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Ammonium is the preferred source of nitrogen for planktonic foraminifer and their dinoflagellate symbionts
The symbiotic planktonic foraminiferaOrbulina universainhabits open ocean oligotrophic ecosystems where dissolved nutrients are scarce and often limit biological productivity. It has previously been proposed thatO. universameets its nitrogen (N) requirements by preying on zooplankton, and that its symbiotic dinoflagellates recycle metabolic 'waste ammonium' for their N pool. However, these conclusions were derived from bulk(15)N-enrichment experiments and model calculations, and our understanding of N assimilation and exchange between the foraminifer host cell and its symbiotic dinoflagellates remains poorly constrained. Here, we present data from pulse-chase experiments with(13)C-enriched inorganic carbon,N-15-nitrate, and(15)N-ammonium, as well as a(13)C- and(15)N- enriched heterotrophic food source, followed by TEM (transmission electron microscopy) coupled to NanoSIMS (nanoscale secondary ion mass spectrometry) isotopic imaging to visualize and quantify C and N assimilation and translocation in the symbiotic system. High levels of(15)N-labelling were observed in the dinoflagellates and in foraminiferal organelles and cytoplasm after incubation with(15)N-ammonium, indicating efficient ammonium assimilation. Only weak(15)N-assimilation was observed after incubation with(15)N-nitrate. Feeding foraminifers with(13)C- and(15)N-labelled food resulted in dinoflagellates that were labelled with(15)N, thereby confirming the transfer of(15)N-compounds from the digestive vacuoles of the foraminifer to the symbiotic dinoflagellates, likely through recycling of ammonium. These observations are important for N isotope-based palaeoceanographic reconstructions, as they show that delta N-15 values recorded in the organic matrix in symbiotic species likely reflect ammonium recycling rather than alternative N sources, such as nitrates.
Journal Article
Ice nucleation by water-soluble macromolecules
Cloud glaciation is critically important for the global radiation budget (albedo) and for initiation of precipitation. But the freezing of pure water droplets requires cooling to temperatures as low as 235 K. Freezing at higher temperatures requires the presence of an ice nucleator, which serves as a template for arranging water molecules in an ice-like manner. It is often assumed that these ice nucleators have to be insoluble particles. We point out that also free macromolecules which are dissolved in water can efficiently induce ice nucleation: the size of such ice nucleating macromolecules (INMs) is in the range of nanometers, corresponding to the size of the critical ice embryo. As the latter is temperature-dependent, we see a correlation between the size of INMs and the ice nucleation temperature as predicted by classical nucleation theory. Different types of INMs have been found in a wide range of biological species and comprise a variety of chemical structures including proteins, saccharides, and lipids. Our investigation of the fungal species Acremonium implicatum, Isaria farinosa, and Mortierella alpina shows that their ice nucleation activity is caused by proteinaceous water-soluble INMs. We combine these new results and literature data on INMs from fungi, bacteria, and pollen with theoretical calculations to develop a chemical in-terpretation of ice nucleation and water-soluble INMs. This has atmospheric implications since many of these INMs can be released by fragmentation of the carrier cell and subsequently may be distributed independently. Up to now, this process has not been accounted for in atmospheric models.
Journal Article
U.S.-European Collaboration in Space Science
U.S.-European Collaboration in Space Science reviews the past 30 years of space-based research across the Atlantic. The book, which was prepared jointly with the European Space Science Committee (under the aegis of the European Science Foundation) begins with a broad survey of the historical and political context of U.S.-European cooperation and collaboration in space.
The focus of the book is a set of 13 U.S.-European missions in astrophysics, space physics, planetary sciences, earth sciences, and life and microgravity research that illustrate \"lessons learned\" on the evolution of the cooperation, mission planning and scheduling, international agreements, cost-sharing, management, and scientific output.
These lessons form the basis of the joint committee's findings and recommendations, which serve to improve the future conduct and enhance the scientific output of U.S.-European cooperation and collaboration in space science.
eBook
Physics and philosophy of nature in Greek Neoplatonism : proceedings of the European Science Foundation Exploratory Workshop (Il Ciocco, Castelvecchio-Pascoli, June 22-24, 2006)
The articles in this volume concentrate on Neoplatonic philosophy of nature from Plotinus to Simplicius, and on its main conceptual features and its relation to the previous philosophical and scientific traditions. The papers were presented at a conference sponsored by the European Science Foundation in Castelvecchio Pascoli in June 2006. This volume makes an important contribution to the understanding of Greek Neoplatonism and its historical significance.
eBook
Planetary Protection Classification of Sample Return Missions from the Martian Moons
An international consensus policy to prevent the biological cross-contamination of planetary bodies exists and is maintained by the Committee on Space Research (COSPAR) of the International Council for Science, which is consultative to the United Nations Committee on the Peaceful Uses of Outer Space. Currently, COSPAR's planetary protection policy does not specify the status of sample-return missions from Phobos or Deimos, the moons of Mars. Although the moons themselves are not considered potential habitats for life or of intrinsic relevance to prebiotic chemical evolution, recent studies indicate that a significant amount of material recently ejected from Mars could be present on the surface of Phobos and, to a lesser extent, Deimos.
This report reviews recent theoretical, experimental, and modeling research on the environments and physical conditions encountered by Mars ejecta during certain processes. It recommends whether missions returning samples from Phobos and/or Deimos should be classified as \"restricted\" or \"unrestricted\" Earth return in the framework of the planetary protection policy maintained by COSPAR. This report also considers the specific ways the classification of sample return from Deimos is a different case than sample return from Phobos.
eBook
Casparian strip diffusion barrier in Arabidopsis is made of a lignin polymer without suberin
Casparian strips are ring-like cell-wall modifications in the root endodermis of vascular plants. Their presence generates a paracellular barrier, analogous to animal tight junctions, that is thought to be crucial for selective nutrient uptake, exclusion of pathogens, and many other processes. Despite their importance, the chemical nature of Casparian strips has remained a matter of debate, confounding further molecular analysis. Suberin, lignin, lignin-like polymers, or both, have been claimed to make up Casparian strips. Here we show that, in Arabidopsis, suberin is produced much too late to take part in Casparian strip formation. In addition, we have generated plants devoid of any detectable suberin, which still establish functional Casparian strips. In contrast, manipulating lignin biosynthesis abrogates Casparian strip formation. Finally, monolignol feeding and lignin-specific chemical analysis indicates the presence of archetypal lignin in Casparian strips. Our findings establish the chemical nature of the primary root-diffusion barrier in Arabidopsis and enable a mechanistic dissection of the formation of Casparian strips, which are an independent way of generating tight junctions in eukaryotes.
Journal Article
Emotion in dialogic interaction : advances in the complex
This volume contains a selection of papers given at the European Science Foundation Exploratory Workshop on 'Emotion in Dialogic Interaction' at the University of Münster in October 2002. In the literature, the complex network of 'emotion in dialogic interaction' is mostly addressed by reducing the complex and separating emotions or defining them by means of simple artificial units. The innovative claim of the workshop was to analyse emotion as an integrated component of human behaviour in dialogic interaction as demonstrated by recent findings in neurology and to develop a linguistic model which is able to deal with the complex integrated whole. Specific emphasis was laid on communicative means for expressing emotions and on emotional principles in dialogue. Furthermore, the issue of specific European principles for dealing with emotions was highlighted.
eBook