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1.
Occurrence and activity of the hydrogen uptake enzyme were studied in root nodule homogenates made from plants of Alnus incana (L.) Moench collected from field sites in the northern part of Sweden. Nitrogenase (EC 1.7.99.2) activity (estimated by acetylene reduction) and hydrogen evolution were studied in excised nodules. All Frankia sources showed acetylene reduction activity, and possessed a hydrogen uptake system. Hydrogen uptake in nodule homogenates from the Frankia sources measured at 23.8 μM H2 ranged from 0.04 to 5.0 μmol H2 (g fresh weight nodule)−1 h−1. The H2 uptake capacity of nodule homogenates from one of the Frankia sources was almost 8 times higher than the hydrogen evolution from nitrogenase, both expressed on a nodule fresh weight basis. Frankia sources from field sites 6 and 11 showed Km for H2 of 13.0 and 23.6 μM H2, respectively. This indicates similarities in the hydrogen uptake enzymes in the two Frankia sources. It is concluded that hydrogen uptake is a common characteristic in Frankia.  相似文献   

2.
Actinorhizal nodules do not usually evolve H2 due to the action of an uptake hydrogenase. We have found that nodules of several Frankia symbioses evolved large amounts of H2 gas when returned to air following exposure to 10 kPa C2HT2 during an acetylene reduction assay. Increased H2 evolution in air persisted for several days when intact root systems of Alnus incana (L.) Moench (inoculated with Frankia UGL 011101) were treated with 10 kPa C.H2 for 1 h. Full recovery of uptake hydrogenase activity required 4 to 8 days. Studies with crude homogenates of nodules of the same plants showed that hydrogenase (measured amperometrically with phenazine metho-sulfate as electron acceptor) was directly affected, since activity in treated nodules was only 10% of that in untreated nodules. A survey of actinorhizal symbioses revealed variation in the effect of an acetylene reduction assay on hydrogen metabolism. Nodules of three species, including Alnus rubra Bong, inoculated with Frankia HFPArD. showed complete inactivation of hydrogenase. H2 evolution in air was 25% of the C2H2 reduction rate and H, evolution in Ar/O2 was equal to the QH2 reduction rate. Two symbioses, Ceanothus americanus L. (soil inoculant) and Batista glomerata Baill. (soil inoculant) showed no change following an acetylene reduction assay. A third group of symbioses showed an intermediate response.  相似文献   

3.
Nitrogenase activity, hydrogen evolution, biomass production and nodulation were studied in threeCasuarina species,C. equisetifolia Forst.,C. glauca Sieber ex Spreng andC. obesa Miq., either inoculated with a crushed nodule inoculum prepared fromC. glauca nodules or inoculated with the pure cultureHFP CcI3. Nodulation was also studied inC. cristata Miq. inoculated with the above mentionedFrankia sources. C. equisetifolia, C. glauca andC. obesa were nodulated when inoculated with both of theFrankia inoculum, whileC. cristata was very poorly nodulated. Nitrogenase activity per plant and on a nodule dry weight basis was significantly highest inC. glauca inoculated withC. glauca inoculum after 150 days from planting. This difference decreased and at 217 days from planting there was no significant difference between the symbioses, except forC. obesa inoculated withC. glauca inoculum which showed the significantly lowest nitrogenase activity. After 150 days from planting relative efficiency of nitrogenase was lowest inC. equisetifolia inoculated withHFP CcI3 and inC. equisetifolia inoculated withC. glauca inoculum. Biomass production was similar inC. glauca inoculated withC. glauca inoculum, inC. equisetifolia inoculated withHFP CcI3 and inC. obesa inoculated withHFP CcI3 at the final harvest. The data presented here show that there is a strong interrelationship between host plant and endobiont. This interrelationship is of considerable importance when introducing Casuarina symbioses for production of fuel wood.  相似文献   

