Melatonin delays leaf senescence of postharvest Chinese flowering cabbage through ROS homeostasis

Mechanistic insights into the enhancement of storage quality characteristics of fresh goji berry through non-thermal optical treatments (UV-C and IPL)

Non-thermo-optical treatments (NTO), characterized by low heat and non-damaging attributes, show promise as postharvest technologies. We hypothesize that NTO, specifically ultraviolet-C (UV-C) and intense pulsed light (IPL), can positively impact preserving fresh goji berry quality during storage in multiple aspects. The findings indicated that UV-C and IPL irradiations delayed the senescence process in postharvest goji berries. Several physiological and biochemical traits were influenced, including moisture loss, respiration rate, ethylene production reduction, and maintaining firmness. Furthermore, the ascorbate-glutathione (AsA-GSH) cycle and antioxidant enzyme activity were induced. Transcriptome analysis identified 12,230 differentially expressed genes (DEGs). During storage, UV-C and IPL irradiations downregulated genes related to respiration (HK, PDH, CS) and ethylene release (ACO) while upregulating genes associated with antioxidant enzymes (SOD, CAT, APX) and overall inducing the ascorbate-glutathione cycle. This indicates that UV-C and IPL irradiations can comprehensively delay the postharvest senescence and improve the storage quality of fresh goji berries.

Enhancing the antioxidant system and preserving nutritional quality of Indian Ber (Ziziphus mauritiana L.) fruit following melatonin application

The Ber fruit (Ziziphus mauritiana) is both economically valuable and nutritionally rich, but maintaining its freshness after harvest remains a challenge. This study evaluates melatonin's (MT) role in preserving ber fruit (cv. Umran) quality during cold storage. Physiologically mature fruit were treated with MT (0, 25, 50, 75 and 100 μM) for 30 min at 24 ± 2 °C and stored for 28 days at 6.5 ± 1 °C with 85-90 % relative humidity. Control fruit were dipped in distilled water. Compared to control on the last day, MT (100 μM) significantly reduced ethylene evolution (28 %), respiration rate (19 %), minimized weight loss (40 %) and retained higher firmness (35 %). Treated fruit exhibited higher total soluble solids (19 %), glucose (15 %), fructose (25 %) and sucrose (16 %). MT (100 μM) also retained 51 % more ascorbic acid, 16 % higher total phenols, and 37 % greater titratable acidity while lower polyphenol oxidase activity by 24 %, mitigating peel browning. Antioxidant activity was 30 % higher and antioxidant enzyme activities of superoxide dismutase, catalase and guaiacol peroxidase were sustained at higher levels in MT (100 μM) by 53 %, 51 %, and 131 %, respectively. Multivariate analysis confirmed MT's efficacy, with PCA explaining 85.2 % of variance in quality attributes and Pearson's correlation showing a strong positive relationship between postharvest quality and antioxidant system. These findings highlight MT (100 μM) as a promising phytohormonal treatment to extend ber fruit shelf life while maintaining nutritional and sensory quality, with potential commercial applications in postharvest management.

Impact of climate change on the toxicity of bisphenol A in Mytilus galloprovincialis and assessment of phycoremediation using Nannochloropsis salina via a multi-biomarker strategy and modeling

In the current study, the mussels Mytilus galloprovincialis, exposed to four varying temperatures (17, 20, 23, and 26 °C), were contaminated with 50 μg/L of bisphenol A both with and without Nannochloropsis salina. The toxicity evaluation is determined by quantifying various biomarkers related to oxidative stress, neurotoxicity, and cellular damage. The key findings indicate that the toxicity of bisphenol A is heightened by rising temperature. The impact of bisphenol A is most evident at 26 °C, leading to excessive production of reactive oxygen species, depletion of non-enzymatic antioxidants, and activation of antioxidant enzymes (catalase and glutathione-S-transferase). The rise in malondialdehyde levels confirms lipid peroxidation caused by bisphenol A and intensified by thermal stress. These findings have been supported by strong molecular interactions between bisphenol A and lectin mytilec apo-form and proximal thread matrix protein 1 from M. galloprovincialis following the computational modeling assay. The incorporation of N. salina as a food additive helped, firstly, to mitigate the stress effects and, secondly, resulted in a noticeable enhancement of oxidative balance and filtration ability, along with decreased lipid peroxidation.

Microplastics impacts the toxicity of antibiotics on Pinellia ternata: An exploration of their effects on photosynthesis, oxidative stress homeostasis, secondary metabolism, the AsA-GSH cycle, and metabolomics

Antibiotics and microplastics (MPs) are two new types of contaminants that are widely existent in agricultural systems. MPs could act as carriers of antibiotics, and affect the bioavailability and degradation of antibiotics, causing a combined effect on plant growth. The aim of the present experiment was to explore the effects of the treatments of oxytetracycline (OTC, 100 mg kg-1) alone and in combination with polyethylene microplastics (PE-MPs, 0.1 %, 1 %, 3 %) on P. ternata phenotypic parameters, photosynthetic system, reactive oxygen species (ROS), secondary metabolism, ascorbate-glutathione (AsA-GSH) cycle, and metabolomics. Results demonstrated that exposure to OTC alone reduced P. ternata fresh weight by causing oxidative damage, reducing photosynthetic pigment and secondary metabolite contents. OTC + MP0.1 group alleviated OTC stress to P. ternata by increasing photosynthetic pigment contents and antioxidant enzyme activities. OTC + MP3 group significantly reduced plant height of P. ternata. In addition, metabolomics analysis showed that OTC treatment interfered with pantothenate and CoA biosynthesis. The OTC + MP0.1 group activated pantothenate and CoA biosynthesis and glutathione metabolism. The significance of this study lies in clarifying the effects of OTC on medicinal plants and whether its influence mechanism is regulated by the concentration of MPs.

Effects of Moringa oleifera leaf-derived carbon dots treatment on ROS metabolism regulation for postharvest flowering Chinese cabbage preservation

Postharvest flowering Chinese cabbage is prone to rapid senescence and quality deterioration during storage at room temperature. The imbalance of reactive oxygen species (ROS) metabolism is one of the critical factors leading to this process. In this study, we synthesized Moringa oleifera leaf-derived carbon dots (MoCDs) and investigated the effects of MoCDs treatment on ROS metabolism regulation for postharvest flowering Chinese cabbage preservation. The results showed that MoCDs exhibited more efficient antioxidant activity than M. oleifera extract, attributed to their abundant surface functional groups, including hydroxyl, carboxyl, and amino groups, and an extensive sp2-hybridized carbon network. Moreover, MoCDs treatment could reduce the accumulation of hydrogen peroxide and superoxide anion radical in postharvest flowering Chinese cabbage by generally enhancing the activities of a series of key antioxidant enzymes and increasing the contents of non-enzymatic antioxidants, which significantly delayed leaf senescence and deterioration of appearance and nutritional quality of postharvest flowering Chinese cabbage during storage. In summary, as an effective antioxidant, MoCDs entered leaf cells to scavenge excessive ROS directly; as an elicitor, MoCDs enhanced the ROS scavenging ability of the endogenous antioxidant defense system in postharvest flowering Chinese cabbage. These dual protective mechanisms synergistically regulated ROS metabolism, thus benefiting the postharvest preservation of flowering Chinese cabbage.

