Melatonin Pretreatment Research Articles

Melatonin attenuated inflammatory reaction by inhibiting the activation of p38 and NF‑κB in taurocholate‑induced acute pancreatitis.

The aim of the present study was to investigate the protective mechanism underlying of melatonin in severe acute pancreatitis (SAP). A total of 64male Sprague‑Dawley rats were randomly divided into four groups: The sham operation (SO) group, SAP group, melatonin treatment (MLT) group and p38 inhibitor (SB203580) treatment (SB) group. Acute pancreatitis was induced by 5% taurocholate through retrograde infusion into the biliopancreatic ducts. The melatonin and SB203580 treatment groups were administered with MLT and SB 30min before operation the induction of SAP. Rats in each group were euthanized at 6 and 12h following SAP induction. Blood and pancreatic tissues were removed for inflammatory examination. Peripheral blood mononuclear cells (PBMCs) were isolated following sacrifice to measure the phosphorylation of p38 and nuclear factor‑κB (NF‑κB was measured as p65 and phosphorylation of p65). The pretreatment of melatonin significantly attenuated the severity of pancreatitis. In addition, melatonin also reduced serum amylase and proinflammatory cytokine levels, including tumor necrosis factor‑α, interleukin (IL)‑1 and IL‑6. The mean pathological scores for pancreatic tissues in the MLT group were higher than those for samples in the SO group, but were lower than those for samples in the SAP group at each time-point. Phosphorylation of p38 and p65 levels in the melatonin treatment group were lower than that in the SAP group, and higher in the SAP group than in the SO group, and the SB203580 treatment group. Furthermore, melatonin significantly inhibited the activation of p38 and NF‑κB in PBMCs. The authors revealed that melatonin may attenuate inflammatory reactions by inhibiting the activation of p38 MAPK and NF‑κB in both acute pancreatitis rats and PBMCs. SAP is a severe disease with a high risk of morbidity and mortality. It is important to attenuated inflammatory reaction in acute pancreatitis. Thus, the authors studied melatonin, which is synthesized by the pineal gland and released into the blood. Previous studies have shown that melatonin serves a protective role in the early course of human acute pancreatitis, and melatonin concentration variations are closely related to the severity of acute pancreatitis. It may be concluded that melatonin may attenuates inflammatory reactions by inhibiting the activation of p38 MAPK and NF‑κB in both acute pancreatitis rats and PBMCs.

Effects of Exogenous Melatonin on Methyl Viologen-Mediated Oxidative Stress in Apple Leaf.

Oxidative stress is a major source of damage of plants exposed to adverse environments. We examined the effect of exogenous melatonin (MT) in limiting of oxidative stress caused by methyl viologen (MV; paraquatin) in apple leaves (Malus domestica Borkh.). When detached leaves were pre-treated with melatonin, their level of stress tolerance increased. Under MV treatment, melatonin effectively alleviated the decrease in chlorophyll concentrations and maximum potential Photosystem II efficiency while also mitigating membrane damage and lipid peroxidation when compared with control leaves that were sprayed only with water prior to the stress experiment. The melatonin-treated leaves also showed higher activities and transcripts of antioxidant enzymes superoxide dismutase, peroxidase, and catalase. In addition, the expression of genes for those enzymes was upregulated. Melatonin-synthesis genes MdTDC1, MdT5H4, MdAANAT2, and MdASMT1 were also upregulated under oxidative stress in leaves but that expression was suppressed in response to 1 mM melatonin pretreatment during the MV treatments. Therefore, we conclude that exogenous melatonin mitigates the detrimental effects of oxidative stress, perhaps by slowing the decline in chlorophyll concentrations, moderating membrane damage and lipid peroxidation, increasing the activities of antioxidant enzymes, and changing the expression of genes for melatonin synthesis.

Melatonin attenuates lung ischaemia-reperfusion injury via inhibition of oxidative stress and inflammation.

