Melatonin plays multifunctional role in horticultural crops against environmental stresses: A review

Background Most of postharvest fruits are highly perishable, which limits greatly marketability and potential expansion. In recent years, significant progresses on understanding the role of melatonin in delaying senescence have been achieved while the melatonin as a postharvest alternative in maintaining quality and extending shelf life of postharvest fruit has been developed. Scope and approach This paper reviews the recent progresses in the multiple functions of melatonin, summaries the detection, content and synthesis of endogenous melatonin in postharvest fruit, discusses the possible mechanisms of melatonin in maintaining quality and extending shelf life of postharvest fruit, emphasizes the beneficial effects of the melatonin-related handling and provides the future research direction for postharvest alternative. Key findings and conclusions The amount of melatonin in postharvest fruit is relatively low and affected greatly by many factors. The major precursors and genes of melatonin biosynthetic pathway have been identified in various fruits. Exogenous melatonin treatment not only delayed ripening, senescence and quality deterioration, but also enhanced disease resistance and chilling tolerance of postharvest fruit. The multiple biological functions of melatonin in postharvest fruit were attributed to the induction and interaction with reactive oxygen species and nitric oxide and coordination with plant hormones and other signaling molecules, which enhanced antioxidant and defense systems, reduced oxidative damage, and maintained energy of postharvest fruit.

Insights into the roles of melatonin in maintaining quality and extending shelf life of postharvest fruits


 Phytomelatonin, a multifunctional molecule presents in plants studied to date, has an important role in plants as a modulatory agent (biostimulator), which improves their tolerance response to both biotic and abiotic stress. In the primary metabolism of plants, melatonin improves the photosynthesis rate and efficiency, as well related actions such as stomatal conductance, intercellular CO2 and Rubisco activity; it has also been seen to downregulate some senescence transcription factors. Melatonin upregulates many enzyme transcripts related to carbohydrates (including sucrose and starch), amino acids and lipid metabolism, optimizing N, P and S uptake. With respect to the plant secondary metabolism, a clear increase in polyphenol, glucosinolate, terpenoid and alkaloid levels has been described in numerous melatonin-treated plants. Generally, the most important genes of these secondary biosynthesis pathways were upregulated by melatonin. The great regulatory capacity of melatonin is a result of its control of the redox and plant hormone networks. Melatonin acts as a plant master regulator, up/down-regulating different plant hormone levels and signalling, and is a key piece in redox homeostasis; besides having a capacity to counteract and tolerate diverse critical situations such as pathogen infections or abiotic stresses. Possible future applications of melatonin for crop improvement and postharvest product preservation are proposed.

Phytomelatonin: an unexpected molecule with amazing performances in plants

Novel insights in health-promoting properties of sweet cherries.

Melatonin: Biosynthesis, content, and function in horticultural plants and potential application

Although the effects of melatonin on plant abiotic and biotic stress resistance have been explored in recent decades, the accumulation of endogenous melatonin in plants and its influence on fruit quality remains unclear. In the present study, melatonin accumulation levels and the expression profiles of five synthesis genes were investigated during fruit and leaf development in sweet cherry (Prunus avium L.). Melatonin was strongly accumulated in young fruits and leaves, then decreased steadily with maturation. Transcript levels of PacTDC and PacSNAT were highly correlated with melatonin content in both fruit and leaves, indicating their importance in melatonin accumulation. Furthermore, application of 50 and 100 μmol·L-1 of melatonin to leaves had a greater influence on fruit quality than treatments applied to fruits, by significantly improving fruit weight, soluble solids content, and phenolic content including total phenols, flavanols, total anthocyanins, and ascorbic acid. Meanwhile, melatonin application promoted the antioxidant capacity of fruit assayed by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis (3-ethylben zothiazoline-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP). These results provide insights into the physiological and molecular mechanisms underlying melatonin metabolism of sweet cherry.

Melatonin Accumulation in Sweet Cherry and Its Influence on Fruit Quality and Antioxidant Properties.

