摘要 :
Ascorbate peroxidases (APXs) are heme peroxidases involved in the control of hydrogen peroxide levels and signal transduction pathways related to development and stress responses. Here, a total of 238 APX , 30 APX-related ( APX-R ...
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Ascorbate peroxidases (APXs) are heme peroxidases involved in the control of hydrogen peroxide levels and signal transduction pathways related to development and stress responses. Here, a total of 238 APX , 30 APX-related ( APX-R ), and 34 APX-like ( APX-L ) genes were identified from 24 species from the Poaceae family. Phylogenetic analysis of APX indicated five distinct clades, equivalent to cytosolic ( cAPX ), peroxisomal ( pAPX ), mitochondrial ( mitAPX ), stromal ( sAPX ), and thylakoidal ( tAPX ) isoforms. Duplication events contributed to the expansion of this family and the divergence times. Different from other APX isoforms, the emergence of Poaceae mitAPXs occurred independently after eudicot and monocot divergence. Our results showed that the constitutive silencing of mitAPX genes is not viable in rice plants, suggesting that these isoforms are essential for rice regeneration or development. We also obtained rice plants silenced individually to sAPX isoforms, demonstrating that, different to plants double silenced to both sAPX and tAPX or single silenced to tAPX previously obtained, these plants do not show changes in the total APX activity and hydrogen peroxide content in the shoot. Among rice plants silenced to different isoforms, plants silenced to cAPX showed a higher decrease in total APX activity and an increase in hydrogen peroxide levels. These results suggest that the cAPXs are the main isoforms responsible for regulating hydrogen peroxide levels in the cell, whereas in the chloroplast, this role is provided mainly by the tAPX isoform. In addition to broadening our understanding of the core components of the antioxidant defense in Poaceae species, the present study also provides a platform for their functional characterization.
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摘要 :
Ascorbate peroxidase (APX) is a class I heme peroxidase. It has two sites for binding of substrates. One is close to the gamma-heme edge and is used for oxidation of ascorbate; the other is at the delta-heme edge and is used for b...
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Ascorbate peroxidase (APX) is a class I heme peroxidase. It has two sites for binding of substrates. One is close to the gamma-heme edge and is used for oxidation of ascorbate; the other is at the delta-heme edge and is used for binding of aromatic substrates [Gumiero et al., (2010) Arch. Biochem. Biophys. 500, 13-20]. In this work, we have examined the structural factors that control binding at the delta-heme edge by replacement of Ala134 in APX with a proline residue that is more commonly found in other class II and III peroxidases. Kinetic data indicate that replacement of A1a134 by proline has only a small effect on the catalytic mechanism, or the oxidation of ascorbate or guaiacol. Chemical modification with phenylhydrazine indicates that heme accessibility close to the delta-heme edge is only minorly affected by the substitution. We conclude that the A134P mutation alone is not enough to substantially affect the reactivity of APX towards aromatic substrates bound at the delta-heme edge. The data are relevant to the recent application of APX (APEX) in cellular imaging.
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摘要 :
Adverse conditions often induce an increase in active oxygen species (AOS) such as hydrogen peroxide (H2O2). H2O2 is converted to water, and thus becomes detoxified by enzymes such as ascorbate peroxidase (APX; EC 1.11.1.11). APX ...
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Adverse conditions often induce an increase in active oxygen species (AOS) such as hydrogen peroxide (H2O2). H2O2 is converted to water, and thus becomes detoxified by enzymes such as ascorbate peroxidase (APX; EC 1.11.1.11). APX activity is estimated by the disappearance rate of ascorbic acid, which becomes oxidized. However, ascorbate is also a substrate of guaiacol peroxidase (POX; EC 1.11.1.7). PDX oxidizes phenols (including flavonoids), whereby ascorbate accepts an electron from phenoxyl or flavonoid radicals. Ascorbate becomes thereby converted to the monodehydroascorbate radical, which subsequently can become converted to dehydroascorbate. PDX isozymes therefore convert hydrogen peroxide to water and oxidize ascorbate, just as APX does. PDX activity is usually estimated by monitoring the formation of tetraguaiacol from guaiacol. This reaction is not specific, as some APX isozymes show rather high activity when using guaiacol or similar phenols as a substrate. It is concluded that APX activity can easily be confounded with PDX activity, and vice versa. Proper methods should be used to separate the two enzyme activities.
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Selenium (Se) is regarded as an antioxidant in animal and human nutrition, but its biological role in plants needs to be clarified. Plants vary considerably in their ability to tolerate Se, and their biochemical response to Se may...
