Do hotspots fall within protected areas? A Geographic Approach to Planning analysis of regional freshwater biodiversity

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Evidence of local adaptation to coarse-grained environmental variation in Arabidopsis thaliana

Plants can achieve an appropriate phenotype in particular conditions either constitutively or plastically, depending in part on the grain size of the environmental conditions being considered. Coarse-grained environmental variation should result in selection for local adaptation and no selection on plasticity to novel levels of the coarse-grained environmental factors. We tested the hypotheses that natural populations of the well-studied model system Arabidopsis thaliana are locally adapted to spatially coarse-grained environmental variation, and that the photoperiodic regime per se is at least partially responsible for that local adaptation, by exposing natural populations to photoperiodic regimes characteristic of their native and foreign (novel) environments. We also tested the hypothesis that plasticity to novel photoperiodic regimes should appear random. We found that populations showed evidence of local adaptation at a spatially coarse grain, although not to photoperiodic regime per se. We also found that the plasticities to novel photoperiodic regimes appeared random and did not generally show evidence of adaptive divergence. Our study highlights the need for caution in extrapolating from the finding of local adaptation to the causes of local adaptation.     

Agrobacterium ParA/MinD-like VirC1 spatially coordinates early conjugative DNA transfer reactions

Agrobacterium tumefaciens translocates T-DNA through a polar VirB/D4 type IV secretion (T4S) system. VirC1, a factor required for efficient T-DNA transfer, bears a deviant Walker A and other sequence motifs characteristic of ParA and MinD ATPases. Here, we show that VirC1 promotes conjugative T-DNA transfer by stimulating generation of multiple copies per cell of the T-DNA substrate (T-complex) through pairwise interactions with the processing factors VirD2 relaxase, VirC2, and VirD1. VirC1 also associates with the polar membrane and recruits T-complexes to cell poles, the site of VirB/D4 T4S machine assembly. VirC1 Walker A mutations abrogate T-complex generation and polar recruitment, whereas the native protein recruits T-complexes to cell poles independently of other polar processing factors (VirC2, VirD1) or T4S components (VirD4 substrate receptor, VirB channel subunits). We propose that A. tumefaciens has appropriated a progenitor ParA/MinD-like ATPase to promote conjugative DNA transfer by: (i) nucleating relaxosome assembly at oriT-like T-DNA border sequences and (ii) spatially positioning the transfer intermediate at the cell pole to coordinate substrate-T4S channel docking.     

Evolution of intrahepatic carbon, nitrogen, and energy metabolism in a D-galactosamine-induced rat liver failure model

A clearer picture of the hepatic metabolic pathways affected by fulminant hepatic failure (FHF) would help develop nutritional support and nonsurgical therapies for FHF. We characterized the evolution of hepatic metabolism in a rat model of FHF using an isolated perfused liver system together with a mass-balance model of intermediary metabolism. Principal component analysis (PCA) was used to identify potential new sensitive markers for FHF. To induce FHF, rats were given two D-galactosamine injections under fasting conditions. Controls were fasted only. Livers were harvested 1, 4, 8, and 12 h later and perfused with Eagle minimal essential medium supplemented with amino acids and bovine serum albumin, and equilibrated with 95% O2/5% CO2. At the 1 h time point, lactate release increased concomitant with a decrease in gluconeogenesis, TCA cycle and mitochondrial electron transport fluxes. At 4 h, amino acid metabolism and urea cycle fluxes were significantly depressed. By 8 h, gluconeogenesis had switched to glycolysis. By 12 h, amino acid metabolism was broadly inhibited, and there was a net release of many amino acids. Mass-balance analysis shows that the main source of ATP production in the FHF liver gradually changed from mitochondrial oxidative phosphorylation to glycolysis. PCA suggests that a linear combination of glucose, lactate, and glutamine concentrations in arterial plasma is a sensitive marker for FHF. We conclude that D-galactosamine causes early mitochondrial dysfunction while glycolytic ATP synthesis remains functional. Markers that are indirectly linked to these pathways may be used to evaluate the progression of FHF.     

Quantitative effects of thermal injury and insulin on the metabolism of the skeletal muscle using the perfused rat hindquarter preparation

Injury from a severe burn or trauma can propel the body into a hypermetabolic state that can lead to the significant erosion of lean muscle mass. Investigations describing this process have been somewhat limited due to the lack of adequate experimental models. Here we report the use of a perfused rat hindquarter preparation to study the consequences of a moderate burn injury (approximately 20% total body surface area), with or without the addition of exogenous insulin (12.5 mU/mL), on the fluxes of major metabolites across the isolated skeletal muscle. The metabolic flux data was further analyzed using metabolic flux analysis (MFA), which allows for the estimation of the impact of these conditions on the intracellular muscle metabolism. Results indicate that this model is able to capture the increased rate of proteolysis, glutamine formation, and the negative nitrogen balance associated with the burn-induced hypermetabolic state. The inclusion of exogenous insulin resulted in significant changes in several fluxes, including an increase in the metabolism of glucose and the flux through the pentose phosphate pathway, as well as a reduction in the metabolism of glutamine, alanine, and leucine. However, insulin administration did not affect the nitrogen balance or the rate of proteolysis in the muscle, as has been suggested using other techniques. The use of the perfused hindquarter model coupled with MFA is a physiologically relevant and experimentally flexible platform for the exploration of skeletal muscle metabolism under catabolic conditions, and it will be useful in quantifying the specific metabolic consequences of other therapeutic advances.     