Grape buds exhibit non-uniform, or delayed, break in early spring in subtropical regions because the accumulation of chilling is insufficient. Hydrogen cyanamide (H2CN2, HC) can partially replace chilling to effectively promote bud sprouting and is used widely in warm winter areas. However, the exact underlying mechanism of grape bud release from endodormancy induced by HC remains elusive. In this study, the transcriptome of grape winter buds under in vitro conditions following HC and water treatment (control) was analyzed using RNA-seq technology. A total of 6772 differentially expressed genes (DEGs) were identified. Furthermore, the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that starch and sucrose metabolism and plant hormone signaling transduction were most enriched out of the 50 total pathways. HC treatment induced the upregulated expression of sucrose synthase (SUS), sucrose phosphate synthase (SPS), α-amylase (AM), and β-amylase (BM) and downregulated expression of sucrose invertase (INV), hexokinase (HK), fructokinase (FK), soluble starch synthase (SS), and granule-bound starch synthase (GBSS). Hence, the starch concentration in the HC-treated group was significantly lower than that in control, whereas soluble sugar content in the HC-treated group increased quickly and was higher than that in control between 0 and 8 d. The concentration of indoleacetic acid (IAA) and zeatin (ZT) increased, whereas that of abscisic acid (ABA) and gibberellin (GA) decreased in HC treated group, which coincided with the expression level of genes involved in above hormone signals. The content of hydrogen peroxide (H2O2) and enzyme activity of superoxide dismutase (SOD) and peroxidase (POD) were increased in grape buds with HC treatment, whereas catalase (CAT) activity was decreased. HC treatment increased the expression of POD, SOD, primary amine oxidase (PAO), polyamine oxidase (PAOX), and glutathione peroxidase (GSH-Px). Based on these results, it is possible to propose a mechanistic model that underlies the regulation of endodormancy release in grapevine buds by exogenous HC application.

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Hydrogen cyanamide induces grape bud endodormancy release through carbohydrate metabolism and plant hormone signaling

In order to study the effect of exogenous melatonin (MT) on breaking the dormancy of kiwifruit seeds, in this experiment, the kiwi fruit seeds were kept at 4°Cfor 15 days. At the same time, we used different concentration gibberellin (GA) and MT solution to treat the seeds, and calculated germination rate (GR) and germination potential (GP) of seeds. Compared with the control treated with water with no any germination (CK), MT treatments promoted the GR to 10%-16%, and the GP increased to 4%-7%. And 50μmol/L MT treatment had the best results, with 16% GR and 7% GP respectively. GA treatments promoted the GR to 15%-30%, and the GP increased to 8%-12%. And 50μmol/L MT treatment had the best results, with 30% GR and 12% GP respectively. The results showed that MT and GA may have some effects on breaking kiwi seed dormancy, and GA had better effect.

https://iopscience.iop.org/article/10.1088/1755-1315/237/5/052073/pdf

Effect of Melatonin on the Breaking Dormancy of Kiwifruit Seeds

In order to explore the accumulation characteristics of melatonin in sweet cherry leaves, the melatonin content was measured every 4h for a whole day in mature leaves of 'Hongdeng' and the expression patterns of related synthetic genes were investigated. The melatonin content displayed double peaks at 14:00 and 22:00, respectively, speculating that high temperature and strong light intensity promote the synthesis of melatonin in leaves. In addition, expression pattern of 5 melatonin synthesis genes TDC , T5H1 , T5H2 , SNAT and ASMT were investigated by qRT-PCR. Among them, expression level of PacTDC , PacASMT , PacT5H1 and PacSNAT was positively related to the accumulation of melatonin. This study provides new information on melatonin synthesis in plants, especially in sweet cherry.

/pdf/diurnal-variation-of-melatonin-content-in-sweet-cherry-28ds31vvls.pdf

Diurnal variation of melatonin content in sweet cherry leaves

To study the influence of temperature and growth regulating substances on seed germination, kiwi seeds stored at 4°C refrigerated for 55 days were used as experimental materials. The treatments were set as below: (1) poikilothermal (25°C 8h/4°C 16h) or constant temperature (25°C 24h) treatment; (2) treated with melatonin and gibberellin under constant temperature; (3) treated with melatonin and gibberellin under poikilothermal. The germination rate and germination potential of the treated seeds were analyzed statistically. The results showed that the germination rate of seeds could be increased by poikilothermal treatment, especially for the variety MW2, and the germination rate reached to 86.86%. Under constant temperature, gibberellin had a significant effect on the germination of kiwi seeds, while melatonin had no effect. Under the condition of polikilothermal, gibberellin and melatonin treatment alone can obviously promote the germination of kiwi seeds, while the application of gibberellin and melatonin at the same time can promote the germination of kiwi seeds, but there was no synergistic effect.

https://iopscience.iop.org/article/10.1088/1755-1315/237/5/052074/pdf

Tian Shen

Papers

Melatonin Accumulation in Sweet Cherry and Its Influence on Fruit Quality and Antioxidant Properties.

Hydrogen cyanamide induces grape bud endodormancy release through carbohydrate metabolism and plant hormone signaling

Effect of Melatonin on the Breaking Dormancy of Kiwifruit Seeds

Diurnal variation of melatonin content in sweet cherry leaves

Effects of Temperature, Melatonin and Gibberellin on Kiwi Seed Germination