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241.
A. Le Ralec 《BioControl》1995,40(1):87-93
Using transmission electron microscopy, egg content is studied in 10 parasitoid species, which either feed on host hemolymph or do not. As expected, hydropic eggs were found to contain little yolk which is only lipoid. In host-feeding species, the yolk contains a great number of typical protein bodies whereas in species that do not host-feed and which produce large eggs, the yolk contain very different bodies. 相似文献
242.
Sandra Irene Pitta-Alvarez Ana María Giulietti 《In vitro cellular & developmental biology. Plant》1995,31(4):215-220
Summary
Brugmansia candida hairy roots, obtained by infection withAgrobacterium rhizogenes LBA 9402, exhibit, after subculturing in liquid media, a tendency towards dedifferentiation. It has been found that the following
strategies can be applied to inhibit this dedifferentiation and preserve normal root morphology: (a) lowering both the mineral
and sucrose concentration in the media employed so as to diminish osmotic stress (a condition to which these roots appear
to be particularly susceptible); (b) employing antiauxins in appropriate concentrations; and (c) maintaining the hairy roots
on solid media prior to use in production processes in liquid media. The first strategy suggested does not favor alkaloid
productivity, but in this case a two-step method could be attempted: biomass with normal root morphology could be obtained
in a first stage using low sucrose concentrations, and in a second stage, sucrose could be increased in order to achieve higher
productivity. In all the clones ofB. candida obtained, alkaloid production was biased towards scopolamine. 相似文献
243.
C. Kevers B. Bisbis F. Le Dily J. P. Billard C. Huault Th. Gaspar 《In vitro cellular & developmental biology. Plant》1995,31(2):122-126
The transfer of light-cultured green normal (N) and white habituated (HNO) sugarbeet callus to darkness reduced the growth
of N callus and improved growth and delayed necrosis in the HNO callus. The decrease of dry matter of N callus under darkness
was accompanied by a reduced content of carotenoids and by decreased CO2 fixation, which was compensated by an increased dependency on externally supplied sucrose. The levels of some organic nitrogen
compounds such as glutamate, proline, and free polyamines were not affected by transfer to darkness of N or HNO callus. Darkness
decreased ethylene emissions in both callus types. In the HNO callus, the sucrose growth dependency and the CO2 fixation were unaffected by darkness. Chlorophylls were absent both in light and darkness, whereas some carotenoids were
accumulated in the HNO callus only in dark conditions. In another connection, a significant increase of peroxidase activity,
which did not occur in the N callus, was induced by darkness in the HNO callus. A decreased content of thio-barbituric acid
(TBA)-reactive substances was measured in the HNO callus transferred to darkness, whereas an increase was noticed in the N
callus placed in the same conditions. These metabolic changes and the reduction of cellular damage in darkness revealed light-induced
stress reactions leading to necrosis and to reduced growth of HNO callus. It appeared that darkness allowed the HNO callus
to avoid the photooxidation stress. Therefore, the favorable effect of darkness on HNO growth might be explained by the suppression
of photooxidative damage due to the absence of carotenoids. The higher peroxidase activity in the HNO callus maintained in
darkness raised the problem of heme synthesis in this heterotrophic callus. 相似文献
244.
Abstract. The Argentine Chaco is a mosaic of grassland and open forest habitats maintained by natural disturbance activities such as fire. Since the introduction of domestic livestock and other human activities, the balance of this mosaic has been significantly altered, both in plant species and structural composition. This study focuses on the impact of such changes on the diversity of ground-dwelling arthropods within semi-arid Chaco forest. Quantitative measures of habitat structure and arthropod diversity were taken in forest areas previously subjected to grazing, logging and ploughing. Results indicated that arthropod diversity was smaller on sites with reduced structural complexity, with marked changes in arthropod family composition. The habitat components relating to plant architectural and vertical diversity were particularly influential on arthropod diversity. The guild size ratio of predatory to non-predatory arthropods also differed significantly between habitats suggesting a change in the resource base available to some groups. The latter suggests a shift in the functional organisation of the forest ecosystem which could have important repercussions for the diversity of other trophic levels. 相似文献
245.
An RNA pseudoknot is an essential structural element of the internal ribosome entry site located within the hepatitis C virus 5' noncoding region. 总被引:8,自引:2,他引:6
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Translation of the human hepatitis C virus (HCV) RNA genome occurs by a mechanism known as "internal ribosome entry." This unusual strategy of translation is employed by naturally uncapped picornaviral genomic RNAs and several cellular mRNAs. A common feature of these RNAs is a relatively long 5' noncoding region (NCR) that folds into a complex secondary structure harboring an internal ribosome entry site (IRES). Evidence derived from the use of dicistronic expression systems, combined with an extensive mutational analysis, demonstrated the presence of an IRES within the HCV 5'NCR. The results of our continued mutational analysis to map the critical structural elements of the HCV IRES has led to the identification of a pseudoknot structure upstream of the initiator AUG. The evidence presented in this study is based upon the mutational analysis of the putative pseudoknot structure. This is further substantiated by biochemical and enzymatic probing of the wild-type and mutant 5'NCR. Further, the thermodynamic calculations, based upon a modified RNAKNOT program, are consistent with the presence of a pseudoknot structure located upstream of the initiator AUG. Maintenance of this structural element is critical for internal initiation of translation. The pseudoknot structure in the 5'NCR represents a highly conserved feature of all HCV subtypes and members of the pestivirus family, including hog cholera virus and bovine viral diarrhea virus. 相似文献
246.
