Changes in water structure induced by a hydrophobic solute probed by simulation of the water hydrogen bond angle and radial distribution functions.

In order to better characterize changes in water structure induced by a hydrophobic solute the oxygen-oxygen and hydrogen-hydrogen radial distribution functions (goo(r), ghh(r)) and the hydrogen bond angle distribution function p(theta) for water molecules in the first hydration shell of the tetramethyl ammonium (TMA) cation were computed using Monte Carlo simulations. goo(r) and ghh(r) were corrected for the effect of solute volume exclusion on the local solvent density so that intrinsic structural changes independent of local solvent density variations could be detected. Comparison of ghh(r) of TMA's first hydration shell water with ghh(r) for bulk water shows subtle but clear evidence of structure formation induced by the ion. These changes in ghh(r) are very similar to those seen experimentally for larger tetra-alkyl ammonium ions in previous neutron diffraction experiments. Larger changes in p(theta) in the first hydration shell of TMA were seen. Comparison of changes in p(theta) with changes in goo(r) and ghh(r) show that the angle distribution function provides the most sensitive way to analyze water structure changes associated with hydrophobic solvation.     

Greater nitrogen and/or phosphorus availability increase plant species’ cover and diversity at a High Arctic polar semidesert

Enhanced nitrogen (N) deposition at high latitudes is a circumpolar phenomenon. Low soil phosphorus (P), however, may limit vegetation responses to increased N inputs. From 2000 to 2002, the effects of N at 0, 0.5 (a rate occurring in Greenland and Iceland) and 5 (equivalent to deposition in areas of Europe) g N m⁻² a⁻¹ and P (0.1 g m⁻² a⁻¹) treatments on plant species’ cover and diversity were determined at a polar semidesert site (ambient deposition c 0.1 g N m⁻² a⁻¹) in Svalbard (79°N). The largest response was to combined 5 g N plus 1 g P m⁻² a⁻¹, where cover of Saxifraga oppositifolia increased c fourfold, density of Salix polaris leaves c ninefold, seedlings of several ‘new’ species (Draba oxycarpa, Saxifraga caespitosa, Sagina nivalis) were established and ‘immigration’ of Bryum arcticum and ‘extinction’ of Schistidium apocarpum were observed. There were fewer, less pronounced, effects on the plant community at 0.5 g N m⁻² a⁻¹. Low P availability did indeed appear to restrict vegetation response to N. There was a trend for plant species’ richness and diversity to increase with 1 g P m⁻² a⁻¹ at 0 and 0.5 g N m⁻² a⁻¹, but not at 5 g N m⁻². Plant species showed individualistic responses so that generalisation by functional type was not possible. Such increased colonisation by moss species of bare soil, and greater densities of previously unrecorded angiosperm seedlings, are not usually observed in more closed (subarctic) tundra as a response to N and P additions. These changes are likely to influence significantly nutrient cycles, whole system carbon budgets and surface energy and water balances. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Reduced variation in transgene expression from a binary vector with selectable markers at the right and left T-DNA borders

A new binary vector for Agrobacterium-mediated plant transformation was constructed, in which two selectable markers, for kanamycin and hygromycin resistance, were placed next to the right and left T-DNA borders, respectively, and a CaMV 35S promoter-driven β-glucuronidase (GUS) gene was placed between these markers as a reporter gene (transgene). Using double antibiotic selection, all transgenic tobacco plants carrying at least one intact copy of the T-DNA expressed the transgene, and this population exhibited reduced variability in transgene expression as compared with that obtained from the parent vector pBI121. Absence of the intact transgene was the major reason for transgenic plants with little or no transgene expression. Integration of truncated T-DNAs was also observed among transgenic plants that expressed the transgene and carried multiple T-DNA inserts. The copy number of fully integrated T-DNAs was positively associated with transgene expression levels in R₀ plants and R₁ progeny populations. Variability due to position effect was determined among 17 plants carrying a single T-DNA insert. The coefficient of variability among these plants was only 35.5%, indicating a minor role for position effects in causing transgene variability. The new binary vector reported here can therefore be used to obtain transgenic populations with reduced variability in transgene expression.     

Human MC4R variants affect endocytosis,trafficking and dimerization revealing multiple cellular mechanisms involved in weight regulation

1. Download : Download high-res image (276KB)
2. Download : Download full-size image

     

Hepatic amoebiasis at high altitude

Latent amoebiasis is aggravated at high altitude. Protean manifestations are common. Fever is usually absent. Liver tenderness is not a feature and may have to be specially elicited. Leucocytosis is rare. Bowel symptoms inspite of presence of intestinal ulcerations are usually absent. Response to treatment with emetine or chloroquin is unsatisfactory and relapse rate is high. These points may interest mountaineers and other sojourners to high altitude.     

Muscle glycolipids in inherited muscular dystrophy of chickens

Gangliosides and neutral glycolipids of muscles from normal and dystrophic chickens were studied. Total glycolipid content of the degenerating muscles was higher than the normal muscles. In addition, the myopathic muscles contained a ganglioside which was absent in the unaffected muscles from normal and dystrophic chickens. Based on the thin-layer chromatographic mobility, treatment with neuraminidases from Vibrio cholerae and Arthrobacter ureafaciens, and reactivity of the asialo-derivative towards anti-ganglio-N-triaosylceramide antibody, the dystrophic-specific ganglioside was tentatively identified as G_M2. Data obtained from young and old dystrophic chickens suggested a direct relationship of this ganglioside to muscular dystrophy.