X-Ray Microanalysis in Cryosections of Natively Frozen Paramecium Caudatum with Regard to Ion Distribution in Ciliates

Cells of Paramecium caudatum were shock-frozen without pretreatment for cryoultramicrotomy and freeze-dried for subsequent X-ray microanalysis. Na, Mg, P, S, Cl, K, and Ca were detected in different amounts in several subcellular compartments. In particular, calcium was localized below the cell surface (pellicle). Trichocysts were found to contain significant amounts of Na in their base but not in the tip. Na, Mg, P, S, Cl, K, Ca were found in electron dense deposits within the lumen of the contractile vacuole. A small K concentration was found in the cytoplasm and in the mitochondria. X-ray microanalysis of the element distribution in different subcellular compartments provides information for the understanding of cellular functions such as exocytosis, locomotion, and ion regulation

The Influence of Different Cryopreparations on the Distribution of Ions in Bullfrog Myocard Cells

Bullfrog heart muscle trabecula are shock-frozen in liquid propane cooled by liquid nitrogen and then processed for X-ray microanalysis in two different ways: 1. Freeze-drying followed by vacuum embedding. 2. Cryoultramicrotomy and freeze-drying. Stained sections of freeze-dried, embedded tissue exhibit detailed ultrastructure, but are useless for X-ray microanalysis. Unstained, dry cut plastic-sections are suitable for X-ray microanalysis, but the ultrastructure appears faint. Higher electron optical contrast and peak-to-background ratio of X-ray spectra are generally obtained in freeze-dried cryosections. Both preparation methods show that the X-ray spectra are influenced by the quality of cryofixation. The phosphorus/potassium ratio in nuclei increases with increasing ice crystal size

Evolutionary Origin and Phylogeography of the Diploid Obligate Parthenogen Artemia parthenogenetica (Branchiopoda: Anostraca)

Background: Understanding the evolutionary origin and the phylogeographic patterns of asexual taxa can shed light on the origin and maintenance of sexual reproduction. We assessed the geographic origin, genetic diversity, and phylogeographic history of obligate parthenogen diploid Artemia parthenogenetica populations, a widespread halophilic crustaceanPeer reviewe

A versatile synthesis method of dendrites-free segmented nanowires with a precise size control

We report an innovative strategy to obtain cylindrical nanowires combining well established and low-cost bottom-up methods such as template-assisted nanowires synthesis and electrodeposition process. This approach allows the growth of single-layer or multi-segmented nanowires with precise control over their length (from few nanometers to several micrometers). The employed techniques give rise to branched pores at the bottom of the templates and consequently dendrites at the end of the nanowires. With our method, these undesired features are easily removed from the nanowires by a selective chemical etching. This is crucial for magnetic characterizations where such non-homogeneous branches may introduce undesired features into the final magnetic response. The obtained structures show extremely narrow distributions in diameter and length, improved robustness and high-yield, making this versatile approach strongly compatible with large scale production at an industrial level. Finally, we show the possibility to tune accurately the size of the nanostructures and consequently provide an easy control over the magnetic properties of these nanostructures

Mitochondrial DNA Regionalism and Historical Demography in the Extant Populations of Chirocephalus kerkyrensis (Branchiopoda: Anostraca)

Background: Mediterranean temporary water bodies are important reservoirs of biodiversity and host a unique assemblage of diapausing aquatic invertebrates. These environments are currently vanishing because of increasing human pressure. Chirocephalus kerkyrensis is a fairy shrimp typical of temporary water bodies in Mediterranean plain forests and has undergone a substantial decline in number of populations in recent years due to habitat loss. We assessed patterns of genetic connectivity and phylogeographic history in the seven extant populations of the species from Albania, Corfu Is. (Greece), Southern and Central Italy. Methodology/Principal Findings: We analyzed sequence variation at two mitochondrial DNA genes (Cytochrome Oxidase I and 16s rRNA) in all the known populations of C. kerkyrensis. We used multiple phylogenetic, phylogeographic and coalescence-based approaches to assess connectivity and historical demography across the whole distribution range of the species. C. kerkyrensis is genetically subdivided into three main mitochondrial lineages; two of them are geographically localized (Corfu Is. and Central Italy) and one encompasses a wide geographic area (Albania and Southern Italy). Most of the detected genetic variation (<81%) is apportioned among the aforementioned lineages. Conclusions/Significance: Multiple analyses of mismatch distributions consistently supported both past demographic and spatial expansions with the former predating the latter; demographic expansions were consistently placed during interglacial warm phases of the Pleistocene while spatial expansions were restricted to cold periods. Coalescence methods revealed a scenario of past isolation with low levels of gene flow in line with what is already known for other co-distributed fairy shrimps and suggest drift as the prevailing force in promoting local divergence. We recommend that these evolutionary trajectories should be taken in proper consideration in any effort aimed at protecting Mediterranean temporary water bodies

