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1.
Uptake hydrogenase activity in nodules of green gram ( Vigna radiata (L.) (Wilczek)), black gram ( Vigna mungo (L.) (Hepper)), cowpea ( Vigna unguiculata (L.) and cluster bean ( Cyamopsis tetragonoloba (L.) ( Taub.)), formed with two Hup + (S24 and CT2014) and one Hup − (M11) Rhizobium strains, was determined at different levels of external H2 in air atmosphere. Nodules of all the 4 host species formed by
inoculation with strains S24 and CT2014, showed H2 uptake but not those formed with strain M11. H 2 uptake rates were higher in 1 and 2% H 2 in air atmosphere (v/v) than at 5 or 10% levels in all the host species. Variations in the relative rates of H 2 uptake were observed both, due to host species as well as due to Rhizobium strains. However, no host dependent complete repression of the expression of H 2 uptake activity was observed in nodules of any of the host species formed with Hup + strains. 相似文献
2.
We describe a strategy to establish cyanobacterial strains with high levels of H 2 production that involves the identification of promising wild-type strains followed by optimization of the selected strains
using genetic engineering. Nostoc sp. PCC 7422 was chosen from 12 other heterocystous strains, because it has the highest nitrogenase activity. We sequenced
the uptake hydrogenase (Hup) gene cluster as well as the bidirectional hydrogenase gene cluster from the strain, and constructed
a mutant (Δ hupL) by insertional disruption of the hupL gene. The Δ hupL mutant produced H 2 at 100 μmoles mg chlorophyll a
-1 h -1, a rate three times that of the wild-type. The Δ hupL cells could accumulate H 2 to about 29% (v/v) accompanied by O 2 evolution in 6 days, under a starting gas phase of Ar + 5% CO 2. The presence of 20% O 2 in the initial gas phase inhibited H 2 accumulation of the Δ hupL cells by less than 20% until day 7. 相似文献
3.
Summary Small samples of soil amended with 2% (w/w) of glucose were preincubated either aerobically or anaerobically and then assayed
(N 2
15 and C 2H 2-C 2H 4) either aerobically or anaerobically for different time periods. One-hour C 2H 2-C 2H 4 assays showed greatest activity when anaerobic assay followed anaerobic preincubation. During the anaerobic preincubation
a lag of 12–24 h occurred before rapid increase in one-hour assay activity was observed. When aerobic assay followed aerobic
preincubation a longer lag was observed and lower activities were obtained. When anaerobic assay followed aerobic preincubation
(or vice versa) negligible activities were observed in short assays, and longer assays showed increasing activity related to changes in
atmosphere and/or microbial population in the closed system.
Preincubation of soil on a diffusion gradient at a series of different partial pressures of oxygen confirmed the above pattern
and showed that as preincubation pO 2 increased, the anaerobic assay activity rapidly decreased. As preincubation pO 2 decreased from 0.2 atm the aerobic assay activity decreased but less rapidly.
The activities observed were related to the sizes of the Azotobacter and Clostridium populations. There was no evidence of
aerobic or anaerobic C 2H 2 reduction in any cultures of ‘oligonitrophiles’ isolated.
Incorporation of N 2
15 was related to C 2H 2 reduction activity in the soil system studied. However, observed C 2H 4/N 2 molar ratios ranged from 10 to 22 and appeared to be highest in samples which were preincubated anaerobically.
Issued as Macdonald College Journal Series No. 618 and as Canadian IBP contribution No. 84. 相似文献
4.