Proteomic and physiological analyses reveal the mechanisms through which melatonin ameliorates heat stress-induced photoinhibition in Nicotiana tabacum

Raising temperature-induced heat stress under climate warming scenarios has become a predominant threat to crop growth and productivity. As a pleiotropic signaling molecule, melatonin offers an innovative solution for enhancing plant thermotolerance, although its mechanisms, particularly regarding leaf photosynthesis, remain insufficiently understood. This study employed proteomic and physiological analyses to reveal the potential benefits of endogenous melatonin in alleviating heat stress-induced damage to the photosynthetic performance of Nicotiana tabacum plants. Foliar application of melatonin at 50 μM effectively ameliorated heat stress induced-photoinhibition by preventing pigment degradation, enhancing Rubisco and FBPase activities, stimulating RuBP carboxylation and regeneration, and improving light energy transfer and utilization.The changes resulted in increased light-saturated photosynthesis rate and photochemical efficiency. Melatonin application also elevated starch and soluble sugar contents by stimulating photosynthetic carbon assimilation and suppressing dark respiration, thereby counteracting the harmful impact of heat stress. Proteomic analysis revealed that melatonin significantly upregulated the expression of two key enzymes (glutamyl-tRNA reductase and monomethyl ester aerobic oxidative cyclase) involved in the chlorophyll biosynthetic pathway, enhanced the expression of three proteins (PSII cytochrome b559, protein H, and 10 kDa polypeptide) related to the PSII photochemical reaction, stimulated the expression of fructose-1,6-bisphosphatase linked to the Calvin cycle, and increased the expression of granule-bound starch synthase related to carbohydrate metabolism, thereby positively mediating the photodamage induced by heat stress to plant photosynthetic performance. These results highlight the potential of endogenous melatonin application as an effective approach for boosting crop photosynthetic performance and thermotolerance to global warming.

Melatonin maintains postharvest quality by modulating the metabolisms of cell wall and sugar in flowering Chinese cabbage

Melatonin is known to delay postharvest nutrient loss. However, its specific roles in regulating cell wall and sugar metabolism to maintain postharvest quality in flowering Chinese cabbage remain unclear. In this study, postharvest flowering Chinese cabbage was treated with melatonin (100 µmol L- 1) to investigate the cell wall and sugar metabolisms. Our research found that melatonin supplementation increased levels of important nutrients like ascorbic acid, sugars, soluble protein, carotenoid, and glucosinolates. It also enhanced various cell wall components (cellulose, hemicellulose, lignin, and protopectin) while reducing water-soluble pectin accumulation. Melatonin helped stabilize cell wall by reducing the expression of genes related to cell wall degradation (BrBGAL4, BrPG, BrCEL3, and BrPME3), inhibiting activities of cell wall-degrading enzymes like pectin methylesterase and cellulase, and improving expressions of cellulose biosynthesis-related genes (BrCesA1, BrCesA3.1, and BrCesA3.2). Additionally, it boosted sugar accumulation by increasing activities of sucrose synthetase and sucrose phosphate synthetase, upregulating expressions of BrSUS1, BrSUS5, BrSPS1F, BrSPS3F, BrSPS4F, and suppressing activities of neutral invertase and acidic invertase and expressions of genes involved in sugar metabolism (BrSUS3, BrINV, BrSWEET2, BrSWEET4, and BrSWEET17). This study highlights melatonin's vital roles in maintaining postharvest quality and offers practical insights for improving market performance of flowering Chinese cabbage.

Facilitating Maize Seed Germination Under Heat Stress via Exogenous Melatonin

Seed germination is a critical phase during which plants are particularly sensitive to environmental stresses, especially heat stress, due to the high metabolic and physiological activities required for initial growth. Melatonin (MT), a key antioxidant, is crucial for assisting plants in managing abiotic stresses. While the impact of melatonin on heat stress has been explored in other developmental stages or species, this is the first study to specifically focus on its role during maize seed germination under heat stress. The treatment with 50 μM melatonin significantly enhanced seed germination under heat stress by improving antioxidant capacity, osmotic regulation, and hydrolytic enzyme activity, likely through the modulation of key signaling pathways, thus reducing oxidative damage and starch content. Furthermore, melatonin application promoted the accumulation of endogenous gibberellins (GAs) and significantly inhibited abscisic acid (ABA) content, thereby maintaining a dynamic equilibrium between these phytohormones. Principal component analysis and correlation analysis provided deeper insights into the overall effects of these physiological and biochemical parameters. Integrated transcriptomic and metabolomic analysis revealed that melatonin exerted its regulatory effects by modulating key genes and pathways associated with antioxidant defense, stress responses, and plant hormone signal transduction. Furthermore, melatonin significantly modulated the GA and ABA signaling pathways, starch and sucrose metabolism, and phenylpropanoid biosynthesis, thereby reducing oxidative damage induced by heat stress and strengthening the defense mechanisms of maize seeds. The alignment between the qRT-PCR findings and transcriptomic data further validated the robustness of these underlying mechanisms. In conclusion, this study provides novel insights into the role of melatonin in enhancing maize seed germination under heat stress and offers a promising strategy for improving crop heat tolerance through melatonin application in agricultural practices.

Effects of exogenous melatonin on the growth and photosynthetic characteristics of tomato seedlings under saline-alkali stress

Saline-alkali stress is a major abiotic stress factor that adversely affects the growth, development, and yield of crops by disrupting ion homeostasis, osmotic balance, and metabolic processes. This study was designed to explore the alleviating effect of melatonin on the growth and development of tomato plants under saline-alkali stress conditions and to screen for optimal concentrations to alleviate the stress. Tomato variety 'Condine Red' was used as the test material, and a total of six treatments were designed including no saline-alkali stress and no melatonin spray as control (CK), and foliar spraying of 0, 50, 100, 150, and 200 µmol·L- 1 melatonin under saline-alkali stress (75 mmol·L- 1), which were used to determine the growth and photosynthetic characteristics of tomato plants. The results showed that saline-alkali stress significantly inhibited plant height, stem diameter, root activity and biomass accumulation, significantly reduced the chlorophyll content of tomato leaves and the efficiency of photosynthetic electron transfer from primary quinone receptor QA to secondary quinone receptor QB, and caused significant deformation of the fast chlorophyll fluorescence induced kinetic curve (OJIP), inhibiting photosynthesis. Exogenous melatonin could improve tomato tolerance to saline-alkali stress, and the effect depended on the concentration. In this experiment, treatment with 100 µmol·L- 1 melatonin showed the strongest positive effect on the growth of tomato plants under saline-alkali stress according to the comprehensive evaluation of principal components. In addition, changes in photosynthetic chlorophyll fluorescence parameters and chlorophyll fluorescence induction curves after melatonin treatment highlighted that melatonin could improve the response of the photosynthetic system to saline-alkali stress by enhancing quenching of excess excitation energy and protecting the photosynthetic electron transport system. Collectively, exogenous melatonin pretreatment increased root activity, chlorophyll content and improved photosystem processes, thereby alleviating tomato growth under saline-alkali stress. The results of this study lay the foundation for the practical application of melatonin in saline-alkali stress.

Exogenous nitric oxide treatment delays the senescence of postharvest mung bean sprouts by regulating ascorbic acid metabolism

BACKGROUND

This study evaluated the effects of nitric oxide (NO) treatment on ascorbic acid (AsA) metabolism and mung bean sprout quality. It examined changes in the AsA content, enzyme activity associated with AsA metabolism, antioxidant capacity, cell membrane composition, and cellular structure to clarify the effects of NO on mung bean sprouts.

RESULTS

Nitric oxide treatment preserved mung bean sprout quality by enhancing significantly the activity of enzymes involved in the l-galactose pathway (including guanosine diphosphate (GDP)glutathione (-d-mannose pyrophosphorylase, GDP-mannose-3',5'-epimerase, GDP-l-galactose phosphorylase, l-galactose-1-phosphate phosphatase, l-galactose dehydrogenase, and l-galactose-1,4-lactone dehydrogenase) and the AsA-glutathione (GSH)(Beijing Solarbio Science and Technology Co.,Ltd., Beijing, China) cycle (including ascorbate peroxidase, ascorbic acid oxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase) during the germination and storage stage. Increased enzyme activity led to an increase in AsA content and enhanced antioxidant capacity, and reduced the membrane lipid damage in mung bean sprouts. This was demonstrated by higher levels of DPPH radical scavenging capacity, unsaturated fatty acids and phospholipids, along with lower levels of hydrogen peroxide, superoxide anions, and malondiadehyde, in NO-treated mung bean sprouts. Scanning electron microscopy also revealed that NO treatment maintained the integrity of the cellular structure of the mung bean sprouts.

