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1.
Shoot/root grafting studies showed organ and host cultivar effects on net H 2 evolution from Pisum sativum L. root nodules. Net H 2 evolution from those nodules represents the sum of H 2 formed by Rhizobium nitrogenase and H 2 oxidized by any uptake hydrogenase present in the bacteria. Grafts between pea cultivars `JI1205' or `Alaska' and `Feltham First' in symbioses with R. leguminosarum 128C53 showed that shoots of both JI1205 and Alaska increased H 2 uptake significantly (P ≤ 0.05) in Feltham First root nodules. The same plants also had less net H 2 evolution at similar rates of C 2H 2 reduction than plants formed by grafting Feltham First shoots on Feltham First roots. Although JI1205 and Alaska shoots increased H 2-uptake activity of Feltham First root nodules 28 days after the graft was made, intermediate to high levels of H 2 uptake activity were still present in nodules on roots of both JI1205 and Alaska grafted to Feltham First shoots. These results indicate the presence of a transmissible shoot factor(s) which can increase uptake hydrogenase activity in a Rhizobium symbiont and show that root genotype also can influence that parameter. Parallel grafting experiments using the same pea cultivars in symbioses with R. leguminosarum strain 300, which lacks uptake hydrogenase activity, suggested that a transmissible shoot factor(s) altered H2 formation from nitrogenase by changing the electron allocation coefficient of that enzyme complex. The root and shoot factor(s) detected in this study had no permanent effect on strain 128C53. Bacterial cells isolated from Feltham First nodules with low H2 uptake activity formed root nodules on JI1205 and Alaska with high H2 uptake activity. Bacteroids isolated from nodules on intact JI1205, Alaska, or Feltham First plants with high, medium, or low H2 uptake activity, respectively, maintained those phenotypes during in vitro assays. 相似文献
2.
Summary The hydrogenase found in Rhizobium bacteroids is compared with that found in Azotobacter and found, in all respects examined, to be similar. When three host species were inoculated with Rhizobium, strain 311, different amounts of hydrogenase activity were found in Pisum sativum and Vicia bengalensis while the enzyme was absent from nodules of Vicia faba. Of four different strains of Rhizobium examined only two strains possessed the hydrogenase when present in pea root nodules. The role of the hydrogenase in nitrogen fixation is discussed and it is tentatively concluded that the overall efficiency of the nitrogen fixation process is increased by its presence. 相似文献
3.
Summary Hydrogen uptake is thought to increase the efficiency of nitrogen fixation by recycling H 2 produced by nitrogenase that would otherwise be lost by diffusion. Here we demonstrate the capacity of eight Rhizobium strains to take up molecular hydrogen. Uptake by nodule homogenates from Robinia pseudoacacia was measured amperometrically under nitrogenase repression. Markedly lower activities were found than in soybean nodules. In addition hydrogenase activity was detected by the ability of bacteroids to reduce methylene blue in the presence of hydrogen. It was demonstrated that hydrogenase structural genes are present in the black locust symbiont, Rhizobium sp. strain R1, using hybridization with a plasmid, which contained hydrogenase genes from R. leguminosarum bv. viceae. 相似文献
4.
Hydrogen evolution from a nitrogenase-catalyzed reaction in nodules has been proposed as one of the main causes of inefficiency
in the Rhizobium-legume symbiosis. We have evaluated the energy efficiency of the nitrogen fixation by chickpeas as affected by specific strains
of Rhizobium. All seventeen strains tested produced nodules that evolved amounts of hydrogen ranging from 2.4 to 7.5 μmol/h×g fresh nodule
weight. The equivalent energy losses represented from 31% to 58% of the nitrogenase activity estimated as acetylene reduction.
No hydrogen uptake hydrogenase activity was detected in any of the bacteroid suspensions from nodules produced by the strains
examined. The need to select strains of chickpea rhizobia with higher energy efficiency to improve productivity is emphasized. 相似文献
5.