In this survey we describe the influence of hydrogen oxidation on the physiology of Rhizobium ORS 571. The presence of hydrogen is required for the synthesis of hydrogenase. Carbon substrates do not repress the synthesis
of hydrogenase. The respiratory system contains cytrochromes of the b- and c-type. Cytochrome a
600 is present after growth at high oxygen tensions. The nature of the terminal oxidases functioning at low oxygen tensions has
not been established yet. → H +/O values with endogenous substrates are between 6 and 7. The results show the presence of two phosphorylation sites: site
1 (ATP/2e=1.0) and site 2(ATP/2e=1.33). By measuring molar growth yields it has been demonstrated that carbon-limited, nitrogen-fixing
cultures obtain additional ATP from hydrogen oxidation, and that site 2 of oxidative phosphorylation is passed during hydrogen
oxidation. A method is described to calculate ATP/N 2 values (the total amount of ATP used by nitrogenase during the fixation of 1 mol N 2) and H 2/N 2 ratios (mol hydrogen formed per mol N 2 fixed) in aerobic organisms. For Rhizobium ORS 571 the ATP/N 2 value is about 40 and the H 2/N 2 ratio is between 5 and 7.5. Cells obtained from oxygen-limited nitrogen-fixing cultures contain 30–40% poly-β-hydroxybutyrate,
which explains the high molar growth yields found. Hydrogen has not been detected in the effluent gas of these cultures, which
may point to reoxidation of the hydrogen formed at nitrogen fixation. Calculations show that the effect of hydrogen reoxidation
on the efficiency of nitrogen fixation (g N fixed × mol −1 substrate converted) is not very large and that the actual H 2/N 2 ratio is of much more importance.
After addition of hydrogen to succinate-limited, ammonia-assimilating cultures, an initial increase of the Y succinate value (g dry wt × mol −1 succinate) is followed by a gradual decrease. This is accompanied by a large decrease of the
value, and an increased permeability of the cytoplasmic membrane to protons. The results may be explained by a transition
of the culture from an energy-limited state to a carbon-limited state. 相似文献
6.
Summary The influence of seasonal variation on nitrogenase (N 2-ase) activity of undisturbed soil-plant cores of Panicum maximum var. trichoglume was measured using the C 2H 2 reduction assay.
The largest N 2-ase activity in the field, 14.7 g N ha −1 day −1, occurred in spring when soil moisture was high, soil temperature was low and nitrogenous fertiliser influence was at a minimum.
The potential N 2-ase activity of the cores, measured under controlled conditions, reached a maximum of 27.2 g N ha −1 day −1 and averaged 26.3 g N ha −1 day −1 over the 14 month sampling period.
N 2-ase activity was positively correlated ( P=0.05) with field soil moisture and negatively correlated with field soil temperature (r=0.59 and −0.78 respectively). Multiple
regression showed that 69% of the variation of N 2-ase activity in the field was associated with the combined effects of soil moisture and soil temperature.
Nitrogen fixing bacteria were isolated from the roots of P. maximum and based upon morphology, biochemical tests and fluorescent antibody reaction, were found to be closely related to Azospirillum lipoferum. 相似文献
7.
Summary The biological nature of soil H 2-consumption has been investigated. Soil microorganisms were capable to remove H 2 present in the gas phase at concentrations in the range of 200 ppm at rates varying between 0.2 and 1.0 l.min –1. 100 g –1. Free soil enzymes did not contribute significantly at the H 2 concentrations tested. Oxygen seemed to be the predominant electron acceptor. The influence of microbiological and physical soil properties on the H 2-uptake activity was examined for 38 soils.A highly significant correlation between biomass-C and H 2-uptake rate of the soil was noted, suggesting that the latter parameter might be useful as an indirect estimation of soil microbial biomass. The correlation was however not applicable for soils recently grown with legumes. Indeed, soya plants nodulated with a Rhizobium strain with a weak hydrogen uptake capability, strongly increased the hydrogen oxidizing capability of the surrounding soil. 相似文献
8.
Heavy water (H 218O) has been used to label DNA of soil microorganisms in stable isotope probing experiments, yet no measurements have been
reported for the 18O content of DNA from soil incubated with heavy water. Here we present the first measurements of atom% 18O for DNA extracted from soil incubated with the addition of H 218O. Four experiments were conducted to test how the atom% 18O of DNA, extracted from Ponderosa Pine forest soil incubated with heavy water, was affected by the following variables: (1)
time, (2) nutrients, (3) soil moisture, and (4) atom% 18O of added H 2O. In the time series experiment, the atom% 18O of DNA increased linearly ( R
2 = 0.994, p < 0.01) over the first 72 h of incubation. In the nutrient addition experiment, there was a positive correlation ( R
2 = 0.991, p = 0.006) between the log 10 of the amount of tryptic soy broth, a complex nutrient broth, added to soil and the log 10 of the atom% 18O of DNA. For the experiment where soil moisture was manipulated, the atom% 18O of DNA increased with higher soil moisture until soil moisture reached 30%, above which 18O enrichment of DNA declined as soils became more saturated. When the atom% 18O for H 2O added was varied, there was a positive linear relationship between the atom% 18O of the added water and the atom% 18O of the DNA. Results indicate that quantification of 18O incorporated into DNA from H 218O has potential to be used as a proxy for microbial growth in soil. 相似文献
9.
