Arsenic shoot-grain relationships in field grown rice cultivars

Arsenic (As) accumulation in rice grains is a risk to human health. The mechanism of transfer of As from the shoot into the grain during grain filling is unknown at present. In this study As speciation in the shoot and grains at maturity were examined, and the relationships between phosphorus (P) and As, and silicon (Si) and As were established in a wide range of cultivars grown in As contaminated field trials in Bangladesh and China. No correlations were observed between shoot and grain speciation, with the inorganic form comprising 93.0-97.0% of As in the shoot and 63.0-83.7% in the grains. The percentage of dimethylarsinic acid (DMA) was between 1.4 and 6.6% in the shoot and 14.6 and 37.0% in the grains; however, the concentrations were comparable, ranging from 0.07 to 0.26 mg kg(-1) in the shoots and 0.03 to 0.25 mg kg(-1) in the grains. A positive correlation was observed between shoot As and shoot Si, however, no correlation was observed between shoot Si and grain As. A significant negative correlation was observed between shoot P and grain As concentrations. These results suggest that the translocation of As into the grain from the shoots is potentially using P rather than Si transport mechanisms. The findings also indicate that inorganic As and DMA translocation to the grain differ considerably.

Environmental and genetic control of arsenic accumulation and speciation in rice grain:comparing a range of common cultivars grown in contaminated sites across Bangladesh, China, and India

The concentration of arsenic (As) in rice grains has been identified as a risk to human health. The high proportion of inorganic species of As (As(i)) is of particular concern as it is a nonthreshold, class 1 human carcinogen. To be able to breed rice with low grain As, an understanding of genetic variation and the effect of different environments on genetic variation is needed. In this study, 13 cultivars grown at two field sites each in Bangladesh, India, and China are evaluated for grain As. There was a significant site, genotype, and site by genotype interaction for total grain As. Correlations were observed only between sites in Bangladesh and India, not between countries or within the Chinese sites. For seven cultivars the As was speciated which revealed significant effects of site, genotype, and site by genotype interaction for percentage As(i). Breeding low grain As cultivars that will have consistently low grain As and low As(i), over multiple environments using traditional breeding approaches may be difficult, although CT9993-5-10-1-M, Lemont, Azucena, and Te-qing in general had low grain As across the field sites.

Theatricality, irony and artifice in Gustave Courbet's self-portraits

This article considers the role of theatre as a questioning of Realism in the art of Gustave Courbet

CO2 uptake by a soil microcosm

Sequestration of CO2 via biological sinks is a matter of great scientific importance due to the potential lowering of atmospheric CO2. In this study, a custom built incubation chamber was used to cultivate a soil microbial community to instigate chemoautotrophy of a temperate soil. Real-time atmospheric CO2 concentrations were monitored and estimations of total CO2 uptake were made. After careful background flux corrections, 4.52 +/- 0.05 g CO2 kg I dry soil was sequestered from the chamber atmosphere over 40 h. Using isotopically labelled (CO2)-C-13 and GCMS-IRMS, labelled fatty acids were identified after only a short incubation, hence confirming CO2 sequestration for soil. The results of this in vivo study provide the ground work for future studies intending to mimic the in situ environment by providing a reliable method for investigating CO2 uptake by soil microorganisms.(C) 2012 Elsevier Ltd. All rights reserved.

Relative role of deterministic and stochastic determinants of soil animal community: a spatially explicit analysis of oribatid mites

1. Ecologists are debating the relative role of deterministic and stochastic determinants of community structure. Although the high diversity and strong spatial structure of soil animal assemblages could provide ecologists with an ideal ecological scenario, surprisingly little information is available on these assemblages.
2. We studied species-rich soil oribatid mite assemblages from a Mediterranean beech forest and a grassland. We applied multivariate regression approaches and analysed spatial autocorrelation at multiple spatial scales using Moran's eigenvectors. Results were used to partition community variance in terms of the amount of variation uniquely accounted for by environmental correlates (e.g. organic matter) and geographical position. Estimated neutral diversity and immigration parameters were also applied to a soil animal group for the first time to simulate patterns of community dissimilarity expected under neutrality, thereby testing neutral predictions.
3. After accounting for spatial autocorrelation, the correlation between community structure and key environmental parameters disappeared: about 40% of community variation consisted of spatial patterns independent of measured environmental variables such as organic matter. Environmentally independent spatial patterns encompassed the entire range of scales accounted for by the sampling design (from tens of cm to 100 m). This spatial variation could be due to either unmeasured but spatially structured variables or stochastic drift mediated by dispersal. Observed levels of community dissimilarity were significantly different from those predicted by neutral models.
4. Oribatid mite assemblages are dominated by processes involving both deterministic and stochastic components and operating at multiple scales. Spatial patterns independent of the measured environmental variables are a prominent feature of the targeted assemblages, but patterns of community dissimilarity do not match neutral predictions. This suggests that either niche-mediated competition or environmental filtering or both are contributing to the core structure of the community. This study indicates new lines of investigation for understanding the mechanisms that determine the signature of the deterministic component of animal community assembly.

AKT in Stromal Fibroblasts Controls Invasion of Epithelial Cells

The tumour microenvironment has an important role in cancer progression and recent reports have proposed that stromal AKT is activated and regulates tumourigenesis and invasion. We have shown, by immuno-fluorescent analysis of oro-pharyngeal cancer biopsies, an increase in AKT activity in tumour associated stromal fibroblasts compared to normal stromal fibroblasts. Using organotypic raft co-cultures, we show that activation of stromal AKT can induce the invasion of keratinocytes expressing the HPV type 16 E6 and E7 proteins, in a Keratinocyte Growth Factor (KGF) dependent manner. By depleting stromal fibroblasts of each of the three AKT isoforms independently, or through using isoform specific inhibitors, we determined that stromal AKT2 is an essential regulator of invasion and show in oro-pharyngeal cancers that AKT2 specific phosphorylation events are also identified in stromal fibroblasts. Depletion of stromal AKT2 inhibits epithelial invasion through activating a protective pathway counteracting KGF mediated invasions. AKT2 depletion in fibroblasts stimulates the cleavage and release of IL1B from stromal fibroblasts resulting in down-regulation of the KGF receptor (fibroblast growth factor receptor 2B (FGFR2B)) expression in the epithelium. We also show that high IL1B is associated with increased overall survival in a cohort of patients with oro-pharyngeal cancers. Our findings demonstrate the importance of stromal derived growth factors and cytokines in regulating the process of tumour cell invasion.