Lung ischaemia-reperfusion injury is a complex pathophysiological process due to the production of reactive oxygen species and the generation of inflammatory reaction. We investigated the protective effects and the corresponding mechanism of melatonin (MT), a potent free-radical scavenger, on lung injury induced by ischaemia-reperfusion in a mouse model. Adult male C57BL/6J mice (n = 30) were randomly and equally allocated into 5 groups: sham controls, IR, IR + 10 mg/kg MT, IR + 20 mg/kg MT and IR + 30 mg/kg MT. Lung ischaemia-reperfusion injury was induced by thoracotomy followed by clamping of the left hilum for 1 h and subsequent reperfusion for 2 h. Histological scoring analysis showed that lung parenchymal damage was ameliorated in the melatonin pretreatment groups when compared with the IR group, with the IR + 20 mg/kg MT group showing the strongest effect among the melatonin pretreatment groups. Wet-to-dry weight ratio, detection of malondialdehyde, protein expressions of inflammatory factors (tumour necrosis factor-α, interleukin-1β, NF-κB and IKK-γ) and apoptotic factors (cleaved caspase-3 and Bax/Bcl-2), as well as TUNEL assay showed changes similar to those of the lung injury scores in all groups. In contrast, the examination of superoxide dismutase showed a pattern contrary to that of the lung injury score in all groups. In addition, immunohistochemistry staining showed that the expressions of the antioxidants glutathione peroxidase and glutathione reductase were increased in the melatonin pretreatment groups. This study demonstrated that melatonin pretreatment attenuated lung ischaemia-reperfusion injury via inhibition of oxidative stress, inflammation and apoptosis.

Radioprotective effect of melatonin on expression of Cdkn1a and Rad50 genes in rat peripheral blood.

Ionizing radiation is a critical threat to biomolecules, especially DNA. Various combinatorial compounds have been studied to protect this biomolecule. Melatonin has been reported as a direct and indirect free radical scavenger, but in this study, we explored the effect of melatonin on assisting in DNA repair by expression of Cdkn1a and Rad50; both of these genes are involved in DNA repair signaling, induced by radiation in rat peripheral blood. Rats were irradiated with single whole-body linear accelerator X-ray radiation doses of 2 and 8 Gy with or without melatonin (100 mg/kg body weight) pretreatments. The rats were randomly divided into nine groups and given an intraperitoneal injection of melatonin or the same volume of vehicle alone 1 h before radiation. Blood samples were taken 8, 24, and 48 h postradiation to measure gene expression of Cdkn1a and Rad50 using quantitative reverse transcription polymerase chain reaction technique. Melatonin pretreatment increased the expression of Cdkn1a and Rad50 in 8 and 24 h postradiations (2 and 8 Gy) (P < 0.05), and there was no significant difference in 48 h postradiation compared to the radiation-only and vehicle plus radiation (2 and 8 Gy) groups. Based on our results, pretreatment with melatonin (100 mg/kg) may ameliorates injurious effects of 2 and 8 Gy ionization radiation by increasing the expression level of Cdkn1a and Rad50 in rat peripheral blood and assist in DNA double-strand breaks repair, especially during the early postradiation.

Physiological and biochemical analyses reveal drought tolerance in cool-season tall fescue (

Tall fescue (Festuca arundinacea Schreb.) is a widely used, cool-season turf grass and is relatively sensitive to water stress. Melatonin has been reported to improve abiotic stress tolerance in many plants. In this study, we demonstrated that, although shoot height and fresh weight of tall fescue seedlings were significantly reduced by drought stress, they were increased by melatonin pre-treatment compared with control plants. Chemical analyses showed that tall fescue seedlings pre-treated with melatonin exhibited decreased levels of reactive oxygen species, electrolyte leakage and malondialdehyde, but higher levels of antioxidant enzyme activities (catalase, and peroxidase) and total chlorophyll content, compared with untreated seedlings. Leaf water loss was also partially mitigated and leaf water content increased by melatonin application, resulting in improved plant growth under drought stress. Moreover, root growth of tall fescue seedlings was promoted by melatonin under osmotic stress. The results show that drought tolerance was improved in cool-season tall fescue by application of exogenous melatonin. Therefore, melatonin may potentially be used as a protectant for plants against the deleterious effects of drought or water-deficit stress.

