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11.
C Pasqualini B Kerdelhue 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1985,300(17):637-642
The effect of estradiol on anterior pituitary dopaminergic receptor content was studied in vivo and in vitro, in relation with the serum PRL secretion. A progressive and significant decrease in the number of these receptors was observed, a few hours before the serum release of PRL induced in ovariectomized females by a sequential treatment with different doses of estradiol benzoate. This decrease in the number of dopaminergic membrane receptors can be obtained as well in vitro, when anterior pituitaries, from ovariectomized rats, are incubated with 17 beta-estradiol. These results suggest that the stimulatory effect of estradiol on PRL secretion may be due, at least in part, to the direct "desensitization" to DA of anterior pituitary cells, which is produced by the decrease of dopaminergic receptor level. 相似文献
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13.
The effect of grazing on primary productivity and phosphorus cycling in autotrophic streams was studied using the snail Goniobasis clavaeformes. Snails were added to each of three replicate laboratory stream channels, receiving once-through flow of groundwater, in densities of 2.1, 3.0, and 4.2 g ash free dry mass (AFDM)/m2. A fourth channel received no snails and served as an ungrazed control. Presence of snail grazers resulted in a large reduction in aufwuchs biomass, primary productivity, and biotic phosphorus uptake; a modest reduction in fine particulate organic matter (FPOM); and an increase in the fraction of stream particulate organic matter (POM) exported as seston. Although primary production and aufwuchs biomass continued to decline with increasing snail density, phosphorus uptake increased. This increased phosphorus uptake is attributed to abiotic sorption to inorganic surfaces exposed as a result of efficient removal of aufwuchs at high snail densities. Although snail densities were chosen to bracket the density measured in a natural stream, the experimental densities may result in considerably higher grazing pressure on aufwuchs due to the absence of alternate food sources (e.g., coarse particulate organic matter) usually found in natural streams. Presence of snail grazers increased the spiralling length of phosphorus, primarily by reducing aufwuchs biomass and consequently reducing uptake of phosphorus from the water. Presence of snails also increased downstream transport velocity of phosphorus bound to organic particles. These results follow the patterns predicted in a previous theoretical analysis for mildly phosphorus-limited streams. 相似文献
14.
The effect of starvation and alloxan-diabetes on the contents of citrate and other metabolic intermediates in rat liver 总被引:1,自引:1,他引:0 下载免费PDF全文
1. The content of citrate in ;freeze-clamped' livers from starved and alloxan-diabetic rats was measured by using the specific citrate assay method of Gruber & Moellering (1966). 2. The content of citrate fell progressively during a period of 48hr. starvation to reach a plateau value that is 50% of the value for livers from fed rats. Some possible explanations for the conflicting reports of changes in hepatic citrate content during starvation are discussed. 3. The hepatic contents of ATP, pyruvate, lactate, glycogen and the hexose phosphates were decreased during starvation, whereas those of acetyl-CoA and AMP were increased. 4. Acute alloxan-diabetes produced similar changes in the contents of these metabolic intermediates. 5. The effects of starvation and diabetes on the citrate and acetyl-CoA contents are discussed in relation to control of gluconeogenesis, fatty acid synthesis and the activity of citrate synthase. 相似文献
15.
Carole H. Sellem Annie Sainsard-Chanet Léon Belcour 《Molecular & general genetics : MGG》1990,224(2):232-240
Summary In the filamentous fungus Podospora anserina, the amplification as circular DNA molecules of the first intron (intron ) of the CO1 mitochondrial gene, encoding the cytochrome oxidase subunit 1, is known to be strongly associated with aging of strains. In this study we have attempted to detect the protein potentially encoded by the open reading frame (ORF) contained in this intron. This was done by the Western blot technique using specific antisera raised against three polypeptides encoded by three non-overlapping fragments of this ORF adapted to the universal code and overexpressed in Escherichia coli. We examined about thirty independent subclones of Podospora derived from two different geographic races (A, s), using wild-type and mutant strains, young and senescent cultures. A 100 kDa polypeptide, encoded by the class II intron , was detected in five senescent subclones which all showed strong amplification of the intronic sequence (Sen DNA ). 相似文献
16.
