The Antioxidant Defense System of Tomato (Solanum lycopersicum L.) Varieties under Drought Stress and upon Post-Drought Rewatering.

Water shortage induces physiological, biochemical, and molecular alterations in plant leaves that play an essential role in plant adaptive response. The effects of drought and post-drought rewatering on the activity of antioxidant enzymes and levels of H2O2, phenolic compounds, ascorbic acid, and proline were studied in six local tomato (Solanum lycopersicum L.) varieties. The contents of H2O2 and ascorbic acid increased in all drought-exposed tomato plants and then decreased upon rewatering. The level of phenolic compounds also decreased in response to water shortage and then recovered upon rehydration, although the extent of this response was different in different varieties. The activities of ascorbate peroxidase (APX) and guaiacol peroxidase (POX) and the content of proline significantly increased in the drought-stressed plants and then decreased when the plants were rewatered. The activities of 8 constitutive APX isoforms and 2 constitutive POX isoforms varied upon exposure to drought and were observed after rewatering in all studied varieties. The information on the response of tomato plants to drought and subsequent rewatering is of great importance for screening and selection of drought-tolerant varieties, as well as for development of strategies for increasing plant productivity under adverse environmental conditions.

APEX2-Mediated Proximity Protein Labeling in Dictyostelium.

Largely due to its simplicity, while being more like human cells compared to other experimental models, Dictyostelium continues to be of great use to discover basic molecular mechanisms and signaling pathways underlying evolutionarily conserved biological processes. However, the identification of new protein interactions implicated in signaling pathways can be particularly challenging in Dictyostelium due to its extremely fast signaling kinetics coupled with the dynamic nature of signaling protein interactions. Recently, the proximity labeling method using engineered ascorbic acid peroxidase 2 (APEX2) in mammalian cells was shown to allow the detection of weak and/or transient protein interactions and also to obtain spatial and temporal resolution. Here, we describe a protocol for successfully using the APEX2-proximity labeling method in Dictyostelium. Coupled with the identification of the labeled proteins by mass spectrometry, this method expands Dictyostelium's proteomics toolbox and should be widely useful for identifying interacting partners involved in a variety of biological processes in Dictyostelium.

The effect of pre- and post-harvest sodium nitroprusside treatments on the physiological changes of cut Alstroemeria aurea 'Orange Queen' during vase life.

Cut flowers deteriorate rapidly after harvest, lasting mere days. To extend their vase life, various postharvest techniques are employed. Due to limited knowledge about the postharvest physiology of Alstroemeria cut flowers and the specific role of secondary compounds and antioxidant systems in their protection, this study investigated the optimal dosage of sodium nitroprusside (SNP) as a nitric oxide (NO) donor to enhance quality and antioxidant defenses. Preharvest foliar application of SNP at 0, 50, 100, and 200 µM followed by short-term pulsing treatments upon harvest at the same concentrations were applied in a factorial design. Results revealed that a preharvest 100 µM SNP treatment combined with a 50 µM postharvest pulse significantly increased the total amount of phenols (over 20%), antioxidant capacity (more than doubled), and the activity of two antioxidant enzymes (ascorbate peroxidase by over 35% and guaiacol peroxidase by about 20%). Notably, this combination also diminished ion leakage (by about 20%), ultimately extending the vase life by more than 40% compared to untreated plants. Therefore, SNP application at these specific dosages proves effective in bolstering Alstroemeria cut flower quality and vase life through enhanced total phenols and a strengthened antioxidant system.

Unveiling silicon-mediated cadmium tolerance mechanisms in mungbean (Vigna radiata (L.) Wilczek): Integrative insights from gene expression, antioxidant responses, and metabolomics.

