How does sulphur availability modify N acquisition of white clover (Trifolium repens L.)?

The role of S in legume growth, N uptake, and N2 fixation was investigated using white clover (Trifolium repens L.) as a model species. We examined whether the effect of sulphate addition on N fixation resulted from a stimulation of host plant growth, a specific effect of S on nodulation, or a specific effect of S on nodule metabolism. Clones of white clover, inoculated with Rhizobium leguminosarum, were grown for 140 d in a hydroponic system with three levels of sulphate concentration (0 mM, 0.095 mM, and 0.380 mM). Nodule morphological and biochemical traits, such as root length, nodule biomass and volume, nodule protein contents (nitrogenase and leghaemoglobin obtained by an immunological approach), and root amino acid concentrations, were used to analyse the effect of sulphate availability on N2 fixation. The application of sulphate increased whole plant dry mass, root length, and nodule biomass, expressed on a root-length basis. N uptake proved less sensitive than N2 fixation to the effects of S-deficiency, and decreased as a consequence of the lower root length observed in S-deficient plants. N2 fixation was drastically reduced in S-deficient plants as a consequence of a low nodule development, but also due to low nitrogenase and leghaemoglobin production. This effect is likely to be due to down-regulation by a N-feedback mechanism, as, under severe S-deficiency, the high concentration of whole plant N and the accumulation of N-rich amino acids (such as asparagine) indicated that the assimilation of N exceeded the amount required for plant growth

Flux lipolytiques et jeûne prolongé chez le manchot royal

Ce travail a pour but l'étude des flux lipolytiques et de leur régulation, et des interactions entre substrats métaboliques in vivo lors du jeûne prolongé, et particulièrement au passage phase II-phase III, dans des conditions environnementales naturelles chez le manchot royal. Ce travail montre que: Malgré l'état critique (mais non total) d'épuisement des réserves lipidiques lors de la phase III: -la production des acides gras non-estérifiés (AGNE) par le tissu adipeux et la disponibilité plasmatique des AGNE ne sont pas diminuées. La disponibilité plasmatique des AGNE pour les voies oxydatives n'est pas proportionnelle à la taille des réserves lipidiques (article1). -la réponse lipolytique au glucagon est maintenue. La sensibilité lipolytique du tissu adipeux au glucagon n'est pas affectée par la diminution de la taille des cellules adipeuses (article 2). Lors de la phase II du jeûne, une inhibition de l'oxydation des AGNE, par perfusion de mercaptoacétate, simule les changements métaboliques et hormonaux marquant le passage phase II-phase III (article 3). Ces résultats soutiennent l'hypothèse que le passage phase II-phase III et la stimulation du comportement alimentaire qui y est associée, sont induits par une réduction de l'oxydation des AGNE, indépendante de leur disponibilité. Ce travail suggère aussi que lors du jeûne prolongé: - le métabolisme des protéines n'est pas modulé par la seule disponibilité des AGNE, mais dépend de leur oxydation. - la corticostérone est le lien entre l'oxydation des AGNE et le catabolisme des protéines. -la disponibilité du glucose contrôle la composition du mélange de substrats qui est oxydé pour la production d'énergie (article 4). Ce contrôle dépend de l'état métabolique et hormonal (ex, stressés vs non-stressés) des animaux.The aim of this work is to study in vivo, the lipolytic fluxes, their regulation, and substrate interactions in prolonged fasting king penguins in their natural environment. It particularly focuses on the phase II-phase III transition. This work shows that: In phase III of fasting, the production of non-esterified fatty acids (NEFA) by the adipose tissue and the plasma availability of NEFA are not decreased, despite the critical (but still incomplete) exhaustion of fat stores. Plasma NEFA availability for oxidation is not directly proportional to the size of fat stores (article 1). Lipolytic response to glucagon is also maintained at this state of fasting. The lipolytic sensitivity of adipose tissue to glucagon is not lowered as fat cell size decreases (article 2). In phase II of fasting, an inhibition of fatty acid oxidation (induced by mercaptoacetate) mimics the metabolic and hormonal changes characterizing the phase II-phase III transition (article 3). These results support the hypothesis that a reduction in NEFA oxidation, independent of their availability induces the entrance into phase III and the associated stimulation of feeding behavior. This work also suggests that during prolonged fasting: - Protein metabolism is related to NEFA oxidation and not only by the availability of these fuels. - Corticosterone constitutes a link between NEFA oxidation and protein metabolism. - The availability of glucose is an important determinant of the substrate mix that is oxidized for energy production (article 4). This control depends on the metabolic and/or hormonal status (i.e. stressed vs. non-stressed) of the animals.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

A study of the dynamics of seed banks in a complex dune system, with the aim of restoration.

International audienceTo assess the possibility of restoring the original plant community of grey dune from a pine plantation, a synchronic study of the seed banks of three habitats, the grey dune, the pine plantation, and a clearing, was conducted at Quiberon (France). Five stations were selected: a Grey dune, Pine plantation 1, Pine plantation 2, Clearing 1, and Clearing 2. In contrast to the pine plantations, clearing 1, subject to heavy human disturbance, had a great similarity between its seed banks and its established vegetation. The larger clearing (C2) tend to resemble the grey dune, whereas the other was dominated by ruderal species. The analysis of the seed banks demonstrated differences between the clearings and the pine plantations from which they were derived. The potential vegetation of the clearings was closer to that of the grey dune and had a larger number of species with a short life cycle than the pine plantations. The seed banks of the pine plantations were not similar to that of the grey dune, but also differed from that of closed vegetation. This study suggested that it may not be possible to obtain a short term restoration of a grey dune after just clear felling only with the help of seed banks. On the other hand, seed dissemination could facilitate a restoration in a larger time scale as for clearings