CONCLUSION

Nitric oxide accelerates AsA metabolism effectively by regulating the biosynthesis and regeneration of AsA in mung bean sprouts. These changes increased AsA levels, alleviated membrane lipid damage, delayed senescence, and maintained the quality of mung bean sprouts during storage. © 2024 Society of Chemical Industry.

Exogenous melatonin delays leaves senescence and enhances saline and alkaline stress tolerance in grape seedlings

Saline and alkaline stress is one of the major abiotic stresses facing agricultural production, which severely inhibits the growth and yield of plant. The application of plant growth regulators can effectively prevent crop yield reduction caused by saline and alkaline stress. Exogenous melatonin (MT) can act as a signaling molecule involved in the regulation of a variety of physiological processes in plants, has been found to play a key role in enhancing the improvement of plant tolerance to abiotic stresses. However, the effects of exogenous MT on saline and alkaline tolerance of table grape seedlings and its mechanism have not been clarified. The aim of this study was to investigate the role of exogenous MT on morphological and physiological growth of table grape seedlings (Vitis vinifera L.) under saline and alkaline stress. The results showed that saline and alkaline stress resulted in yellowing and wilting of grape leaves and a decrease in chlorophyll content, whereas the application of exogenous MT alleviated the degradation of chlorophyll in grape seedling leaves caused by saline and alkaline stress and promoted the accumulation of soluble sugars and proline content. In addition, exogenous MT increased the activity of antioxidant enzymes, which resulted in the scavenging of reactive oxygen species (ROS) generated by saline and alkaline stress. In conclusion, exogenous MT was involved in the tolerance of grape seedlings to saline and alkaline stress, and enhanced the saline and alkaline resistance of grape seedlings to promote the growth and development of the grape industry in saline and alkaline areas.

Trans-2-hexenal reduces postharvest mango stem-end rot by oxidative damage to Neofusicoccum parvum cell membranes

Neofusicoccum parvum is one of the most hazardous pathogens causing mango fruit decay. The present study utilized trans-2-hexenal (TH), a typical antifungal component of plant essential oils (EOs), to control N. parvum both in vivo and in vitro, and attempted to explore the mechanisms involved. The findings showed that at concentrations greater than 0.4 µL/mL, TH exhibited exceptional antifungal activity against N. parvum in vitro. TH application led to the disruption of the structural integrity of both cell walls and cell membranes, with a particular impact on the latter, as evidenced by the dramatically increased propidium iodide level, as well as reduced total lipids and ergosterol content. Further DCFH-DA staining experiments showed that TH induced mycelial reactive oxygen species (ROS) accumulation, which exacerbated cell membrane lipid peroxidation. For easier application of TH, we fabricated aerogel-loaded TH (ALTH) materials, which demonstrated excellent antifungal activity in vitro. Infestation studies on fruits demonstrated that ALTH mitigated mango stem-end rot in a dose-dependent fashion, with a concentration of 40 µL/L showing efficacy comparable to the conventional fungicide prochloraz, while maintaining fruit quality. In light of these results, TH works by inducing ROS buildup and oxidative damage to the cell membrane of N. parvum, and is a particularly promising preservative for preventing postharvest infections in mangoes.

L-Cysteine Treatment Delays Leaf Senescence in Chinese Flowering Cabbage by Regulating ROS Metabolism and Stimulating Endogenous H2S Production

Leaf senescence is a major concern for postharvest leafy vegetables, as leaves are highly prone to yellowing and nutrient loss, resulting in reduced commercial value and limited shelf-life. This study aimed to investigate the effect of L-cysteine (L-cys) on postharvest Chinese flowering cabbage stored at 20 °C. The results showed that 0.5 g L-1 L-cys treatment effectively slowed leaf senescence by downregulating chlorophyll degradation genes (BrNYC1, BrNOL, BrPPH, BrPAO, BrNYE, and BrSAGs) and senescence marker gene BrSAG12. Moreover, this treatment exhibited positive influence on the nutritional quality of cabbage. Also, L-cys treatment maintained ROS homeostasis, preventing excessive ROS accumulation and lipid membrane oxidation. L-cys treatment also maintained a higher total antioxidant capacity and scavenging rate of •OH and O2•-. Additionally, L-cys treatment maintained high levels of ascorbate and glutathione and activated antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and the expression of the encoding genes. Furthermore, L-cys treatment elevated endogenous H2S levels, which are correlated with increased L-cysteine desulfhydrase activity and the upregulation of H2S biosynthesis-related genes. These findings suggest that L-cys can delay leaf senescence by reducing chlorophyll breakdown, maintaining ROS homeostasis, and stimulating endogenous H2S production.

The role of gibberellin synthase gene VvGA2ox7 acts as a positive regulator to salt stress in Arabidopsis thaliana

BACKGROUND

Soil salinity is an important environmental component affecting plant growth and yield, but high-salinity soils are a major constraint to the development of the grape industry. Previous studies have provided lines of evidence that gibberellins (GAs) play a significant regulatory role in plant responses to salt stress. However, it remains unclear whether GA2ox, a key enzyme that maintains the balance of bioactive gibberellins and intermediates in plants, is involved in the mechanism of salt stress tolerance in grapes.

RESULTS

In this study, we found that GA2ox7 positively modulates salt stress via its ectopic expression in Arabidopsis thaliana. The GA2ox7 gene cloned from grape was a hydrophilic protein, its CDS length was 1002 bp. Besides, VvGA2ox7 protein contained DIOX_N and 2OG-FeII_Oxy domains and was localized at the nucleus and cytoplasm. Yeast two-hybrid (Y2H) showed VvARCN1, VvB5R, VvRUB2, and VvCAR11 might be potential interaction proteins of VvGA2ox7. Compared with the wild type, overexpression of VvGA2ox7 in Arabidopsis thaliana enhanced antioxidant enzymatic activities and proline, chlorophyll, and ABA contents, and decreased relative electrical conductivity, malondialdehyde, and GA3 contents. Moreover, overexpression of VvGA2ox7 positively regulated the expression of salt stress response genes (KAT1, APX1, LEA, P5CS1, AVP1, CBF1), indicating that the VvGA2ox7 overexpression improved the salt stress tolerance of plants.

CONCLUSIONS

Taken together, this investigation indicates that VvGA2ox7 may act as a positive regulator in response to salt stress and provide novel insights for a deeper understanding of the role of VvGA2ox7 in grapes.

tert-Butylhydroquinone alleviates a postharvest pericarp browning of longan fruit by regulating antioxidant metabolism

Harvested longan fruit is prone to pericarp browning, which restricts preservation quality and shortens fruit shelf life. The antioxidant system can defend against oxidative stress-mediated quality deterioration such as fruit browning. This study aimed to evaluate the effect of tert-butylhydroquinone (TBHQ) on anti-browning ability of longan fruit in association with redox metabolism. The results indicated that the application of 0.02% TBHQ significantly suppressed the progression of pericarp browning. In comparison with control, TBHQ treatment decreased the contents of hydrogen peroxide (H2O2), superoxide radical (O2 -⋅), and malondialdehyde, and retained high levels of ascorbic acid (AsA), glutathione (GSH), total phenolics as well as 1,1-diphenyl-2-picrylhydrazyl scavenging rate. Enhanced enzymatic activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase, and dehydroascorbate reductase (DHAR), but decreased activities of polyphenol oxidase and peroxidase were also observed in TBHQ-treated fruit. Gene expression analysis indicated that redox metabolism-related genes, including DlSOD, DlCAT, DlGR, and DlAPX, were upregulated after TBHQ treatment. Correlation analysis suggested that antioxidants, including AsA, GSH, CAT, APX, SOD, and DHAR, were negatively correlated to reactive oxygen species production and percarp browning. These results suggest that TBHQ is effective in alleviating pericarp browning by increasing antioxidant capacity of longan fruit.

