Melatonin retards senescence via regulation of the electron leakage of postharvest white mushroom (Agaricus bisporus)

Phytic Acid Delays the Senescence of Rosa roxburghii Fruit by Regulating Antioxidant Capacity and the Ascorbate-Glutathione Cycle

Rosa roxburghii fruit has a short postharvest shelf life, with rapid declines in quality and antioxidant capacity. This research assessed how phytic acid affects the antioxidant capacity and quality of R. roxburghii fruit while in the postharvest storage period and reveals its potential mechanism of action. The findings suggested that phytic acid treatment inhibits the production of malondialdehyde (MDA) and enhances the activities and expressions of glutathione peroxidase (GPX), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) while decreasing the generation of superoxide anions (O2•-) and hydrogen peroxide (H2O2). Phytic acid treatment activates the ascorbate-glutathione (AsA-GSH) cycle and enhances the activity and expression of key enzymes in the cycle: ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR). It also increases the levels of non-enzymatic antioxidants, such as ascorbic acid (AsA) and glutathione (GSH), while reducing the production of dehydroascorbic acid (DHA) and oxidized glutathione (GSSG). Moreover, phytic acid treatment enhances the ratios of AsA/DHA and GSH/GSSG, maintaining the reduced state of the fruit. In summary, phytic acid improves antioxidant defense system and activates the AsA-GSH cycle, alleviating oxidative damage and ensuring R. roxburghii fruit quality after harvest.

Recent Advances in Postharvest Application of Exogenous Phytohormones for Quality Preservation of Fruits and Vegetables

The increasing global population has heightened the demand for food, leading to escalated food production and, consequently, the generation of significant food waste. Factors such as rapid ripening, susceptibility to physiological disorders, and vulnerability to microbial attacks have been implicated as contributing to the accelerated senescence associated with food waste generation. Fruits and vegetables, characterized by their high perishability, account for approximately half of all food waste produced, rendering them a major area of concern. Various postharvest technologies have thus been employed, including the application of phytohormone treatments, to safeguard and extend the storability of highly perishable food products. This review, therefore, explores the physicochemical properties and biological aspects of phytohormones that render them suitable for food preservation. Furthermore, this review examines the effects of externally applied phytohormones on the postharvest physiology and quality attributes of fresh produce. Finally, the review investigates the mechanisms by which exogenous phytohormones preserve food quality and discusses the associated limitations and safety considerations related to the use of these compounds in food applications.

Melatonin Maintains Postharvest Quality in Fresh Gastrodia elata Tuber by Regulating Antioxidant Ability and Phenylpropanoid and Energy Metabolism During Storage

Melatonin treatment has been reported to effectively preserve and improve the postharvest quality of fruits and vegetables during storage. This research focused on examining the significance of melatonin on maintaining the quality of fresh Gastrodia elata tubers throughout the storage period. The findings demonstrated that melatonin application effectively reduced the deterioration rate and inhibited the rise in respiratory rate, malondialdehyde content, and weight loss, while slowing down the decline in soluble solid content. Melatonin treatment led to a decrease in hydrogen peroxide production and a rise in non-enzymatic antioxidant concentrations, including ascorbic acid. Furthermore, it boosted both the activity and expression of indispensable antioxidant enzymes, like superoxide dismutase, catalase, and ascorbate peroxidase. Additionally, melatonin treatment promoted the accumulation of total phenols, flavonoids, and lignin in fresh G. elata, while enhancing both the activity and expression of critical enzymes in the phenylpropanoid pathway, including phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, and 4-coumarate-CoA ligase. Moreover, melatonin treatment boosted the activity and expression of energy-associated enzymes including H+-ATPase, succinate dehydrogenase, Ca2+-ATPase, and cytochrome C oxidase, contributing to the improvement of energy levels in fresh G. elata. In summary, melatonin enhances the antioxidant potential and reduces oxidative damage in fresh G. elata by activating reactive oxygen species, phenylpropanoid metabolism, and energy metabolism, thereby maintaining its postharvest quality.