Cadmium (Cd), one of the most phytotoxic heavy metals, is a major contributor to yield losses in several crops. Silicon (Si) is recognized for its vital role in mitigating Cd toxicity, however, the specific mechanisms governing this mitigation process are still not fully understood. In the present study, the effect of Si supplementation on mungbean (Vigna radiata (L.) Wilczek) plants grown under Cd stress was investigated to unveil the intricate pathways defining Si derived stress tolerance. Non-invasive leaf imaging technique revealed improved growth, biomass, and photosynthetic efficiency in Si supplemented mungbean plants under Cd stress. Further, physiological and biochemical analysis revealed Si mediated increase in activity of glutathione reductase (GR), ascorbate peroxidase (APX), and catalase (CAT) enzymes involved in reactive oxygen species (ROS) metabolism leading to mitigation of cellular damage and oxidative stress. Untargeted metabolomic analysis using liquid chromatography coupled with mass spectrometry (LC-MS/MS) provided insights into Si mediated changes in metabolites and their respective pathways under Cd stress. Alteration in five different metabolic pathways with major changes in flavanols and flavonoids biosynthesis pathway which is essential for controlling plants antioxidant defense system and oxidative stress management were observed. The information reported here about the effects of Si on photosynthetic efficiency, antioxidant responses, and metabolic changes will be helpful in understanding the Si-mediated resistance to Cd stress in plants.

Comprehensive evaluation of drought tolerance of six Chinese chestnut varieties (clones) based on flavonoids and other physiological indexes.

Flavonoids are crucial secondary metabolites that possess the ability to mitigate UV damage and withstand both biotic and abiotic stresses. Therefore, it is of immense significance to investigate the flavonoid content as a pivotal indicator for a comprehensive assessment of chestnut's drought tolerance. This study aimed to determine the flavonoid content and drought tolerance-related physiological and biochemical indices of six chestnut varieties (clones) grafted trees-Qianxi 42 (QX42), Qinglong 45 (QL45), Yanshanzaofeng (YSZF), Yanzi (YZ), Yanqiu (YQ), and Yanlong (YL)-under natural drought stress. The results were used to comprehensively analyze the drought tolerance ability of these varieties. The study revealed that the ranking of drought tolerance indices in terms of their ability to reflect drought tolerance was as follows: superoxide (oxide) dismutase (SOD) activity, ascorbate peroxidase (APX) activity, flavone content, catalase (CAT) activity, proline (PRO) content, soluble sugar content, peroxidase (POD) activity, betaine content, flavonol content, hydrogen peroxide (H2O2) content, soluble protein content, superoxide ion (OFR) content, superoxide (ion OFR) production rate, malondialdehyde (MDA) content, chlorophyll content. Through principal component analysis, the contents of flavonoids and flavonols can be used as indicators for comprehensive evaluation of drought tolerance of chestnut. The comprehensive evaluation order of drought tolerance of grafted trees of 6 chestnut varieties (Clones) was: QL45 > QX42 > YQ > YZ > YSZF > YL.

The RXLR effector PpE18 of Phytophthora parasitica is a virulence factor and suppresses peroxisome membrane-associated ascorbate peroxidase NbAPX3-1-mediated plant immunity.

Phytophthora parasitica causes diseases on a broad range of host plants. It secretes numerous effectors to suppress plant immunity. However, only a few virulence effectors in P. parasitica have been characterized. Here, we highlight that PpE18, a conserved RXLR effector in P. parasitica, was a virulence factor and suppresses Nicotiana benthamiana immunity. Utilizing luciferase complementation, co-immunoprecipitation, and GST pull-down assays, we determined that PpE18 targeted NbAPX3-1, a peroxisome membrane-associated ascorbate peroxidase with reactive oxygen species (ROS)-scavenging activity and positively regulates plant immunity in N. benthamiana. We show that the ROS-scavenging activity of NbAPX3-1 was critical for its immune function and was hindered by the binding of PpE18. The interaction between PpE18 and NbAPX3-1 resulted in an elevation of ROS levels in the peroxisome. Moreover, we discovered that the ankyrin repeat-containing protein NbANKr2 acted as a positive immune regulator, interacting with both NbAPX3-1 and PpE18. NbANKr2 was required for NbAPX3-1-mediated disease resistance. PpE18 competitively interfered with the interaction between NbAPX3-1 and NbANKr2, thereby weakening plant resistance. Our results reveal an effective counter-defense mechanism by which P. parasitica employed effector PpE18 to suppress host cellular defense, by suppressing biochemical activity and disturbing immune function of NbAPX3-1 during infection.

APEX2-based proximity proteomic analysis identifies candidate interactors for Plasmodium falciparum knob-associated histidine-rich protein in infected erythrocytes.

