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11.
Interactions between the roach,Rutilus rutilus,and waterfowl populations of Lough Neagh,Northern Ireland 总被引:2,自引:0,他引:2
Ian J. Winfield Denise K. Winfield Catherine M. Tobin 《Environmental Biology of Fishes》1992,33(1-2):207-214
Synopsis Following the introduction of roach, Rutilus rutilus, to a large eutrophic lake in ca. 1973, a subsequent increase in the abundance of this cyprinid through the 1970s was accompanied by a decline in the numbers of one of the lake&s most abundant overwintering waterfowl, the tufted duck, Aythya fuligula, and an increase in overwintering piscivorous great crested grebes, Podiceps cristatus. We suggest that these contrasting trends are causally related and that competition for benthos and increased prey availability are the mechanisms responsible for the changes in the tufted duck and grebe populations respectively. In agreement with these hypotheses, a reduction in the roach population during the mid 1980s was accompanied by a recovery of tufted ducks and a decline of grebes. 相似文献
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Summary The cloning, sequencing and mutational analysis of the Bradyrhizobium japonicum symbiotic nitrogen fixation genes fixL and fixJ are reported here. The two genes were adjacent and probably formed an operon, fixLJ. The predicted FixL and FixJ proteins, members of the two-component sensor/regulator family, were homologous over almost their entire lengths to the corresponding Rhizobium meliloti proteins (approx. 50% identity). Downstream of the B. japonicum fixJ gene was found an open reading frame with 138 codons (ORF138) whose product shared 36% homology with the N-terminal part of FixJ. Deletion and insertion mutations within fixL and fixJ led to a loss of approximately 90% wildtype symbiotic nitrogen fixation (Fix) activity, whereas an ORF138 mutant was Fix+. In fixL, fixJ and ORF138 mutant backgrounds, the aerobic expression of the fixR-nifA operon was not affected. NifA itself did not regulate the expression of the fixJ gene. Thus, the B. japonicum FixL and FixJ proteins were neither involved in the regulation of aerobic nifA gene expression nor in the anaerobic NifA-dependent autoregulation of the fixRnifA operon; rather they appeared to control symbiotically important genes other than those whose expression was dependent on the NifA protein. The fixL and fixJ mutant strains were unable to grow anaerobically with nitrate as the terminal electron acceptor. Therefore, some of the FixJ-dependent genes in B. japonicum may be concerned with anaerobic respiration. 相似文献
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Epiphytic bacteria: development of a method for determining respiring bacteria on leaves 总被引:2,自引:2,他引:0
A method was developed for studying the total numbers and the proportion of active bacteria on leaf surfaces. It involves staining gelatin impressions of leaves treated with an electron transport system indicator, 2-( p -iodophenyl)-3-( p -nitrophenyl)-5-phenyl tetrazolium chloride (INT). The method is rapid, inexpensive and allows simultaneous observation of numbers, ecology and respiratory activity of epiphytic bacteria. The total numbers of epiphytic bacteria for four species of aquatic plants varied between 0.6 to 10.2 times 106 /cm2 . The proportion of active bacteria on leaves of aquatic plants ranged from 2.2 to 42.9%. The method was also applied to a comparison of surface fouling of glass slides and aquatic leaf surfaces, indicating significant differences in numbers of bacteria but little difference in the proportion active on the two surfaces. 相似文献
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Amira Klip Denise Walker Kathleen J. Ransome Dean W. Schroer Gustav E. Lienhard 《Archives of biochemistry and biophysics》1983,226(1):198-205
The glucose transporter in the plasma membrane of rat skeletal muscle has been identified by two approaches. In one, the transporter was detected as the polypeptide that was differentially labeled by photolysis with [3H]cytochalasin B in the presence of l- and d-glucose. [3H]Cytochalasin B is a high-affinity ligand for the transporter that is displaced by d-glucose. In the other, the transporter was detected by means of its reaction with rabbit antibodies against the purified glucose transporter from human erythrocytes. By both procedures, the transporter was found to be a polypeptide with a mobility corresponding to a molecular weight of 45,000–50,000 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. 相似文献
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Lateral asymmetry refers to unequal fluorescent intensity between adjacent regions of sister chromatids. It has been observed in the centromeric regions of mitotic chromosomes of mouse or human origin when cells are grown in 5-bromo-2-deoxyuridine (BrdU) for a single round of DNA synthesis. The chromosome-orientation fluorescence in situ hybridization (CO-FISH) technique was used with pseudodiploid mouse cells to show that the regions of asymmetrical brightness coincide with major satellite repetitive DNA, and that the more heavily BrdU-substituted chromatid is the one that fluoresces less brightly. These observations support a 20 year old hypothesis on the origin of lateral asymmetry. Other observations suggest that differential loss of DNA from the heavily substituted chromatid also contributes to lateral asymmetry. 相似文献