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1.
Jessica A. Kozlowski Jennifer Price Lisa Y. Stein 《Applied and environmental microbiology》2014,80(16):4930-4935
Nitrite reductase (NirK) and nitric oxide reductase (NorB) have long been thought to play an essential role in nitrous oxide (N2O) production by ammonia-oxidizing bacteria. However, essential gaps remain in our understanding of how and when NirK and NorB are active and functional, putting into question their precise roles in N2O production by ammonia oxidizers. The growth phenotypes of the Nitrosomonas europaea ATCC 19718 wild-type and mutant strains deficient in expression of NirK, NorB, and both gene products were compared under atmospheric and reduced O2 tensions. Anoxic resting-cell assays and instantaneous nitrite (NO2−) reduction experiments were done to assess the ability of the wild-type and mutant N. europaea strains to produce N2O through the nitrifier denitrification pathway. Results confirmed the role of NirK for efficient substrate oxidation of N. europaea and showed that NorB is involved in N2O production during growth at both atmospheric and reduced O2 tensions. Anoxic resting-cell assays and measurements of instantaneous NO2− reduction using hydrazine as an electron donor revealed that an alternate nitrite reductase to NirK is present and active. These experiments also clearly demonstrated that NorB was the sole nitric oxide reductase for nitrifier denitrification. The results of this study expand the enzymology for nitrogen metabolism and N2O production by N. europaea and will be useful to interpret pathways in other ammonia oxidizers that lack NirK and/or NorB genes. 相似文献
2.
Hydroxylamine oxidation and subsequent nitrous oxide production by the heterotrophic ammonia oxidizer Alcaligenes faecalis 总被引:9,自引:0,他引:9
Nitrous oxide (N2O), a greenhouse gas, is emitted during autotrophic and heterotrophic ammonia oxidation. This emission may result from either
coupling to aerobic denitrification, or it may be formed in the oxidation of hydroxylamine (NH2OH) to nitrite (NO2
−). Therefore, the N2O production during NH2OH oxidation was studied with Alcaligenes faecalis strain TUD. Continuous cultures of A. faecalis showed increased N2O production when supplemented with increasing NH2OH concentrations. 15N-labeling experiments showed that this N2O production was not due to aerobic denitrification of NO2
−. Addition of 15N-labeled NH2OH indicated that N2O was a direct by-product of NH2OH oxidation, which was subsequently reduced to N2. These observations are sustained by the fact that NO2
− production was low (0.23 mM maximum) and did not increase significantly with increasing NH2OH concentration in the feed. The NH2OH-oxidizing capacity increased with increasing NH2OH concentrations. The apparent V
max and K
m were 31 nmol min−1 mg dry weight−1 and 1.5 mM respectively. The culture did not increase its growth yield and was not able to use NH2OH as the sole N source. A non-haem hydroxylamine oxidoreductase was partially purified from A. faecalis strain TUD. The enzyme could only use K3Fe(CN)6 as an electron acceptor and reacted with antibodies raised against the hydroxylamine oxidoreductase of Thiosphaera pantotropha.
Received: 1 September 1998 / Received revision: 5 November 1998 / Accepted: 7 November 1998 相似文献
3.
Gyöngyi Kenesi Hesham M. Shafik Attila W. Kovács Sándor Herodek Mátyás Présing 《Hydrobiologia》2009,623(1):191-202
The aim of this research was to test whether NH4
+ and NO3
− affect the growth, P demand, cell composition and N2 fixation of Cylindrospermopsis raciborskii under P limitation. Experiments were carried out in P-limited (200 μg l−1 PO4-P) chemostat cultures of C. raciborskii using an inflowing medium containing either 4,000 μg l−1 NH4-N, 4,000 μg l−1 NO3-N or no combined N. The results showed the cellular N:P and C:P ratios of C. raciborskii decreased towards the Redfield ratio with increasing dilution rate (D) due to the alleviation of P limitation. The cellular C:N and carotenoids:chlorophyll-a ratios also decreased with D, predominantly as a result of an increase in the chlorophyll-a and N content. The NH4
+ and NO3
− supply reduced the P maintenance cell quota of C. raciborskii. Consequently, the biomass yield of the N2-grown culture was significantly lower. The maximum specific growth rate of N2-grown culture was also the lowest observed. It is suggested that these differences in growth parameters were caused by the
P and energy requirement for heterocyte formation, nitrogenase synthesis and N2 fixation. N2 fixation was partially inhibited by NO3
− and completely inhibited by NH4
+. It was probably repressed through the high N content of cells at high dissolved N concentrations. These results indicate
that C. raciborskii is able to grow faster and maintain a higher biomass under P limitation where a sufficient supply of NH4
+ or NO3
− is maintained. Information gained about the species-specific nutrient and pigment stoichiometry of C. raciborskii could help to access the degree of nutrient limitation in water bodies.
