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101.
Barbara O'Callaghan Monique Synguelakis Gildas Le Gal La Salle Nicolas Morel 《Biology of the cell / under the auspices of the European Cell Biology Organization》1994,81(2):121-130
Summary— A major antigen of the brush border membrane of Torpedo marmorata kidney was identified and purified by immunoprecipitation. The sequence of its 18 N terminal amino acids was determined and found to be very similar to that of mammalian aminopeptidase N (EC 3.4.11.2). Indeed aminopeptidase N activity was efficiently immunoprecipitated by monoclonal antibody 180K1. The purified antigen gives a broad band at 180 kDa after SDS-gel electrophoresis, which, after treatment by endoglycosidase F, is converted to a thinner band at 140 kDa. This antigen is therefore heavily glycosylated. Depending on solubilization conditions, both the antigen and peptidase activity were recovered either as a broad peak with a sedimentation coefficient of 18S (2% CHAPS) or as a single peak of 7.8S (1% CHAPS plus 0.2 % C12E9), showing that Torpedo aminopeptidase N behaves as an oligomer stabilized by hydrophobic interactions, easily converted into a 160 kDa monomer. The antigen is highly concentrated in the apical membrane of proximal tubule epithelial cells (600 gold particles/μm2 of brush border membrane) whereas no labeling could be detected in other cell types or in other membranes of the same cells (basolatéral membranes, vacuoles or vesicles). Monoclonal antibodies prepared here will be useful tools for further functional and structural studies of Torpedo kidney aminopeptidase N. 相似文献
102.
Effects of medium carbon-to-nitrogen ratio on biofilm formation and plasmid stability 总被引:1,自引:0,他引:1
Biofilm formation and plasmid segregational instability in biofilm cultures of Escherichia coli DH5alpha (pMJR1750) were investigated under different medium-carbon-to-nitrogen (C/N) ratios. At C/N ratios of 0.07 and 1, net accumulation of both biofilm plasmid-bearing and plasmid-free cells continued through the entire experiment without attaining any apparent steady state. At C/N ratios of 5 and 10, net biofilm cell accumulation for the two populations reached apparent steady states after 84 and 72 h, respectively. At C/N ratios of 0.07 and 1, polysaccharide production increased slowly and reached about 2g alginate equivalent/cm(2) by the end of both experiments. At a C/N ratio of 5, polysaccharide increase significantly after 84 h, reaching about 7mug alginate equivalent/cm(2) prior to termination. At a C/N ratio of 10, polysaccharide increased significantly after 72 h and reached 21 mug alginate equivalent/cm(2) at 108 h. At C/N ratios of 0.07 and 1, protein production reached 6.5 and 4 mug/cm(2), respectively. At C/N ratios of 5 and 10, protein production increased slightly for the first 84 h and reached a maximum at 108 h, at 3 and 2 mug/cm(2), respectively, then decreased over the last 12 h of the experiment. Ratios of polysaccharide to protein increased with increasing C/N ratios. At C/N ratios of 0.07 and 1, the ratios between extracellular polysaccharide (EP) and protein were no more than 205 mug polysaccharide/mug protein, whereas those at C/N ratios of 5 and 10 increased to about 7 and 12 mug polysaccharide/mug protein, respectively.Probabilities of plasmid loss in the biofilm cultures increased with increasing C/N ratios. At C/N ratios of 0.07, 1, and 5, the probabilities of plasmid loss were 0.0013 +/- 0.011, 0.020 +/- 0.006 and 0.122 +/- 0.021, respectively. At a C/N ratio of 10, the probability of plasmid loss was significantly higher, reaching 0.38 +/- 0.125. The increase of probability of plasmid loss at higher C/N ratios results from competition between cell replication and extracellular polysaccharide production. (c) 1994 John Wiley & Sons, Inc. 相似文献
103.
104.
