Modeled responses of terrestrial ecosystems to elevated atmospheric CO2: a comparison of simulations by the biogeochemistry models of the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP)

Although there is a great deal of information concerning responses to increases in atmospheric CO₂ at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated CO₂ is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response of terrestrial ecosystems to elevated CO₂. In this study, we analyze the responses of net primary production (NPP) to doubled CO₂ from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP): BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States, doubled atmospheric CO₂ causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response to doubled CO₂ and the mean annual temperature and annual precipitation of biomes or grid cells indicate that there are negative relationships between precipitation and the response of NPP to doubled CO₂ for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled CO₂ for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO₂ is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO₂ is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO₂ is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial pattern of NPP responses, and represents, in part, conceptual uncertainty about controls over NPP responses. Progress in reducing these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen, and water cycles influence the response of NPP to elevated atmospheric CO₂. Received: 13 December 1996 / Accepted: 20 November 1997     

A Novel Synaptobrevin/VAMP Homologous Protein (VAMP5) Is Increased during In Vitro Myogenesis and Present in the Plasma Membrane

cDNA clones encoding a novel protein (VAMP5) homologous to synaptobrevins/VAMPs are detected during database searches. The predicted 102–amino acid VAMP5 harbors a 23-residue hydrophobic region near the carboxyl terminus and exhibits an overall amino acid identity of 33% with synaptobrevin/VAMP1 and 2 and cellubrevin. Northern blot analysis reveals that the mRNA for VAMP5 is preferentially expressed in the skeletal muscle and heart, whereas significantly lower levels are detected in several other tissues but not in the brain. During in vitro differentiation (myogenesis) of C2C12 myoblasts into myotubes, the mRNA level for VAMP5 is increased ~8- to 10-fold. Immunoblot analysis using antibodies specific for VAMP5 shows that the protein levels are also elevated ~6-fold during in vitro myogenesis of C2C12 cells. Indirect immunofluorescence microscopy and immunoelectron microscopy reveal that VAMP5 is associated with the plasma membrane as well as intracellular perinuclear and peripheral vesicular structures of myotubes. Epitope-tagged versions of VAMP5 are similarly targeted to the plasma membrane.     

Late thrombotic occlusion of a malapposed stent 10 months after intracoronary brachytherapy

We report a patient who received a stent following intracoronary 3-irradiation. Despite a good initial angiographic result, the stent appeared to be not fully expanded on intravascular ultrasound imaging at 6-month follow-up. Four months later, sudden thrombotic occlusion occurred shortly after aspirin cessation.     

Caveolae and sorting in the trans-Golgi network of epithelial cells.

VIP21 is a 21 kDa membrane protein present in TGN-derived transport vesicles isolated from the epithelial MDCK cell line. The membrane topology and subcellular localization of VIP21 were studied using antibodies against the N- and C-terminal domains. The protein was found to have a structure with little or no exposure to the exoplasmic side of the membrane. VIP21 was localized to the TGN, consistent with its presence in TGN-derived transport vesicles. Unexpectedly, it was also very abundant in the non-clathrin-coated plasma membrane invaginations called caveolae. We have previously proposed that VIP21 is associated with glycosphingolipid-enriched membrane domains in the TGN which may be involved in the sorting of proteins into vesicles directed to the apical plasma membrane. Caveolae are specialized lipid structures with similarities to the glycolipid microdomains in the TGN. The presence of VIP21 in both locations suggests that the mechanisms governing inclusion of proteins into caveolar plasma membrane domains are related to the processes of protein and lipid sorting at the TGN. This connection is confirmed by the recent finding that the amino acid sequence of VIP21 is almost identical to that of caveolin, a protein previously localized to caveolae.     

Bordetella pertussis adenylate cyclase: purification and characterization of the toxic form of the enzyme.

Bordetella pertussis produces a calmodulin-sensitive adenylate cyclase (AC) which is an essential virulence factor in mammalian pertussis. Here we report the purification and characterization of the toxic form of the enzyme, which penetrates eukaryotic cells and generates high levels of intracellular cAMP. This form was purified from an extract of B.pertussis strain carrying a recombinant plasmid which over-produced both enzymatic and toxic activities of the enzyme. Western blot analysis of the extract using anti-B.pertussis AC antibodies detected only one protein of 200 kd. However, gel filtration of the extract resolved two peaks of enzymatic activity. The first peak of aggregated material contained greater than 70% of the total enzymatic activity, and the second peak contained the majority of the toxic activity. Purification of the enzyme from both peaks yielded proteins of 200 kd, with similar biochemical and immunological properties. Yet only the enzyme purified from the second peak could penetrate human lymphocyte and catalyse the formation of intracellular cAMP. B.pertussis AC gene expressed in Escherichia coli produced a calmodulin-dependent enzyme of 200 kd, which lacked lymphocyte penetration capacity. It is proposed that a post-translational modification that occurs in B.pertussis but not in E.coli confers upon the 200 kd protein of B.pertussis AC the toxic properties.     

Mutagenicity evaluation of HC Blue No. 1 and HC Blue No. 2, II. Effect on the in vitro induction of unscheduled DNA synthesis in rat, mouse, rabbit, hamster, and monkey primary hepatocytes

2 hair dyes, HC Blue No. 1 and HC Blue No. 2, were evaluated for the in vitro induction of unscheduled DNA synthesis (UDS) in primary hepatocytes of rat, mouse, hamster, rabbit and monkey. NC Blue No. 1, which is identified as a carcinogen by the National Toxicology Program, induced UDS in all 5 systems. HC Blue No. 2, which is identified as a non-carcinogen, induced UDS in rat, mouse, hamster and rabbit primary hepatocytes. 3-Methylcholanthrene and methyl methanesulfonate were used as positive controls to determine the sensitivity of the test system.     

An intragenic distribution bias of DNA uptake sequences in <Emphasis Type="Italic">Pasteurellaceae</Emphasis> and <Emphasis Type="Italic">Neisseriae</Emphasis>

   

Most sequenced strains from Pasteurellaceae and Neisseriae contain hundreds to thousands of uptake sequence (US) motifs in their genome, which are associated with natural competence for DNA uptake. The mechanism of their recognition is still unclear, and I searched for intragenic location patterns of these motifs for clues about their distribution. In all cases, one orientation of the US has a higher occurrence in the reading frame, and in all Pasteurellaceae, the US and the reverse complement motifs are biased towards the gene termini. These findings could help design experimental set-ups to study preferential DNA uptake, thereby further unravelling the phenomenon of natural competence.