Handling editor: Luigi Naselli-Flores 相似文献
4.
Katja Pörtl Sophie Zechmeister-Boltenstern Wolfgang Wanek Per Ambus Torsten W. Berger 《Plant and Soil》2007,295(1-2):79-94
Natural 15N abundance measurements of ecosystem nitrogen (N) pools and 15N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ15N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure
spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ15N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ15N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand:
5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in 15N of all soil N pools. Denitrification represented the main N2O-producing process in the mixed forest stand as we detected a significant 15N enrichment of its substrate NO3− (3.6 ± 4.5‰) compared to NH4+ (−4.6 ± 2.6‰) and its product N2O (−11.8 ± 3.2‰). In a 15N-labelling experiment in the spruce stand, nitrification contributed more to N2O production than denitrification. Moreover, in natural abundance measurements the NH4+ pool was slightly 15N-enriched (−0.4 ± 2.0 ‰) compared to NO3− (−3.0 ± 0.6 ‰) and N2O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N2O. The more positive δ15N values of N2O in the spruce stand than in the mixed stand point to extensive microbial N2O reduction in the spruce stand. Combining natural 15N abundance and 15N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately. 相似文献
5.
T. Rütting D. Huygens C. Müller O. Van Cleemput R. Godoy P. Boeckx 《Biogeochemistry》2008,90(3):243-258
Nitrite (NO2
−) is an intermediate in a variety of soil N cycling processes. However, NO2
− dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics
were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3
−, NH4
+ and NO2
−. Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of
functional links between (1) NH4
+ oxidation, the main process for NO2
− production (nitritation), and NO2
− reduction, and (2) oxidation of soil organic N, the dominant NO3
− production process in this soil, and dissimilatory NO3
− reduction to NH4
+ (DNRA). The production of NH4
+ via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the
rate of DNRA was several magnitudes higher than the rate of other NO3
− reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process
in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic
conditions of this Nothofagus ecosystem. 相似文献
6.
7.
Massive anthropogenic acceleration of the global nitrogen (N) cycle has stimulated interest in understanding the fate of excess
N loading to aquatic ecosystems. Nitrate (NO3
−) is traditionally thought to be removed mainly by microbial respiratory denitrification coupled to carbon (C) oxidation,
or through biomass assimilation. Alternatively, chemolithoautotrophic bacterial metabolism may remove NO3
− by coupling its reduction with the oxidation of sulfide to sulfate (SO4
2−). The NO3
− may be reduced to N2 or to NH4
+, a form of dissimilatory nitrate reduction to ammonium (DNRA). The objectives of this study were to investigate the importance
of S oxidation as a NO3
− removal process across diverse freshwater streams, lakes, and wetlands in southwestern Michigan (USA). Simultaneous NO3
− removal and SO4
2− production were observed in situ using modified “push-pull” methods in nine streams, nine wetlands, and three lakes. The
measured SO4
2− production can account for a significant fraction (25–40%) of the overall NO3
− removal. Addition of 15NO3
− and measurement of 15NH4
+ production using the push–pull method revealed that DNRA was a potentially important process of NO3
− removal, particularly in wetland sediments. Enrichment cultures suggest that Thiomicrospira denitrificans may be one of the organisms responsible for this metabolism. These results indicate that NO3
−-driven SO4
2− production could be widespread and biogeochemically important in freshwater sediments. Removal of NO3
− by DNRA may not ameliorate problems such as eutrophication because the N remains bio-available. Additionally, if sulfur (S)
pollution enhances NO3
− removal in freshwaters, then controls on N processing in landscapes subject to S and N pollution are more complex than previously
appreciated.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
Jirko Holst Chunyan Liu Nicolas Brüggemann Klaus Butterbach-Bahl Xunhua Zheng Yuesi Wang Shenghui Han Zhisheng Yao Jin Yue Xingguo Han 《Ecosystems》2007,10(4):623-634
Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N2O, NO and NO2 were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R.
