Relation between algal available phosphate in the sediments of the River Garonne and chemically-determined phosphate fractions

Concentrations of total and inorganic phosphate were measured in forty-seven sediments of the River Garonne (France) using an anion resin, NaOH 0.1 M, Ca-NTA and Na-EDTA. Algal available P was measured using Scenedesmus crassus. The sediments presented a wide range of Tot-P concentrations (226 to 923 μg g⁻¹). Resin P varied between 1.1 to 55.5 μg g⁻¹ and NaOH-P between 3.5 to 262 μg g⁻¹. NTA-P and EDTA-P varied between 13.9 and 178 μg g⁻¹ and between 14.4 to 261 μg g⁻¹ respectively. Algal available P varied between 8.8 to 262 μg g⁻¹/ All forms of P are highly correlated and specially with algal available P (r = 0.70, 0.77, 0.88 and 0.77 for resin-P, NaOH-P, NTA-P and EDTA-P respectively). Nevertheless the partial correlation between EDTA-P and algal available P dropped to 0.05 when the concentration of NTA-P was considered as constant, indicating a spurious correlation with apatitic phosphate (extracted by Na-EDTA). Because of the strongest R ² and the lowest standard error of estimate, phosphate extracted by Ca-NTA can be considered as the best predictor of algal available phosphate.     

A new spin label method for the measurement of erythrocyte internal microviscosity

A new spin-label method for the measurement of the internal microviscosity of erythrocyte is presented. The spin label used is 2,2',5,5'-tetramethyl-3-maleimidopyrrolidinyl-N-oxyl (MAL-5) which penetrates inside the red blood cell and binds covalently on cytoplasmic glutathione. After washing off the external label, 98% of the electron paramagnetic signal is due to the labelled glutathione. This signal allows one to measure the rotational correlation time of the label. A calibration curve established with spin-labelled glutathione in sucrose solutions of increasing viscosity is used to convert the measured rotation times into viscosity units. This method avoids the use of unphysiological salts like potassium ferricyanide, and permits the study of red blood cells in various suspension media. In normal human subjects, the mean value of microviscosity is 4.45 +/- 0.16 mPa . s at 20 degrees C in isotonic saline (25 subjects) and 6 +/- 0.25 mPa . s in plasma. The variations of microviscosity as a function of the osmolarity of the medium are explained according to a theoretical model taking into account the variations of the red blood cell volume and the viscometric properties of haemoglobin.     

Genotypic variation in source and sink traits affects the response of photosynthesis and growth to elevated atmospheric CO2

This study aimed to understand the response of photosynthesis and growth to e-CO₂ conditions (800 vs. 400 μmol mol⁻¹) of rice genotypes differing in source–sink relationships. A proxy trait called local C source–sink ratio was defined as the ratio of flag leaf area to the number of spikelets on the corresponding panicle, and five genotypes differing in this ratio were grown in a controlled greenhouse. Differential CO₂ resources were applied either during the 2 weeks following heading (EXP1) or during the whole growth cycle (EXP2). Under e-CO₂, low source–sink ratio cultivars (LSS) had greater gains in photosynthesis, and they accumulated less nonstructural carbohydrate in the flag leaf than high source–sink ratio cultivars (HSS). In EXP2, grain yield and biomass gain was also greater in LSS probably caused by their strong sink. Photosynthetic capacity response to e-CO₂ was negatively correlated across genotypes with local C source–sink ratio, a trait highly conserved across environments. HSS were sink-limited under e-CO₂, probably associated with low triose phosphate utilization (TPU) capacity. We suggest that the local C source–sink ratio is a potential target for selecting more CO₂-responsive cultivars, pending validation for a broader genotypic spectrum and for field conditions.     

Infectious salmon anaemia virus (ISAV) isolated from the ISA disease outbreaks in Chile diverged from ISAV isolates from Norway around 1996 and was disseminated around 2005, based on surface glycoprotein gene sequences

Background

All viruses in the family Bunyaviridae possess a tripartite genome, consisting of a small, a medium, and a large RNA segment. Bunyaviruses therefore possess considerable evolutionary potential, attributable to both intramolecular changes and to genome segment reassortment. Hantaviruses (family Bunyaviridae, genus Hantavirus) are known to cause human hemorrhagic fever with renal syndrome or hantavirus pulmonary syndrome. The primary reservoir host of Sin Nombre virus is the deer mouse (Peromyscus maniculatus), which is widely distributed in North America. We investigated the prevalence of intramolecular changes and of genomic reassortment among Sin Nombre viruses detected in deer mice in three western states.

Methods

Portions of the Sin Nombre virus small (S) and medium (M) RNA segments were amplified by RT-PCR from kidney, lung, liver and spleen of seropositive peromyscine rodents, principally deer mice, collected in Colorado, New Mexico and Montana from 1995 to 2007. Both a 142 nucleotide (nt) amplicon of the M segment, encoding a portion of the G2 transmembrane glycoprotein, and a 751 nt amplicon of the S segment, encoding part of the nucleocapsid protein, were cloned and sequenced from 19 deer mice and from one brush mouse (P. boylii), S RNA but not M RNA from one deer mouse, and M RNA but not S RNA from another deer mouse.

