Exogenous Melatonin Treatment Research Articles

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.

Genome-wide identification of the B3 gene family in soybean and the response to melatonin under cold stress.

Melatonin is a multipotent molecule that exists widely in animals and plants and plays an active regulatory role in abiotic stresses. The B3 superfamily is a ubiquitous transcription factor with a B3 functional domain in plants, which can respond temporally to abiotic stresses by activating defense compounds and plant hormones. Despite the fact that the B3 genes have been studied in a variety of plants, their role in soybean is still unknown. The regulation of melatonin on cold resistance of soybean and the response of B3 genes to cold stress were investigated by measuring biochemical indexes of soybean. Meanwhile, the genome-wide identification of B3 gene family was conducted in soybean, and B3 genes were analyzed based on phylogeny, motifs, gene structure, collinearity, and cis-regulatory elements analysis. We found that cold stress-induced oxidative stress in soybean by producing excessive reactive oxygen species. However, exogenous melatonin treatment could increase the content of endogenous melatonin and other hormones, including IAA and ABA, and enhance the antioxidative system, such as POD activity, CAT activity, and GSH/GSSG, to scavenge ROS. Furthermore, the present study first revealed that melatonin could alleviate the response of soybean to cold stress by inducing the expression of B3 genes. In addition, we first identified 145 B3 genes in soybean that were unevenly distributed on 20 chromosomes. The B3 gene family was divided into 4 subgroups based on the phylogeny tree constructed with protein sequence and a variety of plant hormones and stress response cis-elements were discovered in the promoter region of the B3 genes, indicating that the B3 genes were involved in several aspects of the soybean stress response. Transcriptome analysis and results of qRT-PCR revealed that most GmB3 genes could be induced by cold, the expression of which was also regulated by melatonin. We also found that B3 genes responded to cold stress in plants by interacting with other transcription factors. We found that melatonin regulates the response of soybean to cold stress by regulating the expression of the transcription factor B3 gene, and we identified 145 B3 genes in soybean. These findings further elucidate the potential role of the B3 gene family in soybean to resist low-temperature stress and provide valuable information for soybean functional genomics study.

Effects of curcumin and melatonin treatment in the cerebral cortex of adult rats.

The study investigated the effect of exogenous melatonin and (or) curcumin treatment on the cerebral cortex of adult rats. In this context, malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH), superoxide dismutase (SOD), nuclear factor E2-related factor 2 (Nrf2) and SIRT2 protein expression were examined. A total of 30 Wistar albino rats involved in the study were randomly divided into five groups. Over 30 days, the control groups received phosphate-buffered saline or dimethyl sulfoxide injections, and the treatment groups received melatonin, curcumin, or a combination of melatonin and curcumin injections. In the cerebral cortex homogenates, the MDA, GSH, and sum of NO were respectively determined by the thiobarbituric acid, modified Ellman and Griess test methods. The SOD and Nrf2 levels were examined using the ELISA method and SIRT2 protein expression using the Western blot technique. The study found that both melatonin and curcumin treatments significantly reduced lipid peroxidation and SIRT2 protein expression levels (p < 0.05) and increased the Nrf2 level in the cytoplasm (p < 0.05). The study revealed that curcumin and melatonin treatments reduced MDA and SIRT2 protein expression level and increased intracellular Nrf2, GSH, and SOD in the cortex tissue. We also found that the combined melatonin and curcumin treatment produced no synergistic effect.

The melatonin system is expressed in the ovine uterus: effect of the day of the oestrous cycle and undernutrition.

Melatonin influences female reproduction, but expression of the melatonin system has not been characterised in the ovine uterus. We aimed to determine whether synthesising enzymes (arylalkylamine N-acetyltransferase (AANAT) and N-acetylserotonin-O-methyltransferase (ASMT)), melatonin receptors 1 and 2 (MT1 and MT2), and catabolising enzymes (myeloperoxidase (MPO) and indoleamine 2,3-dioxygenase 1 and 2 (IDO1 and 2)), are expressed in the ovine uterus, and if they are influenced by the oestrous cycle (Experiment 1) or by undernutrition (Experiment 2). In Experiment 1, gene and protein expression was determined in sheep endometrium samples collected on days 0 (oestrus), 5, 10 and 14 of the oestrous cycle. In Experiment 2, we studied uterine samples from ewes fed either 1.5 or 0.5times their maintenance requirements. We have demonstrated the expression of AANAT and ASMT in the endometrium of sheep. AANAT and ASMT transcripts, and AANAT protein were more elevated at day 10, then decreased to day 14. A similar pattern was observed for MT2 , IDO1 , and MPO mRNA, which suggests that the endometrial melatonin system might be influenced by ovarian steroid hormones. Undernutrition increased AANAT mRNA expression, but seemed to decrease its protein expression, and increased MT2 and IDO2 transcripts, whereas ASMT expression was unaffected. The melatonin system is expressed in the ovine uterus and is affected by oestrous cycle and undernutrition. The results help explain the adverse effects of undernutrition on reproduction in sheep, and the success of exogenous melatonin treatments in improving reproductive outcomes.