Melatonin mitigates thioacetamide-induced hepatic fibrosis via antioxidant activity and modulation of proinflammatory cytokines and fibrogenic genes

AimsThe potential antifibrotic effects of melatonin against induced hepatic fibrosis were explored. Main methodsRats were allocated into four groups: placebo; thioacetamide (TAA) (200mg/kg bwt, i.p twice weekly for two months); melatonin (5mg/kgbwt, i.p daily for a week before TAA and continued for an additional two months); and melatonin plus TAA. Hepatic fibrotic changes were evaluated biochemically and histopathologically. Hepatic oxidative/antioxidative indices were assessed. The expression of hepatic proinflammatory cytokines (tumor necrosis factor-α, and interleukin-1β), fibrogenic-related genes (transforming growth factor-1β, collagen I, collagen, III, laminin, and autotaxin) and an antioxidant-related gene (thioredoxin-1) were detected by qRT-PCR. Key findingsIn fibrotic rats, melatonin lowered serum aspartate aminotransferase, alanine aminotransferase, and autotaxin activities, bilirubin, hepatic hydroxyproline and plasma ammonia levels. Melatonin displayed hepatoprotective and antifibrotic potential as indicated by mild hydropic degeneration of some hepatocytes and mild fibroplasia. In addition, TAA induced the depletion of glutathione, glutathione s-transferase, glutathione peroxidase, superoxide dismutase, catalase, and paraoxonase-1 (PON-1), while inducing the accumulation of malondialdehyde, protein carbonyl (C=O) and nitric oxide (NO), and DNA fragmentation. These effects were restored by melatonin pretreatment. Furthermore, melatonin markedly attenuated the expression of proinflammatory cytokines and fibrogenic genes via the upregulation of thioredoxin-1 mRNA transcripts. SignificanceMelatonin exhibits potent anti-inflammatory, antioxidant and fibrosuppressive activities against TAA-induced hepatic fibrogenesis via the suppression of oxidative stress, DNA damage, proinflammatory cytokines and fibrogenic gene transcripts. In addition, we demonstrate that the antifibrotic activity of melatonin is mediated by the induction of thioredoxin-1 with attenuation of autotaxin expressions.

Melatonin pretreatment improves vanadium stress tolerance of watermelon seedlings by reducing vanadium concentration in the leaves and regulating melatonin biosynthesis and antioxidant-related gene expression

Vanadium (V) is an important heavy metal with ubiquitous presence in the Earth’s crust, but limited information is available as to its effect on plants and management strategies. Melatonin is a widely studied biomolecule; it acts as an antioxidant and a signaling molecule that enhances the abiotic stress tolerance of plants. Melatonin improves copper, zinc, and cadmium tolerance in plants. In this study, we investigated the response of watermelon seedlings to V stress and the potential role of melatonin in enhancing V stress tolerance of watermelon seedlings. The results showed that seedlings pretreated with melatonin (0.1μM) exposed to V (50mg/L) had a higher relative chlorophyll content (SPAD index), photosynthetic assimilation, and plant growth compared with non-melatonin pretreated seedlings. Melatonin pretreatment lowered leaf and stem V concentrations by reducing V transport from root to shoot. Melatonin pretreatment enhanced superoxide dismutase (SOD) and catalase (CAT) activities, and reduced the hydrogen peroxide (H2O2) and malondialdehyde (MDA) content of watermelon seedlings, by regulating melatonin biosynthesis and gene expression for superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione peroxidase, and glutathione S-transferase. So far as we know, these results are the first evidence that melatonin improves plant growth of watermelon seedlings under vanadium stress conditions. Considering these observations, melatonin can be utilized to reduce the availability of V to plants, and improve plant growth and V stress tolerance.

