Mineralogy and petrology of comet 81P/Wild 2 nucleus samples

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.     

Reversible, metal-free hydrogen activation

Although reversible covalent activation of molecular hydrogen (H2) is a common reaction at transition metal centers, it has proven elusive in compounds of the lighter elements. We report that the compound (C6H2Me3)2PH(C6F4)BH(C6F5)2 (Me, methyl), which we derived through an unusual reaction involving dimesitylphosphine substitution at a para carbon of tris(pentafluorophenyl) borane, cleanly loses H2 at temperatures above 100 degrees C. Preliminary kinetic studies reveal this process to be first order. Remarkably, the dehydrogenated product (C6H2Me3)2P(C6F4)B(C6F5)2 is stable and reacts with 1 atmosphere of H2 at 25 degrees C to reform the starting complex. Deuteration studies were also carried out to probe the mechanism.     

A genome-wide association study identifies IL23R as an inflammatory bowel disease gene

The inflammatory bowel diseases Crohn's disease and ulcerative colitis are common, chronic disorders that cause abdominal pain, diarrhea, and gastrointestinal bleeding. To identify genetic factors that might contribute to these disorders, we performed a genome-wide association study. We found a highly significant association between Crohn's disease and the IL23R gene on chromosome 1p31, which encodes a subunit of the receptor for the proinflammatory cytokine interleukin-23. An uncommon coding variant (rs11209026, c.1142G>A, p.Arg381Gln) confers strong protection against Crohn's disease, and additional noncoding IL23R variants are independently associated. Replication studies confirmed IL23R associations in independent cohorts of patients with Crohn's disease or ulcerative colitis. These results and previous studies on the proinflammatory role of IL-23 prioritize this signaling pathway as a therapeutic target in inflammatory bowel disease.     

Two contrasting laboratory methods improve <Emphasis Type="Italic">Silphium integrifolium</Emphasis> Michx. germination rate to agronomically acceptable levels

Organic dormancy, the inability to germinate under favorable conditions, is a common problem in many crop species and their wild relatives, leading to more variable emergence, plant density, and growth rates, thus increasing costs, and lowering yield. To overcome these problems, several different methods have been developed for various crop and model plants. However, in the emerging crop being bred from wild and semi-domesticated Silphium, no such method has been established thus far. The objective of this study was to identify a dormancy-breaking assay to increase the seed germination rate. Seeds of three different Silphium integrifolium Michx. genotypes were treated with five chemical and one cold treatment, and dried before or after the treatment at 27 °C or 40 °C. Untreated, dried seeds were taken as control. Seeds soaked for 24 h in a ethephon/potassium nitrate solution followed by a 72 h drying step at 40 °C showed an increase of germination to up to 90?±?2% compared to control seeds (3?±?0% and 5?±?1%). We identified the minimum time frame of cold stratification needed to enhance seed germination in Silphium, and found that cold stratification was nearly as good as the chemical treatment. Our results provide two alternate ways to treat S. integrifolium seeds for breaking organic dormancy, which will help to facilitate future research in the Silphium domestication community. The fact that our optimal treatments were similar to protocols developed for sunflower suggests that these methods may also be applicable to many related economically important Asteraceae species.     

Leaching of PCE-based Superplasticiser from Microfine Cement: a Chemical and Ecotoxicological Point of View

The construction materials industry faces major challenges since 2013 when the European Construction Products Regulation was implemented, especially in the sector of environmentally friendly construction products. This study determined concentrations of leachable inorganic and organic compounds from microfine cement paste with and without superplasticiser addition. Furthermore, the leached superplasticiser amounts were detected via LC-MS. The multi-method approach was supplemented by ecotoxicological assays. Phytotoxicity was tested with white mustard (Sinapis alba) and cress (Lepidium sativum). The mutagenic and genotoxic potential of the leachates was tested with the Ames fluctuation assay and the umuC assay. As leaching protocol, the European horizontal dynamic surface leaching test was used. The cement paste samples with superplasticiser followed the wash-off effect with a total organic carbon release up to 43 mmol/m², whereas the release of samples without superplasticiser was driven by diffusion. The ecotoxicological assays showed a clear time depending behaviour. No cytotoxicity and mutagenicity could be observed; anyhow some leachates show minor genotoxic potential. In all tests, a clear difference between the samples with and without superplasticiser could be detected.This study clearly demonstrates the importance of further studies in the field of leaching of construction products.     

Changes in soil microbial substrate utilization in response to altered litter diversity and precipitation in a Mediterranean shrubland

This study aimed at quantifying the consequences of reduced precipitation and plant diversity on soil microbial community functioning in a Mediterranean shrubland of southern France. Across a natural gradient of shrub species diversity, we established a total of 92 plots (4 × 4 m) with and without a moderate rain exclusion treatment of about 12 % of total precipitation. Shrub diversity included all possible combinations of the four dominant species (Cistus albidus, Quercus coccifera, Rosmarinus officinalis, and Ulex parviflorus). Respective leaf litter mixtures of these species combinations were exposed in all plots over 2 years. We quantified how litter species richness and the reduction in precipitation affected the soil microbial substrate utilization (measured by CO₂ evolution using the MicroResp method) on soil samples collected underneath each individual litter mixture after 1 and 2 years of decomposition. Moderate precipitation reduction had a minor impact, but litter species richness and the dissimilarity in phenolic concentrations (estimated using Rao’s quadratic entropy) showed a positive effect on the diversity of substrates metabolized by the microbial communities. Moreover, litter species richness increased soil microbial activity by increasing the catabolic diversity of the soil microbial community. These effects were mostly driven by the presence of Quercus and Ulex leaf litter, which at the same time reduced microbial metabolic dominance, while the presence of Rosmarinus had opposite effects. Our data suggest that plant species loss can have stronger effects on the functioning of soil microbial communities than moderate drought, with potentially important feedbacks on biogeochemical cycling in Mediterranean shrubland ecosystems.     

Genetic diversity and origin of North American green foxtail [<Emphasis Type="Italic">Setaria viridis</Emphasis> (L.) Beauv.] accessions

Setaria viridis (L.) P. Beauv. and its domesticated form, S. italica (L.) P. Beauv., have been developed over the past few years as model systems for C₄ photosynthesis and for the analysis of bioenergy traits. S. viridis is native to Eurasia, but is now a ubiquitous weed. An analysis of the population structure of a set of 232 S. viridis lines, mostly from North America but also comprising some accessions from around the world, using 11 SSR markers, showed that S. viridis populations in the US largely separate by latitude and/or climatic zone. S. viridis populations from the Northern US and Canada (north of 44°N) group with accessions from Western Europe, while populations in the Mid and Southern US predominantly group with accessions from Turkey and Iran. We hypothesize that S. viridis in the US was most likely introduced from Europe, and that introductions were competitive only in regions that had climatic conditions that were similar to those in the regions of origins. This hypothesis is supported by the fact that Canadian S. viridis lines were fast cycling and undersized when grown in the Mid-Western and Southern US compared to their morphology in their native environment. A comparison of the population structure obtained with 11 SSR markers and ~40,000 single nucleotide polymorphisms (SNPs) in a common set of S. viridis germplasm showed that both methods essentially yielded the same groupings, although admixture was identified at a higher frequency in the SNP analysis. Small numbers of SSR markers can thus be used effectively to discern the population structure in this inbreeding species.