Lepidium latifolium: plant nutrient competition-soil interactions

Exotic weeds are invading rangelands of the western United States at unprecedented rates. Understanding plant-soil relationships and competitive interactions of invasive weeds is crucial in long-term control strategies. In a greenhouse experiment, we investigated the influence of soil nutrient depletion on plant growth and plant competition between the exotic invasive weeds, Lepidium latifolium (invading wetlands) and Bromus tectorum (invading a multitude of habitats). Plants were grown individually and in combination until L. latifolium flowered, then roots and aboveground mass were harvested. Soil in individual pots was homogenized, subsamples collected for nutrient analyses, and the soil was re-planted to the same species, grown, and harvested twice more for a total of three growth cycles. As nutrient supplying capacity of the soil declined through growth cycles, aboveground mass of L. latifolium decreased significantly (PА.05) and growth potential of B. tectorum surpassed that of L. latifolium. Only bicarbonate-extractable soil ortho-P positively correlated with plant mass of L. latifolium. A separate experiment demonstrated that L. latifolium has a narrow window of soil water potentials for optimal growth; greatest growth at -20 kPa with significantly declining growth at saturation and -400 kPa. Our data suggest that L. latifolium primarily invades wetlands because the high soil water content reduces tortuosity and allows efficient transport of nutrients to this sparsely rooted species. When soil moisture and/or the nutrient supplying capacity of the soil declines, plants with greater root density can out-compete L. latifolium. Monocultural stands of L. latifolium may be self-limiting in time as available nutrients, particularly P, are biocycled to drier upper soil layers.     

Chemoenzymatic synthesis of homogeneous ultralow molecular weight heparins

Ultralow molecular weight (ULMW) heparins are sulfated glycans that are clinically used to treat thrombotic disorders. ULMW heparins range from 1500 to 3000 daltons, corresponding from 5 to 10 saccharide units. The commercial drug Arixtra (fondaparinux sodium) is a structurally homogeneous ULMW heparin pentasaccharide that is synthesized through a lengthy chemical process. Here, we report 10- and 12-step chemoenzymatic syntheses of two structurally homogeneous ULMW heparins (MW = 1778.5 and 1816.5) in 45 and 37% overall yield, respectively, starting from a simple disaccharide. These ULMW heparins display excellent in vitro anticoagulant activity and comparable pharmacokinetic properties to Arixtra, as demonstrated in a rabbit model. The chemoenzymatic approach is scalable and shows promise for a more efficient route to synthesize this important class of medicinal agent.     

Neutral models for the analysis of broad-scale landscape pattern

The relationship between a landscape process and observed patterns can be rigorously tested only if the expected pattern in the absence of the process is known. We used methods derived from percolation theory to construct neutral landscape models,i.e., models lacking effects due to topography, contagion, disturbance history, and related ecological processes. This paper analyzes the patterns generated by these models, and compares the results with observed landscape patterns. The analysis shows that number, size, and shape of patches changes as a function of p, the fraction of the landscape occupied by the habitat type of interest, and m, the linear dimension of the map. The adaptation of percolation theory to finite scales provides a baseline for statistical comparison with landscape data. When USGS land use data (LUDA) maps are compared to random maps produced by percolation models, significant differences in the number, size distribution, and the area/perimeter (fractal dimension) indices of patches were found. These results make it possible to define the appropriate scales at which disturbance and landscape processes interact to affect landscape patterns.     

Acidic mammalian chitinase in asthmatic Th2 inflammation and IL-13 pathway activation

Chitin is a surface component of parasites and insects, and chitinases are induced in lower life forms during infections with these agents. Although chitin itself does not exist in humans, chitinases are present in the human genome. We show here that acidic mammalian chitinase (AMCase) is induced via a T helper-2 (Th2)-specific, interleukin-13 (IL-13)-mediated pathway in epithelial cells and macrophages in an aeroallergen asthma model and expressed in exaggerated quantities in human asthma. AMCase neutralization ameliorated Th2 inflammation and airway hyperresponsiveness, in part by inhibiting IL-13 pathway activation and chemokine induction. AMCase may thus be an important mediator of IL-13-induced responses in Th2-dominated disorders such as asthma.     

Ordering in a fluid inert gas confined by flat surfaces

High-resolution transmission electron microscopy images of room-temperature fluid xenon in small faceted cavities in aluminum reveal the presence of three well-defined layers within the fluid at each facet. Such interfacial layering of simple liquids has been theoretically predicted, but observational evidence has been ambiguous. Molecular dynamics simulations indicate that the density variation induced by the layering will cause xenon, confined to an approximately cubic cavity of volume approximately 8 cubic nanometers, to condense into the body-centered cubic phase, differing from the face-centered cubic phase of both bulk solid xenon and solid xenon confined in somewhat larger (>/=20 cubic nanometer) tetradecahedral cavities in face-centered cubic metals. Layering at the liquid-solid interface plays an important role in determining physical properties as diverse as the rheological behavior of two-dimensionally confined liquids and the dynamics of crystal growth.