Modalities of colonization of woody savannah by dry forest plants in New Caledonia

Modalities of colonization of woody savannah by dry forest plants in New Caledonia. -Dry forests are the most endangered tropical forests in the world. Fortunately, they sometimes show some ability to colonize abandoned lands. Such a colonization potential has been investigated in the south of New Caledonia (Pacific Ocean). We analyzed the composition of the vegetation from transects from dry forest to proximate woody savannah, where an extension of the forest had been observed from the analysis of old aerial pictures. Three transects were followed in each of the four studied sites. Among 52 observed species, six were observed in more than 50% of the plots belonging to colonized sites. Among these six species, four provided suckers: Croton insularis, Elattostachys apetala, Emmenosperma pancherianum and Halfordia kendac. Ornithochory and barochory represented the dominant modes of seed dispersal of the colonizing species. Consequently, we conclude that fire control and bird conservation are relevant components of the conservation strategy of dry forest in New Caledonia.Dry forests are the most endangered tropical forests in the world. Fortunately, they sometimes show some ability to colonize abandoned lands. Such a colonization potential has been investigated in the south of New Caledonia (Pacifi c Ocean). We analyzed the composition of the vegetation from transects from dry forest to proximate woody savannah, where an extension of the forest had been observed from the analysis of old aerial pictures. Three transects were followed in each of the four studied sites. Among 52 observed species, six were observed in more than 50% of the plots belonging to colonized sites. Among these six species, four provided suckers: Croton insularis, Elattostachys apetala, Emmenosperma pancherianum and Halfordia kendac. Ornithochory and barochory represented the dominant modes of seed dispersal of the colonizing species. Consequently, we conclude that fire control and bird conservation are relevant components of the conservation strategy of dry forest in New Caledoni

A mathematical model of tumour & blood pHe regulation: The HCO-3/CO2 buffering system

Malignant tumours are characterised by a low, acidic extracellular pH (pHe) which facilitates invasion and metastasis. Previous research has proposed the potential benefits of manipulating systemic pHe, and recent experiments have highlighted the potential for buffer therapy to raise tumour pHe, prevent metastases, and prolong survival in laboratory mice. To examine the physiological regulation of tumour buffering and investigate how perturbations of the buffering system (via metabolic/respiratory disorders or changes in parameters) can alter tumour and blood pHe, we develop a simple compartmentalised ordinary differential equation model of pHe regulation by the View the MathML source buffering system. An approximate analytical solution is constructed and used to carry out a sensitivity analysis, where we identify key parameters that regulate tumour pHe in both humans and mice. From this analysis, we suggest promising alternative and combination therapies, and identify specific patient groups which may show an enhanced response to buffer therapy. In addition, numerical simulations are performed, validating the model against well-known metabolic/respiratory disorders and predicting how these disorders could change tumour pHe

Expression of Rh Glycoproteins in the Mammalian Kidney

Ammonia metabolism is a fundamental process in the maintenance of life in all living organisms. Recent studies have identified ammonia transporter family proteins in yeast (Mep), plants (Amt), and mammals (Rh glycoproteins). In mammalian kidneys, where ammonia metabolism and transport are critically important for the regulation of systemic acid-base homeostasis, basolateral Rh B glycoprotein and apical/basolateral Rh C glycoprotein are expressed along the distal nephron segments. Data from experimental animal models and knockout mice suggest that the Rh glycoproteins appear to mediate important roles in urinary ammonia excretion

The rhesus protein RhCG: a new perspective in ammonium transport and distal urinary acidification

