The role of glucose-6-phosphate dehydrogenase in reactive oxygen species metabolism in apple exocarp induced by acibenzolar-S-methyl

Bacillus amyloliquefaciens LY-1 culture broth enhances the storage properties of fresh litchi through acting on ROS metabolism

The impacts of Bacillus amyloliquefaciens LY-1 culture broth (BLCB) on the fruit storage properties and reactive oxygen species (ROS) metabolism of postharvest 'Wuye' litchis were studied. In comparation with control fruit, BLCB-treated litchis showed a lower fruit disease index, a higher rate of commercially acceptable fruit, higher amounts of pericarp pigments (total phenolics, anthocyanin, carotenoid, chlorophyll and flavonoid), higher chromaticity C, a*, b* and L* values but lower hue angle h° of fruit surface. Additionally, BLCB-treated litchis exhibited lower malonaldehyde (MDA) accumulation and superoxide anion radical (O2.-) production rate, higher APX, CAT and SOD activities, higher GSH and AsA amounts, higher reducing power, and higher ability of scavenging DPPH radical. Furthermore, the pericarp browning index and fruit disease index were positively correlated with O2.- production rate. These findings suggested that BLCB treatment increased the storability of postharvest litchi fruit through enhancing scavenging capacity of ROS and inhibiting overaccumulation of ROS.

Mechanism of plasma-activated water on the regulation of storage quality of fresh-cut carrots and activation of its antioxidant defence system

This study investigated the impact of plasma-activated water (PAW) on the storage quality of fresh-cut carrots (FCC). The findings revealed that PAW treatment, particularly the 3-min immersion method, led to a substantial enhancement in the quality of the stored carrots. Specifically, the PAW-3 min group decreased by 20.08 %, 55.34 %, and 52.66 % in L*, a*, and b* values respectively (comparing storage days 7 d to 0 d). Notably, the PAW-3 min group demonstrated the least decrease in brightness and exhibited superior yellow color retention compared to the other treatment groups. Concerning weight, a 4.86 % decrease was observed in the PW group from day 0 to day 7 of storage, while the PAW-5 min group exhibited a 2.06 % decrease, suggesting that prolonging the PAW treatment time enhances the retention of sample weight. With regard to hardness, the PAW-3 min group exhibited the least weight loss of 4.62 % among all the treatment groups. The H2O2, a reactive oxygen content, increased from 6.22 ± 0.26 μmol/g to 10.55 ± 0.13 μmol/g with the extension of PAW treatment time, achieving an enzyme inhibition of browning, thus controlling water evaporation and microbial activity. The study demonstrated that PAW ensured uniform water distribution, activated the antioxidant system, and promoted phenolic compound synthesis. It was determined that extended treatment times resulted in cellular damage, and that shorter PAW treatment times (1 to 3 min) were optimal. The findings of this study suggest that this non-chemical method is effective in extending the shelf-life of FCC.

Inducing resistance of postharvest fruits and vegetables through acibenzolar-S-methyl application: A review of implications and mechanisms

Significant losses of vegetables and fruits occur at multiple stages, including harvest, sorting, storage, and transportation, primarily due to mechanical damage, pathogen invasion, and the natural process of senescence. To mitigate postharvest decay and maintain superior quality of produce, conventional techniques such as low temperature storage and synthetic fungicide treatment are widely employed. Acibenzolar-S-methyl (ASM), an effective plant resistance inducers, has demonstrated its efficacy in protecting against a diverse range of fungal and bacterial pathogens. The present review primarily concludes that exogenous application of ASM effectively maintains postharvest quality, delays senescence, and controls decay of postharvest fruits and vegetables through the following mechanisms: (1) modulation of signal transduction pathways including Ca2+ signal, H2O2, and mitogen-activated protein kinase cascades; (2) regulation of reactive oxygen species metabolism; (3) accumulation of pathogenesis-related proteins; (4) activation of the phenylpropanoid pathway; (5) regulation of energy metabolism; and (6) mediation of fatty acid metabolism. Taken together, ASM is a potent activator that enhances resistance against a wide range of postharvest pathogens and effectively preserves the storage quality of horticultural products.