China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed
since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other.
Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were
in a range of 0.5–4.1 mg N kg−1 soil dry weight day−1. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly
higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification
and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15%
of the observed site differences in gross N turnover rates. N2O and NO
x
flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between
plots. Mean values of N2O fluxes varied between 0.39 and 1.60 μg N2O-N m−2 h−1, equivalent to 0.03–0.14 kg N2O-N ha−1 y−1, and were considerably lower than previously reported for the same region. NO
x
flux rates ranged between 0.16 and 0.48 μg NO
x
-N m−2 h−1, equivalent to 0.01–0.04 kg NO
x
-N ha−1 y−1, respectively. N2O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only
less than 20% of the flux variance. 相似文献
9.
The loss of nitrogen (N) from field-applied animal manure through ammonia (NH3) volatilisation and nitrous oxide (N2O) emission is of major environmental concern. Both lime and dicyandiamide (DCD) have been suggested as amendments that can
mitigate N2O emissions, but simultaneously increase the risk of NH3 volatilisation. This study evaluated the impact of lime and DCD on NH3 and N2O emissions following application of liquid hog manure. Hydrated lime (Ca(OH)2) was added to an acidic soil to achieve three pH levels (4.7, 6.3 and 7.4). Soil samples (100 g) were then placed in 500
ml screw-top Mason-jars and de-ionised water was added to bring the samples to 50, 70 and 90% water-filled pore space (WFPS).
Slurry was applied at a rate equivalent to 116,000 l ha−1, while DCD was applied at 30% of the NH4-N rate applied. Jars were sealed and incubated at 21°C for 21 d. Ammonia volatilisation was quantified using boric acid traps,
while N2O gas concentration was analysed using gas chromatography. Dicyandiamide had no effect (P>0.05) on either NH3 or N2O emissions. Both NH3 and N2O emissions increased (P<0.05) as WFPS increased, with emissions ranging from 0.9 to 1.4 kg NH3-N ha−1 and 123 to 353 g N2O-N ha−1, respectively. Liming decreased (P<0.01) N2O emissions from 547 to 46 g N2O-N ha−1, but increased (p<0.01) NH3 volatilisation from 0.36 to 1.92 kg NH3-N ha−1. Results suggest that liming to a pH ≥6.3 can reduce N2O emissions, however, this reduction will be accompanied by a substantial loss of NH3.
Section Editor: H. Lambers 相似文献
10.
Niels Thomas Eriksen Frederik Kier Riisgård William Stuart Gunther Jens Jørgen Lønsmann Iversen 《Journal of applied phycology》2007,19(2):161-174
Growth of the green algae Chlamydomonas reinhardtii and Chlorella sp. in batch cultures was investigated in a novel gas-tight photobioreactor, in which CO2, H2, and N2 were titrated into the gas phase to control medium pH, dissolved oxygen partial pressure, and headspace pressure, respectively.
The exit gas from the reactor was circulated through a loop of tubing and re-introduced into the culture. CO2 uptake was estimated from the addition of CO2 as acidic titrant and O2 evolution was estimated from titration by H2, which was used to reduce O2 over a Pd catalyst. The photosynthetic quotient, PQ, was estimated as the ratio between O2 evolution and CO2 up-take rates. NH4
+, NO2
−, or NO3
− was the final cell density limiting nutrient. Cultures of both algae were, in general, characterised by a nitrogen sufficient
growth phase followed by a nitrogen depleted phase in which starch was the major product. The estimated PQ values were dependent on the level of oxidation of the nitrogen source. The PQ was 1 with NH4
+ as the nitrogen source and 1.3 when NO3
− was the nitrogen source. In cultures grown on all nitrogen sources, the PQ value approached 1 when the nitrogen source was depleted and starch synthesis became dominant, to further increase towards
1.3 over a period of 3–4 days. This latter increase in PQ, which was indicative of production of reduced compounds like lipids, correlated with a simultaneous increase in the degree
of reduction of the biomass. When using the titrations of CO2 and H2 into the reactor headspace to estimate the up-take of CO2, the production of O2, and the PQ, the rate of biomass production could be followed, the stoichiometrical composition of the produced algal biomass could be
estimated, and different growth phases could be identified. 相似文献
11.
