Les nappes alluviales de la Basse Somme revisitées

The new approach of the fluviatile sequence preserved downstream of Abbeville from Port-le-Grand to Saint-Valery, brings together two sets of complementary data in a same canvas. The first set combines the field records of V. Commont and A. Briquet slightly above the basal cravels. The second set encompasses the data gained for the high and very high terraces mapped in the eighties. They point to a succession of ten main terraces and two second order ones, occurring in continuity with the Abbeville terrace system. The upper terrace being related to Jaramillo, we are dealing with one million year strong regional record with a high-resolution palaeoenvironmental signature fitting in with the ODP 677 marine isotopic record and with the Chinese loess record. In this way, the laminar tool-kit of Croix-l’Abbé could be positioned in the middle part of MIS 8, around 250 ka.     

Methyl chloride isotopic signatures from Irish forest soils and a comparison between abiotic and biogenic methyl halide soil fluxes

Forest soils demonstrate in a microcosm the difficulties that are faced in quantifying methyl halide budgets. Carbon isotopic analyses have been proposed as a potential tool to address these concerns and in this study we have measured significant enrichment of the methyl chloride ¹³C/¹²C isotopic ratio (from ?40.2 ± 0.8‰ to ?33.4 ± 7.4‰) after 9 min chamber emplacement on local Irish forest soils. This enrichment occurred independent of direction of methyl chloride fluxes. Measurements from soil cores in a flow‐through system (FTS) are comparable with chamber‐based isotopic measurements and indicate that methyl chloride produced abiotically from organic soil horizons has an isotopic ¹³C signature of ?53 ± 49‰, significantly less depleted than previously reported. Average net methyl chloride, methyl bromide and methyl iodide fluxes from soils (77.8 ± 2.1, 1.25 ± 3.63 and 0.35 ± 2.00 μg MeX m^?2 day^?1, respectively) are in line with previously reported values; however, a better understanding of spatial and temporal variability is needed for budget quantification. Methyl halide fluxes from FTS soil cores demonstrate that, on a per gram basis, most consumption occurs through biologically driven processes in the O horizon, with progressively smaller contributions in deeper horizons. Sporadic biogenic production was observed in shallow soil horizons only. Abiotic production was at most one‐tenth the net biological reaction rate in the O horizon and did not appear to be significantly different from zero in lower horizons. Modelled emissions based upon observed and reported rates for production, consumption and diffusion within the soil atmosphere system are unable to replicate all observed isotopic signatures from chamber fluxes.     

Evidence for transketolase-like TKTL1 flux in CHO cells based on parallel labeling experiments and 13C-metabolic flux analysis

The pentose phosphate pathway (PPP) is a fundamental component of cellular metabolism. It provides precursors for the biosynthesis of nucleotides and contributes to the production of reducing power in the form of NADPH. It has been hypothesized that mammalian cells may contain a hidden reaction in PPP catalyzed by transketolase-like protein 1 (TKTL1) that is closely related to the classical transketolase enzyme; however, until now there has been no direct experimental evidence for this reaction. In this work, we have applied state-of-the-art techniques in ¹³C metabolic flux analysis (¹³C-MFA) based on parallel labeling experiments and integrated flux fitting to estimate the TKTL1 flux in CHO cells. We identified a set of three parallel labeling experiments with [1-¹³C]glucose+[4,5,6-¹³C]glucose, [2-¹³C]glucose+[4,5,6-¹³C]glucose, and [3-¹³C]glucose+[4,5,6-¹³C]glucose and developed a new method to measure ¹³C-labeling of fructose 6-phosphate by GC-MS that allows intuitive interpretation of mass isotopomer distributions to determine key fluxes in the model, including glycolysis, oxidative PPP, non-oxidative PPP, and the TKTL1 flux. Using these tracers we detected a significant TKTL1 flux in CHO cells at the stationary phase. The flux results suggest that the main function of oxidative PPP in CHO cells at the stationary phase is to fuel the TKTL1 reaction. Overall, this study demonstrates for the first time that carbon atoms can be lost in the PPP, by means other than the oxidative PPP, and that this loss of carbon atoms is consistent with the hypothesized TKTL1 reaction in mammalian cells.     

