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991.
León A. Bravo Gustavo E. Zúñiga Miren Alberdi Luis J. Corcuera 《Physiologia plantarum》1998,103(1):17-23
The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley ( Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT50 , ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT50 and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT50 of leaves of cold‐acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT50 decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance. 相似文献
992.
993.
David T. Evans Marian S. Piekarczyk Luis Cadavid Virginia S. Hinshaw D. I. Watkins 《Immunogenetics》1998,47(3):206-211
The products of the highly polymorphic and variable major histocompatibility complex (MHC) class I loci play a crucial role
in host defenses against infectious disease. While similar alleles have been found in closely related species, sharing of
a functional MHC class I allele between two species has never been reported. Here we show that an identical functional MHC
class I molecule is present in two different primate species with an approximate divergence time of 0.7 million years. Lymphocytes
from the red-crested tamarin (Saguinus geoffroyi) expressed an MHC class I allele (Sage-G
*
01) that was identical in coding sequence to an MHC class I allele (Saoe-G
*
08) found in the cotton-top tamarin (Saguinus oedipus). Furthermore, influenza virus-specific cytotoxic T lymphocytes (CTLs) generated in the cotton-top tamarin killed lymphocytes
expressing the influenza virus nucleoprotein (NP) from the red-crested tamarin. Since the influenza virus NP epitope is bound
by Saoe-G*08 in the cotton-top tamarin, it is likely that this molecule is functional in both species. These data provide the first
evidence that functional MHC class I molecules can be maintained entirely intact in two separate species.
Received: 6 June 1997 / Revised: 21 July 1997 相似文献
994.
Osmotic Swelling-Induced Changes in Cytosolic Calcium Do Not Affect Regulatory Volume Decrease in Rat Cultured Suspended Cerebellar Astrocytes 总被引:2,自引:1,他引:1
Sandra Morales-Mulia Luis Vaca Arturo Hernandez-Cruz Herminia Pasantes-Morales 《Journal of neurochemistry》1998,71(6):2330-2338
Abstract: Hyposmotic swelling-induced changes in intracellular Ca2+ concentration ([Ca2+]i) and their influence on regulatory volume decrease (RVD) were examined in rat cultured suspended cerebellar astrocytes. Hyposmotic media (50 or 30%) evoked an immediate rise in [Ca2+]i from 117 nM to a mean peak increase of 386 (50%) and 220 nM (30%), followed by a maintained plateau phase. Ca2+ influx through the plasmalemma as well as release from internal stores contributed to this osmosensitive [Ca2+]i elevation. Omission of external Ca2+ or addition of Cd2+, Mn2+, or Gd3+ did not reduce RVD, although it was decreased by La3+ (0.1–1 mM). Verapamil did not affect either the swelling-evoked [Ca2+]i or RVD. Maneuvers that deplete endoplasmic reticulum (ER) Ca2+ stores, such as treatment (in Ca2+-free medium) with 0.2 µM thapsigargin (Tg), 10 µM 2,5-di-tert-butylhydroquinone, 1 µM ionomycin, or 100 µM ATP abolished the increase in [Ca2+]i but did not affect RVD. However, prolonged exposure to 1 µM Tg blocked RVD regardless of ER Ca2+ content or cytosolic Ca2+ levels. Ryanodine (up to 100 µM) and caffeine (10 mM) did not modify [Ca2+]i or RVD. BAPTA-acetoxymethyl ester (20 µM) abolished [Ca2+]i elevation without affecting RVD, but at higher concentrations BAPTA prevented cell swelling and blocked RVD. We conclude that the osmosensitive [Ca2+]i rise occurs as a consequence of increased Ca2+ permeability of plasma and organelle membranes, but it appears not relevant as a transduction signal for RVD in rat cultured cerebellar astrocytes. 相似文献
995.
Role of Potassium Channels in Amyloid-Induced Cell Death 总被引:20,自引:1,他引:19
Luis V. Colom Maria E. Diaz David R. Beers Alan Neely Wen-jie Xie Stanley H. Appel 《Journal of neurochemistry》1998,70(5):1925-1934
Abstract: Basal forebrain cholinergic neurons are severely depleted early in Alzheimer's disease and appear particularly susceptible to amyloid β-peptide (Aβ) toxicity in vivo. To model this effect in vitro, a cholinergic septal cell line (SN56) was exposed to Aβ. SN56 cells exhibited a tetraethylammonium (TEA)-sensitive outward K+ current with delayed rectifier characteristics. Increases of 64% (±19; p < 0.02) and 44% (±12; p < 0.02) in K+ current density were noted 6–12 and 12–18 h following the addition of Aβ to SN56 cell cultures, respectively. Morphological observation and staining for cell viability showed that 25 ± 4 and 39 ± 4% of SN56 cells were dead after 48- and 96-h exposures to Aβ, respectively. Perfusion of SN56 cells with 10–20 mM TEA blocked 71 ± 6 to 92 ± 2% of the outward currents, widened action potentials, elevated [Ca2+]i, and inhibited 89 ± 14 and 68 ± 14% of the Aβ toxicity. High [K+]o, which depolarizes cell membranes and increases [Ca2+]i, also protected SN56 cells from Aβ toxicity. This effect appeared specific since glucose deprivation of SN56 cells did not alter K+ current density and TEA did not protect these cells from hypoglycemic cell death. Furthermore, Aβ was toxic to a dopaminergic cell line (MES23.5) that expressed a K+ current with delayed rectifier characteristics; K+ current density was not altered by Aβ and MES23.5 cells were not protected by TEA from Aβ toxicity. In contrast, a noncholinergic septal cell line (SN48) that shows minimal outward K+ currents was resistant to the toxicity of Aβ. These data suggest that a K+ channel with delayed rectifier characteristics may play an important role in Aβ-mediated toxicity for septal cholinergic cells. 相似文献
996.
