μM Melatonin Research Articles

Melatonin Treatment Enhances the Growth and Productivity of Useful Metabolites in the In Vitro Culture of Spirodela polyrhiza.

Spirodela polyrhiza (Araceae family) is a duckweed species that serves as a potential resource for feed, food, bioremediation, and pharmaceutical applications. In this study, we assessed the effects of different concentrations of melatonin (0, 0.1, 1, and 10 μM) on the growth of S. polyrhiza during in vitro culture and the metabolic profiles and productivities of useful metabolites using gas chromatography-mass spectrometry coupled with multivariable statistical analysis. We found that exogenous melatonin significantly improved the total dry weight and altered the metabolic profiles of S. polyrhiza cultures. Melatonin significantly enhanced the cellular production of useful metabolites, such as γ-aminobutyric acid, dopamine, threonine, valine, and phytosterols. The volumetric productivities (mg/L) of γ-aminobutyric acid, dopamine, campesterol, β-sitosterol, and stigmasterol were the highest in the presence of 10 μM melatonin on day 12. Moreover, the productivities of ascorbic acid and serotonin were the highest in the presence of 1 μM melatonin on day 12. Therefore, melatonin could be used to enhance the production of biomass and useful metabolites during large-scale S. polyrhiza cultivation in cosmetic, food/feed, and pharmaceutical industries.

Melatonin Involved in Protective Effects against Cadmium Stress in Wolffia arrhiza.

Melatonin (MT) is a new plant hormone that protects against adverse environmental conditions. In the present study, the responses of Wolffia arrhiza exposed to cadmium (Cd) and MT were analyzed. Quantitative analysis of MT and precursors of its biosynthesis was performed using LC-MS-MS. The photosynthetic pigments and phytochelatins (PCs) contents were determined using HPLC, while protein and monosaccharides, stress markers, and antioxidant levels were determined using spectrophotometric methods. Interestingly, the endogenous level of MT and its substrates in W. arrhiza exposed to 1-100 µM Cd was significantly higher compared to the control. Additionally, the application of 25 µM MT and Cd intensified the biosynthesis of these compounds. The most stimulatory effect on the growth and content of pigments, protein, and sugars was observed in plants treated with 25 µM MT. In contrast, Cd treatment caused a decrease in plant weight and level of these compounds, while the application of 25 µM MT mitigated the inhibitory effect of Cd. Additionally, Cd enhanced the level of stress markers; simultaneously, MT reduced their content in duckweed exposed to Cd. In plants treated with Cd, PC levels were increased by Cd treatment and by 25 µM MT. These results confirmed that MT mitigated the adverse effect of Cd. Furthermore, MT presence was reported for the first time in W. arrhiza. In summary, MT is an essential phytohormone for plant growth and development, especially during heavy metal stress.

Melatonin Promotes Rice Seed Germination under Drought Stress by Regulating Antioxidant Capacity

Drought stress is a serious threat to the germination of plant seeds and the growth of seedlings. Melatonin has been proven to play an important role in alleviating plant stress. However, its effect on seed germination under drought conditions is still poorly understood. Therefore, we studied the effects of melatonin on rice seed germination and physiological characteristics under drought stress. Rice seeds were treated with different concentrations of melatonin (i.e., 0, 20, 100, and 500 μM) and drought stress was simulated with 5% polyethylene glycol 6000 (PEG6000). The results showed that 100 μM melatonin can effectively improve the germination potential, rate and index; the vigor index of rice seeds; and the length of the shoot and root. In addition, that treatment also increased the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and reduced the content of malondialdehyde (MDA). The grey relational grade between the shoot MDA content and the melatonin seed-soaking treatment was the highest, which could be useful for evaluating the effect of melatonin on drought tolerance. Two-way analysis of variance showed that the effect of single melatonin treatment on rice seeds was more significant than that of single drought stress and interaction treatment of drought and melatonin (p < 0.05). The subordinate function results showed that 100 μM melatonin significantly improved the germination and physiological indexes of rice seeds and effectively alleviated the adverse effects of drought stress on rice seedlings. The results helped to improve the understanding of the morphological and physiological involvement of melatonin in promoting seed germination and seedling development under drought stress.