Preharvest sodium selenite treatments affect the growth and enhance nutritional quality of purple leaf mustard with abundant anthocyanin

Both selenium (Se) and anthocyanins are crucial for maintaining human health. Preharvest Se treatments could promote anthocyanin biosynthesis and augment Se levels in vegetables, helping to combat Se deficiencies in dietary intake. However, it remains unknown whether preharvest Se treatment could balance growth and anthocyanin biosynthesis in plants and what the appropriate treatment concentration is. In this study, preharvest treatments with sodium selenite at varying concentrations (0, 5, 10, and 30 mg/kg) affect the growth and nutritional quality of purple leaf mustard (Brassica juncea) with abundant anthocyanins. Lower Se concentrations (≤10 mg/kg) of preharvest treatments enhanced photosynthesis, facilitated root system development, consequently elevated the biomass. Conversely, higher Se levels (≥30 mg/kg) reduced photosynthesis and biomass. The dosage-dependent effects of Se treatments were corroborated through seedlings cultivated in hydroponic conditions. Moreover, nearly all Se treatments elevated the contents of various nutrients in leaf mustard, particularly anthocyanin and organic se. These results suggest an overall enhancement in nutritional quality of leaf mustard plants. Furthermore, the application of 10 mg/kg Se significantly enhanced the activity of phenylalanine ammonia-lyase and upregulated the expression of 12 genes pivotal for anthocyanin biosynthesis, further demonstrating the fortified effects of Se enrichment on anthocyanins in leaf mustard. Low-level Se treatments resulted in heightened antioxidant activity (APX, CAT, and POD), mitigating reactive oxygen species induced by increasing Se content in tissues. The enhanced antioxidant activities may be beneficial for the normal growth of leaf mustard under Se stress conditions. In conclusion, our study demonstrated preharvest Se treatment at 10 mg/kg could balance the growth and anthocyanin biosynthesis in purple leaf mustard. This study offers valuable insights into anthocyanin fortification through Se enrichment methods in agricultural practices, ensuring that such fortification does not compromise leafy vegetable yield.

Melatonin Rinsing Treatment Associated with Storage in a Controlled Atmosphere Improves the Antioxidant Capacity and Overall Quality of Lemons

Antioxidant capacity is one of the most important biological activities in fruits and vegetables and is closely related to human health. In this study, 'Eureka' lemons were used as experimental materials and stored at 7-8 °C MT (melatonin, 200 μmol, soaked for 15 min) and CA (controlled atmosphere, 2-3% O2 + 15-16% CO2) individually or in combination for 30 d. The changes in lemon fruits' basic physicochemical properties, enzyme activities, and antioxidant capacities were studied. Comparing the combined treatment to the control, the outcomes demonstrated a significant reduction in weight loss, firmness, stomatal opening, and inhibition of polyphenol oxidase (PPO) and peroxidase (POD) activities. Additionally, the combined treatment maintained high levels of titratable acidity (TA), vitamin C (VC), total phenolic content (TPC), and antioxidant capacity and preserved the lemon aroma. Meanwhile, the correlation between fruit color, aroma compounds, and antioxidant capacity was revealed, providing valuable insights into the postharvest preservation of lemons. In conclusion, the combined treatment (MT + CA) was effective in maintaining the quality and antioxidant capacity of lemons.

Exogenous Ergothioneine and Glutathione Limit Postharvest Senescence of Arugula

Arugula is susceptible to postharvest deterioration. We tested the impact of exogenous antioxidant (i.e., ergothioneine and glutathione) dip solutions on arugula quality during storage at 4 °C or 10 °C for up to 17 days relative to a non-antioxidant treatment. Leaves from each dip treatment and storage temperature were assessed for visual quality and endogenous antioxidant metabolite profiles. Overall, leaf discolouration, wilting, and decay were more rapid at 10 °C than at 4 °C. Both antioxidant treatments limited leaf discolouration at 4 °C. Exogenous ergothioneine reduced wilting at 4 °C, whereas exogenous glutathione limited the incidence of leaf decay. At 10 °C, glutathione reduced the incidence of discolouration and decay, whereas both antioxidant dip treatments limited the decline in leaf yellowing. Ergothioneine was solely detected in ergothioneine-treated leaves; a decrease occurred within the first two days of storage but was unchanged thereafter. Although both antioxidant treatments did not affect endogenous glutathione concentrations at either storage temperature, glutathione disulfide was stable within the glutathione-treated leaves, whereas it increased in the other treatments. Ascorbate degradation was delayed in ergothioneine-treated leaves at 4 °C relative to all other treatments, whereas both antioxidant treatments little affected ascorbate metabolism in leaves stored at 10 °C.

Evolution of reactive oxygen species cellular targets for plant development

Reactive oxygen species (ROS) are the key players in regulating developmental processes of plants. Plants have evolved a large array of gene families to facilitate the ROS-regulated developmental process in roots and leaves. However, the cellular targets of ROS during plant evolutionary development are still elusive. Here, we found early evolution and large expansions of protein families such as mitogen-activated protein kinases (MAPK) in the evolutionarily important plant lineages. We review the recent advances in interactions among ROS, phytohormones, gasotransmitters, and protein kinases. We propose that these signaling molecules act in concert to maintain cellular ROS homeostasis in developmental processes of root and leaf to ensure the fine-tuning of plant growth for better adaptation to the changing climate.

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.

Titanium dioxide nanoparticles alleviates polystyrene nanoplastics induced growth inhibition by modulating carbon and nitrogen metabolism via melatonin signaling in maize

BACKGROUND

Nanoplastics, are emerging pollutants, present a potential hazard to food security and human health. Titanium dioxide nanoparticles (Nano-TiO2), serving as nano-fertilizer in agriculture, may be important in alleviating polystyrene nanoplastics (PSNPs) toxicity.

RESULTS

Here, we performed transcriptomic, metabolomic and physiological analyzes to identify the role of Nano-TiO2 in regulating the metabolic processes in PSNPs-stressed maize seedlings (Zea mays L.). The growth inhibition by PSNPs stress was partially relieved by Nano-TiO2. Furthermore, when considering the outcomes obtained from RNA-seq, enzyme activity, and metabolite content analyses, it becomes evident that Nano-TiO2 significantly enhance carbon and nitrogen metabolism levels in plants. In comparison to plants that were not subjected to Nano-TiO2, plants exposed to Nano-TiO2 exhibited enhanced capabilities in maintaining higher rates of photosynthesis, sucrose synthesis, nitrogen assimilation, and protein synthesis under stressful conditions. Meanwhile, Nano-TiO2 alleviated the oxidative damage by modulating the antioxidant systems. Interestingly, we also found that Nano-TiO2 significantly enhanced the endogenous melatonin levels in maize seedlings. P-chlorophenylalanine (p-CPA, a melatonin synthesis inhibitor) declined Nano-TiO2-induced PSNPs tolerance.

CONCLUSIONS

Taken together, our data show that melatonin is involved in Nano-TiO2-induced growth promotion in maize through the regulation of carbon and nitrogen metabolism.

