Subarctic forest-tundra vegetation gradients: The sigmoid wave hypothesis

Abstract. Spatial changes in tree and upland tundra cover in response to a complex environmental gradient and to landscape factors were investigated in the high subarctic forest-tundra of NW Canada. Vegetation and terrain studies provided ground truth for a grid of 1314 air photos which covered 24 % of the Canadian high subarctic and some of the adjacent low subarctic and low arctic. Across the high subarctic, gradual spatial change in % cover of tree and upland tundra vegetation is typical at both high and low cover values, with more rapid change occurring at intermediate cover. Cover gradients of zonal tree and tundra vegetation in the forest-tundra region in general follow a sigmoid pattern. Tundra and tree patch sizes increase in area and variability with higher tundra and tree cover, respectively.     

Mouse blastocyst immunosurgery with commercial antiserum to mouse erythrocytes

Summary Immunosurgery is a useful technique for the isolation of inner cell masses from murine blastocysts. Conventionally, rabbit antisera made ad hoc against murine splenic or fetal cells or fibroblasts have been used as antibody sources. We investigated the feasibility of using commercially available rabbit antiserum to murine erythrocytes (anti-RBC) and compared it with rabbit antiserum generated ad hoc to murine L-cells (anti-L-cell). Our results indicate that anti-RBC is at least as effective as anti-L-cell serum for the immunosurgical isolation of inner cell masses, which became either miniblastocysts (later forming outgrowths) or embryoid bodies (undergoing ectoderm-endodermlike differentiation within 48 h). Because anti-RBC is commercially available, the technical modification described herein increases the accessibility of the immunosurgical protocol for the isolation of murine inner cell masses.     

The role of mineral compounds and chemical conditions in the binding of phosphate in the Ems estuary

In the Ems estuary the gradients in dissolved phosphorus and iron are non-conservative and opposite. The relations between different mineral compounds, environmental conditions and phosphate concentrations were studied, in an attempt to explain this. Laboratory experiments on water samples from the reaches with high concentrations of phosphate and of suspended matter revealed a low concentration of calcite-bound phosphorus in the middle reaches of the estuary (only 0.07%). Therefore, it is concluded that calcite possibly plays only a modest role in phosphate distribution in the Ems estuary. Further experiments revealed that nearly 70% of the particulate inorganic phosphorus is iron-bound. It is demonstrated that organic coatings on minerals inhibit phosphate release at a low redox potential. Moreover, the organic matter itself contained c. 20% of particulate phosphorus. Approximately 10% of the particulate phosphorus may be associated with clay minerals. It is concluded that in addition to biological processes, the phosphorus associated with ironoxyhydroxides may be crucial for the seasonal variation of the phosphate concentrations in the water.     

High-performance liquid chromatographic separation of aprotinin-like inhibitors and their determination in very small amounts

A reversed-phase high-performance liquid chromatographic method for the determination and quantitative recovery of fully active aprotinin (the basic pancreatic trypsin inhibitor or Kunitz inhibitor) and aprotinin-like inhibitors in amounts down to 0.5 μg is reported. The method, which allows separation of aprotinin isoinhibitors characterized by small differences in the primary structure with respect to aprotinin itself, appears to be suitable for the quantitation and identification of aprotinin-like inhibitors in human biological fluids, in which they appear to be present at very low levels.     

A Glycoprotein Expressed by Human Fibrous Astrocytes is a Hyaluronate-Binding Protein and a Member of the CD44 Family

We have isolated and characterized an antigen from normal human brain called p80, so called because it migrated with an Mr of 80 kDa on SDS PAGE. The Mr of 80 kDa consists of a protein of about 55-60 kDa and carbohydrate (20-25 kDa). The carbohydrate is almost entirely of the N-linked type, although a small amount of O-linked carbohydrate was detected. Cross-reactivity with monoclonal antibodies A3D8 and A1G3 showed that p80 could therefore be considered an isoform of the CD44 adhesion molecules. In addition, specific binding to hyaluronate which was not competed for by proteoglycan demonstrated that it involved different sites than the proteoglycan binding sites. We also observed that fucoidan and dextran sulphate increased the binding by 200-250% while chondroitin sulphate C also increased the binding but to a lesser extent. Heparin, heparan sulphate and chondroitin sulphates A and B did not have such an effect. The binding of p80 to hyaluronate was pH dependent with a maximum at pH 6.4. We concluded that p80 was an astrocyte specific adhesion molecule.     

