Regeneration Of Ascorbic Acid Research Articles

High-barrier, flexible, hydrophobic, and biodegradable cellulose-based films prepared by ascorbic acid regeneration and low temperature plasma technologies

Regenerated cellulose (RC) films are considered a sustainable packaging material that can replace non-degradable petroleum-based plastics. However, their susceptibility to water vapor and oxygen can limit their effectiveness in protecting products. This study introduces a novel approach for enhancing RC films to create durable, flexible, hydrophobic, high-barrier, and biodegradable packaging materials. By exploring the impact of ascorbic acid coagulation bath treatment and plasma-enhanced chemical vapor deposition (PECVD) on the properties of RC films, we found that the coagulation bath treatment facilitated the organized reconfiguration of cellulose chains, while PECVD applied a dense SiOx coating on the film surface. The results demonstrated a significant enhancement in water vapor and oxygen barrier properties of the composite film, almost reaching the level of commercial barrier films. Moreover, the composite film displayed exceptional biodegradability, fully degrading in soil within 35 days. Additionally, it showcased impressive mechanical strength, hydrophobic characteristics, and freshness preservation, positioning it as a valuable option for bio-based high-barrier packaging applications.

New insights into the relationship between clock genes and ascorbic acid metabolism in spinach during pre- and postharvest periods

In this study, the effects of light and dark conditions on the expression of candidate clock genes (SoLHY, SoPRR5, and SoTOC1), photoreceptor genes (SoPHYA, SoPHYB, and SoZTL), ascorbic acid (AsA) synthesis genes (SoVTC2 and SoGLDH), an AsA degradation gene (SoAPX), an AsA regeneration gene (SoMDHAR), and AsA content of spinach during the pre- and postharvest periods were investigated. The AsA content decreased under constant dark storage, whereas the AsA content was efficiently maintained under a light/dark cycle. Gene expression with rhythmic signals confirmed by the JTK_CYCLE method (P ≤ 0.05) was used for the analysis of partial correlation coefficients. Strong correlations between SoLHY and SoVTC2 were observed under all investigated conditions. AsA synthesis regulation via the clock gene LHY was stable and likely not altered by harvesting stress and/or external light stimuli. After harvesting, SoPRR5 was negatively correlated with SoVTC2. This finding suggested that a reduction in the SoPRR5 expression level might be an alternative way to induce/maintain AsA content during storage. Additionally, the expression of the photoreceptor genes SoPHYA and SoZTL was moderately correlated with that of SoVTC2 during cultivation. Surprisingly, these correlations were not observed during storage even in the presence of light. Instead, SoPHYA expression was correlated with that of another AsA synthesis gene, SoGLDH, under light/dark storage. Moreover, under constant dark storage, SoZTL expression showed a strong correlation with SoVTC2. The considerable variation in the relationship between the expression levels of AsA-related genes and photoreceptor genes during cultivation and storage indicates the contribution of light regulators to maintaining AsA rhythm in spinach. In summary, this study is the first to suggest possible crosslinking of external signals (light/dark), photoreceptor genes, clock genes, and AsA metabolism genes, which are related to changes in the quality of spinach during the pre- and postharvest periods.

Genome-Wide Identification and Comparative Transcriptome Methods Reveal FaMDHAR50 Regulating Ascorbic Acid Regeneration and Quality Formation of Strawberry Fruits.

Ascorbic acid (AsA) is a crucial water-soluble antioxidant in strawberry fruit, but limited research is currently available on the identification and functional validation of key genes involved in AsA metabolism in strawberries. This study analyzed the FaMDHAR gene family identification, which includes 168 genes. Most of the products of these genes are predicted to exist in the chloroplast and cytoplasm. The promoter region is rich in cis-acting elements related to plant growth and development, stress and light response. Meanwhile, the key gene FaMDHAR50 that positively regulates AsA regeneration was identified through comparative transcriptome analysis of 'Benihoppe' strawberry (WT) and its natural mutant (MT) with high AsA content (83 mg/100 g FW). The transient overexpression experiment further showed that overexpression of FaMDHAR50 significantly enhanced the AsA content by 38% in strawberry fruit, with the upregulated expression of structural genes involved in AsA biosynthesis (FaGalUR and FaGalLDH) and recycling and degradation (FaAPX, FaAO and FaDHAR) compared with that of the control. Moreover, increased sugar (sucrose, glucose and fructose) contents and decreased firmness and citric acid contents were observed in the overexpressed fruit, which were accompanied by the upregulation of FaSNS, FaSPS, FaCEL1 and FaACL, as well as the downregulation of FaCS. Additionally, the content of pelargonidin 3-glucoside markedly decreased, while cyanidin chloride increased significantly. In summary, FaMDHAR50 is a key positive regulatory gene involved in AsA regeneration in strawberry fruit, which also plays an important role in the formation of fruit flavor, apperance and texture during strawberry fruit ripening.