Hydrogen evolution from root nodules has been reported to make N 2 fixation by some legume- Rhizobium symbiotic systems inefficient. We have surveyed the extent of H 2 evolution and estimated relative efficiencies of nodules of Austrian winter peas formed by 15 strains of R. leguminosarum. Their rates of H 2 evolution in air were about 30% of the rates of H 2 evolution under an atmosphere in which N 2 was replaced by Ar. Relative efficiency values based on C 2H 2 reduction rates ranged from 0.55 to 0.80. With some of the strains, hydrogenase activities were demonstrated in intact nodules and in bacteroids, but the levels of activity were insufficient to recycle all the H 2 evolved by the nitrogenase system. In both intact nodules and bacteroids the hydrogenase is less sensitive to O 2 damage than the nitrogenase system, so H 2 uptake capacity was observed in intact nodules by suppressing the nitrogenase-dependent H 2 evolution with an atmosphere containing a high O 2 concentration, and in bacteroids by using aerobically prepared bacteroid suspensions. The hydrogenase activity of both was dependent on O 2 consumption. A K
mfor H 2 of near 4 M was determined in suspension of bacteroids from nodules formed by strains 128C53 and 128C56. 相似文献
6.
The gas exchange characteristics of intact attached nodulated roots of pea ( Pisum sativum cv. Finale X) and lupin ( Lupinus albus cv. Ultra) were studied under a number of environmental conditions to determine whether or not the nodules regulate resistance to oxygen diffusion. Nitrogenase activity (H 2 evolution) in both species was inhibited by an increase in rhizosphere pO 2 from 20% to 30%, but recovered within 30 min without a significant increase in nodulated root respiration (CO 2 evolution). These data suggest that the nodules possess a variable barrier to O 2 diffusion. Also, nitrogenase activity in both species declined when the roots were either exposed to an atmosphere of Ar:O 2 or when the shoots of the plants were excised. These declines could be reversed by elevating rhizosphere pO 2, indicating that the inhibition of nitrogenase activity resulted from an increase in gas diffusion resistance and consequent O 2-limitation of nitrogenase-linked respiration. These results indicate that nodules of pea and lupin regulate their internal O 2 concentration in a manner similar to nodules of soybean, despite the distinct morphological and biochemical differences that exist between the nodules of the 3 species. Experiments in which total nitrogenase activity (TNA = H 2 production in Ar:O 2) in pea and lupin nodules was monitored while rhizosphere pO 2 was increased gradually to 100%, showed that the resistance of the nodules to O 2 diffusion maintains nitrogenase activity at about 80% of its potential activity (PNA) under normal atmospheric conditions. The O 2-limitation coefficient of nitrogenase (OLC N= TNA/PNA) declined significantly with prolonged exposure to Ar:O 2 or with shoot excision. Together, these results indicate a significant degree of O 2-limitation of nitrogenase activity in pea and lupin nodules, and that yields may be increased by realizing full potential activity. 相似文献
7.
When cyanide is gradually added to a nitrogenfixing culture, Rhizobium ORS 571 is capable of assimilating large amounts of cyanide using its nitrogenase. Under these conditions the molar growth yield on succinate ( Y
succ) increases from 27 at the start of cyanide addition to 38 at the end. The respiratory chain of cells grown at a concentration of 7 mM cyanide is still very sensitive to cyanide. The increase in growth yield is explained by a decrease in hydrogen production by nitrogenase as soon as cyanide is assimilated. This is confirmed by calculating the influence of hydrogen production on Y
succ. Hydrogen production by nitrogenase has a greater influence on growth yields than the presence or absence of hydrogenase activity. At the end of cyanide addition when all cell nitrogen is synthesized from cyanide and no nitrogen fixation occurs, nitrogenase will be in a very oxidized state. 相似文献
8.
