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901.
Immaculada Martin Josep A. Villena Marta Giralt Roser Iglesias Teresa Mampel Octavi Vińas Francesc Villarroya 《Molecular and cellular biochemistry》1996,154(2):107-111
The action of thyroid hormones on the expression of the mitochondrial ATP synthase -subunit gene (ATPsyn) is controversial. We detected a binding site for the thyroid hormone receptor between-366 and-380 in the human ATPsyn gene by DNase I footprint analysis and band-shift assays. However, expression vectors in which the chloramphenicol acetyl transferase (CAT) reporter gene is driven by the 5 upstream region of ATPsyn gene were unresponsive to T3 when transiently transfected to HepG2 or GH4C1 cells. CAT constructs driven by the rat phosphoenolpyruvate carboxykinase (PEPCK) or the growth hormone (GH) promoters were stimulated several fold by T3 in parallel experiments. It is proposed that the biological effects of thyroid hormones on the ATPsyn expression occur through indirect mechanisms. 相似文献
902.
The localization of the ai adrenoceptors (1-AR) in the heart tissues from rat and human and in the cultured heart cells from neonatal rats was studied by indirect immunofluorescence and postembedding electronmicroscopical immuno-gold technique. With antipeptide antibodies directed against the second extracellular loop of the human 1-AR (AS sequence 192–218), this receptor was found to be localized along the sarcolemma in both human and rat hearts. Similar localization sites were detected in cultivated rat neonatal cardiomyocytes. Beside the localization in cardiomyocytes, 1-AR were identified in endothelial cells of capillaries and smooth muscle cells of coronary vessels, in neuronal endings, in mast cells of cultivated heart cells but not, or in less amount in fibroblasts. Interestingly, in the right atrium of rat heart the localization of 1-AR was found to be near or on atrial natriuretic factor (ANF) granules, providing the basis for the -adrenergic influence on ANF release. The immunocytochemical studies further confirm and complete the findings known by using autoradiographic binding studies with specific ligands. 相似文献
903.
Stable carbon isotopes as indicators of increased water use efficiency and productivity in white spruce (Picea glauca (Moench) Voss) seedlings 总被引:6,自引:1,他引:5
The relationship among water use efficiency (WUE), productivity and carbon isotopic composition (δ13C) in white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings representing 10 controlled crosses were planted in the field in individual buried sand-filled cylinders. The soil water content in the cylinders was measured using time domain reflectometry over two growing seasons and seedling water use determined by water balance. Two watering treatments were imposed: irrigation and dry land. There was significant (1.6–2.0%c) genetic variation in needle δ13C. Ranking of crosses in terms of δ13C was generally maintained over watering treatments and there was not a significant genetic versus environmental interaction. There was a positive correlation between δ13C and both intrinsic and long-term WUE (more positive δ13C with increased WUE) and between δ13C and productivity, suggesting a correlation due to variation in photosynthetic capacity. Root to shoot ratios did not increase in water-stressed plants, indicating that responses to drought were primarily at the level of gas exchange, rather than through morphological changes. Our results indicate that it should be possible to use δ13C as a surrogate for WUE and to select white spruce genotypes for high WUE without compromising yield. 相似文献
904.
Hydraulic control of stomatal conductance in Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and alder [Alnus rubra (Bong)] seedlings 总被引:1,自引:0,他引:1
Experiments were conducted on 1-year-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and 2- to 3-month-old alder [Alnus rubra (Bong)] seedlings growing in drying soils to determine the relative influence of root and leaf water status on stomatal conductance (gc). The water status of shoots was manipulated independently of that of the roots using a pressure chamber that enclosed the root system. Pressurizing the chamber increases the turgor of cells in the shoot but not in the roots. Seedling shoots were enclosed in a whole-plant cuvette and transpiration and net photosynthesis rates measured continuously. In both species, stomatal closure in response to soil drying was progressively reversed with increasing pressurization. Responses occurred within minutes of pressurization and measurements almost immediately returned to pre-pressurization levels when the pressure was released. Even in wet soils there was a significant increase in gc with pressurization. In Douglas fir, the stomatal response to pressurization was the same for seedlings grown in dry soils for up to 120 d as for those subjected to drought stress over 40 to 60 d. The stomatal conductance of both Douglas fir and alder seedlings was less sensitive to root chamber pressure at higher vapour pressure deficits (D), and stomatal closure in response to increasing D from 1.04 to 2.06 kPa was only partially reversed by pressurization. Our results are in contrast to those of other studies on herbaceous species, even though we followed the same experimental approach. They suggest that it is not always appropriate to invoke a ‘feedforward’ model of short-term stomatal response to soil drying, whereby chemical messengers from the roots bring about stomatal closure. 相似文献
905.