Ascorbate−glutathione cycle involving in response of Bangia fuscopurpurea (Bangiales, Rhodophyta) to hyposalinity

Bangia fuscopurpurea is a widespread intertidal seaweed that is commercially cultured in China. This seaweed is frequently exposed to hyposalinity stress, but little is known about the adaptation mechanisms. Ascorbate−glutathione (AsA−GSH) cycle plays important roles in many organisms under a variety of abiotic stress, including hyposaline stress. In this study, we investigated the response of key metabolites and enzymes involved in the AsA−GSH cycle of B. fuscopurpurea under hyposalinity, with the addition of exogenous GSH and Lbuthionine-sulfoximine (BSO). The quantification of BfAPX gene expression was assessed across varied treatment regimens. And the putative interaction proteins of BfAPX were screened by yeast two hybrid system. It was found that under hyposalinity (15 and/or 0 psu), the content of reduced glutathione (GSH), total glutathione (GSH+ oxidized glutathione, GSSG) and cysteine, the ratio of GSH/GSSG and ascorbic acid (AsA)/ dehydroascorbic acid (DHA), and the activity of ascorbic acid peroxidase (APX) and monodehydroascorbate reductase (MDHAR) was significantly up-regulated. The hyposality-promoted GSH/GSSG was weakened while the glutathione reductase (GR) activity was promoted by adding exogenous GSH and BSO. The hyposality-promoted AsA/DHA ratio was strengthened by exogenous GSH but weakened by BSO. The dehydroascorbate reductase (DHAR) activity had no significant changes either with or without exogenous GSH under all salinities, while DHAR activity together with DHA content was enhanced by BSO. The expression of APX gene markedly increased under hyposalinity+BSO treatment. Putative interacting proteins of APX, including glutamate dehydrogenase 1a and fructose diphosphate aldolase, were identified through screening. The results indicated that the AsA−GSH cycle was involved in response of B. fuscopurpurea to hyposalinity by means of increasing GSH/GSSG ratio (through promoting GSH biosynthesis pathway and GSH regeneration from GSSG by GR catalyzation) and AsA/DHA ratio (promoting AsA regeneration through MDHAR). These findings would contribute to improve the aquaculture of this promising economic species and unveil how intertidal seaweeds address the global climate challenges.

The impact of cadmium stress on the ascorbate-glutathione pathway and ascorbate regeneration in tea plants

Ascorbic acid (AsA) and glutathione (GSH) contribute to defense responses under abiotic stresses. The present study explored the ascorbate-glutathione cycle and ascorbate regeneration under high concentration (30 mM) of cadmium in the tea plant (Camellia sinensis L.). The tea leaves showed speckles and necrosis from the third day of Cd treatment. The content of superoxide anion (O2.-) and hydrogen peroxide (H2O2) in the leaves were significantly higher until the seventh day after Cd treatment. The content of O2.- and H2O2 were the highest on the fifth day (212.7 and 153.6 % of the control, respectively). The AsA content increased (86.9 %) on the first day after Cd treatment and decreased significantly in the subsequent days, while GSH showed a reverse trend. The enzymatic activity assays showed that dehydroascorbate reductase (DHAR) and glutathione reductase (GR) involved in AsA regeneration were downregulated considerably after Cd foliar application. In contrast, the activities of ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR) increased on the first day and then declined. Reverse-transcription quantitative PCR showed upregulation of glutathione synthetase (CsGSHS), γ-glutamylcysteine synthetase (Csγ-ECS), and CsMDHAR of the AsA regeneration pathway and downregulation of CsDHAR and CsGR. The expressions of GDP-L-galactose phosphorylase (CsGGP), L-galactose-1-phosphate phosphatase (CsGPP), and L-galactono- 1,4-lactone dehydrogenase (CsGaILDH) of the L-galactose pathway were also downregulated. The results indicated that AsA, which can respond to Cd stress of plants by increasing antioxidant ability, was consumed to scavenge ROS; moreover, Cd stress inhibited AsA synthesis and regeneration, which made that tea plants suffering severe damage.

