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11.
Mikael Hedrén 《Plant Systematics and Evolution》1996,201(1-4):31-55
Taxa endemic to North-western Europe are rare, but the orchid genusDactylorhiza contains several species restricted to this area. Evidence from morphological and cytological studies have indicated that some species may have arisen recently and may be of hybrid origin. In the present report, I use allozymes to characterize the genomes in various species ofDactylorhiza and evaluate the possibilities for rapid evolutionary change in the genus. Allotetraploid species have evolved repeatedly from two principal diploid ancestral lineages. These lineages include extant diploid and autotetraploid species, from which allotetraploid derivatives may still arise. It is suggested that allotetraploidization dominates over introgression as speciation mechanism in the genus. The more common and widespread allotetraploid species could be characterized by their allozyme characters over considerable distances, indicating that each of them may have a unique origin and that they have spread from their ancestral populations to the present distribution areas. However, it is also possible that some allotetraploid species contain local populations that have been independently derived from the ancestral lineages. 相似文献
12.
Summary Isolated cod brain microtubules from the cold-adapted Atlantic cod (Gadus morhua) have previously been shown to be highly detyrosinated, a post-translational modification of tubulin usually found in stable
subsets of microtubules. In this study we found this was not restricted only to isolated brain microtubules. Microtubules
in primary cultures of brain and skin cells were composed of both tyrosinated (Tyr)- and detyrosinated (Glu)-tubulin seen
by immunocytochemistry. Immunoelectron microscopy of isolated microtubules showed that individual microtubules were composed
of a mixture of Tyr- and Glu-tubulin. Leukocytes with extending lamellopodia contained only microtubules stained with the
antibody against Tyr-tubulin, and isolated heart tubulin lacked both Tyr- and Glu-tubulin, suggesting that a relative high
level of detyrosination is a characteristic of most, but not all, cod microtubules. Brain cell microtubules were more resistant
to mitotic inhibitors than skin cell microtubules, but this was not correlated to a difference in detyrosination. Brain and
skin cell microtubules were only partially disassembled when incubated at 0°C. Upon reassembly of microtubules at 12°C, microtubules
were still made of mixtures of Tyr- and Glu-tubulin, indicating that detyrosination of assembled microtubules is rapid and/or
that in cod cells, in contrast to mammalian cells, Glu-tubulin can reassemble to microtubules. Our data show that most cod
microtubules are highly detyrosinated, but this is not the cause of their cold adaptation or drug stability. 相似文献
13.
Biogeochemical cycling of sulfur and iron in sediments of a south-east Asian mangrove,Phuket Island,Thailand 总被引:1,自引:1,他引:0
Marianne Holmer Erik Kristensen Gary Banta Kim Hansen Mikael Hjort Jensen Nipuvan Bussawarit 《Biogeochemistry》1994,26(3):145-161
Benthic sulfate reduction and sediment pools of sulfur and iron were examined during January 1992 at 3 stations in the Ao Nam Bor mangrove, Phuket, Thailand. Patterns of sulfate reduction rates (0–53 cm) reflected differences in physical and biological conditions at the 3 stations, and highest rates were found at the vegetated site within the mangrove (Rhizophora apiculata) forest. Due to extended oxidation of mangrove sediments, a large portion of the added35S-label was recovered in the chromium reducible pools (FeS2 and S0) (41–91% of the reduced sulfur). Pyrite was the most important inorganic sulfur component, attaining pool sizes 50–100 times higher than acid volatile pools (FeS). HCl-extractable (0.5 M HCl) iron pools, including Fe(II)HCl and Fe(III)HCl, were generally low and Fe(III)HCl was only present in the upper surface layers (0–5 cm). Maximum concentrations of dissolved Fe2+ (35–285 M) occurred just about the depth where dissolved H2S accumulated. Furthermore Fe2+ and H2S coexisted only where concentrations of both were low. There was an accumulation of organic sulfur in the deep sediment at 2 stations in the inner part of the mangrove. The reoxidation of reduced sulfides was rapid, and storage of sulfur was minor in the upper sediment layers, where factors like bioturbation, the presence of roots, or tidal mixing enhance oxidation processes.Author of correspondence. 相似文献
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Henrik Skovgård Jonna Tomkiewicz Gösta Nachman Mikael Münster-Swendsen 《Experimental & applied acarology》1993,17(1-2):59-76
The population dynamics of the cassava green mite Mononychellus tanajoa was studied on cassava during 35 weeks (early March to first of November 1989) in an experimental field near Lake Victoria in Western Kenya. The mite population peaked at the onset of the long dry season with 1,100 mites/leaf, declined sharply to a level of about 300 individuals/leaf, not to increase again until the next rainy season commenced. An indigenous phytoseiid predator Iphiseius degenerans was abundant during the dry spell with a maximum about 9 predators/leaf.A nonlinear regression analysis revealed that food depletion in combination with I. degenerans predation limited the population growth of the mites, whereas rain intensity had no effect. The predator exhibited no aggregative response to high densities of M. tanajoa and stayed mainly in the lower part of the canopy while the spider mites preferred the top, indicating that I. degenerans is a generalist predator without capacity to control M. tanajoa alone. However, in combination with another density dependent factor, such as food depletion, the predator may have prevented the spider mites from causing complete defoliation during the dry season. 相似文献
16.
