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Query: UNIPROT:P06889 (Mol)
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Ascorbic acid (vitamin C) is an abundant component of plants. It reaches a concentration of over 20 mM in chloroplasts and occurs in all cell compartments, including the cell wall. It has proposed functions in photosynthesis as an enzyme cofactor (including synthesis of ethylene, gibberellins and anthocyanins) and in control of cell growth. A biosynthetic pathway via GDP-mannose, GDP-L-galactose, L-galactose, and L-galactono-1,4-lactone has been proposed only recently and is supported by molecular genetic evidence from the ascorbate-deficient vtc 1 mutant of Arabidopsis thaliana. Other pathways via uronic acids could provide minor sources of ascorbate. Ascorbate, at least in some species, is a precursor of tartrate and oxalate. It has a major role in photosynthesis, acting in the Mehler peroxidase reaction with ascorbate peroxidase to regulate the redox state of photosynthetic electron carriers and as a cofactor for violaxanthin de-epoxidase, an enzyme involved in xanthophyll cycle-mediated photoprotection. The hypersensitivity of some of the vtc mutants to ozone and UV-B radiation, the rapid response of ascorbate peroxidase expression to (photo)-oxidative stress, and the properties of transgenic plants with altered ascorbate peroxidase activity all support an important antioxidative role for ascorbate. In relation to cell growth, ascorbate is a cofactor for prolyl hydroxylase that posttranslationally hydroxylates proline residues in cell wall hydroxyproline-rich glycoproteins required for cell division and expansion. Additionally, high ascorbate oxidase activity in the cell wall is correlated with areas of rapid cell expansion. It remains to be determined if this is a causal relationship and, if so, what is the mechanism. Identification of the biosynthetic pathway now opens the way to manipulating ascorbate biosynthesis in plants, and, along with the vtc mutants, this should contribute to a deeper understanding of the proposed functions of this multifaceted molecule.
Crit Rev Biochem Mol Biol 2000
PMID:Ascorbic acid in plants: biosynthesis and function. 1100 3

We used a variety of nitric oxide (NO) donors to demonstrate that NO inhibits the activities of tobacco catalase and ascorbate peroxidase (APX). This inhibition appears to be reversible because removal of the NO donor led to a significant recovery of enzymatic activity. In contrast, APX and catalase were irreversibly inhibited by peroxynitrite. The ability of NO and peroxynitrite to inhibit the two major H2O2-scavenging enzymes in plant cells suggests that NO may participate in redox signaling during the activation of defense responses following pathogen attack.
Mol Plant Microbe Interact 2000 Dec
PMID:Nitric oxide inhibition of tobacco catalase and ascorbate peroxidase. 1110 31

The mitochondria of legume root nodules are critical to sustain the energy-intensive process of nitrogen fixation. They also generate reactive oxygen species at high rates and thus require the protection of antioxidant enzymes and metabolites. We show here that highly purified mitochondria from bean nodules (Phaseolus vulgaris L. cv. Contender x Rhizobium leguminosarum bv. phaseoli strain 3622) contain ascorbate peroxidase primarily in the inner membrane (with lesser amounts detected occasionally in the matrix), guaiacol peroxidases in the outer membrane and matrix, and manganese superoxide dismutase (MnSOD) and an ascorbate-regenerating system in the matrix. This regenerating system relies on homoglutathione (instead of glutathione) and pyridine nucleotides as electron donors and involves the enzymes monodehydroascorbate reductase, dehydroascorbate reductase, and homoglutathione reductase. Homoglutathione is synthesized in the cytosol and taken up by the mitochondria and bacteroids. Although bacteroids synthesize glutathione, it is not exported to the plant in significant amounts. We propose a model for the detoxification of peroxides in nodule mitochondria in which membrane-bound ascorbate peroxidase scavenges the peroxide formed by the electron transport chain using ascorbate provided by L-galactono-1,4-lactone dehydrogenase in the inner membrane. The resulting monodehydroascorbate and dehydroascorbate can be recycled in the matrix or cytosol. In the matrix, the peroxides formed by oxidative reactions and by MnSOD may be scavenged by specific isozymes of guaiacol peroxidase, ascorbate peroxidase, and catalase.
Mol Plant Microbe Interact 2001 Oct
PMID:The antioxidants of legume nodule mitochondria. 1160 58