Evaluating drought stress tolerance in different Camellia sinensis L. cultivars and effect of melatonin on strengthening antioxidant system

• In this study, the tolerance of different cultivars to drought stress have been determined. • We can suggest cultivar DG 39 and DN as tolerant cultivars to drought stress, and this cultivar can be used in breeding programs (hybridization). • Exogenously applied melatonin improve the ability of tea seedlings to tolerate drought stress. Drought stress really restring the growth and development of tea plant and affecting quality and yield. In tea growing areas of Iran, drought stress is a serious problem that affects the yield and quality of green leaves, therefore introducing cultivars that tolerate drought stress is one of the breeding purpose. To distinguish the variations in four tea cultivars response to drought stress and the role of melatonin in reducing the destructive effects of drought stress, an experiment was done at Tea Research Center of Iran, using the factorial based on completely randomized design with three replicates. The first experimental factor was the cultivar at 4 levels (DG39, DG7, DN and Kashef) and the second factor was irrigation interruption treatment at 5 levels, including control (full irrigation), irrigation interruption for 7 days with 100 µm melatonin foliar application, irrigation interruption for 7 days without melatonin foliar application, irrigation interruption for 14 days with melatonin foliar application and irrigation interruption for 14 days without melatonin foliar application. The study indicated that the physiological and biochemical traits were significantly different among the cultivars and treatments. Based on some traits such as malondialdehyde, the activities of antioxidant enzymes (CAT, POD), carotenoid and polyphenol content, DG 39 and based on traits such as proline, total sugar and chlorophyll content, DN are introduced as the cultivars that showed better tolerance to drought stress and these cultivars can be used in future breeding programs. Also melatonin treatment significantly enhanced the drought tolerance of tea seedlings, as demonstrated by decreased membrane damage, raised the concentration of proline, total protein, and total sugar and enhanced the activities of catalase and peroxidase during drought stress.

Hormonal homeostasis associated with effective induction of triticale microspore embryogenesis

The endogenous level of cytokinins (CKs) and auxins (Auxs) was analyzed in isolated microspores and ovaries of two doubled haploid (DH) lines of triticale (× Triticosecale Wittm.) to better understand the mechanism of microspore embryogenesis (ME)—the most efficient and widely applied method of producing DHs. The responsiveness of the studied lines to ME significantly varied. ME was induced by pre-treating tillers with low temperature (4 °C for 3 weeks) alone or in combination with synthetic auxin (2,4-D), auxin inhibitor (PCIB) or melatonin (MEL) applied for 4 days before microspore isolation. Hormonal profile analyses, accompanied by ME effectiveness evaluation confirmed the multi-level crosstalk of Auxs/CKs and the specific hormonal homeostasis required for effective microspore reprogramming. It was found that triticale microspores contained mainly cis zeatin derivatives: cis-zeatin-O-glucoside (cZOG), cis-zeatin riboside (cZR) and cis-zeatin (cZ), as well as indole-3-acetic acid (IAA) and IAA-aspartate (IAAsp). Increased ME efficiency was associated with higher contents of most of the identified CKs and Auxs, as well as the higher active Aux/active CK ratio. Trans CK isoforms were detected only in ovaries, confirming their importance as a source of bioactive molecules stimulating embryogenic development. Two of the pre-treatments tested: 12.5 μM PCIB and 50 μM MEL decreased the active Aux/active CK ratio, which was accompanied by an increase in the regeneration efficiency.