Two novel denitrifying bacteria were successfully isolated from industrial wastewater and soil samples. Using morphological,
biochemical/biophysical and 16S rRNA gene analyses, these two bacteria were identified as Stenotrophomonas sp. ZZ15 and Oceanimonas sp. YC13, respectively. Both of these two bacteria showed efficient NO3
−-N removing abilities under a semi-anaerobic condition without obvious accumulation of NO2
−-N, N2O-N and NH4
+-N. NO3
−-N removal from paper mill wastewater was also successful by treatments with either a denitrifier or an immobilization method.
Therefore, this study provides valuable denitrifying bacteria in biotreatment of industrial wastewater and other environmental
pollution caused by NO3
−/NO2
−. 相似文献
12.
The ability of an ecosystem to retain anthropogenic nitrogen (N) deposition is dependent upon plant and soil sinks for N,
the strengths of which may be altered by chronic atmospheric N deposition. Sugar maple (Acer saccharum Marsh.), the dominant overstory tree in northern hardwood forests of the Lake States region, has a limited capacity to take
up and assimilate NO3−. However, it is uncertain whether long-term exposure to NO3− deposition might induce NO3− uptake by this ecologically important overstory tree. Here, we investigate whether 10 years of experimental NO3− deposition (30 kg N ha−1 y−1) could induce NO3− uptake and assimilation in overstory sugar maple (approximately 90 years old), which would enable this species to function
as a direct sink for atmospheric NO3− deposition. Kinetic parameters for NH4+ and NO3− uptake in fine roots, as well as leaf and root NO3− reductase activity, were measured under conditions of ambient and experimental NO3− deposition in four sugar maple-dominated stands spanning the geographic distribution of northern hardwood forests in the
Upper Lake States. Chronic NO3− deposition did not alter the V
max or K
m for NO3− and NH4+ uptake nor did it influence NO3− reductase activity in leaves and fine roots. Moreover, the mean V
max for NH4+ uptake (5.15 μmol 15N g−1 h−1) was eight times greater than the V
max for NO3− uptake (0.63 μmol 15N g−1 h−1), indicating a much greater physiological capacity for NH4+ uptake in this species. Additionally, NO3− reductase activity was lower than most values for woody plants previously reported in the literature, further indicating
a low physiological potential for NO3− assimilation in sugar maple. Our results demonstrate that chronic NO3− deposition has not induced the physiological capacity for NO3− uptake and assimilation by sugar maple, making this dominant species an unlikely direct sink for anthropogenic NO3− deposition. 相似文献
13.
Microbial degradation and metabolic pathway of pyridine by a <Emphasis Type="Italic">Paracoccus</Emphasis> sp. strain BW001 总被引:2,自引:0,他引:2
A bacterial strain using pyridine as sole carbon, nitrogen and energy source was isolated from the activated sludge of a coking
wastewater treatment plant. By means of morphologic observation, physiological characteristics study and 16S rRNA gene sequence
analysis, the strain was identified as the species of Paracoccus. The strain could degrade 2,614 mg l−1 of pyridine completely within 49.5 h. Experiment designed to track the metabolic pathway showed that pyridine ring was cleaved
between the C2 and N, then the mineralization of the carbonous intermediate products may comply with the early proposed pathway and the
transformation of the nitrogen may proceed on a new pathway of simultaneous heterotrophic nitrification and aerobic denitrification.
During the degradation, NH3-N occurred and increased along with the decrease of pyridine in the solution; but the total nitrogen decreased steadily and
equaled to the quantity of NH3-N when pyridine was degraded completely. Adding glucose into the medium as the extra carbon source would expedite the biodegradation
of pyridine and the transformation of the nitrogen. The fragments of nirS gene and nosZ gene were amplified which implied that the BW001 had the potential abilities to reduce NO2
− to NO and/or N2O, and then to N2. 相似文献
14.