Effect and Mechanism of L-Arginine against Alternaria Fruit Rot in Postharvest Blueberry Fruit

This study aimed to explore the impact of L-arginine (Arg) on the development of resistance to Alternaria tenuissima (A. tenuissima) in blueberries. The metabolism of reactive oxygen species, pathogenesis-related proteins (PRs), and jasmonic acid (JA) biosynthesis pathways were analyzed, including changes in activity and gene expression of key enzymes. The results indicated that Arg treatment could prevent the development of Alternaria fruit rot in postharvest blueberries. In addition, it was also found to induce a burst of hydrogen peroxide in the blueberries early on during storage, thereby improving their resistance to A. tenuissima. Arg treatment was observed to increase the activity of antioxidant enzymes (peroxidase, catalase, superoxide dismutase, and ascorbate peroxidase) and related gene expression, as well as the total levels of phenolics, flavonoids, and anthocyanin in the blueberries. The activity and gene expression of the PRs (chitinase and β-1,3-glucanase) were elevated in Arg-treated blueberries, boosting their resistance to pathogens. Additionally, a surge in endogenous JA content was detected in Arg-treated blueberries, along with upregulated expression of key genes related the JA biosynthesis pathway (VcLOX1, VcAOS1, VcAOC, VcAOC3, VcOPR1, VcOPR3, VcMYC2, and VcCOI1), thereby further bolstering disease resistance. In conclusion, Arg treatment was determined to be a promising prospective method for controlling Alternaria fruit rot in blueberries.

Hydrogen Peroxide Promotes Tomato Leaf Senescence by Regulating Antioxidant System and Hydrogen Sulfide Metabolism

Hydrogen peroxide (H2O2) is relatively stable among ROS (reactive oxygen species) and could act as a signal in plant cells. In the present work, detached tomato leaves were treated with exogenous H2O2 at 10 mmol/L for 8 h to study the mechanism of how H2O2 regulates leaf senescence. The data indicated that H2O2 treatment significantly accelerated the degradation of chlorophyll and led to the upregulation of the expression of leaf senescence-related genes (NYC1, PAO, PPH, SGR1, SAG12 and SAG15) during leaf senescence. H2O2 treatment also induced the accumulation of H2O2 and malondialdehyde (MDA), decreased POD and SOD enzyme activities and inhibited H2S production by reducing the expression of LCD1/2 and DCD1/2. A correlation analysis indicated that H2O2 was significantly and negatively correlated with chlorophyll, the expression of leaf senescence-related genes, and LCD1/2 and DCD1/2. The principal component analysis (PCA) results show that H2S showed the highest load value followed by O2•-, H2O2, DCD1, SAG15, etc. Therefore, these findings provide a basis for studying the role of H2O2 in regulating detached tomato leaf senescence and demonstrated that H2O2 plays a positive role in the senescence of detached leaves by repressing antioxidant enzymes and H2S production.

Prolong the postharvest shelf life of spinach through the antioxidative ability of melatonin

Spinach is also known as Persian cuisine, it is rich in nutrients such as protein, vitamin C and minerals, and has high nutritional value. In this study, Spinach was treated with melatonin in order to prolong its shelf life. Melatonin has strong antioxidant effects as an endogenous free radical scavenger. The spinach was sprayed with 0.10, 0.20 and 0.30 mg/mL melatonin solution after harvesting, and distilled water was used as control for low temperature storage at 4 °C. The results showed that melatonin spraying Spinach delayed the degradation of chlorophyll, especially the treatment of 0.20 mg/mL melatonin was the most effective. The content of soluble sugar and soluble protein in spinach tissue was kept high, the accumulation of malondialdehyde (MDA) was reduced, and the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were increased. These findings suggested that melatonin treatment may be a useful technique to prolong the postharvest life of spinach and improve its quality.

Melatonin Postharvest Treatment in Leafy 'Fino' Lemon Maintains Quality and Bioactive Compounds

Spain is a great producer of organic lemon; however, it is necessary to reduce the losses caused by post-harvest diseases. Melatonin (MEL) is a naturally occurring compound with physiological functions in fruit growth and ripening and is able to modulate postharvest ripening and senescence, most of it being concentrated in climacteric fruit. Thus, the aim of this study was to apply MEL to organic lemon fruit with stems and leaves (LEAF) and to organic lemon without those components (LEAFLESS) after harvesting and storage during 21 days at 2 °C to understand the effects of this treatment on the fruit quality. For this purpose, two experiments were carried out. First, MEL was applied at 0.01 mM, 0.1 mM and 1.0 mM by immersion for 15 min on lemon fruits, and the quality parameters and bioactive compounds of the fruit were analysed. Subsequently, a second experiment was carried out where the best concentration (1 mM) was selected and another time (15 and 30 min) was added, with the same quality parameters being analysed. As a result, we observed that all MEL treatments showed positive effects on weight loss reduction, softening (higher fruit firmness), total acidity and lower colour changes. Total phenols increased in MEL-treated lemons, both in peel and juice. For the three concentrations tested, the best efficiency was obtained with MEL at 1.0 mM, while LEAF lemons were the most effective. In conclusion, lemons containing stems and leaves (LEAF) improved preservability by using MEL at 1.0 mM with better organoleptic quality and enhanced phenolic compounds.

Nutrient Metabolism Pathways Analysis and Key Candidate Genes Identification Corresponding to Cadmium Stress in Buckwheat through Multiomics Analysis

Fagopylum tatarium (L.) Gaertn (buckwheat) can be used both as medicine and food and is also an important food crop in barren areas and has great economic value. Exploring the molecular mechanisms of the response to cadmium (Cd) stress can provide the theoretical reference for improving the buckwheat yield and quality. In this study, perennial tartary buckwheat DK19 was used as the experimental material, its key metabolic pathways in the response to Cd stress were identified and verified through transcriptomic and metabolomic data analysis. In this investigation, 1798 metabolites were identified through non-targeted metabolomic analysis containing 1091 up-regulated and 984down-regulated metabolites after treatment. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differential metabolites was significantly enriched in galactose metabolism, glycerol metabolism, phenylpropane biosynthesis, glutathione metabolism, starch and sucrose metabolism. Linkage analysis detected 11 differentially expressed genes (DEGs) in the galactose metabolism pathway, 8 candidate DEGs in the lipid metabolism pathway, and 20 candidate DEGs in the glutathione metabolism pathway. The results of our study provided useful clues for genetically improving the resistance to cadmium by analyzing the molecular mechanism of cadmium tolerance in buckwheat.

Effect of oxyresveratrol on the quality and membrane lipid metabolism of shiitake mushroom (Lentinus edodes) during storage

The effect of oxyresveratrol on postharvest quality and membrane lipid metabolism of shiitake mushroom was investigated. The result exhibited that oxyresveratrol retarded browning, maintained firmness and alleviated occurrence of decay of shiitake mushroom. The oxidation and hydrolysis of membrane phospholipids were suppressed by oxyresveratrol treatment, which was associated with reduced LOX and PLD activities and increased SOD and CAT activities. The membrane lipidomics of shiitake mushroom was determined by LC-MS. 385 lipid species and 13 fatty acids in membrane lipids were identified by multiple reaction monitoring method. Compared with control group, the phospholipic acid and lysophospholipid reduced by 29.24% and 21.29% in oxyresveratrol-treated group, respectively, which alleviated hydrolysis of phospholipid. Meanwhile, oxyresveratrol maintained the unsaturation of fatty acids and alleviated oxidation of phospholipid. These results demonstrated that oxyresveratrol could play a dual role of inhibiting the oxidation and hydrolysis of phospholipids to mitigate cellular damage of shiitake mushroom.

Preharvest Application of Sodium Nitroprusside Alleviates Yellowing of Chinese Flowering Cabbage via Modulating Chlorophyll Metabolism and Suppressing ROS Accumulation

Chinese flowering cabbage is prone to senescence and yellowing after harvest, leading to a huge postharvest loss. Nitric oxide (NO) is a multifunctional plant growth regulator, but the effect of preharvest application of NO on the storage quality of Chinese flowering cabbage remains unclear. Preharvest application of 50 mg L^-1 sodium nitroprusside (SNP, a NO donor) to the roots obviously reduced leaf yellowing in Chinese flowering cabbage during storage. Proteomic analysis reveals 198 differentially expressed proteins (DEPs) in SNP-treated plants compared to the control. The main DEPs were significantly enriched in chlorophyll metabolisms, phenylpropanoid synthesis, and antioxidant pathways. SNP treatment enhanced chlorophyll biosynthesis and suppressed chlorophyll-degradation-related proteins and genes. It also modulated flavonoid-biosynthesis-related genes, and 21 significantly regulated flavonoids were identified in SNP-treated plants. The enhanced antioxidant capacity in SNP-treated plants was able to decrease chlorophyll catabolism by inhibiting peroxidase-mediated chlorophyll bleaching. Collectively, preharvest SNP treatment modulated chlorophyll metabolism and preserved chlorophyll content in leaves during storage. Moreover, SNP treatment enhanced flavonoid synthesis, suppressed reactive oxygen species accumulation, and delayed the senescence process, thereby maintaining leaf greening in Chinese flowering cabbage. These findings highlight the role of exogenous NO in alleviating yellowing of leafy vegetables.

