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991.
† Michel Bureau †Jacques Laschet Mercédès Bureau-Heeren Benoît Hennuy Arlette Minet Pierre Wins Thierry Grisar 《Journal of neurochemistry》1995,65(5):2006-2015
Abstract: GABAA receptors were characterized in cellular fractions isolated from adult bovine brain. The fraction enriched in cortical astrocytes is very rich in high-affinity binding sites for [3 H]flunitrazepam and other "central-type" benzodiazepine ligands. The amount of specific [3 H]flunitrazepam binding was more than five times higher in the glial fraction than in synaptosomal and perikaryal fractions. [3 H]Flunitrazepam was displaced by low concentrations of clonazepam and other specific ligands for central GABAA receptors. Specific binding sites for GABA, flunitrazepam, barbiturates, and picrotoxin-like convulsants were characterized. Allosteric interactions between the different sites were typical of central-type GABAA receptors. The presence of α-subunit(s), as revealed by [3 H]flunitrazepam photoaffinity labeling, was demonstrated in all brain fractions at molecular mass 51–53 kDa. Photoaffinity labeling was highest in the glial fraction. However, in primary cultured astrocytes from neonate rat cortex, no photoaffinity labeling was detected. Information obtained from astrocytes in culture should thus be taken with caution when extrapolated to differentiated astroglial cells. Our results actually show that, in mature brain, most of the fully pharmacologically active GABAA receptors are extrasynaptic and expressed in astroglia. 相似文献
992.
Ana María Bravo-Angel Heinz-Albert Becker Reinhard Kunze Barbara Hohn Wen-Hui Shen 《Molecular & general genetics : MGG》1995,248(5):527-534
A reverse genetic system for studying excision of the transposable elementDs1 in maize plants has been established previously. In this system, theDs1 element, as part of the genome of maize streak virus (MSV), is introduced into maize plants via agroinfection. In the presence
of theAc element, excision ofDs1 from the MSV genome results in the appearance of viral symptoms on the maize plants. Here, we used this system to study DNA
sequences requiredin cis for excision ofDs1. TheDs1 element contains theAc transposase binding motif AAACGG in only one of its subterminal regions (defined here as the 5′ subterminal region). We showed
that mutation of these motifs abolished completely the excision capacity ofDs1. This is the first direct demonstration that the transposase binding motifs are essential for excision. Mutagenesis with
oligonucleotide insertions in the other (3′) subterminal region resulted in elements with either a reduced or an increased
excision efficiency, indicating that this subterminal region also has an important function. 相似文献
993.
Non-antagonistic interactions between arthropods and leaves of insectivorous plants with adhesive traps so far have never been reported. The mites are common prey of such plants, but we have found a new subspecies of the mite Oribatula tibialis living on the leaves of Pinguicula longifolia. Because of its small size and the low glandular density of the host, the mite moves without being trapped by the mucilaginous droplets of the leaf surface. P. longifolia provides shelter and food for the mite, while the plant may also benefit because of its fungivorous and scavenging activities. This new interaction is another dramatic example of widespread miteplant associations. 相似文献
994.
A five year study was conducted in a 100–120 year old even-aged sugar maple stand in southern Quebec (46°07N 73° 56W; 305 m altitude) to explore the effect of different fertilization formulations aimed at 1) correcting the most common nutrient deficiencies observed in declining maple stands (K and Mg), 2) decreasing soil acidity, and 3) simulating enrichment with atmospheric N. Seven fertilizer mixtures were applied in the spring of 1987: 400 kg ha-1 of K2SO4, CaCO3, CaMg(CO3)2, (NH4)2SO4, complete fertilizer (Maplegro) and 800 kg ha-1 of an equal mixture of K2SO4+CaCO3 or K2SO4+CaMg(CO3)2. The site was divided into twenty-four 25×25 m plots and treatments including control were replicated three times. Leaves and soils (organic and mineral) were sampled in 1987, 1988 and 1991. Trees were cored at 1.2 m to measure their response in diameter growth. The application of K2SO4+CaMg(CO3)2 was the only treatment that significantly increased (+13%) the average growth rate over the five year period after fertilization. The application of (NH4)2SO4, Maplegro, CaMg(CO3)2 and K2SO4 reduced growth relative to the control for the five year period by 29, 24, 20 and 12 %, respectively. Positive and negative effects on growth can be explained mainly in terms of changes in leaf K. Both the application of Maplegro and (NH4)2SO4 increased soil P availability. Overall, the rate of growth showed a cubic pattern of change over the 5 year period with peaks in 1988 and 1991. Trees in control plots went from a limiting foliar status of Ca and Mg, and surplus N in 1987 to a surplus of Ca and Mg, and lower N concentration in 1991. Our results suggest that nutrient deficiencies observed at our site were associated with a disturbance of the biogeochemical cycle of nutrients rather than soil nutrient depletion.Abbreviations BS
base saturation
- CEC
cation exchange capacity
- DRIS
diagnosis and recommendation integrated system 相似文献
995.