Urinary acidification is a complex process requiring the coordinated action of enzymes and transport proteins and resulting in the removal of acid and the regeneration of bicarbonate. Proton secretion is mediated by luminal H(+)-ATPases and requires the parallel movement of NH(3), and its protonation to NH(4)(+), to provide sufficient buffering. It has been long assumed that ammonia secretion is a passive process occurring by means of simple diffusion driven by the urinary trapping of ammonium. However, new data indicate that mammalian cells possess specific membrane proteins from the family of rhesus proteins involved in ammonia/μm permeability. Rhesus proteins were first identified in yeast and later also in plants, algae, and mammals. In rodents, RhBG and RhCG are expressed in the collecting duct, whereas in humans only RhCG was detected. Their expression increases with maturation of the kidney and accelerates after birth in parallel with other acid-base transport proteins. Deletion of RhBG in mice had no effect on renal ammonium excretion, whereas RhCG deficiency reduces renal ammonium secretion strongly, causes metabolic acidosis in acid-challenged mice, and impairs restoration of normal acid-base status. Microperfusion experiments or functional reconstitution in liposomes demonstrates that ammonia is the most likely substrate of RhCG. Similarly, crystal structures of human RhCG and the homologous bacterial AmtB protein suggest that these proteins may form gas channels.Kidney International advance online publication, 6 October 2010; doi:10.1038/ki.2010.386

Fast and Selective ammonia transport by aquaporin-8

The transport of ammonia/ammonium is fundamental to nitrogen metabolism in all forms of life. So far, no clear picture has emerged as to whether a protein channel is capable of transporting exclusively neutral NH(3) while excluding H(+) and NH(4)(+). Our research is the first stoichiometric study to show the selective transport of NH(3) by a membrane channel. The purified water channel protein aquaporin-8 was reconstituted into planar bilayers, and the exclusion of NH(4)(+) or H(+) was established by ensuring a lack of current under voltage clamp conditions. The single channel water permeability coefficient of 1.2 x 10(-14) cm(3)/subunit/s was established by imposing an osmotic gradient across reconstituted planar bilayers, and resulting minute changes in ionic concentration close to the membrane surface were detected. It is more than 2-fold smaller than the single channel ammonia permeability (2.7 x 10(-14) cm(3)/subunit/s) that was derived by establishing a transmembrane ammonium concentration gradient and measuring the resulting concentration increases adjacent to the membrane. This permeability ratio suggests that electrically silent ammonia transport may be the main function of AQP8

Valorisation chimique du dioxyde de carbone (synthon et solvant en catalyse moléculaire pour la synthèse de carbonates de dialkyle)

L objectif de cette thèse a été de contribuer à l étude de la synthèse de carbonates de dialkyle par réaction de carbonatation des alcools en développant une voie catalytique. Afin de mieux comprendre le mode d action du catalyseur et d améliorer sa productivité, nous nous sommes intéressés à la relation existant entre sa structure et son activité. Différents complexes organostanniques de type R2Sn(OCH3)2 ont été synthétisés puis leur réactivité vis-à-vis du CO2 a été étudiée. En conditions CO2/CH3OH supercritiques et selon la nature du précurseur, plusieurs espèces dormantes de nucléarités différentes ont pu être caractérisées. Les études cinétiques ont montré que le nombre d espèces actives impliquées dans le mécanisme de formation du DMC dépendait de la nature du précurseur. L étude de l effet de la pression nous a conduit à évoluer vers les systèmes dilués afin d accroître la concentration en espèces actives monomères et d éviter la désactivation par agrégation.The objective of this thesis was to contribute to the study of the synthesis of dialkyl carbonates by direct carbonation of alcohols by developing a catalytic way. In order to understand the reaction mechanism and to improve its effectiveness, we were interested in the relation between the structure and the activity of the catalyst. Various organotin complexes of the family R2Sn(OCH3)2 have been synthesised and their reactivity towards CO2 been studied. Under supercritical CO2/CH3OH conditions and depending on the nature of the precursor, several resting species of different nuclearity have been characterized. Kinetic studies have revealed that the number of active species implied in the mechanism of DMC formation depended on the nature of the precursor. The study of pressure effect led us to evolve toward diluted systems in order to increase the concentration of active monomer species and to avoid catalyst deactivation by aggregation.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF