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21.
Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe 总被引:27,自引:2,他引:25
Small-scale spatial heterogeneity of soil organic matter (SOM) associated with patterns of plant cover can strongly influence population and ecosystem dynamics in dry regions but is not well characterized for semiarid grasslands. We evaluated differences in plant and soil N and C between soil from under individual grass plants and from small openings in shortgrass steppe. In samples from 0 to 5 cm depth, root biomass, root N, total and mineralizable soil N, total and respirable organic C, C:N ratio, fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants than soil from openings. These differences, which were consistent for two sites with contrasting soil textures, indicate strong differentiation of surface soil at the scale of individual plants, with relative enrichment of soil under plants in total and active SOM. Between-microsite differences were substantial relative to previously reported differences associated with landscape position and grazing intensity in shortgrass steppe. We conclude that microscale heterogeneity in shortgrass steppe deserves attention in investigation of controls on ecosystem and population processes and when sampling to estimate properties at plot or site scales. 相似文献
22.
A 23-year-old man developed thrombocytopenic purpura at the end of the second week of the clinical evolution of hepatitis A confirmed by viral markers. The bone marrow of this patient showed megakaryocytic hyperplasia. Circulating in his serum immune complexes were demonstrated by solid phase conglutinin enzymo-immunoassay. Platelet-reactive serum factors were also detected by an indirect immunofluorescence test using fresh donor platelets as targets. The evolution of both the hepatitis and the purpura were benign with no therapy other than bedrest. Platelet count normalized within five weeks of the onset of purpura, and IgM antibodies against hepatitis A virus as well as circulating immune complexes dropped to normal levels. It is postulated that the thrombocytopenia of this case was caused by nonspecific deposition of immune complexes at the platelet surface. 相似文献
23.
Wolfgang K. G. Krietsch Manfred Dünnwald Ingrid M. Linke Theodor Bücher 《Molecular & general genetics : MGG》1985,200(3):497-499
Summary The stability of allelic gene expression of X-linked phosphoglycerate kinase was studied in seven carriers of a rare genetic variant named PGK München. The enzymatic activities in erythrocytes of five heterozygous females and three hemizygous males were determined repeatedly over a period of 10 years (1975–1984) and shown to remain constant. As the phosphoglycerate kinase activity is lower in cells expressing the PGK München allele, the ratio of the two cell types in all heterozygous females of the PGK München kindred could be calculated from the PGK activity and from the known allozyme activities in erythrocytes of homozygous wild type or hemizygous PGK München carriers. Since the maternal or paternal origin of both alleles is known from the pedigree, the quantitative expression of the maternally derived allozyme in heterozygous women could be determined. In heterozygous carriers the cell pool expressing the maternally inherited allele was significantly increased, independently, of the PGK allele linked to the maternal X chromosome (P<0.001). Our data show that inactivation of one of the two X chromosomes in human female erythropoietic stem cell precursors may be non-random, at least in the kindred and cell populations described here. The results are discussed in the context of random X chromosome inactivation (Lyon hypothesis).Dedicated to J.S., the senior of the family studied, on the occasion of her 80th birthday 相似文献
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26.
Irma van Die Ingrid van Megen Wiel Hoekstra Hans Bergmans 《Molecular & general genetics : MGG》1984,194(3):528-533
Summary The genes responsible for the formation of the F72 fimbriae of the uropathogenic E. coli strain AD110 (O6:K2:H1:F7) have been cloned on the recombinant plasmid pPIL110-35 (Van Die et al. 1983). The F72 fimbriae, like the F71 fimbriae of AD110, are responsible for mannose resistant haemagglutination (MRHA).The molecular organisation of the genes of pPIL110-35 involved in the expression of MRHA was studied by: (a) analysis of transposon and Tn5 insertion mutants. Mutations that cause an MRHA-deficient phenotype were located in discrete groups within an 11.5 kb restriction fragment of pPIL110-35, separated by insertion mutations that do not inactivate MRHA. (b) complementation experiments. Restriction fragments of pPIL110-35 subcloned in the vector pBR322 were tested for their ability to complement transposon insertion mutations in the corresponding regions of pPIL110-35. Five complementation groups were distinguished.Five genes (designated A-E) involved in the expression of MRHA can be distinguished by these results. The products of these genes were analysed in minicells. The results indicate that gene B codes for a 75 K dalton protein, gene C for a 23 K dalton protein and gene E for a 36 K dalton protein. No product of gene D was observed. Gene A probably codes for the 17 K dalton subunit polypeptide of the F72 fimbriae, as will be discussed. 相似文献
27.
Summary Trichoderma reesei was grown on sulfite pulp and the major cellobiohydrolase of the culture filtrate was purified to homogeneity. The distance distribution function p(r) measured by the small angle X-ray scattering technique indicates that the enzyme molecule has a rather unusual tadpole like shape with an isotropic head and a long tail. The maximum length is 18 nm and the largest diameter is 4.4 nm. 相似文献
28.
29.
Jana Pospíšilová Jiřina Slavíkovà J. Tupý Ingrid Tiohá T. Gichner 《Biologia Plantarum》1983,25(3):237-240
30.
U. Ingrid Richardson 《Life sciences》1983,33(20):1981-1988
Synthetic corticotropin-releasing factor (CRF) stimulates ACTH secretion in the clonal mouse pituitary cell strain AtT20/D16v (D16) in a dose-dependent manner with a half-maximal effect at 2×10?9M. A single dose of 5×10?9M CRF maximally stimulates the rate of ACTH secretion during the initial two hrs of treatment. During the period of maximal CRF stimulation intracellular hormone concentration declines progressively to a nadir at 4 hrs. During the ensuing 24 hrs of incubation intracellular hormone levels in CRF-stimulated cells increase gradually toward control values. Somatostatin (SRIF) inhibits the secretory response to CRF. This action of SRIF is dose-dependent with a half-maximal effect at 1×10?9M and results in decreased maximal ACTH secretion with little effect on the ED50 for CRF. 相似文献