The effect of host plant cultivar on H 2 evolution by root nodules was examined in symbioses between Pisum sativum L. and selected strains of Rhizobium leguminosarum. Hydrogen evolution from root nodules containing Rhizobium represents the sum of H 2 produced by the nitrogenase enzyme complex and H 2 oxidized by any uptake hydrogenase present in those bacterial cells. Relative efficiency (RE) calculated as RE = 1 − (H 2 evolved in air/C 2 H 2 reduced) did not vary significantly among `Feltham First,' `Alaska,' and `JI1205' peas inoculated with R. leguminosarum strain 300, which lacks uptake hydrogenase activity (Hup −). That observation suggests that the three host cultivars had no effect on H 2 production by nitrogenase. However, RE of strain 128C53 was significantly (P ≤ 0.05) greater in symbiosis with cultivar JI1205 than in root nodules of Feltham First. At a similar rate of C 2H 2 reduction on a whole-plant basis, nearly 24 times more H 2 was evolved from the Feltham First/128C53 symbiosis than from the JI1205/128C53 association. Root nodules from the Alaska/128C53 symbiosis had an intermediate RE over the entire study period, which extended from 21 to 36 days after planting. Direct assays of uptake hydrogenase by two methods showed significant (P ≤ 0.05) host cultivar effects on H 2 uptake capacity of both strain 128C53 and the genetically related strain 3960. The 3H 2 incorporation assay showed that strains 128C53 and 3960 in symbiosis with Feltham First had about 10% of the uptake hydrogenase activity measured in root nodules of Alaska or JI1205. These data are the first demonstration of significant host plant effects on rhizobial uptake hydrogenase in a single plant species. 相似文献
9.
Several unicellular and filamentous, nitrogen-fixing and non-nitrogen-fixing cyanobacterial strains have been investigated on the molecular and the physiological level in order to find the most efficient organisms for photobiological hydrogen production. These strains were screened for the presence or absence of hup and hox genes, and it was shown that they have different sets of genes involved in H 2 evolution. The uptake hydrogenase was identified in all N 2-fixing cyanobacteria, and some of these strains also contained the bidirectional hydrogenase, whereas the non-nitrogen fixing strains only possessed the bidirectional enzyme. In N 2-fixing strains, hydrogen was mainly produced by the nitrogenase as a by-product during the reduction of atmospheric nitrogen to ammonia. Therefore, hydrogen production was investigated both under non-nitrogen-fixing conditions and under nitrogen limitation. It was shown that the hydrogen uptake activity is linked to the nitrogenase activity, whereas the hydrogen evolution activity of the bidirectional hydrogenase is not dependent or even related to diazotrophic growth conditions. With regard to large-scale hydrogen evolution by N 2-fixing cyanobacteria, hydrogen uptake-deficient mutants have to be used because of their inability to re-oxidize the hydrogen produced by the nitrogenase. On the other hand, fermentative H 2 production by the bidirectional hydrogenase should also be taken into account in further investigations of biological hydrogen production.Abbreviations Chl
chlorophyll
- MV
methyl viologen 相似文献
10.
Nitrogenase activity in the Gunnera Nostoc symbiosis is shown to respond dramatically to the addition of glucose. H 2 can replace glucose in stimulating nitrogenase activity, but there is no H 2 stimulation in the presence of excess glucose. Net hydrogen evolution is strongly stimulated by addition of glucose. We postulate that carbohydrate supply and uptake hydrogenase can moderate the apparent activity of nitrogenase by supplying reductant and/or ATP. The recycling of a large proportion of the electron flux in nitrogenase through uptake hydrogenase maintains a high level of potential nitrogenase ready to take advantage of an influx of carbohydrate. 相似文献
11.
Four strains of Rhizobium (R. trifolii RCL10, R. japonicum S19 and SB16, and Rhizobium sp. NEA4) were demonstrated to grow lithoautotrophically with molecular hydrogen as sole electron donor and with ammonium or with N 2 as N source. All of them showed ribulose-1,5-bisphosphate carboxylase activity and hydrogenase (H 2-uptake) activity with methylene blue and oxygen as electron acceptors. For R. japonicum SB 16, a doubling time under autotrophic conditions of 30 h and a specific hydrogenase activity (methylene blue reduction) in crude extracts of 1.4 U/mg protein were calculated. Rhizobium hydrogenase is a membrane-bound enzyme. It is mainly detectable in particulate cell fractions, it cross-reacts with the antibodies of the membrane-bound hydrogenase of Alcaligenes eutrophus, and is unable to reduce NAD. The isolated hydrogenase is a relatively oxygen-sensitive enzyme with a half-life of three days when stored at 4°C under air. 相似文献
12.
