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981.
Edward B. Rastetter Bonnie L. Kwiatkowski Séverine Le Dizès John E. Hobbie 《Biogeochemistry》2004,69(1):37-62
The down-slope movement of water and nutrients should link plant and soil processes along hill slopes. This linkage ought to be particularly strong in Arctic ecosystems where permafrost confines flowing water near the surface. We examined whether these hill-slope processes are important in assessments of the responses of Arctic tundra to changes in CO2 and climate using the Marine Biological Laboratory–General Ecosystem Model. Because higher rates of water flow decrease the distance over which nutrients must diffuse to the roots, down-slope vegetation is more productive under current conditions. In response to elevated CO2 and a warmer, wetter climate, the relative increase in carbon stored in vegetation and soils was higher uphill, but the absolute increase was higher downhill. Very little of the increase in carbon anywhere on the hill slope resulted from an increase in total ecosystem nitrogen. Instead, the increases were associated with increases in vegetation C:N ratio (woodiness) and with the redistribution of nitrogen from soils (low C:N) to vegetation (high C:N). Because these changes are fueled by nitrogen already in place, the down-slope movement of nitrogen does not appear to be a major determinant of the responses of Arctic tundra to changes in CO2 and climate. 相似文献
982.
Kriloff A Germain D Canoville A Vincent P Sache M Laurin M 《Journal of evolutionary biology》2008,21(3):807-826
Bone microanatomy appears to track changes in various physiological or ecological properties of the individual or the taxon. Analyses of sections of the tibia of 99 taxa show a highly significant (P 相似文献
983.
Construction, alignment and analysis of twelve framework physical maps that represent the ten genome types of the genus Oryza 总被引:1,自引:0,他引:1
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Kim H Hurwitz B Yu Y Collura K Gill N SanMiguel P Mullikin JC Maher C Nelson W Wissotski M Braidotti M Kudrna D Goicoechea JL Stein L Ware D Jackson SA Soderlund C Wing RA 《Genome biology》2008,9(2):R45-15
We describe the establishment and analysis of a genus-wide comparative framework composed of 12 bacterial artificial chromosome fingerprint and end-sequenced physical maps representing the 10 genome types of Oryza aligned to the O. sativa ssp. japonica reference genome sequence. Over 932 Mb of end sequence was analyzed for repeats, simple sequence repeats, miRNA and single nucleotide variations, providing the most extensive analysis of Oryza sequence to date. 相似文献
984.
Monk TH Begley AE Billy BD Fletcher ME Germain A Mazumdar S Moul DE Shear MK Thompson WK Zarotney JR 《Chronobiology international》2008,25(1):83-98
A laboratory study of sleep and circadian rhythms was undertaken in 28 spousally bereaved seniors (> or =60 yrs) at least four months after the loss event. Measures taken included two nights of polysomnography (second night used), approximately 36 h of continuous core body temperature monitoring, and four assessments of mood and alertness throughout a day. Preceding the laboratory study, two-week diaries were completed, allowing the assessment of lifestyle regularity using the 17-item Social Rhythm Metric (SRM) and the timing of sleep using the Pittsburgh Sleep Diary (PghSD). Also completed were questionnaires assessing level of grief (Texas Revised Inventory of Grief [TRIG] and Index of Complicated Grief [ICG]), subjective sleep quality (Pittsburgh Sleep Quality Index [PSQI]), morningness-eveningness (Composite Scale of Morningness [CSM]), and clinical interview yielding a Hamilton Depression Rating Scale (HDRS) score. Grief was still present, as indicated by an average TRIG score of about 60. On average, the bereaved seniors habitually slept between approximately 23:00 and approximately 06:40 h, achieving approximately 6 h of sleep with a sleep efficiency of approximately 80%. They took about 30 min to fall asleep, and had their first REM episode after 75 min. About 20% of their sleep was in Stage REM, and about 3% in Stages 3 or 4 (slow wave sleep). Their mean PSQI score was 6.4. Their circadian temperature rhythms showed the usual classic shape with a trough at approximately 01:00 h, a fairly steep rise through the morning hours, and a more gradual rise to mid-evening, with an amplitude of approximately 0.8 degrees C. In terms of lifestyle regularity, the mean regularity (SRM) score was 3.65 (slightly lower than that usually seen in seniors). Mood and alertness showed time-of-day variation with peak alertness in the late morning and peak mood in the afternoon. Correlations between outcome sleep/circadian variables and level of grief (TRIG score) were calculated; there was a slight trend for higher grief to be associated with less time spent asleep (p=0.07) and reduced alertness at 20:00 h (p=0.05). Depression score was not correlated with TRIG score (p>0.20). When subjects were divided into groups by the nature of their late spouse's death (expected/after a long-term chronic illness [n=18] versus unexpected [n=10]), no differences emerged in any of the variables. In conclusion, when studied at least four months after the loss event, there appears to be some sleep disruption in spousally bereaved seniors. However, this disruption does not appear to be due to bereavement-related disruptions in the circadian system. 相似文献
985.