We analysed pathogenesis-related expression of genes, that are assumed to be involved in ubiquitous plant defence mechanisms like the oxidative burst, the hypersensitive cell death reaction (HR) and formation of localized cell wall appositions (papillae). We carried out comparative northern blot and RT-PCR studies with near-isogenic barley (Hordeum vulgareL. cv. Pallas) lines (NILs) resistant or susceptible to the powdery mildew fungus race A6 (Blumeria graminis f.sp. hordei, BghA6). The NILs carrying one of the R-genes Mla12, Mlg or the mlo mutant allele mlo5 arrest fungal development by cell wall appositions (mlo5) or a HR (Mla12) or both (Mlg). Expression of an aspartate protease gene, an ascorbate peroxidase gene and a newly identified cysteine protease gene was up-regulated after inoculation with BghA6, whereas the constitutive expression-level of a BAS gene, that encodes an alkyl hydroperoxide reductase, was reduced. Expression of a newly identified barley homologue of a mammalian cell death regulator, Bax inhibitor 1, was enhanced after powdery mildew inoculation. An oxalate oxidase-like protein was stronger expressed in NILS expressing penetration resistance. A so far unknown gene that putatively encodes the large subunit of a superoxide generating NADPH oxidases was constitutively expressed in barley leaves and its expression pattern did not change after inoculation. A newly identified barley Rac1 homologue was expressed constitutively, such as the functionally linked NADPH oxidase gene. Gene expression patterns are discussed with regard to defence mechanisms and signal transduction.
Plant Mol Biol 2001 Dec
PMID:Differential expression of putative cell death regulator genes in near-isogenic, resistant and susceptible barley lines during interaction with the powdery mildew fungus. 1178 35

Tolerance against oxidative stress generated by high light intensities or the catalase inhibitor aminotriazole (AT) was induced in intact tobacco plants by spraying them with hydrogen peroxide (H2O2). Stress tolerance was concomitant with an enhanced antioxidant status as reflected by higher activity and/or protein levels of catalase, ascorbate peroxidase, guaiacol peroxidases, and glutathione peroxidase, as well as an increased glutathione pool. The induced stress tolerance was dependent on the dose of H2O2 applied. Moderate doses of H2O2 enhanced the antioxidant status and induced stress tolerance, while higher concentrations caused oxidative stress and symptoms resembling a hypersensitive response. In stress-tolerant plants, induction of catalase was 1.5-fold, that of ascorbate peroxidase and glutathione peroxidase was 2-fold, and that of guaiacol peroxidases was approximately 3-fold. Stress resistance was monitored by measuring levels of malondialdehyde, an indicator of lipid peroxidation. The levels of malondialdehyde in all H2O2-treated plants exposed to subsequent high light or AT stress were similar to those of unstressed plants, whereas lipid peroxidation in H2O2-untreated plants stressed with either high light or AT was 1.5- or 2-fold higher, respectively. Although all stress factors caused increases in the levels of reduced glutathione, its levels were much higher in all H2O2-pretreated plants. Moreover, significant accumulation of oxidized glutathione was observed only in plants that were not pretreated with H2O2. Extending the AT stress period from 1 to 7 days resulted in death of tobacco plants that were not pretreated with H2O2, while all H2O2-pretreated plants remained little affected by the prolonged treatment. Thus, activation of the plant antioxidant system by H2O2 plays an important role in the induced tolerance against oxidative stress.
Cell Mol Life Sci 2002 Apr
PMID:Hydrogen peroxide protects tobacco from oxidative stress by inducing a set of antioxidant enzymes. 1202 76