Summary In pea cv. Afghanistan a recessive gene sym 6 prevents the full expression of nitrogenase activity in root nodules, induced
by Rhizobium leguminosarum strain F 13. In contrast, nitrogenase activity is fully expressed in pea cv. Iran. A comparison of the reciprocal hybrids
of these two plants showed that the size of the plant was determined by the mother plant (maternal effect). Therefore the
shoot weight and the total amount of nitrogen fixed are not suitable as parameters for a genetic analysis. The % nitrogen
of the shoot and the specific activity of the nodules per gram of nodules are more reliable, but for practical purposes the
specific activity of the nodules expressed per gram of shoot tissue can be used. 相似文献
13.
Changes in glutamine synthetase activity located in the cytosol of root nodules were followed in pea ( Pisum sativum L.) plants in relation to their nitrogenase activity. The highest glutamine synthetase activity was found in young nodules
(15 days after inoculation) and its changes in 17-to 45-day-old plants showed a positive correlation with nitrogenase activity.
In contrast to nitrogenase activity, changes in glutamine synthetase activity during the day and night period could not be
unequivocally interpreted in terms of diurnal fluctuation. 相似文献
14.
Host plant specificity was examined in symbiosis between Rhizobium strains isolated from legume-tree root nodules and herbaceous or woody legumes from which they were isolated. Strain GRH2 isolated from Acacia cyanophylla formed effective nodules on Acacia, Prosopis and Medicago sativa as well. Nitrogenase activity, measured as acetylene reduction, of strain GRH2 in symbiosis with Prosopis chilensis was the highest ( P 0.05) among the tropical legumes studied and was similar to those found for other associations involving herbaceous legumes. Relative efficiency of nitrogenase varied from 0.3 to near 1 during the light time of the photoperiod. However no hydrogen uptake activity was detected by the amperometric method used. Rhizobium strains GRH3, GRH5 and GRH9 isolated from A. melanoxylon, P. chilensis and Sophora microphylla, respectively, also showed a very low host-range specificity. All isolates were infective and effective on at least one of the herbaceous legumes tested. These data demonstrate the lack of specificity of Rhizobium strains isolated from nitrogen-fixing tree root nodules and that these strains can form effective nodules on herbaceous legumes. 相似文献
15.
Acetylene reduction, deuterium uptake and hydrogen evolution were followed in in-vivo cultures of Azospirillum brasilense, strain Sp 7, by a direct mass-spectrometric kinetic method. Although oxygen was needed for nitrogenase functioning, the enzyme was inactivated by a fairly low oxygen concentration in the culture and an equilibrium had to be found between the rate of oxygen diffusion and bacterial respiration. A nitrogenase-mediated hydrogen evolution was observed only in the presence of carbon monoxide inhibiting the uptake hydrogenase activity which normally recycles all the hydrogen produced. However, under anaerobic conditions and in the presence of deuterium, a bidirectional hydrogenase activity was observed, consisting in D 2 uptake and in H 2 and HD evolution. In contrast to the nitrogenase-mediated H 2 production, this anaerobic H 2 and HD evolution was insensitive to the presence of acetylene and was partly inhibited by carbon monoxide. It was moreover relatively unaffected by the deuterium partial pressure. These results suggest that the anaerobic H 2 and HD evolution can be ascribed to a reverse hydrogenase activity under conditions where D 2 is saturating the uptake process and scavenging the electron acceptors. Although the activities of both nitrogenase and hydrogenase were thus clearly differentiated, a close relationship was found between their respective functioning conditions. 相似文献
16.