Taccardi B Punske BB Macchi E Macleod RS Ershler PR 《American journal of physiology. Heart and circulatory physiology》2008,294(4):H1753-H1766
Published studies show that ventricular pacing in canine hearts produces three distinct patterns of epicardial excitation: elliptical isochrones near an epicardial pacing site, with asymmetric bulges; areas with high propagation velocity, up to 2 or 3 m/s and numerous breakthrough sites; and lower velocity areas (<1 m/s), where excitation moves across the epicardial projection of the septum. With increasing pacing depth, the magnitude of epicardial potential maxima becomes asymmetric. The electrophysiological mechanisms that generate the distinct patterns have not been fully elucidated. In this study, we investigated those mechanisms experimentally. Under pentobarbital anesthesia, epicardial and intramural excitation isochrone and potential maps have been recorded from 22 exposed or isolated dog hearts, by means of epicardial electrode arrays and transmural plunge electrodes. In five experiments, a ventricular cavity was perfused with diluted Lugol solution. The epicardial bulges result from electrotonic attraction from the helically shaped subepicardial portions of the wave front. The high-velocity patterns and the associated multiple breakthroughs are due to involvement of the Purkinje network. The low velocity at the septum crossing is due to the missing Purkinje involvement in that area. The asymmetric magnitude of the epicardial potential maxima and the shift of the breakthrough sites provoked by deep stimulation are a consequence of the epi-endocardial obliqueness of the intramural fibers. These results improve our understanding of intramural and epicardial propagation during premature ventricular contractions and paced beats. This can be useful for interpreting epicardial maps recorded at surgery or inversely computed from body surface ECGs. 相似文献
986.
Di Pasqua AJ Sharma KK Shi YL Toms BB Ouellette W Dabrowiak JC Asefa T 《Journal of inorganic biochemistry》2008,102(7):1416-1423
We here measure the toxicity of MCM-41, a mesoporous silica nanomaterial, two of its functionalized analogs, AP-T, which has grafted aminopropyl groups and MP-T, which has grafted mercaptopropyl groups, and spherical silica nanoparticles (SiO2), toward human neuroblastoma (SK-N-SH) cells. Since the particles studied are not soluble in aqueous media, the metric used to report the cytotoxicity of these materials is a new quantity, Q50, which is the number of particles required to inhibit normal cell growth by 50%. Determining the number of particles per gram of material applied to the cells required both the calculated and experimentally determined surface areas of these nanomaterials. This study shows that Q50 increases in the order, MCM-41 < MP-T < AP-T ≈ SiO2, showing that on a per particle basis, MCM-41 is the most cytotoxic material studied. For the three mesoporous silica materials in this study, cytotoxicity appears related to the adsorptive surface area of the particle, although the nature of the functional group cannot be ruled out. Silica nanospheres have the lowest surface area of the particles studied but since they exhibit a Q50 value similar to that of AP-T, shape may also be important in the cytotoxicity of these materials. 相似文献
987.
Metabolic assays are a preferred method for evaluation of Candida albicans viability after exposure to antimicrobial agents in cases in which the culture is a complex mixture of yeast and filamentous forms. There is a lack of published data indicating the strength of the correlation between metabolic assays and viable cell numbers determined by a standard assay such as colony forming units (CFU). We developed a kinetic metabolic assay (KMA) for quantifying viable cells which was tested on yeast cells in both exponential and stationary phase using alamarBlue and XTT as metabolic indicators. The KMA enabled quantification of the viable population over a range of 10(1) to 10(7) cells that linearly correlated (R(2)>0.98) with estimates made by enumeration of CFU regardless of the indicator or growth phase of the cells. Linear relationships were used to calibrate the KMA in terms of equivalent CFU. Viable cell populations were then determined after exposure to AmB. These results were compared with those obtained by direct enumeration of CFU. There were significant correlations between KMA-derived equivalent CFU and direct CFU estimates of viable cell populations for exponential-phase cells. However, the proportions of viable cells based on the KMA were consistently lower than those obtained directly by CFU. This trend was substantially more pronounced for stationary phase cells. These results show that even in the relatively simple case in which only the yeast form is present, the relationship between assessment by metabolic assays and CFU is perturbed by exposure to an antimicrobial and that, furthermore, growth phase alters the nature of the perturbation. 相似文献
988.