The interaction of Plasmodium falciparum-infected red blood cells (iRBCs) with the vascular endothelium plays a crucial role in malaria pathology and disease. KAHRP is an exported P. falciparum protein involved in iRBC remodelling, which is essential for the formation of protrusions or "knobs" on the iRBC surface. These knobs and the proteins that are concentrated within them allow the parasites to escape the immune response and host spleen clearance by mediating cytoadherence of the iRBC to the endothelial wall, but this also slows down blood circulation, leading in some cases to severe cerebral and placental complications. In this work, we have applied genetic and biochemical tools to identify proteins that interact with P. falciparum KAHRP using enhanced ascorbate peroxidase 2 (APEX2) proximity-dependent biotinylation and label-free shotgun proteomics. A total of 30 potential KAHRP-interacting candidates were identified, based on the assigned fragmented biotinylated ions. Several identified proteins have been previously reported to be part of the Maurer's clefts and knobs, where KAHRP resides. This study may contribute to a broader understanding of P. falciparum protein trafficking and knob architecture and shows for the first time the feasibility of using APEX2-proximity labelling in iRBCs.

Investigating Epidermal Growth Factor Receptor Trafficking with High-Resolution Enzymatic Protein-Tagging and Transmission Electron Microscopy.

Enzymatic ascorbate peroxidase (APEX) tagging allows for high-resolution, three-dimensional protein distribution analyses in cells and tissues. This chapter describes the application of APEX-tagging to visualize the trafficking of the epidermal growth factor receptor (EGFR) during epidermal growth factor-mediated receptor activation. Here, we describe the preparation of cells, methods to validate the stimulation of the EGFR, and visualization of the APEX-resolved distribution of the EGFR in the transmission electron microscope.

APX2 Is an Ascorbate Peroxidase-Related Protein that Regulates the Levels of Plastocyanin in Chlamydomonas.

The function of ascorbate peroxidase-related (APX-R) proteins, present in all green photosynthetic eukaryotes, remains unclear. This study focuses on APX-R from Chlamydomonas reinhardtii, namely, ascorbate peroxidase 2 (APX2). We showed that apx2 mutants exhibited a faster oxidation of the photosystem I primary electron donor, P700, upon sudden light increase and a slower re-reduction rate compared to the wild type, pointing to a limitation of plastocyanin. Spectroscopic, proteomic and immunoblot analyses confirmed that the phenotype was a result of lower levels of plastocyanin in the apx2 mutants. The redox state of P700 did not differ between wild type and apx2 mutants when the loss of function in plastocyanin was nutritionally complemented by growing apx2 mutants under copper deficiency. In this case, cytochrome c6 functionally replaces plastocyanin, confirming that lower levels of plastocyanin were the primary defect caused by the absence of APX2. Overall, the results presented here shed light on an unexpected regulation of plastocyanin level under copper-replete conditions, induced by APX2 in Chlamydomonas.

Investigation of morpho-physiolgical traits and gene expression in barley under nitrogen deficiency.

Nitrogen (N) is an essential element for plant growth, and its deficiency influences plants at several physiological and gene expression levels. Barley (Hordeum vulgare) is one of the most important food grains from the Poaceae family and one of the most important staple food crops. However, the seed yield is limited by a number of stresses, the most important of which is the insufficient use of N. Thus, there is a need to develop N-use effective cultivars. In this study, comparative physiological and molecular analyses were performed using leaf and root tissues from 10 locally grown barley cultivars. The expression levels of nitrate transporters, HvNRT2 genes, were analyzed in the leaf and root tissues of N-deficient (ND) treatments of barley cultivars after 7 and 14 days following ND treatment as compared to the normal condition. Based on the correlation between the traits, root length (RL) had a positive and highly significant correlation with fresh leaf weight (FLW) and ascorbate peroxidase (APX) concentration in roots, indicating a direct root and leaf relationship with the plant development under ND. From the physiological aspects, ND enhanced carotenoids, chlorophylls a/b (Chla/b), total chlorophyll (TCH), leaf antioxidant enzymes such as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT), and root antioxidant enzymes (APX and POD) in the Sahra cultivar. The expression levels of HvNRT2.1, HvNRT2.2, and HvNRT2.4 genes were up-regulated under ND conditions. For the morphological traits, ND maintained root dry weight among the cultivars, except for Sahra. Among the studied cultivars, Sahra responded well to ND stress, making it a suitable candidate for barely improvement programs. These findings may help to better understand the mechanism of ND tolerance and thus lead to the development of cultivars with improved nitrogen use efficiency (NUE) in barley.

