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991.
Isolda Luna Vega Othón Alcántara Ayala Raúl Contreras-Medina Armando Ponce Vargas 《Biodiversity and Conservation》2006,15(12):3773-3799
The main goal of this study is to document the biogeographical patterns, current status and conservation of 24 species of
vascular plants in Mexico, all of them recorded in some risk category in the Mexican official publication named ‘Norma Oficial
Mexicana 059’ (NOM-059) and some of them in the IUCN red lists (the World Conservation Union) and CITES (Convention on International
Trade in Endangered Species); many of these species are linked to Mexican cloud forests and other temperate vegetation types.
Distribution maps of these 24 species were generated with information obtained from specialized literature, herbarium specimens,
institutional databases, and field work; with this information, the patterns of richness and endemism of these species were
obtained. For this, the Mexican territory was divided using a grid system based on a chart index (scale 1:50,000 system composed
by grids of 15' × 20'). Also, we up to date the knowledge of these species and their populations and current habitats, and
evaluate their geographic distribution in relation to the current Mexican National Parks and Reserves System and Mexican Priority
Regions for Conservation. We also discuss some changes of categories in the NOM-059 and suggest the urgent incorporation of
some of the species in the recent IUCN Red Data List of Threatened Species (2003). Most of the species studied require special
policies for their conservation due to problems that affect their natural populations; also we consider that these taxa are
underrepresented in the current Mexican System of Natural Protected Areas, especially those with restricted distributions. 相似文献
992.
Kai-Hung Fang 《Inorganica chimica acta》2006,359(2):441-450
A series of new iridium complexes with isoquinoline derivative ligands were synthesized for application in organic light-emitting diodes (OLEDs). It is demonstrated that varying the substituents at the 2′- or 4′-positions of the isoquinoline ligand makes the color tuning possible. Because of the steric effect, the 6′-substituted complexes: bis[1-(6′-methyl)phenylisoquinolinato-N,C2′] iridium(III) (acetylacetonate) (6b1), bis[1-(6′-trifluoromethyl)phenylisoquinolinato-N,C2′] iridium(III) (acetylacetonate) (6b2), and bis[1-(6′-methoxy)phenylisoquinolinato-N,C2′] iridium(III) (acetylacetonate) (6b3) show red-shift effect with respect to the 4′-substituted complexes: bis[1-(4′-methyl)phenylisoquinolinato-N,C2′] iridium(III) (acetylacetonate) (6a1), bis[1-(4′-trifluoromethyl)phenylisoquinolinato-N,C2′] iridium(III) (acetylacetonate) (6a2), and bis[1-(4′-methoxy)phenylisoquinolinato-N,C2′] iridium(III) (acetylacetonate) (6a3). All of these complexes are suitable for the red phosphorescent materials in OLEDs. 相似文献
993.
We measured the costs of mounting a humoral immune response using two novel antigens (tetanus and diphtheria) in two shorebird
species (Scolopacidae): Red Knot (Calidris canutus, measured in autumn) and Ruff (Philomachus pugnax, measured in spring). Metabolic rate was measured during the preinjection phase, at the building phase of the primary immune
response, and at peak secondary immune response by determining the oxygen consumption of the postabsorptive birds at rest.
Confirming earlier studies, Red Knots and Ruffs responded with lower antibody titers to the diphtheria than to the tetanus
antigen. Although Red Knots and Ruffs produced the same amounts of antibodies, Red Knots showed a significant 13% increase
in basal metabolic rate (BMR) during the secondary antibody response, whereas Ruffs showed a 15%, but only marginally significant,
reduction in BMR. The results from this study suggest that the energetic costs of an immune response may be small, but the
"negative cost" in Ruffs hints at the possibility of resource reallocation and the concomitant difficulty of measuring such
costs during "basal" metabolic rate measurements. 相似文献
994.