Rat liver mitochondria were examined for their ability to reduce dehydroascorbic acid to ascorbic acid in an -lipoic acid dependent or independent manner. The a-lipoic acid dependent reduction was stimulated by factors that increased the NADH dependent reduction of -lipoic acid to dihydrolipoic acid in coupled reactions. Optimal conditions for dehydroascorbic acid reduction to ascorbic acid were achieved in the presence of pyruvate, -lipoic acid, and ATP. Electron transport inhibitors, rotenone and antimycin A, further enhanced the dehydroascorbic acid reduction. The reactions were strongly inhibited by 1 mM iodoacetamide or sodium arsenite. Mitoplasts were qualitatively similar to intact mitochondria in dehydroascorbate reduction activity. Pyruvate dehydrogenase and -ketoglutarate dehydrogenase reduced dehydroascorbic acid to ascorbic acid in an -lipoic acid, coenzyme A, and pyruvate or -ketoglutarate dependent fashion. Dehydroascorbic acid was also catalytically reduced to ascorbic acid by purified lipoamide dehydrogenase in an -lipoic acid (K
0.5=1.4±0.8 mM) and lipoamide (K
0.5=0.9±0.3 mM) dependent manner. 相似文献
906.
Kerry R. Emslie M. Barrie Coukell Debra Birch Keith L. Williams 《Journal of biotechnology》1996,50(2-3):149-159
We have previously reported expression of the rotavirus outer capsid glycoprotein, VP7, in the relatively new expression host, Dictyostelium discoideum. To optimise yields of recombinant VP7, we examined the role of Ca2+ since stability of both VP7 and mature rotavirus during a rotavirus infection are calcium-dependent. Low micromolar levels of free extracellular Ca2+ were required to maximise yields of VP7 in D. discoideum whilst levels of VP7 were reduced following depletion of intracellular Ca2+ reserves using A23187 and EGTA. Immunoblot analysis suggested that VP7 was being degraded in an intracellular compartment. Immunoprecipitation with a conformation-dependent neutralising antibody confirmed that EGTA-induced Ca2+ chelation alters the conformation of VP7. These results suggest that stability of VP7 is dependent on maintaining adequate levels of intracellular Ca2+ and that conformational changes in VP7 which occur following depletion of Ca2+ reserves induce rapid proteolysis of the protein. Since these results establish conditions for expressing optimal levels of VP7 in the correct conformation they have important implications for the development of a subunit vaccine based on recombinant VP7. 相似文献
907.
Summary Late Arenigian biohermal reef mounds and biostromes within the shallow-marine platform facies of the upper San Juan Formation
of the Precordillera (Western Argentina) represent a new Early Ordovician reef type. The meter-sized reefs are dominated byZondarella communis n.g. n. sp. The new taxon is characterized by domical, bulbous and laminar morphotypes exhibiting growth layers and thin
horizontal and vertical as well as intermingled skeletal elements included within different sets. The fossil maybe compared
with stromatolites and stromatoporoids but an interpretation as primitive stromatoporoids is favoured. 相似文献
908.
To clarify the mechanism of aluminum (Al) toxicity and Al tolerance, we isolated a new clone (pAL201) from a tobacco cDNA library. Northern blot hybridization analysis indicated that the expression of pAL201 is induced by Al treatment and phosphate (P1 ) starvation. The complete cDNA sequence suggested that this clone encodes a moderately anionic peroxidase (EC 1.11.1.7). Analysis by isoelectric focussing indicated that a moderately anionic peroxidase (approximately pI 6.7) and two cationic peroxidases (pI 9.2 and 9.7) in the soluble fraction are activated by Al treatment and P1 starvation, while two moderately anionic isozymes are repressed by these stresses. We suppose that Al ion stress can control the activity of some peroxidase isozymes, one of which is probably induced by enhanced gene expression of pAL201. There is a possibility that some of these isozymes have some functions in Al ion stress. 相似文献
909.
910.
Plasma membrane flavins and pterins are considered to mediate important physiological functions such as blue light photoperception and redox activity. Therefore, the presence of flavins and pterins in the plasma membrane of higher plants was studied together with NAD(P)H-dependent redox activities. Plasma membranes were isolated from the apical hooks of etiolated bean seedlings (Phaseolus vulgaris L. cv. Limburgse Vroege) by aqueous two-phase partitioning. Fluorescence spectroscopy revealed the presence of two chromophores. The first showed excitation maxima at 370 and 460 nm and an emission peak at 520 nm and was identified as a flavin. The second chromophore was probably a pterin molecule with excitation peaks at 290 and 350 nm and emission at 440 nm. Both pigments are considered intrinsic to the plasma membrane since they could not be removed by treatment with hypotonic media containing high salt and low detergent concentrations. The flavin concentration was estimated at about 500 pmol mg?1 protein. However difficulties were encountered in quantifying the pterin concentrations. Protease treatments indicated that the flavins were non-covalently bound to the proteins. Separation of the plasma membrane proteins after solubilisation by octylglucoside, on an ion exchange system (HPLC, Mono Q), resulted in a distinct protein fraction showing flavin and pterin fluorescence and NADH oxidoreductase activity. The flavin of this fraction was identified as flavin mononucleotide (FMN) by HPLC analysis. Other minor peaks of NADH:acceptor reductase activity were resolved on the column. The presence of distinct NAD(P)H oxidases at the plasma membrane was supported by nucleotide specificity and latency studies using intact vesicles. Our work demonstrates the presence of plasma membrane flavins as intrinsic chromophores, that may function in NAD(P)H-oxidoreductase activity and suggests the presence of plasma membrane bound pterins. 相似文献