Targeting novel regulated cell death: disulfidptosis in cancer immunotherapy with immune checkpoint inhibitors

The battle against cancer has evolved over centuries, from the early stages of surgical resection to contemporary treatments including chemotherapy, radiation, targeted therapies, and immunotherapies. Despite significant advances in cancer treatment over recent decades, these therapies remain limited by various challenges. Immune checkpoint inhibitors (ICIs), a cornerstone of tumor immunotherapy, have emerged as one of the most promising advancements in cancer treatment. Although ICIs, such as CTLA-4 and PD-1/PD-L1 inhibitors, have demonstrated clinical efficacy, their therapeutic impact remains suboptimal due to patient-specific variability and tumor immune resistance. Cell death is a fundamental process for maintaining tissue homeostasis and function. Recent research highlights that the combination of induced regulatory cell death (RCD) and ICIs can substantially enhance anti-tumor responses across multiple cancer types. In cells exhibiting high levels of recombinant solute carrier family 7 member 11 (SLC7A11) protein, glucose deprivation triggers a programmed cell death (PCD) pathway characterized by disulfide bond formation and REDOX (reduction-oxidation) reactions, termed "disulfidptosis." Studies suggest that disulfidptosis plays a critical role in the therapeutic efficacy of SLC7A11high cancers. Therefore, to investigate the potential synergy between disulfidptosis and ICIs, this study will explore the mechanisms of both processes in tumor progression, with the goal of enhancing the anti-tumor immune response of ICIs by targeting the intracellular disulfidptosis pathway.

New insights into the mechanisms of plant isotope fractionation from combined analysis of intramolecular 13C and deuterium abundances in Pinus nigra tree-ring glucose

Understanding isotope fractionation mechanisms is fundamental for analyses of plant ecophysiology and paleoclimate based on tree-ring isotope data. To gain new insights into isotope fractionation, we analysed intramolecular 13C discrimination in tree-ring glucose (Δi', i = C-1 to C-6) and metabolic deuterium fractionation at H1 and H2 (εmet) combinedly. This dual-isotope approach was used for isotope-signal deconvolution. We found evidence for metabolic processes affecting Δ1' and Δ3', which respond to air vapour pressure deficit (VPD), and processes affecting Δ1', Δ2', and εmet, which respond to precipitation but not VPD. These relationships exhibit change points dividing a period of homeostasis (1961-1980) from a period of metabolic adjustment (1983-1995). Homeostasis may result from sufficient groundwater availability. Additionally, we found Δ5' and Δ6' relationships with radiation and temperature, which are temporally stable and consistent with previously proposed isotope fractionation mechanisms. Based on the multitude of climate covariables, intramolecular carbon isotope analysis has a remarkable potential for climate reconstruction. While isotope fractionation beyond leaves is currently considered to be constant, we propose significant parts of the carbon and hydrogen isotope variation in tree-ring glucose originate in stems (precipitation-dependent signals). As basis for follow-up studies, we propose mechanisms introducing Δ1', Δ2', Δ3', and εmet variability.

Assessing the effects of dual functional V-type cornstarch films added with kiwifruit peel extracts on preservation of fresh-cut kiwifruits: A metabolomics study