Synergistic Effects of Tragacanth and Anti-ethylene Treatments on Postharvest Quality Maintenance of Mango (Mangifera indica L.)

Mango (Mangifera indica L.) is one of the most popular tropical fruits grown in Egypt and several other countries, making it a potential export commodity. Excessive deterioration after harvest requires various treatments to maintain fruit quality. We evaluated the treatments effects of melatonin (MT) as an anti-ethylene agent and tragacanth gum (TRG) as an edible coating individually and together (MT-TRG) before storing mangoes at 12 °C for 32 days under 85-90% relative humidity. Compared with control, all treatments were significantly effective in preserving fruit quality. Fruits treated with MT-TRG showed significantly lower decay values, respiration rates, ethylene production, and weight loss than untreated fruits. MT-TRG treatment significantly enhanced fruit quality, thereby maintaining fruit appearance, flesh color, firmness, total soluble solids and phenolic contents, and pectin methyl esterase, polyphenol oxidase, and peroxidase activities during the storage period. We propose 200 µM MT + 1% TRG as a safe postharvest treatment to reduce the deterioration of mangoes and maintain fruit quality.

Morphological and Physiological Mechanisms of Melatonin on Delaying Drought-Induced Leaf Senescence in Cotton

Leaf senescence reduces the photosynthetic capacity of leaves, thus significantly affecting the growth, development, and yield formation of cotton. Melatonin (MT) is a multipotent substance proven to delay leaf senescence. However, its potential mechanism in delaying leaf senescence induced by abiotic stress remains unclear. This study aimed to explore the effect of MT on delaying drought-induced leaf senescence in cotton seedlings and to clarify its morphological and physiological mechanisms. Drought stress upregulated the leaf senescence marker genes, destroyed the photosystem, and led to excessive accumulation of reactive oxygen species (ROS, e.g., H₂O₂ and O₂^-), thus accelerating leaf senescence. However, leaf senescence was significantly delayed when 100 μM MT was sprayed on the leaves of the cotton seedlings. The delay was embodied by the increased chlorophyll content, photosynthetic capacity, and antioxidant enzyme activities, as well as decreased H₂O₂, O₂^-, and abscisic acid (ABA) contents by 34.44%, 37.68%, and 29.32%, respectively. MT significantly down-regulated chlorophyll degradation-related genes and senescence marker genes (GhNAC12 and GhWRKY27/71). In addition, MT reduced the chloroplast damage caused by drought-induced leaf senescence and maintained the integrity of the chloroplast lamellae structure under drought stress. The findings of this study collectively suggest that MT can effectively enhance the antioxidant enzyme system, improve photosynthetic efficiency, reduce chlorophyll degradation and ROS accumulation, and inhibit ABA synthesis, thereby delaying drought-induced leaf senescence in cotton.

Genetic and evolutionary dissection of melatonin response signaling facilitates the regulation of plant growth and stress responses

The expansion of gene families during evolution could generate functional diversity among their members to regulate plant growth and development. Melatonin, a phylogenetically ancient molecule, is vital for many aspects of a plant's life. Understanding the functional diversity of the molecular players involved in melatonin biosynthesis, signaling, and metabolism will facilitate the regulation of plant phenotypes. However, the molecular mechanism of melatonin response signaling elements in regulating this network still has many challenges. Here, we provide an in-depth analysis of the functional diversity and evolution of molecular components in melatonin signaling pathway. Genetic analysis of multiple mutants in plant species will shed light on the role of gene families in melatonin regulatory pathways. Phylogenetic analysis of these genes was performed, which will facilitate the identification of melatonin-related genes for future study. Based on the abovementioned signal networks, the mechanism of these genes was summarized to provide reference for studying the regulatory mechanism of melatonin in plant phenotypes. We hope that this work will facilitate melatonin research in higher plants and finely tuned spatio-temporal regulation of melatonin signaling.

Functions of Melatonin during Postharvest of Horticultural Crops

Melatonin, a tryptophan-derived molecule, is endogenously generated in animal, plant, fungal and prokaryotic cells. Given its antioxidant properties, it is involved in a myriad of signaling functions associated with various aspects of plant growth and development. In higher plants, melatonin (Mel) interacts with plant regulators such as phytohormones, as well as reactive oxygen and nitrogen species including hydrogen peroxide (H2O2), nitric oxide (NO) and hydrogen sulfide (H2S). It shows great potential as a biotechnological tool to alleviate biotic and abiotic stress, to delay senescence and to conserve the sensory and nutritional quality of postharvest horticultural products which are of considerable economic importance worldwide. This review provides a comprehensive overview of the biochemistry of Mel, whose endogenous induction and exogenous application can play an important biotechnological role in enhancing the marketability and hence earnings from postharvest horticultural crops.

6-Benzyladenine Treatment Maintains Storage Quality of Chinese Flowering Cabbage by Inhibiting Chlorophyll Degradation and Enhancing Antioxidant Capacity

The cytokinin 6-benzyladenine (6-BA) is widely used to regulate the growth of horticultural crops. However, it is not clear how postharvest treatment with 6-BA at various concentrations affects the quality of Chinese flowering cabbage. In this study, harvested Chinese flowering cabbage was foliar sprayed with 6-BA solution at concentrations of 5, 10, 20, 40, and 80 mg·L^-1. All 6-BA treatments protected the quality of Chinese flowering cabbage during storage, and the treatment with 20 and 40 mg·L^-1 6-BA showed the most obvious effect. Treatment with 6-BA reduced leaf yellowing degree and weight loss rate; maintained high chlorophyll a and chlorophyll b contents; suppressed the declines in ascorbic acid and soluble protein; enhanced antioxidant capacity; and reduced oxidative damage in cabbage leaves. Furthermore, 6-BA treatment upregulated the expression of antioxidant genes and the activities of SOD, POD, and CAT, while inhibiting the expression of senescence-related gene (BrSAG12) and chlorophyll catabolic genes (BrPAO, BrPPH, BrSGR1, BrNYC1, BrRCCR). These results suggest that postharvest 6-BA treatment enhances antioxidant capacity, delays leaf senescence, and inhibits chlorophyll degradation, thereby maintaining the quality of Chinese flowering cabbage during storage. The findings of this study provide a candidate method for preserving Chinese flowering cabbage after harvest.

Free Radicals Mediated Redox Signaling in Plant Stress Tolerance

Abiotic and biotic stresses negatively affect plant cellular and biological processes, limiting their growth and productivity. Plants respond to these environmental cues and biotrophic attackers by activating intricate metabolic-molecular signaling networks precisely and coordinately. One of the initial signaling networks activated is involved in the generation of reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS). Recent research has exemplified that ROS below the threshold level can stimulate plant survival by modulating redox homeostasis and regulating various genes of the stress defense pathway. In contrast, RNS regulates the stress tolerance potential of crop plants by modulating post-translation modification processes, such as S-nitrosation and tyrosine nitration, improving the stability of protein and DNA and activating the expression of downstream stress-responsive genes. RSS has recently emerged as a new warrior in combating plant stress-induced oxidative damage by modulating various physiological and stress-related processes. Several recent findings have corroborated the existence of intertwined signaling of ROS/RNS/RSS, playing a substantial role in crop stress management. However, the molecular mechanisms underlying their remarkable effect are still unknown. This review comprehensively describes recent ROS/RNS/RSS biology advancements and how they can modulate cell signaling and gene regulation for abiotic stress management in crop plants. Further, the review summarizes the latest information on how these ROS/RNS/RSS signaling interacts with other plant growth regulators and modulates essential plant functions, particularly photosynthesis, cell growth, and apoptosis.