Carole Mign Grard Prensier Agns Cornu Elisabeth Grenet 《Biology of the cell / under the auspices of the European Cell Biology Organization》1996,88(3):137-144
Summary— Arabinoxylans were localised by immunocytochemistry using polyclonal antibodies in the cell walls of the apical internode of maize after degradation in the rumen. In order to understand the significance of arabinoxylan in digestibility property, two lines of maize differing in digestibility were used. Wide variations in the intensity of labelling were observed in the four tissues studied (sclerenchyma, fibres, xylem and parenchyma) from the first hours of incubation in the rumen. Incubation time in the rumen greatly influences the intensity of labelling. 相似文献
17.
Elisabeth Steichen-Gersdorf Holly H. Gallion Deborah Ford Catherine Girodet Douglas F. Easton Richard A. DiCioccio Gareth Evans Margaret A. Ponder Carole Pye Sylvie Mazoyer Tetsuro Noguchi Fabienne Karengueven Hagay Sobol A. Hardouin Yves-Jean Bignon M. Steven Piver Simon A. Smith Bruce A. J. Ponder 《American journal of human genetics》1994,55(5):870-875
In a study of nine families with “site-specific” ovarian cancer (criterion: three or more cases of epithelial ovarian cancer and no cases of breast cancer diagnosed at age <50 years) we have obtained evidence of linkage to the breast-ovarian cancer susceptibility gene, BRCA1 on 17q12-21. If the risk of cancer in these families is assumed to be restricted to the ovary, the best estimate of the proportion of families linked to BRCA1 is .78 (95% confidence interval .32–1.0). If predisposition to both breast and ovarian cancer is assumed, the proportion linked is 1.0 (95% confidence interval .46–1.0). The linkage of familial site-specific ovarian cancer to BRCA1 indicates the possibility of predictive testing in such families; however, this is only appropriate in families where the evidence for linkage to BRCA1 is conclusive. 相似文献
18.
Influence of nitrate on uptake of ammonium by nitrogen-depleted soybean: is the effect located in roots or shoots? 总被引:4,自引:1,他引:3
Saravitz Carole H.; Chaillou Sylvain; Musset Joanne; Raper C. David Jr.; Morot-Gaudry Jean-Francis 《Journal of experimental botany》1994,45(11):1575-1584
In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom]plants that were subjected to 15 d of nitrogen deprivation inflowing hydroponic culture, concentrations of nitrogen declinedto 1.0 and 1.4mmol Ng1 dry weight in shoots and roots,respectively, and the concentration of soluble amino acids (determinedas primary amines) declined to 40µmol g1 dry weightin both shoots and roots. In one experiment, nitrogen was resuppliedfor 10 d to one set of nitrogen-depleted plants as 1.0 mol m3NH4+ to the whole root system, to a second set as 0.5 mol m3NH4+ plus 0.5 mol m3 NO3 to the whole root system,and to a third set as 1.0 mol m3 NH4+ to one-half ofa split-root system and 1.0 mol m3 NO3 to theother half. In a second experiment, 1.0 mol m3 of nitrogenwas resupplied for 4 d to whole root systems in NH4+ : NO3ratios of 1:0, 9:1, and 1:1. Nutrient solutions were maintainedat pH 6.0. When NH4+ was resupplied in combination with NO3 to thewhole root system in Experiment I, cumulative uptake of NH4+for the 10 d of resupply was about twice as great as when NH4+was resupplied alone. Also, about twice as much NH4+ as NO3was taken up when both ions were resupplied to the whole rootsystem. When NH4+ and NO3 were resupplied to separatehalves of a split-root system, however, cumulative uptake ofNH4+ was about half that of NO3. The uptake of NH4+,which is inhibited in nitrogen-depleted plants, thus is facilitatedby the presence of exogenous NO3, and the stimulatingeffect of NO3 on uptake of NH4+ appears to be confinedto processes within root tissues. In Experiment