Fractionation of stable iron isotopes in higher plants

Although the fractionation of stable iron isotopes by biological processes in the environment is currently a matter of intense debate, the isotope fractionation associated with the growth of higher plants has, to date, not been characterized. We show that iron isotope fractionation induced by higher plants is substantial and also generates systematic plant-specific patterns. We suggest a hypothesis in which these patterns mirror the two different strategies that plants have developed to incorporate iron from the soil: reduction of Fe(III) in soils by strategy I plants results in the uptake of iron, which is depleted in 56Fe by up to 1.6 per mil relative to 54Fe when compared to the available Fe in soils; complexation with siderophores by strategy II plants results in the uptake of iron that is 0.2 per mil heavier than that in soils. Furthermore, younger parts of strategy I plants get increasingly depleted in heavy isotopes as the plant grows, while strategy II plants incorporate nearly the same isotope composition throughout. This points to entirely different translocation mechanisms between strategy I and II plants. Such presumably redox-related differences in translocation have been under debate up to now. We conclude that plant metabolism represents an important cause of isotopic variation in the biogeochemical cycling of Fe. Therefore, heavy stable metal isotope systems now start to be viable indicators of geosphere-biosphere metal transfer processes.     

Analysis of guarana seeds II. Studies on the composition of the tannin fraction

Summary The content of the total tannins, proanthocyanidins and prototannins in the seeds of guarana, Paullinia cupana var. sorbilis HKB (Sapindaceae) was studied. A total tannin content of 12.1% dry matter was found in air dried samples. Reversed-phase high-performance liquid chromatography (RP-HPLC) analysis resulted in 6.0% (+)-catechin and 3.8% (–)-epicatechin on an average. Hydrolysable tannins were not detectable. The results for one of two analyzed ground samples from the Brazilian market were substantially lowered. It is concluded that this product was adulterated with another no tannin containing material.

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Zur Analytik von Guarana. II. Zusammensetzung der Gerbstoffe

Zusammenfassung Der Gehalt an Gesamtgerbstoffen, Proanthocyanidinen und Prototanninen im Samen von Guarana,Paullinia cupana var.sorbilis HKB (Sapindaceae), wurde untersucht. In lufttrockenen Samen wurde ein Gesamttanningehalt von 12,1% i. T. gefunden, die Proanthocyanidin-Bestimmung ergab einen Gehalt von 10,7%; mittels RP-HPLC-Analyse wurden 6,0% an (+)-Catechin und 3,8% (–)-Epicatechin gefunden. Hydrolysierbare Tannine waren nicht nachweisbar. Bei einer von zwei untersuchten gemahlenen Proben des brasilianischen Handels waren alle Analysenwerte erheblich erniedrigt, was auf eine Streckung des Produkts mit nicht gerbstoffhaltigem Material schließen läßt.

     

Various cytosine/adenine permease homologues are involved in the toxicity of 5-fluorocytosine in Saccharomyces cerevisiae

5-Fluorocytosine (5-FC), a medically applied antifungal agent (Ancotil), is also active against the model organism Saccharomyces cerevisiae. 5-FC uptake in S. cerevisiae was considered to be mediated by the FCY2-encoded cytosine/adenine permease. By applying a highly sensitive assay, a low-level but dose-dependent toxicity of 5-FC in fcy2 mutants was detected, whereas cells deficient in the cytosine deaminase (encoded by FCY1), which is essential for intracellular conversion of 5-FC to 5-fluorouracil, display strong dose-independent resistance. Thus, an alternative, Fcy2-independent access pathway for 5-FC exists in S. cerevisiae. A genome-wide search for cytosine permease homologues identified two uncharacterized candidate genes, designated FCY21 and FCY22, both of which exhibit highest similarity to FCY2. Disruption of either FCY21 or FCY22 resulted in strains displaying low-level resistance, indicating the functional involvement of both gene products in 5-FC toxicity. When mutations in FCY21 or FCY22 were combined with the FCY2 disruption, both double mutants displayed stronger resistance when compared to the FCY2 mutant alone. Disruptions in all three permease genes consequently conferred the highest degree of resistance, not only towards 5-FC but also to the toxic adenine analogon 8-azaadenine. As residual 5-FC sensitivity was, however, even detectable in the fcy2 fcy21 fcy22 mutant, we analysed the relevance of other FCY2 homologues, i.e. TPN1, FUR4, DAL4, FUI1 and yOR071c, for 5-FC toxicity. Among these, Tpn1, Fur4 and the one encoded by yOR071c were found to contribute significantly to 5-FC toxicity, thus revealing alternative entry routes for 5-FC via other cytosine/adenine permease homologues.     

Die Wärmeausdehnung kubisch-flächenzentrierter Eisenlegierungen

Dilatometrische Messungen zwischen ?200 und 500 °C an Eisen-Nickel-, Eisen-Mangan- und Eisen-Mangan-Nickel-Legierungen. Einfluß von Kohlenstoff, Chrom und Kupfer auf Wärmeausdehnung und magnetische Eigenschaften. Ermittlung der Volumenmagnetostriktion an den ferromagnetisch und antiferromagnetisch geordneten Legierungen. Vergleich der relativen Längenänderung zwischen 20 und ?200 °C bei verschiedenen Werkstoffen.     

