Fossilized nuclei and germination structures identify Ediacaran "animal embryos" as encysting protists   总被引：1，自引：0，他引：1  

Huldtgren T  Cunningham JA  Yin C  Stampanoni M  Marone F  Donoghue PC  Bengtson S 《Science (New York, N.Y.)》2011,334(6063):1696-1699

Globular fossils showing palintomic cell cleavage in the Ediacaran Doushantuo Formation, China, are widely regarded as embryos of early metazoans, although metazoan synapomorphies, tissue differentiation, and associated juveniles or adults are lacking. We demonstrate using synchrotron-based x-ray tomographic microscopy that the fossils have features incompatible with multicellular metazoan embryos. The developmental pattern is comparable with nonmetazoan holozoans, including germination stages that preclude postcleavage embryology characteristic of metazoans. We conclude that these fossils are neither animals nor embryos. They belong outside crown-group Metazoa, within total-group Holozoa (the sister clade to Fungi that includes Metazoa, Choanoflagellata, and Mesomycetozoea) or perhaps on even more distant branches in the eukaryote tree. They represent an evolutionary grade in which palintomic cleavage served the function of producing propagules for dispersion.  相似文献   

Increasing river discharge to the Arctic Ocean   总被引：10，自引：0，他引：10  

Peterson BJ  Holmes RM  McClelland JW  Vörösmarty CJ  Lammers RB  Shiklomanov AI  Shiklomanov IA  Rahmstorf S 《Science (New York, N.Y.)》2002,298(5601):2171-2173

Synthesis of river-monitoring data reveals that the average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by 7% from 1936 to 1999. The average annual rate of increase was 2.0 +/- 0.7 cubic kilometers per year. Consequently, average annual discharge from the six rivers is now about 128 cubic kilometers per year greater than it was when routine measurements of discharge began. Discharge was correlated with changes in both the North Atlantic Oscillation and global mean surface air temperature. The observed large-scale change in freshwater flux has potentially important implications for ocean circulation and climate.  相似文献   

Conditional dynamics of interacting quantum dots     

Robledo L  Elzerman J  Jundt G  Atatüre M  Högele A  Fält S  Imamoglu A 《Science (New York, N.Y.)》2008,320(5877):772-775

Conditional quantum dynamics, where the quantum state of one system controls the outcome of measurements on another quantum system, is at the heart of quantum information processing. We demonstrate conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot. Interaction between the dots is mediated by the tunnel coupling between optically excited states and can be optically gated by applying a laser field of the right frequency. Our results represent substantial progress toward realization of an optically effected controlled-phase gate between two solid-state qubits.  相似文献   

Fluorometric detection of enzyme activity with synthetic supramolecular pores     

Das G  Talukdar P  Matile S 《Science (New York, N.Y.)》2002,298(5598):1600-1602

The reversible blockage of synthetic pores formed by rigid-rod beta barrels, either by substrates or products, was used to sense a variety of enzymatic reactions in high-throughput format with "naked-eye" fluorescent detection. Improvement of sensor sensitivity beyond three orders of magnitude by straightforward internal mutations underscores the functional plasticity of rigid-rod beta barrels. Such detectors of enzyme activity with the aforementioned characteristics are needed in areas as diverse as proteomics and environmentally benign organic synthesis.  相似文献   

Was there really an Archean phosphate crisis?     