Henrik Skovgård Jonna Tomkiewicz Gösta Nachman Mikael Münster-Swendsen 《Experimental & applied acarology》1993,17(1-2):41-58
The effect of the cassava green mite Mononychellus tanajoa on the growth and yield of cassava Manihot esculenta was studied over a 10-month period in two field trials near Lake Victoria in Kenya. One plot was maintained free of mites by means of acaricide, while the other was artificially infested.The highest population density of M. tanajoa occurred during the dry season. A maximum leaf area index (LAI) of about 2 was reached at the onset of the dry season. The total leaf area of mite infested plants was reduced compared with uninfested plants during the dry spell. During the following rainy season infested plants recovered and attained the same leaf area as uninfested plants. A multiple regression model predicting the leaf area showed that 58% of the seasonal variation could be explained by plant age, soil water, and leaf injury.The net growth rate of infested plants was lower than that of uninfested plants. Maximum values of 21 (infested plants) and 49 (uninfested plants) g m-2 week-1 were attained at the onset of the second rainy season. No difference was found between uninfested and infested plants with respect to net assimilation rates per unit leaf area during the dry season. The net assimilation rates reached a maximum almost at the same time as the growth rates, but the infested plants peaked slightly earlier and at a lower level than the uninfested plants.
M. tanajoa did not affect the relative allocation of dry matter into stems and storage roots, but the absolute allocation of dry matter declined with increasing mite injury. Thus, after 10 months the dry matter of infested plants was reduced by 29% and 21% for storage roots and stems, respectively, compared with the uninfested plants. 相似文献
17.
Terje Kalland Mikael Dohlsten Lars Abrahmsén Gunnar Hedlund Per Björk Peter A. Lando Anette Sundstedt Eva Åkerblom Peter Lind 《Cell biochemistry and biophysics》1993,22(1-3):147-164
The bacterial superantigen staphylococcal enterotoxin A (SEA) is an extremely potent activator of T lymphocytes when presented on MHC class II antigens. In order to induce T lymphocytes to reject a tumor, we substituted the specificity of SEA for MHC class II molecules with specificity for tumor cells by combining SEA with a MAb recognizing colon carcinomas. Chemical conjugates or recombinant fusion proteins of the MAb C215 and SEA retained excellent antigen binding properties whereas the binding to MHC class II was markedly reduced. The hybrid proteins directed SEA responsive T cells to tumors with specificity determined by the specificity of the MAb. Significant tumor cell killing was obtained at picomolar concentrations of the hybrid proteins and was the result of direct cell mediated by cytotoxicity as well as production of tumoricidal cytokines by T cells. Targeting of superantigens represents a novel approach to specific immunomodulation and deserves further study as a potential therapy for malignant disease. 相似文献
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Stephen M. Henry Per-?ke Jovall Sohbat Ghardashkhani Mikael L. Gustavsson Bo E. Samuelsson 《Glycoconjugate journal》1995,12(3):309-317
Total non-acid glycosphingolipids were isolated from the plasma of a healthy red blood cell group O Le(a-b-) salivary ABH secretor individual. Glycolipids were fractionated by HPLC and combined into eight fractions based on chromatographic and immunoreactive properties. These glycolipid fractions were analysed by thin-layer chromatography and tested for Lewis activity with antibodies reactive to the type 1 precursor (Lec), H type 1 (Led), Lea and Leb epitopes. Fractions were structurally characterized by mass spectrometry (EI-MS and LSIMS) and proton NMR spectroscopy. Expected blood group glycolipids, such as H type 1, (Fuc1-2Gal1-3GlcNAc1-3Gal1-4Glc1-1Cer) were immunochemically and structurally identified. Inconsistent with the red cell phenotype and for the first time, small quantities of Leb blood group glycolipids (Fuc1-2Gal1-3(Fuc1-4)GlcNAc1-3Gal1-4Glc1-1Cer) were immunochemically and structurally identified in the plasma of a Lewis-negative individual. These findings confirm recent immunological evidence suggesting the production of small amounts of Lewis antigens by Lewis negative individuals.
Abbreviations: HPLC, high performance liquid chromatography; TLC, (high performance) thin layer chromatography; EI-MS, electron impact ionisation mass spectrometry; LSIMS, liquid secondary ion mass spectrometry; NMR, nuclear magnetic resonance spectroscopy. The sugar types are abbreviated to Hex for hexose, HexNAc forN-acetylhexosamine and dHex for deoxyhexose (fucose). The ceramide types are abbreviated to d for dihydroxy and t for trihydroxy base, n for non-hydroxy and h for hydroxy fatty acids; LCB, long chain base. 相似文献