The Effect of Cold Plasma Treatment on the Storage Stability of Mushrooms (Agaricus bisporus)

Postharvest Agaricus bisporus is susceptible to browning, water loss, and microbial infection. In order to extend its shelf life, cold plasma technology was used to treat and evaluate A. bisporus. Firstly, according to the results of a single factor test and response surface analysis, the optimal conditions for cold plasma treatment were determined as a voltage of 95 kV, a frequency of 130 Hz, and a processing time of 10 min. Secondly, storage experiments were carried out using the optimized cold plasma treatment. The results showed that the cold plasma treatment in the packaging significantly reduced the total viable count in A. bisporus by approximately 16.5%, maintained a browning degree at 26.9% lower than that of the control group, and a hardness at 25.6% higher than that of the control group. In addition, the cold plasma treatment also helped to preserve the vitamin C and total protein content of A. bisporus. In conclusion, cold plasma treatment showed great potential in enhancing the postharvest quality of fresh A. bisporus.

Streptomyces-Secreted Fluvirucin B6 as a Potential Bio-Fungicide for Managing Banana Fusarium Wilt and Mycotoxins and Modulating the Soil Microbial Community Structure

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc TR4) is the most destructive soil-borne fungal disease. Until now, there has been a lack of effective measures to control the disease. It is urgent to explore biocontrol agents to control Foc TR4 and the secretion of mycotoxin. In this study, fluvirucin B6 was screened from Streptomyces solisilvae using an activity-guided method. Fluvirucin B6 exhibited strong antifungal activity against Foc TR4 (0.084 mM of EC50 value) and significantly inhibited mycelial growth and spore germination. Further studies demonstrated that fluvirucin B6 could cause the functional loss of mitochondria, the disorder of metabolism of Foc TR4 cells, and the decrease of enzyme activities in the tricarboxylic acid cycle and electron transport chain, ultimately inhibiting mycotoxin metabolism. In a pot experiment, the application of fluvirucin B6 significantly decreased the incidence of banana Fusarium wilt and the amount of Foc TR4 and controlled fungal toxins in the soil. Additionally, fluvirucin B6 could positively regulate the changes in the structure of the banana rhizosphere microbial community, significantly enriching beneficial microbes associated with disease resistance. In summary, this study identifies fluvirucin B6, which plays versatile roles in managing fungal diseases and mycotoxins.

Phytomelatonin: From Intracellular Signaling to Global Horticulture Market

Melatonin (N-acetyl-5-methoxytryptamine), a well-known mammalian hormone, has been having a great relevance in the Plant World in recent years. Many of its physiological actions in plants are leading to possible features of agronomic interest, especially those related to improvements in tolerance to stressors and in the postharvest life of fruits and vegetables. Thus, through the exogenous application of melatonin or by modifying the endogenous biosynthesis of phytomelatonin, some change can be made in the functional levels of melatonin in tissues and their responses. Also, acting in the respective phytomelatonin biosynthesis enzymes, regulating the expression of tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), N-acetylserotonin O-methyltransferase (ASMT), and caffeic acid O-methyltransferase (COMT), and recently the possible action of deacetylases on some intermediates offers promising opportunities for improving fruits and vegetables in postharvest and its marketability. Other regulators/effectors such as different transcription factors, protein kinases, phosphatases, miRNAs, protein-protein interactions, and some gasotransmitters such as nitric oxide or hydrogen sulfide were also considered in an exhaustive vision. Other interesting aspects such as the role of phytomelatonin in autophagic responses, the posttranslational reprogramming by protein-phosphorylation, ubiquitylation, SUMOylation, PARylation, persulfidation, and nitrosylation described in the phytomelatonin-mediated responses were also discussed, including the relationship of phytomelatonin and several plant hormones, for chilling injury and fungal decay alleviating. The current data about the phytomelatonin receptor in plants (CAND2/PMTR1), the effect of UV-B light and cold storage on the postharvest damage are presented and discussed. All this on the focus of a possible new action in the preservation of the quality of fruits and vegetables.

