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排序方式: 共有322条查询结果,搜索用时 15 毫秒
1.
n-butyrate and dexamethasone synergistically modulate the surface expression of epidermal growth factor receptors in cultured rat hepatocytes 总被引:1,自引:0,他引:1
n-Butyrate was previously found to increase the epidermal growth factor (EGF) receptor binding in primary cultures of rat hepatocytes. We show here that butyrate and dexamethasone synergistically modulate the surface expression of the EGF receptors. The butyrate-induced enhancement of high-affinity EGF binding was only slight in the absence of glucocorticoid, but was strongly and dose-dependently amplified by dexamethasone. Butyrate counteracted the inhibition by insulin of the dexamethasone-induced increase in EGF binding. The results indicate that the glucocorticoid has a permissive effect on a butyrate-sensitive process that determines the surface expression of the high-affinity class of EGF receptors. 相似文献
2.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
3.
4.
Kirsten Christoffersen Bo Riemann Lone R. Hansen Annette Klysner Helle B. Sørensen 《Microbial ecology》1990,20(1):253-272
Plankton community structure and major pools and fluxes of carbon were observed before and after culmination of a bloom of cyanobacteria in eutrophic Frederiksborg Slotssø, Denmark. Biomass changes of heterotrophic nanoflagellates, ciliates, microzooplankton (50 to 140 μm), and macrozooplankton (larger than 140 μm) were compared to phytoplankton and bacterial production as well as micro- and macrozooplankton ingestion rates of phytoplankton and bacteria. The carbon budget was used as a means to examine causal relationships in the plankton community. Phytoplankton biomass decreased and algae smaller than 20 μm replacedAphanizomenon after the culmination of cyanobacteria. Bacterial net production peaked shortly after the culmination of the bloom (510 μg C liter?1 d?1 and decreased thereafter to a level of approximately 124 μg C liter?1 d?1. Phytoplankton extracellular release of organic carbon accounted for only 4–9% of bacterial carbon demand. Cyclopoid copepods and small-sized cladocerans started to grow after the culmination, but food limitation probably controlled the biomass after the collapse of the bloom. Grazing of micro- and macrozooplankton were estimated from in situ experiments using labeled bacteria and algae. Macrozooplankton grazed 22% of bacterial net production during the bloom and 86% after the bloom, while microzooplankton (nauplii, rotifers and ciliates larger than 50 μm) ingested low amounts of bacteria and removed 10–16% of bacterial carbon. Both macro-and microzooplankton grazed algae smaller than 20 μm, although they did not control algal biomass. From calculated clearance rates it was found that heterotrophic nanoflagellates (40–440 ml?1) grazed 3–4% of the bacterial production, while ciliates smaller than 50 μm removed 19–39% of bacterial production, supporting the idea that ciliates are an important link between bacteria and higher trophic levels. During and after the bloom ofAphanizomenon, major fluxes of carbon between bacteria, ciliates and crustaceans were observed, and heterotrophic nanoflagellates played a minor role in the pelagic food web. 相似文献
5.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献
6.
Mesocosms (4.5 m3) situated in a closed bay area were used to investigate the effect of protozoan predation on nonindigenous bacteria. Pseudomonas fluorescens strain Agl was released into mesocosms as a single inoculum of 1 × 105 cells ml–1 (final concentration) or as four inocula (same concentration each) at intervals of 3 days. Mesocosms that had received growth media corresponding to the inoculum served as controls. Numbers of P. fluorescens Ag1 decreased rapidly whether released as single or multiple inocula. Direct estimation of protozoan predation using fluorescently labeled P. fluorescens from log phase and starved cultures, respectively, revealed that natural populations of heterotrophic nanoflagellates consumed substantial amounts of the nonindigenous bacterial strain. The volume of fluorescently labeled cells prepared from starved cells was 68% of log phase cell volume, but the individual clearance of the small cells was five to seven times higher than that of the log phase bacteria. The natural populations of nanoflagellates consumed 34–62% of P. fluorescens Ag1 daily if starved bacteria were offered as food, and 3–13% if the cells were in the logarithmic growth phase. This suggests that the effect of protozoan predation on nonindigenous bacterial strains is substantial because cultured bacteria are likely to starve in natural environments. The addition of P. fluorescens Ag1 and the growth medium enhanced the abundance of natural bacteria, chlorophyll a, heterotrophic nanoflagellates, and ciliates, but it did not improve the growth conditions for the released strain. The effects on the indigenous populations were more pronounced after addition of fresh medium than following inoculation with cells, which possibly was due to the lower nutrient content of spent medium. However, these results, based on direct estimation of protozoan predation on log phase and starved nonindigenous bacteria, point to the conclusion that mortality induced by bacterivorous predators is the key factor determining removal of nonindigenous bacteria introduced in natural aquatic systems.