Effects of exogenous melatonin on antioxidant capacity in Actinidia seedlings under salt stress

To investigate the alleviation of exogenous melatonin (MT) in Actinidia seedlings under 100 mM NaCl stress, one-year-old Actinidia deliciosa seedlings were treated with 0.1, 0.5 and 1μM of exogenous melatonin solution, respectively. The results showed that the antioxidant substance (ASA, TPC, TFC and TFAC) contents and antioxidative capacity (DPPH, ABTS and FRAP) of Actinidia seedlings under salt stress were significantly increased compared with the CK. At the same time, the antioxidant substance contents of Actinidia seedlings with MT pretreatment were significantly higher than those of CK and S, then the antioxidative capacity was improved, and the damage of Actinidia seedlings under salt stress was alleviated. And the treatment with 0.1μM MT solution was the most significant.

Melatonin-mediated upregulation of Sirt3 attenuates sodium fluoride-induced hepatotoxicity by activating the MT1-PI3K/AKT-PGC-1α signaling pathway

Mitochondrial reactive oxygen species (ROS) production has been implicated in the pathogenesis of fluoride toxicity in liver. Melatonin, an indolamine synthesized in the pineal gland, was previously shown to protect against sodium fluoride (NaF)-induced hepatotoxicity. This study investigated the protective effects of melatonin pretreatment on NaF-induced hepatotoxicity and elucidates the potential mechanism of melatonin-mediated protection. Reducing mitochondrial ROS by melatonin substantially attenuated NaF-induced NADPH oxidase 4 (Nox4) upregulation and cytotoxicity in L-02 cells. Melatonin exerted its hepatoprotective effects by upregulating Sirtuin 3 (Sirt3) expression level and its activity. Melatonin increased the activity of manganese superoxide dismutase (SOD2) by promoting Sirt3-mediated deacetylation and promoted SOD2 expression through Sirt3-regulated DNA-binding activity of forkhead box O3 (FoxO3a), thus inhibiting the production of mitochondrial ROS induced by NaF. Notably, increased peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) by melatonin activated the Sirt3 expression, which was regulated by an estrogen-related receptor (ERR) binding element (ERRE) mapped to Sirt3 promoter region. Analysis of the cell signaling pathway profiling systems and specific pathway inhibition indicated that melatonin enhances PGC-1α expression by activating the PI3K/AKT signaling pathway. Importantly, inhibition of melatonin receptor (MT)-1 blocked the melatonin-activated PI3K/AKT-PGC-1α-Sirt3 signaling. Mechanistic study revealed that the protective effects of melatonin were associated with down-regulation of JNK1/2 phosphorylation. Our findings provided a theoretical basis that melatonin mitigated NaF-induced hepatotoxicity, which, in part, was mediated through the activation of the Sirt3 pathway.

Melatonin application confers enhanced salt tolerance by regulating Na+ and Cl− accumulation in rice

