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白腹锦鸡,红腹锦鸡,中国雉鸡SC组型的比较研究 总被引:1,自引:0,他引:1
以微铺展—硝酸银染色技术制备三种鸡的SC标本,进行电镜观察。结果表明:三种鸡的SC组非常相似,即2n=82,ZZ/ZW型性别决定,雄性为ZZ。除1号SC和Z-SC为中着丝粒外,其余均为端着丝粒。Z-SC的相对长度有明显的细胞间差异;平均相对长度度介于第3和第4号SC之间。三者SC组型上的差异主要表现在相应SC长度上的不同。并对其亲缘关系及在鸟类进化中的可能地位进行了讨论。此外,在微铺展法制备的锦鸡精母细胞SC标本中还发现了巨大中心粒,这在高等动物尚属首次。 相似文献
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A Szyszka D Nowak A Ponizyński A Cie?liński Z Brocki 《Polski tygodnik lekarski (Warsaw, Poland : 1960)》1991,46(6-7):109-111
An average follow-up period of 16 patients was 28 months following an implantation of the artificial aortic valve for its insufficiency. In 10 operated patients who were able to continue their occupation exercise tolerance increased by two classes, according to NYHA. Blood pressure gradient decreased significantly from 61.8 to 37.5 mmHg, cardiac volume index decreased from 639 to 602 ml/m2. Echocardiographically measured muscle mass of the left ventricle, end-diastolic and end-systolic volumes, and the left atrial dimensions decreased significantly following surgery. A significance of the relation of the left ventricle volume to its mass <4 as a prognostic factor in aortic valve replacement has also been confirmed. 相似文献
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Rhizome dynamics and resource storage in Phragmites australis 总被引:6,自引:1,他引:5
Wilhelm Granéli Stefan E. B. Weisner Mark D. Sytsma 《Wetlands Ecology and Management》1992,1(4):239-247
Seasonal changes in rhizome concentrations of total nonstructural carbohydrates (TNC), water soluble carbohydrates (WSC), and mineral nutrients (N, P and K) were monitored in two Phragmites australis stands in southern Sweden. Rhizome biomass, rhizome length per unit ground area, and specific weight (weight/ length ratio) of the rhizomes were monitored in one of the stands.Rhizome biomass decreased during spring, increased during summer and decreased during winter. However, changes in spring and summer were small (< 500 g DW m-2) compared to the mean rhizome biomass (approximately 3000 g DW m–2). Winter losses were larger, approximately 1000 g DW m-2, and to a substantial extent involved structural biomass, indicating rhizome mortality. Seasonal changes in rhizome length per unit ground area revealed a rhizome mortality of about 30% during the winter period, and also indicated that an intensive period of formation of new rhizomes occurred in June.Rhizome concentrations of TNC and WSC decreased during the spring, when carbohydrates were translocated to support shoot growth. However, rhizome standing stock of TNC remained large (> 1000 g m–2). Concentrations and standing stocks of mineral nutrients decreased during spring/ early summer and increased during summer/ fall. Only N, however, showed a pattern consistent with a spring depletion caused by translocation to shoots. This pattern indicates sufficient root uptake of P and K to support spring growth, and supports other evidence that N is generally the limiting mineral nutrient for Phragmites.The biomass data, as well as increased rhizome specific weight and TNC concentrations, clearly suggests that reloading of rhizomes with energy reserves starts in June, not towards the end of the growing season as has been suggested previously. This resource allocation strategy of Phragmites has consequences for vegetation management.Our data indicate that carbohydrate reserves are much larger than needed to support spring growth. We propose that large stores are needed to ensure establishment of spring shoots when deep water or stochastic environmental events, such as high rhizome mortality in winter or loss of spring shoots due to late season frost, increase the demand for reserves. 相似文献
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A homologue of the Escherichia coli DsbA protein involved in disulphide bond formation is required for enterotoxin biogenesis in Vibrio cholerae 总被引:22,自引:0,他引:22
A strain of Vibrio cholerae, which had been engineered to express high levels of the non-toxic B subunit (EtxB) of Escherichia coli heat-labile enterotoxin, was subjected to transposon (TnphoA) mutagenesis. Two chromosomal TnphoA insertion mutations of the strain were isolated that showed a severe defect in the amount of EtxB produced. The loci disrupted by TnphoA in the two mutant derivatives were cloned and sequenced, and this revealed that the transposon had inserted at different sites in the same gene. The open reading frame of the gene predicts a 200-amino-acid exported protein, with a Cys-X-X-Cys motif characteristic of thioredoxin, protein disulphide isomerase, and DsbA (a periplasmic protein required for disulphide bond formation in E. coli). The V. cholerae protein exhibited 40% identity with the DsbA protein of E. coli, including 90% identity in the region of the active-site motif. Introduction of a plasmid encoding E. coli DsbA into the V. cholerae TnphoA derivatives was found to restore enterotoxin formation, whilst expression of Etx or EtxB in a dsbA mutant of E. coli confirmed that DsbA is required for enterotoxin formation in E. coli. These results suggest that, since each EtxB subunit contains a single intramolecular disulphide bond, a transient intermolecular interaction with DsbA occurs during toxin subunit folding which catalyses formation of the disulphide in vivo. 相似文献