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101.
Nitrification rates were measured along a salinity gradient in the Rhône River estuary, using specific inhibitors (allylthiourea and chlorate) coupled with the measurement of change in nitrite concentration and inorganic carbon uptake by nitrifiers. Rates of ammonium and nitrite oxidation were similar up to 15 practical salinity units (from 1 to 2 mol N oxidized liter-1 day-1). For higher salinities, nitrite and ammonium oxidation rates were 0.14 and 0.23 mol N oxidized liter-1 day-1, respectively. Ammonium oxidizers assimilated 19–150 × 10–3 mol C liter-1 day-1, while nitrite oxidizers fixed 4.8–72.6 × 10–3 mol C liter-1 day-1. The amounts of nitrogen oxidized and C incorporated demonstrated a linear correlation (r 2 > 0.99). The ratio of N oxidized to C incorporated ranged between 14.3 to 12.3 for ammonium oxidizers, and between 31.6 and 29 for nitrite oxidizers, the lower values being measured in seawater. Offprint requests to: M. Bianchi.  相似文献   
102.
Ischemia-induced brain iron delocalization: Effect of iron chelators   总被引:5,自引:0,他引:5  
Tissue damage in cerebral ischemia may be produced by acidosis-induced delocalization of intracellular iron which acts as a catalyst in oxidative reactions. Acidosis was induced either by homogenization and incubation of rat cortical homogenates in acidified buffers or by submitting hyperglycemic rats to complete ischemia, a procedure that leads to intracellular lactic acidosis. The level of low molecular weight species (LMWS) iron was measured after filtration of tissue homogenates through a 10,000 Mr ultrafiltration membrane. When cortical tissue was homogenized in buffer pH 7, the level of LMWS iron was equal to 0.21 μg/g. It was significantly enhanced by acidification of the homogenization medium, reaching 0.34 μg/g at pH 6 and 0.75 μg/g at pH 5. When the tissue was homogenized in water, the LMWS iron level reached 0.17 μg/g in normoglycemic rats and 0.38 μg/g (p < 0.5) in hyperglycemic rats. Both aerobic incubation of homogenates for 1 h at 37°C and inclusion of EDTA in the homogenization medium led to further increases in the iron level. In order to demonstrate the deleterious role of iron in brain ischemia, the effect of treatment with bipyridyl, an iron-chelating agent, was assessed by measuring regional brain edema by the specific gravity method, 24 h following induction of thrombotic brain infarction. The treatment significantly attenuated the development of brain edema, reducing the water content of the infarcted area by about 2.5%. Taken together, these results support the hypothesis that a significant component of brain ischemic injury involves an iron-dependent mechanism.  相似文献   
103.
Time-course tracer studies were performed on the metabolism of trans-cinnamic acid-[3-14C] and trans-p-coumaric acid-[2-14C] in the  相似文献   
104.
Summary This paper deals with a computer-aided study of the associations between acrocentric chromosomes as well as between those other chromosomes which in our investigations were revealed to be significantly closer to each other than random. The chromosome pairs were identified by a trypsinbanding technique. The method used has been elaborated previously with the specific aim of determining associations in a manner that avoids all subjective criteria.The tendency for association between homologous chromosomes is in decreasing order: 21 and 13>1>14, 18 and 19>17. Among the nonhomologous acrocentric chromosomes the significant tendencies for associations are between D-D: 13–14>13–15>14–15; between D-G: 13–21>14–21>13–22>15–22.The implication of the different tendencies to associate are dicussed in terms of aetiology of numerical and structural chromosome abnormalities.  相似文献   
105.
Enumeration of alphafetoprotein (AFP) secreting cells in subcultures of rat hepatoma McA-RH7777 has been achieved by a reverse hemolytic plaque assay. The proportion of the cell population engaged in AFP production varies during the growth. Its maximum is reached during the late exponential phase and precedes the maximum of daily AFP accumulation in the culture medium. Then the proportion of AFP secreting cells decreases whereas AFP accumulation remains high, suggesting a change in AFP secretion rate.  相似文献   
106.