The measurement of multiple spray deposits by sequential application of metal chelate tracers

Chelates of the transition metals copper, cobalt, manganese and zinc, available as foliar feeds, were identified as the most suitable spray tracers for comparisons of deposits arising from up to four sequential applications to a single target. Their use minimised many of the disadvantages associated with other commonly used tracers such as visible and fluorescent dyes, and it was possible to quantify each tracer when present on the target in ratios of up to 100:1. Each spray solution contained a single chelate at a metal concentration of 1 g litre^?1. The recovery of metal chelates from plant tissue may not be quantitative, as a consequence of absorption or adsorption by leaves for example. The food colorant tartrazine, at a concentration of 10 g litre^?1, was shown to be a suitable internal standard for estimation of percentage recovery. Combined spray deposits were recovered readily from apple leaves and fruit by aqueous extraction and analysed by atomic absorption spectroscopy. The spray deposit of each metal tracer was calculated from the raw analytical data using procedures for generating calibration curves designed to optimise the accuracy of the analysis.     

Tracing sources of carbon and hydrogen to stored lipids in the migratory moth,Mythimna unipuncta using stable isotopes (δ2H, δ13C)

Stable isotope measurements of insect tissues can be used to determine origin and migratory patterns. The isotopic links between diet and stored lipids in laboratory reared true armyworm moths (Mythimna unipuncta, Haw.) were investigated using δ¹³C and δ²H measurements. Newly emerged moths were fed synthetic nectars, consisting of different carbohydrate and water sources that were isotopically distinct from those in the larval diet. After 4 days of feeding, insects were sacrificed, and fat‐body lipids were extracted for isotopic analysis. When held on a constant nectar source, adult diet contributed ～87% of the C and 44% H of lipids. For H, 27% and ～ 17% of lipid was derived from carbohydrates and water, respectively, with the remainder presumably from the larval stage. When the isotopic composition of the nectar source was switched there was rapid and exponential temporal change in lipid isotopic profiles. The relevance of our findings to tracing origins of stored lipids in migrant Lepidoptera is discussed.     

Hydrologic Variability of Small, Northern Michigan Lakes Measured by the Addition of Tracers

The hydraulic residence time (or flushing rate of water) is a key variable for any aquatic ecosystem and is used in many types of models and calculations. Rather than being measured directly, the hydraulic residence time is usually inferred from estimates of watershed size, precipitation, and water yield. Such estimates can be problematic in any environment but are especially so in environments in which flat or complex topography makes delineations of mapped watershed boundaries difficult to discern. We added lithium bromide, (LiBr) to three small seepage lakes in the flat topography of the Upper Peninsula of Michigan to provide an independent estimate of the water residence time. Water residence time [volume/(outflow + evaporation)] averaged 921 ± 381 (SD) days among lakes and years and ranged from 400 to 1661 days at the extremes. This variation was not clearly related to year-to-year variation in precipitation, which was relatively constant [0.26 ± 0.06 (SD) cm day (d)^{− 1}]. The addition of the tracer (along with measurements of lake volume) enabled us to estimate, independent from other hydrologic information, the flow of water leaving the lakes in seepage plus surface outflow. This value, in conjunction with measurement of precipitation and evaporation, enabled us to calculate complete water budgets for these lakes. Among lakes and years, the groundwater input averaged 0.48 ± 0.36 cm d^{− 1} and accounted for 57%± 19% of total water input. This estimate was larger by 150% than that obtained by multiplying precipitation (minus estimated evapotranspiration) times a mapped value of the watershed areas. Our analysis enables us to calculate the relative significance of groundwater and precipitation for solutes such as phosphorus, hydrogen ion, and dissolved organic carbon. Received 17 February 1998; accepted 19 February 1998.     

Biosynthesis of peptide fragments of eukaryotic GPCRs in Escherichia coli by directing expression into inclusion bodies

Biosynthesis of peptides in heterologous systems is often a prerequisite to biophysical analyses. Large amounts of peptides, in particular portions of membrane proteins, are needed to optimize conditions for secondary and tertiary structure analysis. Chemical synthesis of these peptides is limited by their high hydrophobicity and also due to the need to incorporate isotopic labels for high resolution NMR analysis. In this protocol, we describe a method for the heterologous expression and purification of unlabeled and isotopically labeled peptide fragments of Ste2p, an integral membrane G protein‐coupled receptor. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.