The mitigating effects of melatonin (MT) treatment on salt-stressed seed germination capacity and of MT pretreatment (including the whole period of seed germination and seedling cultivation) on the salt tolerance of two rice (Oryza sativa L. ssp. japonica) cultivars, Liaojing 4 (LJ4, salt tolerant) and Nipponbare (Nipp, salt sensitive), and the related physiological and molecular events were investigated in this study. The results showed that when additional MT solutions (10–500 μM) were added, the NaCl-decreased seed germination potential (GP), germination index (GI) and vigor index (VI) of LJ4 and Nipp were clearly restored. When MT pretreatment occurred during the period of seed germination and seedling cultivation prior to NaCl stress, relative electrolytic leakage in roots and leaves clearly decreased and thus restored the root vigor and growth of both plants. This could be fulfilled by multiple physiological mechanisms. For example, improving seed germination ability (GP, GI and VI), strengthening root vigor, reducing Na+ and Cl− contents in roots and leaves (especially for Cl− in roots and Na+ in leaves), and enhancing the activities of antioxidant enzymes (such as catalase and superoxide dismutase) in roots and leaves resulted in a decrease in H2O2 level. Moreover, the reduced contents of Na+ and Cl− in the roots and leaves of both salt-stressed rice plants under MT pretreatment displayed clear relations with the enhanced transcription of OsSOS1 in roots and of OsCLC1 and OsCLC2 in roots and leaves. These results could indicate that soaking with MT during seed germination and/or root application of MT at the seedling stage are very simple operations that require small doses and can effectively solve the problems of low germination rate and poor seedling establishment in saline soils. Therefore, these results provide a theoretical basis and technical support for the chemical regulation of salt tolerance and cultivation practices of rice and other crops in saline areas.

Melatonin protects chondrocytes from impairment induced by glucocorticoids via NAD+-dependent SIRT1

Intra-articular injection of glucocorticoids is used to relieve pain and inflammation in osteoarthritis patients, which is occasionally accompanied with the serious side effects of glucocorticoids in collagen-producing tissue. Melatonin is the major hormone released from the pineal gland and its beneficial effects on cartilage has been suggested. In the present study, we investigated the protective role of melatonin on matrix degeneration in chondrocytes induced by dexamethasone (Dex). The chondrocytes isolated from mice knee joint were treated with Dex, melatonin, EX527 and siRNA targeted for SIRT6, respectively. Dex treatment induced the loss of the extracellular matrix, NAD+/NADH ratio and NADPH concentration in chondrocytes. Melatonin alone have no effect on the quantity of proteoglycans and collagen type IIa1, however, the pretreatment of melatonin reversed the negative effects induced by Dex. Meanwhile, the significant decrease in NAD+/NADH ratio and NADPH concentration in Dex group were up-regulated by pretreatment of melatonin. Furthermore, it was revealed that inhibition of SIRT1 blocked the protective effects of melatonin. The enhancement of NAD+-dependent SIRT1 activity contributes to the chondroprotecfive effects of melatonin, which has a great benefit to prevent dexamethasone-induced chondrocytes impairment.

Melatonin pre-treatment mitigates SHSY-5Y cells against oxaliplatin induced mitochondrial stress and apoptotic cell death.

Oxaliplatin (Oxa) treatment to SH-SY5Y human neuroblastoma cells has been shown by previous studies to induce oxidative stress, which in turn modulates intracellular signaling cascades resulting in cell death. While this phenomenon of Oxa-induced neurotoxicity is known, the underlying mechanisms involved in this cell death cascade must be clarified. Moreover, there is still little known regarding the roles of neuronal mitochondria and cytosolic compartments in mediating Oxa-induced neurotoxicity. With a better grasp of the mechanisms driving neurotoxicity in Oxa-treated SH-SY5Y cells, we can then identify certain pathways to target in protecting against neurotoxic cell damage. Therefore, the purpose of this study was to determine whether one such agent, melatonin (Mel), could confer protection against Oxa-induced neurotoxicity in SH-SY5Y cells. Results from the present study found Oxa to significantly reduce SH-SY5Y cell viability in a dose-dependent manner. Alternatively, we found Mel pre-treatment to SH-SY5Y cells to attenuate Oxa-induced toxicity, resulting in a markedly increased cell viability. Mel exerted its protective effects by regulating reactive oxygen species (ROS) production and reducing superoxide radicals inside Oxa-exposed. In addition, we observed pre-treatment with Mel to rescue Oxa-treated cells by protecting mitochondria. As Oxa-treatment alone decreases mitochondrial membrane potential (Δψm), resulting in an altered Bcl-2/Bax ratio and release of sequestered cytochrome c, so Mel was shown to inhibit these pathways. Mel was also found to inhibit proteolytic activation of caspase 3, inactivation of Poly (ADP Ribose) polymerase, and DNA damage, thereby allowing SH-SY5Y cells to resist apoptotic cell death. Collectively, our results suggest a role for melatonin in reducing Oxa induced neurotoxicity. Further studies exploring melatonin’s protective effects may prove successful in eliciting pathways to further alter the neurotoxic pathways of platinum compounds in cancer treatment.