Combined effects of zinc oxide nanoparticles and melatonin on wheat growth, chlorophyll contents, cadmium (Cd) and zinc uptake under Cd stress

Zinc oxide nanoparticles (ZnONPs) and melatonin (MT) have been known to regulate heavy metal toxicities in plants in some studies, the effect of their combined use on cadmium (Cd) uptake by wheat (Triticum aestivum L.) and underlying mechanisms is largely unknown. Thus, plant growth, uptake and translocation of Cd mediated by soil applied ZnONPs and foliar applied MT were investigated in wheat grown in Cd polluted soil under ambient conditions. The results depicted that ZnONPs stimulated the growth, chlorophyll contents, and yield of wheat in a dose additive way and this effect was further increased with foliar application of MT. 100 mg/kg of ZnONPs alone enhanced the grain yield by 60.5 % and this increase was about 177.5 % under combined ZnONPs and 100 μM MT treatment. ZnONPs treatments decreased Cd concentration whereas increased zinc (Zn) concentrations in shoots, roots, husks and grains and the effect was further increased with exogenous MT combined with NPs in a dose-additive way. 50 and 100 mg/kg ZnONPs treatments alone decreased grain Cd by 6.5 %, and 20 % and increased the Zn concentration by 20.1 % and 24 % than control. 100 mg/kg ZnONPs +100 μM MT treatment decreased the grain Cd by 63.5 % and increased grain Zn by 51 % than control treatment. Total Cd uptake (tissues biomass × Cd concentration in respective tissues) in shoots, roots, husks and grains increased with ZnONPs alone or combined with MT than control whereas soil post-harvest bioavailable Cd concentration decreased with treatments than control. The Cd reduction in grains was due to increase in biomass and Zn concentration thereby decreasing bioavailable Cd in soil and its accumulation in plants. This study suggested that combined use of ZnONPs and MT may provide new approaches for minimizing Cd and biofortification of Zn in edible parts of plants.

In vitro approach points to a chemotactic effect of melatonin on ram spermatozoa

Sperm orientation mechanisms, such as chemotaxis, are essential for the sperm to reach the oocyte and fertilize it. Melatonin is secreted by the cumulus cells and is also present in the follicular fluid in mammals. The presence of membrane receptors for melatonin in ram spermatozoa, and its proven involvement in the sperm functionality, may suggest a possible role in the guided movement towards the oocyte. Hence, the objective of the present work is to study the in vitro potential chemotactic action of melatonin on ram spermatozoa, analysing the influence of the season (breeding and non-breeding) and the sperm capacitation state. The first experimental approach consisted in the inclusion of melatonin in the upper layer of a swim-up selection method. During the non-breeding season, the presence of melatonin at 100 pM and 1 μM concentrations significantly increased the cell recovery rate, and induced changes in the sperm location of the MT2 melatonin receptor, compared with the standard swim-up. Moreover, the selected sperm population with 100 pM melatonin presented a higher percentage of capacitated spermatozoa. The greater recovery rate obtained with melatonin could be due to the stimulation of sperm movement in random directions, i.e., a chemokinetic effect, or due to a guided movement (chemotaxis) towards the gradient of the melatonin. To elucidate this issue, together with the study of the influence of the sperm capacitation status, we performed a second experimental approach which consisted in the use of chemotaxis chambers and an open-source software (Open-CASA) that analyses the sperm trajectories towards the hormone gradient and calculates a chemotaxis index (SL index). There was a significant difference between the SL index in the presence of 1 μM melatonin and the control without hormone. This effect was only observed in capacitated spermatozoa with cAMP-elevating agents (Cap-CK samples) obtained during the non-breeding season. These results would point to an in vitro chemotactic effect of melatonin on ram spermatozoa, although chemokinesis cannot be ruled out. Nonetheless, the inclusion of this hormone in the swim-up procedure could enhance the sperm recovery rate.

Exogenous melatonin application mitigates the adverse impact of drought stress at panicle initiation and anthesis stages in rice (Oryza sativa)