VvMYB14 participates in melatonin-induced proanthocyanidin biosynthesis by upregulating expression of VvMYBPA1 and VvMYBPA2 in grape seeds.

This work demonstrated that melatonin increases continuously in seeds, particularly seed coats, during berry ripening. Exogenous melatonin treatments significantly increased the proanthocyanidin (PA) content, partially through ethylene signaling, in seed coats. VvMYB14 expression exhibited patterns similar to melatonin accumulation over time, which was largely induced by melatonin treatment in seed coats during berry ripening. Additionally, VvMYB14 bound to the MBS element of the VvMYBPA1 promoter to activate expression. VvMYB14 overexpression largely upregulated expression of VvMYBPA1, VvMYBPA2 and VvLAR1 and increased the PA content in grape seed-derived calli. Similar increases in AtTT2 and AtBAN expression and PA content were found in VvMYB14-overexpressing Arabidopsis seeds. It was also observed that VvMYB14 overexpression increased ethylene production and thereby induced expression of VvERF104, which bound to the ERF element of the VvMYBPA2 promoter and activated its expression. Additionally, VvERF104 suppression reduced the VvMYB14 overexpression-induced increases in expression of VvMYBPA2 and VvLAR1 and PA content. Further experiments revealed that melatonin-induced increases in the expression of VvMYBPA1, VvMYBPA2, VvERF104 and VvLAR1 and PA accumulation were significantly reduced in VvMYB14-suppressing grape calli and leaves. Collectively, VvMYB14 mediates melatonin-induced PA biosynthesis by directly transactivating VvMYBPA1 expression and indirectly upregulating VvMYBPA2 expression via VvERF104.

Exogenous melatonin treatment reduces postharvest senescence and maintains the quality of papaya fruit during cold storage.

Exogenous melatonin (EMT) application has been used to reduce postharvest senescence and improve the quality and antioxidant enzyme activities of papaya fruits during cold storage. The effects of exogenous melatonin application (1. 5 mM) were investigated on papaya fruits during cold storage (10°C ± 2°C) for 28 days in the present study. The EMT treatment delayed postharvest senescence significantly with lower maturing status compared with untreated papaya fruits (control). In addition, EMT treatment maintained substantially higher titratable acidity values and ascorbic acid content but significantly lower soluble solids content and lower weight loss compared with the untreated fruits. Concerning the antioxidant capacity, the EMT-treated papaya fruit exhibited markedly higher total phenolic content and, consequently, higher DPPH-radical scavenging activity than the control group. The EMT treatment not only kept a higher enzyme activity of superoxide dismutase, peroxidase, and catalase but also significantly inhibited the accumulation of hydrogen peroxide and malondialdehyde, along with satisfying sensory attributes. The findings of this study indicated that EMT application could be commercially used as an eco-friendly strategy to reduce postharvest senescence and maintain the fresh-like quality traits of papaya fruit during cold storage.

Melatonin-Induced Detoxification of Organic Pollutants and Alleviation of Phytotoxicity in Selected Horticultural Crops

Environmental pollution with organic pollutants has increased drastically in recent decades. Despite the importance of minimizing organic pollutant content such as pesticide residue in edible crops, our understanding of induced xenobiotic metabolism in plants is poor. Melatonin is a potent stress-relieving biomolecule, which exerts beneficial effects on xenobiotic metabolism in plants. Exogenous melatonin treatment not only improves photosynthesis, antioxidant defense, and plant growth but also reduces pollutant residue and xenobiotic uptake. The overexpression of melatonin biosynthetic genes enhances organic pollutant metabolism, while the suppression of endogenous melatonin biosynthesis increases organic pollutant residue in horticultural products. Studies have revealed that the glutathione-dependent detoxification pathway plays a critical role in the melatonin-induced enhanced detoxification of xenobiotics. Moreover, a role for RESPIRATORY BURST HOMOLOG (RBOH)-derived reactive oxygen species signaling has been revealed which potentially acts upstream of glutathione-dependent xenobiotic metabolism. Based on the literature, here, we reviewed the effects of organic pollutants on plants and how melatonin aids plants in enduring the effects of organic pollutant-induced stress. We also discussed the potential melatonin signaling mechanism in enhanced pesticide metabolism. Our assessment suggests that melatonin has positive impacts on plant tolerance to organic pollution, which can be used to improve the food safety of edible horticultural crops.