Zinc oxide nanoparticles mediated cytotoxicity, mitochondrial membrane potential and level of antioxidants in presence of melatonin

Zinc oxide nanoparticles (ZnO NPs) are widely used in a variety of products and are currently being investigated for biomedical applications. However, they have the potential to interact with macromolecules like proteins, lipids and DNA within the cells which makes the safe biomedical application difficult. The toxicity of the ZnO NP is mainly attributed reactive oxygen species (ROS) generation. Different strategies like iron doping, polymer coating and external supply of antioxidants have been evaluated to minimize the toxic potential of ZnO NPs. Melatonin is a hormone secreted by the pineal gland with great antioxidant properties. The melatonin is known to protect cells from ROS inducing external agents like lipopolysaccharides. In the present study, the protective effect of melatonin on ZnO NPs mediated toxicity was evaluated using C6 glial cells. The Cytotoxicity, mitochondrial membrane potential and free radical formation were measured to study the effect of melatonin. Antioxidant assays were done on mice brain slices, incubated with melatonin and ZnO NPs. The results of the study reveal that, instead of imparting a protective effect, the melatonin pre-treatment enhanced the toxicity of ZnO NPs. Melatonin increased antioxidant enzymes in brain slices.

Effects of Melatonin on Anti-oxidative Systems and Photosystem II in Cold-Stressed Rice Seedlings.

Melatonin (N-acetyl-5-methoxytryptamine) plays important role in multiple plant developmental processes and stress responses. We investigated the possible mediatory role of melatonin in growth, photosynthesis, and the response to cold stress in rice by using three different experiments: soaking seed; immersing roots, and spraying to leaves with 0, 20, or 100 μM melatonin. After 6 days of cold stress, the growth of rice seedlings was significantly inhibited, but this inhibition was alleviated by exogenous melatonin. Furthermore, exogenous melatonin pretreatment alleviated the accumulation of reactive oxygen species, malondialdehyde and cell death induced by cold stress. Melatonin pretreatment also relieved the stress-induced inhibitions to photosynthesis and photosystem II activities. Further investigations showed that, antioxidant enzyme activities and non-enzymatic antioxidant levels were increased by melatonin pretreatments. The treatment methods of seed soaking and root immersion were more effective in improving cold stress resistance than the spraying method. The results also indicated the dose-dependent response of melatonin on rice physiological, biochemical, and photosynthetic parameters.

Melatonin pretreatment improves gastric mucosal blood flow and maintains intestinal barrier function during hemorrhagic shock in dogs.

Melatonin improves hepatic perfusion after hemorrhagic shock and may reduce stress-induced gastric lesions. This study was designed to investigate whether pretreatment with melatonin may influence gastric mucosal microcirculatory perfusion (μflow), oxygenation (μHbO2 ), or intestinal barrier function during physiological and hemorrhagic conditions in dogs. In a randomized crossover study, five anesthetized foxhounds received melatonin 100μgkg-1 or vehicle (ethanol 5%) intravenously in the absence or presence of hemorrhagic shock (60minutes, -20% blood volume). Systemic hemodynamic variables, gastric mucosal perfusion, and oxygenation were recorded continuously; intestinal barrier function was assessed intermittently via xylose absorption. During hemorrhagic shock, melatonin significantly attenuated the decrease in μflow, compared with vehicle (-19±9 vs -43±10aU, P<.05), without influence on μHbO2 . A significant increase in xylose absorption was detected during hemorrhage in vehicle-treated dogs, compared with sham-operated animals (13±2 vs 8±1 relative amounts, P<.05); this was absent in melatonin-treated animals (6±1 relative amounts). Melatonin did not influence macrocirculation. Melatonin improves regional blood flow suggesting improved oxygen delivery in gastric mucosa during hemorrhagic shock. This could provide a mechanism for the observed protection of intestinal barrier function in dogs.