Metabolomic and Transcriptomic Analyses Revealed Lipid Differentiation Mechanisms in Agaricus bisporus at Ambient Conditions

Agaricus bisporus is one of the most popular mushroom species in the world; however, mushrooms are highly susceptible to browning due to the absence of a protective cuticle layer and high respiration rate. The molecular mechanism underlying the process of mushroom browning needs to be explored. Here, we analyzed the transcriptomic and metabolomic data from A. bisporus at ambient temperature. Specifically, a total of 263 significantly changed metabolites and 4492 differentially expressed genes were identified. Lipid metabolites associated with cell membrane degradation were predominantly up-regulated during ambient storage. Transcriptomic data further revealed the alterations of the expression of membrane lipid metabolism-related enzymes. Additionally, energy metabolic processes and products such as glycolysis and linoleic acid changed significantly during ambient storage, indicating their potential roles in the quality deterioration of A. bisporus. These findings provide new insights into the underlying lipid metabolic mechanisms of A. bisporus during postharvest ambient storage and will provide values for mushroom preservation techniques.

Recent advances and role of melatonin in post-harvest quality preservation of shiitake (Lentinula edodes)

Shiitake mushrooms are renowned for their popularity and robust nutritional value, are susceptible to spoilage due to their inherent biodegradability. Nevertheless, because of their lack of protection, these mushrooms have a short shelf life. Throughout the post-harvest phase, mushrooms experience a persistent decline in quality. This is evidenced by changes such as discoloration, reduced moisture content, texture changes, an increase in microbial count, and the depletion of nutrients and flavor. Ensuring postharvest quality preservation and prolonging mushroom shelf life necessitates the utilization of post-harvest preservation techniques, including physical, chemical, and thermal processes. This review provides a comprehensive overview of the deterioration processes affecting mushroom quality, covering elements such as moisture loss, discoloration, texture alterations, increased microbial count, and the depletion of nutrients and flavor. It also explores the key factors influencing these processes, such as temperature, relative humidity, water activity, and respiration rate. Furthermore, the review delves into recent progress in preserving mushrooms through techniques such as drying, cooling, packaging, irradiation, washing, and coating.

Long non-coding RNAs and their potential function in response to postharvest senescence of Sparassis latifolia during cold storage

Long non-coding RNAs (lncRNAs) have been shown to play crucial roles in response to aging processes. However, how lncRNAs regulate postharvest senescence of Sparassis latifolia (S. latifolia) with oriented polypropylene (OPP) film packing during cold storage remains unclear. In this study, we performed RNA-seq using the fruiting bodies of S. latifolia stored at 4 ℃ for 0, 8, 16 and 24 days after harvest, and profiled the lncRNA and mRNA transcriptome, respectively. In total, 1003 putative lncRNAs were identified, and there were 495, 483 and 162 differentially expressed (DE) lncRNAs, and 3680, 3941 and 1870 differentially expressed mRNAs after 8, 16 and 24 days of storage, respectively, compared to 0 day of storage. Target genes of differentially expressed lncRNAs were found to significantly associate with carbon and energy metabolism, response to abiotic stimulus, amino acid biosynthesis and metabolism, and protein synthesis and transcription. In addition, DE-lncRNA-mRNA co-expression networks in response to aging stress were also constructed. Taken together, these results confirm the regulatory role of lncRNAs in postharvest senescence of S. latifolia and will facilitate for improving preservation method.