Performance of superstrate multijunction amorphous silicon-based solar cells using optical layers for current management

The performance of multijunction amorphous silicon-based thin film solar cells has been reported using thin layers of TiO₂ and SiO_x acting as refractive index matching optical layers for different interfaces of the superstrate device structure. Improvement of short-circuit current from the sub-cells of a-Si/μc-Si cells is demonstrated with TiO₂ as anti-reflection layer at TCO/Si interface and SiO_x as intermediate-reflector layer between two sub-cells. An initial efficiency of 11.8% is achieved by applying both the TiO₂ and SiO_x optical layers in a-Si/μc-Si solar cell.     

Human Liver Fatty Acid Binding Protein‐1 T94A Variant,Nonalcohol Fatty Liver Disease,and Hepatic Endocannabinoid System

Hepatic endocannabinoids (EC) and their major binding/“chaperone” protein (i.e., liver fatty acid binding protein‐1 [FABP1]) are associated with development of nonalcoholic fatty liver (NAFLD) in animal models and humans. Since expression of the highly prevalent human FABP1 T94A variant induces serum lipid accumulation, it is important to determine its impact on hepatic lipid accumulation and the EC system. This issue was addressed in livers from human subjects expressing only wild‐type (WT) FABP1 T94T (TT genotype) or T94A variant (TC or CC genotype). WT FABP1 males had lower total lipids (both neutral cholesteryl esters, triacylglycerols) and phospholipids than females. WT FABP1 males' lower lipids correlated with lower levels of the N‐acylethanolamide DHEA and 2‐monoacylglycerols (2‐MAG) (2‐OG, 2‐PG). T94A expression in males increased the hepatic total lipids (triacylglycerol, cholesteryl ester), which is consistent with their higher level of CB1‐potentiating 2‐OG and lower antagonistic EPEA. In contrast, in females, T94A expression did not alter the total lipids, neutral lipids, or phospholipids, which is attributable to the higher cannabinoid receptor‐1 (CB1) agonist arachidonoylethanolamide (AEA) and its CB1‐potentiator OEA being largely offset by reduced potentiating 2‐OG and increased antagonistic EPEA. Taken together, these findings indicate that T94A‐induced alterations in the hepatic EC system contribute at least in part to the hepatic accumulation of lipids associated with NAFLD, especially in males.     

Impact of Fabp1 Gene Ablation on Uptake and Degradation of Endocannabinoids in Mouse Hepatocytes

Liver fatty‐acid‐binding protein (FABP1, L‐FABP) is the major cytosolic binding/chaperone protein for both precursor arachidonic acid (ARA) and the endocannabinoid (EC) products N‐arachidonoylethanolamine (AEA) and 2‐arachidonoylglycerol (2‐AG). Although FABP1 regulates hepatic uptake and metabolism of ARA, almost nothing is known regarding FABP1’s impact on AEA and 2‐AG uptake, intracellular distribution, and targeting of AEA and 2‐AG to degradative hepatic enzymes. In vitro assays revealed that FABP1 considerably enhanced monoacylglycerol lipase hydrolysis of 2‐AG but only modestly enhanced AEA hydrolysis by fatty‐acid amide hydrolase. Conversely, liquid chromatography–mass spectrometry of lipids from Fabp1 gene‐ablated (LKO) hepatocytes confirmed that loss of FABP1 markedly diminished hydrolysis of 2‐AG. Furthermore, the real‐time imaging of novel fluorescent NBD‐labeled probes (NBD‐AEA, NBD‐2‐AG, and NBD‐ARA) resolved FABP1’s impact on uptake vs intracellular targeting/hydrolysis. FABP1 bound NBD‐ARA with 2:1 stoichiometry analogous to ARA, but bound NBD‐2‐AG and NBD‐AEA with 1:1 stoichiometry—apparently at different sites in FABP1’s binding cavity. All three probes were taken up, but NBD‐2‐AG and NBD‐AEA were targeted to lipid droplets. LKO reduced the uptake of NBD‐ARA as expected, significantly enhanced that of NBD‐AEA, but had little effect on NBD‐2‐AG. These data indicated that FABP1 impacts hepatocyte EC levels by binding EC and differentially impacts their intracellular hydrolysis (2‐AG) and uptake (AEA).     

Spherical Visibility Sampling

Many 3D scenes (e.g. generated from CAD data) are composed of a multitude of objects that are nested in each other. A showroom, for instance, may contain multiple cars and every car has a gearbox with many gearwheels located inside. Because the objects occlude each other, only few are visible from outside. We present a new technique, Spherical Visibility Sampling (SVS), for real‐time 3D rendering of such – possibly highly complex – scenes. SVS exploits the occlusion and annotates hierarchically structured objects with directional visibility information in a preprocessing step. For different directions, the directional visibility encodes which objects of a scene's region are visible from the outside of the regions' enclosing bounding sphere. Since there is no need to store a separate view space subdivision as in most techniques based on preprocessed visibility, a small memory footprint is achieved. Using the directional visibility information for an interactive walkthrough, the potentially visible objects can be retrieved very efficiently without the need for further visibility tests. Our evaluation shows that using SVS allows to preprocess complex 3D scenes fast and to visualize them in real time (e.g. a Power Plant model and five animated Boeing 777 models with billions of triangles). Because SVS does not require hardware support for occlusion culling during rendering, it is even applicable for rendering large scenes on mobile devices.     

Optimal strategies for maintaining a chain of relays between an explorer and a base camp

We envision a scenario with robots moving on a terrain represented by a plane. A mobile robot, called explorer is connected by a communication chain to a stationary base camp. The chain is expected to pass communication messages between the explorer and the base camp. It is composed of simple, mobile robots, called relays.