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排序方式: 共有642条查询结果,搜索用时 11 毫秒
1.
Dual-Label Radioisotope Method for Simultaneously Measuring Bacterial Production and Metabolism in Natural Waters 总被引:2,自引:2,他引:0
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Robert B. Jonas Jon H. Tuttle Daphne L. Stoner Hugh W. Ducklow 《Applied microbiology》1988,54(3):791-798
Bacterial production and amino acid metabolism in aquatic systems can be estimated by simultaneous incubation of water samples with both tritiated methyl-thymidine and 14C-labeled amino acids. This dual-label method not only saves time, labor, and materials, but also allows determination of these two parameters in the same microbial subcommunity. Both organic carbon incorporation and respiration can be estimated. The results obtained with the dual-label technique are not significantly different from single-radiolabel methods over a wide range of bacterial activity. The method is particularly suitable for large-scale field programs and has been used successfully with eutrophic estuarine samples as well as with oligotrophic oceanic water. In the mesohaline portion of Chesapeake Bay, thymidine incorporation ranged seasonally from 2 to 635 pmol liter−1 h−1 and amino acid turnover rates ranged from 0.01 to 28.4% h−1. Comparison of thymidine incorporation with amino acid turnover measurements made at a deep, midbay station in 1985 suggested a close coupling between bacterial production and amino acid metabolism during most of the year. However, production-specific amino acid turnover rates increased dramatically in deep bay waters during the spring phytoplankton bloom, indicating transient decoupling of bacterial production from metabolism. Ecological features such as this are readily detectable with the dual-label method. 相似文献
2.
Daphne Gail Fautin 《Environmental Biology of Fishes》1986,15(3):171-180
Synopsis The 25 species ofAmphiprion and one ofPremnas (family Pomacentridae) are obligate symbionts of 10 species of facultatively symbiotic sea anemones. Throughout the tropical
Indo-West Pacific range of the relationship, a fish species inhabits only certain of the hosts potentially available to it.
This specificity is due to the fishes. Five fishes occupy six sea anemone species at Lizard Island, Great Barrier Reef, Australia.Entacmaea quadricolor harborsP. biaculeatus, A. melanopus andA. akindynos. Adults ofPremnas occur deeper than about 3 m in large, primarily solitary actinians; juveniles may occupy peripheral members ofEntacmaea clones in shallow water. Specimens ofA. melanopus live exclusively in clonal anemones, which are found no deeper than 3 m. Most individuals ofA. akindynos inEntacmaea are juveniles, occurring shallow and deep, in solitary anemones or at the margins of clones. Interspecific as well as intraspecific
social control of growth may be responsible for keeping fish small at clone fringes. Conspicuous specimens ofE. quadricolor depend upon their anemonefish to survive. Actinians cleared of symbionts disappeared within 24 h, probably having been eaten
by reef fishes.Entacmaea, the most abundant and widespread host actinian at Lizard Island and throughout the range of the association, is also arguably
the most attractive to anemonefishes. I believe its vulnerability to predation was a factor in its evolving whatever makes
it desirable to fishes. Experimental transfers pitted fish of one species against those of another, controlling for ecophenotype
of host, and sex, size and number of fish. Competitive superiority was in the same order as abundance and over-all host specificity:P. biaculeatus, A. melanopus, A. akindynos. At least three factors are necessary to explain patterns of species specificity - innate or learned host preference, competition,
and stochastic processes. 相似文献
3.
4.
Donald H. Williamson Malcolm J. Gardner Peter Preiser Daphne J. Moore Kaveri Rangachari Robert J. M. Wilson 《Molecular & general genetics : MGG》1994,243(2):249-252
In common with other Apicomplexan parasites, Plasmodium falciparum carries two extrachromosomal DNAs, one of which, the 6 kb element, is undoubtedly mitochondrial. The second, generally referred to as the 35 kb circle, is of unknown provenance, but the nature and organization of its genetic content makes a mitochondrial association unlikely and the molecule has features reminiscent of plastid genomes. We now report the occurrence on the circle of an open reading frame specifying a predicted 470 amino acid protein that shares more than 50% identity with a gene currently known only on the plastome of red algae. This high degree of conservation confirms the 35 kb circle's plastid ancestry, and we speculate that it may have originated from the rhodoplast of an ancient red algal endosymbiont in the progenitor of the Apicomplexa. 相似文献
5.
Daphne J. Fairbairn 《Population Ecology》1994,36(2):157-163
The hypothesis that the morphological, physiological, and behavioral traits comprising the migratory syndrome in insects are genetically correlated through pleiotropic effects of genes controlling the titre of a common hormonal determinant is explored. Evidence that juvenile hormone (JH) influences the component traits of the migratory syndrome is presented, and thus JH is assumed to be the underlying, common determinant. However, readers are cautioned that this does not imply that JH is solely responsible for these traits, nor is this necessary for the arguments presented. For wing dimorphic taxa, the “correlated traits hypothesis” predicts covariance within wing morphs between JH titre and the proportion winged. Four simple genetic models for wing-morph determination are considered: single-locus with short-winged (SW) dominant; single-locus with long-winged (LW) dominant; polygenic, fixed threshold, shifting distribution; and polygenic, shifting threshold, fixed distribution. In each case, wing morphology is assumed to be a threshold trait with the liability being JH titre at some critical stage of development. All models predict covariation between %LW and the mean JH titre of at least one of the wing morphs, but the form and direction of the relationship depends critically on the genetic model used. The results suggest that we should expect the traits associated with the migratory syndrome, and hence the trade-offs associated with the evolution of wing dimorphism, to be correlated with proportion winged and, in this sense, to be frequency-dependent. 相似文献
6.