Foliar application of plant growth regulators (PGRs) and nutrients are being employed increasingly as a management option in recent years. Such a new compound to be explored for stress mitigation is melatonin. Melatonin, an indoleamine compound, plays an important role in plant stress defense. Studies reveal that exogenous treatment or ectopic overexpression of melatonin biosynthetic genes improve the resistance against a series of stressors in crops. But there is still opacity about the mechanisms through which melatonin confers drought tolerance in rice. To clear this ambiguity, we studied the impact of foliar application of melatonin in rice under water-stressed conditions. A glasshouse experiment was conducted at the Department of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore during kharif 2021. The study focussed on standardizing the optimum melatonin concentration and disseminating the physiological traits involved in conferring melatonin-mediated drought tolerance in rice. The trial was laid in a factorial completely randomized design with six treatments imposed at panicle initiation and anthesis stages in a separate set of plants replicated four times. Drought stress was imposed at panicle initiation and anthesis by withholding water for seven days, while the absolute control was watered regularly. Foliar spray of 200 and 250 µM melatonin was given, when the absolute control and control plants were left untreated. The results interpreted that drought stress significantly altered the chlorophyll content, leaf water status, lipid peroxidation and electrolyte leakage. The exogenous application of melatonin alleviated the adversative effects of drought stress by improving the osmolyte accumulation and antioxidant enzyme activity, including catalase, superoxide dismutase and ascorbate peroxidase. Therefore, it is concluded that foliar application of 200 µM melatonin was most effective in mitigating the negative influences of drought stress in rice by enhancing the antioxidant system which effectively scavenges the drought-induced reactive oxygen species.

Melatonin promotes iron uptake and accumulation in peach

• Melatonin promoted growth of peach. • Melatonin increased iron content in peach. • Melatonin increased chemical form of iron content that can be absorbed by plants. Iron deficiency leads to stunted growth in fruit trees and reduces the yield and quality of fruits. To increase the uptake of iron in fruit trees and provide a reference to control iron deficiency, the effects of different concentrations of melatonin (MT) on iron uptake in peach ( Prunus persica ) were studied by a pot experiment. Concentrations of 0, 50, 100, 150, and 200 µM MT were used in this experiment. MT increased the biomass of peach. Concentrations of 100, 150, and 200 µM MT increased the contents of total and active iron in peach. Concentration of 150 µM MT got the maxmiums of total iron contents in stems and leaves, which increased by 28.79% and 36.11%, respectively, compared with the control. Correspondingly, concentrations of 100 and 150 µM MT upregulated the genes related to iron absorption, including the ferric reduction oxidase 7 ( FRO7 ), vacuolar iron transporter 1 ( VIT1 ), and ferric reduction oxidase 4 ( FRO4 ), while downregulating the vacuole genes vacuolar iron transporter homolog 4 ( VITH4 ) and natural resistance-associated macrophage protein 3 ( NRAMP3 ) that are related to vacuolar iron transport. The concentrations of absorbable iron forms, including the water soluble iron, adsorbed iron, carbonate and strongly adsorbed iron, and manganese oxide bound iron, in the soil increased, and the soil pH value decreased following the addition of 100, 150, and 200 µM MT. A correlation analysis showed that the contents of total and active iron in peach correlated with the biomass, soil pH value, absorbable soil iron forms, and level of expression of the iron absorption related genes. These observations indicate that treated with 100–200 µM MT could promote the iron uptake and accumulation in peach by regulating the physiological metabolism related to iron.

Melatonin reduces cadmium accumulation via mediating the nitric oxide accumulation and increasing the cell wall fixation capacity of cadmium in rice

Melatonin (MT) is participated in plants’ response to cadmium (Cd) tolerance, although its work model remains elusive. Here, the function of MT in adjusting Cd accumulation in rice was investigated. ‘Nipponbare’ (Nip) was cultured in the -Cd (1/2 Kimura B), -Cd + MT (1/2 Kimura B with 1 μM MT), +Cd (1/2 Kimura B plus 1 μM Cd) and +Cd + MT (1/2 Kimura B with 1 μM Cd and 1 μM MT) nutrient solutions for 7 d. Cd markedly induced the endogenous MT accumulation in rice roots and shoots, even within 1 h. MT applied exogenously elevated the hemicelluloses level, which in turn increased the cell wall’s binding capacity to Cd. Furthermore, MT applied exogenously down-regulated the transcription level of Natural Resistance-Associated Macrophage Protein 1 (OsNRAMP1), OsNRAMP5, a major facilitator superfamily gene (OsCd1), and IRON-REGULATED TRANSPORTER 1 (OsIRT1), all of which were responsible for Cd intake, thus less Cd was entered into roots. Moreover, MT applied exogenously also up-regulated transcription level of Cadmium accumulation in Leaf 1 (OsCAL1) and Heavy Metal ATPase 3 (OsHMA3), two genes both attributed to the decreased Cd accumulation in shoots through expelling Cd out of cells and chelating Cd in the vacuoles, respectively. In addition, MT applied exogenously further aggravated the production of nitric oxide (NO) that induced by Cd, while application of a NO donor-SNP mimicked this alleviatory effect of the MT, indicating MT decreased rice Cd accumulation relied on the accumulation of NO.