Crosstalk between melatonin and reactive oxygen species in fruits and vegetables post-harvest preservation: An update

Fruits and vegetables contain numerous nutrients, such as vitamins, minerals, phenolic compounds, and dietary fibers. They reduce the incidence of cardiovascular diseases and the risk of certain chronic diseases, and improve the antioxidant and anti-inflammatory capacity. Moreover, melatonin was found in various fruits and vegetables species. Melatonin acts as a multifunctional compound to participate in various physiological processes. In recent years, many advances have been found that melatonin is also appraised as a key modulator on the fruits and vegetables post-harvest preservation. Fruits and vegetables post-harvest usually elicit reactive oxygen species (ROS) generation and accumulation. Excess ROS stimulate cell damage, protein structure destruction, and tissue aging, and thereby reducing their quality. Numerous studies find that exogenous application of melatonin modulates ROS homeostasis by regulating the antioxidant enzymes and non-enzymatic antioxidants systems. Further evidences reveal that melatonin often interacts with hormones and other signaling molecules, such as ROS, nitric oxide (NO), hydrogen sulfide (H₂S), and etc. Among these 'new' molecules, crosstalks of melatonin and ROS, especially the H₂O₂ produced by RBOHs, are provided in fruits and vegetables post-harvest preservation in this review. It will provide reference for complicated integration of both melatonin and ROS as signal molecules in future study.

Comparative transcriptome analyses shed light on the regulation of harvest duration and shelf life in sweet corn

Harvest duration and postharvest shelf life are two of the most important characters for sweet corn. However, the regulatory mechanism remains unclear. We performed a comparative transcriptome analysis of long harvest-duration and shelf-life sweet corn (LHS) and short harvest-duration and shelf-life field corn (SHS) at three stages, i.e. 10 days after pollination (10DAP), 22 days after pollination (22DAP), and 7 days after harvest (7DAH). We have observed the major transcriptome changes accompanying the harvest process in LHS corn. Gene expression pattern analysis and differentially expressed genes (DEGs) functional enrichments suggested an association between ROS metabolism in kernels with harvest duration and postharvest shelf life. The genes encoding cytochrome P450, peroxidase, peroxiredoxin, glutathione peroxidase, and glutathione S-transferase were upregulated specifically in LHS kernels during and after harvest compared to SHS kernels. These novel findings reveal a new regulatory mechanism of corn post-harvest shelf life and should be useful for extending harvest duration and shelf life for sweet corn.

Fucoidan treatment alleviates chilling injury in cucumber by regulating ROS homeostasis and energy metabolism

INTRODUCTION

Chilling injury is a major hindrance to cucumber fruit quality during cold storage.

METHODS AND RESULTS

In this study, we evaluated the effects of fucoidan on fruit quality, reactive oxygen species homeostasis, and energy metabolism in cucumbers during cold storage. The results showed that, compared with the control cucumber fruit, fucoidan-treated cucumber fruit exhibited a lower chilling injury index and less weight loss, as well as reduced electrolyte leakage and malondialdehyde content. The most pronounced effects were observed following treatment with fucoidan at 15 g/L, which resulted in increased 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radical scavenging rates and reduced superoxide anion production rate and hydrogen peroxide content. The expression and activity levels of peroxidase, catalase, and superoxide dismutase were enhanced by fucoidan treatment. Further, fucoidan treatment maintained high levels of ascorbic acid and glutathione, and high ratios of ascorbic acid/dehydroascorbate and glutathione/oxidized glutathione. Moreover, fucoidan treatment increased the activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase and their gene expression. Fucoidan treatment significantly delayed the decrease in ATP and ADP, while preventing an increase in AMP content. Finally, fucoidan treatment delayed the decrease of energy charge and the activities and gene expression of H⁺-ATPase, Ca²⁺-ATPase, cytochrome c oxidase, and succinate dehydrogenase in cucumber fruits.

CONCLUSION

Altogether, our findings indicate that fucoidan can effectively enhance antioxidant capacity and maintain energy metabolism, thereby improving cucumber cold resistance during cold storage.

Melatonin Preserves the Postharvest Quality of Cut Roses through Enhancing the Antioxidant System

The vase life of cut rose is relatively short, therefore; preserving its postharvest quality via eco-friendly approaches is of particular economic importance. From the previous literature, despite melatonin (MT) plays diverse important roles in the postharvest quality maintenance, its impact on preserving the postharvest quality of cut flowers is really scarce. This research therefore was undertaken to find out the possibility of exogenous MT as an eco-friendly preservative to extend the vase life of cut roses. The flowering stems of Rosa hybrida cv. 'First Red' were pulsed in MT solutions at 0, 0.1, 0.2 and 0.3 mM for 30 min and then transferred to distilled water for evaluation. The vase life was significantly prolonged and relative water content was considerably maintained due to MT application compared to the control, more so with 0.2 mM concentration which nearly doubled the vase life (1.9-fold) higher than the control. SEM investigation showed that MT treatment reduced the stomatal aperture in lower epidermis which was widely opened in control flowers. MT treatment significantly increased the phenol content, glutathione (GSH) content and CAT, APX and GR enzyme activities compared to untreated flowers. Additionally, the radical scavenging capacity in MT-treated flowers was considerably higher than that of control and therefore MT treatment reduced H₂O₂ production and lipid peroxidation, which altogether reflected in membrane stability maintenance.

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

Melatonin (N-acetyl-5-methoxytryptamine) is an indole molecule widely found in animals and plants. It is well known that melatonin improves 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, an increasing number of 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. Here, we review the effects of melatonin on plant vegetative growth and reproductive development, and systematically summarize its molecular regulatory network. Moreover, the effective concentrations of exogenously applied melatonin in different crops or at different growth stages of the same crop are analysed. In addition, we compare endogenous phytomelatonin concentrations in various crops and different organs, and evaluate a 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.

Exogenous Application of Melatonin to Green Horn Pepper Fruit Reduces Chilling Injury during Postharvest Cold Storage by Regulating Enzymatic Activities in the Antioxidant System

Chilling injury (CI) caused by exposure to low temperatures is a serious problem in the postharvest cold storage of pepper fruit. Melatonin (MT) has been reported to minimize CI in several plants. To evaluate the effectiveness of MT to minimize CI in green horn pepper and the possible mechanism involved, freshly picked green horn peppers were treated with MT solution at 100 μmol L−1 or water and then stored at 4 °C for 25 d. Results showed that MT treatment reduced CI in green horn pepper fruit, as evidenced by lower CI rate and CI index. MT treatment maintained lower postharvest metabolism rate and higher fruit quality of green horn peppers, as shown by reduced weight loss and respiratory rate, maintened fruit firmness and higher contents of chlorophyll, total phenols, flavonoids, total soluble solids and ATP. Additionally, the contents of hydrogen peroxide, superoxide radical, and malondialdehyde were kept low in the MT-treated fruit, and the activities of the enzymes peroxidase, superoxide dismutase, and catalase were significantly elevated. Similarly, the ascorbate–glutathione cycle was enhanced by elevating the activities of ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase, to increase the regeneration of ascorbic acid and glutathione. Our results show that MT treatment protected green horn pepper fruit from CI and maintained high fruit quality during cold storage by triggering the antioxidant system

Physiological and Comparative Transcriptome Analysis Reveals the Mechanism by Which Exogenous 24-Epibrassinolide Application Enhances Drought Resistance in Potato (Solanum tuberosum L.)