Exogenous melatonin treatment affects ascorbic acid metabolism in postharvest 'Jinyan' kiwifruit.

Ascorbic acid (AsA) is an important nutritious substance in fruits, and it also can maintain the biological activity of fruits during storage. This research investigated the effect of exogenous melatonin (MT) on AsA metabolism in postharvest kiwifruit. Our results indicated that exogenous MT delayed the decrease of fruit firmness and titratable acid (TA), inhibited the increase of soluble solids content (SSC), reduced the respiration rate and ethylene production, and maintained a higher AsA content in kiwifruit during storage. The high expression of L-galactose pathway key genes in the early storage and regeneration genes in the later storage maintained the AsA content in postharvest kiwifruit. MT treatment enhanced the expression levels of AsA biosynthesis (AcGME2, AcGalDH, and AcGalLDH) and regeneration (AcGR, AcDHAR, and AcMDHAR1) genes. Meanwhile, the expression of the degradation gene AcAO was inhibited in MT-treated kiwifruits.

Hydrogen-rich water maintains the quality of Rosa roxburghii by regulating AsA biosynthesis and regeneration

Rosa roxburghii is of great interest due to its high ascorbic acid (AsA) content, however AsA is readily lost after harvest. This study aimed to explore the effect of hydrogen-rich water (HRW) treatment on AsA metabolism in postharvest R. roxburghii. Results showed that HRW treatment maintained fruit quality and higher AsA content of R. roxburghii during the assay period. HRW treatment up-regulated the expression of AsA synthesis-related genes such as RrGMP, RrGME, RrGGP, RrGalDH, RrGalLDH and RrGalUR, but barely regulated the expression of RrGPP and RrMIOX. HRW promoted the activity and gene expression of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) in the AsA-GSH cycle. More interestingly, seven RrMYBs were significantly upregulated by HRW treatment and their expression trends were highly correlated with AsA content, suggesting that RrMYBs might transcriptionally regulate AsA synthesis and regeneration in postharvest. Our results emphasized that HRW reduced AsA loss, and positively regulated the expression of numerous AsA synthesis and regeneration genes and RrMYBs, thus illustrating a close link between RrMYBs and AsA synthesis and regeneration in postharvest R. roxburghii fruit.

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

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

L-ascorbic acid metabolism in two contrasting hardy kiwifruit (Actinidia arguta) cultivars during fruit development

Hardy kiwifruit (Actinidia arguta) has recently been popular in the fresh market due to its edible skin, and higher level of nutrition especially ascorbic acid (AsA) over kiwifruit (A. deliciosa and A. chinensis). On the behalf of screening high AsA content material for further genetic improvements, to gain a better understanding of the molecular mechanism of AsA metabolism, two hardy kiwifruit cultivars (‘Yilv’ and ‘Lvmi-1′) with contrasting AsA content were selected as materials for analysis. The ‘Yilv’ fruit contained 5 folds higher AsA content than ‘Lvmi-1′. AsA and total AsA (T-AsA) content showed a gradually decreasing in ‘Yilv’, while slightly increasing in ‘Lvmi-1′ during fruit development. However, the content of T-AsA increased with fruit weight in both cultivars. In accordance with AsA content, the expression of genes encoding GDP-L-galactose pyrophosphatase (GGP), L-galactose-1-phosphate phosphatase (GPP) and L-galactono-1,4-latone dehydrogenase (GalLDH), as well as the GalLDH activity were higher in ‘Yilv’ than that in ‘Lvmi-1′. During fruit development, no correlation between the biosynthetic genes expression and AsA pool was observed in each cultivar. In ‘Lvmi-1′ fruit, the expression of genes encoding ascorbate oxidase (AO), monodehydroascorbate reductase (MDHAR), the activity of AO, GDP-D-mannose pyrophosphorylase (GMP) and GGP showed significantly correlations with AsA pool level. In ‘Yilv’ fruit, the expression of MDHAR, the activity of GMP, GGP, GPP, GDP mannose 3′5’-epimerase (GME), GalLDH, myo-inositol oxygenase (MIOX), AO and ascorbate peroxidase (APX) displayed significant correlations with AsA pool. In conclusion, GalLDH was a key enzyme for hardy kiwifruit AsA biosynthesis, MDHAR was more efficient than DHAR in AsA regeneration in ‘Yilv’, AO and APX might be more efficient in AsA oxidation in ‘Lvmi-1′ and ‘Yilv’ respectively. This study explored the different AsA content and potential mechanism in two hardy kiwifruit cultivars, providing a reference for further genetic improvement and high AsA content material selection in cultivation.

