Natural hybridization of two species of tetraploid barbels: Barbus meridionalis and Barbus barbus (Osteichtyes, Cyprinidae) in southern France

Natural hybridization of Barbus barbus and B. meridionalis has been demonstrated in southern France. A genetical study (isozyme electrophoresis) of these species and their hybrids revealed the characteristics of hybridization. Ten enzyme markers and five morphological parameters were used to distinguish between the two parent species. Enzymatic divergence between the parent species included fixed allelic differences at certain loci and reduction in enzymatic activity, including the silencing of certain genes. A morphological study revealed a good correlation between the isozyme markers and morphological characters. Backcrosses were observed and this raises the question of the integrity of the parent species.     

Caractéristiques Ultrastructurales du Cortex et des Membranelles du CiliéEspejoia mucicola (Oligohymenophora, Hymenostomata, Tetrahymenina)

RESUME. L' étude détaillée du cortex et des organelles buccaux adoraux d' Espejoia montre que ce Cilié possède une organisation ultrastructurale comparable à celle des Tétrahyméniens. Tout en restant conforme au plan général d'organisation de ces derniers, des variations spécifiques décelées tant au niveau du cortex d'une part, que des membranelles, d'autre part, font ressortir des affinités trés marquées pour le genre Glaucoma et autres Ciliés voisins. En conséquence, en nous appuyant en outre sur les données récentes de la morphogenèse, nous confirmons la position d' E. mucicola parmi les Tetrahymenina, dans la famille des Glaucomidae.     

Electrochemical State of Potassium and Sodium in Free Cells of Acer pseudoplatanus

The intracellular distribution of K⁺ and Na⁺ ions has been determined by compartmental analysis of isotope exchange. The simultaneous measurement of electrical potentials allowed us to show that the distribution of K⁺ was close to thermodynamic equilibrium while the internal concentration of Na⁺ was well below the value predicted for the equilibrium. The efflux of Na⁺ was more sensitive to temperature than its influx. Both ouabain and variations in the external levels of KCl produced weak and inconsistent effects, observations which would emphasize the difference between the Na⁺ extrusion mechanism of plants and animals. The Na⁺ extrusion system of Acer cells ceased to be functional in Na⁺-depleted cells but recovered its function if the cells were placed in 10 mM NaCl, which suggests that the extrusion system was induced by the level of internal Na⁺ ions.