Transcriptome and hormone Analyses reveal that melatonin promotes adventitious rooting in shaded cucumber hypocotyls.

Melatonin, a multi-regulatory molecule, stimulates root generation and regulates many aspects of plant growth and developmental processes. To gain insight into the effects of melatonin on adventitious root (AR) formation, we use cucumber seedings subjected to one of three treatments: EW (hypocotyl exposed and irrigated with water), SW (hypocotyl shaded and irrigated with water) and SM (hypocotyl shaded and irrigated with 100 µM melatonin). Under shaded conditions, melatonin induced significant AR formation in the hypocotyl. To explore the mechanism of this melatonin-induced AR formation, we used transcriptome analysis to identify 1296 significant differentially expressed genes (DEGs). Comparing SM with SW, a total of 774 genes were upregulated and 522 genes were downregulated. The DEGs were classified among different metabolic pathways, especially those connected with the synthesis of secondary metabolites, with hormone signal transduction and with plant-pathogen interactions. Analyses indicate exogenous melatonin increased contents of endogenous auxin, jasmonic acid, salicylic acid, cytokinin and abscisic acid levels during AR formation. This study indicates melatonin promotes AR formation in cucumber seedings by regulating the expressions of genes related to hormone synthesis, signaling and cell wall formation, as well as by increasing the contents of auxin, cytokinin, jasmonic acid, salicylic acid and abscisic acid. This research elucidates the molecular mechanisms of melatonin's role in promoting AR formation in the hypocotyl of cucumber seedings under shaded conditions.

Exogenous melatonin enhances the growth and production of bioactive metabolites in Lemna aequinoctialis culture by modulating metabolic and lipidomic profiles

BackgroundLemna species are cosmopolitan floating plants that have great application potential in the food/feed, pharmaceutical, phytoremediation, biofuel, and bioplastic industries. In this study, the effects of exogenous melatonin (0.1, 1, and 10 µM) on the growth and production of various bioactive metabolites and intact lipid species were investigated in Lemna aequinoctialis culture.ResultsMelatonin treatment significantly enhanced the growth (total dry weight) of the Lemna aequinoctialis culture. Melatonin treatment also increased cellular production of metabolites including β-alanine, ascorbic acid, aspartic acid, citric acid, chlorophyll, glutamic acid, phytosterols, serotonin, and sucrose, and intact lipid species; digalactosyldiacylglycerols, monogalactosyldiacylglycerols, phosphatidylinositols, and sulfoquinovosyldiacylglycerols. Among those metabolites, the productivity of campesterol (1.79 mg/L) and stigmasterol (10.94 mg/L) were the highest at day 28, when 10 µM melatonin was treated at day 7.ConclusionThese results suggest that melatonin treatment could be employed for enhanced production of biomass or various bioactive metabolites and intact lipid species in large-scale L. aequinoctialis cultivation as a resource for food, feed, and pharmaceutical industries.

Effect of Melatonin and Caffeine Supplementation to Freezing Medium on Cryosurvival of Peruvian Paso Horse Sperm Using a Two-Step Accelerating Cooling Rate.

