Monodehydroascorbic Acid Research Articles

Effects of Foliar Spraying of Organic Selenium and Nano-Selenium Fertilizer on Pak Choi (Brassica chinensis var. pekinensis. cv. ‘Suzhouqing’) under Low Temperature Stress

The effects of foliar spraying of organic selenium and nano-selenium fertilizer on pak choi (Brassica chinensis var. pekinensis. cv. ‘Suzhouqing’) under low temperature were investigated. The impacts on plant growth, antioxidant capacities, and nutritional profiles were studied. Exogenous selenium was applied at three rates: 5, 10, 20 mg L−1, and RNA-Seq technology was used to sequence the transcriptome of leaves. The study revealed that selenium influenced leaf weight and total selenium content through three main mechanisms. First, it protected photosynthetic pigments and boosted photosynthetic capacity by up-regulating LHca2, LHcb1, LHca1, and LHcb4. Second, it enhanced antioxidant capacity by elevating the expression of genes such as superoxide dismutase and monodehydroascorbic acid. Third, it facilitated selenium absorption through endocytosis, transported selenium using the ABC transport gene family, and regulated selenium metabolism-related genes like cysteine synthetase and glutaredoxin. Nine hub genes identified with a weighted gene co-expression network analysis were closely associated with these mechanisms. The results of a functional enrichment analysis were consistent with those of a Gene Ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis conducted on DEGs, thus confirming the reliability of these findings. Therefore, this study can provide scientific basis for pak choi production with selenium fortification by selenium application.

Involvement of Nitric Oxide and Melatonin Enhances Cadmium Resistance of Tomato Seedlings through Regulation of the Ascorbate-Glutathione Cycle and ROS Metabolism.

Melatonin (MT) and nitric oxide (NO) act as signaling molecules that can enhance cadmium (Cd) stress resistance in plants. However, little information is available about the relationship between MT and NO during seedling growth under Cd stress. We hypothesize that NO may be involved in how MT responds to Cd stress during seedling growth. The aim of this study is to evaluate the relationship and mechanism of response. The results indicate that different concentrations of Cd inhibit the growth of tomato seedlings. Exogenous MT or NO promotes seedling growth under Cd stress, with a maximal biological response at 100 μM MT or NO. The promotive effects of MT-induced seedling growth under Cd stress are suppressed by NO scavenger 2-4-carboxyphenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO), suggesting that NO may be involved in MT-induced seedling growth under Cd stress. MT or NO decreases the content of hydrogen peroxide (H2O2), malonaldehyde (MDA), dehydroascorbic acid (DHA), and oxidized glutathione (GSSG); improves the content of ascorbic acid (AsA) and glutathione (GSH) and the ratios of AsA/DHA and GSH/GSSG; and enhances the activities of glutathione reductase (GR), monodehydroascorbic acid reductase (MDHAR), dehydroascorbic acid reductase (DHAR), ascorbic acid oxidase (AAO), and ascorbate peroxidase (APX) to alleviate oxidative damage. Moreover, the expression of genes associated with the ascorbate-glutathione (AsA-GSH) cycle and reactive oxygen species (ROS) are up-regulated by MT or NO under Cd conditions, including AAO, AAOH, APX1, APX6, DHAR1, DHAR2, MDHAR, and GR. However, NO scavenger cPTIO reverses the positive effects regulated by MT. The results indicate that MT-mediated NO enhances Cd tolerance by regulating AsA-GSH cycle and ROS metabolism.

Gaseous ozone regulates reactive oxygen species metabolism and ascorbate–glutathione cycle to delay the senescence of fresh-cut red pitaya (Selenicereus undatus) fruit