Effect of 1-MCP on the regulation processes involved in ascorbate metabolism in kiwifruit

This research was conducted to investigate the mechanism of 1-methylcyclopropene (1-MCP) treatment on ascorbic acid (AsA) content in kiwifruit after harvest. Our findings indicated that 1-MCP treatment postponed the course of fruit senescence and maintained higher contents of AsA and total ascorbic acid (T-AsA) during storage in postharvest kiwifruit. Gene expression analysis revealed that the transcription level of genes involved in AsA metabolic pathway were regulated by 1-MCP treatment. The up-regulation of genes for AsA biosynthesis (AdGME, AdGalDH, AdGalLDH and AdGalUR) and regeneration (AdDHAR and AdGR) and down-regulation of degradation genes (AdAO) collectively contributed to the increase in AsA level in treated kiwifruit during storage. Moreover, the expression level of four candidate bHLH transcription factors, preliminarily screened from the transcriptome database of kiwifruit, was up-regulated by 1-MCP treatment by qPCR analysis. Taken together, our results suggested that due to its positive regulation on numerous ascorbate modifying genes and probably the candidate bHLH transcription factors, 1-MCP had a beneficial effect on AsA content.

Changes of oxidative metabolism in the roots of wheat (Triticum aestivum L.) seedlings in response to elevated ammonium concentrations

To elucidate the response of oxidative metabolism, triggered by elevated ammonium (NH4+) concentrations, on root growth of wheat seedlings, Yumai 49 (NH4+-tolerant) and Lumai 15 (NH4+-sensitive) cultivars were supplied with either 5.0 mmol L−1 NH4+-N (EAC) or 5.0 mmol L−1 NO3–-N (CON) under hydroponic conditions. Root growth in both cultivars was significantly reduced under EAC, and the negative effect was greater in Lumai 15. EAC enhanced the activities of monodehydroascorbate reductase and dehydroascorbate reductase in the roots of both cultivars, while it decreased ascorbic acid (ASA) content and GDP-mannose pyrophosphorylase (GMPase) activity at the 12th day after treatment in Lumai 15 by 62.0 and 71.4%; and in Yumai 49 by 38.8 and 62.2%, respectively, indicating that the regeneration of ASA was increased, but the biosynthesis of ASA was reduced under EAC treatment. Moreover, EAC increased DHA/ASA, reactive oxygen species (ROS), and malondialdehyde contents, as well as antioxidant enzyme activities in the roots of both cultivars. Relatively greater increases in ROS and soluble sugar, and lower antioxidant enzyme activities in Lumai 15 indicate severe disruption of oxidative metabolism when compared to Yumai 49. Results reveal that the reduction of ASA biosynthesis via decreased GMPase activity under the EAC condition probably acts as a trigger for accumulated ROS and imbalanced redox status, resulting in root growth inhibition during wheat seedling growth stage. Yumai 49, being an NH4+ -tolerant cultivar, had the stronger capacity to protect itself from oxidative stress, which allowed it to retain a lower DHA to ASA ratio by maintaining a better redox homeostasis than could be maintained in the NH4+ -sensitive cultivar Lumai 15.