L. Wang H.Y. Lü J. Li G.B. Tong 《Palaeogeography, Palaeoclimatology, Palaeoecology》2006,241(1):118-128
In northern China, the Late Miocene-Pliocene red clay in the eastern Loess Plateau fills a gap of climate records between the well-known loess-soil sequences of the last 2.6 Ma and the Miocene loess-soil sequences from the western Loess Plateau. Previous studies indicate that the red clay is also of wind-blown origin, covering the period from ∼ 7-8 to ∼ 2.6 Ma. The red clay therefore provides a good archive to reconstruct paleoecological succession and paleoclimate change. In this study, a palynological investigation was conducted on the late Miocene-Pliocene red clay sequence at Xifeng, central Loess Plateau, which provides new insights into the nature of the evolution of vegetation and climate change from ∼ 6.2 to ∼ 2.4 Ma. Our results show that during this period the central Loess Plateau region was covered mainly by a steppe vegetation, indicating long lasting dry climatic condition. Three vegetational zones were recognized during this period. Zone A (∼ 6.2 to ∼ 5.8 Ma) is characterized by a steppe ecosystem; Zone B (∼ 5.8 to ∼ 4.2 Ma) is characterized by a significant increase of temperate forest plants, indicating a relatively humid regional climate; Zone C (∼ 4.2 to ∼ 2.4 Ma) indicates a typical steppe ecosystem. The vegetation shift at about 4.5-3.7 Ma, when the temperate forest plants decrease, the vegetation gradually changed to typical grassland and even to desert steppe. This is interpreted to represent a drying event. The uplift of the Tibetan Plateau at about 4.5 Ma that resulted in the intensification of the monsoon reversal is thought to have played an important role in this significant ecological change. High-latitude cooling may have partially contributed to the climate shift during ∼ 4.5 to ∼ 3.7 Ma in the Loess Plateau region, and most likely was the driving force for the ecological shift at about 3.7 Ma. 相似文献
995.
Britt Koskella Curtis M. Lively 《Evolution; international journal of organic evolution》2009,63(9):2213-2221
Host–parasite coevolution is often suggested as a mechanism for maintaining genetic diversity, but finding direct evidence has proven difficult. In the present study, we examine the process of coevolution using a freshwater New Zealand snail ( Potamopyrgus antipodarum ) and its common parasite (the sterilizing trematode, Microphallus sp.) Specifically, we test for changes in genotypic composition of clonal host populations in experimental populations evolving either with or without parasites for six generations. As predicted under the Red Queen model of coevolution, the initially most common host genotype decreased in frequency in the presence, but not the absence, of parasitism. Furthermore, the initially most common host genotype became more susceptible to infection by the coevolving parasite populations over the course of the experiment. These results are consistent with parasite-meditated selection leading to a rare advantage, and they indicate rapid coevolution at the genotypic level between a host and its parasite. 相似文献
996.
Aneil F. Agrawal 《Evolution; international journal of organic evolution》2009,63(8):2131-2141
The Red Queen hypothesis argues that parasites generate selection for genetic mixing (sex and recombination) in their hosts. A number of recent papers have examined this hypothesis using models with haploid hosts. In these haploid models, sex and recombination are selectively equivalent. However, sex and recombination are not equivalent in diploids because selection on sex depends on the consequences of segregation as well as recombination. Here I compare how parasites select on modifiers of sexual reproduction and modifiers of recombination rate. Across a wide set of parameters, parasites tend to select against both sex and recombination, though recombination is favored more often than is sex. There is little correspondence between the conditions favoring sex and those favoring recombination, indicating that the direction of selection on sex is often determined by the effects of segregation, not recombination. Moreover, when sex was favored it is usually due to a long-term advantage whereas short-term effects are often responsible for selection favoring recombination. These results strongly indicate that Red Queen models focusing exclusively on the effects of recombination cannot be used to infer the type of selection on sex that is generated by parasites on diploid hosts. 相似文献
997.
Audrey O.T. Lau Terry F. McElwain Donald P. Knowles Eric H. Roalson 《Experimental parasitology》2009,123(3):236-243
Apicomplexan parasites commonly contain a unique, non-photosynthetic plastid-like organelle termed the apicoplast. Previous analyses of other plastid-containing organisms suggest that apicoplasts were derived from a red algal ancestor. In this report, we present an extensive phylogenetic study of apicoplast origins using multiple previously reported apicoplast sequences as well as several sequences recently reported. Phylogenetic analysis of amino acid sequences was used to determine the evolutionary origin of the organelle. A total of nine plastid genes from 37 species were incorporated in our study. The data strongly support a green algal origin for apicoplasts and Euglenozoan plastids. Further, the nearest green algae lineage to the Apicomplexans is the parasite Helicosporidium, suggesting that apicoplasts may have originated by lateral transfer from green algal parasite lineages. The results also substantiate earlier findings that plastids found in Heterokonts such as Odontella and Thalassiosira were derived from a separate secondary endosymbiotic event likely originating from a red algal lineage. 相似文献
998.