Melatonin systemically ameliorates drought stress-induced damage in Medicago sativa plants by modulating nitro-oxidative homeostasis and proline metabolism.

Recent reports have uncovered the multifunctional role of melatonin in plant physiological responses under optimal and suboptimal environmental conditions. In this study, we explored whether melatonin pretreatment could provoke priming effects in alfalfa (Medicago sativa L.) plants subsequently exposed to prolonged drought stress (7days), by withholding watering. Results revealed that the rhizospheric application of melatonin (10μmolL-1 ) remarkably enhanced the drought tolerance of alfalfa plants, as evidenced by the observed plant tolerant phenotype, as well as by the higher levels of chlorophyll fluorescence and stomatal conductance, compared with nontreated drought-stressed plants. In addition, lower levels of lipid peroxidation (MDA content) as well as of both H2 O2 and NO contents in primed compared with nonprimed stressed plants suggest that melatonin pretreatment resulted in the systemic mitigation of drought-induced nitro-oxidative stress. Nitro-oxidative homeostasis was achieved by melatonin through the regulation of reactive oxygen (SOD, GR, CAT, APX) and nitrogen species (NR, NADHde) metabolic enzymes at the enzymatic and/or transcript level. Moreover, melatonin pretreatment resulted in the limitation of cellular redox disruption through the regulation of the mRNA levels of antioxidant and redox-related components (ADH, AOX, GST7, GST17), as well via osmoprotection through the regulation of proline homeostasis, at both the enzymatic (P5CS) and gene expression level (P5CS, P5CR). Overall, novel results highlight the importance of melatonin as a promising priming agent for the enhancement of plant tolerance to drought conditions through the regulation of nitro-oxidative and osmoprotective homeostasis.

Effects of melatonin on seedling growth, mineral nutrition, and nitrogen metabolism in cucumber under nitrate stress.

In China, excessive use of nitrogen fertilizers in glasshouses leads to nitrate accumulations in soil and plants, which then limits productivity. Melatonin, an evolutionarily highly conserved molecule, has a wide range of functions in plants. We analyzed the effects of melatonin pretreatment on the growth, mineral nutrition, and nitrogen metabolism in cucumber (Cucumis sativus L. "Jin You No. 1") when seedlings were exposed to nitrate stress. An application of 0.1mmol/L melatonin significantly improved the growth of plants and reduced their susceptibility to damage due to high nitrate levels (0.6mol/L) during the ensuing period of stress treatment. Although excess nitrate led to an increase in the concentrations of nitrogen, potassium, and calcium, as well as a decrease in levels of phosphorus and magnesium, exogenous melatonin generally had the opposite effect except for a further rise in calcium concentrations. Pretreatment also significantly reduced the accumulations of nitrate nitrogen and ammonium nitrogen and enhanced the activities of enzymes involved in nitrogen metabolism. Expression of Cs-NR and Cs-GOGAT, two genes that function in that metabolism, was greatly down-regulated when plants were exposed to 0.6mol/L nitrate, but was up-regulated in plants that had received the 0.1mmol/L melatonin pretreatment. Our results are the first evidence that melatonin has an important role in modulating the composition of mineral elements and nitrogen metabolism, thereby alleviating the inhibitory effect on growth normally associated with nitrate stress.

Inhibition of iron overload-induced apoptosis and necrosis of bone marrow mesenchymal stem cells by melatonin.