4.
Three different strains of Frankia , the pure cultures AvcI1 and CpI1 and a local strain (crushed nodule inoculum), were compared in symbiosis with one clone of Alnus incana (L.) Moench. Hydrogen metabolism, nitrogenase (EC 1.7.99.2) activity and relative efficiency of nitrogenase were studied as well as growth and nitrogen content of the plants. The local Frankia strain showed no measurable hydrogen uptake but high H2-evolution. No H2-evolution was detected in Frankia AvcI1 because of its hydrogenase activity. CpI1 also had hydrogenase, although only a very small H2-evolution was detected at the end of the growth period. Hydrogenase activity was detected both in pure cultures and nodule homogenates of CpI1 and AvcI1. Growth, biomass production and nitrogen content were highest in alders inoculated with Frankia AvcI1 while the lowest values were found for alders living in symbiosis with the local Frankia strain. The presence of hydrogenase in Frankia seemed to be benefical for growth and biomass production in the alders. However, the strains also differed with respect to spore formation. The local strain, but not AvcI1 and CpI1, formed spores in the root nodules.  相似文献   

5.
Soybean [ Glycine max (L.) Merr. cv. Hobbit] plants were inoculated with a HUP− strain of Bradyrhizobium japonicum (Nitragin 61A118) and either colonized by the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol & Gerd.) Gerd. and Trappe or fertilized with KH2PO4 (nonVAM). They were grown for 50 days in a growth chamber and harvested over a 4-day drought period during which available soil water decreased to 0. Nodule P concentrations and P-use efficiency declined linearly with soil and root water content during the harvest period in both VAM and nonVAM plants. Nitrogenase activity, estimated from H2 evolution and C2H2 reduction data, was also a linear function of declining nodule P concentrations and CO2-exchange rates and showed simular patterns in both treatments. Hydrogen evolution and the relative efficiency of N2 fixation, on the other hand, reacted differently to increasing drought in VAM and nonVAM plants. Differences in the responses of nodule activity in VAM and nonVAM plants to drought are interpreted in terms of demand for nodule P and carbohydrates and of the effects of dehydration on O2 diffusion through nodule tissue.  相似文献   

6.
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   

7.
The effects of short-term NaCl-salinity on nodules of soybean ( Glycine max L. cv. Kingsoy) were studied on hydroponically-grown plants. Both acetylene reducing activity (ARA) and nodule respiration (O2 uptake and CO2 evolution) were immediately inhibited, and the stimulation of them by rising the external partial pressure of O2 (pO2) was diminished by the application of 0.1 M NaCl in the nutrient solution. The permeability of the nodule to O2 diffusion, estimated by O2 consumption or CO2 evolution, was significantly lower in the stressed nodules than in the cootrol ones. The respiratory quotient of intact nodules and the ethanol production of excised nodules were increased by low pO2 and by salt stress. These data confirm that in salt-stressed soybean nodules, O2 availability is reduced and fermentative pathways are stimulated.  相似文献   

8.
Twenty-five isolates of urd bean ( Vigna mungo ) Rhizobium were tested for the presence of an H2-uptake system using triphenyl tetrazolium chloride reduction as the screening procedure. The isolates which reduced the dye rapidly at early stages of growth were found to recycle H2 both in culture as well as in nodules. H2-uptake positive, H2-uptake negative strains and H2-uptake negative mutants were compared on the basis of their effect on dry matter accumulation and N2-fixation. Greenhouse experiments have shown the beneficial effect of the H2-uptake positive system in nodules on N2-fixation. Plants inoculated with H2-uptake positive strains produced higher N content and dry matter over the plants inoculated with H2-uptake negative strains.  相似文献   

9.
Nitrogenase (N2ase; EC 1.18.6.1) activity (H2 evolution) and root respiration (CO2 evolution) were measured under either N2:O2 or Ar:O2 gas mixtures in intact nodulated roots from white clover ( Trifolium repens L.) plants grown either as spaced or as dense stands. The short-term nitrate (5 m M ) inhibition of N2-fixation was promoted by competition for light between clover shoots, which reduced CO2 net assimilation rate. Oxygen-diffusion permeability of the nodule declined during nitrate treatment but after nitrate removal from the liquid medium its recovery parallelled that of nitrogenase activity. Rhizosphere pO2 was increased from 20 to 80 kPa under N2:O2. A simple mono-exponential model, fitted to the nodule permeability response to pO2, indicated NO3 induced changes in minimum and maximum nodule O2-diffusion permeability. Peak H2 production rates at 80 kPa O2 and in Ar:O2 were close to the pre-decline rates at 20 kPa O2. At the end of the nitrate treatment, this O2-induced recovery in nitrogenase activity reached 71 and 82%; for clover plants from spaced and dense stands, respectively. The respective roles of oxygen diffusion and phloem supply for the short-term inhibition of nitrogenase activity in nitrate-treated clovers are discussed.  相似文献   