Ontogenetic trajectories and early shape differentiation of treehopper pronota (Hemiptera: Membracidae)

Membracids (family: Membracidae), commonly known as treehoppers, are recognizable by their enlarged and often elaborated pronota. Much of the research investigating the development and evolution of this structure has focused on the fifth instar to adult transition, in which the pronotum undergoes the largest transformation as it takes on adult identity. However, little is known about the earlier nymphal stages, the degree to which the pronotum develops at these timepoints, and how development has changed relative to the ancestral state. Here, we studied the nymphal stages and adults of five morphologically distinct membracid species and of Aetalion reticulatum (family: Aetalionidae), the outgroup which was used as an ancestral state proxy. We found that shape differentiation in the pronotum of membracids can start as early as the second instar stage. Most shape differentiation occurs within the nymphal stages and not in the embryo since the shape of the first-instar pronotum did not differ from the outgroup species in all but one species we investigated. We found the anterior–posterior axis of the pronotum elongated at a faster relative rate in membracid species than in A. reticulatum, which contributed to the development of exaggerated pronotal size. Finally, we found differences in the morphogenesis of shape across species. We suggest this is due to the developmental and evolutionary divergence of differential growth patterning of the dorsal surface of the pronotum, not only across species, but also between stages within the same species. This lability may contribute to the evolvability and diversification of the membracid pronotum.     

Characteristics and Regulatory Properties of the H+-ATPase in a Plasma Membrane Fraction Purified from Arabidopsis thaliana

The aqueous two-phase partitioning technique was utilized to isolate a plasma membrane (PM) fraction from etiolated seedlings of Arabidopsis thaliana. The purification procedure adopted yielded a fraction highly enriched in PM as compared to inner membranes, with a recovery of about 30%, as judged from the activities of PM markers such as vanadate-sensitive ATPase, FC binding and UDP-glucose sterol glucosyltransferase. The purified PM fraction displayed vanadate-sensitive H⁺ pumping activity. Its purity was confirmed by the biochemical characteristics of its ATPase activity assayed in the absence of Ca²⁺: sensitivity to vanadate (IC₅₀ ca. 1 μM), Mg²⁺-dependence, insensitivity to molybdate, oligomycin and nitrate, pH optimum at 6.6. The PM H⁺-ATPase activity was stimulated by fusicoccin and by a controlled treatment of the PM with trypsin. In both cases stimulation was much stronger on the activity assayed at pH 7.5 than on the activity at pH 6.6. Moreover, neither fusicoccin nor the treatment with trypsin stimulated the portion of activity (30 to 40% at pH 7.5) which decayed upon preincubation of the PM in assay medium without ATP.     

Regulated expression of the rat medium chain hydrolase gene in transgenic rape seed

Medium chain hydrolase (MCH) is an enzyme which regulates the chain length of fatty acid synthesis specifically in the mammary gland of the rat. During lactation, MCH interacts with fatty acid synthase (FAS) to cause premature release of acyl chains, thus providing medium chain fatty acids for synthesis of milk fat. In this study we have investigated the ability of rat MCH to interact with the phylogenetically more distant FAS structure present in plant systems and to cause a perturbation of fatty acid synthesis. Inin vitro experiments, addition of purified MCH to rapeseed homogenates was found to cause a significant perturbation of fatty acid synthesis towards medium chain length products. The rat MCH gene was expressed in transgenic oilseed rape using a seed specific rape acyl carrier protein (ACP) promoter and a rape ACP plastid targeting sequence. Western analysis showed MCH protein to be present in transgenic seed and for its expression to be developmentally regulated in concert with storage lipid synthesis. The chimaeric preprotein was correctly processed and immunogold labelling studies confirmed MCH to be localized within plastid organelles. However, fatty acid analysis of oil from MCH-expressing rape seed showed no significant differences to that from control seed.