Exogenous melatonin treatment affects ascorbic acid metabolism in postharvest 'Jinyan' kiwifruit.

Ascorbic acid (AsA) is an important nutritious substance in fruits, and it also can maintain the biological activity of fruits during storage. This research investigated the effect of exogenous melatonin (MT) on AsA metabolism in postharvest kiwifruit. Our results indicated that exogenous MT delayed the decrease of fruit firmness and titratable acid (TA), inhibited the increase of soluble solids content (SSC), reduced the respiration rate and ethylene production, and maintained a higher AsA content in kiwifruit during storage. The high expression of L-galactose pathway key genes in the early storage and regeneration genes in the later storage maintained the AsA content in postharvest kiwifruit. MT treatment enhanced the expression levels of AsA biosynthesis (AcGME2, AcGalDH, and AcGalLDH) and regeneration (AcGR, AcDHAR, and AcMDHAR1) genes. Meanwhile, the expression of the degradation gene AcAO was inhibited in MT-treated kiwifruits.

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.

Using Exogenous Melatonin, Glutathione, Proline, and Glycine Betaine Treatments to Combat Abiotic Stresses in Crops.

Abiotic stresses, such as drought, salinity, heat, cold, and heavy metals, are associated with global climate change and hamper plant growth and development, affecting crop yields and quality. However, the negative effects of abiotic stresses can be mitigated through exogenous treatments using small biomolecules. For example, the foliar application of melatonin provides the following: it protects the photosynthetic apparatus; it increases the antioxidant defenses, osmoprotectant, and soluble sugar levels; it prevents tissue damage and reduces electrolyte leakage; it improves reactive oxygen species (ROS) scavenging; and it increases biomass, maintains the redox and ion homeostasis, and improves gaseous exchange. Glutathione spray upregulates the glyoxalase system, reduces methylglyoxal (MG) toxicity and oxidative stress, decreases hydrogen peroxide and malondialdehyde accumulation, improves the defense mechanisms, tissue repairs, and nitrogen fixation, and upregulates the phytochelatins. The exogenous application of proline enhances growth and other physiological characteristics, upregulates osmoprotection, protects the integrity of the plasma lemma, reduces lipid peroxidation, increases photosynthetic pigments, phenolic acids, flavonoids, and amino acids, and enhances stress tolerance, carbon fixation, and leaf nitrogen content. The foliar application of glycine betaine improves growth, upregulates osmoprotection and osmoregulation, increases relative water content, net photosynthetic rate, and catalase activity, decreases photorespiration, ion leakage, and lipid peroxidation, protects the oxygen-evolving complex, and prevents chlorosis. Chemical priming has various important advantages over transgenic technology as it is typically more affordable for farmers and safe for plants, people, and animals, while being considered environmentally acceptable. Chemical priming helps to improve the quality and quantity of the yield. This review summarizes and discusses how exogenous melatonin, glutathione, proline, and glycine betaine can help crops combat abiotic stresses.

Exogenous melatonin enhances cell wall response to salt stress in common bean (Phaseolus vulgaris) and the development of the associated predictive molecular markers.

Common bean (Phaseolus vulgaris) is an important food crop; however, its production is affected by salt stress. Salt stress can inhibit seed germination, promote senescence, and modify cell wall biosynthesis, assembly, and architecture. Melatonin, an indole heterocycle, has been demonstrated to greatly impact cell wall structure, composition, and regulation in plants under stress. However, the molecular basis for such assumptions is still unclear. In this study, a common bean variety, "Naihua" was treated with water (W), 70 mmol/L NaCl solution (S), and 100 μmol/L melatonin supplemented with salt solution (M+S) to determine the response of common bean to exogenous melatonin and explore regulatory mechanism of melatonin against salt stress. The results showed that exogenous melatonin treatment alleviated salt stress-induced growth inhibition of the common bean by increasing the length, surface area, volume, and diameter of common bean sprouts. Moreover, RNA sequencing (RNA-seq) and real-time quantitative PCR (qRT-PCR) indicated that the cell wall regulation pathway was involved in the salt stress tolerance of the common bean enhanced by melatonin. Screening of 120 germplasm resources revealed that melatonin treatment improved the salt tolerance of more than 65% of the common bean germplasm materials. Melatonin also up-regulated cell wall pathway genes by at least 46%. Furthermore, we analyzed the response of the common bean germplasm materials to melatonin treatment under salt stress using the key genes associated with the synthesis of the common bean cell wall as the molecular markers. The results showed that two pairs of markers were significantly associated with melatonin, and these could be used as candidate markers to predict whether common bean respond to exogenous melatonin and then enhance salt tolerance at the sprouting stage. This study shows that cell wall can respond to exogenous melatonin and enhance the salt tolerance of common bean. The makers identified in this study can be used to select common bean varieties that can respond to melatonin under stress. Overall, the study found that cell wall could response melatonin and enhance the salt tolerance and developed the makers for predicting varieties fit for melatonin under stress in common bean, which may be applied in the selection or development of common bean varieties with abiotic stress tolerance.