Iron overload induces severe damage to several vital organs such as the liver, heart and bone, and thus contributes to the dysfunction of these organs. The aim of this study is to investigate whether iron overload causes the apoptosis and necrosis of bone marrow mesenchymal stem cells (BMSCs) and melatonin may prevent its toxicity. Perls’ Prussion blue staining showed that exposure to increased concentrations of ferric ammonium citrate (FAC) induced a gradual increase of intracellular iron level in BMSCs. Trypan blue staining demonstrated that FAC decreased the viability of BMSCs in a concentration-dependent manner. Notably, melatonin protected BMSCs against apoptosis and necrosis induced by FAC and it was vertified by Live/Dead, TUNEL and PI/Hoechst stainings. Furthermore, melatonin pretreatment suppressed FAC-induced reactive oxygen species accumulation. Western blot showed that exposure to FAC resulted in the decrease of anti-apoptotic protein Bcl-2 and the increase of pro-apoptotic protein Bax and Cleaved Caspase-3, and necrosis-related proteins RIP1 and RIP3, which were significantly inhibited by melatonin treatment. At last, melatonin receptor blocker luzindole failed to block the protection of BMSCs apoptosis and necrosis by melatonin. Taken together, melatonin protected BMSCs from iron overload induced apoptosis and necrosis by regulating Bcl-2, Bax, Cleaved Caspase-3, RIP1 and RIP3 pathways.

Exogenous Melatonin Confers Salt Stress Tolerance to Watermelon by Improving Photosynthesis and Redox Homeostasis.

Melatonin, a pleiotropic signal molecule, has been shown to play important roles in the regulation of plant growth, development, and responses to environmental stresses. Since a few species have been investigated to unveil the effect of exogenous melatonin on salt stress, the underlying mechanism of melatonin-mediated salt stress tolerance in other plant species still remains largely unknown. In this study, the effects of melatonin on leaf photosynthesis and redox homeostasis in watermelon were examined under salt stress (300 mM NaCl) along with different doses of melatonin (50, 150, and 500 μM) pretreatment. NaCl stress inhibited photosynthesis and increased accumulation of reactive oxygen species and membrane damage in leaves of watermelon seedlings. However, pretreatment with melatonin on roots alleviated NaCl-induced decrease in photosynthetic rate and oxidative stress in a dose-dependent manner. The protection of photosynthesis by melatonin was closely associated with the inhibition of stomatal closure and improved light energy absorption and electron transport in photosystem II, while the reduction of oxidative stress by melatonin was attributed to the improved redox homeostasis coupled with the enhanced activities of antioxidant enzymes. This study unraveled crucial role of melatonin in salt stress mitigation and thus can be implicated in the management of salinity in watermelon cultivation.

Effects of melatonin on photosynthetic performance and antioxidants in melon during cold and recovery

Melatonin (MT), a tryptophan derivative, plays an important role in the function and survival of organisms. To better understand the role of MT in cold tolerance, the melon (Cucumis melo L.) were sprayed with various concentrations of MT (0, 50, 100, 200 or 400 μM), exposed to cold stress (day/night temperature of 12/6 °C) for 7 d, and then returned to optimal conditions (28/18 °C) for 7-d recovery. The foliar application of MT (especially 200 μM) significantly alleviated cold-induced growth suppression, and MT-treated plants recovered more quickly than untreated plants. Further, MT-treated plants had higher chlorophyll content, photosynthetic rate, stomatal conductance, as well as maximal quantum yield of photosystem (PS) II photochemistry, and efficiency of excitation energy capture of open PS II centres under cold stress than untreated plants. Furthermore, exogenous MT significantly reduced malondialdehyde content and markedly increased the activities of antioxidant enzymes superoxide dismutase (SOD), guaiacol peroxidase (POD), and catalase (CAT) under cold stress. MT also increased expression of antioxidant genes CmSOD, CmPOD, and CmCAT under cold stress. The results indicate that MT pretreatment alleviated the detrimental effects of cold stress and accelerateds the recovery mainly by enhancing photosynthesis and antioxidant capacity in melon leaves.