Mechanical damage during processing can accelerate the senescence and deterioration of fresh-cut red pitaya (Selenicereus undatus), thereby affecting its nutritional quality and commodity value. In this study, the effects of a low-concentration and long-term (10 μL L−1 for 60 min) gaseous ozone treatment on the quality, reactive oxygen species (ROS) metabolism, and enzyme and non-enzyme antioxidant activities of fresh-cut red pitaya fruit were investigated. The results showed that ozone treatment delayed the decline in fruit firmness, total soluble solids, and titratable acid content. Ozone treatment also maintained a higher free radical scavenging capacity and lower membrane lipid peroxidation than the control treatment. It prevented the rapid increase in ROS level by improving the activity of antioxidant enzymes, including superoxide dismutase, peroxidase, and catalase. Additionally, the treatment activated the ascorbate–glutathione cycle. Compared with the control group, ozone treatment maintained the activities of ascorbic acid peroxidase, dehydroascorbic acid reductase, monodehydroascorbic acid reductase, and glutathione reductase. Although the contents of ascorbic acid (AsA) and dehydroascorbic acid (DHA) decreased within 10 days of storage, the AsA/DHA and glutathione/oxidized glutathione ratios in the ozone-treated group were higher than those in the control group from day 0 to day 6. Thus, ozone treatment regulated ROS metabolism, enhanced the ROS-scavenging system, maintained the redox balance of fresh-cut red pitaya, and delayed senescence.

Integrated transcriptome and metabolome analysis reveals the physiological and molecular responses of allotetraploid rapeseed to ammonium toxicity

Ammonium (NH4+) and nitrate (NO3−) are the main nitrogen (N) sources accessible to plants. However, exclusive NH4+ may causes toxicity to crops. Transcriptomics in conjunction with metabolomics analysis in allotetraploid rapeseed under NH4+ stress showed that NH4+ taken up by roots was mainly transferred to leaves for assimilation. The concentrations of most amino acids, glucose, and glucose-6-phosphate increased whilst malate, succinate, and α-ketoglutarate concentrations decreased in NH4+-treated leaves. Moreover, NH4+ toxicity down-regulated genes related to photosynthesis and impaired the electron transport chain in chloroplasts. The expression of genes related to H2O2 decomposition, as well as the concentrations of monodehydro-ascorbic acid and ascorbic acid, reduced after exposure to NH4+-N, accompanied by higher O2- and H2O2 accumulation. Taken together, our results indicated that the excessive accumulation of NH4+ in plants caused an imbalance of carbon and N metabolism, impaired photosystems and generated reactive oxygen species, which resulted in toxicity to rapeseed.

Silencing of ascorbate oxidase results in reduced growth, altered ascorbic acid levels and ripening pattern in melon fruit

Ascorbate oxidase (AO, EC 1.10.3.3) is a copper-containing enzyme localized at the apoplast, where it catalyzes the oxidation of ascorbic acid (AA) to dehydroascorbic acid (DHA) via monodehydroascorbic acid (MDHA) intermediate. Despite it has been extensively studied, no biological roles have been definitively ascribed. To understand the role of AO in plant metabolism, fruit growth and physiology, we suppressed AO expression in melon (Cucumis melo L.) fruit. Reduction of AO activity increased AA content in melon fruit, which is the result of repression of AA oxidation and simultaneous induction of certain biosynthetic and recycling genes. As a consequence, ascorbate redox state was altered in the apoplast. Interestingly, transgenic melon fruit displayed increased ethylene production rate coincided with elevated levels of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO, EC 1.14.17.4) activity and gene expression, which might contribute to earlier ripening. Moreover, AO suppressed transgenic melon fruit exhibited a dramatic arrest in fruit growth, due to a simultaneous decrease in fruit cell size and in plasmalemma (PM) ATPase activity. All the above, support for the first time, the in vivo AO participation in the rapid fruit growth of Cucurbitaceae and further suggest an alternative route for AA increase in ripening fruit.

Ascorbate in the Apoplast: Metabolism and Functions

Ascorbic acid (AA) is one of the most important antioxidants and redox-active substances of plants found in the apoplast. In the form of ascorbate anion, it can be exported to the cell wall through anion channels, where it is further oxidized to dehydroascorbic acid (DHA) and in this form is translocated back into the cytoplasm through as yet unidentified transporters. In the apoplast AA is exposed to both enzymatic and non-enzymatic oxidation, participating in the antioxidant and pro-oxidant processes: detoxification of O3, generation of hydroxyl radicals, reduction of phenoxyl radicals, etc. The intermediate product of the AA oxidation in apoplast, monodehydroascorbic acid (MDHA), serves as an extracellular electron acceptor for a number of redox chains localized at the plasma membrane (PM). All three forms of ascorbate, AA, DHA and MDHA, can potentially be involved in the cell signalling. Released from the cell through anionic channels during PM depolarization, AA can stimulate the production of hydroxyl radicals that activate Ca2+-permeable channels, and thus trigger Ca2+-signalling. Due to the ability to generate hydroxyl radicals and reduce phenoxyl radicals, AA affects cell wall extensibility and extension growth. By reducing Fe3+ to a freely soluble transport form of Fe2+, AA is involved in iron uptake by root cells. Apoplastic AA also plays an important role in a number of other processes and is potentially a unique signal-regulatory molecule functioning in the plant cell walls.