Structure and evolution of ribonuclease P RNA in Gram-positive bacteria.

The sequences and structures of RNase P RNAs of some Gram-positive bacteria, e.g. Bacillus subtilis, are very different than those of other bacteria. In order to expand our understanding of the structure and evolution of RNase P RNA in Gram-positive bacteria, gene sequences encoding RNase P RNAs from 10 additional species from this evolutionary group have been determined, doubling the number of sequences available for comparative analysis. The enlarged data set allows refinement of the secondary structure model of these unusual RNase P RNAs and the identification of potential tertiary interactions between P10.1 and L12, and between L5.1 and L15.1. The newly-obtained sequences suggest that RNase P RNA underwent an abrupt, dramatic restructuring in the ancestry of the low-G+C Gram-positive bacteria after the divergence of the branches leading to the 'Clostridia and relatives' and the remaining low-G+C Gram-positive species. The unusual structures of the RNase P RNAs of Mycoplasma hyopneumoniae and M.floccularre are apparently derived from RNAs with Bacillus-like structure rather than from intermediate, partially restructured ancestral RNAs. The structure of the RNase P RNA from the photosynthetic Heliobacillus mobilis supports the relationship of this specie with Bacillus and Staphylococcus rather than the 'Clostridia and relatives' as suggested by the sequences of their small-subunit ribosomal RNAs.     

Minimum effective release rate of antifoulants (2): Measurement of the effect of TBT and zosteric acid on hard fouling

A membrane perfusion device for determining minimum effective release rates (MERR) of antifouling agents is described. The technique is applied to known biocidal agents and to a new prospective natural antifouling agent. This method allows controlled and reproducible release rates to be achieved independent of water chemistry and flow near the immersed surface. Unlike constant concentration methods, the device acts similarly to a painted surface, allowing establishment of diffusion gradients, thereby allowing fouling organisms to exhibit natural chemotactic responses to the released toxin. The method was applied at four remote sites to natural populations of fouling organisms. The MERRs of known (tributyltin chloride, dibutyltin chloride, and cupric ion) and experimental (zosteric acid) AF agents were determined. The effective release rates of cupric ion and organotin were consistent with immersed panel data and field observation of ship hulls, while the effective rate of zosteric acid, determined at two test sites, was much higher. Such data provide coatings formulators with valuable information relating to the suitability of an agent for AF coating use.     

Vasopressin inhibits diuresis induced by water immersion in humans.

We tested the hypothesis that 1-desamino-8-D-arginine vasopressin (DDAVP), a V2-receptor agonist, could inhibit the diuresis induced by water immersion in humans. Water and electrolyte excretion, plasma atrial natriuretic factor concentration, and plasma aldosterone concentration were measured initially and after 3 h of water immersion in 13 healthy sodium-replete men given either placebo or 20 micrograms of intranasal DDAVP. Guanosine 3',5'-cyclic monophosphate and urea excretion and urine osmolality were also determined. DDAVP inhibited the diuresis induced by water immersion in men: 758 +/- 168 (SE) ml/3 h in the placebo group vs. 159 +/- 28 ml/3 h in the DDAVP group (P less than 0.05). After 3 h of water immersion, plasma atrial natriuretic factor concentrations were increased from 11 +/- 2 to 20 +/- 4 pg/ml in the placebo group and from 14 +/- 2 to 33 +/- 4 pg/ml in the DDAVP group (P less than 0.05). Plasma aldosterone concentrations were decreased from 98 +/- 18 to 45 +/- 6 pg/ml in the placebo group (P less than 0.05) and from 54 +/- 17 to 25 +/- 5 pg/ml in the DDAVP group (P less than 0.05). Despite these changes in aldosterone and atrial natriuretic factor concentrations, which should increase sodium excretion, DDAVP decreased the natriuresis induced by water immersion in humans: 56 +/- 8 meq Na+/3 h in the placebo group vs. 36 +/- 6 meq Na+/3 h in the DDAVP group (P less than 0.05). DDAVP may be used to prevent the diuresis associated with central redistribution of blood volumes that occur during water immersion.(ABSTRACT TRUNCATED AT 250 WORDS)