To evaluate the effect of ectomycorrhizal colonization on growth and physiological activity of Larix kaempferi seedlings grown under soil acidification, we grew L. kaempferi seedlings with three types of ectomycorrhizae for 180 days in acidified brown forest soil derived from granite. The soil
had been treated with an acid solution (0 (control), 10, 30, 60, and 90 mmol H + kg −1). The water-soluble concentrations of Ca, Mg, K, Al, and Mn increased with increasing amounts of H + added to the soil. Ectomycorrhizal development significantly increased in soil treated with 10 and 30 mmol H + kg −1 but was significantly reduced in soil treated with 60 and 90 mmol H + kg −1. The concentrations of Al and Mn in needles or roots increased with increasing H + added to the soil. The total N in seedlings significantly increased with increasing H + in soil and colonization with ectomycorrhiza. The maximum net photosynthetic rate at light and CO 2 saturation ( P
max) was greater in soil treated with 10 mmol H + kg −1 than in controls, and was less is soils treated with greater than with 30 mmol H + kg −1, especially with 60 and 90 mmol H + kg −1. However, colonization with ectomycorrhiza significantly reduced the concentration of Al and Mn in needles or roots and increased
the values of P
max and total dry mass (TDM). The relative TDM of L. kaempferi seedlings was approximately 40% at a (BC, base cation)/Al ratio of 1.0. However, ectomycorrhizal seedlings had a 100–120%
greater TDM at a BC/Al ratio of 1.0 than non-ectomycorrhizal seedlings, even though the acid treatment reduced their overall
growth. 相似文献
10.
Six calcareous and alluvial soil profiles differing in their texture, CaCO 3 and salinity were chosen from west and middle Nile Delta for the present study. The 1 st and 2 nd profiles from Borg El-Arab area were sandy loam in texture and > 30% CaCO 3, while the 3 rd and 4 th profiles (from Nubaria area) were sandy clay loam and < 30% CaCO 3. The 2 nd and 4 th profiles were taken from cultivated area with maize. The 5 th profile from Epshan area was non-saline clay alluvial soil and the 6 th from El-Khamsen was saline clay alluvial soil. The relation between soil moisture content ( W%) and water vapour pressure ( P/ P
o) was established for the mentioned soils. Data showed that the specific surface area ( S) values were 34–53 and 44–60 m 2/g for calcareous soils of Borg El-Arab and Nubaria areas, 206–219 and 206–249 m 2/g for non-saline and saline clay alluvial soils of Epshan and El-Khamsen areas, respectively. The corresponding values of
the external specific surface area ( S
e) were 16–21, 14–22, 72–86 and 92–112 m 2/g. Submitting W
m+ W
me as an adsorption boundary of moisture films ( W
c) (where W
m is mono-adsorbed layer of water vapour on soil particles and W
me is the external mono-adsorbed layer), the maximum water adsorption capacity ( W
a) was found to be W
c + W
me or W
m + 2 W
me. It was ranged from 1.88 to 2.70%, 1.97 to 2.95%, 9.70–10.70% and 10.80 to 13.12% while the maximum hygroscopic water ( M
H) values were 2.43–3.78%, 2.91–4.65%, 16–17% and 18.30–21.9% for the studied soil profiles respectively. The residual moisture
content ( θ
r) at pF 7 and P/ P
o = 0 was ranged from 0.0005–0.0010%, 0.0007–0.0019% and 0.0043–0.0048% in Borg El-Arab, Nubaria and Epshan soil profiles,
respectively.
