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1.
The (C2H4+ H2(C2H2))/15N2 ratios of 15 clover- Rhizobium symbionts. soybean, and black medick symbionts were measured. Relative efficiency based on the C2H4 production and on 15N2 incorporation were compared, and in most symbionts there was little difference between the two measures of relative efficiency. Total measurable electron flux through nitrogenase during acetylene reduction and 15N2 incorporation were nearly equal for most symbionts studied. The relative efficiency and the (C2H4+ H2(C2H2))/15N2 ratio showed an inverse correlation. Use of this ratio appears preferable to use of the ratio of C2H2 reduction/N2 reduction. Some evolution of H2 was observed in the presence of C2H2.  相似文献   

2.
Cadmium is a toxic metal that produces disturbances in plant antioxidant defences giving rise to oxidative stress. The effect of this metal on H2O2 and O2·? production was studied in leaves from pea plants growth for 2 weeks with 50 µm Cd, by histochemistry with diaminobenzidine (DAB) and nitroblue tetrazolium (NBT), respectively. The subcellular localization of these reactive oxygen species (ROS) was studied by cytochemistry with CeCl3 and Mn/DAB staining for H2O2 and O2·?, respectively, followed by electron microscopy observation. In leaves from pea plants grown with 50 µm CdCl2 a rise of six times in the H2O2 content took place in comparison with control plants, and the accumulation of H2O2 was observed mainly in the plasma membrane of transfer, mesophyll and epidermal cells, as well as in the tonoplast of bundle sheath cells. In mesophyll cells a small accumulation of H2O2 was observed in mitochondria and peroxisomes. Experiments with inhibitors suggested that the main source of H2O2 could be a NADPH oxidase. The subcellular localization of O2·? production was demonstrated in the tonoplast of bundle sheath cells, and plasma membrane from mesophyll cells. The Cd‐induced production of the ROS, H2O2 and O2·?, could be attributed to the phytotoxic effect of Cd, but lower levels of ROS could function as signal molecules in the induction of defence genes against Cd toxicity. Treatment of leaves from Cd‐grown plants with different effectors and inhibitors showed that ROS production was regulated by different processes involving protein phosphatases, Ca2+ channels, and cGMP.  相似文献   

3.
4.
The quantitative relationship between C2H2 reduction, H2 evolution and 15N2 fixation was investigated in excised root nodules from pea plants ( Pisum sativum L. cv. Bodil) grown under controlled conditions. The C2H2/N2 conversion factor varied from 3.31 to 5.12 between the 32nd and the 67th day after planting. After correction for H2 evolution in air, the factor (C2H2-H2)/N2 decreased to values near the theoretical value 3, or in one case to a value significantly ( P < 0.05) below 3. The proportion of the total electron flow through nitrogenase, which is not wasted in H2 production but used for N2 reduction, is often stated as the relative efficiency (1-H2/C2H2). This factor varied significantly ( P < 0.05) during the growth period. The actual allocation of electrons to H2 and N2, expressed as the H2/N2 ratio, was independent of plant age, however. This discrepancy and the observation that the (C2H2-H2)/N2 conversion factor tended to be lower than 3, suggests that the C2H2reduction assay underestimates the total electron flow through nitrogenase.  相似文献   

5.
Generation of H2O2 in Brain Mitochondria   总被引:2,自引:2,他引:0  
Generation of H2O2 by rat brain mitochondria using succinate and glycerol-1-phosphate as substrates has been demonstrated. Earlier workers were unable to detect this activity in sucrose-Tris buffer. We found that this was due to a lag in the expression of activity in sucrose medium. Using phosphate buffer (50 mM), good rates are now obtained. Generation of H2O2 by rat brain mitochondria required the presence of antimycin A and was dependent on the substrates succinate and glycerol-1-phosphate. Low rates were obtained with NAD+-linked substrates and none with choline, glutamate, and NADH. The Km and Vmax values for H2O2 generation were considerably lower than the corresponding values for the respective dehydrogenase activity, measured by dye reduction. Oxygen-radical scavengers inhibited H2O2 generation, suggesting oxygen radical involvement. Depletion of ubiquinone from mitochondria resulted in loss of H2O2 generation. Reconstitution of such depleted particles with ubiquinone restored the capacity to generate H2O2 in a concentration-dependent manner. Levels of H2O2 production were found to be maximal in cerebellum. Brain mitochondria from rabbit, hamster, mouse, and guinea pig also have the capacity to generate H2O2 on oxidation of glycerol-1-phosphate.  相似文献   