Drought stress is a key factor limiting the growth and tuber yield of potatoes (Solanum tuberosum L.). Brassinosteroids (BRs) have been shown to alleviate drought stress in several plant species; however, little is known about the physiological and molecular mechanisms by which BRs enhance drought resistance in potatoes. Here, we characterized changes in the physiology and transcriptome of the tetraploid potato variety ‘Xuanshu-2′ in response to drought stress after 24-epibrassinolide (EBR) pretreatment. The abscisic acid (ABA) content, photosynthetic capacity, and the activities of antioxidant enzymes were increased; the intercellular CO2 concentration, relative conductivity, reactive oxygen species, malondialdehyde, proline, and soluble sugar content were decreased after EBR pretreatment compared with plants under drought stress. Transcriptome analysis revealed 1330 differently expressed genes (DEGs) involved in the response to drought stress after EBR pretreatment. DEGs were enriched in plant hormone signal transduction, starch and sucrose metabolism, circadian rhythm, flavonoid biosynthesis, and carotenoid biosynthesis. DEGs associated with the BR signaling and biosynthesis pathways, as well as ABA metabolic pathways were identified. Our findings provide new insights into the mechanisms by which BRs enhance the drought resistance of potatoes.

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.

Benzoic Acid, Chlorine Dioxide, and 1-Methylcyclopropene Induce Flavonoid Metabolic Shifts in Postharvest Flowering Chinese Cabbage Revealed by High-Dimensional Analytical Data

Flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) is one of the most popular vegetables in China. However, the loss of the functional ingredients in postharvest flowering Chinese cabbage during storage is still serious, owing to the unclear causes of the metabolic shifts. Herein, benzoic acid, chlorine dioxide, and 1-methylcyclopropene (1-MCP) could maintain the quality of postharvest flowering Chinese cabbage, and 1-MCP showed the best effect. Furthermore, transcript-metabolite profiling of the treatments revealed a transcript-metabolite correlation network of the flavonoid biosynthesis pathways with a range of 3 to 3662 differentially expressed genes (DEGs) and a range of 23 to 37 differentially accumulated metabolites (DAMs). Surprisingly, 1-MCP had the best effect on shelf life among the treatments, although chlorine dioxide could stimulate the expression of four critical differential genes (Bra007142, Bra008792, Bra009358, and Bra027457) involved in delaying flavonoid degradation (hesperetin, chalcone, rutin, baicalein). As a result, our findings will help to improve our understanding of the regulation of flavonoid production in relation to the quality of postharvest flowering Chinese cabbage during storage.

Melatonin Positively Regulates Both Dark- and Age-Induced Leaf Senescence by Reducing ROS Accumulation and Modulating Abscisic Acid and Auxin Biosynthesis in Cucumber Plants

Melatonin (MT), as a signaling molecule, plays a vital role in regulating leaf senescence in plants. This study aimed to verify the antioxidant roles of MT in delaying dark- or age-induced leaf senescence of cucumber plants. The results showed that endogenous MT responds to darkness and overexpression of CsASMT, the key gene of MT synthesis, and delays leaf senescence stimulated by darkness, as manifested by significantly lower malonaldehyde (MDA) and reactive oxygen species (ROS) contents as well as higher activities and gene expression of antioxidant enzymes compared to the control. Moreover, MT suppressed both age- or dark-induced leaf senescence of cucumber, as evidenced by a decrease in senescence-related gene SAG20 and cell-death-related gene PDCD expression and ROS content and an increase in antioxidant capacity and chlorophyll biosynthesis compared with the H2O-treated seedlings. Meanwhile, the suppression of age-induced leaf senescence by melatonin was also reflected by the reduction in abscisic acid (ABA) biosynthesis and signaling pathways as well as the promotion of auxin (IAA) biosynthesis and signaling pathways in cucumber plants in the solar greenhouse. Combining the results of the two separate experiments, we demonstrated that MT acts as a powerful antioxidant to alleviate leaf senescence by activating the antioxidant system and IAA synthesis and signaling while inhibiting ABA synthesis and signaling in cucumber plants.

Influence of sequential exogenous pretreatment and contact ultrasound-assisted air drying on the metabolic pathway of glucoraphanin in broccoli florets

In this investigation, the combinations of exogenous pretreatment (melatonin or vitamin C) and contact ultrasound-assisted air drying were utilized to dry broccoli florets. To understand the influences of the studied dehydration methods on the conversion of glucoraphanin to bioactive sulforaphane in broccoli, various components (like glucoraphanin, sulforaphane, myrosinase, etc.) and factors (temperature and moisture) involved in the metabolism pathway were analyzed. The results showed that compared with direct air drying, the sequential exogenous pretreatment and contact ultrasound drying shortened the drying time by 19.0-22.7%. Meanwhile, contact sonication could promote the degradation of glucoraphanin. Both melatonin pretreatment and vitamin C pretreatment showed protective effects on the sulforaphane content and myrosinase activity during the subsequent drying process. At the end of drying, the sulforaphane content in samples dehydrated by the sequential melatonin (or vitamin C) pretreatment and ultrasound-intensified drying was 14.4% (or 26.5%) higher than only air-dried samples. The correlation analysis revealed that the exogenous pretreatment or ultrasound could affect the enzymatic degradation of glucoraphanin and the generation of sulforaphane through weakening the connections of sulforaphane-myrosinase, sulforaphane-VC, and VC-myrosinase. Overall, the reported results can enrich the biochemistry knowledge about the transformation of glucoraphanin to sulforaphane in cruciferous vegetables during drying, and the combined VC/melatonin pretreatment and ultrasound drying is conducive to protect bioactive sulforaphane in dehydrated broccoli.

Melatonin in Brassicaceae: Role in Postharvest and Interesting Phytochemicals

Brassicaceae plants are of great interest for human consumption due to their wide variety and nutritional qualities. Of the more than 4000 species that make up this family, about a hundred varieties of 6-8 genera are extensively cultivated. One of the most interesting aspects is its high content of glucosinolates, which are plant secondary metabolites with widely demonstrated anti-oncogenic properties that make them healthy. The most relevant Brassicaceae studies related to food and melatonin are examined in this paper. The role of melatonin as a beneficial agent in seedling grown mainly in cabbage and rapeseed and in the postharvest preservation of broccoli is especially analyzed. The beneficial effect of melatonin treatments on the organoleptic properties of these commonly consumed vegetables can be of great interest in the agri-food industry. Melatonin application extends the shelf life of fresh-cut broccoli while maintaining optimal visual and nutritional parameters. In addition, an integrated model indicating the role of melatonin on the organoleptic properties, the biosynthesis of glucosinolates and the regulatory action of these health-relevant compounds with anti-oncogenic activity is presented.

Specificity of H2O2 signaling in leaf senescence: is the ratio of H2O2 contents in different cellular compartments sensed in Arabidopsis plants?

Leaf senescence is an integral part of plant development and is driven by endogenous cues such as leaf or plant age. Developmental senescence aims to maximize the usage of carbon, nitrogen and mineral resources for growth and/or for the sake of the next generation. This requires efficient reallocation of the resources out of the senescing tissue into developing parts of the plant such as new leaves, fruits and seeds. However, premature senescence can be induced by severe and long-lasting biotic or abiotic stress conditions. It serves as an exit strategy to guarantee offspring in an unfavorable environment but is often combined with a trade-off in seed number and quality. In order to coordinate the very complex process of developmental senescence with environmental signals, highly organized networks and regulatory cues have to be in place. Reactive oxygen species, especially hydrogen peroxide (H2O2), are involved in senescence as well as in stress signaling. Here, we want to summarize the role of H2O2 as a signaling molecule in leaf senescence and shed more light on how specificity in signaling might be achieved. Altered hydrogen peroxide contents in specific compartments revealed a differential impact of H2O2 produced in different compartments. Arabidopsis lines with lower H2O2 levels in chloroplasts and cytoplasm point to the possibility that not the actual contents but the ratio between the two different compartments is sensed by the plant cells.