Results

Two of 20 viruses were found to be reassortants. Within virus sequences from different rodents, the average rate of synonymous substitutions among all pair-wise comparisons (π_s) was 0.378 in the M segment and 0.312 in the S segment sequences. The replacement substitution rate (π_a) was 7.0 × 10^-4 in the M segment and 17.3 × 10^-4 in the S segment sequences. The low π_a relative to π_s suggests strong purifying selection and this was confirmed by a Fu and Li analysis. The absolute rate of molecular evolution of the M segment was 6.76 × 10^-3 substitutions/site/year. The absolute age of the M segment tree was estimated to be 37 years. In the S segment the rate of molecular evolution was 1.93 × 10^-3 substitutions/site/year and the absolute age of the tree was 106 years. Assuming that mice were infected with a single Sin Nombre virus genotype, phylogenetic analyses revealed that 10% (2/20) of viruses were reassortants, similar to the 14% (6/43) found in a previous report.

Conclusion

Age estimates from both segments suggest that Sin Nombre virus has evolved within the past 37–106 years. The rates of evolutionary changes reported here suggest that Sin Nombre virus M and S segment reassortment occurs frequently in nature.     

Diet variability among insular populations of Podarcis lizards reveals diverse strategies to face resource‐limited environments

Access to resources is a dynamic and multicausal process that determines the success and survival of a population. It is therefore often challenging to disentangle the factors affecting ecological traits like diet. Insular habitats provide a good opportunity to study how variation in diet originates, in particular in populations of mesopredators such as lizards. Indeed, high levels of population density associated with low food abundance and low predation are selection pressures typically observed on islands. In the present study, the diet of eighteen insular populations of two closely related species of lacertid lizards (Podarcis sicula and Podarcis melisellensis) was assessed. Our results reveal that despite dietary variability among populations, diet taxonomic diversity is not impacted by island area. In contrast, however, diet disparity metrics, based on the variability in the physical (hardness) and behavioral (evasiveness) properties of ingested food items, are correlated with island size. These findings suggest that an increase in intraspecific competition for access to resources may induce shifts in functional components of the diet. Additionally, the two species differed in the relation between diet disparity and island area suggesting that different strategies exist to deal with low food abundance in these two species. Finally, sexual dimorphism in diet and head dimensions is not greater on smaller islands, in contrast to our predictions.     

Gene conversion at different points in the mitotic cycle of Saccharomyces cerevisiae

Summary In the Saccharomyces cerevisiae mitotic cycle, the timing of radiation-induced gene conversion has been studied using thermosensitive cell division cycle mutants. The cells were found to perform conversion at different G1 or post-replication steps. A lower yield in induction is found during the G2 phase and is explained by the competition for recombinational repair between sister chromatids and homologous chromosomes. The results are discussed in relation to repair.     

Purification and Preliminary Biochemical Characterisation of the Human and Rat Forms of the Central Nervous System-Specific Molecule, F3-87-8

The F3-87-8 monoclonal antibody recognises a phylogenetically conserved antigenic determinant found exclusively in the mammalian CNS. We used this monoclonal antibody as the major purification step for obtaining pure. F3-87-8-bearing molecules from rat and human brains for biochemical analysis. In both rat and man, the F3-87-8 molecule is a heavily glycosylated protein, consisting of 47.6 and 47.0% carbohydrate by weight, respectively. In both species, it occurs as a doublet on polyacrylamide gel electrophoresis in sodium dodecyl sulphate, the Mr of the human form being 130,000 and 100,000. In the rat, the Mr of the doublet is slightly but consistently lower than in man, and the higher-Mr band is more pronounced. The amino acid composition of the rat and human forms is virtually identical, with a high content of serine and threonine. Significant differences are seen in carbohydrate composition, the rat form containing more sialic acid and neutral sugar and less hexosamine than the human form. beta-Elimination studies, in conjunction with carbohydrate analysis, suggest the presence of approximately 40 O-linked and 10-15 N-linked oligosaccharides per polypeptide chain of 500 amino acids, the N-linked chains predominantly of the high-mannose type. This makes it likely that the molecule adopts an extended rather than a coiled conformation on the membrane.     

Experimental studies on some factors influencing phosphorus solubilization in connexion with the drawdown of a reservoir

The periodical drawdown of reservoirs affects the phosphorus cycle. During the dry period the sediments are in immediate contact with the atmosphere, while part of them are resuspended when the water rises again. Experimental studies on the sediments of the Puyvalador reservoir (Pyrenees, France), which is subjected to a considerable drawdown every year, show that the quantity of phosphorus solubilized after resuspension of these sediments varies according to the speed with which the water rises, the preceding desiccation of the sediments and the origin of the water used in the experiments. The intensity with which the sediments are stirred depends on the refilling rate. The observed differences related to the origin of the water of the affluent streams are attributed to their initial ortho-phosphate content and their difference in pH. These variations related to drawdown make it necessary to take this important phenomenon into account when studying the solubilization of phosphorus in reservoirs.