IONIC CONDUCTIVITY MEASUREMENTS OF HEAVILY DOPED AgCl : Cd CRYSTALS

Nous avons mesuré la conductivité ionique de AgCl, fortement dopé par Cd2+ (0 à 5 000 ppm). Dans le domaine de température 250-400 K, nous avons étudié la solubilité de Cd++ dans AgCl. Pour la discussion des résultats obtenus en mesurant la conductivité ionique au-dessous de 240 K et pour expliquer les énergies d'Arrhénius très élevées dans ce domaine de température, nous avons proposé les deux modèles suivants : 1) Association des dipôles aux agrégats plus grands. 2) Précipitations d'une superstructure : CdCl2, 6 AgCl.Ionic conductivity measurements in heavily doped AgCl : Cd crystals (from 0 to 5 000 ppm) were carried out. A solubility curve of Cd2+ in AgCl for the temperature range 250 K to 400 K is presented. Very high Arrhenius energies were measured below 240 K. A dipole association model and a superstructure model are discussed to explain the obtained conductivity data. It is shown that the experimental results can appropriately be described by the assumption of the precipitation of this superstructure (CdCl2. 6 AgCl)

PRECIPITATION PHENOMENA IN HEAVILY DOPED AgCl : Cd2+-CRYSTALS

Nous avons étudié le mécanisme de la précipitation dans les cristaux de chlorure d'argent fortement dopés avec Cd2+ utilisant quatre méthodes différentes : conductivité ionique (IC) thermocourant de dépolarisation (ITC), diffusion des rayons X aux petits angles (SAXS) et diffusion de la lumière. Pour contrôler nos méthodes nous avons exécuté des mesures IC et ITC, utilisant aussi des cristaux dopés avec Cd2+ au-dessous de la limite de solubilité. Les résultats sont en accord avec ceux trouvés dans la littérature. Par des mesures de IC et ITC nous avons trouvé que, dans les cristaux fortement dopés, les particules précipitantes peuvent injecter (accepter) des lacunes d'argent (Ag-) dans le réseau entourant. Evaluant les résultats de SAXS et de la diffusion de la lumière nous proposons le modèle suivant pour le mécanisme de la précipitation dans les cristaux fortement dopés : Les particules précipitantes sont composées d'un coeur de la phase CdCl2, entouré d'une couche composée de dipôles [Cd2+-Ag-]. L'existence d'une telle couche peut expliquer les résultats obtenus par les mesures IC et ITC.Ionic conductivity-, ITC-, small angle X-ray scattering-, and light scattering measurements were carried out to study precipitation phenomena in heavily doped AgCl : Cd2+ crystals. For ionic conductivity- and ITC-measurements we additionally used crystals with low doping concentrations to check our methods ; the resulting values for activation enthalpies were in good accordance with those in the literature. From the ionic conductivity- and ITC-measurements we conclude that the precipitated particles in the heavily doped crystals may inject Ag+-vacancies into the matrix thus ionizing themselves. In this way, the particles act as sinks or traps for Ag+-vacancies. From small angle X-ray measurements, confirmed by light scattering experiments a model is deduced for the mechanism of precipitation in the supersaturated crystal. In this model, the finall precipitated particle consists of a core of CdCl2 surrounded by a shell of Cd2+-Ag+-vacancy dipoles. Such a shell would give an understanding of the results obtained by ionic conductivity and ITC-measurements