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排序方式: 共有457条查询结果,搜索用时 18 毫秒
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2.
Lampert Winfried Fleckner Walter Pott Eckart Schober Ursula Störkel Karl-Ulrich 《Hydrobiologia》1989,(1):415-424
Bioassays of different complexity were compared with respect to their capability to predict the environmental impact of the herbicide atrazine in aquatic systems. Acute toxicity tests with Daphnia did not yield meaningful results. Sublethal tests with Daphnia (feeding inhibition, reduction of growth and reproduction) were more sensitive, but effective concentrations of atrazine were still rather high (2 mg/L). A relatively complicated artificial food chain system that incorporated direct and indirect effects on Daphnia yielded significant reduction of daphnid population growth at 0.1 mg/L. Enclosure experiments with natural communities were by far the most sensitive tools. Community responses could be measured at concentrations as low as 1 µg/L and 0.1 µg atrazine/L. At the lowest concentration, however, communities recovered after three weeks. We conclude that in complex systems indirect effects can be more important than direct effects, so that, contrary to the conditions in simple tests, non-target organisms may be the better indicators of herbicide stress to natural communities. 相似文献
3.
Piotr Borsuk Marek Gniadkowski Ewa Bartnik Piotr P. Stępień 《Journal of molecular evolution》1988,28(1-2):125-130
Summary AllAspergillus nidulans 5S rRNA pseudogenes known so far are the result of integration of an approx. 0.2-kbp-long DNA sequence into the 5S rRNA genes. This sequence, called block C, is present in at least five copies in theA. nidulans genome and seems to be associated either with 5S rRNA genes or pseudogenes. In contrast to the 78% sequence conservation of the C-block in pseudogenes, the truncated 5 halves of the pseudogenes are very highly conserved (96.9–100%). We postulate that the 5S rRNA pseudogenes are still a subject of concerted evolution. The C-block sequence shows similarity to the switch region of the mouse heavy chain immunoglobulin gene. A characteristic motif GGGTGAG is repeated several times in both sequences; the sequence conservation is 63%. 相似文献
4.
Current concepts of the developmentally controlled multigene family of intermediate filament (IF) proteins expect the origin of their complexity in evolutionary precursors preceding all vertebrate classes. Among invertebrates, however, firm ultrastructural as well as molecular documentation of IFs is restricted to some giant axons and to epithelia of a few molluscs and annelids. As Ascaris lumbricoides is easily dissected into clean tissues, IF expression in this large nematode was analyzed by electron microscopic and biochemical procedures and a monoclonal antibody reacting with all mammalian IF proteins. We document for the first time the presence of IFs in muscle cells of an invertebrate. They occur in three muscle types (irregular striated pharynx muscle, obliquely striated body muscle, uterus smooth muscle). IFs are also found in the epithelia studied (syncytial epidermis, intestine, ovary, testis). Immunoblots on muscles, pharynx, intestine, uterus, and epidermis identify a pair of polypeptides (with apparent molecular masses of 71 and 63 kD) as IF constituents. In vitro reconstitution of filaments was obtained with the proteins purified from body muscle. In the small nematode Caenorhabditis elegans IF proteins are so far found only in the massive desmosome-anchored tonofilament bundles which traverse a special epithelial cell type, the marginal cells of the pharynx. We speculate that IFs may occur in most but perhaps not all invertebrates and that they may not occur in all cells in large amounts. As electron micrographs of the epidermis of a planarian--a member of the Platyhelminthes--reveal IFs, the evolutionary origin of this cytoplasmic structure can be expected either among the lowest metazoa or already in some unicellular eukaryotes. 相似文献
5.