Foliar application of 5-aminolevulinic acid (ALA) alleviates NaCl stress in cucumber (Cucumis sativus L.) seedlings through the enhancement of ascorbate-glutathione cycle

The natural plant growth regulator 5-aminolevulinic acid (ALA) promotes plant growth. The present study assessed the effects of exogenously applied ALA (25 mg L−1) on the growth and H2O2 scavenging system (ascorbate-glutathione cycle, AsA-GSH cycle) under NaCl stress (50 mmol L−1) in cucumber (Cucumis sativus L.) seedlings. Growth of cucumber seedlings was significantly inhibited by NaCl stress. Moreover, NaCl caused accumulation of H2O2 and malonaldehyde (MDA) as well as dehydroascorbic acid (DHA) and oxidized glutathione (GSSG) in cucumber leaves. However, the application of ALA reversed the adverse effect of NaCl on growth of the cucumber seedlings by increasing the shoots and roots biomass. The application of ALA also increased the contents of AsA and GSH of the seedlings under moderate salt stress. The ratios of reduced/oxidized antioxidant, such as AsA/DHA and GSH/GSSG, in seedlings under NaCl treatment were also improved by ALA, indicating that the regeneration efficiency of antioxidants could be promoted by exogenous ALA. In addition, exogenous ALA also promoted the activities of enzymes involved in the AsA-GSH cycle, including ascorbic acid oxidase (AAO), ascorbate peroxidase (APX), monodehydroascorbic acid reductase (MDHAR), dehydroascorbic acid reductase (DHAR) and glutathione reductase (GR). These results suggested that ALA alleviate the damages caused by NaCl through the enhancement of the AsA-GSH pathway in cucumber seedlings.

Analysis of Antioxidant Enzyme Activity Involved in Ascorbate-glutathione Cycle in Green-flesh Kiwifruits

To compare the activities of enzymes related to ascorbate-glutathione cycle (AsA-GSH cycle) in different varieties, the fruits of five green-fleshed kiwifruit varieties were used as materials and activities of ascorbate peroxidase (APX), monodehydroascorbic acid (MDHA), dehydroascorbate reductase (DHAR) were measured by ultraviolet spectrophotometry. Results showed that ‘Cuiyu’ had higher MDHAR activities. The higher enzyme activity is responsible for the higher accumulation of AsA in kiwifruit. All of these results indicated that there were significant differences in the activities of enzymes in 5 kiwifruit genotypes.

Hypothesis for the Mechanism of Ascorbic Acid Activity in Living Cells Related to Its Electron-Accepting Properties.

Electron-accepting properties, and in particular resonance dissociative electron attachment (DEA) to ascorbic acid (AA), are investigated by means of DEA spectroscopy in vacuo. The experimental features are assigned in silico and discussed in relation to expected dissociative electron transfer processes in vivo with the support of density functional theory calculations and the polarizable continuum model. It is shown that formation of the two most abundant AA metabolites in living cells, namely monodehydroascorbic acid and dehydroascorbic acid, can be stimulated by cellular electron transfer to AA under reductive conditions. Prooxidant effects caused by AA are suggested to be mediated by hydroxyl radicals formation via the DEA mechanism. The involvement of excited electronic states under UV-irradiation in plants could open additional DEA channels leading to specific AA activity forbidden under dark state conditions.