This research examined the antioxidant and cryoprotective effects of melatonin (ME) and caffeine (CAF) supplementation in freezing medium on the cryosurvival of Peruvian Paso horse sperm using a two-step accelerating cooling rate. Twenty ejaculates from four adult and fertile stallions were recovered, initially diluted with INRA-96®, and finally frozen with INRA-Freeze® with either no supplementation (as control), 1 μM ME, or 2 mM CAF using a two-ramp freezing system content inside a cryogenic-box and liquid nitrogen vapors. The sperm kinematic parameters and integrity of the plasma and acrosomal membranes of fresh semen and cryopreserved samples were evaluated using the CASA system (SCA-Evolution® 2018) and PI/fluorescein isothiocyanate-conjugated peanut (Arachis hypogaea) agglutinin double fluorescent test, respectively. The oxidative stress of post-thaw sperm samples was also assessed using the CellRox Deep Red fluorescence test. The results showed that curvilinear velocity and average-path velocity were greater (p < 0.05) after freezing with CAF than the control group. In addition, there were significance differences (p < 0.01) between stallions (1-4) in post-thaw kinematic parameters regardless of ME or CAF addition. Both ME and CAF improved (p < 0.05) the proportion of sperm with intact plasma membranes and intact acrosomes. Nevertheless, neither CAF nor ME improved the oxidative stress after the cryopreservation process.

Alleviation Mechanism of Melatonin in Chickpea (Cicer arietinum L.) under the Salt Stress Conditions

Melatonin (MT) is considered to be a hormone involved in increasing tolerance in plants under stress. The effect of different doses (0, 50, and 100 µM) of MT on the growth, biochemical and physiological properties of chickpea under salt stress was investigated. Salt stress significantly suppressed the growth, leaf relative water content (LRWC), chlorophyll reading value (CRV), chlorophyll a, chlorophyll b, and total chlorophyll. Salinity conditions also caused a decrease in macro- and micronutrients, while electrolyte leakage (EL), hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline contents, catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities increased under salinity conditions. MT treatments increased plant fresh weight, plant dry weight, root fresh weight, root dry weight, plant height, stem diameter, LRWC, CRV, chlorophyll a, chlorophyll b, total chlorophyll, total carotene of chickpea seedlings under 75 and 150 mM NaCl compared to the non-MT treatment. Especially, 100 µM MT treatment under 75 and 150 mM salinity conditions reduced the H2O2 and MDA contents compared to the non-MT-treated plants. Moreover, exogenous MT increased the K+/Na+ and Ca+2/Na+ ratios under salt stress conditions. It could be concluded exogenous MT treatments alleviated the salt stress on chickpea by modulating physiological and biochemical properties. Especially 100 µM MT treatment can be suggested for decreasing the negative influence of salinity on chickpea seedlings.

Melatonin promoted osteogenesis of human periodontal ligament cells by regulating mitochondrial functions through the translocase of the outer mitochondrial membrane 20.

Melatonin plays an important role in various beneficial functions, including promoting differentiation. However, effects on osteogenic differentiation, especially in human periodontal cells (hPDLCs), still remain inconclusive. Mitochondria are highly dynamic organelles that play an important role in various biological processes in cells, including energy metabolism and oxidative stress reaction. Furthermore, the translocase of the outer mitochondrial membrane 20 (TOM20) is responsible for recognizing and transporting precursor proteins. Thus, the objective of this study was to evaluate the functionality of melatonin on osteogenesis in human periodontal cells and to explore the involved mechanism of mitochondria. The hPDLCs were extracted and identified by flow cytometry and multilineage differentiation. We divided hPDLCs into control group, osteogenic induction group, and osteogenesis with melatonin treatment group (100, 10, and 1μM). Then we used a specific siRNA to achieve interference of TOM20. Alizarin red and Alkaline phosphatase staining and activity assays were performed to evaluate osteogenic differentiation. Osteogenesis-related genes and proteins were measured by qPCR and western blot. Mitochondrial functions were tested using ATP, NAD+/NADH, JC-1, and Seahorse Mito Stress Test kits. Finally, TOM20 and mitochondrial dynamics-related molecules expression were also assessed by qPCR and western blot. Our results showed that melatonin-treated hPDLCs had higher calcification and ALP activity as well as upregulated OCN and Runx2 expression at mRNA and protein levels, which was the most obvious in 1μM melatonin-treated group. Meanwhile, melatonin supplement elevated intracellular ATP production and mitochondrial membrane potential by increasing mitochondrial oxidative metabolism, hence causing a lower NAD+ /NADH ratio. In addition, we also found that melatonin treatment raised TOM20 level and osteogenesis and mitochondrial functions were both suppressed after knocking down TOM20. We found that melatonin promoted osteogenesis of hPDLCs and 1μM melatonin had the most remarkable effect. Melatonin treatment can reinforce mitochondrial functions by upregulating TOM20.