Exogenous melatonin treatment on post-harvest jujube fruits maintains physicochemical qualities during extended cold storage.

This study was conducted to investigate the visual appearance and physicochemical changes of postharvest jujube fruits (Ziziphus jujuba Mill. cv. Shucuizao) stored under 0 °C for 15 days. The fruits were dipped in 0 (control), 50, 100, 200 and 400 µM melatonin solutions after harvest. The results showed that treatment with a suitable melatonin concentration improved the rate of crisp fine fruits, delayed weight loss and firmness decline, and suppressed changes in total soluble solids (TSS) and titratable acidity (TA) contents of jujube fruits compared with the control. In addition, jujube fruits soaked with melatonin showed improved antioxidant capacity through increased ascorbic acid (AsA) content, enhanced superoxide dismutase (SOD) activity, and decreased malonaldehyde (MDA) content. As a result, 50 µM melatonin showed the greatest improvement of visual appearance and quality maintenance, and could be used as an effective treatment to preserve postharvest jujube fruit.

Effect of Melatonin on Fruit Quality via Decay Inhibition and Enhancement of Antioxidative Enzyme Activities and Genes Expression of Two Mango Cultivars during Cold Storage

The postharvest deterioration of mango fruits is a critical issue limiting mango storage and preservation due to its climacteric nature. This study evaluated the storage behavior of two mango cultivars and their response to exogenous melatonin (MT, 1000 μmol L−1) treatment in attenuating fruit decay and enhancing fruits’ physiological and metabolic processes and gene relative expression subjected to cold storage. MT treatment in both mango cultivars significantly delayed weight loss, firmness, respiration rate, and decay incidence. However, MT did not influence the TSS, TA, and TSS:TA ratio regardless of the cultivar. Moreover, MT inhibited the decrease in total phenol and flavonoid content and AsA content while delaying the increase in the MDA content of mango during storage in both cultivars. In addition, MT dramatically inhibited the enzyme activity of PPO. In contrast, an increase in the activities of antioxidant enzymes (SOD and APX) and PAL and their genes’ relative expression was noticed in MT-treated fruits versus control in both cultivars. However, MT treatment was cultivar dependent in most parameters under study. These results demonstrated that MT treatment could be an essential postharvest treatment in minimizing decay, maintaining fruit quality, and extending mango fruits’ postharvest shelf life by enhancing the physiological and metabolic processes during cold storage.

Postharvest Exogenous Melatonin Treatment of Table Grape Berry Enhances Quality and Maintains Bioactive Compounds during Refrigerated Storage

Table grape berries are classified as a perishable crop that deteriorates quickly after harvest. The application of melatonin after harvest was found to be effective for retarding senescence and slowing ripening. In the current study, we tested the influence of two melatonin concentrations (50 and 100 µmol) as a postharvest application on quality, bioactive compounds, and enzyme activities of grape berries cv “Crimson” stored at 0 ± 1 °C and 90% relative humidity (RH) for 35 days. Our results indicated that melatonin application extends the shelf-life of berries by reducing weight loss and maintaining total soluble solids (TSS), titratable acidity (TA), berry adherence strength, and firmness. Melatonin treatment also reduced pectin methyl esterase (PME) and polygalactouranase (PG) enzyme activities compared to the control. Moreover, O2•− and H2O2 rates in berries were reduced by high melatonin concentration. Moreover, peroxidase (POD) and catalase (CAT) enzyme activities were increased by melatonin application. Our findings suggested using melatonin postharvest to increase shelf life and maintain quality attributes during refrigerated storage, which could be advantageous on a large scale.