10.
Abstract Hydrogen consumption was measured in hot geothermal water from two ponds of the San Federigo solfatara, Tuscany, Italy, where emanation gases contained approx. 4% H2. H2 consumption was completely inhibited by NaOH and partially by HgCl2 indicating microbial utilization. Aerobic and anaerobic H2 consumption activities coexisted in the same water with aerobic activity being higher in one pond and anaerobic activity in the other. The kinetics of H2 consumption were consistent with those of 'Knallgas', methanogenic or sulfidogenic bacteria.  相似文献   

11.
Aims:  Development of the resazurin microplate method (RMM) as a novel test system for the evaluation of the antimicrobial activity of antiseptics and disinfectants. The validated RMM was subsequently applied for the evaluation of hydrogen peroxide (H2O2) and stabilized H2O2 combination products.
Methods and Results:  The European Committee for Standardization prescribes the plate count challenge test (PCCT) for antiseptic and disinfectant efficacy testing. This protocol was adapted to a microplate-based assay, using resazurin as viability indicator. The RMM was as accurate as the PCCT, had an identical detection limit and showed high intermediate precision. Using the validated RMM, it was shown that H2O2 combined with silver possessed a higher bactericidal and fungicidal activity compared to native H2O2 with and without glycerol.
Conclusions:  Validation showed that the RMM may replace the PCCT. When applying the RMM, H2O2 combined with silver was clearly a more potent disinfectant compared to H2O2 in killing bacteria and fungi.
Significance and Impact of the Study:  The RMM is easier to use for antimicrobial efficacy testing of antiseptics and disinfectants. As the RMM is in accordance with the norms of the European Committee for Standardization, it may become a more cost-effective alternative to the more laborious PCCT reference method. H2O2 with silver may replace native H2O2 to increase overall disinfection efficiency.  相似文献   

12.
Abstract: Hydrogen peroxide (H2O2) is produced from several sources in brain and may be involved in neurodegeneration and second messenger signaling. Little is known about the effects of H2O2 on transmitter storage in brain synaptic vesicles. Neurotransmitter uptake into synaptic vesicles is driven by an electrochemical proton gradient generated by the vacuolar H+-ATPase (V-ATPase) in the vesicle membrane. We report here that the V-ATPase in bovine brain synaptic vesicles is highly sensitive to inhibition by micromolar concentrations of H2O2. Glutamate uptake by the vesicles is also inhibited, very likely as a secondary consequence of ATPase inactivation. Dithiothreitol or reduced glutathione reverse H2O2-induced inhibition of the V-ATPase, and ATP or GTP partially protect the ATPase from inhibition by H2O2. These and other results suggest that the mechanism of inhibition of the V-ATPase by H2O2 involves oxidation of a reactive cysteine sulfhydryl group in the ATP binding site. Inhibition of V-ATPase activity would decrease the amount of transmitter stored in synaptic vesicles and thus down-regulate transmitter release during episodes of oxidative stress or in response to second messenger signaling.  相似文献   

13.
Aims:  The aim of this study was to enrich, characterize and identify strict anaerobic extreme thermophilic hydrogen (H2) producers from digested household solid wastes.
Methods and Results:  A strict anaerobic extreme thermophilic H2 producing bacterial culture was enriched from a lab-scale digester treating household wastes at 70°C. The enriched mixed culture consisted of two rod-shaped bacterial members growing at an optimal temperature of 80°C and an optimal pH 8·1. The culture was able to utilize glucose, galactose, mannose, xylose, arabinose, maltose, sucrose, pyruvate and glycerol as carbon sources. Growth on glucose produced acetate, H2 and carbon dioxide. Maximal H2 production rate on glucose was 1·1 mmol l−1 h−1 with a maximum H2 yield of 1·9 mole H2 per mole glucose. 16S ribosomal DNA clone library analyses showed that the culture members were phylogenetically affiliated to the genera Bacillus and Clostridium. Relative abundance of the culture members, assessed by fluorescence in situ hybridization, were 87 ± 5% and 13 ± 5% for Bacillus and Clostridium , respectively.
Conclusions:  An extreme thermophilic, strict anaerobic, mixed microbial culture with H2-producing potential was enriched from digested household wastes.
Significance and Impact of the Study:  This study provided a culture with a potential to be applied in reactor systems for extreme thermophilic H2 production from complex organic wastes.  相似文献   

