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91.
Supernumerary chromosomes of two types have been observed in the grasshopper Eyprepocnemis plorans subsp. plorans. One of these (the B-type) is similar in size to an S autosome; the other is smaller (B-type). Both are telocentric and mitotically stable. The frequencies of individuals with the B-type supernumeraries in five natural populations were 56, 56, 70, 71 and 30 per cent respectively. The equivalent levels of the B-type supernumerary were 0, 0, 13, 3 and 0 per cent respectively. Because of the relative infrequency of the B-type only the B-type has been studied in detail. In males with 1B, anaphase I segregation of X and B was random in four populations but non-random in that from Otivar. Here the B was distinctive in having a secondary constriction near the centromere. A study of chiasma frequency among A-chromosomes revealed that the B-type supernumerary increases significantly both the mean chiasma frequency and the between-cell variance. A comparison of body morphometrics failed to reveal any effect of these B-chromosomes on the exophenotype. 相似文献
92.
Cytogenetic aspects of the cryptobranchid salamander Andrias davidianus of western China have been studied, including chromosome number and morphology, C-band patterns, meiosis, and the chromosomal localization of ribosomal 5S RNA genes. Our data regarding chromosome number (2n=60) and general chromosome morphology largely confirm the results of Morescalchi et al. (1977). The karyotype consists of 16 pairs of macrochromosomes that decrease gradually in relative length to 14 pairs of microchromosomes. Telocentric chromosomes are a conspicuous feature of the karyotype, representing more than half the genome. Differential staining reveals that all of the chromosomes, except four pairs of microchromosomes, have C-band heterochromatin in their centromeric regions, the amount varying irrespective of chromosome size. Faint bands of interstitial and telomeric C-band heterochromatin are found in mitotic chromosomes but are not seen in meiotic preparations. In C-banded mitotic preparations from a female, one of the smallest macrochromosome pairs is heteromorphic in respect to C-band heterochromatin and centromere position. In situ hybridization of an iodinated 5S RNA probe to meiotic chromosome preparations reveals that this repeated gene is clustered near the telomeric region of chromosome 7, a medium size telocentric, a location corresponding to a band of heterochromatin. Studies of spermatocytes indicate that the process of meiosis in A. davidianus closely resembles that of more advanced salamanders, and that the microchromosomes are meiotically stable. The significance of microchromosomes and chromosome morphology in the reorganization of salamander genomes during evolution is discussed on the basis of cytogenetic data available for A. davidianus and various other primitive and advanced salamanders. 相似文献
93.
Sequence of the S-layer gene of Thermus thermophilus HB8 and functionality of its promoter in Escherichia coli.
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The nucleotide sequence of the slpA gene, which is responsible for the synthesis of the S-layer protein of Thermus thermophilus HB8, is described. This gene is transcribed as a unit in which the coding region is preceded by a 127-base-long leader mRNA sequence. The promoter region is also recognized by the RNA polymerase of Escherichia coli because of the presence of homologous -35 and -10 boxes. Homologies with other promoters from Thermus spp. are also presented. 相似文献
94.
An arctic river was fertilized continuously through the ice-free season with phosphoric acid beginning in 1983. The epilithic
diatom community increased in biomass in the first two years in response to the added limiting nutrient (Peterson et al., 1983). The diatom community switched from one dominated by Hannea arcus to one dominated by species of Achnanthes and Cymbella. The immediate responses to the P-addition were decreases in both
the Shannon diversity and evenness indices. By the second year, the community diversity increased downriver reaching maximal
species richness (110–127 spp). In 1985–1987, the epilithic algal biomass decreased an order of magnitude with both whole-river
PO4 (1985, 1987) and PO4 + NH4 addition (1986). In the 5th summer of fertilization, the reduction in biomass was clearly caused by a numerical increase
of grazing, refugia-building chironomids (Orthocladiinae, primarily) (Gibeau, 1991; Gibeau, Miller, Hershey, in prep.). We
assume the algal biomass reduction in the 3rd and 4th years was similarly caused by grazers with a two year time lag in the
numerical response of these monovoltine species. The evenness of the community increased in 1986 as if it might have been
grazed; however the number of immigrants was reduced. The community became dominated by Eunotia, Cymbella and Achnanthes,
species either fast growing or more prostrate, as the erect species of Hannea Diatoma, and Fragillaria declined. A detrended
correspondence analysis of the temporal and spatial diatom samples in species space (186 spp.) showed that the largest variation
in the community was between years and less variation was associated with river fertilization.
Samples from bioassay tubes run by Peterson et al. (1983) in the Kuparuk River showed P and N + P limitation as found in the river in 1983–84. Like the river samples, the
largest change in the diatom community occurred between 15 and 25 day samples, more than that induced by fertilization. Diatoms
sampled from all treatments taken at day 25 were more similar to one another than those sampled at day 15. Diatoms colonizing
glass slides used in the bioassay tubes were dominated by Achnanthes linearis and Cymbella minuta. Of the 84 species found in bioassays, 26 species were present in all river samples for 4 years. Differences in the communities
discriminated by multivariate methods were cause by changes in rare species and abundance patterns of common species. 相似文献
95.