Properties of an active film based on glutenin/tamarind gum and loaded with binary microemulsion of melatonin/pummelo essential oil and its preservation for Agaricus bisporus

In order to improve the effectiveness of the active packaging, we aimed to develop an active packaging film with unidirectional sustained release, high barrier protection, and seamless attachment between the layers. An active film based on glutenin/tamarind gum loaded with the binary microemulsion of melatonin/pummelo essential oil (G/T-M-E) with sustained release and combination effects of internal and external layers was prepared. The outer barrier layer exerted an excellent protective barrier effect after adding (3-chloropropyl) triethoxysilane, which effectively reduced external interference and the ineffective diffusion of active substances in the inner layer. The effective attachment of melatonin and essential oil layer in the G/T-M-E film enhanced antioxidation, microorganism inhibition, and free-radical-scavenging properties, which effectively delayed the senescence of post-harvest white mushrooms. Furthermore, the G/T-M-E exhibited excellent tensile strength, barrier capacity, and load-bearing strength, which had a potential, positive effect on food preservation. Therefore, this film is highly recommended for packaging purposes.

High AIECL performance of tetraphenylethene derivatives originated from the linear increasing of benzene ring and solvent regulation for sensitive measurement of melatonin

The efficiency of aggregation-induced electrochemiluminescence (AIECL) in tetraphenylethene (TPE) derivatives were significantly enhanced by combining the regulation of molecular structure and solvent. Firstly, the linear increase of the benzene ring resulted in enhanced molecular aggregation and promoted the electrochemical reaction of the anode, due to increased molecular conjugation and higher lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO). The ECL efficiency of 4,4,4,4-(Ethene-1,1,2,2-tetrayl) tetrakis (([1,1,4,1-terphenyl]-4-carbaldehyde)) (T3) nanoparticles (NPs) with more benzene rings were 5558 times that of 4,4,4,4-(ethene-1,1,2,2-tetrayl) tetrabenzaldehyde (T1) NPs, and its relative ECL efficiency of T3 NPs reached 55.58% compared to the [Ru (bpy)3]2+/tripropylamine (TPrA) system. Furthermore, solvents with different polarities played a crucial role in modulating the degree of molecular aggregation, which also effectively facilitated the AIE process and reduced the aggregation-caused quenching (ACQ) effect caused by excessively dense aggregation. This aspect had often been overlooked in previous AIECL studies. T3 NPs demonstrated optimal ECL performance at fw = 70% (fw was the H2O content in tetrahydrofuran (THF)/H2O), and its ECL efficiency was 232 times greater than fw = 100% and 1853 times greater than fw = 0%. Additionally, it was found that melatonin (MT), one of the hormones widely used to treat insomnia, exhibited antioxidant and free radical scavenging properties, which exerted a significant quenching effect on the ECL of the T3 NPs/TPrA system. Consequently, a sensitive sensing platform was developed for MT with a low detection limit of 8.78 × 10-10 mol L-1, which promoted the application of AIECL in efficient ultra-sensitive biosensing.

Melatonin Treatment Maintains the Quality of Fresh-Cut Gastrodia elata under Low-Temperature Conditions by Regulating Reactive Oxygen Species Metabolism and Phenylpropanoid Pathway

The application of melatonin (MT) has been shown to improve the quality during the storage of fruits and vegetables. The primary objective of this study is to investigate the effects of MT on the quality of fresh-cut Gastrodia elata during low-temperature (4 °C) storage. The results indicated that MT treatment not only suppressed the respiratory rate and malondialdehyde content but also slowed down the decline in total acidity and total soluble solids, effectively inhibiting microbial growth and enhancing the product safety of fresh-cut G. elata. The treatment with MT reduced the superoxide anions and hydrogen peroxide production, as well as inhibiting the activity and expression of peroxidase and polyphenol oxidase. Additionally, it led to increased activity and the expression of antioxidant-related enzymes, including superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase, and dehydroascorbate reductase, while also resulting in elevated levels of ascorbic acid and glutathione. Furthermore, the treatment with MT induced an increase in the total phenolic and flavonoid content of fresh-cut G. elata and enhanced the activity and expression of key enzymes involved in the phenylpropanoid pathway (phenylalanine ammonia-lyase, cinnamate-4-hydroxylase, 4-coumarate: CoA ligase). In summary, MT enhances the antioxidant capacity by activating both the ROS metabolism and phenylpropanoid pathway, thus maintaining the quality of fresh-cut G. elata.

