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1.
Populations of the vernal cladoceranDaphniopsis ephemeralis are found in woodland ponds throughout southern Ontario. The species reproduces by cyclic parthenogenesis, and genotype frequencies
at allozyme loci are ordinarily in good agreement with Hardy-Weinberg expectations. Occasional heterozygote deficiencies are
apparently the consequence of admixture of ephippial hatchlings produced in temporally separated bouts of sexual reproduction.
Considerable heterogeneity in genotypic frequencies exists among local populations in southwestern Ontario, indicating that
gene flow among populations is restricted. Inbreeding coefficients suggest that populations receive an average of 0.3 migrants
per generation. The completion of a sexual life cycle is made possible despite the brief persistence of populations by the
emergence of males from ephippial eggs and by the production of equal numbers of male and female progeny in the first parthenogenetic
brood. 相似文献
2.
Three high molecular weight protease inhibitors of rat plasma. Isolation, characterization, and acute phase changes 总被引:1,自引:0,他引:1
K Lonberg-Holm D L Reed R C Roberts R R Hebert M C Hillman R M Kutney 《The Journal of biological chemistry》1987,262(1):438-445
Rat blood plasma contains three high molecular weight thiol ester-containing proteinase inhibitors, alpha 1-macroglobulin (alpha 1M), alpha 1-inhibitor III (alpha 1I3), and alpha 2-macroglobulin (alpha 2M). Rat serums have been analyzed using a two-dimensional gel electrophoretic technique which optimizes recovery of high molecular weight proteins. alpha 1M, and (alpha beta)4-tetramer in native solution, separated in the second sodium dodecyl sulfate-containing electrophoretic dimension as a disulfide-linked (alpha beta)2-dimer with an approximate Mr of 360 kDa. alpha 1I3 separated in the gels as a single 190-kDa polypeptide. It is also a monomer in native solution by ultracentrifugation criteria. Native rat alpha 2M is a tetramer, but it separates in the gels as a disulfide-linked dimer with an Mr of approximately 360 kDa. The kinetics of changes in concentration of these proteins during the induction of polyarthritis was also measured by quantitative immunoelectrophoresis. In rats with adjuvant-induced polyarthritis, the concentration of alpha 1I3 dramatically decreases and alpha 2M appears and continues to increase in a biphasic manner for 2 weeks. The alpha 1M concentration remains relatively constant. All three macroglobulins were purified utilizing modern rapid chromatographic techniques, and parallel comparisons of their native physicochemical properties were carried out. The N-terminal sequence of the alpha-chain of rat alpha 1M was also shown to share sequence homology with that of alpha 2M. In agreement, Esnard et al. (Esnard, F., Gutman, N., El Moujahed, A., and Gauthier, F. (1985) FEBS Lett. 182, 125-129) recently reported that alpha 1I3 also contains a thiol ester bond, as do alpha 1M and alpha 2M, since it reacts covalently with [14C]methylamine and is cleaved autolytically at 80 degrees C. We have examined negatively stained preparations of native, trypsin-treated, and methylamine-treated human alpha 2M, rat alpha 2M, and rat alpha 1M in the electron microscope. Trypsin appears to convert globular ring-shaped native molecules to rectangular box-like structures, in agreement with the conclusions of a recent report on human alpha 2M (Tapon-Bretaudiere, J., Bros, A., Couture-Tosi, E., and Delain, E. (1985) EMBO J. 4, 85-89). 相似文献
3.
C N Hebert S Edwards S Bushnell P C Jones C T Perry 《Journal of biological standardization》1985,13(3):243-253
The critical statistical parameters of an enzyme-linked immunosorbent assay were determined to enable quantitation of antibody responses in cattle affected with infectious bovine rhinotracheitis. A system of controlling well-to-well variations in optical density reading across a microtitre plate was evolved and dose--response assays were carried out to determine the dilution of serum which gave the greatest discrimination between acute and convalescent sera from an infected animal. Use of a standard serum was studied in further assays. An increase in optical density value of 0.15 was set as a diagnostic criterion for a significantly rising antibody response. This compared well with the conventional criterion of a fourfold rise in virus neutralizing antibody titre. 相似文献
4.
Localization of specific rDNA spacer sequences to the mouse L-cell nucleolar matrix. 总被引:2,自引:0,他引:2
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R I Bolla D C Braaten Y Shiomi M B Hebert D Schlessinger 《Molecular and cellular biology》1985,5(6):1287-1294
Mouse L-cell nucleoli were isolated from sonicated nuclei by centrifugation and extensively treated with pancreatic DNase or micrococcal nuclease to obtain "core nucleoli." Core nucleoli still contained the precursors to rRNA and about 1% of the total nuclear DNA, which remained tightly bound even after the removal of some chromatin proteins with 2 M NaCl. The core nucleolar DNA electrophoresed in a series of discrete bands, 20 to about 200 base pairs in length. Hybridization tests with specific DNA probes showed that the DNA was devoid of sequences complementary to mouse satellite, mouse Alu-like, and 5S RNA sequences. It also lacked sequences coding for cytoplasmic rRNA species, since it did not hybridize to the 18S to 28S portion of rDNA in Northern blot analyses and none of it was protected by hybridization to a 100-fold excess of total cytoplasmic RNA in S1 nuclease assays. However, the core nucleolar DNA did hybridize to nontranscribed and external transcribed spacer rDNA sequences. We infer that specific portions of rDNA are protected from DNase action by a tight association with nucleolar structural proteins. 相似文献
5.