Fresh-cut fruit, with nutrition and convenience, has a broad market demand. However, its shelf life is shortened due to its tissue damage. Therefore, the development of cost-effective and eco-friendly multifunctional packaging materials to extend the shelf life of fresh-cut fruits is urgently needed. A cornstarch-based film (CS film) was successfully prepared using V-type corn starch as an ethylene scavenger and kiwifruit peel extract (KPE) as an antioxidant. The film containing 4.00 % (v/v) KPE had a DPPH radical scavenging capability of 52.1 % ± 2.4 % and ABTS radical scavenging capability of 70.4 % ± 4.4 %. The amount of ethylene harvested was 17.27 cm3 g-1. In addition, the malondialdehyde content of fresh-cut kiwifruits covered by CS film decreased by 42.82 % compared with PE film after 72 h, and the hardness increased 71.20 %. And the CS film could regulate ethylene and oxygen concentration, and extending the fresh life of kiwifruit from 3 days to 15 days. Metabolomics and transcriptomic analyses revealed that the CS film regulated ethylene self-promotion and the balance of reactive oxygen species metabolism. As a result, these reduced sugar synthesis and metabolism, which helped to maintain the freshness of fresh-cut kiwifruit. These findings can serve as a reference for developing techniques to preserve the packaging of fresh-cut fruits.

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.

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.

Effects of Ultra-High-Pressure Treatment on Chemical Composition and Biological Activities of Free, Esterified and Bound Phenolics from Phyllanthus emblica L. Fruits

Phyllanthus emblica L. fruits (PEFs) were processed by ultra-pressure (UHP) treatment and then extracted by the ultrasonic-assisted extraction method. The influence of UHP on the phenolic composition, enzyme inhibitory activity and antioxidant activity of the free, esterified, and bound phenolic fractions from PEFs were compared. UHP pretreatment of PEFs significantly increased the total phenolic and flavonoid contents (p < 0.05). A total of 24 chemical compositions were characterized in normal and UHP-treated PEFs by UHPLC-ESI-HRMS/MS. Compared with normal PEFs, these three different phenolic fractions had stronger antioxidant activities and inhibitory effects on the intracellular reactive oxygen species (ROS) production in H2O2-induced HepG2 cells (p < 0.05). The ROS inhibition might be due to an up-regulation of the expressions of superoxide dismutase (SOD) and glutathione (GSH) activities. In addition, these three different phenolic fractions also significantly inhibited the activities of metabolic enzymes, including α-glucosidase, α-amylase and pancreatic lipase. This work may provide some insights into the potential economics and applications of PEFs in food and nutraceutical industries.

Screening of core microorganisms in healthy and diseased peaches and effect evaluation of biocontrol bacteria (Burkholderia sp.)

Biological antagonists serve as the most important green alternatives to chemical fungicides, a class of microorganism that inhibits the growth of pathogenic fungi to reduce fruit incidence. In this paper, healthy and diseased peach fruit was selected for amplicon sequencing of the epiphytic microbiota on their surface to obtain a comprehensive understanding. Community structure, diversity and LefSe analysis were performed to screen Acetobacter, Muribaculaceae and Burkholderia as the core bacteria, Mycosphaerella, Penicillium and Alternaria as the core fungi, they showed significant differences and were highly enriched. Two strains fungi (Penicillium K3 and N1) and one strain antagonistic bacteria (Burkholderia J2) were isolated. The in intro test results indicated the bacterial suspension, fermentation broth and volatile organic compounds of antagonistic bacteria J2 were able to significantly inhibit pathogen growth. In vivo experiments, peach was stored at 28 °C for 6 days after different treatments, and samples were taken every day. It was found that Burkholderia J2 enhanced peach resistance by increasing the activities of antioxidant-related enzymes such as SOD, POD, PAL, PPO, GR, MDHAR, and DHAR. The results improved that Burkholderia J2 has great biocontrol potential and could be used as a candidate strain for green control of blue mold.

