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排序方式: 共有522条查询结果,搜索用时 15 毫秒
471.
472.
Florence Goubet Christopher J. Barton Jennifer C. Mortimer Xiaolan Yu Zhinong Zhang Godfrey P. Miles Jenny Richens Aaron H. Liepman Keith Seffen Paul Dupree 《The Plant journal : for cell and molecular biology》2009,60(3):527-538
Mannans are hemicellulosic polysaccharides that have previously been implicated as structural constituents of cell walls and as storage reserves but which may serve other functions during plant growth and development. Several members of the Arabidopsis cellulose synthase-like A (CSLA) family have previously been shown to synthesise mannan polysaccharides in vitro when heterologously expressed. It has also been found that CSLA7 is essential for embryogenesis, suggesting a role for the CSLA7 product in development. To determine whether the CSLA proteins are responsible for glucomannan synthesis in vivo , we characterised insertion mutants in each of the nine Arabidopsis CSLA genes and several double and triple mutant combinations. csla9 mutants showed substantially reduced glucomannan, and triple csla2csla3csla9 mutants lacked detectable glucomannan in stems. Nevertheless, these mutants showed no alteration in stem development or strength. Overexpression of CSLA2, CSLA7 and CSLA9 increased the glucomannan content in stems. Increased glucomannan synthesis also caused defective embryogenesis, leading to delayed development and occasional embryo death. The embryo lethality of csla7 was complemented by overexpression of CSLA9 , suggesting that the glucomannan products are similar. We conclude that CSLA2, CSLA3 and CSLA9 are responsible for the synthesis of all detectable glucomannan in Arabidopsis stems, and that CSLA7 synthesises glucomannan in embryos. These results are inconsistent with a substantial role for glucomannan in wall strength in Arabidopsis stems, but indicate that glucomannan levels affect embryogenesis. Together with earlier heterologous expression studies, the glucomannan deficiency observed in csla mutant plants demonstrates that the CSLA family encodes glucomannan synthases. 相似文献
473.
474.
The chlorellavorus bacterium (Bdellovibrio chlorellavorus Gromov and Mamkaeva 1972) attaches to (but does not enter) cells of the unicellular green alga,Chlorella, which is killed and the cell contents of which are digested. The bacterium is pleomorphic (vibrios 0.3 μm wide; cocci 0.6
μm wide), and it has a Gram-negative cell wall structure pili, and a single, unsheathed, polar flagellum. Division may occur
only in bacterial cells attached to algal cells, an attachment mediated by a pad (245×36 nm) of unknown composition. Bacterial
growth occurs only in the presence of liveChlorella cells, and not on various bacteriological culture media, killedChlorella cells, 4 strains ofPrototheca, or 24 strains of Gram-negative bacteria. The chlorellavorus bacterium may not require algal protein synthesis, since the
bacterium grows on algae in the presence of cycloheximide (30 μg/ml). Although the DNA base composition of the chlorellavorus
bacterium (50 mol % G+C) is in the same range asBdellovibrio bacteriovorus, its ultrastructure, developmental cycle, host range, and format of its intermicrobial association all distinguish the chlorellavorus
bacterium from members of the genusBdellovibrio. 相似文献
475.
The brominated aryl-polyene, (xanthomonadin) pigments-characteristic of the nonphotosynthetic and phytopathogenic bacteria belonging to the genusXanthomonas-were examined for their role in protecting these bacteria against photobiological destruction of some as-yet unknown vital cellular component(s). Survival of a pigmented wild-type strain (ICPB XJ103) ofXanthomonas juglandis and a colorless mutant strain (ICPB XJ103-31) derived from it were compared after exposure to visible light in the presence of an exogenous photosensitizer, toluidine blue. Under these conditions, the survival of the pigmented wild-type strain was approximately two order of magnitude greater than the survival of the colorless mutant strain. Both strains were fully protected in the dark in the presence of toluidine blue. Although the oxygen-free controls were inconclusive-and the mechanisms(s) and target(s) remain unknown-the results do indicate that xanthomonadin pigments protect against photokilling. 相似文献
476.
477.
478.
Joan E. Harrison K. G. McNeill J. M. Finlay R. H. Sheppard D. C. Mortimer 《CMAJ》1966,94(21):1092-1097
Long-term bone calcium metabolism was measured using a whole body counter apparatus and the radioisotopes calcium-47 and strontium-85. Strontium was given with calcium in a single intravenous injection in order to estimate long-term retention of calcium. Calcium-47, with a short radio-active half-life, was measured directly for 20 days, and then indirectly from strontium retention for periods up to 200 days.The standard parameters of calcium transport were measured and, as well, a new parameter, calcium accretion to the fixed bone pool. These studies were carried out on 13 subjects, six of whom were selected “normals” and seven were patients with osteoporosis. Calcium accretion to the fixed bone pool, the new index of bone formation, varied from 100 to 210 mg. of calcium daily in normal subjects and from 70 to 340 mg./day in patients with osteoporosis. These values are one-third of those for the accretion to the total bone pool, the previously reported bone formation rate. 相似文献
479.
M. POLSINELLI, P. ROMANO, G. SUZZI AND R. MORTIMER. 1996. On the basis of the levels of secondary product formation four different phenotypes were represented among the 28 strains of Saccharomyces cerevisiae isolated during the spontaneous fermentation of grape juice. The genetic analysis indicated that four different strains, representing each phenotypic class, were derived, one from the other, by mutation. The spontaneous fermentation of a Malvasia must was dominated by different strains of Saccharomyces cerevisiae at different stages of fermentation. 相似文献
480.
Anthony S. Fauci Tohru Murakami David D. Brandon D.Lynn Loriaux Mortimer B. Lipsett 《Cellular immunology》1980,49(1):43-50
Glucocorticosteroid receptors were measured in subpopulations of human peripheral blood T cells identified by the presence of an Fc receptor for IgG (TG) or an Fc receptor for IgM (TM). TM cells are selectively depleted from the circulation by in vivo administration of glucocorticosteroids as opposed to TG cells which are relatively resistant to the lymphodepletive effects of these hormones. However, this selective lymphodepletive effect of glucocorticosteroids on TM cells could not be explained on the basis of detectable differences in intracytoplasmic glucocorticosteroid receptors in these T-cell subpopulations since TG and TM cells had quantitatively similar glucocorticosteroid receptors as well as remarkably similar dexamethasone binding affinities and dissociation constants. Hence, the strikingly different effects of glucocorticosteroids on the circulatory kinetics of TG and TM cells must be explained by mechanisms other than those at the level of the glucocorticosteroid receptor. 相似文献