Amino acid sequence of Manduca sexta adipokinetic hormone elucidated by combined fast atom bombardment (FAB)/tandem mass spectrometry 总被引:1,自引:0,他引:1
R Ziegler K Eckart H Schwarz R Keller 《Biochemical and biophysical research communications》1985,133(1):337-342
Combination of Fast Atom Bombardment Tandem Mass Spectrometry with Amino Acid Analysis assigns the amino acid sequence of the Manduca sexta adipokinetic hormone as pGlu-Leu-Thr-Phe-Thr-Ser-Ser-Trp-GlyNH2. Similarities and differences with other invertebrate hormones and with mammalian glucagon are discussed. 相似文献
6.
Summary Analysis by gas chromatography revealed the presence of small amounts of squalene, but not lanosterol nor ergosterol in Pythium paroecandrum, P. ultimum, P. graminicola, and P. arrhenomonas. However, when acetate-14C was used as a precursor for sterols, even squalene was not found in P. graminicola. The deficiency in the sterol synthesizing mechanism may therefore be at or before the squalene forming step. Both squalene and ergosterol were present in the mycelium of Rhizoctonia solani, as shown by both gas chromatography and by the incorporation of acetate-14C into ergosterol. The absence of ergosterol in Pythium and its presence in Rhizoctonia is consistant with the resistance to the antibiotic filipin of Pythium species and the sensitivity of R. solani. 相似文献
7.
Summary The growth of several Pythium species is increased between 65 and 100% if cholesterol is added to the growth medium. The optimum concentration is 15 mcg per ml. Mycelium of Pythium ultimum, in which cholesterol is present, incorporates glucose-U-14C and releases 14CO2 at a faster rate than the corresponding sterol free mycelium. In sterol containing cells, more 14CO2 is produced from a given amount of absorbed glucose-U-14C than in sterol free cells, there is thus in sterol containing hyphae a higher level of energy production. This condition can account for the increase in growth due to cholesterol. Only if sterols are present in the cellular membranes of Pythium species is the optimum synthetic capacity reached. 相似文献
8.
Summary In tip-growingChara rhizoids, the in-vivo saltatory movements of Golgi vesicles were recorded. The movements in radial direction back and forth between the ER aggregate and the plasma membrane occurred three times more often than movements passing the ER aggregate tangentially. The mean velocity of the class of Golgi vesicles observed (0.4–1 m in diameter) was approx. 0.3 m/s. Higher speed of 1–1.5 m/s occurred only in radial directions. Possibly, the ER aggregate is involved in guidance of the Golgi vesicles.Abbreviations DIC
differential interference contrast
- ER
endoplasmic reticulum
- OsFeCN
osmium tetroxide-potassium ferricyanide
Dedicated to the memory of Professor O. Kiermayer 相似文献
9.
Quantification of net nitrogen mineralization (NNM) in soils is indispensable in order to optimize N fertilization of crops.
Two long-term laboratory incubation methods were applied to determine rates of net nitrogen mineralization (rNNM) of soils from two sites of arable land (sandy loam soil, silty loam soil) at four temperature levels (2°C, 8°C, 14°C, 21°C).
Since variability within replicates was small, the modified 12-week incubation method of Stanford and Smith (1972) using disturbed
soils allowed to establish reliable Arrhenius functions with reasonable expenditure. The fit of the functions derived from
the 5-month incubation of 23 undisturbed soil columns (4420 cm3) was worse. This was caused by greater variability and less differentiation between temperature levels. Results of both experiments
could be described best by zero-order kinetics. Mean mineralization rates of disturbed samples were approximately twice as
high than those of undisturbed samples. The suitability of both methods for the prediction of NNM at site conditions is discussed.
Actual respiration (AR) at incubation temperatures and substrate induced respiration (SIR) were measured at the end of the
incubation of undisturbed soil columns. The results presented reveal that soil microbial communities develop in a different
manner during long-term incubation at different temperatures. This behavior offends the underlying assumption that soil microbes
remain in steady-state during incubation and that rising rates are physiological reactions to temperature enhancement. Therefore
soil microbial biomass (SMB) dynamics during the experiment has to be accounted for when rates of NNM and Arrhenius functions
are established. R Merck Section editor 相似文献
10.