Silvana Ficarra Ester Tellone Bruno Giardina Roberto Scatena Annamaria Russo Francesco Misiti M. Elisabetta Clementi Deborah Colucci Ersilia Bellocco Giuseppina Laganà Davide Barreca Antonio Galtieri 《The Journal of membrane biology》2009,228(1):43-49
Considering its complex molecular pathophysiology, beta-thalassemia could be a good in vivo model to study some aspects related
to erythrocyte functions with potential therapeutic implications not only within the frame of this particular hemoglobinopathy
but also with respect to conditions in which the cellular milieu, altered by a deranged anion exchanger, could display a significant
pathogenetic role (i.e., erythrocyte senescence, complications of red cell storage, renal tubular acidosis and some abnormal
protein thesaurismosis). This work evaluates the anionic influx across band 3 protein in normal and beta-thalassemic red blood
cells (RBCs) and ghosts. Since redox-mediated injury is an important pathway in the destruction of beta-thalassemic RBCs,
we studied the anion transport and the activity of caspase 3 in the absence and presence of t-butylhydroperoxide in order to evaluate the effect of an increase of cellular oxidative stress. Interestingly, beta-thalassemic
erythrocytes show a faster rate of anion exchange than normal RBCs and absence of any modulation mechanism of anion influx.
These findings led us to formulate a hypothesis about the metabolic characteristics of beta-thalassemic erythrocytes, outlining
that one of the main targets of caspase 3 in RBCs is the cytoplasmic domain of band 3 protein. 相似文献
999.
In this work, we developed a novel enzymatic method for measuring phosphatidic acid (PA) in cultured cells. The enzymatic reaction sequence of the method involves hydrolysis of PA to produce glycerol-3-phosphate (G3P), which is then oxidized by G3P oxidase to generate hydrogen peroxide. In the presence of peroxidase, hydrogen peroxide reacted with Amplex Red to produce highly fluorescent resorufin. We found that lipase from Pseudomonas sp. can completely hydrolyze PA to G3P and FAs. The calibration curve for PA measurement was linear between 20 and 250 µM, and the detection limit was 5 µM (50 pmol in the reaction mixture). We also modified the method for the enzymatic measurement of lysophosphatidic acid. By this new method, we determined the PA content in the lipid extract from HEK293 cells. The cellular content of PA was decreased with increasing cell density but not correlated with the proliferation rate. The diacylglycerol kinase inhibitor markedly reduced the cellular PA content, suggesting the diacylglycerol kinase activity was involved in a large part of the PA production in HEK293 cells. This novel method for PA quantification is simple, rapid, specific, sensitive, and high-throughput and will help to study the biological functions of PA and its related enzymes. R59949相似文献
1000.
Davis RW Volponi JV Jones HD Carvalho BJ Wu H Singh S 《Biotechnology and bioengineering》2012,109(10):2503-2512
Detailed in this study are the results of fluorometric assays used to assess the impact of gradual nutrient limitation versus punctuated nitrate limitation on the lipid content and morphology of Neochloris oleoabundans cells in batch culture. Punctuated nitrate limitation was imposed during pre‐log, log, late‐log, stationary, and senescent growth phases, and the cells were analyzed by bulk fluorescence emission, flow cytometry, and hyperspectral fluorescence imaging. In addition to intrinsic spectroscopic signatures provided by scatter and endogenous fluorescence, Nile Red staining was employed to monitor relative changes in lipid concentration. Analysis of the fluorescence images and temporal data sets was performed using multivariate curve resolution and fitting to logistic growth models to extract parameters of interest. The spectral components independently isolated from the image and temporal data sets showed close agreement with one another, especially relating to chlorophylls and Nile Red in polar and neutral lipid fractions, respectively. The fastest accumulation and highest total neutral lipid per cell and per chlorophyll were obtained with punctuated nitrate limitation during log phase growth on day 4 of culture. The presence of unbound chlorophyll in the resulting lipid bodies supports a membrane recycling TAG accumulation mechanism mediated by chloropolast–ER lipid exchange. Furthermore, an increase in cell size, indicated by forward scatter, was also found to correlate with increased neutral lipid, providing a size selection mechanism for passive harvest of algal cells at peak lipid enrichment. Biotechnol. Bioeng. 2012; 109: 2503–2512. © 2012 Wiley Periodicals, Inc. 相似文献