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Selenium (Se) is regarded as an antioxidant in animal and human nutrition, but its biological role in plants needs to be clarified. Plants vary considerably in their ability to tolerate Se, and their biochemical response to Se may be affected by liming or P fertilization. Two greenhouse experiments were conducted with white clover (Trifolium repens L.) to evaluate Se accumulation, tolerance, and the antioxidant response at increasing selenite supply levels (from 0 to 60 g Se ha-p#) and the effect of lime and P on both the Se uptake and the antioxidant activity of plants treated with 0, 20 and 40 g Se ha-p#. Selenium concentration in plant tissues was increased by Se applications, and plant growth was reduced at Se supply levels above 20 g ha-p#. At shoot concentration up to 200 og kg-p# DW, Se promoted antioxidant ability by increasing the free radical scavenging activity and by inhibiting lipid peroxidation (TBARS), whereas above this level TBARS accumulation increased. Significant changes in the activities of peroxidase (POD) and ascorbate peroxidase (APX) enzymes were also observed as a consequence of the increase in shoot Se concentration. The application of lime and P improved the plant nutrition, which increased the dry matter yield and enhanced the plant's antioxidative system. Under different combinations of soil acidity and P fertilization a differential uptake of Se by the plant occurred. These factors appear to be responsible for beneficial or detrimental effects of Se in terms of lipid peroxidation of biological membranes and the activation of POD and APX in white clover.
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In this study, the protective role of organic selenium against salt stress on Hordeum vulgare L. and Triticum aestivum L. were determined. Seeds, treated with 0.004 M organic selenium in the pre-application, were germinated in env...
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In this study, the protective role of organic selenium against salt stress on Hordeum vulgare L. and Triticum aestivum L. were determined. Seeds, treated with 0.004 M organic selenium in the pre-application, were germinated in environments exposed to 50, 100 and 200 mM salt stress (NaCl), in comparison to seeds without selenium treatment. The effects of 0.004 M organic selenium on peroxidase, ascorbate peroxidase, and lipid peroxidation were investigated in both plants. An evaluation of their germination and enzyme activities showed that organic selenium resulted in salient improvement when compared to the plants directly exposed to salt stress. The present study suggests that selenium can play a protective role during salt stress by enhancing the antioxidant defense system.
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The interactions of heme peroxidase enzymes with their substrates have been studied for many years, but only in the last decade or so has structural information begun to appear. This review looks at crystal structures for a number...
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The interactions of heme peroxidase enzymes with their substrates have been studied for many years, but only in the last decade or so has structural information begun to appear. This review looks at crystal structures for a number of heme peroxidases in complex with a number of (mainly organic) substrates. It examines the nature and location of the binding interaction, and explores functional similarities and differences across the family.
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In the present study, interaction of 4 levels of manganese (Mn2+) (0, 100, 200, and 400mM) and 4 levels of pH (4.5, 5.5, 6.5, and 7.5) were investigated on some physiological parameters of Brassica oleracea L. after 30days of grow...
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In the present study, interaction of 4 levels of manganese (Mn2+) (0, 100, 200, and 400mM) and 4 levels of pH (4.5, 5.5, 6.5, and 7.5) were investigated on some physiological parameters of Brassica oleracea L. after 30days of growth (15days treatment) in hydroponic culture. Results showed that with an increase in manganese concentration, soluble carbohydrates, protein, and ascorbate contents also increased in shoots and roots of Brassica oleracea L. However, higher concentration of manganese reduced soluble carbohydrates, protein and ascorbate contents in the same plant. As manganese concentration increased, catalase activity in roots and shoots was also remarkably increased. Moreover, root peroxidase activity at pH 4.5 increased with an increase in manganese concentration and this increase was highest at pH 4.5 and 400mM manganese concentration.
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Four apple cultivars: 'Sampion, 'Jonagold', 'Gloster' and 'Elise' kept in common cold storage (1°C, 95-97% RH) were tested. The content of glutathione in the apple peel remained nearly at the same level during storage, while its ...