Effects of Feeding and Drinking on Acetylcholine Release in the Nucleus Accumbens, Striatum, and Hippocampus of Freely Behaving Rats 总被引:4,自引:0,他引:4
Gregory P. Mark Pedro Rada Emmanuel Pothos Bartley G. Hoebel 《Journal of neurochemistry》1992,58(6):2269-2274
Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatum (STR), and hippocampus (HIPP) using microdialysis in 30-min intervals before, during, and after free-feeding in 20-h food-deprived rats. The effects on ACh in the NAC and STR were also observed in response to water intake in 20-h water-deprived animals. Neostigmine was used in the perfusate to improve ACh recovery. Basal ACh was sensitive to tetrodotoxin and low calcium, and therefore largely neuronal in origin. Feeding caused a 38% increase in extracellular ACh in the NAC and no change in the STR or HIPP. Dopamine was also increased in the NAC (48%) and to a lesser extent in the STR (21%) following feeding. Drinking caused 18-20% increases in ACh release in both the NAC and STR. In a separate experiment, ACh release in the NAC was monitored in 10-min intervals during free-feeding; ACh increased in the interval immediately following maximal food intake. These results suggest a site-specific increase in ACh release following feeding that cannot be solely attributed to the activation associated with this behavior. 相似文献
96.
Summary Papain was able to catalyze the one-step synthesis of Gly-Gly-PheNH2, from N-unprotected amino acid derivatives. Maximum synthetic activity was obtained for a pH value of 6.5 and for a ]PheNH2]/[Gly-GlyOEt] ratio of 6. The presence of an organic cosolvent, such as ethylene glycol, influenced the synthetic activity. Synthetic yield was higher than 65% for a 12.5 M cosolvent concentration. 相似文献
97.
98.
Monod's equation adequately described aerobic biodegradation rates of benzene and toluene by the microbial population of a sandy aquifer when these compounds were initially present at concentrations lower than 100 mg/l each. Concentrations higher than 100 mg/l were inhibitory, and no benzene or toluene degradation was observed when these compounds were initially present at 250 mg/l each. The Monod coefficients were calculated as k = 8.3 g-benzene/g-cells/day and Ks = 12.2 mg/l for benzene, and k = 9.9 g-toluene/g-cells/day and Ks = 17.4 mg/l for toluene. Specific first-order coefficients would be 0.68 l/mg.day for benzene and 0.57 l.mg.day for toluene. 相似文献
99.
Lisbeth E. Gomez Pedro A.F. Lehmann 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1992,575(2)
A sensitive gas chromatographic method with flame ionization detection was developed for the analysis in plasma of the novel anticonvulsant d,l-3-hydroxy-3-ethyl-3-phenylpropionamide (HEPP), using d,l-2-hydroxy-2-ethyl-2-phenylacetamide as the internal standard. HEPP was extracted from alkalinized plasma into dichloromethane and quantified after derivatization with bis(trimethylsilyl)-trifluoroacetamide. Standard curves were linear from 0.5 to 50 and from 2 to 100 μg/ml of plasma, using 1.5 and 5 μg of the internal standard, respectively. The lower limit of detection at a signal-to-noise ratio of 3 standard deviations was 0.33 μg/ml of sample. The sensitivity, accuracy and reproducibility of the method were shown to be satisfactory for pharmacokinetic studies of HEPP. After intraperitoneal administration of 50 mg/kg to Wistar rats, the principal kinetic parameters were: absorption half-life = 0.04 h; volume of distribution = 1.32 l/kg; clearance = 4.40 ml/min; peak concentration = 50 μg/ml; peak time = 0.25 h; mean residence time = 4.55 h. 相似文献
100.
We assessed the effect of eel (Anguilla anguilla) removal from three sites of a Cantabrian stream upon its subsequent densities. In the first sample (Sept. 1986) numbers
and densities were estimated as 43, 45 and 84 ind and 3490, 3030 and 3750 ind ha −1. Removal of these eels reduced the subsequent numbers and densities which, except on two occasions, were never reached again
during the two years (eleven estimates) of study. Highest densities were recorded in the uppermost site in May and July, 1987,
coincident with a strong drought and the lowest densities occurred in 1988 during a normal wet year. We hypothesize first
that, because of a selective underground homing behaviour of eels, electro-fishing is inefficient and results in underestimates
of the population. Second, seasonal variations of water discharge and droughts may not influence the homing behaviour of'eels
until a threshold of dryness is reached. If this occurs, eels abandon their refuges and move towards the stream bottom. It
seems that in Arroyo Chabatchos this threshold was exceeded in the summer of 1987 when the highest densities were estimated.
The re-colonization of these sites experimentally depleted of eels, is a slow procces that lasts for, at least, two years. 相似文献