Glucose-6-Phosphate Dehydrogenases: The Hidden Players of Plant Physiology

Glucose-6-phosphate dehydrogenase (G6PDH) catalyzes a metabolic hub between glycolysis and the pentose phosphate pathway (PPP), which is the oxidation of glucose-6-phosphate (G6P) to 6-phosphogluconolactone concomitantly with the production of nicotinamide adenine dinucleotide phosphate (NADPH), a reducing power. It is considered to be the rate-limiting step that governs carbon flow through the oxidative pentose phosphate pathway (OPPP). The OPPP is the main supplier of reductant (NADPH) for several "reducing" biosynthetic reactions. Although it is involved in multiple physiological processes, current knowledge on its exact role and regulation is still piecemeal. The present review provides a concise and comprehensive picture of the diversity of plant G6PDHs and their role in seed germination, nitrogen assimilation, plant branching, and plant response to abiotic stress. This work will help define future research directions to improve our knowledge of G6PDHs in plant physiology and to integrate this hidden player in plant performance.

Benzothiadiazole enhances ascorbate recycling and polyphenols accumulation in blueberry in a cultivar-dependent manner

Benzothiadiazole (BTH) is a functional analogue of salicylic acid able to induce systemic acquired resistance in many horticultural crops. The aim of the work was to investigate how BTH may affect i) fruit quality, ii) ascorbic acid (AsA) oxidation and recycling metabolism and iii) phenolic compounds accumulation, during development and ripening of berries from the two selected cultivars. Blueberry (Vaccinium corymbosum L.) plants (cv 'Brigitta' and 'Duke') were treated with 0.118 mM BTH every two weeks during ripening, then all fruits of each plant were harvested and divided in four developmental stages. Results indicated that BTH had no marked effects on fruit quality parameters. During the first developmental stage, BTH negatively affected dry matter in both cv, while soluble solids and AsA content were affected in 'Duke'. In fully ripe berries, BTH reduced dry matter in 'Duke' and enhanced soluble solids content in 'Brigitta', while diminishing titratable acidity. AsA content was positively affected by BTH in 'Duke', but not in 'Brigitta'. The effect of BTH on the enzymes involved in AsA recycling was recorded in berries at the third (fruit more than half pigmented) and fourth developmental stages. After treatment, in both cv ascorbate peroxidase (APX) activity increased in fully ripe berries, while monodehydroascorbate reductase (MDHAR) activity was stimulated at the third ripening stage. Conversely, the activities of dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were enhanced only in 'Brigitta' and in 'Duke', respectively. BTH stimulated total polyphenols, flavonoid and anthocyanin accumulation in 'Brigitta' and in 'Duke' at the third and fourth ripening stages. In fully ripe berries, BTH enhanced the accumulation of delphinidins, cyanidins, petunidins and peonidins in 'Brigitta', while in 'Duke' it increased all classes of anthocyanidins, including malvidin. On the contrary, the relative proportion of the individual anthocyanins was only slightly affected by BTH treatment, mainly regarding delphinidin and malvidin at the third and fourth stage of ripening of 'Duke' and 'Brigitta', respectively. These results show that preharvest BTH application can positively impact on fruit bioactive compounds levels, affecting AsA recycling and content and increasing polyphenols accumulation in fruit, but partly depending on cv and ripening stage.

Genome-Wide Investigation of G6PDH Gene in Strawberry: Evolution and Expression Analysis during Development and Stress

As one of the key enzymes in the pentose phosphate pathway (PPP), glucose-6-phosphate dehydrogenase (G6PDH) provides NADPH and plays an important role in plant development and stress responses. However, little information was available about the G6PDH genes in strawberry (Fragaria × ananassa). The recent release of the whole-genome sequence of strawberry allowed us to perform a genome-wide investigation into the organization and expression profiling of strawberry G6PDH genes. In the present study, 19 strawberry G6PDH genes (FaG6PDHs) were identified from the strawberry genome database. They were designated as FaG6PDH1 to FaG6PDH19, respectively, according to the conserved domain of each subfamily and multiple sequence alignment with Arabidopsis. According to their structural and phylogenetic features, the 19 FaG6PDHs were further classified into five types: Cy, P1, P1.1, P2 and PO. The number and location of exons and introns are similar, suggesting that genes of the same type are very similar and are alleles. A cis-element analysis inferred that FaG6PDHs possessed at least one stress-responsive cis-acting element. Expression profiles derived from transcriptome data analysis exhibited distinct expression patterns of FaG6PDHs genes in different developmental stages. Real-time quantitative PCR was used to detect the expression level of five types FaG6PDHs genes and demonstrated that the genes were expressed and responded to multiple abiotic stress and hormonal treatments.

