrimental effect on the shoot length, root length, and root and shoot fresh weights of rice seedlings by 11.96%, 27.77%, 25.69%, and 18.67%, respectively as compared to the control treatment. However, exogenous MT application increased these parameters and reduced B accumulation in aboveground parts (14.05%) of the plant. Exogenous MT also increased the endogenous melatonin content and antioxidant enzyme activities (64.45%, 71.61%, 237.64%, and 55.42% increase in superoxide dismutase, ascorbate peroxidase, and peroxidase activities, respectively), while decreasing reactive oxygen species levels and oxidized forms of glutathione and ascorbic acid. Additionally, MT enhanced the biosynthesis of proline by decreasing proline dehydrogenase (ProDH) and increasing the GSH (glutathione) and ASA (ascorbic acid) contents. Exogenous MT also increased cell wall components that can increase B adsorption to the cell wall. Overall, these findings suggest that MT application can be a potential solution for strengthening the stress tolerance of rice seedlings, particularly under conditions of B toxicity. In regions where soil contains high levels of boron, the use of MT could enhance rice crop yields and quality.

Melatonin treatment promotes cold adaptation and spring growth of tea plants

Cold stress can seriously affect the yield and quality of spring tea, ultimately leading to decreases in the economic benefits of tea production. Although melatonin can enhance the cold resistance of young tea plants indoors, its effects on mature tea plants in tea gardens and on the spring tea yield and quality remain unknown. In this study, we determined the optimal exogenous melatonin treatment concentration (100 µmol/L) and revealed that an exogenous melatonin treatment for 2 months can protect mature tea plants (Camellia sinensis cv. ‘Yinghong No. 9’) in tea gardens from cold stress. Following the application of exogenous melatonin, the quality of spring tea was not significantly affected, and the growth of spring tea was stimulated. Combining the melatonin and cover treatments was more effective in promoting spring tea growth. The study results may be used to further increase the yield and preserve the quality of spring tea under cold stress conditions.

Molecular and functional insights into MaTDC and MaASMT genes associated with melatonin biosynthesis and low temperature stress in banana

The melatonin biosynthesis in plant is mainly catalyzed by tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT). In this study, nine MaTDCs, one MaT5H, one MaSNAT, and twenty-four MaASMTs were identified from Musa acuminate genome. The MaTDC and MaASMT gene families were further studied through bioinformatics analysis and expression pattern analysis under low temperature and exogenous melatonin treatments. MaTDCs and MaASMTs could be classified into two and five subfamilies, respectively. These classifications were strongly supported by their gene structures and protein conserved motifs. The expression of MaTDC4–1, MaTDC7–1, MaTDC8–2, MaTDC10–1 and MaASMT10–1 and the content of endogenous melatonin in banana leaf were significantly promoted by low temperature. Moreover, the promoting effects of combined low temperature and exogenous melatonin treatment were more significant. Notably, the expression of MaTDC4–1, MaTDC8–2, MaTDC10–1 and MaASMT10–1 was not only low temperature inducible but also very significantly or significantly positively correlated with the melatonin content. Moreover, transient overexpression of MaTDC4–1 and MaASMT4–2 greatly increased the melatonin accumulation in tobacco leaf. Our study revealed the contributions of MaTDC and MaASMT genes and melatonin to the banana cold resistance.

A cysteine-rich secretory protein involves in phytohormone melatonin mediated plant resistance to CGMMV

BackgroundMelatonin is considered to be a polyfunctional master regulator in animals and higher plants. Exogenous melatonin inhibits plant infection by multiple diseases; however, the role of melatonin in Cucumber green mottle mosaic virus (CGMMV) infection remains unknown.ResultsIn this study, we demonstrated that exogenous melatonin treatment can effectively control CGMMV infection. The greatest control effect was achieved by 3 days of root irrigation at a melatonin concentration of 50 μM. Exogenous melatonin showed preventive and therapeutic effects against CGMMV infection at early stage in tobacco and cucumber. We utilized RNA sequencing technology to compare the expression profiles of mock-inoculated, CGMMV-infected, and melatonin+CGMMV-infected tobacco leaves. Defense-related gene CRISP1 was specifically upregulated in response to melatonin, but not to salicylic acid (SA). Silencing CRISP1 enhanced the preventive effects of melatonin on CGMMV infection, but had no effect on CGMMV infection. We also found exogenous melatonin has preventive effects against another Tobamovirus, Pepper mild mottle virus (PMMoV) infection.ConclusionsTogether, these results indicate that exogenous melatonin controls two Tobamovirus infections and inhibition of CRISP1 enhanced melatonin control effects against CGMMV infection, which may lead to the development of a novel melatonin treatment for Tobamovirus control.

