Assessing the importance of a self-generated detachment process in river biofilm models

1. Epilithic biofilm biomass was measured for 14 months in two sites, located up‐ and downstream of the city of Toulouse in the Garonne River (south‐west France). Periodical sampling provided a biomass data set to compare with simulations from the model of Uehlinger, Bürher and Reichert (1996: Freshwater Biology, 36 , 249–263.), in order to evaluate the impact of hydraulic disturbance. 2. Despite differences in application conditions (e.g. river size, discharge, frequency of disturbance), the base equation satisfactorily predicted biomass between low and high water periods of the year, suggesting that the flood disturbance regime may be considered a universal mechanism controlling periphyton biomass. 3. However modelling gave no agreement with biomass dynamics during the 7‐month long low water period that the river experienced. The influence of other biomass‐regulating factors (temperature, light and soluble reactive phosphorus) on temporal biomass dynamics was weak. 4. Implementing a supplementary mechanism corresponding to a temperature‐dependent self‐generated loss because of heterotrophic processes allowed us to accurately reproduce the observed pattern: a succession of two peaks. This case study suggests that during typical summer low water periods (flow stability and favourable temperature) river biofilm modelling requires self‐generated detachment to be considered.     

l-Phenylalanyl-l-Glutamate-Stimulated, Chloride-Dependent Glutamate Binding Represents Glutamate Sequestration Mediated by an Exchange System

Stimulation of glutamate binding by the dipeptide L-phenylalanyl-L-glutamate (Phe-Glu) was inhibited by the peptidase inhibitor bestatin, suggesting that the stimulation was caused by glutamate liberated from the dipeptide and not by the dipeptide itself. It further suggests that this form of glutamate binding should be reinterpreted as glutamate sequestration and that stimulation of binding both by dipeptides and after preincubation with high concentrations of glutamate is likely to be due to counterflow accumulation. Several other criteria indicate that most of glutamate binding stimulated by chloride represents glutamate sequestration: Binding is reduced when the osmolarity of the incubation medium is increased, when membranes incubated with [3H]glutamate are lysed before filtration, and when membranes are made permeable by transient exposure to saponin. Moreover, dissociation of bound glutamate after a 100-fold dilution of the incubation medium is accelerated about 50 times by the addition of glutamate to the dilution medium. This result would be anomalous if glutamate were bound to a receptor site; it suggests instead that glutamate is transported in and out of membrane vesicles by a transport system that preferentially mediates exchange between internal and external glutamate. Glutamate binding contains a component of glutamate sequestration even when measured in the absence of chloride. Sequestration is adequately abolished only after treating membranes with detergents; even extensive lysis, sonication, and freezing/thawing may be insufficient.     

血革螨科二新种（蜱螨亚纲）

本文记述了血革螨科两新种:大理血革螨Haemogamasus daliensis sp.nov.和中华真厉螨Eulaelaps sinensis sp.nov.。该文对新种的形态特征作了描述,并与近似种进行了比较。     

The flea ovary: ultrastructure and analysis of cell clusters

Panoistic ovarioles are found in the order of fleas (Siphonaptera). Only in some species of the Hystrichopsylloidea do polytrophic meroistic ovaries occur. No stem cells and no dividing cystocytes are found in female imagines of Hystrichopsylla talpae. However, each germ cell cluster consists of 32 cells which are generated by five mitotic cycles during the pupal stage. One of the cells containing five intercellular bridges becomes the oocyte, the others serve as nurse cells. Thus, germ cell cluster formation follows the 2(n)-rule. However, no polyfusome is found and nurse cells do not form a rosette. Furthermore, nurse cells remain small and show the same ultrastructural characters as the oocytes, which became distinguishable from nurse cells only by their enhanced growth during pre-vitellogenesis. The first phase of pre-vitellogenesis is dominated by the production of an unknown cytoplasmatic component, consisting of spherical particles, clearly distinguishable from ribosomes by diameter and contrast. The next phase is characterized by a tremendous increase in the production of ribosomes. During this second phase another cytoplasmic component consisting of ball-like structures becomes prominent. During pre-vitellogenesis, germ cell nuclei undergo a pronounced structural change in which, finally, numerous extranucleolar particles predominate. Thus, H. talpae has a polytrophic meroistic ovary, but its oocyte genomes behave panoistically.     

Specific binding of three neurotoxins with phospholipase A2 activity to synaptosomal membrane preparations from the guinea pig brain

Snake presynaptic toxins such as crotoxin, β-bungarotoxin and taipoxin block neuromuscular transmission through inhibiting the release of acetylcholine by their phospholipase A₂ activities. On the other hand, many other phospholipase A₂s show little neurotoxicity. It is likely that the difference lies in whether high affinity binding to nerve cell membranes exists or not. To test this idea, crotoxin, β-bungarotoxin and taipoxin were first radioactively labeled with Na(¹²⁵I) without loss of their neurotoxicity. Using the radioactive toxins we have found that each of the three showed specific binding to synaptosomal membranes from guinea pig brain. In contrast, we could not detect specific binding of a non-neurotoxic pancreatic phospholipase A₂. Crotoxin and taipoxin, but not β-bungarotoxin, also bound specifically to membrane preparation from other tissues. The binding of each toxin was not greatly affected by the other two toxins. The photoaffinity labeling technique has been used to obtain further information about the components which bind crotoxin. For this purpose, (¹²⁵I) crotoxin was derivatized with N-hydroxysuccinimidyl-4-azidobenzoate. Autoradiographic analysis of the membranes following photoirradiation in the presence of the modified crotoxin revealed that an 85K dalton component was preferentially covalently conjugated with the crotoxin analogue in a specific manner.     

Comparative antioxidant enzyme study in freshwater fishes. II. Distribution of antioxidant enzymes and lipid peroxidation in omnivorous fish organs

Comparative studies were performed on the activities of superoxide dismutases, catalase and glutathione peroxidase in organ homogenates from three omnivorous fishes, the barbel, crucian carp and common carp. The lipid peroxidation and protein contents of organ homogenates were also compared. These comparative measurements primarily provide control values for subsequent toxicological examinations. The highest total superoxide dismutase activities were found in the liver or roe, kidney, heart and spleen in every cases. The antioxidant enzyme activities and other studied parameters of the organ homogenates partly appear to depend on the feeding mode, but are rather characteristic of the fish variety.     

Blood osmolality in vitro: dependence on PCO2, lactic acid concentration, and O2 saturation

Changes of osmolality (Osm) were measured by freezing-point determination in true plasma of 10 healthy subjects. This was done after equilibration with CO2 (0.5-10.0%), after the addition of lactic acid (10 and 20 mmol/l), and after deoxygenation. The graph for the dependence of Osm on CO2 partial pressure (PCO2) in oxygenated blood resembles the classical CO2 absorption curve. The increase of Osm with PCO2 (approximately 0.2 mosmol . kg H2O-1 . Torr-1) is almost as great as the increase in dissolved CO2 plus bicarbonate (HCO-3). Addition of lactic acid shifts the curve upward by only 0.6 mosmol/mmol because of displacement of HCO-3. Deoxygenation has no significant effect at constant PCO2 despite an increase in [HCO-3]. This is probably due to the binding of 2,3-diphosphoglycerate to hemoglobin. It can be seen in the Osm-pH diagram that differences between CO2 and lactic acid titration largely disappear. For each lactic acid concentration there is a linear dependence corresponding to the linear [HCO-3]-pH relation in plasma. At constant pH, Osm increases after deoxygenation. The observed in vitro relation might explain part of the osmolality increase during physical exercise.