Melatonin (N-acetyl-5-methoxytryptamine) is an indole molecule widely found in animals and plants. Melatonin is well-known to improve plant resistance to various biotic and abiotic stresses due to its potent free radical scavenging ability while being able to modulate plant signaling and response pathways through mostly unknown mechanisms. In recent years, more and more studies have shown that melatonin plays a crucial role in improving crop quality and yield by participating in the regulation of various aspects of plant growth and development. This article mainly reviews the effects of melatonin on plant vegetative growth and reproductive development, and systematically summarizes the molecular regulatory network of melatonin. At the same time, the effective concentrations of exogenously applied melatonin in different crops or different growth stages of the same crop are analyzed. In addition, this article compares endogenous phytomelatonin concentrations in various crops and different organs, and analyzes the potential function of phytomelatonin in plant circadian rhythms. The prospects of different approaches in regulating crop yield and quality through exogenous application of appropriate concentrations of melatonin, endogenous modification of phytomelatonin metabolism-related genes, and the use of nanomaterials and other technologies to improve melatonin utilization efficiency are also discussed.

Functions and prospects of melatonin in plant growth, yield and quality.

Application of hydrogen-rich water (HRW) can extend the shelf life of fruit and vegetables, but the effect of preservation on Rosa sterilis fruit is not known. This study found that HRW treatment retarded the increase in decay incidence, weight loss, respiration rate and malondialdehyde content and slowed down the decrease of titratable acid, total soluble solids and firmness in R. sterilis fruit. HRW treatment reduced hydrogen peroxide and the superoxide anion production while elevating the activity and expression of antioxidant-related enzymes, such as superoxide dismutase, catalase, dehydroascorbate reductase, glutathione reductase, ascorbate peroxidase and reductase in R. sterilis fruit. HRW treatment increased ascorbic acid and glutathione levels, while reducing the content of oxidised glutathione and dehydroascorbate. Furthermore, HRW treatment increased the activities and expression of H+-ATPase, succinate dehydrogenase, Ca2+-ATPase and cytochrome C oxidase, promoted levels of ADP and ATP and decreased the AMP content in R. sterilis fruit. These results indicated that HRW maintains the quality of R. sterilis by regulating the antioxidant capacity and energy status during storage at ambient temperature. 

Hydrogen-rich water treatment maintains the quality of Rosa sterilis fruit by regulating antioxidant capacity and energy metabolism

Caffeic acid enhances storage ability of apple fruit by regulating fatty acid metabolism

Derived from tryptophan, melatonin (MT; N-acetyl-5-methoxytryptamine) is a ubiquitous indoleamine that is widely distributed in species ranging from microorganisms to mammals. It has been associated to play vital roles in the human body like cardiac rhythms, immunological enhancement, and antioxidant activity. In plants, it is a pleiotropic molecule with multiple roles, as it not only performs extensive functions like delaying senescence, growth and development regulation, exerting antioxidant effects, and facilitating adaption of plants to certain biotic and abiotic stress responses but also provides resistance to chilling injury and disease development. This paper reviews the latest progress in the multiple roles of MT in fruits, summarizes the pathways for its biosynthesis, and presents the relation of MT with plant hormones, like auxin, cytokinin, ethylene, gibberellins, abscisic acid, jasmonic, and salicylic acid, and highlights the effect of postharvest application of MT on physiology and quality of fruits, action mechanisms, and safety regulations of MT. Recent trends focus on using alternatives that are safe for postharvest produce and do not have major side effects. MT is a better alternative to hazardous chemicals being commercially used in the postharvest management of fruits and providing future directions for its utilization. 

Rui Huang

Papers

Postharvest melatonin dipping maintains quality of apples by mediating sucrose metabolism.

γ-Aminobutyric acid regulates mitochondrial energy metabolism and organic acids metabolism in apples during postharvest ripening

Trehalose maintains the quality of Malus domestica by mediating sucrose and respiratory metabolism

Caffeic acid enhances storage ability of apple fruit by regulating fatty acid metabolism

Organic acids metabolism and GABA shunt involved in maintaining quality of Malus domestica by methyl jasmonate treatment.