Selective Inhibition of Ammonium Oxidation and Nitrification-Linked N2O Formation by Methyl Fluoride and Dimethyl Ether 总被引:4,自引:2,他引:2 下载免费PDF全文
Laurence G. Miller M. Denise Coutlakis Ronald S. Oremland Bess B. Ward 《Applied microbiology》1993,59(8):2457-2464
Methyl fluoride (CH3F) and dimethyl ether (DME) inhibited nitrification in washed-cell suspensions of Nitrosomonas europaea and in a variety of oxygenated soils and sediments. Headspace additions of CH3F (10% [vol/vol]) and DME (25% [vol/vol]) fully inhibited NO2- and N2O production from NH4+ in incubations of N. europaea, while lower concentrations of these gases resulted in partial inhibition. Oxidation of hydroxylamine (NH2OH) by N. europaea and oxidation of NO2- by a Nitrobacter sp. were unaffected by CH3F or DME. In nitrifying soils, CH3F and DME inhibited N2O production. In field experiments with surface flux chambers and intact cores, CH3F reduced the release of N2O from soils to the atmosphere by 20- to 30-fold. Inhibition by CH3F also resulted in decreased NO3- + NO2- levels and increased NH4+ levels in soils. CH3F did not affect patterns of dissimilatory nitrate reduction to ammonia in cell suspensions of a nitrate-respiring bacterium, nor did it affect N2O metabolism in denitrifying soils. CH3F and DME will be useful in discriminating N2O production via nitrification and denitrification when both processes occur and in decoupling these processes by blocking NO2- and NO3- production. 相似文献
15.
Ingo Schmidt 《Current microbiology》2009,59(2):130-138
The ammonia oxidizers Nitrosomonas europaea and Nitrosomonas eutropha are able to grow chemoorganotrophically under anoxic conditions with pyruvate, lactate, acetate, serine, succinate, α-ketoglutarate,
or fructose as substrate and nitrite as terminal electron acceptor. The growth yield of both bacteria is about 3.5 mg protein
(mmol pyruvate)−1 and the maximum growth rates of N. europaea and N. eutropha are 0.094 d−1 and 0.175 d−1, respectively. In the presence of pyruvate and CO2 about 80% of the incorporated carbon derives from pyruvate and about 20% from CO2. Pyruvate is used as energy and only carbon source in the absence of CO2 (chemoorganoheterotrophic growth). CO2 stimulates the chemoorganotrophic growth of both ammonia oxidizers and the expression of ribulose bisphosphate carboxylase/oxygenase
is down-regulated at increasing CO2 concentration. Ammonium, although required as nitrogen source, is inhibitory for the chemoorganotrophic metabolism of N. europaea and N. eutropha. In the presence of ammonium pyruvate consumption and the expression of the genes aceE, ppc, gltA, odhA, and ppsA (energy conservation) as well as nirK, norB, and nsc (denitrification) are reduced. 相似文献
16.
Wetlands are often highly effective nitrogen (N) sinks. In the Lake Waco Wetland (LWW), near Waco, Texas, USA, nitrate (NO3−) concentrations are reduced by more than 90% in the first 500 m downstream of the inflow, creating a distinct gradient in
NO3− concentration along the flow path of water. The relative importance of sediment denitrification (DNF), dissimilatory NO3− reduction to ammonium (DNRA), and N2 fixation were examined along the NO3− concentration gradient in the LWW. “Potential DNF” (hereafter potDNF) was observed in all months and ranged from 54 to 278 μmol N m−2 h−1. “Potential DNRA” (hereafter potDNRA) was observed only in summer months and ranged from 1.3 to 33 μmol N m−2 h−1. Net N2 flux ranged from 184 (net denitrification) to −270 (net N2 fixation) μmol N m−2 h−1. Nitrogen fixation was variable, ranging from 0 to 426 μmol N m−2 h−1, but high rates ranked among the highest reported for aquatic sediments. On average, summer potDNRA comprised only 5% (±2%
SE) of total NO3− loss through dissimilatory pathways, but was as high as 36% at one site where potDNF was consistently low. Potential DNRA
was higher in sediments with higher sediment oxygen demand (r
2 = 0.84), and was related to NO3− concentration in overlying water in one summer (r
2 = 0.81). Sediments were a NO3− sink and accounted for 50% of wetland NO3− removal (r
2 = 0.90). Sediments were an NH4+ source, but the wetland was often a net NH4+ sink. Although DNRA rates in freshwater wetlands may rival those observed in estuarine systems, the importance of DNRA in
freshwater sediments appears to be minor relative to DNF. Furthermore, sediment N2 fixation can be extremely high when NO3− in overlying water is consistently low. The data suggest that newly fixed N can support sustained N transformation processes
such as DNF and DNRA when surface water inorganic N supply rates are low. 相似文献
17.