Grassland species are more efficient in acquisition of S from the atmosphere when pedospheric S availability decreases

International audienceAims Plants can absorb Sulfur (S) either through roots as sulfate or via leaves in a gas form such as SO2 or H2S. This study aims to examine whether the most efficient competitors for root uptake of sulfate among grassland species are also those with the greatest ability for foliar uptake and to test whether all species can increase their ability to use atmospheric S when available sulfate decreases. Methods Six grassland species were grown together in a non-S-enriched-atmosphere for 60 days with two levels of sulfate concentrations. Sulfate was 34S-enriched to distinguish root uptake of sulfate and foliar uptake of gaseous S. Results Grasses were more competitive for sulfate uptake and more efficient at producing biomass for the same amount of S in comparison to the non-fixing forb and the legumes. All species studied were able to increase their ability to use atmospheric sources of S when sulfate availability decreased. The percentage of S derived from the atmosphere was strongly related to sulfate concentration in leaves. Conclusion Grasses were more efficient for root sulfate uptake but forbs seemed more efficient for foliar uptake. Sulfate in plant tissues could play a key role in regulation between the foliar and root S uptake

Is white clover able to switch to atmospheric sulphur sources when sulphate availability decreases?

International audienceSulphur (S) is one of the very few nutrients that plants can absorb either through roots as sulphate or via leaves in a gas form such as SO2 or H2S. This study was realized in a non-S-enriched atmosphere and its purpose was to test whether clover plants can increase their ability to use atmospheric S when sulphate availability decreases. A novel methodology measuring the dilution of S-34 provided from a nutrient solution by atmospheric S-32 was developed to measure S acquisition by Trifolium repens L. Clones of white clover were grown for 140 d in a hydroponic system with three levels of sulphate concentrations. S concentration in plants decreased with S deficiency and plant age. In the experimental conditions used here, S derived from atmospheric deposition (Sdad) constituted from 36% to 100% of the total S. The allocation of S coming from atmospheric and pedospheric sources depends on organs and compounds. Nodules appeared as major sinks for sulphate. A greater proportion of atmospheric S was observed in buffer-soluble proteins than in the insoluble S fraction. Decreasing the S concentration in the nutrient solution resulted in an increase in the Sdad:leaf area ratio and in an increase in the leaf:stolon and root:shoot mass ratios, suggesting that a plasticity in the partitioning of resources to organs may allow a higher gain of S by both roots and leaves. This study shows that clover can increase its ability to use atmospheric S even at low concentration when pedospheric S availability decreases

The relationships between soil seed bank, aboveground vegetation and disturbances in an eutrophic alluvial wetland of Western France

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One-pot enyne metathesis/Diels–Alder reaction for the construction of highly functionalized novel polycyclic aza-compounds

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The predominance of <em>Lactobacillus sanfranciscensis</em> in French organic sourdoughs and its impact on related bread characteristics

International audienceFourteen bakeries located in different regions of France were selected. These bakers use natural sourdough and organic ingredients. Consequently, different organic sourdoughs used for the manufacture of French bread were studied by the enumeration of lactic acid bacteria (LAB) and 16S rRNA sequencing of the isolates. In addition, after DNA extraction the bacterial diversity was assessed by pyrosequencing of the 16S rDNA V1-V3 region. Although LAB counts showed significant variations (7.6-9.5log10CFU/g) depending on the sourdough studied, their identification through a polyphasic approach revealed a large predominance of Lactobacillus sanfranciscensis in all samples. In ten sourdoughs, both culture and independent methods identified L. sanfranciscensis as the dominant LAB species identified. In the remaining sourdoughs, culture methods identified 30-80% of the LAB as L. sanfranciscensis whereas more than 95% of the reads obtained by pyrosequencing belonged to L. sanfranciscensis. Other sub-dominant species, such as Lactobacillus curvatus, Lactobacillus hammesii, Lactobacillus paralimentarius, Lactobacillus plantarum, Lactobacillus pentosus, and Lactobacillus sakei, were also identified. Quantification of L. sanfranciscensis by real-time PCR confirmed the predominance of this species ranging from 8.24 to 10.38log10CFU/g. Regarding the acidification characteristics, sourdough and related bread physico-chemical characteristics varied, questioning the involvement of sub-dominant species or L. sanfranciscensis intra-species diversity and/or the role of the baker's practices

Tradeoff between the Conservation of Soil C Stocks and Vegetation Productivity in Temperate Grasslands

International audienceGrassland management affects ecosystem services such as the conservation of C stocks. The aim of this study was to analyze the relation between vegetation production and soil C stocks for a set of seven temperate grasslands of various productivity levels. We estimated vegetation production directly through measurements of aboveground biomass (>5 cm), stubble and root biomass, and indirectly via plant community functioning. Soil C stocks were measured for bulk soil (organic C, SOC) and hot-water-extractable C (HWC) of topsoil. Plant community functioning was characterized by community-weighted mean (CWM) traits and functional diversity index. Results show a negative relation between biomass production and SOC stock. The tradeoff between productivity and SOC stock could be linked to plant community functioning and particularly Leaf Dry Matter content (LDMC CWM) which appeared to be the most relevant descriptor of plant community functioning. High SOC stock could be associated to low productivity, conservative strategy (high LDMC CWM), low soil labile C content and grassland age. Our results show a strong direct effect of management and grassland age on plant community, which in turn affects plant tissue quality and subsequent organic matter mineralization. Old permanent grasslands appeared less productive but represent an occasion for C storage and thus global change mitigation