The inter-relations between the surface area and the hygroscopic moisture parameters of the soils under investigation were
as follows
Calcareous soils; W
m = 0.40 M
H, W
c = 0.55 M
H, W
a = 0.70 M
H, S = 14 M
H
Non-saline soil; W
m = 0.35 M
H, W
c = 0.49 M
H, W
a = 0.63 M
H, S = 13 M
H
Saline soil; W
m = 031 M
H, W
c = 0.45 M
H, W
a = 0.59 M
H, S = 12 M
H
These relations give possibility to deduce the soil moisture adsorption capacities and specific surface area via maximum hygroscopic
water, which can be obtained through the experimental determination of water vapor adsorption isotherms. 相似文献
11.
The influence of (NH 4) 2SO 4 concentration and dilution rate ( D) on actual and potential H 2 photoproduction has been studied in ammonium-limited chemostat cultures of Rhodobacter capsulatus B10. The actual H 2 production in a photobioreactor was maximal (approx. 80 ml h −1 l −1) at D = 0.06 h −1 and 4 mM (NH 4) 2SO 4. However, it was lower than the potential H 2 evolution (calculated from hydrogen evolution rates in incubation vials), which amounted to 100–120 ml h −1 l −1 at D = 0.03–0.08 h −1. Taking into account the fact that H 2 production in the photobioreactor under these conditions was not limited by light or lactate, another limiting (inhibiting)
factor should be sought. One possibility is an inhibition of H 2 production by the H 2 accumulated in the gas phase. This is apparent from the non-linear kinetics of H 2 evolution in the vials or from its inhibition by the addition of H 2; initial rates were restored in both cases after the vials had been refilled with argon. The actual H 2 production in the photobioreactor at D = 0.06 h −1 was shown to increase from approximately 80 ml h −1 l −1 to approximately 100 ml h −1 l −1 under an argon flow at 100 ml min −1. Under maximal H 2 production rates in the photobioreactor, up to 30% of the lactate feedstock was utilised for H 2 production and 50% for biomass synthesis.
Received: 22 April 1997 / Received revision: 14 July 1997 / Accepted: 27 July 1997 相似文献
12.
Summary Isotopic 15N 2 experiments confirmed nitrogen fixation in Parasponia parviflora. The conversion ratio C 2H 4/N 2 was 6.7 under the experimental conditions employed. Measurements of the δ 15N in leaves of Parasponia and Trema showed on the basis of these determinations that Parasponia parviflora possesses N 2-fixing capacity and can be distinguished in this respect from the non-nitrogen-fixing Trema cannabina tested by the same method. Therefore, δ 15N can be used to monitor N 2 fixation in natural ecosystems. Hydrogen evolution and the relative efficiency of N 2 fixation in this relation have been determined. Detached Parasponia parviflora root nodules grown in soil and tested in an argon/oxygen atmosphere produced appr. 4 μmol H 2.h −1.g −1 fresh weight root nodules. The relative efficiency of hydrogen utilization as measured in argon, air, and in the presence
of C 2H 2 10% (v/v) was for both equations
used for to express this efficiency 0.96 and 0.97, respectively. This indicates that Parasponia like the root nodules of
some actinorhizal symbioses (Alnus, Myrica, Elaeagnus) and some tropical legumes ( Vigna sinensis) has evolved mechanisms of minimizing net hydrogen production in air, thus increasing the efficiency of electron transfer
to nitrogen. The oxygen relation of nitrogen fixation (C 2H 2) in Parasponia parviflora root nodules was determined. The nitrogenase activity of Parasponia root nodules increased at increasing oxygen concentrations
up till c. 40% O 2. At oxygen levels above 40% O 2, the nitrogenase activity of the root nodules was nil or very erratic suggesting that at these oxygen levels the nitrogenase
is not longer protected against the harmful effect of oxygen. In this respect Parasponia root nodules differ from actinorhizal
root nodules in other nonlegumes, where optimal nitrogenase activity was observed in the range of 12–25% oxygen. Respiration
experiments with Parasponia root nodules showed that in the range 10, 20, and 40% oxygen, the respiration rate (CO 2 evolution) increased concomitantly with an increase of the acetylene reduction rate. The CO 2/C 2H 4 values obtained varied between 8.1 and 19.2, being therefore 2–3 times higher than similar estimations in some actinorhizal
and legume root nodules. The respiratory quotient (RQ) of detached Parasponia parviflora root nodules was in air initially approximately 2.0, but this value dropped to about 1.0 in a 3-hours period. 相似文献
13.