6.
Abstract The regenerated shoots from sodium sulphate (Na2SO4) grown callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) were evaluated for Na2SO4 tolerance based on shoot proliferation and rooting in vitro, and seed germination in vivo in response to Na2SO4. An increase in Na2SO4 concentration resulted in significantly decreasing shoot fresh weight, number of shoots, shoot length and leaf size, and increasing per cent shoot dry weight of both control and Na2SO4-grown cultures. In rooting, shoots of Na2SO4-grown cultures exhibited the highest per cent rooting (85%) in the presence of 1% w/v Na2SO4. However, per cent rooting, root number per rooted cutting and root fresh weight decreased significantly with increasing Na2SO4 concentration when shoots were transferred to the medium in the absence of Na2SO4 for 4-monthly passages. Following acclimatization of the rooted shoots of Na2SO4-grown cultures, phenotypic variation was observed during growth and development. There were 13.2% sterile plants. Fertile plants were sorted into normal (N), tolerant (T), and sensitive (S) categories and the respective percentages of plants were 31.6, 44.7 and 10.5, based on per cent germination, germination velocity index and seedling survival to Na2SO4. The response of N, T and S types to Na2SO4 in subsequent shoot proliferation was similar to that of seed germination.  相似文献   

7.
The objective of this study was to investigate the behaviour of different legumes against salinity and water stress, thus trying to discover simultaneous adaptations to both stresses. The nitrogen fixation, transpiration, predawn leaf water potential, and stomatal response of Medicago sativa L. (cvs. Tierra de Campos and Aragon), Trifolium repens L. (cv. Aberystwyth S-184) and T. brachycalycinum Katzn. et Morley (= T. subterraneum L. cv. Clare) were compared at three levels of stress (0.05, 0.3 and 0.5 MPa of either NaCl or polyethylene glycol 6000) in nutrient solution. The plants were stressed for three days and then returned to control nutrient solution. The changes in the parameters analyzed were dependent on the proportion of stress treatments and the nature of the species, always being greater in plants from PEG than from NaCl solutions. Transfer of lucerne and subclover plants from NaCl at 0.05 MPa to a non-saline medium resulted in an increase of nitrogen fixation above the level of the non-salinized control plants, especially significant in lucerne. Analysis of possible inorganic impurities in commercial PEG suggest that such type of impurities are not responsible for the toxic effects reported. Plant damage resulting from PEG treatment was apparently due to penetrations of PEG (as determined qualitatively by using the tetraiodinebismuthic acid technique) or low-molecular organic impurities into the plant. – The results are discussed as part of the adaptation of the different species to salinity and water stress. The best performance was given by "Tierra de Campos".  相似文献   

8.
The hydrogen peroxide (H2O2) stress response in Enterococcus faecalis ATCC19433 was investigated. A 2·4 mmol l−1 H2O2 pretreatment conferred protection against a lethal concentration (45 mmol l−1) of this agent. The relatively high concentrations of H2O2 used for adaptation and challenge treatments in Ent. faecalis emphasised the strong resistance towards oxidative stress in this species. Various stresses (NaCl, heat, ethanol, acidity and alkalinity) induced weak or strong H2O2 cross-protection. This paper describes the involvement of protein synthesis in the active response to lethal dose of H2O2, in addition to the impressive enhancement of synthesis of five H2O2 stress proteins. Combined results suggest that these proteins might play an important role in the H2O2 tolerance response.  相似文献   

9.
Abstract Cell envelopes of Pseudomonas fluorescens , cytoplasmic membrane, peptidoglycan and outer membrane were obtained from a fractionation procedure and tested for their metal binding capacity. Isolated envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) were chemically modified and functional carboxyl groups transformed to electropositive amine groups, using carbodiimide ethylenediamine. Transformation of carboxyl groups was evaluated by measuring total amine groups in all fractions (modified or not). Using equilibrium dialysis and Scatchard plots for the data, we have established that isolated unmodified cell envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) possess at least two types of metal binding sites with different association constants ( K a and K 'a). Introduction of positive charges into the bacterial envelopes resulted in the disappearance of one type of metal binding site which had the highest association constant value for Ni2+, Cu2+ and Zn2+. All fractions, modified or not, always presented at least two types of binding sites with different association constants for Cd2+.  相似文献   

10.
Abstract A stainless steel cylinder filled with soil was flushed upstream with a H2/CO2/air mixture. The consequence was a strong enrichment of the aerobic, autotrophic hydrogen-oxidising microflora, which reached densities enabling them to oxidize 84.5 ml H2· dm−2· h−1 in the first 25-cm layer. H2 concentration profiles, hydrogen uptake activity and cell numbers correlated well with each other. Most of the organisms isolated were dinitrogen fixers. Thus, soils containing hydrogen-oxidising bacteria may act as a biological shield between H2-rich environments and air, and may be utilized as biofilters, e.g., in the waste-processing industry.  相似文献   

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