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While the adaptive significance of discontinuous reaction norms is generally accepted, the evolutionary interpretation of continuous response curves remains speculative, and the occurrence of internal constraints is often suggested as an explanation of experimental observations. In Drosophila melanogaster, various morphometrical traits exhibit convex reaction norms to growth temperature, with a maximum...
L'effet de la rhizosphere sur la mineralisation de l'azote organique du sol est quantifie par comparaison de la mineralisation de l'azote dans un sol rhizospherique (sol cultive en ray-grass, plante a forte densite racinaire) et dans un sol non rhizospherique (sol sans vegetation). En utilisant trois approches differentes, on montre que la plante induit une augmentation de la mineralisation nette,...
Les puffins cendres Calonectris diomedea borealis de Selvagem Grande (30 o 09'N, 15 o 52'W) s'alimentent pendant l'incubation essentiellement dans le courant des Canaries, le long des cotes marocaines ou, en raison de l'enrichissement des eaux de surface par la remontee d'eaux froides profondes, la productivite est considerable. Les cotes marocaines sont atteintes 36 h environ apres...
Une vase sableuse, dont les particules fines d'un diametre inferieur a 63 μm representent 84,7 % en poids du sediment, a ete recoltee sur une zone d'abandon de materiel ostreicole usage recouvert de coaltar dans le bassin d'Arcachon. Ce sediment s'est revele fortement pollue par les hydrocarbures aromatiques polycycliques (HAPs) ; leur teneur de 10 348 ng/g -1 de sediment atteint les...
Using specific radio-immunoassays for rainbow trout GTH I and GTH II, the effects of testosterone and estradiol 17β have been studied or reinvestigated on the regulation of the secretion and the synthesis of the these two pituitary gonadotropins in the immature rainbow trout. After steroid implantation, the GTH II pituitary concentration is stimulated by testosterone and estradiol 17β for the entire...
L'activite hyaluronidasique de cellules cancereuses humaines a ete recherchee dans les milieux de culture de huit lignees etablies a partir de tumeurs primaires et de quatre lignees etablies a partir de metastases. Elle a ete retrouvee dans huit milieux de culture. Dans trois lignees cellulaires issues de tumeurs primaires l'activite etait inferieure a 0,035 pU/cellule/heure. Elle etait 5 a 100 fois...
Une experimentation in vitro a ete conduite a l'aide d'une population de polychetes galericoles Nereis diversicolor afin de mettre en evidence le role du macrobenthos sur l'expression de la denitrification en presence d'hydrocarbures. La comparaison de l'activite denitrifiante entre des sediments temoins (sans macrofaune) et experimentaux (avec macrofaune) contamines ou non par des hydrocarbures a...
We have recently developed a flow cytometric assay for the quantitation of erythrophagocytosis, using PKH 26-labeled erythrocytes as the target cells. Using this assay we have shown that there is extensive phagocytosis of desialylated erythrocytes. Furthermore, we have demonstrated that it is the densest population of erythrocytes obtained on a self-forming gradient of Percoll that shows the greatest...
One of the unsolved problems in plant biochemistry has been the identification of the regulatory cysteines in the reductively light-activated and -inactivated chloroplast enzymes. Homology modeling based on the sequences of these enzymes and the three-dimensional structures of homologous enzymes has now allowed tentative identification of the redox-sensitive Cys residues in four light-activated chloroplast...
Three sulphur-amino acids, taurine, hypotaurine and thiotaurine, are shown to exist in deep-sea symbiotic mussels. Their relative and absolute importance differs in the three species of mussels studied and seems to be related to the metabolism of the symbionts. Thiotaurine only occurs in high concentration in thiotrophic species, whereas hypotaurine and taurine are found in all the species studied...
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