Rapid De Novo Evolution of X Chromosome Dosage Compensation in Silene latifolia, a Plant with Young Sex Chromosomes

Evidence for dosage compensation in Silene latifolia, a plant with 10-million-year-old sex chromosomes, reveals that dosage compensation can evolve rapidly in young XY systems and is not an animal-specific phenomenon

Gas phase dehydration of lactic acid to acrylic acid over alkaline earth phosphates catalysts: efficiency and identification of selective active sites. [+ affiche]

Internationa

Etude des propriétés physiques du film passif forme sur un acier 316L

nationalLes plaques bipolaires constitutives des piles à combustible de type PEMFC, généralement en graphite, ne sont disponibles commercialement qu'à des prix très élevés. Les métaux et alliages présentent un ensemble de propriétés qui en font des candidats de choix pour la conception et la réalisation de plaques bipolaires compactes, légère et bon marché. Toutefois, les plaques de type métallique sont sujettes à des problèmes de corrosion du fait de l'environnement acide que constitue le cœur de pile. Parmi les matériaux métalliques envisagés, ceux capables de se passiver sont donc privilégiés. A ce titre les aciers inoxydables sont principalement étudiés. Leur résistance vis-à-vis de la corrosion est en effet assurée par la formation d'un film d'oxyde de quelques nanomètres. Pour autant l'existence de ce film est susceptible de faire chuter le rendement électrique des piles du fait de sa faible conductivité. Cette étude porte sur la caractérisation par techniques électrochimiques et majoritairement par SIE des propriétés physiques d'un film passif formé sur acier 316L en milieu pile simulé (solution aqueuse à pH 4,5 contenant 10 ppm d'ions fluorures). Les propriétés de l'interface film/électrolyte ont pu être simulées par l'intermédiaire d'un circuit électrique équivalent. Les paramètres physiques disponibles issus de la simulation sont la résistance de transfert de charge, la capacité de double couche et la capacité de charge d'espace. Afin de compléter ces mesures des tracés types Mott-Schottky ont été également réalisées afin d'avoir accès au nombre de porteurs de charge et au potentiel de bande plate. Sur la base de ces paramètres physiques, l'évolution des propriétés du film formé en milieu aéré et désaéré est discutée ainsi que l'impact d'un élément d'addition : le cérium. Dans ce dernier cas, la composition du film formé a été également déterminée par des analyses XPS

Thermal diffusion of molybdenum in apatite

AC

Evidence of anti-coking behavior of La 0.8Sr 0.2Cr 0.98Ru 0.02O 3 as potential anode material for Solid Oxide Fuel Cells directly fed under methane

La 0.8Sr 0.2CrO 3 (LSC) based Ru catalysts are very active in methane steam reforming. Nevertheless, they can be easily poisoned under water-deficient conditions. Ru can be deposited as metallic ruthenium particles decorating the LSC grains or be inserted as Ru ions in the perovskite structure. Both Ru-promoted LSC catalysts were studied in methane steam reforming under water-deficient conditions and characterized after testing. Catalytic activity tests showed that ruthenium metal species are deactivated under water-deficient atmosphere, while ruthenium species inserted in LSC presented a remarkable stability and catalytic activity where residual steam plays a key role. Very unreactive carbon species responsible for deactivation were detected by temperature-programmed oxidation and transmission electron microscopy over metallic ruthenium species. Such species were not observed when ruthenium species are inserted and stabilized into the LSC structure. La 0.8Sr 0.2Cr 0.98Ru 0.02O 3 appears therefore as a highly promising anti-coking anode material for Solid Oxide Fuel Cells directly fed with methane or natural gas and operating under water-deficient conditions. © 2012 Elsevier Inc. All rights reserved

Study of mechanisms involved in thermal migration of molybdenum and rhenium in apatites

ACEThe aim of this work is to characterise the retention properties of apatites, studied as potential inert matrices, towards the long-lived fission product $^{99}$Tc (T=210 000 years) in radioactive waste disposal. The study was made using two stable homologous elements of Tc: molybdenum which has the same mass as technetium, and rhenium which is the chemical analogue of Tc. These elements were introduced in apatite samples by ion implantation and their profiles were determined by Rutherford backscattering spectroscopy (RBS). The coupling of X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) analysis showed the oxidation of molybdenum and rhenium during annealing. Using these results on Mo and Re behaviour, assumptions were made on the migration of technetium

Analysis and evolution of two functional Y-linked loci in a plant sex chromosome system.

White campion (Silene latifolia) is one of the few examples of plants with separate sexes and with X and Y sex chromosomes. The presence or absence of the Y chromosome determines which type of reproductive organs--male or female--will develop. Recently, we characterized the first active gene located on a plant Y chromosome, SlY1, and its X-linked homolog, SlX1. These genes encode WD-repeat proteins likely to be involved in cell proliferation. Here, we report the characterization of a novel Y-linked gene, SlY4, which also has a homolog on the X chromosome, SlX4. Both SlY4 and SlX4 potentially encode fructose-2,6-bisphosphatases. A comparative molecular analysis of the two sex-linked loci (SlY1/SlX1 and SlY4/SlX4) suggests selective constraint on both X- and Y-linked genes and thus that both X- and Y-linked copies are functional. Divergence between SlY4 and SlX4 is much greater than that between the SlY1 and SlX1 genes. These results suggest that, as for human XY-linked genes, the sex-linked plant loci ceased recombining at different times and reveal distinct events in the evolutionary history of the sex chromosomes

SlY1, the first active gene cloned from a plant Y chromosome, encodes a WD-repeat protein.

Unlike the majority of flowering plants, which possess hermaphrodite flowers, white campion (Silene latifolia) is dioecious and has flowers of two different sexes. The sex is determined by the combination of heteromorphic sex chromosomes: XX in females and XY in males. The Y chromosome of S.latifolia was microdissected to generate a Y-specific probe which was used to screen a young male flower cDNA library. We identified five genes which represent the first active genes to be cloned from a plant Y chromosome. Here we report a detailed analysis of one of these genes, SlY1 (S.latifolia Y-gene 1). SlY1 is expressed predominantly in male flowers. A closely related gene, SlX1, is predicted to be located on the X chromosome and is strongly expressed in both male and female flowers. SlY1 and SlX1 encode almost identical proteins containing WD repeats. Immunolocalization experiments showed that these proteins are localized in the nucleus, and that they are most abundant in cells that are actively dividing or beginning to differentiate. Interestingly, they do not accumulate in arrested sexual organs and represent potential targets for sex determination genes. These genes will permit investigation of the origin and evolution of sex chromosomes in plants