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Four apple cultivars: 'Sampion, 'Jonagold', 'Gloster' and 'Elise' kept in common cold storage (1°C, 95-97% RH) were tested. The content of glutathione in the apple peel remained nearly at the same level during storage, while its precursors (particularly y-glutamylcysteine) as well as glutathione reductase activity successively increased. The decrease of ascorbate content and ascorbate peroxidase activity was observed after 60 days of storage and then their levels significantly increased. Apple fleshand seeds exhibited nearly the same tendencies related to compounds mentioned above. The reduction level of both hydrophilic antioxidant in the peel was increasing with the longer time of storage. Activity of catalase significantly decreased during storage, but only in the apple peel. Out of all cultivars the highest antioxidant potential related to tested compounds and enzyme activity was noted for 'Sampion'. The great differences between apple peel, flesh and seed in antioxidant content were measured. On average, the content of ascorbate in the peel was from approximately 3 ('Gloster') to above 7-times higher ('Sampion') in comparison with the flesh. Seeds contained very small amounts of ascorbate, on average 49 ug g~(-1) f.m. As opposed to ascorbate, content of low molecular weight thiols and GR activity in the seeds were considerably higher in comparison with apple flesh and peel. The content of cysteine, y-glutamylcysteine, total glutathione and glutathione reductase activity was higher respectively by 125.7%, 80.0%, 158.8% and 28.3% in comparison with the peel, and by 198.0%, 80.0%, 466.1% and 377.8% in comparison with the flesh. Apple peel, then flesh and seeds exhibited the highest ascorbate peroxidase and catalase activity.
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H2O2 is reduced by an ascorbate-specific peroxidase (APX) in chloroplasts, generating the monodehydroascorbate (MDA) radical as the primary oxidation product. Using EPR spectroscopy we have measured the light-driven formation and ...
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H2O2 is reduced by an ascorbate-specific peroxidase (APX) in chloroplasts, generating the monodehydroascorbate (MDA) radical as the primary oxidation product. Using EPR spectroscopy we have measured the light-driven formation and decay of this species in thylakoids containing active APX. Illumination caused a rapid exponential rise in the steady-state MDA radical concentration in the absence of added electron acceptors other than O2. This increase was sensitive to KCN and catalase and was prevented by anaerobic conditions, demonstrating the requirement for APX activity and endogenously generated H2O2, i.e., the Mehler reaction. When the illumination was removed, a second, transient increase in the radical signal was observed, indicating that photoreduction of the MDA radical and O2 were occurring simultaneously in the light. This interpretation is also supported by the sigmoidal behavior of the chlorophyll dependence of MDA radical formation in illuminated thylakoids. Ferredoxin lowered the light-induced, steady-state MDA radical concentration, and is thus implicated as the physiological photoreductant for this Hill acceptor. In the absence of uncoupler, NADP+ prevented formation of the MDA radical by lowering the flux to molecular O2. However, in the presence of uncoupler (5 mM NH4Cl) this constraint was apparently overcome, i.e., net formation of the radical occurred. The EPR method represents a novel approach to investigating the interaction of O2 and ascorbate metabolism in chloroplasts under a variety of physiologically relevant conditions, to be applied in future studies of plant response to environmental stress.
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摘要 :
Selenium (Se) is regarded as an antioxidant in animal and human nutrition, but its biological role in plants needs to be clarified. Plants vary considerably in their ability to tolerate Se, and their biochemical response to Se may...
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Selenium (Se) is regarded as an antioxidant in animal and human nutrition, but its biological role in plants needs to be clarified. Plants vary considerably in their ability to tolerate Se, and their biochemical response to Se may be affected by liming or P fertilization. Two greenhouse experiments were conducted with white clover (Trifolium repens L.) to evaluate Se accumulation, tolerance, and the antioxidant response at increasing selenite supply levels (from 0 to 60 g Se ha−1) and the effect of lime and P on both the Se uptake and the antioxidant activity of plants treated with 0, 20 and 40 g Se ha−1. Selenium concentration in plant tissues was increased by Se applications, and plant growth was reduced at Se supply levels above 20 g ha−1. At shoot concentration up to 200 μg kg−1 DW, Se promoted antioxidant ability by increasing the free radical scavenging activity and by inhibiting lipid peroxidation (TBARS), whereas above this level TBARS accumulation increased. Significant changes in the activities of peroxidase (POD) and ascorbate peroxidase (APX) enzymes were also observed as a consequence of the increase in shoot Se concentration. The application of lime and P improved the plant nutrition, which increased the dry matter yield and enhanced the plant’s antioxidative system. Under different combinations of soil acidity and P fertilization a differential uptake of Se by the plant occurred. These factors appear to be responsible for beneficial or detrimental effects of Se in terms of lipid peroxidation of biological membranes and the activation of POD and APX in white clover.
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