Genome-wide identification and analysis of ascorbate peroxidase (APX) gene family in hemp (Cannabis sativa L.) under various abiotic stresses.

Ascorbate peroxidase (APX) plays a critical role in molecular mechanisms such as plant development and defense against abiotic stresses. As an important economic crop, hemp (Cannabis sativa L.) is vulnerable to adverse environmental conditions, such as drought, cold, salt, and oxidative stress, which lead to a decline in yield and quality. Although APX genes have been characterized in a variety of plants, members of the APX gene family in hemp have not been completely identified. In this study, we (1) identified eight members of the CsAPX gene family in hemp and mapped their locations on the chromosomes using bioinformatics analysis; (2) examined the physicochemical characteristics of the proteins encoded by these CsAPX gene family members; (3) investigated their intraspecific collinearity, gene structure, conserved domains, conserved motifs, and cis-acting elements; (4) constructed a phylogenetic tree and analyzed interspecific collinearity; and (5) ascertained expression differences in leaf tissue subjected to cold, drought, salt, and oxidative stresses using quantitative real-time-PCR (qRT-PCR). Under all four stresses, CsAPX6, CsAPX7, and CsAPX8 consistently exhibited significant upregulation, whereas CsAPX2 displayed notably higher expression levels under drought stress than under the other stresses. Taken together, the results of this study provide basic genomic information on the expression of the APX gene family and pave the way for studying the role of APX genes in abiotic stress.

Ascorbate peroxidase in fruits and modulation of its activity by reactive species.

Ascorbate peroxidase (APX) is one of the enzymes of the ascorbate-glutathione cycle and is the key enzyme that breaks down H2O2 with the aid of ascorbate as an electron source. APX is present in all photosynthetic eukaryotes from algae to higher plants and, at the cellular level, it is localized in all subcellular compartments where H2O2 is generated, including the apoplast, cytosol, plastids, mitochondria, and peroxisomes, either in soluble form or attached to the organelle membranes. APX activity can be modulated by various post-translational modifications including tyrosine nitration, S-nitrosation, persulfidation, and S-sulfenylation. This allows the connection of H2O2 metabolism with other relevant signaling molecules such as NO and H2S, thus building a complex coordination system. In both climacteric and non-climacteric fruits, APX plays a key role during the ripening process and during post-harvest, since it participates in the regulation of both H2O2 and ascorbate levels affecting fruit quality. Currently, the exogenous application of molecules such as NO, H2S, H2O2, and, more recently, melatonin is seen as a new alternative to maintain and extend the shelf life and quality of fruits because they can modulate APX activity as well as other antioxidant systems. Therefore, these molecules are being considered as new biotechnological tools to improve crop quality in the horticultural industry.

Physiological function and regulation of ascorbate peroxidase isoforms.

Ascorbate peroxidase (APX) reduces H2O2 to H2O by utilizing ascorbate as a specific electron donor and constitutes the ascorbate-glutathione cycle in organelles of plants including chloroplasts, cytosol, mitochondria, and peroxisomes. It has been almost 40 years since APX was discovered as an important plant-specific H2O2-scavenging enzyme, during which time many research groups have conducted molecular physiological analyses. It is now clear that APX isoforms function not only just as antioxidant enzymes but also as important factors in intracellular redox regulation through the metabolism of reactive oxygen species. The function of APX isoforms is regulated at multiple steps, from the transcriptional level to post-translational modifications of enzymes, thereby allowing them to respond flexibly to ever-changing environmental factors and physiological phenomena such as cell growth and signal transduction. In this review, we summarize the physiological functions and regulation mechanisms of expression of each APX isoform.

5-Aminolevulinic acid treatment mitigates pesticide stress in bean seedlings by regulating stress-related gene expression and retrotransposon movements.