Renata Matraszek 《Acta Physiologiae Plantarum》2008,30(3):361-370
The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity
of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO3
−–N, NH4
+–N, NH4NO3). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in
lettuce plants supplied with nitrate nitrogen (NO3
−–N) or mixed (NH4NO3) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction
of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity
in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants.
At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants
treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of
significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed
nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically
significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with
NO3
−–N or NH4NO3. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the
enzyme activity in the roots of NO3
−-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution
contained ammonium nitrogen (NH4
+–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs,
especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with
ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated
with NH4
+–N the enzyme activity in roots was even higher than in those supplied with NO3
−–N. 相似文献
18.
Summary A simple and efficient micropropagation method was established for direct protocorm-like body (PLB) formation and plant regeneration
from flower stalk internodes of a sympodial orchid, Epidendrum radicans. Small transparent tissues formed on surfaces and cut ends of flower stalk internodes on a modified half-strength Murashige
and Skoog basal medium with or without thidiazuron (TDZ) after 1–2 wk of culture. In the light, the transparent tissues enlarged
and turned into organized calluses on most of the explants. However, PLBs formed only on a medium supplemened with 0.45 μM TDZ within 2 mo. of culture. Sucrose, NH4NO3, and KNO3 were used in media to test their effects on PLB proliferation and shooting. The best response on number of PLBs per tube
was 23.6 at 40 gl−1 sucrose, 825 mgl−1 NH4NO3, and 950 mgl−1 KNO3, and the highest number of PLBs with shoots was found at 10 gl−1 sucrose, 825 mgl−1 NH4NO3, and 950 mgl−1 KNO3. Homogenized PLB tissues produced by blending were used to test the effects of four cytokinins [TDZ, N6-benzyladenine (BA), zeatin-riboside, and kinetin] on PLB proliferation and shoot formation. The best responses on number
of PLBs per tube, proliferation rate, and number of PLBs with shoots per tube were obtained at 4.44 μM BA, 0.28 μM zeatin-riboside, and 1.39 μM kinetin, respectively. Normal plantlets converted from PLBs on the same TDZ-containing medium after 1 mo. of culture. The
optimized procedure required about 12–13 wk from the initiation of PLBs to plantlet formation. The regenerated plants grew
well with an almost 100% survival rate when acclimatized in a greenhouse. 相似文献
19.
Denitrification activity of Bradyrhizobium sp. isolated from Argentine soybean cultivated soils 总被引:1,自引:0,他引:1
Leticia Andrea Fernández Elda Beatriz Perotti Marcelo Antonio Sagardoy Marisa Anahí Gómez 《World journal of microbiology & biotechnology》2008,24(11):2577-2585
Two hundred and fifty strains, all of them representatives of native Bradyrhizobium sp., isolated from soils cultivated with soybean have been characterized by their denitrification activity. In addition,
the denitrification potential of those soils was also measured by evaluating the most-probable-number (MPN) of denitrifying
bacteria and the denitrification enzyme assay (DEA). Of the 250 isolates tested, 73 were scored as probable denitrifiers by
a preliminary screening method. Only 41 were considered denitrifiers because they produced gas bubbles in Durham tubes, cultures
reached an absorbance of more than 0.1 and NO3− and NO2− were not present. Ten of these 41 were selected to confirm denitrification and to study denitrification genes. According
to N2O production and cell protein concentration with NO3−, the isolates could be differentiated in three categories of denitrifiers. The presence of the napA, nirK, norC and nosZ genes was detected by production of a diagnostic PCR product using specific primers. RFLP from the 16S-23S rDNA spacer region
(IGS) revealed that denitrifiers strains could be characterized as Bradyrhizobium japonicum and strains which were non-respiratory denitrifiers as B. elkanii. 相似文献
20.
The kinetics of NH4
+ and NO3
− uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N
species, the Vmax of NH4
+ uptake was higher than that of NO3
− uptake. The Km of NH4
+ uptake and Km of NO3
− uptake differed not significantly. When both NH4
+ and NO3
− were present, the Vmax for NH4
+ uptake became slightly higher, and the Km for NH4
+ uptake remained in the same order. Under these conditions the NO3
− uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH4
+ occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap} 相似文献