B. Canguilhem A. Malan M. Masson-Pévet P. Nobelis R. Kirsch P. Pévet J. Le Minor 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1994,163(8):690-698
Temporal patterns of hibernation were studied by continuous monitoring of body temperature by radiotelemetry over 6 months in European hamsters, Cricetus cricetus, at constant temperature and photoperiod. Entrances into hibernation occurred mostly at the end of the night (0000–0800 hours), while arousals were randomly distributed between day and night. This is at variance with a control of bout duration by a clock with a period of 24 h. Consequently, the timing of entrances implies a phase-resetting of the circadian clock on each arousal. Persistence of circadian rhythmicity with a period different from 24 h during deep hibernation was investigated examining whether the durations of torpor bouts were integer multiples of a constant period. A non-parametric version of the classical contingency test of periodicity was developed for this purpose. Periods ranging from 21 to 29 h were tested. Nine animals out of ten showed at least one significant period in this range (P<0.01), either below 24 h (21.8±0.5 h, n=4) or above (27.3±0.5 h, n=7). However, we have found a theoretical model of bout durations for which the contingency test of periodicity sometimes gives false significant results. This indicates that the power of the test is weak. With this reservation our results suggest that a circadian oscillator controls the duration of a bout of hibernation, which would occur after an integer, but variable and possibly temperature-dependent number of cycles.Abbreviations b
a contingency test (see Appendix)
- SCN
suprachiasmatic nuclei
-
period
-
T
b
body temperature 相似文献
247.
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
248.
G. Ferretti M. V. Narici T. Binzoni L. Gariod J. F. Le Bas H. Reutenauer P. Cerretelli 《European journal of applied physiology and occupational physiology》1994,68(2):111-115
The relationships between absolute peak muscle power (W
peak), muscle cross sectional area (CSAtot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20–35 years; B, 9 S aged 35–50 years; C, 9 S aged more than 50 years; D, 13 children aged 8–13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The W
peak was measured during a maximal vertical high jump off both feet on a force platform. The CSAtot was measured anthropometrically. The [ATP] and [PC] were determined by 31Phosphorus nuclear magnetic resonance spectroscopy. The W
peak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSAtot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in W
peak were only partially accounted for by changes in CSAtot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of W
peak with increasing age and training. An important role may be played by hormonal, particularly at puberty, and neural factors. 相似文献
249.
Use of Genetic and Physical Mapping to Locate the Spinal Muscular Atrophy Locus between Two New Highly Polymorphic DNA Markers 总被引:9,自引:2,他引:7
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Olivier Clermont Philippe Burlet Lydie Burglen Suzie Lefebvre Fabrice Pascal John McPherson John J. Wasmuth Daniel Cohen Denis Le Paslier Jean Weissenbach Mark Lathrop Arnold Munnich Judith Melki 《American journal of human genetics》1994,54(4):687-694
The gene for autosomal recessive forms of spinal muscular atrophy (SMA) has recently been mapped to chromosome 5ql3, within a 4-cM region between the blocks D5S465/D5S125 and MAP-1B/D5S112. We identified two new highly polymorphic microsatellite DNA markers—namely, AFM265wf5 (D5S629) and AFM281yh9 (D5S637)—which are the closest markers to the SMA locus. Multilocus analysis by the location-score method was used to establish the best estimate of the SMA gene location. Our data suggest that the most likely location for SMA is between locus D5S629 and the block D5S637/D5S351/MAP-1B/D5S112/D5S357. Genetic analysis of inbred SMA families, based on homozygosity by descent and physical mapping using mega-YACs, gave additional information for the loci order as follows: cen–D5S6–D5S125/D5S465–D5S435–D5S629–SMA–D5S637–D5S351–MAP–1B/D5S112–D5S357–D5S39–tel. These data give the direction for bidirectional walking in order to clone this interval and isolate the SMA gene. 相似文献
250.
Cloning, expression, and nucleotide sequence of genes involved in production of lactococcin DR, a bacteriocin from lactococcus lactis subsp. lactis. 总被引:6,自引:4,他引:2
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A Rince A Dufour S Le Pogam D Thuault C M Bourgeois J P Le Pennec 《Applied microbiology》1994,60(5):1652-1657
The partial nucleotide sequence of a Lactococcus lactis subsp. lactis ADRIA 85LO30 bacteriocin-producing operon was determined. The first two open reading frames of the operon are necessary to get bacteriocin expression in L. lactis IL1403R. 相似文献