LC/MS- and GC/MS-based metabolomic profiling to determine changes in flavor quality and bioactive components of Phlebopus portentosus under low-temperature storage

Introduction

Low temperature is the most common method used to maintain the freshness of Phlebopus portentosus during long-distance transportation. However, there is no information regarding the nutritional changes that occur in P. portentosus preserved postharvest in low temperature.

Methods

In this study, the changes in flavor quality and bioactive components in fruiting bodies stored at 4 °C for different storage periods were determined through LC/MS and GC/MS analyses. Sampling was performed at 0, 3, 5, 7, and 13 days storage.

Results and Discussion

Based on the results, the metabolites present in caps and stipes were different at the same period and significantly different after 7 days of storage. A total of 583 and 500 different metabolites were detected in caps and stipes, respectively, and were mainly lipids and lipid-like molecules, organic acids and derivatives, organic oxygen compounds and others. Except for prenol lipids and nucleotides, the expression levels of most metabolites increased with longer storage time. In addition, geosmin was identified as the major contributor to earthy-musty odors, and the level of geosmin was increased when the storage time was short.

Conclusion

The variations in these metabolites might cause changes in flavor quality and bioactive components in P. portentosus. Variations in these metabolites were thoroughly analyzed, and the results revealed how storage processes affect the postharvest quality of P. portentosus for the first time.

Emerging technologies for preservation and quality evaluation of postharvest edible mushrooms: A review

Edible mushrooms are the highly demanded foods of which production and consumption have been steadily increasing globally. Owing to the quality loss and short shelf-life in harvested mushrooms, it is necessary for the implementation of effective preservation and intelligent evaluation technologies to alleviate this issue. The aim of this review was to analyze the development and innovation thematic lines, topics, and trends by bibliometric analysis and review of the literature methods. The challenges faced in researching these topics were proposed and the mechanisms of quality loss in mushrooms during storage were updated. This review summarized the effects of chemical processing (antioxidants, ozone, and coatings), physical treatments (non-thermal plasma, packaging and latent thermal storage) and other emerging application on the quality of fresh mushrooms while discussing the efficiency in extending the shelf-life. It also discussed the emerging evaluation techniques based on the various chemometric methods and computer vision system in monitoring the freshness and predicting the shelf-life of mushrooms which have been developed. Preservation technology optimization and dynamic quality evaluation are vital for achieving mushroom quality control. This review can provide a comprehensive research reference for reducing mushroom quality loss and extending shelf-life, along with optimizing efficiency of storage and transportation operations.

Advances in the Role and Mechanisms of Essential Oils and Plant Extracts as Natural Preservatives to Extend the Postharvest Shelf Life of Edible Mushrooms

China has a large variety of edible mushrooms and ranks first in the world in terms of production and variety. Nevertheless, due to their high moisture content and rapid respiration rate, they experience constant quality deterioration, browning of color, loss of moisture, changes in texture, increases in microbial populations, and loss of nutrition and flavor during postharvest storage. Therefore, this paper reviews the effects of essential oils and plant extracts on the preservation of edible mushrooms and summarizes their mechanisms of action to better understand their effects during the storage of mushrooms. The quality degradation process of edible mushrooms is complex and influenced by internal and external factors. Essential oils and plant extracts are considered environmentally friendly preservation methods for better postharvest quality. This review aims to provide a reference for the development of new green and safe preservation and provides research directions for the postharvest processing and product development of edible mushrooms.

