Effect of HCO - 3 concentration in the absorption solution on the energetic coupling of H+-cotransports in roots of Zea mays L.

The effect of HCO ₃ ^- on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO₂ partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H⁺ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO ₃ ^- accumulation were slowed down, while ⁸⁶Rb⁺ uptake and K⁺ accumulation rates were increased by HCO ₃ ^- . These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H⁺ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO₂/H₂CO₃/HCO ₃ ^- accelerated the diffusion of equivalent H⁺ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW fresh weight - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - J_aa acetic acid influx - J_K ⁺ K⁺ influx - J_Pi orthophosphate influx - Mes 2-(N-morpholino)ethanesulfonic acid - pCO₂ CO₂ partial pressure - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Characterization of the histamine releasing effect of neurotensin in the rat heart

Bolus injections of neurotensin (NT) in the rat perfused heart elicited a transient, dose-dependent histamine release. The histamine releasing effect of NT appears to be independent of the heart rate and coronary perfusion pressure and it was not influenced by atropine, propanolol, prazosin, methysergide, ketanserin, indomethacin, morphine, lidocaine or by removal of the atria. However, it was potentiated by adenosine, inhibited by sub-stimulatory concentrations of NT and the mast cell membrane stabilizing drug cromoglycate but was unaltered by the calcium antagonist verapamil. The absence of calcium in the heart perfusate suppressed the histamine releasing effect of NT. These results suggest that the histamine releasing effect of NT in the rat heart results from a direct effect on ventricular mast cells and is calcium-dependent.     

Colorimetric determination of catechol siderophores in microbial cultures

A highly sensitive spectrophotometric method for the selective detection of catechol compounds such as catechol siderophores (e.g., enterobactin) is described. The basis of the method involves the ability of the vicinal aromatic hydroxyl groups under acidic conditions to bring about a reduction of Fe3+ (from ferric ammonium citrate) to Fe2+. Detection of Fe2+ in the presence of Fe3+ is made with 1,10-phenanthroline under previously established conditions. The assay mixture is heated at 60 degrees C for 1 h to accelerate the development of color which is subsequently measured at 510 nm. The Beer-Lambert law is obeyed over the range of 0.16 to 60 microM 2,3-dihydroxybenzoic acid. Compared to the Arnow nitration method, the assay is more responsive, is approximately seven times more sensitive, and is effective with catechols substituted at positions 3 and 4. The method gives positive results with catechols such as DL-DOPA, L-dopamine, (+/-)-epinephrine, and DL-norepinephrine. Very rapid color development is obtained with ascorbic acid and p-diols, while m-diols are poorly detected. Low degrees of reactivity are shown by hydroxylamino and hydroxamate compounds. Phenolic, sulfydryl, indolyl, and quinonyl derivatives do not interfere with the reaction. The method has been adapted to determine catechol compounds in the culture medium of bacterial cells grown at different iron concentrations.     

Two outer membrane transport systems for vitamin B12 in Salmonella typhimurium.

The involvement of an outer membrane transport component for vitamin B12 uptake in Salmonella typhimurium, analogous to the btuB product in Escherichia coli, was investigated. Mutants of S. typhimurium selected for resistance to bacteriophage BF23 carried mutations at the btuB locus (butBS) (formerly called bfe, at the analogous map position as the E. coli homolog) and were defective in high-affinity vitamin B12 uptake. The cloned E. coli btuB gene (btuBE) hybridized to S. typhimurium genomic DNA and restored vitamin B12 transport activity to S. typhimurium btuBS mutants. An Mr-60,000 protein in the S. typhimurium outer membrane was repressed by growth with vitamin B12 and was eliminated in a btuBS mutant. The btuBS product thus appears to play the same role in vitamin B12 transport by S. typhimurium as does the E. coli btuBE product. A second vitamin B12 transport system that is not present in E. coli was found by cloning a fragment of S. typhimurium DNA that complemented btuB mutants for vitamin B12 utilization. In addition to this plasmid with a 6-kilobase insert of S. typhimurium DNA, vitamin B12 utilization by E. coli btuB strains required the btuC and btuD products, necessary for transport across the cytoplasmic membrane, but not the btuE or tonB product. The plasmid conferred low levels of vitamin B12-binding and energy-dependent transport activity but not susceptibility to phage BF23 or utilization of dicyanocobinamide. The cloned S. typhimurium DNA encoding this new transport system did not hybridize to the btuBE gene or to E. coli chromosomal DNA and therefore does not carry the S. typhimurium btuBS locus. Increased production of an Mr -84,000 polypeptide associated with the outer membrane was seen. The new locus appears to be carried on the large plasmid in most S. typhimurium strains. Thus S. typhimurium possesses both high- and low-affinity systems for uptake of cobalamins across the outer membrane.     

Characterization of Xanthomonas campestris Pathovars by rRNA Gene Restriction Patterns

Genomic DNA of 191 strains of the family Pseudomonadaceae, including 187 strains of the genus Xanthomonas, was cleaved by EcoRI endonuclease. After hybridization of Southern transfer blots with 2-acetylamino-fluorene-labelled Escherichia coli 16+23S rRNA probe, 27 different patterns were obtained. The strains are clearly distinguishable at the genus, species, and pathovar levels. The variability of the rRNA gene restriction patterns was determined for four pathovars of Xanthomonas campestris species. The 16 strains of X. campestris pv. begoniae analyzed gave only one pattern. The variability of rRNA gene restriction patterns of X. campestris pv. manihotis strains could be related to ecotypes. In contrast, the variability of patterns observed for X. campestris pv. malvacearum was not correlated with pathogenicity or with the geographical origins of the strains. The highest degree of variability of DNA fingerprints was observed within X. campestris pv. dieffenbachiae, which is pathogenic to several hosts of the Araceae family. In this case, variability was related to both host plant and pathogenicity.     

The distribution of coastal fish eDNA sequences in the Anthropocene

Aim

Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.

Location

Tropical, temperate and polar coastal areas.

Time period

Present day.

Major taxa studied

Marine fishes.

Methods

We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.

Results

We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.

Main conclusions

Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions.     

Effects of arachidonic acid and indomethacin on the in vitro release of prostaglandins by aortic strips of spontaneously hypertensive rats

Aortic strips removed from spontaneously hypertensive (SH) rats and preincubated with arachidonic acid (1.0 X 10(-5) g/ml) for 15 min produced two times more prostaglandin (PG) like material than aortae unexposed to the precursor of PG biosynthesis. The stimulating effect of arachidonic acid was largely inhibited by indomethacin (1.0 X 10(-5) g/ml). Also, the release of PG-like material by aortic strips derived from SH rats treated with an intravenous injection of indomethacin (10 mg/kg) was inhibited by 74% compared with the control tissues. These results raised the possibility that the in vivo conversion of arachidonic acid by large arteries of SH rats may contribute to the hypotensive effect of this PG precursor in SH rats.