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71.
The organic content of the surficial sediment: a method for the study of ecosystems development in abandoned river channels 总被引:1,自引:0,他引:1
To characterise different abandoned river channels, a simple index of the surface sediment was developed i.e. the content of organic matter (expressed as C × N) plotted in relation to that of CaCO3. The age of the channels studied ranges from 20 to 300 years. Some of them still contain water; others are silted up. Two types are distinguished. The ecosystems of the first one are closed and show a slow rate of development governed by autogenous processes. Those of the second type are more open and show a fast rate of development mainly controlled by allogenous processes. These distinctions are used in a diagrammatic model of the dynamics of Rhône River alluvial plain to be used in fundamental or applied future research. 相似文献
72.
Radioiodination of highly purified human follicle-stimulating hormone (hFSH) (4000 IU/mg) was performed every other week for 23 weeks using 2 mCi carrier free Na 125I (Amersham Corp., 15 mCi/μg I2) in the presence of lactoperoxidase. Incorporation of 125I into hFSH was determined by the method of [7.]Biochem. J. 89, 114). Hormone binding was studied in vitro under steady-state conditions (16 h, 20°C) using different calf testis membrane preparations having similar receptor characteristics. Each 125I-hFSH preparation was characterized for maximum bindability, specific activity of bindable radioligand as determined by self-displacement analysis, and by determination of Ka and Rt. Incorporation of 125I into FSH was relatively constant over the large number of experiments (62.4 ± 6.4 μCi/μg; n = 23). By comparison, however, specific radioactivity of the receptor bindable fraction of 125I-hFSH was related to the lot of 125I utilized, and was significantly (P ≤ 0.01) lower and more variable (28.7 ± 10.5 μCi/μg). Maximum bindability of 125I-hFSH was not correlated to specific activity (r = 0.06) but was negatively correlated to hFSH 125I incorporation (r = −0.47; P ≤ 0.05). These observations demonstrate the need to assess the quality of each batch of radioligand before undertaking radioligand-receptor assays and suggest that differences in Na125I lots affect specific radioactivity of the radioligand and its receptor binding characteristics. 相似文献
73.
Aminoglycoside suppression at UAG, UAA and UGA codons in Escherichia coli and human tissue culture cells 总被引:6,自引:0,他引:6
Robin Martin Anne E. Mogg Louise A. Heywood Lars Nitschke Julian F. Burke 《Molecular & general genetics : MGG》1989,217(2-3):411-418
Summary We have compared the suppression of nonsense mutations by aminoglycoside antibiotics inEscherichia coli and in human 293 cells. Six nonsense alleles of the chloramphenicol acetyl transferase (cat) gene, in the vector pRSVcat, were suppressed by growth in G418 and paromomycin. Readthrough at UAG, UAA and UGA codons was monitored with enzyme assays
for chloramphenicol acetyl transferase (CAT), in stably transformed bacteria and during transient expression from the same
plasmid in human 293 tissue culture cells. We have found significant differences in the degree of suppression amongst three
UAG codons and two UAA codons in different mRNA contexts. However, the pattern of these effects are not the same in the two
organisms. Our data suggest that context effects of nonsense suppression may operate under different rules inE. coli and human cells. 相似文献
74.
75.
Ecological genetics of salt resistance in the clonal perennial, Agrostis stolonifera L. 总被引:2,自引:2,他引:0
C. KIK 《The New phytologist》1989,113(4):453-458
76.
P. Plaha G. S. Sethi 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(5):685-688
Summary Thirteen wheat-like advanced-generation triticale x wheat derivatives, having tetraploid wheat cytoplasm from triticale, were reciprocally crossed with three improved bread wheats, and the resulting F1s were evaluated for determining the comparative performance of the bread wheat and triticale cytoplasms for different traits. Significant reciprocal differences in the mean performance were observed for days to heading, days to maturity, spikes/plant, flag-leaf area, peduncle length, plant height, spike length, grains/spike, 1,000-grain weight, grain yield and grain protein content, and most of them were in favour of hexaploid wheat cytoplasm. However, this superiority of the hexaploid cytoplasm was not universal for a particular trait, implying that the differences in the performance of the evaluated reciprocal crosses depended not solely on the cytoplasmic background, but also on the interplay of the specific genotype with the cytoplasm. 相似文献
77.
When cells of the unicellular green alga Chlamydomonas reinhardtii were subjected to microwave irradiation at 2.45 GHz, nitrite uptake kinetics still obeyed the Michaelis-Menten equation, the Km of the process remaining constant, whereas V
max
increased, which indicates an enhanced nonthermal permeability in irradiated cells. 相似文献
78.
79.
Summary Because seed size is often associated with survival and reproduction in plant populations, genetic variation for seed size may be reduced or eliminated by natural selection. To test this hypothesis we assessed genetic sources of variation in seed size in a population ofPhlox drummondii to determine whether genetic differences among seeds influence the size they attain. A diallel cross among 12 plants from a population at Bastrop, Texas, USA allowed us to partition variance in the mass of seeds among several genetic and parental effects. We found no evidence of additive genetic variance or dominance genetic variance for seed mass in the contribution of plants to their offspring. Extranuclear maternal effects accounted for 56% of the variance in seed mass. A small interaction was observed between seed genotype and maternal plant. Results of this study support theory that predicts little genetic variation for traits associated with fitness. 相似文献
80.
Influence of environmental factors on 2,4-dichlorophenoxyacetic acid degradation by Pseudomonas cepacia isolated from peat 总被引:1,自引:0,他引:1
A Pseudomonas cepacia, designated strain BRI6001, was isolated from peat by enrichment culture using 2,4-dichlorophenoxyacetic acid (2,4-D) as the sole carbon source. BRI6001 grew at up to 13 mM 2,4-D, and degraded 1 mM 2,4-D at an average starting population density as low as 1.5 cells/ml. Degradation was optimal at acidic pH, but could also be inhibited at low pH, associated with chloride release from the substrate, and the limited buffering capacity of the growth medium. The only metabolite detected during growth on 2,4-D was 2,4-dichlorophenol (2,4-DCP), and degradation of the aromatic nucleus was by intradiol cleavage. Growth lag times prior to the on-set of degradation, and the total time required for degradation, were linearly related to the starting population density and the initial 2,4-D concentration. BRI6001, grown on 2,4-D, oxidized a variety of structurally similar chlorinated aromatic compounds accompanied by stoichiometric chloride release. 相似文献