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51.
Hegde SS Vetting MW Roderick SL Mitchenall LA Maxwell A Takiff HE Blanchard JS 《Science (New York, N.Y.)》2005,308(5727):1480-1483
Fluoroquinolones are gaining increasing importance in the treatment of tuberculosis. The expression of MfpA, a member of the pentapeptide repeat family of proteins from Mycobacterium tuberculosis, causes resistance to ciprofloxacin and sparfloxacin. This protein binds to DNA gyrase and inhibits its activity. Its three-dimensional structure reveals a fold, which we have named the right-handed quadrilateral beta helix, that exhibits size, shape, and electrostatic similarity to B-form DNA. This represents a form of DNA mimicry and explains both its inhibitory effect on DNA gyrase and fluoroquinolone resistance resulting from the protein's expression in vivo. 相似文献
52.
B. H. Howard M. S. Ridout 《The Journal of Horticultural Science and Biotechnology》2013,88(6):673-680
The length of the annual shoots produced on hedges of the plum rootstock Prunus insititia ‘Pixy’ was determined more by the duration of their growth than by their growth rate. The most dominant shoots from the distal part of the framework grew for more than 16 weeks while weak shoots from lower down the framework stopped growing in half that time. There was a curvilinear relationship between shoot length and the proximal diameter of the cutting prepared from it, for shoots from various sources comprising different levels of winter pruning and different parts of the framework of the bush. The extent to which rooting potential was expressed was determined by the management of the rooting medium. When this was too wet, cutting bases developed necrosis which was particularly prevalent in the thinner cuttings. This problem was avoided by planting cuttings with their bases on rapidly draining sand rather than in granulated bark. Under these circumstances percentage rooting decreased with increasing cutting thickness. Before necrosis was controlled in this way rooting increased with increasing proximal stem diameter up to 6-8 mm, reflecting the susceptibility of thin cuttings to over-wet conditions. 相似文献
53.
Cattle infested with the common cattle grub, Hypoderma lineatum (Villers) develop specific humoral antibodies and a cellular immune reaction, defined by delayed-type hypersensitivity, to purified H. lineatum proteins. This investigation was designed to study the antigen-specific bovine lymphocyte response to hypodermin A (HyA), a serine protease of larval first-instar H. lineatum. Calves were vaccinated with either native or denatured HyA, and challenge-infested with H. lineatum. The kinetic development of a cellular immune response to HyA was monitored during vaccination and infestation. The HyA-specific responses were highly variable and weak during vaccination and infestation. Although HyA-specific lymphocyte blastogenic responses were observed, no correlation was noted between the magnitude of antigen-specific, peripheral lymphocyte proliferation and larval mortality. In striking contrast to responses observed during infestation, intense HyA-specific lymphocyte responses were observed with 3 calves 6 months after recovery from infestation. In addition, those responses were further heightened by a 250 micrograms booster injection of pure HyA. 相似文献
54.
Ninety eight parous fallow does received laparoscopic intrauterine insemination of frozen-thawed semen at one of 2 fixed intervals following oestrus synchronisation treatment. Semen was collected from a Mesopotamian (Dama dama mesopotamica) and a crossbred (F1) (Dama dama dama x Dama dama mesopotamica) fallow buck. Does were inseminated at either 56 or 66 hours after the removal of an intravaginal controlled internal drug releasing device. Eighty eight does received a single straw of frozen-thawed semen containing a total of 50 x 10(6) spermatozoa, while the remaining 10 received split straws containing 25 x 10(6) spermatozoa. Overall, the use of F1 semen containing 50 x 10(6) spermatozoa resulted in a 68% (17/25) conception rate compared with the Mesopotamian semen, which resulted in a 41% (26/63) conception rate. Conceptions were also achieved using 25 x 10(6) spermatozoa of either Mesopotamian or F1 semen (3/8 versus 2/2, respectively). Overall, the conception rate was higher for F1 than Mesopotamian semen (P less than 0.025) and there was a significant interaction with time of insemination (P less than 0.05); for F1 semen there was no difference in conception rate at the 2 insemination times, but for Mesopotamian semen conception was significantly higher (P less than 0.005) following insemination at 66 hours than at 56 hours. 相似文献
55.
56.
Monoclonal antibodies (mAbs) specific for bovine CD4 and CD5 antigens have been found to identify polymorphic determinants on these molecules. In the case of CD5, mAb IL-A67 recognises one allotypic form of the antigen while four other CD5-specific mAbs in the workshop (CC17, CC29, BLT-1 and 8C11) recognise a second allotype. The CD4-specific mAbs submitted to the workshop reacted with the cells of all animals tested. However, a further two mAbs (CC26 and IL-A18) specific for CD4 were found to react with cells only from about 85% of animals tested. Sequential immuno-precipitation experiments together with family studies showed that the allotypes of CD4 and CD5 are both inherited in a simple Mendelian manner and are co-dominantly expressed. One of the CD5 allotypes was not detected in Bos taurus animals while the gene frequency of the second allotype was only about 10% in the B. indicus animals tested. The gene frequency of the CD4 allotype detected by CC26 and IL-A18 was similar in the two sub-species. 相似文献
57.