Niels Kroer 《FEMS microbiology ecology》1994,13(3):217-224
Abstract Cell volume, carbon and nitrogen content were determined for bacteria grown in batch cultures in water samples collected at five localities in western Florida, USA. Cultures were set up by inoculating 0.2 μm filtered water with 2.5 to 7.0% of 1.0 μm filtered water. Biovolumes of the bacteria were measured by epifluorescence photomicrography. Bacterial carbon and nitrogen contents were determined with a CHN analyser. During incubations, bacterial volumes doubled from 0.070±0.037 μ m3 (mean ± S.E.) to 0.153 ± 0.036 μ m3 at early stationary phase. Bacterial C:N ratios ranged between 2.8 and 10.3, with a mean of 6.5, and were inversely correlated with cell volumes. Conversion factors for volume to carbon and nitrogen content were relatively high and variable, ranging from 0.21 to 161 pg C μm−3 (mean: 0.72 pg C μm−3 ) and from 0.05 to 0.25 pg N μm−3 (mean: 0.12 pg N μm−3 ). Small cells contained more C and N per unit volume than did large cells. The data suggested that biovolume to biomass conversion factors may be higher than previously thought and may be highly variable both temporally and geographically. 相似文献
105.
106.
Bi-directional transfer of nitrogen between alfalfa and bromegrass: Short and long term evidence 总被引:2,自引:0,他引:2
Transfer of N from legumes to associated non-legumes has been demonstrated under a wide range of conditions. Because legumes
are able to derive their N requirements from N2 fixation, legumes can serve, through the transfer of N, as a source of N for accompanying non-legumes. Studies, therefore,
are often limited to the transfer of N from the legume to the non-legume. However, legumes preferentially rely on available
soil N as their source of N. To determine whether N can be transferred from a non-legume to a legume, two greenhouse experiments
were conducted. In the short-term N-transfer experiment, a portion of the foliage of meadow bromegrass (Bromus riparius Rhem.) or alfalfa (Medicago sativa L.) was immersed in a highly labelled 15N-solution and following a 64 h incubation, the roots and leaves of the associated alfalfa and bromegrass were analyzed for
15N. In the long-term N transfer experiment, alfalfa and bromegrass were grown in an 15N-labelled nutrient solution and transplanted in pots with unlabelled bromegrass and alfalfa plants. Plants were harvested
at 50 and 79 d after transplanting and analyzed for 15N content. Whether alfalfa or bromegrass were the donor plants in the short-term experiment, roots and leaves of all neighbouring
alfalfa and bromegrass plants were enriched with 15N. Similarly, when alfalfa or bromegrass was labelled in the long-term experiment, the roots and shoots of neighbouring alfalfa
and bromegrass plants became enriched with 15N. These two studies conclusively show that within a short period of time, N is transferred from both the N2-fixing legume to the associated non-legume and also from the non-legume to the N2-fixing legume. The occurrence of a bi-directional N transfer between N2-fixing and non-N2-fixing plants should be taken into consideration when the intensity of N cycling and the directional flow of N in pastures
and natural ecosystems are investigated. 相似文献
107.
Increased biomass production in terrestrial ecosystems with elevated atmospheric CO2 may be constrained by nutrient limitations as a result of increased requirement or reduced availability caused by reduced
turnover rates of nutrients. To determine the short-term impact of nitrogen (N) fertilization on plant biomass production
under elevated CO2, we compared the response of N-fertilized tallgrass prairie at ambient and twice-ambient CO2 levels over a 2-year period. Native tallgrass prairie plots (4.5 m diameter) were exposed continuously (24 h) to ambient
and twice-ambient CO2 from 1 April to 26 October. We compared our results to an unfertilized companion experiment on the same research site. Above-
and belowground biomass production and leaf area of fertilized plots were greater with elevated than ambient CO2 in both years. The increase in biomass at high CO2 occurred mainly aboveground in 1991, a dry year, and belowground in 1990, a wet year. Nitrogen concentration was lower in
plants exposed to elevated CO2, but total standing crop N was greater at high CO2. Increased root biomass under elevated CO2 apparently increased N uptake. The biomass production response to elevated CO2 was much greater on N-fertilized than unfertilized prairie, particularly in the dry year. We conclude that biomass production
response to elevated CO2 was suppressed by N limitation in years with below-normal precipitation. Reduced N concentration in above- and belowground
biomass could slow microbial degradation of soil organic matter and surface litter, thereby exacerbating N limitation in the
long term. 相似文献
108.