Three metabolic pathways are responsible for the accumulation and maintenance of high AsA content in kiwifruit (Actinidia eriantha)

BackgroundActinidia eriantha is a precious material to study the metabolism and regulation of ascorbic acid (AsA) because of its high AsA content. Although the pathway of AsA biosynthesis in kiwifruit has been identified, the mechanism of AsA metabolism and regulation is still unclear. The purpose of this experiment is to reveal the AsA metabolic characteristics of A. eriantha ‘Ganmi 6’ from the molecular level, and lay a theoretical foundation for the research on the genetic improvement of kiwifruit quality.ResultsWe found that AsA reached the accumulation peak at S7 (110 DAF) during the process of fruit growth and development. The activity of GalDH, GalLDH, MDHAR and DHAR in fruit was similar to AsA accumulation trend, and both of them were significantly positively correlated with AsA content. It was speculated that GalDH and GalLDH were key enzymes in AsA biosynthesis, while MDHAR and DHAR were key enzymes in AsA regeneration cycle, which together regulated AsA accumulation in fruit. Also, we identified 98,656 unigenes with an average length of 932 bp from the transcriptome libraries using RNA-seq technology after data assembly. There were 50,184 (50.87%) unigenes annotations in four databases. Two thousand nine hundred forty-nine unigenes were enriched into the biosynthesis pathway of secondary metabolites, among which 133 unigenes involved in the AsA and aldehyde metabolism pathways, and 23 candidate genes related to AsA biosynthesis, cycling and degradation were screened out.ConclusionsConsidering gene expression levels and changes of physiological traits and related enzyme activity, we concluded that the accumulation of AsA depends mainly on the L-galactose pathway, and the D-galacturonic acid pathway and AsA recycling pathway as the secondary pathways, which co-maintain the high AsA content in fruit of A. eriantha.

SAT-132 The Secretory Vesicle Membrane Protein, CYB561, Promotes the Growth and Metastatic Potential of Castration-Resistant Neuroendocrine Prostate Cancer

An increase in the population of neuroendocrine (NE) differentiated (NED) cells and their secretory products are closely correlated with prostate cancer (PCa) resistance to existing therapies and eventual progression to castration-resistant PCa (CRPC). It is hypothesized that NED cells secrete neuropeptides that support tumor growth and induce aggressiveness of adjacent proliferating tumor cells through a paracrine mechanism. A gene that is constitutively expressed in secretory vesicles of NE cells, and has been previously found to be highly expressed in CRPC and cancer of several tissues is Cytochrome b561 (CYB561). The CYB561 gene encodes a secretory vesicle transmembrane protein that primarily functions in the regeneration of ascorbic acid, a necessary step in the α-amidation activation process in the biosynthesis of most neuropeptides. The CYB561 protein also exhibits ferrireductase activity and may contribute in regulating iron transport and metabolism, which are two other pathways often dysregulated in cancer. These findings led us to hypothesize that CYB561 may be a key player in the NE differentiation process that drives the progression of prostate cancers into the more aggressive NE subtype. In our study, we found that CYB561 expression is higher in metastatic and NE PCa (NEPC) models compared to normal prostate epithelia, and that its expression is not affected by androgen treatment or steroid deprivation. Lentiviral-mediated knockdown of CYB561 in the NEPC cell line, PC-3, decreased the expression of genes involved in NE differentiation and labile iron pool storage, decreased cell proliferation, reduced cell survival in a colony formation assay, and slowed down cell migration in a wound-healing assay. Treatment of normal prostate epithelial cells, PNT1A, with conditioned media from CYB561 knockdown PC-3 cells led to a decrease in proliferation rate when compared to treatment of PNT1A cells with media from CYB561 expressing (control) PC-3 cells. Taken together, our findings demonstrate the role of CYB561 in supporting the growth and metastatic potential of NEPC cells, and highlights the potential use of CYB561 as a therapeutic target and biomarker that can be used to identify more aggressive disease.