Excess of free iron is thought to harm plant cells by enhancing the intracellular production of reactive oxygen intermediates (ROI). Cytosolic ascorbate peroxidase (cAPX) is an iron-containing, ROI-detoxifying enzyme induced in response to iron overload or oxidative stress. We studied the expression of cAPX in leaves of de-rooted bean plants in response to iron overload. cAPX expression, i.e., mRNA and protein, was rapidly induced in response to iron overload. This induction correlated with the increase in iron content in leaves and occurred in the light as well as in the dark. Reduced glutathione (GSH), which plays an important role in activating the ROI signal transduction pathway as well as in ROI detoxification, was found to enhance the induction of APX mRNA by iron. To determine whether cAPX induction during iron overload was due to an increase in the amount of free iron, which serves as a co-factor for cAPX synthesis, or due to iron-mediated increase in ROI production, we tested the expression of APX in leaves under low oxygen pressure. This treatment, which suppresses the formation of ROI, completely abolished the induction of cAPX mRNA during iron overload, without affecting the rate of iron uptake by plants. Taken together, our results suggest that high intracellular levels of free iron in plants lead to the enhanced production of ROI, which in turn induces the expression of cAPX, possibly using GSH as an intermediate signal. We further show, using cAPX-antisense transgenic plants, that cAPX expression is essential to prevent iron-mediated tissue damage in tobacco.
Plant Mol Biol 2002 Jul
PMID:Reactive oxygen intermediates and glutathione regulate the expression of cytosolic ascorbate peroxidase during iron-mediated oxidative stress in bean. 1209 Jun 19

The primary target for light-chilling stress in chilling-sensitive cucumber leaves is the chloroplast Cu,Zn-Superoxide dismutase, followed by subsequent inactivation of the photosystem (PS) I by reactive oxygen species (ROS). To test this hypothesis, two rice cultivars that were different in their ecological origins (a chilling-resistant Stejaree 45 and a chilling-sensitive Milyang 23) were evaluated with respect to photosynthetic properties, the ROS scavenging system, and expression of genes that are involved in sucrose synthesis and allocation upon the light-chilling stress. As expected, when the leaves were exposed to various low temperatures with illumination (150 micromol m(-2)s(-1)) for 6 h, the leaf photosynthesis of Milyang 23 decreased faster than that of Stejaree 45. The light-chilling induced differential photoinhibition of photosynthesis between the two cultivars was caused by the photoin-activation of PSII but not of PSI, since the potential quantum yield of PSII followed a similar trend to the changes in photosynthetic rates. The activities of the two chloroplastic antioxidant enzymes (superoxide dismutase and ascorbate peroxidase) that are known to be sensitive to oxidative stress were barely affected by the light-chilling treatments. Among various genes in sucrose metabolism (such as cytosolic FBPase, SPS, SUT, SuSy, and AGPase), the transcript levels of SuSy in Milyang 23 were significantly decreased by light-chilling stress compared to that of Stejaree 45. Based on these results, we propose that PSII, not PSI, is the sensitive site for light-chilling stress in chilling-sensitive rice. The extent of PSII photoinhibition depends on its capacity for the photochemical utilization of light.
Mol Cells 2002 Jun 30
PMID:Differential susceptibility of photosynthesis to light-chilling stress in rice (Oryza sativa l.) depends on the capacity for photochemical dissipation of light. 1213 82