Phytoplankton community structure and distribution in the nearshore zone of Lake Ontario 总被引:1,自引:1,他引:0
Spatial and temporal distributions of phytoplankton were studied during 1979 in the nearshore zone of Lake Ontario. Genera such as Dinobryon, Oscillatoria, and Gymnodinium tended to be found at discrete depths whereas other genera such as Cryptomonas and Rhodomonas tended to be more uniformly distributed throughout the water column. The discrete depth distribution of some of these genera compared with the weak thermal stabilization of the area suggests depth selection and habitat preference within the algal community.Physical processes probably played a major role in regulating the timing and duration of vertical diatom pulses, and resuspension from the sediment played a major role as to the timing of the autumn growth. Vertical mixing in the nearshore zone was sufficient for some diatom genera such as Tabellaria to maintain populations throughout the summer. These mixing processes, however, affect the stability of community structures and associations that develop within the water column. The role of physical processes and their potential effects on algal production in the Great Lakes is discussed. 相似文献
6.
Summary Cellular impalements were used in combination with standard transepithelial electrical measurements to evaluate some of the determinants of the spontaneous lumen-positive voltage,V
e
, which attends net Cl– absorption,J
Cl
net
, and to assess how ADH might augment bothJ
Cl
met
andV
e
in the mouse medullary thick ascending limb of Henle microperfusedin vitro. Substituting luminal 5mm Ba++ for 5mm K+ resulted in a tenfold increase in the apical-to-basal membrane resistance ratio,R
c
/R
bl
, and increasing luminal K+ from 5 to 50mm in the presence of luminal 10–4
m furosemide resulted in a 53-mV depolarization of apical membrane voltage,V
a
. Thus K+ accounted for at least 85% of apical membrane conductance. Either with or without ADH. 10–4
m luminal furosemide reducedV
e
andJ
Cl
net
to near zero values and hyperpolarized bothV
a
andV
bl
, the voltage across basolateral membranes; however, the depolarization ofV
bl
was greater in the presence than in the absence of hormone while the hormone had no significant effect on the depolarization ofV
a
, Thus ADH-dependent increases inV
b
were referable to greater depolarizations ofV
bl
in the presence of ADH than in the absence of ADH 68% of the furosemide-induced hyperpolarization ofV
a
was referable to a decrease in the K+ current across apical membranes, but, at a minimum, only 19% of the hyperpolarization ofV
bl
could be accounted for by a furosemide-induced reduction in basolateral membrane Cl– current. Thus an increase in intracellular Cl– activity may have contributed to the depolarization ofV
bl
during net Cl– absorption, and the intracellular Cl– activity was likely greater with ADH than without hormone. Since ADH increases apical K+ conductance and since the chemical driving force for electroneutral Na+,K+,2Cl– cotransport from lumen to cell may have been less in the presence of ADH than in the absence of hormone, the cardinal effects of ADH may have been to increase the functional number of both Ba++-sensitive conductance K+ channels and electroneutral Na+,K+,2Cl– cotransport units in apical plasma membranes. 相似文献
7.
8.
R. W. F. Hardy R. C. Burns R. R. Hebert R. D. Holsten E. K. Jackson 《Plant and Soil》1971,35(1):561-590
Summary 1. Characteristics and methodology of the C2H2-C2H4 assay forin situ measurement of N2 fixation are outlined.
2. Electron micrographic analysis of the developmental morphology of the natural soybean symbiosis and C2H2-C2H4 analysis indicate that increasing N2-fixing activity from 12–35 days of age is accompanied by an increase in bacteroid number per cell, bacteroid number per vesicle
and inclusions per bacteroid. The mole ratio of leghemoglobin to nitrogenase also increases from 50 to a relatively constant
plateau of 500 to 1500 during this period. The quantitative validity of the C2H2-C2H4 assay as a measure of N2 fixation during a complete growth cycle of soybeans on nitrogen-free medium is demonstrated by Σ (C2H2→C2H4)×28/3 values which are 75–95% of the values determined for N2 fixed by Kjeldahl analyses.
3. A technique for the establishment of the first callus N2-fixing symbiosis in mixed cultures ofRhizobium legume provides a defined experimental system for exploration of legume symbiosis. N2-fixing activity is about 1% of the natural system and is influenced by exogenous auxins and cytokinins. Morphology, including
infection threads and vesicle enclosed bacteroids, is similar to the nodule system.
4. N2-fixing activity of field-grown soybeans, including varieties which differed in flowering characteristics and maturity dates,
and of peanuts was determined biweekly with the C2H2-C2H4 assay. Activity extended from nodule initiation to senescence and correlated with the nitrogen demands of the plant and in
most cases >90% of the N2 fixed during the 60–70 day period of fruit formation and maturation. A logarithmic relationship between N2-fixing activity and age, and N2 fixed and age was demonstrated as a fundamental characteristic of these annual symbionts,i.e. log N2 fixed =k(t−t
0), wheret
0 is age at activity initiation. The resultant parameters: 1) age at activity initiation, 2) calculated rate of daily increase
(7–9% for soybeans and 7–10% for peanuts), 3) age at end of logarithmic phase (about 80 days for soybeans), and 4) total N2 fixed (about 250 mg per soybean plant) are useful bases for evaluation of environmental, bacterial and host effects on N2 fixation. Various N fertilizers applied at planting and flowering inhibited N2 fixation of soybeans by decreasing the rate of daily increase.
5. Physical and chemical characteristics of nitrogenase, including those of crystalline Mo-Fe protein, reactions of nitrogenase,
and model studies are consistent with a proposed mechanism.
6. Potential utilities of N2 fixation research include increased food protein production via initially enhanced N2 fixation of legumes such as soybeans and eventually extension of N2-fixing symbioses to non-legumes and new chemistry of N2, including the direct incorporation of aerial N2 into important organic compounds.
Contribution No. 1748. 相似文献
9.
10.