Dynamic aspects of ascorbic acid metabolism in the circulation: analysis by ascorbate oxidase with a prolonged in vivo half-life

Because AA (L-ascorbic acid) scavenges various types of free radicals to form MDAA (monodehydroascorbic acid) and DAA (dehydroascorbic acid), its regeneration from the oxidized metabolites is critically important for humans and other animals that lack the ability to synthesize this antioxidant. To study the dynamic aspects of AA metabolism in the circulation, a long acting AOase (ascorbate oxidase) derivative was synthesized by covalently linking PEG [poly(ethylene glycol)] to the enzyme. Fairly low concentrations of the modified enzyme (PEG-AOase) rapidly decreased AA levels in isolated fresh plasma and blood samples with a concomitant increase in their levels of MDAA and DAA. In contrast, relatively high doses of PEG-AOase were required to decrease the circulating plasma AA levels of both normal rats and ODS (osteogenic disorder Shionogi) rats that lack the ability to synthesize AA. Administration of 50 units of PEG-AOase/kg of body weight rapidly decreased AA levels in plasma and the kidney without affecting the levels in other tissues, such as the liver, brain, lung, adrenal grand and skeletal muscles. PEG-AOase slightly, but significantly, decreased glutathione (GSH) levels in the liver without affecting those in other tissues. Suppression of hepatic synthesis of GSH by administration of BSO [L-buthionin-(S,R)-sulfoximine] enhanced the PEG-AOase-induced decrease in plasma AA levels. These and other results suggest that the circulating AA is reductively regenerated from MDAA extremely rapidly and that hepatic GSH plays important roles in the regeneration of this antioxidant.

Altered stomatal dynamics in ascorbate oxidase over-expressing tobacco plants suggest a role for dehydroascorbate signalling

Control of stomatal aperture is of paramount importance for plant adaptation to the surrounding environment. Here, we report on several parameters related to stomatal dynamics and performance in transgenic tobacco plants (Nicotiana tabacum L., cv. Xanthi) over-expressing cucumber ascorbate oxidase (AO), a cell wall-localized enzyme of uncertain biological function that oxidizes ascorbic acid (AA) to monodehydroascorbic acid which dismutates yielding AA and dehydroascorbic acid (DHA). In comparison to WT plants, leaves of AO over-expressing plants exhibited reduced stomatal conductance (due to partial stomatal closure), higher water content, and reduced rates of water loss on detachment. Transgenic plants also exhibited elevated levels of hydrogen peroxide and a decline in hydrogen peroxide-scavenging enzyme activity. Leaf ABA content was also higher in AO over-expressing plants. Treatment of epidermal strips with either 1 mM DHA or 100 microM hydrogen peroxide resulted in rapid stomatal closure in WT plants, but not in AO-over-expressing plants. This suggests that signal perception and/or transduction associated with stomatal closure is altered by AO over-expression. These data support a specific role for cell wall-localized AA in the perception of environmental cues, and suggest that DHA acts as a regulator of stomatal dynamics.

Chemie freier cyclischer vicinaler Tricarbonyl‐Verbindungen (‘1,2,3‐Trione’). Teil 3

AbstractChemistry of Free Cyclic Vicinal Tricarbonyl Compounds (‘1,2,3‐Triones’). Part 3. Polar and Redox Reactions of 1,2,3‐Triones with Enamines of Different Types – News on Oxonol Dyes, Radicals, and Biradicals The central CO groups of cyclic 1,2,3‐triones possess outstanding electrophilic (electron‐pair‐accepting) as well as oxidizing (one‐electron‐accepting) properties. Thus, 1,2,3‐triones are chemically related to 1,2‐ and 1,4‐benzoquinones. Whereas polar reactions with carbanion‐like (electron rich) species give rise to nucleophilic addition reactions to CO groups under exclusive C,C‐bond formation, SET (single‐electron transfer) or redox reactions effect a partial ‘carbonyl Umpolung’ via ketyl intermediates (C,C‐ and/or C,O‐bond formation). Here, we report on numerous reactions between electron‐rich, more‐ or less‐polar enamines with 5,5‐dimethylcyclohexane‐1,2,3‐trione (9a) and 1H‐indene‐1,2,3‐trione (9b). Various new derivatives of basic oxonol dyes were formed, including the first oxonol dye incorporating a 1,3‐dioxocyclohexyl moiety. A novel stable radical, 50/50′, was obtained from 9b and 11a via addition, hydrolysis, and treatment with conc. H2SO4. Radical 50/50′ represents a vinylogous ‘monodehydroreductone’ and is, thus, related to monodehydroascorbic acid (143), to Russell's radical cation (144), to indigo (141/141′), and to quinhydrone.