María-Carmen Rodríguez-Yoldi José-Emilio Mesonero Maríaa-Jesús Rodríguez-Yoldi 《Biological trace element research》1995,50(1):1-11
Zinc is an essential trace element necessary to life. This metal may exert some of its physiological effects by acting directly
on cellular membranes, either by altering permeability or by modulating the activity of membrane-bound enzymes. On the other
hand, calcium is an essential element in a wide variety of cellular activities. The aim of the present work was to study a
possible interaction between zinc and calcium on intestinal transport ofd-galactose in jejunum of rabbit in vitro. In media with Ca2+, when ZnCl2 was present at 0.5 or 1 mM, zinc was found to reduce thed-galactose absorption significantly. In Ca2+-free media, where CaCl2 was omitted and replaced isotonically with choline chloride, the sugar transport was not modified by zinc. Verapamil at 10−6
M (blocking mainly Ca2+ transport) did not modify the inhibitory effect of zinc ond-galactose transport. When 10−6
M of A 23187 (Ca2+-specific ionophore) was added with/without Ca2+ to the media, ZnCl2 produced no change in sugar transport. These results could suggest a possible interaction of calcium and zinc for the same
chemical groups of membrane, which could affect the intestinal absorption of sugars. 相似文献
996.
Jesús Zurdo Miguel A. Centeno José A. Odriozola Concepción Fernández-Cabrera Juan M. Ramírez 《Photosynthesis research》1995,46(1-2):363-369
In previous work (Zurdo J, Fernández-Cabrera C and Ramírez JM (1993) Biochem J 290: 531–537), it had been shown that selective extraction of the carotenoid from the light-harvesting protein 2 (LH2) of Rhodobacter capsulatus induced the dissociation of 800-nm absorbing bacteriochlorophyll (Bchl), a 10-nm red shift of 854-nm Bchl, and a decrease of the stability of the protein in detergent solution. In the present study, the Fourier transform Raman and near-infrared circular dichroism spectra of native and carotenoid-depleted LH2 membrane preparations were compared. It was found that while the coupled carbonyls of 854-nm Bchl remained specifically H-bonded to the peptides after carotenoid extraction, the optical activity of the near-infrared electronic transition was significantly altered. Given the excitonic origin of such optical activity, our data suggest that carotenoid extraction elicits a rearrengement of the chromophore cluster and of the associated polypeptide subunits. This implies a significant role of the carotenoid in maintaining the native quaternary structure of the protein, which would be consistent with the observed dissociation of 800-nm Bchl and the loss of solubilized LH2 stability that result from carotenoid removal. There is no evidence for a similar role of the carotenoid in the LH1 protein.Abbreviations Bchl
bacteriochlorophyll
- FT
Fourier transform
- CD
circular dichroism
- LH1 and LH2
the bacterial light-harvesting proteins 1 and 2
In memoriam of Daniel I. Arnon. 相似文献
997.