Nitric Oxide Made a Major Contribution to the Improvement of Quality in Button Mushrooms (Agaricus bisporus) by the Combined Treatment of Nitric Oxide with 1-MCP

Browning is one of the major effects of shelf-life responsible for the reduction in the commercial value of the button mushrooms (Agaricus bisporus). In this study, the individual and the combined effects of exogenous sodium nitroprusside (SNP, a nitric oxide donor) and 1-methylcyclopropene (1-MCP) on the quality of button mushrooms were evaluated. The results demonstrated that mushrooms treated with SNP+1-MCP promoted reactive oxygen species (ROS) metabolism thereby protecting cell membrane integrity, hindering polyphenol oxidase (PPO) binding to phenolic compounds, and downregulating the PPO activity. In addition, the SNP+1-MCP treatment effectively maintained quality (firmness, color, total phenol, and flavonoid) and mitigated oxidative damage by reducing ROS accumulation and malondialdehyde production through the stimulation of the antioxidant enzymes activities and the enhancement of ascorbic acid (AsA) and glutathione (GSH) contents. Moreover, the correlation analysis validated the above results. The SNP+1-MCP treatment was observed to be more prominent on maintaining quality than the individual effects of SNP followed by 1-MCP, suggesting that the combination of NO and 1-MCP had synergistic effects in retarding button mushrooms senescence, and NO signaling molecules might be predominant in the synergy.

Exogenous Melatonin Alleviated Leaf Yellowing via Inhibiting Respiration and Ethylene Biosynthesis during Shelf Life in Pakchoi

Postharvest yellowing of leafy plant is a manifestation of senescence, and melatonin (MT) is known to delay leaf senescence in some higher plants. Herein, we investigated the effect of exogenous MT treatment on postharvest pakchoi by monitoring the ethylene biosynthesis and respiratory metabolism. Results showed that exogenous MT effectively extended the shelf life, delayed leaf yellowing, minimized the alteration in Fv/Fm ratio and maintained higher integrity of chloroplast in pakchoi. There was a significant correlation between yellowing index, respiration rate and ethylene production. MT treatments greatly delayed the yellowing process of pakchoi that was associated with the reduced activity of glycolysis pathway and tricarboxylic acid cycle (TCA), increased proportion of pentose phosphate pathway (PPP) in respiratory metabolism, as manifested by the lower activity of phosphohexose isomerase (PHI), succinate dehydrogenase (SDH) and cytochrome C oxidase (COX), downregulated the expression of their corresponding genes, but enhanced the activity and expression level of 6 phosphogluconate dehydrogenase (6PGDH). MT also markedly maintain chlorophyll content by inhibiting ethylene production and action during shelf life, likely a consequence of reduced activities of 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO), as well as the expression levels of their related genes. These results collectively indicate that melatonin alleviated leaf yellowing of postharvest pakchoi might be attributed to the suppression of the ethylene biosynthesis and respiratory metabolism, and our findings contribute to provide a good candidate measure for extending shelf life and reducing postharvest loss of pakchoi.

Metabolomics reveals dopa melanin involved in the enzymatic browning of the yellow cultivars of East Asian golden needle mushroom (Flammulina filiformis)

Browning seriously causes postharvest deterioration of the yellow cultivars of Flammulina filiformis, yet the browning process and its mechanism have not been described. Changes of L*, a*, b* values, the browning and whiteness index during air contacted storage were evaluated, uncovering the great loss of brightness and meanwhile the accumulation of yellowness and redness. Browning tissue showed an increase of malondialdehyde, total phenolics, and browning-related enzyme activities of polyphenol oxidase and peroxidase, in contrast to the decrease of bioprotective catalase, superoxide, and dismutase. Non-targeted metabolomics revealed an upregulation of melanin synthesis under oxidation stress, and targeted LC-MS/MS verified the upregulation of l-dopa (3,4-dihydroxy-l-phenylalanine) during browning. Pyrrole-2,3,5-tricarboxylic acid was identified in the degradation products of browning pigments after alkaline hydrogen peroxide by LC-MS/MS, suggesting the existence of 5,6-dihydroxyindole-2-carboxylic acid derived units of eumelanin. Therefore, the biosynthesis of eumelanin via l-dopa pathway could participate in the enzymatic browning of postharvest F. filiformis.