Apoplastic peroxidases and ascorbate are involved in manganese toxicity and tolerance of Vigna unguiculata

Excessive manganese (Mn) supply induced the formation of brown spots on leaves as typical Mn toxicity symptoms in cowpea (Vigna unguiculata L. Walp.) grown in hydroponics. Differences in Mn resistance between cv. TVu 91 (Mn‐sensitive) and cv. TVu 1987 (Mn‐tolerant) expressed in the density of brown spots in older leaves were due to higher Mn tissue tolerance. Apoplastic water‐soluble peroxidase (POD) in the apoplastic washing fluid (AWF) was enhanced by increasing Mn leaf content and generally significantly higher in leaves of cv. TVu 91 than in cv. TVu 1987. Electrophoresis of AWF revealed the presence of several water‐soluble POD isoenzymes. At toxic Mn supply, the activities of these and additional POD isoenzymes increased more in the Mn‐sensitive cultivar. Levels of ascorbic acid in the apoplast and cytoplasm of the Mn‐sensitive cv. TVu 91 decreased with increasing leaf Mn contents, whereas Mn‐tolerant cv. TVu 1987 was not affected. Mn treatment lead to a stimulation of the enzymes of the ascorbic acid regeneration system (monodehydroascorbic acid reductase and glutathione reductase) in both cultivars, but the activation of glutathione reductase was clearly more enhanced in the Mn‐tolerant cultivar TVu 1987. The results provide circumstantial evidence that apoplastic ascorbate and peroxidases are involved in the expression of Mn toxicity and genotypic Mn tolerance.

Detection of Monodehydroascorbic Acid Radical in Sulfite-Treated Leaves and Mechanism of its Formation

The aim of the present study is to detect the monodehydroascorbic acid (MDA) radical in broad bean (Vicia faba L.) leaves which were treated by vacuum-infiltration in Na2SO3 solution and subsequent centrifugation (sulfitetreated leaves). When sulfite-treated leaves were illuminated with white light, the electron spin resonance (ESR) signal of MDA radical was observed. The level of the MDA radical depended on the concentration of sulfite that was used for vacuum-infiltration and on the light intensity of illumination. The formation of the MDA radical in sulfitetreated leaves was inhibited by DCMU or by replacement of air with N2. Glycolaldehyde also inhibited the formation of MDA radical in sulfite-treated leaves. Catalase activity was decreased by the sulfite treatment without affecting significantly the activities of ascorbate peroxidase (AA-POX) and of peroxidase which preferentially oxidizes phenolics (PhOH-POX). From these results, we conclude that the formation of the MDA radical in sulfite-treated leaves is catalyzed by peroxidases using the H2O2 which is generated by photorespiration and the Mehler reaction.

A peroxidase/phenolics/ascorbate system can scavenge hydrogen peroxide in plant cells

The function of a peroxidase/phenolics/ascorbic acid system in plant vacuoles has not yet been well elucidated. We wished to study the redox reactions among hydrogen peroxide, phenolics and ascorbic acid (AA) in the presence of horseradish peroxidase. Horseradish peroxidase oxidized rutin and chlorogenic acid (CGA), compounds present in many kinds of plant. The oxidation was inhibited by AA. As a result of the inhibition. AA was oxidized and when almost all of it had been oxidized, oxidation of the phenolics commenced. Monodehydroascorbic acid (MDA) radical was detected during the oxidation of AA, suggesting that the inhibition of oxidation of rutin and CGA was due to reduction of phenoxyl radicals by AA. By comparison of time courses of changes in levels of AA and MDA radicals, and by kinetic calculation, it is suggested that in addition to AA, MDA radicals may also reduce phenoxyl radicals. It is proposed that the peroxidase/phenolics/AA system can function as a hydrogen peroxide scavenging system.