Konhauser KO  Lalonde SV  Amskold L  Holland HD 《Science (New York, N.Y.)》2007,315(5816):1234

During the Archean, massive amounts of iron were deposited in the form of banded iron formations. It has been suggested that sedimenting particles of ferric oxyhydroxide may have stripped dissolved phosphate from the oceans, causing a reduction in phytoplankton productivity. However, that model does not take into account the high concentration of dissolved silica that was present in seawater at that time. We show experimentally that silica effectively competes with phosphate for sorption sites on ferrihydrite particles. Furthermore, coprecipitation of silica with ferrihydrite reduces particle reactivity toward phosphate. Hence, Archean oceans probably contained considerably more phosphate than previously predicted.  相似文献   

耐盐性Imt1基因表达载体的构建及其在酵母中的高效表达   总被引：2，自引：0，他引：2  

董云洲  沈波 《中国农业科学》1997,30(4):50-55

 将Imt1（Inositol O-methyltransferase，肌醇甲基转移酶）构建成酵母表达载体pBD#-3，在酵母双突变体gpd#+（-）(glycerol 3-phosphate-dehydrogenase,3-磷酸甘油脱氢酶)中高效表达，使gpd#+（-）突变株对氯化钠的耐性由2.5%提高到5.0%。生化分析表明，在每mg干酵母细胞内积累高达2.2nmol的Ononitol(芒柄醇)含量。Western blot分析证明了Imt1基因的表达。这一研究为植物耐盐基因工程开辟了一条新途径。  相似文献   

A global view of gene activity and alternative splicing by deep sequencing of the human transcriptome   总被引：6，自引：0，他引：6  

Sultan M  Schulz MH  Richard H  Magen A  Klingenhoff A  Scherf M  Seifert M  Borodina T  Soldatov A  Parkhomchuk D  Schmidt D  O'Keeffe S  Haas S  Vingron M  Lehrach H  Yaspo ML 《Science (New York, N.Y.)》2008,321(5891):956-960

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Cross-species identification of Mendel's I locus     

Armstead I  Donnison I  Aubry S  Harper J  Hörtensteiner S  James C  Mani J  Moffet M  Ougham H  Roberts L  Thomas A  Weeden N  Thomas H  King I 《Science (New York, N.Y.)》2007,315(5808):73

A key gene involved in plant senescence, mutations of which partially disable chlorophyll catabolism and confer stay-green leaf and cotyledon phenotypes, has been identified in Pisum sativum, Arabidopsis thaliana, and Festuca pratensis by using classical and molecular genetics and comparative genomics. A stay-green locus in F. pratensis is syntenically equivalent to a similar stay-green locus on rice chromosome 9. Functional testing in Arabidopsis of a homolog of the rice candidate gene revealed (i) senescence-associated gene expression and (ii) a stay-green phenotype after RNA interference silencing. Genetic mapping in pea demonstrated cosegregation with the yellow/green cotyledon polymorphism (I/i) first reported by Gregor Mendel in 1866.  相似文献   

Tropical forests revisited     

J. Alberto Gallardo-Cruz  Stefan Schindler 《Landscape Ecology》2011,26(2):295-296

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The formation of terrestrial food webs in glacier foreland: Evidence for the pivotal role of decomposer prey and intraguild predation     

Tanja König  Stefan Scheu 《Pedobiologia》2011,54(2):147-152

We investigated the structure of invertebrate food webs at three glacier foreland sites of an age of 2-34, ca. 60 and ca. 120 years in the European Alps at 2250-2450 m asl. The trophic structure was investigated by analyzing stable isotope ratios of ¹⁵N/¹⁴N and ¹³C/¹²C. The results suggest that the formation of terrestrial food webs during early primary succession heavily relies on prey out of the decomposer system with Collembola being most important. The diet of decomposers likely is based predominantly on allochthonous humus material blown in by wind and deposited by the retreating glacier. Irrespective of the successional stage the animal community consisted mainly of generalist predators with a number of species occurring at each of the successional stages. The results suggest that terrestrial food web formation is associated with a prolongation of food chains caused mainly by predator species switching their diet to include other predators, i.e. by intraguild predation. This suggests that generalist predators, such as cursorial spiders, carabid beetles, harvestman and centipedes, switch prey and include other predators if these are becoming more abundant, i.e. if ecosystems become more productive. Intraguild predation results in complex food webs with high linkage density which likely affects food web functioning and stability.  相似文献