Variabilité à court terme des propriétés physiques,chimiques et biologiques du Saguenay,fjord subarctique du Quebec (Canada)

Tidal variability of water mass characteristics has been assessed in the upper 100 metres of the Saguenay, a subarctic fjord in Québec, Canada. Temperature and salinity show a maximum variability in the 5-15 m layer in which vertical oscillations of a very sharp pycnocline are observed. Phosphates, nitrates and chlorophyll a are highly variable above this pycnocline during a tidal cycle, but dissolved oxygen content is remarkably stable in the whole water column. It is concluded that fluctuations of many variables in the subsurface waters might be large enough to hinder high rates of primary production.     

Productivité comparée des deux étangs situés à proximité du lac Saint-Jean,au Québec

The Comparative Productivity of Two Ponds in the Vicinity of Lake St-John, Québec In 1980 and 1981, the productivity of two ponds near Lake St. John were evaluated. One, the pond of Desbiens, did not communicate with Lake St. John and the other, the pond of St-Gédéon, was connected to the lake. The aim of this study was to evaluate the contribution that a pond could make to the increase in productivity of Lake St. John which is a reservoir. The pond of Desbiens is more productive than Lake St. John but two to three times less than the pond of St-Gédéon. The pond of Desbiens shows an advanced degree of eutrophication whereas the pond of St-Gédéon is similar to the northern lakes by its physico-chemistry, zooplankton, sediments and benthic fauna. If we want to create artificial ponds, for a better productivity of reservoirs, it is important that they be connected to each other.     

Paléoécologie des associations d'ostracodes d'une formation carbonatée à Rudistes en environnement péri-deltaïque: l'exemple du Santonien de la Cadière d'Azur (Sud-Est France)

Paleoecological studies carried out in the Carbonate bank with Rudists of La Cadière d'Azur (Southeast France) and adjacent perideltaic areas have been made in order to define some stages during the evolution of the formation. For each period, type of ostracode assemblage can be proposed. This is undertaken by analysis using both a more precised systematics and especially quantitative methodology, particularly the factorial analysis of correspondances. One purpose of this study is to justify the paleoecological interpretations and moreover to conclude on the autecology of ostracode species. Lastly, it is suggested that carbonate rate (i.e. water content in calcium), turbulence of sea-waters (influencing the grain-size of terrigenous deposits) and perhaps depth are locally important controlling factors of ostracode diversity.     

Structure et composition chimique élémentaire de quelques coquilles d'œufs de dinosaures du Jurassique et du Crétacé d'Amérique du Nord

Structure and chemical composition of some dinosaur eggshells from Jurassic and Cretaceous of North America. Microstructural analyses of some dinosaur eggshells from Jurassic and Cretaceous sites of North America show a large variability in the state of preservation. Outer and inner surfaces are often hidden by secondary deposits, and the tubercles or ridges and spherolites are not visible. Chemical analyses show that some fragments are strongly enriched in Si. There is a good correlation between the preservation of the structures and the chemical contents. Diagenetic processes are different from those described in the samples from Southern France.     

Transport du sulfate à travers la double membrane limitante, ou enveloppe, des chloroplastes d'épinard

Evidence is presented for low rates of carriermediated uptake of sulphate, thiosulphate and sulphite into the stroma of the C3 plant Spinacia oleracea. Uptake of sulphate in the dark was followed using two techniques (1) uptake of sulphate [³⁵S] as determined by silicon oil centrifugal filtration and (2) uptake as indicated by inhibition of CO₂-dependant O₂ evolution rates after addition of sulphate.Sulphate, thiosulphate and sulphite were transported across the envelope leading to an accumulation in the chloroplasts. Sulphate transport had saturation kinetics of the Michaelis-Menten type (Vmax : 25 μmoles . mg⁻¹ chl . h⁻¹ at 22°C ; Km : 2.5 mM). The rate of transport for sulphate was not influenced either by illumination or pH change in the external medium. Phosphate was a competitive inhibitor of sulphate uptake by chloroplasts (Ki : 0.7 mM, fig. 1). The rate of transport for phosphate appeared to be much higher than for sulphate. When the chloroplasts were pre-loaded with labelled sulphate, radioactivity was rapidly released after addition of phosphate into the external medium. Consequently, the transport of sulphate occurs by a strict counter-exchange : for each molecule of sulphate entering the chloroplast, one molecule of phosphate leaves the stroma, and vice-versa.The uptake of sulphate by isolated intact chloroplasts exchanging for internal free phosphate induced a lower rate of photophosphorylation, which in turn inhibited CO₂-dependent O₂ evolution.The presence, on the inner membrane of the chloroplast envelope, of a specific sulphate carrier, distinct from the phosphate translocator, is discussed.     

Séquences tripeptidiques typiques du collagène: étude conformationnelle quantique

Theoretical and experimental investigations on the conformations of synthetic polytripeptides, with Gly-R₂-R₃ general repetitive sequence, are of great interest for the comprehension of the factors wich contribute to the triple helix stabilization.Using appropriate molecules as models, we have investigated by the PCILO method the intrinsic conformational possibilities of each « in situresidue for the following cases: Gly-imino-imino, Gly-amino-imino and Gly-imino-amino which represent the most important sequences occuring in the primary structure of collagen. The computations were carried out taking into account the two pyrrolidine ring puckerings and the preferential side-chains orientations.Extending our previous work concerning the isomeric polytripeptides Gly-X-Pro and Gly-Pro-X with X {Pro, Phe} we have studied the cases of X {Ala, Ser}. In this brief communication, we present a preliminary synthesis of these recent results.     