Melatonin-mediated resistance to copper oxide nanoparticles-induced toxicity by regulating the photosynthetic apparatus, cellular damages and antioxidant defense system in maize seedlings

The pollution of nanoparticles (NPs) has linked with severe negative effects on crop productivity. Thus, effective strategies are needed to mitigate the phytotoxicity of NPs. The aim of present study was to evaluate the efficacy of exogenously applied melatonin (MT) in mitigating the toxic effects of copper oxide nanoparticles (CuO NPs) from maize seedlings. Therefore, we comprehensively investigated the inhibitory effects of MT against CuO NPs-induced toxicity on morpho-physiological, biochemical and ultrastructural levels in maize. Our results show that CuO NPs (300 mg L−1) exposure displayed significantly reduction in all plant growth traits and induced toxicity in maize. Furthermore, 50 μM MT provided maximum plant tolerance against CuO NPs-induced phytotoxicity. It was noticed that MT improved plant growth, biomass, photochemical efficiency (Fv/Fm), chlorophyll contents (Chl a and Chl b), SPAD values and gas exchange attributes (stomatal conductance, net photosynthetic rate, intercellular CO2 concentration and transpiration rate) under CuO NPs stress. In addition, MT enhanced the antioxidant defense system and conferred protection to ultrastructural (mainly chloroplast, thylakoids membrane and plastoglobuli) damages and stomatal closure in maize plants subjected to CuO NPs stress. Together, it can be stated that the exogenous supply of MT improves the resilience of maize plants against the CuO NPs-induced phytotoxicity. Our current findings can be useful for the enhancement of plant growth and yield attributes in CuO NPs-contaminated soils. The reported information can provide insight into the MT pathways that can be used to improve crop stress tolerance in a challenging environment.

Melatonin controls cell proliferation and modulates mitochondrial physiology in pancreatic stellate cells

We have investigated the effects of melatonin on major pathways related with cellular proliferation and energetic metabolism in pancreatic stellate cells. In the presence of melatonin (1 mM, 100 µM, 10 µM, or 1 µM), decreases in the phosphorylation of c-Jun N-terminal kinase and of p44/42 and an increase in the phosphorylation of p38 were observed. Cell viability dropped in the presence of melatonin. A rise in the phosphorylation of AMP-activated protein kinase was detected in the presence of 1 mM and 100 µM melatonin. Treatment with 1 mM melatonin decreased the phosphorylation of protein kinase B, whereas 100 µM and 10 µM melatonin increased its phosphorylation. An increase in the generation of mitochondrial reactive oxygen species and a decrease of mitochondrial membrane potential were noted following melatonin treatment. Basal and maximal respiration, ATP production by oxidative phosphorylation, spare capacity, and proton leak dropped in the presence of melatonin. The expression of complex I of the mitochondrial respiratory chain was augmented in the presence of melatonin. Conversely, in the presence of 1 mM melatonin, decreases in the expression of mitofusins 1 and 2 were detected. The glycolysis and the glycolytic capacity were diminished in cells treated with 1 mM or 100 µM melatonin. Increases in the expression of phosphofructokinase-1 and lactate dehydrogenase were noted in cells incubated with 100 µM, 10 µM, or 1 µM melatonin. The expression of glucose transporter 1 was increased in cells incubated with 10 µM or 1 µM melatonin. Conversely, 1 mM melatonin decreased the expression of all three proteins. Our results suggest that melatonin, at pharmacological concentrations, might modulate mitochondrial physiology and energy metabolism in addition to major pathways involved in pancreatic stellate cell proliferation.

Involvement of ethylene in melatonin-modified photosynthetic-N use efficiency and antioxidant activity to improve photosynthesis of salt grown wheat.