A New Strategy for Microbial Taxonomic Identification through Micro-Biosynthetic Gold Nanoparticles and Machine Learning

Microorganisms can serve as biological factories for the synthesis of inorganic nanomaterials that can become useful as nanocatalysts, energy-harvesting-storage components, antibacterial agents, and biomedical materials. Herein, the development of biosynthesis of inorganic nanomaterials into a simple, stable, and accurate strategy for distinguishing microorganisms from multiple classification levels (i.e., kingdom, order, genus, and species) without gene amplification, biochemical testing, or target recognition is reported. Gold nanoparticles (AuNPs) biosynthesized by different microorganisms differ in color of the solution, and their features can be characterized, including the particle size, the surface plasmon resonance (SPR) spectrum, and the surface potential. The inter-relation between the features of micro-biosynthetic AuNPs and the classification of microorganisms are exploited at different levels through machine learning to establish a taxonomic model. This model agrees well with traditional classification methods that offers a new strategy for microbial taxonomic identification. The underlying mechanism of this strategy is related to the biomolecules produced by different microorganisms including glucose, glutathione, and nicotinamide adenine dinucleotide phosphate-dependent reductase that regulate the features of micro-biosynthetic AuNPs. This work broadens the application of biosynthesis of inorganic materials through micro-biosynthetic AuNPs and machine learning, which holds great promise as a tool for biomedical research.

In situ electrochemical monitoring of ROS influence in the dynamics of ascorbic acid and polyphenolic compounds in apple fruits

In situ recording of the voltammetric profile of different apple (Malus domestica Borkh.) varieties (Golden, Granny Smith, Reineta, Red delicious, Fuji, and Braeburn) without and with ROS generation is reported. The voltammetric response associated to the oxidation of ascorbic acid (AA) and polyphenolic (PPs) components was recorded. The obtained voltammetric profiles were satisfactorily fitted to a theoretical kinetic model consisting of the competing, dual activation pathways of AA and PPs followed by a degradative step. The rate constants for these processes were calculated from voltammetric data revealing significant differences between varieties. The activation pathways as well as the influence of electrochemical ROS generation on it were variety-sensitive while the degradative step was almost variety insensitive and lightly sensitive to ROS generation.

Benzothiazole Treatment Regulates the Reactive Oxygen Species Metabolism and Phenylpropanoid Pathway of Rosa roxburghii Fruit to Delay Senescence During Low Temperature Storage

Rosa roxburghii fruit were used as research objects to study the effects of different concentrations of benzothiazole (BTH) treatment on quality parameters, reactive oxygen species (ROS) metabolism, and the phenylpropanoid pathway during storage at 4°C for 14days. Results showed that BTH effectively delayed senescence with lower decay incidence, weight loss, and lipid peroxidation level and maintained the quality with higher contents of total soluble solid (TSS) content, titratable acidity (TA) in R. roxburghii fruit. Moreover, BTH increased hydrogen peroxide (H₂O₂) content, superoxide anion (O₂ ^•-) production rate, and the activities and expression of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione (GSH) reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and peroxidase (POD), and the contents of GSH and ascorbic acid (AsA), but reduced the oxidized GSH (GSSG) content. In addition, the activities and gene expression of phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate-CoA ligase (4CL) and the concentrations of flavonoids, total phenols, and lignin were significantly elevated by BTH. These findings imply that BTH can delay senescence and maintain the quality of R. roxburghii fruit by modulating ROS metabolism and the phenylpropanoid pathway under low-temperature conditions.