Effect of hydrogen uptake positive (Hup +) strain of Rhizobium sp. (pigeon pea) and VAM fungus ( Glomus fasciculatum) was studied on the symbiotic parameters of pigeon pea ( Cajanus cajan) cv. AL-15 at various levels of phosphorus. The Hup +
Rhizobium strain showed more nodulation, plant biomass and plant nitrogen content than its Hup − counterpart. VAM infection in pigeon pea roots helped in translocating phosphorus from the soil and improved nitrogen fixation.
Similarly, addition of phosphorus was found to play a positive role in enhancing all these parameters. Dual inoculation of
Hup +
Rhizobium strain and VAM significantly increased nodulation, nitrogenase activity, plant nitrogen and phosphorus content and plant
biomass compared to single inoculation of either organism and dual inoculation with Hup − and VAM fungus. 相似文献
14.
The nitrogenase activity, root nodule biomass, and rates of nitrogen (N) fixation were measured in 25-year-old pure north-
and south-facing Robinia pseudoacacia stands in an urban forest of Seoul (Kkachisan Mountain) in central Korea. The nitrogenase activity was estimated using an
acetylene reduction (AR) assay, which showed an increasing trend during the early growing season, with sustained high rates
from June through to September with a decrease thereafter. July had the highest nitrogenase activity rate (micromoles C 2H 4 per gram dry nodule per hour), averaging 95.8 and 115.1 for the north- and south-facing stands, respectively. The maximum
root nodule biomass (kilograms per hectare) was 45.7 and 9.1 for the north- and south-facing stands in July, respectively.
The AR rate appeared to be strongly correlated to the soil temperature ( r
2 = 0.68, P < 0.001) and soil pH ( r
2 = 0.59, P < 0.001) while root nodule biomass was correlated to the soil temperature ( r
2 = 0.36, P < 0.01) and water content ( r
2 = 0.35, P < 0.05). The soil temperature showed clear differences between seasons, while there was a significant difference in soil pH,
organic matter, total N concentrations, and available phosphorus between the north- and south-facing stands. The N 2 fixation rates during the growing season varied from 0.1 to 37.5 kg N ha −1 month −1 depending on the sampling location and time. The annual N 2 fixation rate (kg N per hectare per year) was 112.3 and 23.2 for the north- and south-facing stands, respectively. The differences
in N 2 fixation rate between the two stands were due mainly to the differences in total nodule biomass. 相似文献
15.
The effects of three selected agrochemicals on bacterial diversity in cultivated soil have been studied. The selected agrochemicals
are Cerox (an insecticide), Ceresate and Paraquat (both herbicides). The effect on bacterial population was studied by looking
at the total heterotrophic bacteria presence and the effect of the agrochemicals on some selected soil microbes. The soil
type used was loamy with pH of 6.0–7.0. The soil was placed in opaque pots and bambara bean ( Vigna subterranean) seeds cultivated in them. The agrochemicals were applied two weeks after germination of seeds at concentrations based on
manufacturer’s recommendation. Plant growth was assessed by weekly measurement of plant height, foliage appearance and number
of nodules formed after one month. The results indicated that the diversity index (Di) among the bacteria populations in untreated
soil and that of Cerox-treated soils were high with mean diversity index above 0.95. Mean Di for Ceresate-treated soil was
0.88, and that for Paraquattreated soil was 0.85 indicating low bacterial populations in these treatment-type soils. The study
also showed that application of the agrochemicals caused reduction in the number of total heterotrophic bacteria population
sizes in the soil. Ceresate caused 82.50% reduction in bacteria number from a mean of 40 × 10 5 cfu g −1 of soil sample to 70 × 10 4 cfu g −1. Paraquat-treated soil showed 92.86% reduction, from a mean of 56 × 10 5 cfu g −1 to 40 × 10 4 cfu g −1. Application of Cerox to the soil did not have any remarkable reduction in bacterial population number. Total viable cell
count studies using Congo red yeast-extract mannitol agar indicated reduction in the number of Rhizobium spp. after application of the agrochemicals. Mean number of Rhizobium population numbers per gram of soil was 180 × 10 4 for the untreated soil. Cerox-treated soil recorded mean number of 138 × 10 4 rhizobial cfu g −1 of soil, a 23.33% reduction. Ceresate- and Paraquat-treated soils recorded 20 × 10 4 and 12 × 10 4 cfu g −1 of soil, respectively, representing 88.89% and 93.33% reduction in Rhizobium population numbers. Correspondingly, the mean number of nodules per plant was 44 for the growth in untreated soil, 30 for
the plant in the Cerox-treated soil, 8 for the plant in Paraquat-treated soil and 3 for the plant in Ceresate-treated soil.
