A Simulation of Temporal and Spatial Variations in Carbon at Landscape Level: A Case Study for Lake Abitibi Model Forest in Ontario,Canada

Using a case study of the Lake Abitibi Model Forest (LAMF), this study aims to assess the temporal and spatial variability in carbon storage during 1990–2000, and to present a comprehensive estimation of the carbon budget for LAMF's ecosystems. As well, it provided the information needed by local forest managers to develop ecological and carbon-based indicators and monitor the sustainability of forest ecosystems. Temporal and spatial carbon dynamics were simulated at the landscape level using ecosystem model TRIPLEX1.0 and Geographical Information System (GIS). The simulated net primary productivity (NPP) and carbon storage in forest biomass and soil were compared with field data and results from other studies for Canada's boreal forests. The results show that simulated NPP ranged from 3.26 to 3.34 tC ha⁻¹ yr⁻¹ in the 1990s and was consistent with the range measured during the Boreal Ecosystem-Atmosphere Studies (BOREAS) in central Canada. Modeled NPP was also compared with the estimation from remote sensing data. The density of total above-and belowground biomass was 125.3, 111.8, and 106.5 tC ha⁻¹ for black spruce, trembling aspen, and jack pine in the LAMF ecosystem, respectively. The total carbon density of forested land was estimated at 154.4 tC ha⁻¹ with the proportion of 4:6 for total biomass and soil. The analysis of net carbon balance of ecosystem suggested that the LAMF forest ecosystem was acting as a carbon sink with an allowable harvest in the 1990s.     

The in utero diagnosis and management of alloimmune thrombocytopenia

A case is presented in which percutaneous umbilical sampling (PUBS) was utilized in the second and third trimesters for the diagnosis and management of a pregnancy at risk for neonatal alloimmune thrombocytopenia (NAIT).     

Cells of the connective tissue differentiate and migrate into pollen sacs

In angiosperms, archesporial cells in the anther primordium undergo meiosis to form haploid pollen, the sole occupants of anther sacs. Anther sacs are held together by a matrix of parenchyma cells, the connective tissue. Cells of the connective tissue are not known to differentiate. We report the differentiation of parenchyma cells in the connective tissue of two Gordonia species into pollen-like structures (described as pseudopollen), which migrate into the anther sacs before dehiscence. Pollen and pseudopollen were distinguishable by morphology and staining. Pollen were tricolpate to spherical while pseudopollen were less rigid and transparent with a ribbed surface. Both types were different in size, shape, staining and surface architecture. The ratio of the number of pseudopollen to pollen was 1:3. During ontogeny in the connective tissue, neither cell division nor tetrad formation was observed and hence pseudopollen were presumed to be diploid. Only normal pollen germinated on a germination medium. Fixed preparations in time seemed to indicate that pseudopollen migrate from the connective tissue into the anther sac.     

Hopanoid Biosynthesis and Function in Bacteria

   Hopanoids are pentacyclic triterpenoid lipids occurring in bacteria. They are synthesized from isopentenyl units which are formed in a new biosynthetic route leading to isopentenyl diphosphate. Six C₅ units are joined to form squalene, the immediate precursor in hopanoid synthesis. In a highly complex cyclization reaction that shares considerable similarities with that of oxidosqualene to sterols, the hopane skeleton is formed from squalene by the squalene-hopene cyclase. Recent elucidation of the X-ray structure of this membrane-bound cyclase has shed some light on the properties of this unusual enzyme. The active site is located in a cavity within the enzyme. The squalene substrate diffuses through a channel structure from the membrane into this cavity and is there transformed into hopene. Polar side chains are attached to hopene resulting in the amphiphilic molecular structure of many hopanoids. These hopanoids are membrane components involved in regulating membrane fluidity and stability. However, the many structural variants of hopanoids indicate that they may have other interesting but as yet unknown functions.