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  • Articles  (5)
  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect in vivo of salt stress on the activated oxygen metabolism of mitochondria, was studied in leaves from two NaCl-treated cultivars of Pisum sativum L. with different sensitivity to NaCl. In mitochondria from NaCl-sensitive plants, salinity brought about a significant decrease of Mn-SOD (EC 1. 15. 1. 1) Cu, Zn-SOD I (EC 1. 15. 1. 1) and fumarase (EC 4. 2. 1. 2) activities. Conversely, in salt-tolerant plants NaCl treatment produced an increase in the mitochondrial Mn-SOD activity and, to a lesser extent, in fumarase activity. In mitochondria from both salt-treated cultivars, the internal H2O2 concentration remained unchanged. The NADH- and succinate-dependent generation of O2.−radicals by submitochondrial particles and the lipid peroxidation of mitochondrial membranes, increased as a result of salt treatment, and these changes were higher in NaCl-sensitive than in NaCl-tolerant plants. Accordingly, the enhanced rates of superoxide production by mitochondria from salt-sensitive plants were concomitant with a strong decrease in the mitochondrial Mn-SOD activity, whereas NaCl-tolerant plants appear to have a protection mechanism against salt-induced increased O2.− production by means of the induction of the mitochondrial Mn-SOD activity. These results indicate that in the subcellular toxicity of NaCl in pea plants, at the level of mitochondria, an oxidative stress mechanism mediated by superoxide radicals is involved, and also imply a function for mitochondrial Mn-SOD in the molecular mechanisms of plant tolerance to NaCl.
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 104 (1998), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Peroxisomes are subcellular organelles with an essentially oxidative type of metabolism. The presence in these organelles of superoxide dismutases and the generation of superoxide radicals (O2•−) was first demonstrated in plant tissues and in recent years different experimental evidence has suggested the existence of cellular functions related to activated oxygen species. Some of these functions are analyzed in this work.In purified intact peroxisomes from pea (Pisum sativum L.) leaves, xanthine oxidase and urate oxidase were found to be present. The occurrence and the level of the metabolites xanthine, hypoxanthine, uric acid, and allantoin were studied in extracts of pea leaf peroxisomes by HPLC. Xanthine, uric acid, and allantoin were detected in peroxisomes. These results suggest a cellular role for leaf peroxisomes in the catabolism of purines.In peroxisomal membranes, 3 polypeptides (PMPs) with molecular masses of 18, 29 and 32 kDa, respectively, have been shown to generate superoxide radicals. These PMPs were purified from pea leaf peroxisomal membranes and characterized. While the 18- and 32-kDa PMPs use NADH as electron donor for O2•− production, the 29-kDa PMP was clearly dependent on NADPH.Very recently, the occurrence in pea leaf peroxisomes of all the enzymes of the ascorbate-glutathione cycle has been demonstrated. NADPH is required for the glutathione reductase activity of the cycle and this implies the reduction of NADP+ to NADPH. This recycling function could be carried out by the NADP-dependent glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), and isocitrate dehydrogenase (ICDH). These 3 dehydrogenases have been demonstrated to be present in the matrix of pea leaf peroxisomes.The catabolism of purines, the superoxide-generating PMPs, the ascorbate-glutathione cycle, and the dehydrogenase-mediated recycling of NADPH, are activated oxygen roles of leaf peroxisomes that add to other functions previously known for peroxisomes from eukaryotic cells.
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  • 3
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The peroxisomal manganese superoxide dismutase (perMn-SOD; EC 1.15.1.1) was purified to homogeneity for the first time from peroxisomes of pea (Pisum sativum L.) leaves. Peroxisomes were isolated from pea leaves by sucrose density-gradient centrifugation, and then perMn-SOD was purified from these organelles by two purification steps involving anion-exchange and gel-filtration fast protein liquid chromatography. Pure peroxisomal Mn-SOD had a specific activity of 2 880 units per mg protein and was purified 3 000-fold, with a yield of about 7 µg enzyme per kg pea leaves. The relative molecular mass determined for perMn-SOD was 92 000, and it was composed of four equal subunits of 27 kDa. Ultraviolet and visible absorption spectra of the enzyme showed two absorption maxima at 278 and 483 nm, respectively, and two shoulders at 290 and 542 nm. By isoelectric focusing (pH 5-7), an isoelectric point of 5.53 was determined for perMn-SOD. In immunoblot assays, purified Mn-SOD was recognized by a polyclonal antibody against mitochondrial Mn-SOD (mitMn-SOD) from pea leaves. The amino acid sequence of the N-terminal region of the purified peroxisomal enzyme was determined. A 100% identity was found with the mitMn-SOD from pea leaves, and high identities were also found with Mn-SODs from other plant species.
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 104 (1998), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Gametophytic tissues of plants are an area largely neglected in the broad literature on free radical processes in plants. In order to study the mechanisms of protection against oxidative stress in pollen, the presence of the key antioxidative enzyme superoxide dismutase (SOD; EC 1.15.1.1) was investigated. Crude extracts of olive tree (Olea europaea L.) pollen were subjected to native PAGE in 10% polyacrylamide gels. The SOD activity staining of gels showed the presence of four isoenzymes. All the SODS were completely inhibited by 2 mM KCN and 5 mM H2O2, and therefore belong to the family of CuZn-SODS. Isoelectric focusing (pH 3.5-7) of crude extracts and further detection of SOD activity allowed determination of isoelectric points for the four isoforms, namely 4.60, 4.78, 5.08 and 5.22. The cross-reactivity of pollen extracts with a polyclonal antibody to cytosolic CuZn-SOD from spinach leaves was assayed by western blotting. After SDS-PAGE and immunoblotting, a major polypeptide band of about 16.5 kDa was detected, which is characteristic of the subunit of most CuZn-SODS. Immunocytochemical studies at TEM level using the same antiserum showed that CuZn-SOD was localized in the cytoplasm of both vegetative and generative cells, and also in material adhered to the pollen wall. The olive pollen CuZn-SODS could function in the protection against oxidative stress during pollen development.
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  • 5
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The subcellular localization of superoxide dismutase (SOD; EC. 1.15.1.1) was studied in leaves of two ureide-producing leguminous plants (Phaseolus vulgaris L. cv. Contender and Vigna unguiculata [L.] Walp). In leaves of Vigna and Phaseolus, three superoxide dismutases were found, an Mn-SOD and two Cu, Zn-containing SODs (I and II). Chloroplasts, mitochondria, and peroxisomes were purified by differential and density-gradient centrifugation using either Percoll or sucrose gradients. The yields obtained in intact chloroplasts and peroxisomes from Vigna were considerably higher than those achieved for Phaseolus. Purified chloroplasts only contained the Cu, Zn-SOD II isozyme, but in mitochondria both Mn-SOD and Cu, Zn-SOD I isozymes were present. In purified peroxisomes no SOD activity was detected. The absence of SOD activity in leaf peroxisomes from Vigna contrasts with results reported for the amide-metabolizing legume Pisum sativum L. where the occurrence of Mn-SOD was demonstrated in leaf peroxisomes (del Río et al. 1983. Planta 158: 216–224; Sandalio et al. 1987. Plant Sci. 51: 1–8). This suggests that in leaf peroxisomes from Vigna plants the generation of O2- radicals under normal conditions probably does not take place.
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