Étude ultrastructurale du cycle nucléolaire de Physarum polycephalum après mise en évidence préférentielle des RNP par la réaction régressive à l''EDTA

Nucleolar cycle in Physarum polycephalum was studied using EDTA preferential stain for RNP. We have been able to establish the following.

1. 1. The nucleolar remnants that are observed during mitosis correspond to the fibrillar zones of the interphase nucleolus.

2. 2. In prometaphase and metaphase the nucleolar remnants lie peripherically around the chromosomal mass with which they are only superficially associated.

3. 3. Preribosomal granules appear 10–15 min after metaphase in the prenucleolar bodies.

The results shown that the interphase nucleolus is an assembly of multiple subunits. The relationship between the nucleolar remnants and chromosomes is discussed in the light of the recent understanding of the extrachromosomal nature of rDNA.Le cycle nucléolaire de Physarum polycephalum a été étudié en microscopie électronique après réaction régressive à l'EDTA qui met préférentiellement en évidence les RNP. Nous avons suivi ainsi la dispersion du nucléole en prophase, le devenir des restes nucléolaires au cours de la métaphase et de la télophase, puis l'apparition des corps prénucléolaires en début d'interphase.     

Nucléotides adényliques et assimilation photosynthétique du phytoplancton dans deux lacs du Massif Central français

Adenine Nucleotides and Phytoplanktonic Primary Production in Two Lakes in France The adenine nucleotides concentrations and photosynthetic assimilation of phytoplankton were established during two annual sampling seasons for two lakes with different nutrients concentrations (Lakes Pavin and Aydat). Intensive photosynthetic assimilation of phytoplankton led to a limited but real evolution of the pool of adenine nucleotides towards forms less charged with high energy phosphate bond (ADP and AMP). This evolution is seen as a consequence of the ATP hydrolysis in the process of cell biosynthesis.     

Stabilité du polymorphisme électrophorétique de douze populations naturelles françaises de Drosophila melanogaster

L'évolution dans le temps du polymorphisme de 5 locus enzymatiques a été suivie pour 12 populations naturelles françaises de Drosophila melanogaster. La structure génétique de ces populations ne varie pas, ou peu, d'un automne à l'autre. La bonne résistance au froid des imagos et le fait que la période hivernale suive celle de l'explosion démographique de l'espèce en France, indiquent que les populations analysées ne doivent pas subir d'importantes réductions de leurs effectifs durant l'hiver, susceptibles d'entraîner une forte dérive génétique. Dans ces conditions, le maintien de la même structure d'une année à l'autre peut s'expliquer par le fait que les populations sont panmictiques.     

Effet de l'enrichissement continu en nitrates sur les populations de Diatomées isolées à l'aide d'enceintes expérimentales placées dans un étang oligotrophe

The influence of nitrates (NH₄NO₃ KNO₃ and Ca(NO₃₎₂) on Diatom populations has been studied. These populations were isolated by enclosures with transparent walls, without bottom or lid, placed in an oligotrophic pond. The addition of NH₄NO₃ generally resulted in a decrease in the number of Diatoms and the disappearance of some species. The addition of KNO₃ and Ca(NO₃₎₂ was followed, during some periods, by a very important increase of Achnanthes minutissima, Fragilaria construens and Gomphonema parvulum.     

Groupement et ordination appliqués à l''étude de la répartition de l''épifaune benthique de l''estuaire maritime et du Golfe du Saint-Laurent

Forty-seven navigation buoys were used to collect quantitative samples of epibenthic fauna in the Lower Estuary and Gulf of St. Lawrence. Stations, as described by their sessile species and biomass composition, were grouped using multivariate analysis. A Gower similarity index, modified to take into account the importance of each species in the ecosystem, was used to compare stations. Results obtained by cluster and principal coordinate analyses showed comparable relations between stations. North Shore and Gaspé Coast stations were separated from those of the Lower North Shore, the Mingan Island sector and the Lower Estuary. Stations from the Lower North Shore were also separated from those of the Mingan Island region and of the Lower Estuary, but at a higher level of similarity. All animal assemblages consisted of the following sessile species: Obelia longissima (Pallas), Hiatella arctica (L.), Mytilus edulis L., Balanus balanoides (L.) and B. crenatus (Bruguière). These species formed over 95% of biomass of all sessile species. Differences between the various station assemblages were mainly due to changes in the relative abundance of these species. The geographical gradient of summer surface water temperature best explains the observed clusters. In the Lower Estuary, the spatio-temporal variations of physico-chemical factors and the surface circulation may influence the number of species and their abundance. The circulation systems of the Lower Estuary and near the Mingan Islands might account for the similarity between their assemblages. The same dominant species, Obelia longissima, characterizes the fauna of these two regions.