Capsicum annuum L. is infected by a number of viruses, including the tobacco mosaic virus (TMV). To study the defense-related genes that are induced by TMV in hot peppers, the pepper plant, which is susceptible to P1.2 but resistant to the P0 pathotype of TMV, was inoculated with TMV-P0. Differential screening isolated the genes that were specifically up- or down-regulated during the hypersensitive response (HR). The CaAPX1 cDNA clone that putatively encodes a polypeptide of cytosolic ascorbate peroxidase was selected as an up-regulated gene. It was isolated for further study. The full-length cDNA for CaAPX1, which is 972 bp long, contained the open-reading frame of 250-amino acid residues. A genomic Southern blot analysis showed that there were only limited copies of the CaAPX1 gene in the hot pepper genome. In hot pepper cv. Bugang, which is resistant to TMV-P0 and susceptible to TMV-P1.2, the CaAPX1 gene transcript was accumulated by TMV-P0, but not by TMV-P1.2 inoculation. CaAPX1 transcripts began to accumulate 24 h post-inoculation of TMV-P0, and increased gradually until 96 h. To investigate whether each transcript is induced by other stimuli, the plants were treated with various chemicals and wounding. A striking induction of the CaAPX1 transcript was observed at 2 h. It subsided 12 h after salicylic acid (SA), ethephon, and methyl jasmonate (MeJA) treatments. The response of the gene upon other pathogen infection was also examined by a bacterial pathogen (Xanthomonas campestris pv. vesicatoria race 3) inoculation. The CaAPX1 gene was induced in a hot pepper (C. annuum cv. ECW 20R) that was resistant to this bacterial pathogen, but not in a susceptible hot pepper (C. annuum cv. ECW). These results suggest the possible role(s) for the CaAPX1 gene in plant defense against viral and bacterial pathogen.
Mol Cells 2002 Aug 31
PMID:A hot pepper cDNA encoding ascorbate peroxidase is induced during the incompatible interaction with virus and bacteria. 2345 41

Pepper ascorbate peroxidase-like (CAPOA1), thioredoxin peroxidase-like (CAPOT1), and peroxidase-like (CAPO1) clones were isolated from pepper leaves inoculated with avirulent strain Bv5-4a of Xanthomonas campestris pv. vesicatoria. CAPOA1, CAPOT1, and CAPO1 mRNA disappeared 18 to 30 h after the bacterial infection when the hypersensitive response (HR) was visible. In contrast, peroxidase activity reached a peak at 18 h after infection and then declined at 24 and 30 h when H2O2 accumulation level was maximal. These results suggest that the striking accumulation of H2O2 and strong decrease in peroxidase activity during the programmed cell death may be due to the strong suppression of CAPOA1, CAPOT1, and CAPO1 gene expression. Infection by Phytophthora capsici or Colletotricum gloeosporioides also induced the expression of the three putative peroxidase genes in pepper tissues. CAPOA1 mRNAs were in situ localized in phloem areas of vascular bundles in pepper tissues infected by Colletotricum. coccodes, P. capsici, or C. gloeosporioides. Exogenous treatment with H2O2 strongly induced the CAPOA1 and CAPOT1 transcription 1 h after treatment, while the CAPO1 transcripts accumulated 12 h after H2O2 treatment. We suggest that pepper ascorbate peroxidase and thioredoxin peroxidase genes may function as regulators of H2O2 level and total peroxidase activity in the oxidative burst during the HR to incompatible pathogen interaction in pepper plant.
Mol Plant Microbe Interact 2003 Mar
PMID:Expression of peroxidase-like genes, H2O2 production, and peroxidase activity during the hypersensitive response to Xanthomonas campestris pv. vesicatoria in Capsicum annuum. 1265 Apr 51

Studies on the possible interference of colchicine and H2O2 with the activity of some antioxidant enzymes were carried out on Arabidopsis thaliana v. Columbia grown in Murashige and Skooge nutrient medium. Measurements of superoxide dismutase (SOD), guaiacol peroxidase (POX), ascorbate peroxidase (APX) and catalase (CAT) activities were conducted spectrophotometrically. In the presence of colchicine, SOD activity increased, while CAT, APX and POX activities decreased. Inhibitory H2O2 effects on the activity of the enzymes were found. Colchicine pre-treatment resulted in an increase in CAT activity and a further increase in SOD activity in plants treated with H2O2.
Cell Mol Biol Lett 2003
PMID:The activity of antioxidant enzymes in Arabidopsis thaliana exposed to colchicine and H2O2. 1294 16


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