Correspondence to: K. Christoffersen. 相似文献
7.
Molecular phylogeny and divergence times of drosophilid species 总被引:32,自引:15,他引:17
The phylogenetic relationships and divergence times of 39 drosophilid
species were studied by using the coding region of the Adh gene. Four
genera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (from
Hawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, and
Sophophora--were included. After conducting statistical analyses of the
nucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNA
genes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophila
as the outgroup. The phylogenetic tree obtained showed that the first major
division of drosophilid species occurs between subgenus Sophophora (genus
Drosophila) and the group including subgenera Drosophila and Engiscaptomyza
plus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is then
divided into D. willistoni and the clade of D. obscura and D. melanogaster
species groups. In the other major drosophilid group, Zaprionus first
separates from the other species, and then D. immigrans leaves the
remaining group of species. This remaining group then splits into the D.
repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila,
Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightly
clustered. Each of the D. repleta, D. obscura, and D. melanogaster groups
is monophyletic. The splitting of subgenera Drosophila and Sophophora
apparently occurred about 40 Mya, whereas the D. repleta group and the
Hawaiian drosophilid cluster separated about 32 Mya. By contrast, the
splitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya,
suggesting that Scaptomyza experienced a rapid morphological evolution. The
D. obscura and D. melanogaster groups apparently diverged about 25 Mya.
Many of the D. repleta group species studied here have two functional Adh
genes (Adh-1 and Adh-2), and these duplicated genes can be explained by two
duplication events.
相似文献
8.
9.
Effect of ethylene and carbon dioxide on potato metabolism: stimulation of tuber and mitochondrial respiration, and inducement of the alternative path
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The respiration of potato tubers (Solanum tuberosum var. Russet Burbank) which have been kept at room temperature for 10 days is stimulated upon subsequent treatment with C2H4 (10 microliters per liter) and O2. The respiratory rise reaches a peak in 24 to 30 hours and thereafter declines. Coincident with the rise in tuber respiration is an increase in the respiratory rates of fresh slices and isolated mitochondria. Slices and mitochondria from C2H4- and O2-treated tubers also display substantial resistance to CN, and the resistant respiration is inhibited by hydroxamates.
The longer the tubers are stored after harvest, the less effective is C2H4 in causing CN resistance in slices and mitochondria from treated tubers. Addition of 10% CO2 to the C2H4-O2 mixture, however, causes extensive CN resistance to develop, even in slices and mitochondria from old tubers. The results show that C2H4, O2, and CO2 act synergistically to induce alternative path development in potatoes.
相似文献10.
Sulfate reduction and S-oxidation in a moorland pool sediment 总被引:3,自引:2,他引:1
In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO4
2– reduction rates in the sediment, (2) depletion of SO4
2– in the overlying water column and (3) release of35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO4
2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core35SO4
2– injection. Rates of SO4
2– consumption in the overlying water were estimated by changes in SO4
2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m–2 d–1. Rates of SO4
2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m–2 d–1 (November) to 0.43–1.81 mmol m–2 d–1 (July, August and April). Maximum rates of oxidation to SO4
2– in July 1990 estimated by combination of SO4
2– reduction rates and rates of in situ SO4
2– uptake in the enclosed water column were 10.3 and 10.5 mmol m–2 d–1 at an organic rich and at a sandy site respectively.Experiments with35S2– and35SO4
2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO4
2– and (2) the presence of mainly non SO4
2–-S derived from reduced S transported from the sediment into the overlying water. A35S2– tracer experiment showed that about 7% of35S2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author 相似文献