14.
Soils contain two different activities for oxidation of hydrogen   总被引:1,自引:0,他引:1  
Abstract Hydrogen oxidation rates were measured in a neutral compost soil and an acidic sandy loam at H2 mixing ratios of 0.01 to 5000 ppmv. The kinetics were biphasic showing two different K m values for H2, one at about 10–40 nM dissolved H2, the other at about 1.2–1.4 μM H2. The low- K m activity was less sensitive to chloroform fumigation than the high- K m activity. If sterile soil was amended with Paracoccus denitrificans or a H2-oxidizing strain isolated from compost soil, it exhibited only a high- K m (0.7–0.9 μM) activity. It also failed to utilize H2 mixing ratios below a threshold of 1.6–3.0 ppmv H2 (160–300 mPa). A similar result was obtained when fresh soil samples were suspended in water, and H2 oxidation was determined from the decrease of dissolved H2. However, H2 was again utilized to mixing ratios lower than 0.05 ppmv, if the supernatant of the soil suspension or the settled soil particles were dried onto sterile soil or purified quarz sand. Obviously, soils contain two different activities for oxidation of H2: (1) a high- K m, high-threshold activity which apparently is due to aerobic H2-oxidizing bacteria, and (2) a low- K m, low-threshold activity whose origin is unknown but presumably is due to soil enzymes.  相似文献   

15.
Photosynthetic oxygen evolution within Sesbania rostrata stem nodules   总被引:1,自引:0,他引:1  
The tropical wetland legume, Sesbania rostrata Brem. forms N2-fixing nodules along its stem and on its roots after infection by Azorhizobium caulinodans . The N2-fixing tissue is surrounded by a cortex of uninfected cells which, in the stem nodules (but not the root nodules), contain chloroplasts. The photosynthetic competence of these chloroplasts was assessed through a novel technique involving image analysis of chlorophyll a fluorescence. Calculation of the quantum efficiency of photosystem II (PS II) photochemistry from these images indicated that most of the chloroplasts with potential for non-cyclic photosynthetic electron transport were concentrated within the mid- and inner-cortex, close to the edge of the N2-fixing tissue. PS II activity in the cortical cells was confirmed in vivo using O2-specific microelectrodes which showed that the concentration of O2 (pO2) in the outer cortex could rise from less than 1% up to 23.4% upon increased irradiance of the nodule, but that the pO2 of the inner cortex and infected tissue remained less than 0.0025%. Nitrogenase activity of stem nodules, as measured using a flow-through acetylene reduction assay (no H2 evolution was evident), showed a reversible increase of 28% upon exposure of the nodules to supplemental light. This increase resembled that obtained with stem nodules upon their exposure to an external pO2 of 40%.  相似文献   

16.
A clone of Alnus incana (L.) Moench was grown in symbiosis with a local source of Frankia or with Frankia Ar14. Seven to 9-week-old plants were given 20 m M NH4Cl (20 m M KCl = control) for 3 days. Nitrogenase activity of intact plants decreased gradually within the 3 days of treatment to about 10% of the initial rates. Hydrogen evolution in air and total nitrogenase activity responded similarly to the treatment. Relative efficiency of nitrogenase thus remained the same throughout the study period. Control plants were not affected. Measurements of nitrogenase activity in root nodule homogenates (in vitro measurements) indicated loss of active nitrogenase rather than shortage of energy for nitrogenase activity in Frankia from ammonium-treated plants. Shoots were exposed to 14CO2 and translocation of 14C to Frankia vesicle clusters prepared from root nodules was studied. Frankia vesicle clusters from ammonium-treated plants contained about half as much 14C as those of control plants during all 3 days studied. One explanation for the observed effects is that a reduced supply of carbon to Frankia vesicles in the root nodules caused a reduced metabolic rate, including reduced protein synthesis and synthesis of nitrogenase.  相似文献   