Luis F. Callado J. Javier Meana Bernardo Grijalba Angel Pazos †Magdalena Sastre †Jesús A. García-Sevilla 《Journal of neurochemistry》1998,70(3):1114-1123
Abstract: The α2A- and α2C-adrenoceptor subtypes were evaluated in postmortem brains from suicides with depression (n = 22), suicides with other diagnoses (n = 12), and controls (n = 26). Membrane assays with the antagonist [3H]RX821002 (2-[3H]methoxyidazoxan) suggested the presence of α2A-adrenoceptors in the frontal cortex and both α2C-adrenoceptors and α2A-adrenoceptors in the caudate. The proportions in caudate were similar in controls (α2A, 86%; α2C, 14%), depressed suicides (α2A, 91%; α2C, 9%), and suicides with other diagnoses (α2A, 88%; α2C, 12%). Autoradiography of [3H]RX821002 binding under α2B/C-adrenoceptor-masking conditions confirmed the similar densities of α2A-adrenoceptors in the cortex, hippocampus, and striatum from controls and suicides. In the frontal cortex of depressed suicides, competition of [3H]RX821002 binding by (?)-adrenaline revealed a greater proportion (61 ± 9%) of α2A-adrenoceptors in the high-affinity conformation for agonists than in controls (39 ± 5%). Simultaneous analysis with the agonists [3H]clonidine and [3H]UK14304 and the antagonist [3H]RX821002 in the same depressed suicides confirmed the enhanced α2A-adrenoceptor density when evaluated by agonist, but not by antagonist, radioligands. The results indicate that depression is associated with a selective increase in the high-affinity conformation of the brain α2A-adrenoceptors. 相似文献
997.
Eduardo Eizirik Sandro L. Bonatto Warren E. Johnson Peter G. Crawshaw Jr. Jean Cristophe Vié Dulce M. Brousset Stephen J. O'Brien Francisco M. Salzano 《Journal of molecular evolution》1998,47(5):613-624
The ocelot (Leopardus pardalis) and margay (L. wiedii) are sister-species of Neotropical cats which evolved from a lineage that migrated into South America during the formation
of the Panamanian land bridge 3–5 million years ago. Patterns of population genetic divergence of each species were studied
by phylogenetic analyses of mitochondrial DNA (mtDNA) control region sequences in individuals sampled across the distribution
of these taxa. Abundant genetic diversity and remarkably concordant phylogeographic partitions for both species were observed,
identifying parallel geographic regions which likely reflect historical faunal barriers. Inferred aspects of phylogeography,
population genetic structure, and demographic history were used to formulate conservation recommendations for these species.
In addition, observed patterns of sequence variation provided insight into the molecular evolution of the mtDNA control region
in closely related felids.
Received: 26 January 1998 / Accepted: 14 May 1998 相似文献
998.
Rearrangement of Actin Microfilaments in Plant Root Hairs
Responding to Rhizobium etli Nodulation
Signals 总被引:6,自引:0,他引:6
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Luis Cárdenas Luis Vidali Jimena Domínguez Héctor Pérez Federico Sánchez Peter K. Hepler Carmen Quinto 《Plant physiology》1998,116(3):871-877
The response of the actin cytoskeleton to nodulation (Nod) factors secreted by Rhizobium etli has been studied in living root hairs of bean (Phaseolus vulgaris) that were microinjected with fluorescein isothiocyanate-phalloidin. In untreated control cells or cells treated with the inactive chitin oligomer, the actin cytoskeleton was organized into long bundles that were oriented parallel to the long axis of the root hair and extended into the apical zone. Upon exposure to R. etli Nod factors, the filamentous actin became fragmented, as indicated by the appearance of prominent masses of diffuse fluorescence in the apical region of the root hair. These changes in the actin cytoskeleton were rapid, observed as soon as 5 to 10 min after application of the Nod factors. It was interesting that the filamentous actin partially recovered in the continued presence of the Nod factor: by 1 h, long bundles had reformed. However, these cells still contained a significant amount of diffuse fluorescence in the apical zone and in the nuclear area, presumably indicating the presence of short actin filaments. These results indicate that Nod factors alter the organization of actin microfilaments in root hair cells, and this could be a prelude for the formation of infection threads. 相似文献
999.
Increased Respiration Through Cytochrome d Enhances Microaerobic N2Fixation in Klebsiella Pneumoniae
Nitrogenase activity was increased in a Klebsiella pneumoniae strain (FN27) producing higher amounts of cytochrome d than the wild-type strain. The increased production of cytochrome d in FN27 showed a positive effect on nitrogenase activity in cells cultured with glucose as carbon source at 1 kPa oxygen but a negative effect at higher O2concentrations. In cells cultured with pyruvate as carbon source, FN27 expressed higher activity of nitrogenase at all oxygen tensions tested when compared to the wild-type strain. This analysis shows that the over production of cytochrome d terminal oxidase improves nitrogen fixation in certain culture conditions. 相似文献
1000.