Maintenance of Postharvest Quality and Reactive Oxygen Species Homeostasis of Pitaya Fruit by Essential Oil p-Anisaldehyde Treatment

The performance of p-Anisaldehyde (PAA) for preserving pitaya fruit quality and the underpinning regulatory mechanism were investigated in this study. Results showed that PAA treatment significantly reduced fruit decay, weight loss and loss of firmness, and maintained higher content of total soluble solids, betacyanins, betaxanthins, total phenolics and flavonoids in postharvest pitaya fruits. Compared with control, the increase in hydrogen peroxide (H₂O₂) content and superoxide anion (O₂^•−) production was inhibited in fruit treated with PAA. Meanwhile, PAA significantly improved the activity of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). Moreover, PAA-treated pitaya fruit maintained higher ascorbic acid (AsA) and reduced-glutathione (GSH) content but lower dehydroascorbate (DHA) and oxidized glutathione (GSSG) content, thus sustaining higher ratio of AsA/DHA and GSH/GSSG. In addition, activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydrogenation ascorbic acid reductase (DHAR), as well as the expression of HpSOD, HpPOD, HpCAT, HpAPX, HpGR, HpDHAR and HpMDHAR, were enhanced after PAA treatment. The findings suggest that postharvest application of PAA may be a reliable method to control postharvest decay and preserve quality of harvested pitaya fruit by enhancing the antioxidant potential of the AsA-GSH cycle and activating an antioxidant defense system to alleviate reactive oxygen species (ROS) accumulation.

Acibenzolar-S-Methyl and Resistance Quantitative Trait Loci Complement Each Other to Control Apple Scab and Fire Blight

Diversifying disease control methods is a key strategy to sustainably reduce pesticides. Plant genetic resistance has long been used to create resistant varieties. Plant resistance inducers (PRI) are also considered to promote crop health, but their effectiveness is partial and can vary according to the environment and the plant genotype. We investigated the putative interaction between intrinsic (genetic) and PRI-induced resistance in apple when affected by scab and fire blight diseases. A large F1 mapping population was challenged by each disease after a pre-treatment with acibenzolar-S-methyl (ASM) and compared with the water control. Apple scab and fire blight resistance quantitative trait loci (QTLs) were detected in both conditions and compared. ASM exhibited a strong effectiveness in reducing both diseases. When combined, QTL-controlled and ASM-induced resistance acted complementarily to reduce the symptoms from 85 to 100%, depending on the disease. In our conditions, resistance QTLs were only slightly or rarely affected by ASM treatment, despite their probable implication in various stages of the resistance buildup. Implications of these results are discussed considering already known results, the underlying mechanisms, cross protection of both types of resistance against pathogen adaptation, and practical application in orchard conditions.

Inhibition of downy blight and enhancement of resistance in litchi fruit by postharvest application of melatonin

Litchis are tasty fruit with economic importance. However, the extreme susceptibility of harvested litchis to litchi downy blight caused by Peronophythora litchii leads to compromised quality. This study aimed to study the effects of melatonin on postharvest resistance to P. litchii in 'Feizixiao' litchis. Results showed that melatonin restricted lesion expansion in litchis after P. litchi inoculation. Melatonin enhanced the activities of phenylalanine ammonia-lyase, cinnamate-4-hydroxylase and 4-hydroxycinnamate CoA ligase while promoting the accumulations of phenolics and flavonoids. Nicotinamide adenine dinucleotide phosphate content and glucose-6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase activities were higher in treated fruit than control fruit. Higher energy status along with elevated H⁺-ATPase, Ca²⁺-ATPase, succinate dehydrogenase and cytochrome C oxidase activities were observed in treated fruit. Ultrastructural observation showed reduced damage in mitochondria in treated fruit. The results suggest that melatonin induced resistance in litchis by modulating the phenylpropanoid and pentose phosphate pathways as well as energy metabolism. .