Effect of melatonin on ripening of ‘Pearl’ guava fruit at ambient temperature

In this study, fruit quality and activities of antioxidant and cell wall degrading enzymes, were investigated to explore the effect of exogenousmelatonin on preservation of postharvest guava during storage at room temperature (25℃). The results showed 500 μM melatonin treatmentcould effectively delay the softening and yellowing of guava fruit, and maintain high soluble sugar and vitamin С content, to keep theappearance and nutrient quality. Moreover, the treatment could inhibit PPO (polyphenol oxidase) enzyme activity to prevent browning,but promote POD (peroxidase) and CAT (catalase) enzyme activities to improve the resistance of fruit during storage. Furthermore, PG(polygalacturonase) and PL (pectate lyase) enzyme activities were effectively suppressed to protect the structural integrity of the cellwall in fruit, and delay the softening process. These findings indicate, 500 μM exogenous melatonin treatment could delay the ripeningof postharvest guava fruit, and present application value of preservation.

Melatonin as a Possible Natural Anti-Viral Compound in Plant Biocontrol.

Melatonin is a multifunctional and ubiquitous molecule. In animals, melatonin is a hormone that is involved in a wide range of physiological activities and is also an excellent antioxidant. In plants, it has been considered a master regulator of multiple physiological processes as well as of hormonal homeostasis. Likewise, it is known for its role as a protective biomolecule and activator of tolerance and resistance against biotic and abiotic stress in plants. Since infections by pathogens such as bacteria, fungi and viruses in crops result in large economic losses, interest has been aroused in determining whether melatonin plays a relevant role in plant defense systems against pathogens in general, and against viruses in particular. Currently, several strategies have been applied to combat infection by pathogens, one of them is the use of eco-friendly chemical compounds that induce systemic resistance. Few studies have addressed the use of melatonin as a biocontrol agent for plant diseases caused by viruses. Exogenous melatonin treatments have been used to reduce the incidence of several virus diseases, reducing symptoms, virus titer, and even eradicating the proliferation of viruses such as Tobacco Mosaic Virus, Apple Stem Grooving Virus, Rice Stripe Virus and Alfalfa Mosaic Virus in tomato, apple, rice and eggplant, respectively. The possibilities of using melatonin as a possible natural virus biocontrol agent are discussed.

Exogenous Melatonin Application Induced Morpho-Physiological and Biochemical Regulations Conferring Salt Tolerance in Ranunculus asiaticus L.

This study presents the effects of exogenous melatonin application at different concentrations (50, 100, and 200 μM) on the morphological, physiological, and antioxidant defense systems of the buttercup plant under salinity stress (4.5 and 5.5 dS·m−1 EC). Expectedly, the salinity stress negatively affected the plant growth parameters, cell membrane stability, and POX enzyme activity of R. asiaticus compared to non-stressed plants. However, in a dose-dependent manner, exogenous melatonin foliar application decreased the salt stress-induced symptoms of retarded vegetative growth, physiological characteristics, and oxidative stress level. The results obtained, revealed the significant effectiveness of exogenous melatonin treatment at 200 μM concentration under salt stress conditions by enhancing the plant growth traits such as chlorophyll and carotenoids content, relative water content, proline content, peroxidase enzyme activity (POD), and by the decreased electrolyte leakage rate, and Na+ content, as well as delaying the emergence of flower buds under salinity stress. The salt tolerance index percentages (STI%) for all estimated characters are also calculated for all studied parameters. This study uncovered the beneficial effect of melatonin in reducing salt stress symptoms that can be used to reduce the salinity effect in ranunculus plant production.

Reactive oxygen species signaling is involved in melatonin-induced reduction of chlorothalonil residue in tomato leaves.

Pesticide overuse has led to serious global concerns regarding food safety and environmental pollution. Although the reduction of pesticide residue is critical, our knowledge about induced pesticide metabolism in plants remains fragmentary. Melatonin (N-acetyl-5-methoxytryptamine) is an effective stress-relieving agent in both animals and plants, but little is known about the melatonin signaling mechanism and its effect on pesticide metabolism in plants. Here, we found that exogenous melatonin treatment significantly reduced chlorothalonil residue by 41% but suppression of endogenous melatonin accumulation increased chlorothalonil residue in tomato leaves. Moreover, melatonin increased photosynthesis, Fv/Fm, Calvin cycle enzyme activity, antioxidant enzyme activity, glutathione pool, and RESPIRATORY BURST HOMOLOG1 (RBOH1) expression in tomato leaves. However, the upregulation of RBOH1, CYP724B2, GST1, GST2, GSH and ABC, the increased glutathione concentrations and the activity of detoxification enzymes due to melatonin treatment were all significantly attenuated by the treatment with an NADPH oxidase inhibitor and a ROS scavenger, indicating a clear relationship between the reduction of pesticide residue and induction in detoxifying enzymes and genes upon melatonin treatment in an apoplastic H2O2-dependent manner. These results reveal that melatonin-induced reduction in chlorothalonil residue is mediated by H2O2 signaling in tomato leaves.