Characterization and Structural Determination of Cold-Adapted Monodehydroascorbate Reductase, MDHAR, from the Antarctic Hairgrass Deschampsia Antarctica

Ascorbic acid (AsA) is an abundant component of plants and acts as a strong and active antioxidant. In order to maintain the antioxidative capacity of AsA, the rapid regeneration of AsA is regulated by dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR). To understand how MDHAR functions under extreme temperature conditions, this study characterized its biochemical properties and determined the crystal structure of MDHAR from the Antarctic hairgrass Deschampsia antarctica (DaMDHAR) at 2.2 Å resolution. This allowed for a structural comparison with the mesophilic MDHAR from Oryza sativa L. japonica (OsMDHAR). In the functional analysis, yeast cells expressing DaMDHAR were tolerant to freezing and thawing cycles. It is possible that the expression of DaMDHAR in yeast enhanced the tolerance for ROS-induced abiotic stress.

Molecular cloning and functional characterization of a sweetpotato chloroplast IbDHAR3 gene in response to abiotic stress

Dehydroascorbate reductase (DHAR) plays a critical role in the regeneration of ascorbic acid (AsA), and widely involved in plant tolerance to biotic and abiotic stresses. In this study, the IbDHAR3 gene was cloned from sweetpotato cultivar Xushu 18 by RT-PCR. The full-length of this gene was 813 bp which encodes 270 amino acids. The IbDHAR3 protein contained two conserved domains of glutathione S-transferase (GST) and GST-C-DHAR, and one chloroplast transit peptide with 52 amino acids length. Transient expression in tobacco leaf epidermal cells indicated that IbDHAR3 protein is subcellular localized to chloroplast. The qRT-PCR results revealed that the relative expression level of IbDHAR3 in leaves is much higher than that in other tissues, and could be up-regulated by ABA, drought, salinity, and high-temperature stresses. The seed germination rate and root elongation were increased in contrast to wild type under mannitol and NaCl stresses in T3 transgenic Arabidopsis overexpressing IbDHAR3 gene. The soil drought experiments showed that the overexpression of IbDHAR3 gene in Arabidopsis reduced the malondialdehyde (MDA) and the H2O2 content, enhanced the level of AtGR gene expression, superoxide dismutase (SOD), ascorbate peroxidase (APX), DHAR activity, and the AsA content. Therefore, overexpression of IbDHAR3 gene could enhance the ability of scavenging reactive oxygen species such as H2O2 by promoting AsA-glutathione cycle and related antioxidant enzymes system, thereby contributing to increased stress tolerance in Arabidopsis.

Photogenerated Hole-Induced Chemical Redox Cycling on Bi2S3/Bi2Sn2O7 Heterojunction: Toward General Amplified Split-Type Photoelectrochemical Immunoassay

This work reports the elegant bridging of enzymatic generation of electron donor with photogenerated hole-induced chemical redox cycling amplification (RCA) for innovative photoelectrochemical (PEC) immunoassay, by the aid of a heterojunction photoelectrode with split-type strategy. Specifically, the system was exemplified by the alkaline phosphatase (ALP) catalytic generation of ascorbic acid (AA), the redox cycling of AA by tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of a novel Bi2S3/Bi2Sn2O7 heterojunction and myoglobin (Myo) as the photoelectrode and the target, respectively. After the immunoreaction and ALP-induced production of AA, the subsequent oxidation of AA by the photogenerated holes of the Bi2S3/Bi2Sn2O7 heterojunction could be cycled via the regeneration of AA by TCEP from the oxidized product of dehydroascorbic acid, leading to easy signal amplification for the sensitive immunoassay of Myo in real samples. It is believed that this work provided a basis for further design and development of general RCA-based PEC immunoassays.

Regulation of ascorbic acid metabolism in response to different temperatures in citrus juice sacs in vitro

To elucidate the regulation of ascorbic acid (AsA) metabolism in response to temperatures, three varieties of citrus juice sacs (Valencia orange, Lisbon lemon, and Satsuma mandarin) in in vitro culture system were subjected to different temperatures (10°C, 20°C, and 30°C). The AsA accumulation was induced at 10°C, whereas it was not significantly affected at 30°C as compared with the control at 20°C in juice sacs of the three citrus varieties. The enhancement of AsA accumulation at 10°C was regulated by the expression of genes in AsA biosynthetic, oxidation, and regeneration pathway. In Valencia orange and Satsuma mandarin, the higher expression of CitVTC4 gene in biosynthetic pathway, and the higher expression of CitMDAR1 and CitMDAR2 genes in regeneration pathway, together with the lower expression of CitAO gene in oxidation pathway contributed to the higher AsA level at 10°C. In Lisbon lemon, the higher expressions of CitVTC1, CitVTC2, and CitVTC4 genes in biosynthetic pathway and the lower expression of CitAO gene in oxidation pathway contributed to the higher AsA level at 10°C.