107.
Summary Hepatocytes isolated from neonatal (NN) and adult (AD) rats were seeded on fibronectin coated substratum and cultured in arginine-free medium supplemented with various combinations of insulin, dexamethasone, triiodothyronine (T3), albumin, and transferrin, in presence or absence of fibronectin depleted serum (FDS). The main finding is that in response to certain hormone mixtures, both NN and AD hepatocytes can be stimulated to proliferate, as revealed by an increase in cell number, a [3H]thymidine incorporation into nuclei, and extractable DNA as well as the appearance of mitotic figures. Moreover, this proliferative activity is associated with changes in hepatocyte ploidy. However, the proliferative response of NN hepatocytes to hormone action is much different from that of AD hepatocytes, and the addition of FDS amplifies this activity in NN but inhibits it in AD hepatocyte cultures. Measurements of tyrosine aminotransferase and lactate dehydrogenase activities indicate a good preservation of NN and AD hepatocyte functional integrity under certain culture conditions. A good maintenance of albumin production in NN and AD hepatocyte cultures requires the presence of dexamethasone, whereas theα-fetoprotein production in NN hepatocyte cultures is reduced quite rapidly under most conditions. Noα-fetoprotein is detectable in AD hepatocyte cultures. Part of this work was presented at the 31st Annual Meeting of the Tissue Culture Association, St. Louis, MO, June 1980.  相似文献   
108.
Chinese hamster ovary (CHO) cells were exposed to [3H]ethyl nitrosourea (ENU) or [3H]ethyl methanesulfonate (EMS) and the following DNA ethylation products were quantitated: 3- and 7-ethyladenine, O2-ethylcytosine, 3-, 7- and O6-ethylguanine, O2- and O4-ethyldeoxythymidine and the representative ethylated phosphodiester, deoxythymidylyl (3′–5′)ethyl-deoxythymidine. When mutations at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus induced by these same treaments were compared with the observed ethylation products, mutations were found to correlate best with 3- and O6-ethylguanine. EMS induced approximately twice as many sister-chromatid exchanges (SCEs) as ENU at doses yielding equal mutation frequencies. When SCEs were indirectly compared with DNA ethylation products, 3-ethyladenine and ethylated phosphodiesters related best to SCE formation. Because mutation and SCE induction appear, at least in part, to be related to different DNA adducts, SCE induction by simple ethylating agents may not be a quantitative indicator of potentially mutagenic DNA damage.  相似文献   
109.
Freezing of prokaryotic and eukaryotic microorganisms is the main interest in the study of cold stress responses of living organisms. In parallel, applications which arise from this approach are of two types: (i) optimization of the frozen starters used in food processing; and (ii) improvement of the ex situ preservation of microorganisms in collections. Currently, cryopreservation of microorganisms in collections is carried out in cryotubes, and bibliographical references related to freezing microorganisms packaged in straws are scarce. In this context, a preliminary study was completed to evaluate the technological potential of ionomeric resin straws compared to polycarbonate cryo-tubes. Survival under freezing stress was tested on three microorganisms selected for their biotechnological interest: two lactic acid bacteria, Lactococcus lactis subsp. cremoris and Lactobacillus delbrueckii subsp. bulgaricus and a deuteromycete fungus, Geotrichum candidum. The stress was carried out by repeated freezing-thawing cycles to artificially accelerate the lethal effect of freezing on the microorganisms. Two main results were obtained: (i) the survival rate values (per freezing-thawing cycle) seems to depend on the thermal type of the studied microorganism, and (ii) there was no, under our experimental conditions, significant difference between straws and tubes. However, conservation in the resin straws lead to a slight increase in the survival of L. cremoris and G. candidum compared to microtubes. In those conditions, straws seems an alternative system to securely store frozen microorganisms with three main characteristics: (i) a high resistance to thermal stress, (ii) a safe closing by hermetic weld, and (iii) a system for inviolable identification.  相似文献   
110.
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