Michael Garrick Donna Scott Susannah Walpole Eric Finkelstein Joy Whitbred Sandeep Chopra Lalitha Trivikram David Mayes Daphne Rhodes Kimberly Cabbagestalk Rahmi Oklu Adnan Sadiq Brett Mascia James Hoke Laura Garrick 《Biometals》1997,10(2):65-76
Belgrade rats inherit microcytic, hypochromic anemia as an autosomalrecessive trait (gene symbol b). Erythrocytes and tissue are iron deficientin the face of elevated TIBC (total iron binding capacity) and percent ironsaturation; iron injections increased the number of erythrocytes but theirappearance remained abnormal. We have investigated iron supplements toimprove husbandry of b/b rats and to learn more about the underlying defectand its tissue distribution. Weekly IM (intramuscular) injections ofiron–dextran (Imferon at 30 mg kg) improved the anemia but did not alter thered cell morphology. Certain diets also improved the health of b/b rats whencompared to standard rat chows by the criteria of weight, survival toadulthood, hematology and reproduction. The critical nutritional factorturned out to be iron bioavailability, with ferrous iron added to the dietimproving the health of Belgrade rats without affecting the underlyingerythroid defect. Tissue iron measurements after dietary or parenteralsupplementation confirmed the iron deficient status of untreated b/b rats andestablished that dietary ferrous iron partially relieved this deficiency,with injections leading to greater amounts of tissue iron. Serum iron andTIBC were also found to be elevated in untreated b/b rats, with dietarysupplementation decreasing but not eliminating the elevation in TIBC. Thesestudies indicate that iron supplements can improve the health of b/b ratswithout altering the underlying defect and also suggest that the mutationcould alter iron uptake in the GI (gastrointestinal) tract. 相似文献
7.
Extended models of the ventilatory response to sustained isocapnic hypoxia in humans 总被引:2,自引:0,他引:2
Liang, Pei-Ji, Daphne A. Bascom, and Peter A. Robbins.Extended models of the ventilatory response to sustained isocapnic hypoxia in humans. J. Appl. Physiol. 82(2): 667-677, 1997.The purpose of this study was to examine extensions of a modelof hypoxic ventilatory decline (HVD) in humans. In the original model (model I) devised by R. Painter, S. Khamnei, and P. Robbins(J. Appl. Physiol. 74: 2007-2015, 1993), HVD is modeledentirely by a modulation of peripheral chemoreflex sensitivity. In thefirst extension (model II), a more complicated dynamic is usedfor the change in peripheral chemoreflex sensitivity. In the secondextension (model III), HVD is modeled as a combination ofboth the mechanism of Painter et al. and a component that isindependent of peripheral chemoreflex sensitivity. In all cases, aparallel noise structure was incorporated to describe the stochasticproperties of the ventilatory behavior to remove the correlation of theresiduals. Data came from six subjects from a study by D. A. Bascom, J. J. Pandit, I. D. Clement, and P. A. Robbins (Respir. Physiol.88: 299-312, 1992). For model II, there was a significantimprovement in fit for two out of six subjects. The reasons for thiswere not entirely clear. For model III, the fit was againsignificantly improved in two subjects, but in this case the subjectswere those who had the most marked undershoot and recovery ofventilation at the relief of hypoxia. In these two subjects, thechemoreflex-independent component contributed ~50% to total HVD.In the other four subjects, the chemoreflex-independent componentcontributed ~10% to total HVD. It is concluded that in somesubjects, but not in others, there may be a component of HVD thatis independent of peripheral chemoreflex sensitivity. 相似文献
8.
9.
Cationized ferritin was found to inhibit the lateral mobility of intramembrane proteins in turkey erythrocyte membranes and the activation of adenylate cyclase by the (?)-epinephrine-bound β-adrenergic receptor. It was observed that cationized ferritin has only a small direct effect on the β-receptor and on the adenylate cyclase moiety. It is concluded that the cationized ferritin-induced inhibition of the hormone-dependent cyclase activity results from the inhibition of the lateral mobility of the receptor and therefore a decrease in the bimolecular rate of interaction between the receptor and the enzyme. 相似文献
10.
Daphne Getz John F. Gibson Richard N. Sheppard Kingsley J. Micklem Charles A. Pasternak 《The Journal of membrane biology》1979,50(3-4):311-329
Summary When Lettree cells are exposed to Mn2+, the cation becomes associated with cells in two ways: in a relatively loose and mobile manner that gives a six-line EPR spectrum designated Mn
b
*, and in an immobile, relatively tight manner that gives no detectable EPR spectrum, designated Mn
b
. Mn
b
* is probably on the surface of cells; most Mn
b
is probably inside cells. NMR measurements of Lettree cell suspensions show two water proton relaxation rates and confirm the existence of cell-associated Mn. Human erythrocytes, on the other hand, bind no Mn2+ under these conditions, as judged by EPR and NMR measurements.Virally-treated Lettree cells show an increase in Mn
b
(but not in Mn
b
*). They also show a third water proton relaxation rate. 相似文献