II, resupplyof nitrogen as both NH4+ and NO3 in a ratio of either1:1 or 9:1 enhanced the uptake of NH4+. The enhancement of NH4+uptake was 1.8-fold greater when the NH4+: NO3-resupplyratio was 1:1 than when it was 9:1; however, only 1.3 timesas much NO3 was taken up by plants resupplied with the1 :1 exogenous ratio. The effect of NO3 on enhancementof uptake of NH4+ apparently involves more than net uptake ofNO3 itself and perhaps entails an effect of NO3uptake on maintenance of K+ availability within the plant. Theconcentration of K+ in plants declined slightly during nitrogendeprivation and continued to decline following resupply of nitrogen.The greatest decline in K+ concentration occurred when nitrogenwas resupplied as NH4+ alone. It is proposed that decreasedavailability of K+ within the NH4+-resup-plied plants inhibitedNH4+ uptake through restricted transfer of amino acids fromthe root symplasm into the xylem. Key words: Ammonium, Glycine max, nitrate, nitrogen-nutrition, nitrogen stress, split-root cultures 相似文献
19.
Rhizopus is a zygomycetous genus. Several species of this taxon may infect humans and lower animals. Seventeen isolates ofRhizopus species in three distinct morphological groups were studied: the stolonifer group (sporangiophores greater than 1 mm in height, sporangial diameters of 100–275 µm, branched rhizoids); the arrhizus group (sporangiophores greater than 1 mm in height, branched rhizoids, sporangial diameters of 100–240 µm); and the microsporus group (sporangiophores less than 0.8 mm in height, sporangial diameters less than 100 µm, simple rhizoids). Maximal growth temperatures were characteristic: the stolonifer group grew at 30°C, the arrhizus group grew at 36°C, and the microsporus group grew at 45°C. The DNA mol% G + C base composition of all isolates ranged from 34.9 to 40.2% Species within the three groups were grouped by DNA differences. The arrhizus group was most distinctive with a value of 34.9–36.3%; the stolonifer and microsporus groups had G + C values of 37.0–39.3% and 37.8–40.2%, respectively. Our research clarifies and defines the G-C values of the three important groups ofRhizopus species. 相似文献
20.
Phosphatidylcholine biosynthesis in celery cell suspension cultures with altered sterol compositions
Cell suspension cultures of celery were treated with the plant growth regulator, paclobutrazol. Lipid analysis revealed that use of this xenobiotic had little effect on the quantity or acyl quality of the major phospholipid classes or on the actual amounts of free sterol present in the cell. It did however, cause dramatic changes in the free sterol profile exhibited by treated cultures. In this respect, an increase in 14α-methylsterols was observed.
The synthesis of phosphatidylcholine in celery cell suspension cultures with altered free sterol compositions was studied using two radiolabelled biosynthetic precursors, [3 H-methyl]choline and [3 H-methyl]methionine. The studies showed that the rate of phosphatidylcholine biosynthesis via the CDP-base pathway proceeded at a slower rate in paclobutrazol treated cultures. Accumulation of label phosphocholine was observed arising from reduced CTP:cholinephosphatecytidylyltransferase activity. In contrast, phosphatidylcholine biosynthesis via the sequential methylation of ethanolamine derivatives appeared to be enhanced in cells that had an unusually high 14α-methylsterol content. From these investigations it may be postulated that the biosynthesis of phosphatidylcholine in Apium graveolens suspension cultures may be regulated by membrane sterol composition. 相似文献
The synthesis of phosphatidylcholine in celery cell suspension cultures with altered free sterol compositions was studied using two radiolabelled biosynthetic precursors, [