Stability of hydrophilic gels of tretinoin

Tretinoin is the trans isomeric form of retinoic acid. Its chemical structure includes a functional acid group and a side chain with conjugated double bonds, both susceptible to redox reactions. The vitamin C redox system comprises l-ascorbic acid, monodehydroascorbic acid and dehydroascorbic acid. Each of these substances has different physicochemical properties but possess antioxidant capacity for both hydrophilic and lipophilic substances. The present work is centred on studying the stability of hydrophilic gels of tretinoin prepared with or without antioxidant. HPLC was used to validate the analytical and extraction techniques to determine the amounts of tretinoin remaining. The results indicate that tretinoin undergoes rapid degradation by oxidation of the conjugated double bonds which is neither retarded nor lessened by the presence of antioxidant.

Impact of Aminotriazole and Paraquat on the Oxidative Defence System of Spruce Monitored by Monodehydroascorbic Acid

Keywords Ascorbic acid radical, EPR, Herbicides, Damage to Forest, Antioxidative System

Role of ascorbic acid in metabolism of rat testis and epididymis in relation to the onset of puberty

The metabolism of ascorbic acid, cholesterol, serum testosterone level and activities of 3Β and 17Β hydroxysteroid dehydrogenases were studied in testis and Cauda epididymis of prepubertal, pubertal and postpubertal (5, 15, 30, 45, 55 and 60 day old) rats. The data showed that serum testosterone levels and 3Β and 17Β hydroxysteroid dehydrogenases were increased with the age. The ascorbic acid metabolism was found to be stabilized in testis at day 30 being comparable with the adult, whereas a spurt in its metabolism occurred by day 45 and a significant depletion in ascorbic acid content in relation to the passage of the first wave of spermatozoa through cauda epididymis. The results of this study clearly elucidate that ascorbic acid is involved in metabolism of testis and epididymis in developing postnatal rats, in relation to the increasing demands for attaining a stable hormonal milieu, and the onset of puberty and the passage of the first wave of spermatozoa,via the formation of its free radical monodehydroascorbic acid and charge transfer complex mechanism

Radiation-Induced Free Radicals in l-Ascorbic Acid: An ESR Study

Single crystals of l-ascorbic acid and partially deuterated l-ascorbic acid were irradiated with either X rays or 337.1-nm laser radiation at 77 and 300 K. The same types of radicals are produced by either type of radiation, but their ESR spectra differ in intensity. Four different radicals were characterized and models were suggested for each of them as follows. At 77 K two oxidation products are produced, radical I, monodehydroascorbic acid, and radical IV, produced by the loss of the H attached to C4 of the ring, and one reduction product, radical III. At ∼140 K radical I decays with the loss of the second hydroxyl H to form dehydroascorbic acid, and the adduct radical II is produced in the process. Further warming to 300 K produces no other changes in the radicals. Radicals II, III, and IV are also present in crystals irradiated at 300 K, but the relative proportions of the different kinds of radicals are different than in the crystals irradiated at 77 K and warmed to 300 K. The unpaired electron in a...

Degradation of histamine in the presence of ascorbic acid and Cu2+ ion; involvement of hydrogen peroxide.

In the presence, but not in the absence of Cu2+, ascorbate decomposes histamine in citrate phosphate buffer (pH 6.5) at 37 degrees, but not at 0 degrees. The breakdown is completely inhibited by catalase, but only slightly by superoxide dismutase, and scavengers of OH. like benzoic acid, ethanol or potassium iodide. A1 O2 scavenger, alpha-tocopherol also did not show significant effects on the reaction. On the other hand, addition of H2O2 to the reaction mixture markedly enhances the rate of histamine breakdown induced by ascorbate or ascorbate-Cu2+ systems. However, H2O2 alone cannot breakdown histamine even in the presence of Cu2+. Histamine breakdown induced by ascorbate appears to be dependent upon the autooxidation of this vitamin. From these results and the findings reported by Chatterjee et al. that the products of its aerobic oxidation, dehydroascorbic acid and H2O2 were ineffective in reacting with histamine in the presence of Cu2+, it is concluded that the combination of H2O2 and the intermediate of ascorbate oxidation (monodehydroascorbic acid or other unstable species), both of which are produced during the autooxidation of ascorbate, plays a major role in the histamine transformation by ascorbate-Cu2+ system.