Temperature Acclimation of the Picoalga Ostreococcus tauri Triggers Early Fatty-Acid Variations and Involves a Plastidial ?3-Desaturase

Alteration of fatty-acid unsaturation is a universal response to temperature changes. Marine microalgae display the largest diversity of polyunsaturated fatty-acid (PUFA) whose content notably varies according to temperature. The physiological relevance and the molecular mechanisms underlying these changes are however, still poorly understood. The ancestral green picoalga Ostreococcus tauri displays original lipidic features that combines PUFAs from two distinctive microalgal lineages (Chlorophyceae, Chromista kingdom). In this study, optimized conditions were implemented to unveil early fatty-acid and desaturase transcriptional variations upon chilling and warming. We further functionally characterized the O. tauri ω3-desaturase which is closely related to ω3-desaturases from Chromista species. Our results show that the overall omega-3 to omega-6 ratio is swiftly and reversibly regulated by temperature variations. The proportion of the peculiar 18:5 fatty-acid and temperature are highly and inversely correlated pinpointing the importance of 18:5 temperature-dependent variations across kingdoms. Chilling rapidly and sustainably up-regulated most desaturase genes. Desaturases involved in the regulation of the C18-PUFA pool as well as the Δ5-desaturase appear to be major transcriptional targets. The only ω3-desaturase candidate, related to ω3-desaturases from Chromista species, is localized at chloroplasts in Nicotiana benthamiana and efficiently performs ω3-desaturation of C18-PUFAs in Synechocystis sp. PCC6803. Overexpression in the native host further unveils a broad impact on plastidial and non-plastidial glycerolipids illustrated by the alteration of omega-3/omega-6 ratio in C16-PUFA and VLC-PUFA pools. Global glycerolipid features of the overexpressor recall those of chilling acclimated cells.Développement d'une infrastructure française distribuée pour la métabolomique dédiée à l'innovatio

Probing the interplay between factors determining reaction rates on silica gel using termolecular systems

This article was published in the journal, Photochemical and Photobiological Sciences [© Royal Society of Chemistry and Owner Societies]. The definitive version is available at: http://dx.doi.org/10.1039/c2pp25171jIn this study we have compared energy and electron transfer reactions in termolecular systems using a nanosecond diffuse reflectance laser flash photolysis technique. We have previously investigated these processes on silica gel surfaces for bimolecular systems and electron transfer in termolecular systems. The latter systems involved electron transfer between three arene molecules with azulene acting as a molecular shuttle. In this study we present an alternative electron transfer system using trans β-carotene as an electron donor in order to effectively immobilise all species except the shuttle, providing the first unambiguous evidence for radical ion mobility. In the energy transfer system we use naphthalene, a structural isomer of azulene, as the shuttle, facilitating energy transfer from a selectively excited benzophenone sensitiser to 9-cyanoanthracene. Bimolecular rate constants for all of these processes have been measured and new insights into the factors determining the rates of these reactions on silica gel have been obtained

Synthesis and Photochemistry of a 2,6-Dialkoxyanthracene-containing, Side-Chain-Substituted Liquid-Crystalline Polymer

The synthesis and several aspects of the photophysical and photochemical behavior of a methacrylate polymer substituted, via a flexible methylene chain, with a 2,6-dialkoxyanthracene chromophore are reported. Polarized light microscopy and DSC indicate the polymer is liquid crystalline. The UV-Vis and fluorescence spectra of the polymer indicate both ground and excited state aggregation of the chromophores as evidenced by perturbations of these spectra relative to those of a simple model compound. Chromophore association in the ground state seems to occur even in a good solvent, dichloromethane. Chromophore aggregation effects are enhanced in films of the polymer, particularly after heating or when poor solvents are added to a solution of the polymer in dichloromethane. Steady state and time-resolved fluorescence experiments indicate significant self-quenching of the excited anthracene chromophore even in highly diluted solutions in dichloromethane and the presence of a long-lived (tau = 30.6ns) intramolecular excimer or excited aggregate and a short-lived (tau = 2.0ns) anthracene singlet state. At higher concentrations an intermolecular excimer or excited aggregate is observed. Fluorescence spectra of films indicate the presence of weakly emissive excimers or excited aggregates. Two types of 4 + 4 photocycloaddition products are most likely formed upon UV or visible light irradiation. Photooxidation products are also formed when irradiation is carried out in the presence of oxygen