Overdoses of pesticides lead to a decrease in the yield and quality of plants, such as beans. The unconscious use of deltamethrin, one of the synthetic insecticides, increases the amount of reactive oxygen species (ROS) by causing oxidative stress in plants. In this case, plants tolerate stress by activating the antioxidant defense mechanism and many genes. 5-Aminolevulinic acid (ALA) improves tolerance to stress by acting exogenously in low doses. There are many gene families that are effective in the regulation of this mechanism. In addition, one of the response mechanisms at the molecular level against environmental stressors in plants is retrotransposon movement. In this study, the expression levels of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), and stress-associated protein (SAP) genes were determined by Q-PCR in deltamethrin (0.5 ppm) and various doses (20, 40, and 80 mg/l) of ALA-treated bean seedlings. In addition, one of the response mechanisms at the molecular level against environmental stressors in plants is retrotransposon movement. It was determined that deltamethrin increased the expression of SOD (1.8-fold), GPX (1.4-fold), CAT (2.7-fold), and SAP (2.5-fold) genes, while 20 and 40 mg/l ALA gradually increased the expression of these genes at levels close to control, but 80 mg/l ALA increased the expression of these genes almost to the same level as deltamethrin (2.1-fold, 1.4-fold, 2.6-fold, and 2.6-fold in SOD, GPX, CAT, and SAP genes, respectively). In addition, retrotransposon-microsatellite amplified polymorphism (REMAP) was performed to determine the polymorphism caused by retrotransposon movements. While deltamethrin treatment has caused a decrease in genomic template stability (GTS) (27%), ALA treatments have prevented this decline. At doses of 20, 40, and 80 mg/L of ALA treatments, the GTS ratios were determined to be 96.8%, 74.6%, and 58.7%, respectively. Collectively, these findings demonstrated that ALA has the utility of alleviating pesticide stress effects on beans.

Cold priming on pathogen susceptibility in the Arabidopsis eds1 mutant background requires a functional stromal Ascorbate Peroxidase.

24 h cold exposure (4°C) is sufficient to reduce pathogen susceptibility in Arabidopsis thaliana against the virulent Pseudomonas syringae pv. tomato (Pst) strain even when the infection occurs five days later. This priming effect is independent of the immune regulator Enhanced Disease Susceptibility 1 (EDS1) and can be observed in the immune-compromised eds1-2 null mutant. In contrast, cold priming-reduced Pst susceptibility is strongly impaired in knock-out lines of the stromal and thylakoid ascorbate peroxidases (sAPX/tAPX) highlighting their relevance for abiotic stress-related increased immune resilience. Here, we extended our analysis by generating an eds1 sapx double mutant. eds1 sapx showed eds1-like resistance and susceptibility phenotypes against Pst strains containing the effectors avrRPM1 and avrRPS4. In comparison to eds1-2, susceptibility against the wildtype Pst strain was constitutively enhanced in eds1 sapx. Although a prior cold priming exposure resulted in reduced Pst titers in eds1-2, it did not alter Pst resistance in eds1 sapx. This demonstrates that the genetic sAPX requirement for cold priming of basal plant immunity applies also to an eds1 null mutant background.

Modification in the ascorbate-glutathione cycle leads to a better acclimation to high light in the rose Bengal resistant mutant of Nannochloropsis oceanica.

Understanding how to adapt outdoor cultures of Nannochloropsis oceanica to high light (HL) is vital for boosting productivity. The N. oceanica RB2 mutant, obtained via ethyl methanesulfonate mutagenesis, was chosen for its tolerance to Rose Bengal (RB), a singlet oxygen (1O2) generator. Compared to the wild type (WT), the RB2 mutant showed higher resilience to excess light conditions. Analyzing the ascorbate-glutathione cycle (AGC), involving ascorbate peroxidases (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.8.1.7), in the RB2 mutant under HL stress provided valuable insights. At 250 µmol photon m-2 s-1 (HL), the WT strain displayed superoxide anion radicals (O2▪-) and hydrogen peroxide (H2O2) accumulation, increased lipid peroxidation, and cell death compared to normal light (NL) conditions (50 µmol photon m-2 s-1). The RB2 mutant didn't accumulate O2▪- and H2O2 after HL exposure, and exhibited increased APX, DHAR, and GR activities and transcript levels compared to WT and remained consistent after HL treatment. Although the RB2 mutant had a smaller ascorbate (AsA) pool than the WT, its ability to regenerate dehydroascorbate (DHA) increased post HL exposure, indicated by a higher AsA/DHA ratio. Additionally, under HL conditions, the RB2 mutant displayed an improved glutathione (GSH) regeneration rate (GSH/GSSG ratio) without changing the GSH pool size. Remarkably, H2O2 or menadione (a O2▪- donor) treatment induced cell death in the WT strain but not in the RB2 mutant. These findings emphasize the essential role of AGC in the RB2 mutant of Nannochloropsis in handling photo-oxidative stress.

Graphene oxide-based aerogel stimulates growth, mercury accumulation, photosynthesis-related gene expression, antioxidant efficiency and redox status in wheat under mercury exposure.

Mercury (Hg) pollution is a global concern in cropland systems. Hg contamination causes a disruption in the growth, energy metabolism, redox balance, and photosynthetic activity of plants. In the removal of Hg toxicity, a recent critical strategy is the use of aerogels with biodegradability and biocompatibility. However, it is unknown how graphene oxide-based aerogels stimulate the defense systems in wheat plants exposed to Hg toxicity. Therefore, in this study, the photosynthetic, genetic, and biochemical effects of reduced graphene oxide aerogel treatments (gA; 50-100-250 mg L-1) were examined in wheat (Triticum aestivum) under Hg stress (50 µM HgCl2). The relative growth rate (RGR) significantly decreased (84%) in response to Hg stress. However, the reduced RGR and water relations (RWC) of wheat were improved by gA treatments. The impaired gas exchange levels (stomatal conductance, carbon assimilation rate, intercellular CO2 concentrations, and transpiration rate) caused by stress were reversed under Hg plus gAs. Additionally, stress hampered chlorophyll fluorescence (Fv/Fo, Fv/Fm), and under Hg toxicity the expression of psaA genes was reduced (>0.4-fold), but psaB gene was significantly up-regulated (>3-fold) which are the genes involved in PSI. By increasing expression patterns of both genes relating to PSI, gAs reversed the adverse consequences on Fv/Fo and Fv/Fm in the presence of excessive Hg concentration. The activities of glutathione S-transferase (GST), glutathione reductase (GR), catalase (CAT), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) decreased under Hg toxicity. On the other hand, the activities of superoxide dismutase (SOD), APX, GST, and glutathione peroxidase (GPX) increased following gA treatments against stress, leading to the successful elimination of toxic levels of H2O2 and lipid peroxidation (TBARS content) by decreasing the levels by about 30%, and 40%, respectively. By modulating enzyme/non-enzyme activity/contents including the AsA-GSH cycle, gAs contributed to the protection of the cellular redox state. Most important of all, gA applications were able to reduce Hg intake by approximately 66%. Therefore, these results showed that gAs were effective in highly inhibiting Hg uptake and could significantly increase wheat tolerance to toxicity by eliminating Hg-induced oxidative damage and inhibiting metabolic processes involved in photosynthesis. The findings obtained from the study provide a new perspective on the alleviation roles of reduced graphene oxide aerogels as an effective adsorbent for decreasing damages of mercury toxicity in wheat plants.

Bamboo leaf extract treatment alleviates the surface browning of fresh-cut apple by regulating membrane lipid metabolism and antioxidant properties.

BACKGROUND: The effect of bamboo leaf extract (BLE) on controlling the browning of fresh-cut apple stored at 4 °C was investigated. Browning index, H2 O2 content, O2 - production rate, malondialdehyde (MDA) contents, total phenolic content (TPC) and soluble quinone content (SQC), the activities of polyphenol oxidase (PPO), peroxidase (POD), lipoxygenase (LOX), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), DPPH (2,2-diphenyl-2-picryl-hydrazyl) and ABTS [2,2-azinobis(3-ethylbenzothiazoline- 6-sulfonic acid)] radical scavenging activities, and the expression of genes related to browning were all investigated. RESULTS: BLE effectively alleviated the surface browning of fresh-cut apple, accompanied by a reduction in SQC, LOX activity, H2 O2 , O2 - production rate and MDA accumulation. Furthermore, BLE treatment enhanced the TPC, enzymatic (SOD, CAT, APX and POD) and non-enzymatic antioxidant activities. Principal component analysis and Pearson correlation analysis found the browning inhibition by BLE is not through the reduction of phenolic substrates and PPO activity. CONCLUSION: BLE controls the browning of fresh-cut apple by increasing the antioxidant capacity to scavenge ROS, which could alleviate oxidative damage and maintain the membrane integrity. © 2023 Society of Chemical Industry.

Genome-Wide Identification, Evolutionary Analysis, and Functional Studies of APX Genes in Melon (Cucuis melo L.).

The antioxidative enzyme ascorbate peroxidase (APX) exerts a critically important function through scavenging reactive oxygen species (ROS), alleviating oxidative damage in plants, and enhancing their tolerance to salinity. Here, we identified 28 CmAPX genes that display an uneven distribution pattern throughout the 12 chromosomes of the melon genome by carrying out a bioinformatics analysis. Phylogenetic analyses revealed that the CmAPX gene family comprised seven different clades, with each clade of genes exhibiting comparable motifs and structures. We cloned 28 CmAPX genes to infer their encoded protein sequences; we then compared these sequences with proteins encoded by rice APX proteins (OsAPX2), Puccinellia tenuiflora APX proteins (PutAPX) and with pea APX proteins. We found that the CmAPX17, CmAPX24, and CmAPX27 genes in Clade I were closely related, and their structures were highly conserved. CmAPX27 (MELO3C020719.2.1) was found to promote resistance to 150 mM NaCl salt stress, according to quantitative real-time fluorescence PCR. Transcriptome data revealed that CmAPX27 was differentially expressed among tissues, and the observed differences in expression were significant. Virus-induced gene silencing of CmAPX27 significantly decreased salinity tolerance, and CmAPX27 exhibited differential expression in the leaf, stem, and root tissues of melon plants. This finding demonstrates that CmAPX27 exerts a key function in melon's tolerance to salt stress. Generally, CmAPX27 could be a target in molecular breeding efforts aimed at improving the salt tolerance of melon; further studies of CmAPX27 could unveil novel physiological mechanisms through which antioxidant enzymes mitigate the deleterious effects of ROS stress.

High-Proportion Blue Light Irradiation at the End-of-Production Stage Promotes the Biosynthesis and Recycling of Ascorbate in Lettuce.

Ascorbate (AsA), an essential antioxidant for both plants and the human body, plays a vital role in maintaining proper functionality. Light plays an important role in metabolism of AsA in horticultural plants. Our previous research has revealed that subjecting lettuce to high light irradiation (HLI) (500 µmol·m-2·s-1) at the end-of-production (EOP) stage effectively enhances AsA levels, while the optimal light quality for AsA accumulation is still unknown. In this study, four combinations of red (R) and blue (B) light spectra with the ratio of 1:1 (1R1B), 2:1 (2R1B), 3:1 (3R1B), and 4:1 (4R1B) were applied to investigate the biosynthesis and recycling of AsA in lettuce. The results demonstrated that the AsA/total-AsA content in lettuce leaves was notably augmented upon exposure to 1R1B and 2R1B. Interestingly, AsA levels across all treatments increased rapidly at the early stage (2-8 h) of irradiation, while they increased slowly at the late stage (8-16 h). The activity of L-galactono-1,4-lactone dehydrogenase was augmented under 1R1B treatment, which is pivotal to AsA production. Additionally, the activities of enzymes key to AsA cycling were enhanced by 1R1B and 2R1B treatments, including ascorbate peroxidase, dehydroascorbate reductase, and monodehydroascorbate reductase. Notably, hydrogen peroxide and malondialdehyde accumulation increased dramatically following 16 h of 1R1B and 2R1B treatments. In addition, although soluble sugar and starch contents were enhanced by EOP-HLI, this effect was comparatively subdued under the 1R1B treatment. Overall, these results indicated that AsA accumulation was improved by irradiation with a blue light proportion of over 50% in lettuce, aligning with the heightened activities of key enzymes responsible for AsA synthesis, as well as the accrual of hydrogen peroxide. The effective strategy holds the potential to enhance the nutritional quality of lettuce while bolstering its antioxidant defenses.