Luteolin-induced activation of the phenylpropanoid metabolic pathway contributes to quality maintenance and disease resistance of sweet cherry

Redox imbalance and fungal infection are major causes for quality deterioration and postharvest decay of fruit. Therefore, it is crucial to activate intrinsic antioxidative capacity and disease responses for fruit quality maintenance. Although plant-derived flavonoids have been reported for health-promoting benefits, their roles in the maintenance of fruit quality remains largely unexplored. Here, we exogenously applied luteolin, a flavonoid substance, and further examined its efficacy in maintaining fruit quality and inhibiting fungal diseases in sweet cherry. The results showed that 100 or 200 mg/L luteolin maintained better organoleptic quality and decreased disease incidence during storage. Biochemical assays revealed that luteolin activated the phenylpropanoid metabolic pathway and improved antioxidative capacity, thereby elevating total anthocyanin and flavonoid contents. Notably, luteolin inhibited mycelial growth of fungal pathogens and reduced patulin yield by Penicillium expansum. Collectively, these results suggest that luteolin is a promising alternative for maintaining better fruit quality and ameliorating disease resistance.

Mitogen-Activated Protein Kinase Cascade and Reactive Oxygen Species Metabolism are Involved in Acibenzolar-S-Methyl-Induced Disease Resistance in Apples

Apple fruits were subjected to dipping treatment to explore the effects of acibenzolar-S-methyl (ASM) and the mitogen-activated protein kinase (MAPK) inhibitor PD98059 on lesion growth in fruits inoculated with Penicillium expansum. We investigated the roles of the MAPK cascade and reactive oxygen species metabolism in disease resistance in apples. ASM treatment inhibited lesion growth; suppressed catalase (CAT) activity; increased H₂O₂ content; reduced glutathione and ascorbic acid contents; and increased glutathione reductase, ascorbate peroxidase, peroxidase, superoxide dismutase, and NADPH oxidase activities. Moreover, ASM upregulated MdSOD, MdPOD, MdGR, MdAPX, MdMAPK4, MdMAPK2, and MdMAPKK1 expressions and downregulated MdCAT and MdMAPK3 expressions. PD98059 + ASM treatment increased CAT activity and MdCAT and MdMAPK3 expressions; inhibited MdSOD, MdPOD, MdGR, MdAPX, MdMAPK4, MdMAPK2, and MdMAPKK1 expressions; reduced superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione reductase activities; and reduced glutathione content in apples. These findings indicate that ASM induces disease resistance in apples by regulating the expressions of key genes involved in reactive oxygen species metabolism and the MAPK cascade.

Postharvest Application of Acibenzolar-S-methyl Delays the Senescence of Pear Fruit by Regulating Reactive Oxygen Species and Fatty Acid Metabolism

This study investigated the changes in enzyme activity and gene expression in reactive oxygen species (ROS) and fatty acid metabolism in Docteur Jules Guyot pears after acibenzolar-S-methyl (ASM) treatment to elucidate the role of ROS and fatty acid metabolism in senescence. The results demonstrated that applying ASM postharvest significantly suppressed H₂O₂ content and enhanced catalase and superoxide dismutase activities in pears. Ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase activities and the reduced glutathione content in pears were also induced by ASM. Postharvest ASM dipping remarkably enhanced PcSOD, PcCAT, PcAPX, and PcDHAR expressions and fatty acid synthetase activity in pears. Postharvest applying ASM significantly decreased malondialdehyde content and lipoxygenase, hydroperoxidelyase, alcohol dehydrogenase, and alcohol acyltransferase activities in pears. ASM distinctly inhibited PcPLD, PcLOX, PcHPL, PcADH, and PcAAT expressions in pears. The findings suggest that postharvest applying ASM could modulate ROS and fatty acid metabolism to delay senescence in pears.