Exogenous γ-aminobutyric acid maintains fruit quality of apples through regulation of ethylene anabolism and polyamine metabolism

In this study, 'Golden Delicious' apples were dipped with γ-aminobutyric acid (GABA) solution to investigate the changes of quality parameters, ethylene anabolism, polyamine metabolism and GABA shunt. Results showed that GABA distinctly suppressed respiratory rate, reduced titratable acidity, maintained higher soluble solid content and pericarp firmness of apples. Compared to the control, GABA also repressed the activities and gene expressions of polyamine oxidase (PAO) and diamine oxidase (DAO), enhanced MdMT, MdMS, MdSAMS, MdSAMDC, MdSPDS, MdODC, MdADC, and MdACL5 expressions, and accelerated the accumulation of putrescine, spermidine, and spermine in the exocarp of apples. Moreover, GABA decreased ethylene release, MdACS and MdACO gene expressions in the exocarp. In addition, exogenous GABA activated MdGAD, MdGDH, MdGS expressions and inhibited MdGABA-T and MdSSADH expressions in the GABA shunt, therefore increased endogenous GABA, pyruvic acid and glutamate contents in the exocarp. These findings suggest that exogenous GABA regulates ethylene anabolism, polyamine metabolism and GABA shunt to maintain fruit quality of 'Golden Delicious' apples.

Biosynthetic Pathway and the Potential Role of Melatonin at Different Abiotic Stressors and Developmental Stages in Tolypocladium guangdongense

Melatonin, a bioactive compound and an important signaling molecule produced in plants and animals, is involved in many biological processes. However, its function and synthetic pathways in fungi are poorly understood. Here, the samples from Tolypocladium guangdongense, a highly valued edible fungus with functional food properties, were collected under different experimental conditions to quantify the levels of melatonin and its intermediates. The results showed that the intracellular melatonin content was markedly improved by Congo red (CR), cold, and heat stresses; the levels of intracellular melatonin and its intermediates increased at the primordial (P) and fruiting body (FB) stages. However, the levels of most intermediates exhibited a notable decrease under CR stress. Several genes related to melatonin synthesis, excluding AADC (aromatic-L-amino-acid decarboxylase), were markedly upregulated at an early stage of CR stress but downregulated later. Compared to the mycelial stage, those genes were significantly upregulated at the P and FB stages. Additionally, exogenous melatonin promoted resistance to several abiotic stressors and P formation in T. guangdongense. This study is the first to report melatonin biosynthesis pathway in macro-fungi. Our results should help in studying the diversity of melatonin function and melatonin-synthesis pathways and provide a new viewpoint for melatonin applications in the edible-medicinal fungus.

Exogenous Melatonin Reduces Lignification and Retains Quality of Green Asparagus (Asparagus officinalis L.)

Asparagus (Asparagus officinalis L.) is highly perishable because of its high respiration rate, which continues after harvesting and leads to weight loss, increased hardness, color change, and limited shelf life. Melatonin is an indoleamine that plays an important role in abiotic stress. This study was designed to investigate the effects of melatonin on the quality attributes of green asparagus during cold storage. Green asparagus was soaked in a melatonin solution (50, 100, and 200 μM) for 30 min and then stored at 4 °C under 90% relative humidity for 25 days. The results indicated that melatonin treatment delayed the post-harvest senescence of asparagus and maintained high chlorophyll and vitamin C levels. Melatonin treatment hindered phenylalanine ammonia-lyase and peroxidase activities and reduced lignin content, thereby delaying the increase in firmness. Moreover, melatonin treatment enhanced catalase and superoxide dismutase activities, leading to reduced hydrogen peroxide content. These results indicate that melatonin treatment can be used to maintain the post-harvest quality and prolong the shelf life of green asparagus.