Angel García-Gutiérrez Francisco R. Cantón Fernando Gallardo Francisca Sánchez-Jiménez Francisco M. Cánovas 《Plant molecular biology》1995,27(1):115-128
Pine seedlings are able to accumulate chlorophylls and develop green plastids in a light-independent manner. In this work, we have characterized ferredoxin-dependent glutamate synthase (EC 1.4.7.1; Fd-GOGAT), a key enzyme in nitrogen interconversion during this process. Fd-GOGAT has been purified about 170-fold from cotyledons of maritime pine (Pinus pinaster). As occurs in angiosperms, the native enzyme is a single polypeptide with an apparent molecular mass of 163–168 kDa that is confined to the chloroplast stroma. Polyclonal antibodies generated against the purified enzyme were used to immunoscreen a gt11 expression library from Scots pine (Pinus sylvestris) seedlings and partial cDNA clones were isolated and characterized. The clone with the longest cDNA insert (pGOP44) contained the codification for the C-terminal (550 amino acids) of the pine Fd-GOGAT polypeptide. Immunological cross-reactivity and comparative amino sequence analysis revealed that Fd-GOGAT is a well conserved protein in higher plants. Western blot analyses showed that protein was expressed in chloroplast-containing pine tissues and this expression pattern was not affected by exogenously supplied nitrogen. Fd-GOGAT mRNA, polypeptide and enzyme activity accumulated in substantial amounts in dark-grown pine seedlings. The presence of a functional Fd-GOGAT may be important to provide the required glutamate for the biosynthesis of nitrogen compounds during chloroplast biogenesis in the dark. 相似文献
998.
Genetic transformation of alfalfa somatic embryos and their clonal propagation through repetitive somatic embryogenesis 总被引:3,自引:0,他引:3
Slavica Ninković Jovanka Miljuš-Djukić Mirjana Nešković 《Plant Cell, Tissue and Organ Culture》1995,42(3):255-260
Genetically transformed alfalfa (Medicago sativa L., cv. Zajearska 83) plantlets were obtained by inoculating somatic embryos with Agrobacterium tumefaciens strains A281/pGA472 and LBA4404/pBI121. Single somatic embryos, 5–7 mm long, were released from a repetitively embryogenic culture, wounded, and cocultivated with the bacteria. The agar-solidified culture medium contained mineral salts, vitamins, 40 g l–1 sucrose, 1 g l–1 yeast extract and 0.05 mg l–1 BA. Five clones, transformed with A281/pGA472, and 4 clones transformed with LBA4404/pBI121, were selected for proliferation by repetitive somatic embryogenesis, on media containing 100 mg l–1 of kanamycin. The transformation of kanamycin-resistant clones was confirmed by assaying the activity of neomycin phosphotransferase II and/or -glucuronidase enzymes, and by the Southern blot analysis. It is suggested that the transformation/regeneration system based on somatic embryogenesis may be suitable for establishing transgenic alfalfa lines. The relatively low frequency of embryo transformation is compensated for by abundant proliferation in secondary somatic embryogenesis.Abbreviations BA
6-benzyladenine
- GUS
-glucuronidase
- Km
kanamycin
- NPTII
neomycin phosphotransferase II
- X-gluc
5-bromo-4-chloro-3-indolyl--glucuronic acid
- BM
basal medium 相似文献
999.
J. M. Barrasa S. Camarero A. T. Martínez K. Ruel 《Applied microbiology and biotechnology》1995,43(4):766-770
The ultrastructural patterns characterizing wheat straw degradation by the ligninolytic fungi Phanerochaete chrysosporium and Trametes versicolor were studied. During fungal attack, the less lignified tissues were degraded first, whereas the xylematic and sclerenchymatic fibers underwent a delayed attack. In straw samples degraded by T. versicolor, partial delignification, defibrillation and swelling of cell walls, often causing separation between primary and secondary walls, were observed. By contrast, the formation of erosions and fissures, with minor lignin removal, characterized the attack to the cell wall by P. chrysosporium. At an advanced stage of decay, KMnO4 staining demonstrated abundant electron-dense material around hyphae and in the proximity of the cell-wall surface. In the case of P. chrysosporium, spherical black bodies were found in the erosions and fissures produced during fungal attack. 相似文献
1000.
P J Hurlin C Quéva P J Koskinen E Steingrímsson D E Ayer N G Copeland N A Jenkins R N Eisenman 《The EMBO journal》1995,14(22):5646-5659