17.
Abstract Hydrogen peroxide (H2O2) has been implicated in degradation of wood by both brown-rot and white-rot fungi. This study found that low concentrations of nitrogem and carbohydrates (cellobiose, glucose, xylose and mannose) in an agar medium had little effect on H2O2 production by white-rot fungi. However, low concentrations of nitrogen and carbohydrates stimulated H2O2 production by brown-rot fungi. Use of the chromogen 2,2'-azino-di(3-ethyl benzthiazoline-6-sulphonic acid) (ABTS) with horseradish peroxidase to detect H2O2 by the fungi was slightly better than detection by the chromogen o -dianisidine with horseradish peroxidase. An auxiliary test to check the role of H2O2 in wood decay found that hydrogen peroxide-negative isolates of the white-rot fungi Pharnerochaete chrysosporium and Ganoderma applanatum were unable to decay sweetgum and southern pine.  相似文献   

18.
Abstract— In in vitro experiments on rat hypothalamic homogenates the effects of biogenic amines such as histamine (HA), noradrenaline (NA), dopamine (DA), serotonin (5-HT) and drugs such as isoprenaline (ISP), 2-(2-pyridyl)ethylamine (H2 stimulant—Hls), 4-methyl-histamine (H2 stimulant H2s), mepyramine (H1 antagonistp Hla), cimetidine (H2 antagonist—H2a) were tested on adenylate cyclase activity. HA possessed a powerful stimulating effect on hypothalamic adenylate cyclase activity, higher than that shown by the other substances.
The stimulating effect of HA was greatest in hypothalamic tissue from male rats, while tissue from females showed only a modest stimulation. H2s, induced a greater stimulation of adenylate cyclase than Hls. On the other hand, the H2a inhibited HA stimulation to a greater extent than the Hla, Hla and H2a, when used together, completely inhibited the HA stimulation. HA may have a neurotrans-mitter role in the hypothalamus, and in this area there appears to be a mixed population of H1 and H2 receptors, with a majority of H2 receptors.  相似文献   

19.
Changes in nodule growth and activity and in the concentrations of soluble N compounds in nodules, leaves and xylem sap under conditions of altered N nutrition in the actinorhizal plant Myrica gale L. are reported. Altering the N nutrition of symbiotic plants may alter the internal regulation of combined N which in turn may regulate nodule growth and activity. Flushing nodules daily with 100% O2 caused a decline in amide concentration and an increase in nodule growth although plants had recovered some nitrogenase activity within 4 h of exposure to O2. Samples of nodules, leaves and xylem sap were derivatized and amino acids identified and quantified using either reverse phase high performance liquid chromatography or gas chromatography-mass spectrometry in single ion monitoring mode. The ratio of asparagine in the nodules to that in the xylem was much higher in plants fed N (6.7 for NH+4-fed and 8.3 for NO3-fed plants) than for N2-fixing plants (2.5). Significant amounts of 15N added as 15NH+4 or 15NO3 accumulated in nodules following accumulation in the shoot which is consistent with the translocation of N to the nodules via the phloem. The uptake of 15NH+4 led to the synthesis and subsequent translocation of glutamine in the xylem sap. These results are discussed in terms of the feedback mechanisms that may regulate nitrogen fixation in Myrica root nodules.  相似文献   

20.
Recent research has shown that nodule nitrogen fixation is limited under a wide range of environmental constraints by lowered carbon flux within the nodule due to down-regulation of sucrose synthase activity. The aim of this work was to elucidate whether an increase in both carbon flux and activity of enzymes of carbon metabolism in nodules may lead to an increased nitrogen fixation. We report the effects caused by a continuous exposure to atmospheric CO2 enrichment in nodulated pea plants. CO2 enrichment led to an enhanced whole-plant growth and increased nodule biomass. Moreover, nodules of plants grown at increased CO2 showed a higher sugar content as well as enhancement of some activities related to nodule carbon metabolism, such as sucrose synthase, UDP glucose pyrophosphorylase and phosphoenolpyruvate carboxylase. Indeed, acetylene reduction activity, measured by the classical technique, was increased more than four times. However, when specific nitrogen fixation was determined as hydrogen evolution, no significant differences were detected, consistent with the lack of changes of enzymes involved in nitrogen metabolism such as glutamate synthase and aspartate aminotransferase. These results are discussed in the context of the regulation of nitrogen fixation and nodule metabolism.  相似文献   

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