Exogenous 24-epibrassinolide alleviates zinc-induced toxicity in eggplant (Solanum melongena L.) seedlings by regulating the glutathione-ascorbate-dependent detoxification pathway

ABSTRACTExcessive zinc (Zn) uptake is toxic to both plants and animals. 24-Epibrassinolide (EBL), a plant steroid hormone, plays a pivotal role in regulating plant resistance to various stresses. In this study, the effects of EBL on oxidative stress and components of the ascorbate–glutathione (AsA-GSH) cycle in the leaves of eggplant (Solanum melongena L.) seedlings were investigated under Zn stress. Exogenous 0.1 µM EBL significantly alleviated the oxidative damage caused by Zn stress, as reflected by increased plant growth and decreased accumulations of Zn, hydrogen peroxide (H2O2), and malondialdehyde (MDA). In addition, components of the AsA-GSH metabolism cycle, such as the concentrations of reduced ascorbic acid (AsA) and glutathione (GSH), as well as the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and glutathione synthetase (GS), increased significantly in the presence of EBL under Zn stress. Moreover, exogenous EBL caused a significant increase in the levels of expression of the DHAR, MDHAR, GR, and GS genes in the AsA-GSH cycle during Zn toxicity, showing that EBL could regulate the regeneration of AsA and GSH at the transcriptional level. Taken together, the results of the present study suggest that exogenous EBL confers resistance against Zn-induced oxidative damage by enhancing the ASA-GSH cycle by up-regulating key gene expression and key enzyme activities.

Overexpression of PbDHAR2 from Pyrus sinkiangensis in Transgenic Tomato Confers Enhanced Tolerance to Salt and Chilling Stresses

Ascorbic acid (AsA) is a major antioxidant and redox buffer in plants. Dehydroascorbate reductase (DHAR; EC 1.8.5.1) catalyzes the conversion of dehydroascorbate (DHA) to AsA and is crucial for AsA regeneration. In this study, we developed transgenic tomato plants that overexpressed PbDHAR2 to investigate whether PbDHAR2 could limit the deleterious effects of salt and chilling stresses. These transgenic plants contained significantly higher AsA levels than the wild-type (WT) plants. Overexpression of PbDHAR2 increased the expression of the AsA-glutathione (GSH) cycle genes in transgenic lines under salt and chilling stresses. In addition, the transgenic lines subjected to salt and chilling stresses showed higher levels of antioxidant enzyme activity, lower malondialdehyde (MDA) levels, and higher chlorophyll contents than the WT. Thus, our results demonstrate that the regulation of PbDHAR2 during AsA regeneration contributes to enhanced salt and chilling tolerance in tomato.

Regulation of ascorbic acid metabolism by blue LED light irradiation in citrus juice sacs

In the present study, the effects of red and blue LED lights on the accumulation of ascorbic acid (AsA) were investigated in the juice sacs of three citrus varieties, Satsuma mandarin, Valencia orange, and Lisbon lemon. The results showed that the blue LED light treatment effectively increased the AsA content in the juice sacs of the three citrus varieties, whereas the red LED light treatment did not. By increasing the blue LED light intensity, the juice sacs of the three citrus varieties accumulated more AsA. Moreover, continuous irradiation with blue LED light was more effective than pulsed irradiation for increasing the AsA content in the juice sacs of the three citrus varieties. Gene expression results showed that the modulation of AsA accumulation by blue LED light was highly regulated at the transcription level. The up-regulation of AsA biosynthetic genes (CitVTC1, CitVTC2, CitVTC4, and CitGLDH), AsA regeneration genes (CitMDAR1, CitMDAR2, and CitDHAR) and two GSH-producing genes (CitGR and CitchGR) contributed to these increases in the AsA content in the three citrus varieties.