The involvement of melatonin in the regulation of salt stress acclimation has been shown in plants in this present work. We found that the GOAL cultivar of wheat (Triticum aestivum L.) was the most salt-tolerant among the investigated cultivars, GOAL, HD-2967, PBW-17, PBW-343, PBW-550, and WH-1105 when screened for tolerance to 100 mM NaCl. The application of 100 μM melatonin maximally reduced oxidative stress and improved photosynthesis in the cv. GOAL. Melatonin supplementation reduced salt stress-induced oxidative stress by upregulating the activity of antioxidant enzymes, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR), and reduced the glutathione (GSH) production. This resulted in increased membrane stability, photosynthetic-N use efficiency and photosynthesis in plants. The application of 50 μM of the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) in the presence of melatonin and salt stress increased H2 O2 content but reduced GR activity and GSH, photosynthesis, and plant dry mass. This signifies that melatonin-mediated salt stress tolerance was related to ethylene synthesis as it improved antioxidant activity and photosynthesis of plants under salt stress. Thus, the interaction of melatonin and ethylene bears a prominent role in salt stress tolerance in wheat and can be used to develop salt tolerance in other crops.

Melatonin and 1-Methylcyclopropene Improve the Postharvest Quality and Antioxidant Capacity of ‘Youhou’ Sweet Persimmons during Cold Storage

ABSTRACT The objective of this study was to identify the effects of 100 μM melatonin (MT), 1 μL/L 1-methylcyclopropene (1-MCP), and their combination treatments on the postharvest characteristics, nutritional quality, and antioxidant capacity of ‘Youhou’ persimmons during cold storage at 0°C. Compared with the control fruit, all three treatments suppressed ethylene production and respiration rate, leading to delayed softening, reduced peel discoloration, and soluble solid content loss. These treatments increased plasma membrane stability by inhibiting lipoxygenase activity and decreasing H2O2, electrolyte leakage, and malondialdehyde concentrations, resulting in higher tolerance to chilling injury (CI). At the end of storage, the CI index of fruit treated with MT, 1-MCP, and MT+1-MCP respectively exhibited 54.67%, 14.57%, and 5.54%, which were significantly lower than the control ones (78.36%). In addition, the phenolics, flavonoids, and ascorbic acid contents were also improved by the above treatments, which contributed to higher antioxidant activity than the control fruit at the late stage of storage. The combination of MT and 1-MCP treatment was more effective in improving the postharvest quality and preserving high antioxidant ability levels than either treatment alone, indicating a promising measure to preserve sweet persimmons up to 70 d.

Integrated Physiological, Transcriptomic, and Proteomic Analyses Reveal the Regulatory Role of Melatonin in Tomato Plants' Response to Low Night Temperature.

Melatonin is a direct free radical scavenger that has been demonstrated to increase plants’ resistance to a variety of stressors. Here, we sought to examine the effect of melatonin on tomato seedlings subjected to low night temperatures using an integrated physiological, transcriptomic, and proteomic approach. We found that a pretreatment with 100 μM melatonin increased photosynthetic and transpiration rates, stomatal apertures, and peroxidase activity, and reduced chloroplast damage of the tomato plant under a low night temperature. The melatonin pretreatment reduced the photoinhibition of photosystem I by regulating the balance of both donor- and acceptor-side restriction of PSI and by increasing electron transport. Furthermore, the melatonin pretreatment improved the photosynthetic performance of proton gradient regulation 5 (SlPGR5) and SlPGR5-like photosynthetic phenotype 1 (SlPGRL1)-suppressed transformants under a low night temperature stress. Transcriptomic and proteomic analyses found that the melatonin pretreatment resulted in the upregulation of genes and proteins related to transcription factors, signal transduction, environmental adaptation, and chloroplast integrity maintenance in low night temperature-stressed tomato plants. Collectively, our results suggest that melatonin can effectively improve the photosynthetic efficiency of tomato plants under a low night temperature and provide novel insights into the molecular mechanism of melatonin-mediated abiotic stress resistance.