Actin and microtubules (MT) are targets of numerous molecular pathways that control neurite outgrowth. To generate a neuronal
protrusion, coordinated structural changes of the actin and MT cytoskeletons must occur. Neurite formation occurs when actin
filaments (F-actin) are destabilized, filopodia are extended, and MTs invade filopodia. This process results in either axon
or dendrite formation. Axonal branching involves interplay between F-actin and MTs, with F-actin and MTs influencing polymerization,
stabilization, and maintenance of each other. Our knowledge of the mechanisms regulating development of the axon, however,
far eclipses our understanding of dendritic development and branching. The two classes of neurites, while fundamentally similar
in their ability to elongate and branch, dramatically differ in growth rate, orientation of polarized MT bundles, and mechanisms
that initiate branching. In this review, we focus on how F-actin, MTs, and proteins that link the two cytoskeletons coordinate
to specifically initiate dendritic events.
Penelope C. Georges and Norell M. Hadzimichalis contributed equally. 相似文献
989.
Sweet to the extreme: protein glycosylation in Archaea 总被引:1,自引:0,他引:1
Yurist-Doutsch S Chaban B VanDyke DJ Jarrell KF Eichler J 《Molecular microbiology》2008,68(5):1079-1084
Post-translational modifications account for much of the biological diversity generated at the proteome level. Of these, glycosylation is the most prevalent. Long thought to be unique to Eukarya, it is now clear that both Bacteria and Archaea are also capable of N-glycosylation, namely the covalent linkage of oligosaccharides to select target asparagine residues. However, while the eukaryal and bacterial N-glycosylation pathways are relatively well defined, little is known of the parallel process in Archaea. Of late, however, major advances have been made in describing the process of archaeal N-glycosylation. Such efforts have shown, as is often the case in archaeal biology, that protein N-glycosylation in Archaea combines particular aspects of the eukaryal and bacterial pathways along with traits unique to this life form. For instance, while the oligosaccharides of archaeal glycoproteins include nucleotide-activated sugars formed by bacterial pathways, the lipid carrier on which such oligosaccharides are assembled is the same as used in eukaryal N-glycosylation. By contrast, transfer of assembled oligosaccharides to their protein targets shows Archaea-specific properties. Finally, addressing N-glycosylation from an archaeal perspective is providing new general insight into this event, as exemplified by the solution of the first crystal structure of an oligosaccharide transferase from an archaeal source. 相似文献
990.
DLG-1 Is a MAGUK Similar to SAP97 and Is Required for Adherens Junction Formation 总被引:4,自引:0,他引:4
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Cellular junctions are critical for intercellular communication and for the assembly of cells into tissues. Cell junctions often consist of tight junctions, which form a permeability barrier and prevent the diffusion of lipids and proteins between cell compartments, and adherens junctions, which control the adhesion of cells and link cortical actin filaments to attachment sites on the plasma membrane. Proper tight junction formation and cell polarity require the function of membrane-associated guanylate kinases (MAGUKs) that contain the PDZ protein-protein interaction domain. In contrast, less is known about how adherens junctions are assembled. Here we describe how the PDZ-containing protein DLG-1 is required for the proper formation and function of adherens junctions in Caenorhabditis elegans. DLG-1 is a MAGUK protein that is most similar in sequence to mammalian SAP97, which is found at both synapses of the CNS, as well as at cell junctions of epithelia. DLG-1 is localized to adherens junctions, and DLG-1 localization is mediated by an amino-terminal domain shared with SAP97 but not found in other MAGUK family members. DLG-1 recruits other proteins and signaling molecules to adherens junctions, while embryos that lack DLG-1 fail to recruit the proteins AJM-1 and CPI-1 to adherens junctions. DLG-1 is required for the proper organization of the actin cytoskeleton and for the morphological elongation of embryos. In contrast to other proteins that have been observed to affect adherens junction assembly and function, DLG-1 is not required to maintain cell polarity. Our results suggest a new function for MAGUK proteins distinct from their role in cell polarity. 相似文献