Although a high proportion of fertilizer N may be immobilized in organic forms in the soil, no studies have examined the long-term
availability of residual fertilizer 15N in forestry situations. We investigated this by growing lodgepole pine (Pinus contorta) seedlings in surface (0–10 cm) soil sample eight years after application of 15N-urea, 15NH4NO3 and NH4
15NO3 to lodgepole pine in interior British Columbia. After nine months of growth in the greenhouse, seedlings took up an average
of 8.5% of the 15N and 4.6% of the native N per pot. Most of the mineral N in the pots without seedlings was in the form of nitrate, while
pots with seedlings had very low levels of mineral N. In contrast to the greenhouse study, there was no significantuptake
of 15N by trees in the field study after the first growing season, although half of the soil organic 15N was lost between one and eight years after fertilization. This indicates the need to understand the mechanisms which limit
the uptake of mineral N by trees in the field, and the possible mismatch of tree demand and mineral N availability. 相似文献
109.
An experiment is described in which the magnitude of N transferred from damaged white clover roots to perennial ryegrass was determined, using 15N labelling of the grass plant. There was no effect on the growth and N-fixation of the clover plants after removing part of the root system. The 15N data suggested that N had been acquired by all grass plants, even in plants grown alone with no further N supplied after labelling. However, after quantifying the mobile and stored N pools of the grass plants it was evident that significant transfer of N from clover to grass only took place from damaged clover roots. Dilution of the atom% 15N in the roots of the grass plants grown alone, and in association with undamaged clover roots, was explained by remobilisation of N within the plant. 相似文献
110.
Nutrient distribution in a Swedish tree species experiment 总被引:2,自引:0,他引:2
The influence of four tree species on the distribution of nutrients between different compartments of the ecosystem was examined.
In a randomized block (n=3) experiment in south-western Sweden, Ca, Mg and K were determined as exchangeable amounts in the
mineral soil and as total amounts in the O+A1 horizons (topsoil) and in the aboveground tree biomass. N contents were determined in all compartments as well as P contents
of the aboveground tree biomass and the topsoil. The four tree species planted were: silver fir [Abies alba Mill.] (AA), grand fir [Abies grandis Lindl.] (AG), Norway spruce [Picea abies L. Karst.] (PA) and Japanese larch [Larix leptolepis (Sieb. och Zucc.) Endl.] (LL). At the age of 35–36 years, the total stemwood production of the most productive species, AG,
was estimated at 471 m3 ha−1. In relation to AG, LL had produced 80%, PA 73% and AA 37%.
The system totals [aboveground tree biomass total + topsoil total + exchangeable (Ca, Mg, K) or total (N) in the mineral soil]
of Ca, K and N did not differ significantly at the 5% level between the investigated species. For Mg, the system total in
LL was significantly higher than for the other species.
There was an indication that LL and AA contained higher amounts of Ca, Mg, K and N in the topsoil but less in the biomass
than did AG and PA (partly significant). In the mineral soil, there were no significant differences in the exchangeable pools
of Ca and K, nor in the total amounts of N.
The biomass nutrient concentrations generally decreased in the order: AA > PA > AG > LL. At stem or whole-tree harvest, the
Ca export per biomass unit would more than double in the case of PA compared to LL. LL also contained less N in the biomass
than the other species. However, the N content in the biomass did not differ between the most (AG) and the least (AA) productive
species, although the production of dry weight biomass (standing + harvested) of AG had been twice that of AA. It is concluded
that the nutrient budget of a managed forest may vary considerably depending on the choice of tree species. 相似文献