Summary The Andigena potatoes (Solanum tuberosum ssp.andigena) of the Commonwealth Potato Collection (C.P.C.) were screened for resistance to non-pathotype A populations ofHeterodera rostochiensis. Three populations were used: Duddingston (pathotype B), Nocton (pathotype C) and Changed Little Ouse (pathotype C). Resistance was found in C.P.C. 2775, 2802 and 2805. C.P.C. 2775 also had resistance to pathotype A (Feltwell population) and appeared to have two dominant genes,H
1 giving resistance to pathotype A andH
3 giving resistance to pathotypes B and C. C.P.C. 2802 was susceptible to pathotype A and appeared to have only anH
3-type gene. C.P.C. 2805, which has not been investigated thoroughly because the plants lacked vigour, may also have anH
1 and anH
3 gene. The value of C.P.C. 2775, 2802 and 2805 for breeding nematode-resistant potatoes will only be known when they have been tested with further non-pathotype A populations and when the genetics of resistance have been investigated thoroughly. 相似文献
58.
The effect of Pseudomonas putida (isolate M17) on Rhizobium phaseoli nodulation of the common bean, Phaseolus vulgaris, was investigated under field and greenhouse conditions. The results indicated that P. putida markedly increased nodulation compared to R. phaseoli controls. Furthermore, 2-ketogluconic acid, a phosphate-solubiliring compound, was detected in P. putida M17. This could imply an increased P supply to roots of P. vutgaris, which may function to increase nodules. Bean yields and shoot fresh weight were not significantly altered by the addition of P. putida M17. 相似文献
59.
M. Alisa Mast Donald H. Campbell David P. Krabbenhoft Howard E. Taylor 《Water, air, and soil pollution》2005,164(1-4):21-42
Mercury (Hg) was measured in stream water and precipitation in the Loch Vale watershed in Rocky Mountain National Park, Colorado, during 2001–2002 to investigate processes controlling Hg transport in high-elevation ecosystems. Total Hg concentrations in precipitation ranged from 2.6 to 36.2 ng/L and showed a strong seasonal pattern with concentrations that were 3 to 4 times higher during summer months. Annual bulk deposition of Hg was 8.3 to 12.4 μ g/m2 and was similar to deposition rates in the Midwestern and Northeastern U.S. Total Hg concentrations in streams ranged from 0.8 to 13.5 ng/L and were highest in mid-May on the rising limb of the snowmelt hydrograph. Stream-water Hg was positively correlated with dissolved organic carbon suggesting organically complexed Hg was flushed into streams from near-surface soil horizons during the early stages of snowmelt. Methylmercury (MeHg) in stream water peaked at 0.048 ng/L just prior to peak snowmelt but was at or below detection (< 0.040 ng/L) for the remainder of the snowmelt season. Annual export of total Hg in Loch Vale streams ranged from 1.2 to 2.3 μ g/m2, which was less than 20% of wet deposition, indicating the terrestrial environment is a net sink of atmospheric Hg. Concentrations of MeHg in stream water and corresponding watershed fluxes were low, indicating low methylation rates or high demethylation rates or both. 相似文献
60.
Helen J. Foster Matthew J. Lees Howard S. Wheater Colin Neal Brian Reynolds 《Water, air, and soil pollution》2001,130(1-4):1283-1288
Concern about acidification in upland areas has brought about the need to model the stream hydrochemical response to deposition and land-use changes and calculate critical loads. Application of dynamic models such as MAGIC are preferable to steady-state methods, since they are able to produce an estimate of the time scale required to meet some water chemistry target given a reduction in acid deposition. These models typically consider annual changes in stream chemistry at one point. However, in order to protect biota from 'acid episodes', quantification of temporal variability needs to encompass event responses; in addition spatial variability across the catchment also needs to be considered. In this paper, modelling of both spatial and temporal variability is combined in a new framework which enables quantification of catchment hydrochemical variability in time and space. Both low and high flow hydro-chemical variability are quantified in terms of statistical distributions of ANC (Acid Neutralisation Capacity). These are then input as stochastic variables to an EMMA (End-Member Mixing Analysis) model which accounts for temporal variability and ANC is hence predicted as a function of time and space across the whole catchment using Monte-Carlo simulation. The method is linked to MAGIC to predict future scenarios and may be used by iteration to calculate critical loads. The model is applied to the headwaters of the River Severn at Plynlimon, Wales, to demonstrate its capabilities. 相似文献