The study has confirmed detrimental effect of insecticide on bacterial populations in the soil. Total heterotrophic counts,
rhizobial counts as well as the number of nodules of all samples taken from the chemically treated soils were all low as compared
to values obtained for the untreated soil. However, the effect of the insecticide was minimal in all cases as compared to
the effects of the herbicides on the soil fauna. Indiscriminate use of agrochemicals on farms can therefore affect soil flora
and subsequently food production. 相似文献
16.
Summary The effect of low concentrations of hydrogen peroxide (H 2O 2) (5 × 10 −7−9.5 × 10 −7
M) on cell growth and antibody production was investigated with murine hybridoma cells (Mark 3 and anti-hPL) in culture. Cell
growth, measured by flow cytometry with morphological parameters, was significantly stimulated by H 2O 2 (8 × 10 −7
M) but H 2O 2 concentration of 7 × 10 −6
M and above increased cell death. H 2O 2 stimulation of antibody production was nonsignificant. The metabolism of cells treated with 8 × 10 −7 or 1 × 10 −5
M H 2O 2 was similar to that of the control in terms of glucose and glutamine consumption, lactate and ammonia production, and amino
acid concentrations in the medium. The concentrations of lactate dehydrogenase, a marker of cell death, in test and control
cells were similar. However, concentrations of intracellular free radicals measured by flow cytometry with dihydrorhodamine
123 (DHR 123) and dichlorofluorescein diacetate (DCFH-DA) as fluorochromes were different. The reactive oxygen species content
of cells in 8 × 10 −7
M H 2O 2 was similar to that of the controls, but there was a sudden, marked production of superoxide anions (detected with DHR 123)
and H 2O 2 or peroxides (detected with DCFH-DA) by cells incubated with 1 × 10 −5
M H 2O 2 which increased with increasing H 2O 2 until cell death. 相似文献
17.
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
18.
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
19.
Acetylene reduction, 15N 2 reduction and H 2 evolution were measured in root systems of intact plants of grey alder ( Alnus incana (L.) Moench) in symbiosis with Frankia. The ratios of C 2H 2: 15N 2 were compared with C 2H 2:N 2 ratios calculated from C 2H 2 reduction and H 2 evolution, and with C 2H 2:N 2 ratios calculated from accumulated C 2H 4 production and nitrogen content. It was possible to calculate C 2H 2:N 2 ratios from C 2H 2 reduction and H 2 evolution because this source of Frankia did not show any hydrogenase activity. The ratios obtained using the different methods ranged from 2.72 to 4.42, but these values were not significantly different. It was also shown that enriched 15N could be detected in the shoot after a 1-h incubation of the root-system. It is concluded that the measurement of H 2 evolution in combination with C 2H 2 reduction represents a nondestructive assay for nitrogen fixation in a Frankia symbiosis which shows no detectable hydrogenase activity. 相似文献
20.
Azospirillum isolates were obtained from rhizosphere soil and roots of three cactaceae species growing under arid conditions.
All Azospirillum isolates from rhizosphere and roots of Stenocereus pruinosus and Stenocereus stellatus were identified as A. brasilense; isolates of surface-sterilized roots from Opuntia ficus-indica were both A. brasilense and A. lipoferum. Azospirilla per g of fresh root in the three species ranged from 70×10 3 to 11×10 3. The most active strains in terms of C 2H 2 reduction (25–49.6 nmol/h·ml) and indoleacetic acid (IAA) production (36.5–77 μg/ml) were those identified as A. brasilense and isolated from Stenocereus roots. A. lipoferum isolated from Opuntia roots produced low amounts of IAA (6.5–17.5 μg/ml) and low C 2H 2-reduction activity (17.8–21.2 nmol/h·ml). 相似文献
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