Hydrogenase activity of root nodules in the symbiotic association between Pisum sativum L. and Rhizobium leguminosarum was determined by incubating unexcised nodules with tritiated H 2 and measuring tissue HTO. Hydrogenase activity saturated at 0.50 millimolar H 2 and was not inhibited by the presence of 0.10 atmosphere C 2H 2, which prevented H 2 evolution from nitrogenase. Total H 2 production from nitogenase was estimated as net H 2 evolution in air plus H 2 exchange in 0.10 atmosphere C 2H 2. Although such an estimate of nitrogenase function may not be quantitatively exact, due to uncertain relationships between H 2 exchange and H 2 uptake activity of hydrogenase, differences observed in H 2 exchange under various conditions represent an indication of changes in hydrogenase activity. Hydrogenase activity was lower in associations grown under higher photosynthetic photon flux densities and decreased relative to total H 2 production by nitrogenase. Total H 2 production and hydrogenase activity were maximum 28 days after planting. Thereafter, hydrogenase activity and H 2 production declined, but the potential proportion of nitrogenase-produced H 2 recovered by the uptake hydrogenase system increased. Of five R. leguminosarum strains tested two possessed hydrogenase activity. Strains which had the potential to reassimilate H 2 had significantly higher rates of N 2 reduction than those which did not exhibit hydrogenase activity. 相似文献
17.
Molecular hydrogen inhibits nitrogenase activity in Anabaena pre-illuminated with red or blue light. The inhibitory effect of molecular hydrogen decreased in the presence of oxygen and several electron acceptors. When NH 4Cl and urea were added simultaneously with molecular hydrogen, marked synergistic inhibitory effects took place. The inhibitory effect of molecular hydrogen disappeared or was weakened after the suppression of hydrogenase activity. The addition of O 2 and electron acceptors to systems showed no enhancing effect on the C 2H 2-reducing activity. 相似文献
18.
The effect of waterlogging of root nodules on nitrogenase activity and synthesis was studied in Pisum sativum inoculated with Rhizobium leguminosarum (strain PRE). It was shown that: 1. nitrogenase activity of intact pea plants was decreased by waterlogging, 2. this decrease was paralleled by a decline of the amount of active nitrogenase determined in toluene EDTA treated bacteroids, 3. SDS-polyacrylamide gel electrophoresis revealed that the amount of nitrogenase component II (CII) decreased by waterlogging while the amount of component I (CI) was not markedly affected, and 4. analysis of bacteroid proteins after 35SO 4 labeling of pea plants showed that CII synthesis was repressed while CI synthesis continued indicating that the synthesis of CI and CII is regulated by independent mechanisms. 相似文献
19.
Two pathways of hydrogen uptake in Nostoc muscorum are apparent using either oxygen or nitrogen as electron acceptor. Hydrogen uptake (under argon with some oxygen as electron acceptor assayed in the dark; oxyhydrogen reaction) is found to be more active in dense, light-limited cultures than in thin cultures when light is not limiting. Addition of bicarbonate inhibits this hydrogen uptake, because photosynthesis is stimulated. In a cell-free hydrogenase assay, a 10-fold increase of the activity can be measured, after the cells having been kept under lightlimiting conditions. After incubation under light-saturating conditions, no hydrogen uptake is found, when filaments are assayed under argon plus some oxygen. Assaying these cells under a nitrogen atmosphere, a strong hydrogen uptake occurs. The corresponding cell-free hydrogenase assay exhibits low hydrogenase activity. Furthermore, the hydrogen uptake by intact filaments under nitrogen in the light apparently is correlated with nitrogenase activity. These studies give evidence that, under certain physiological conditions, hydrogen uptake of heterocysts proceeds directly via nitrogenase, with no hydrogenase involved.Abbreviations Chl
chlorophyll
- DCMU (diuron)
3-3,4-dichlorophenyl)-1,1-dimethylurea
- pev
packed cell volume 相似文献
20.
Summary In the growing season no net H 2 evolution is detected when root nodules of Alnus glutinosa are incubated in air or in argon containing 20% O 2. Due to the hydrogenase activity, N 2-fixing root nodules consume added H 2 at a rate of about 1.4 moles H 2.g fresh nodule –1.h –1. The uptake of H 2 is only found in summer. At the end of the season, in autumn, nodules evolve significant quantities of H 2 although the nodules still continue to fix nitrogen.
In-vitro studies with fractionated homogenates of summer-harvested nodules show that the recovery of the hydrogenase is high when using methylene-blue or phenazine metasulfate as electron acceptors. No hydrogenase activity is detected in homogenates of autumn-harvested nodules.The hydrogenase is localised in the microsymbiont. 相似文献
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