Slow heat rate increases yeast thermotolerance by maintaining plasma membrane integrity.

Thermal resistance of Saccharomyces cerevisiae was found to be drastically dependent on the kinetics of heat perturbation. Yeasts were found to be more resistant to a plateau of 1 h at 50 degrees C after a slope of temperature increase (slow and linear temperature increments) than after a shock (sudden temperature change). Thermotolerance was mainly acquired between 40-50 degrees C during a heat slope, i.e., above the maximal temperature of growth. The death of the yeasts subjected to a heat shock might be related to the loss of membrane integrity: intracellular contents extrusion, i.e., membrane permeabilization, was found to precede cell death. However, the permeabilization did not precede cell death during a heat slope and, therefore, membrane permeabilization was a consequence rather than a cause of cell death. During a slow temperature increase, yeasts which remain viable may have time to adapt their plasma membrane and thus maintain membrane integrity.     

Competitive exclusion of diarrheagenic Escherichia coli (ETEC) from human enterocyte-like Caco-2 cells by heat-killed Lactobacillus

Diarrheagenic Escherichia coli (ETEC) bearing CFA/I or CFA/II adhesive factors specifically adhere onto the brush border of the polarized epithelial human intestinal Caco-2 cells in culture. Heat-killed Lactobacillus acidophilus strain LB, that adheres onto Caco-2 cells, inhibits diarrheagenic Escherichia coli adhesion in a concentration-dependent manner. Since the L. acidophilus does not express ETEC-CFA adhesive factors, it can be postulated that the heat-killed L. acidophilus LB cells inhibit diarrheagenic E. coli attachment by steric hindrance of the human enterocytic ETEC receptors.     

Tentative application of the tangent simple system method to the study of the viscoelastic behaviour of blood

The method of the tangent simple systems is applied to the study of the viscoelastic behaviour of human blood in unstationary flow for rectangular steps and triangular ramps of shear rate. The tangent systems we utilize, Maxwell liquids, enable us to determine, at every point of the rheograms, apparent instantaneous values of retardation or relaxation time, viscosity coefficient and elasticity modulus of the studied blood samples, and to plot the curves of variation of these parameters as a function of flow duration. A qualitative interpretation of the results is proposed from data on the aggregation-disaggregation kinetics of red blood cells. Examples are given for samples of normal and pathological bloods.     

Evolution cyclique des glandes cérébrales au cours de l'intermue chez Lithobius forficatus L. (Myriapode Chilopode)

Résumé Chez le Chilopode Lithobius forficatus L., les cellules parenchymateuses des glandes cérébrales présentent, durant l'intermue, un cycle sécrétoire caractérisé essentiellement par l'évolution de l'activité golgienne. Pendant les périodes de sécrétion, les ribosomes, groupés en polysomes, et les éléments ergastoplasmiques sont très abondants; pendant les périodes de repos, les ribosomes sont isolés et l'ergastoplasme est vésiculeux. Les autres organites cellulaires montrent peu de variations.Le cycle sécrétoire ne se superpose pas exactement au cycle d'intermue; il commence lors de la prémue. Peu de temps après l'exuviation, il est possible d'observer des figures qui semblent liées au rejet du produit de sécrétion. L'étude ultrastructurale des glandes cérébrales en fonction de l'intermue confirme l'existence de l'activité cyclique mise en évidence par les résultats expérimentaux.

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Ultrastructural signs of cyclic secretory activity in the cerebral glands of Lithobius forficatus during intermolt

Summary During the molting cycle of Lithobius forficatus L. (Chilopoda), the parenchymal cells of the cerebral glands exhibit signs of cyclic secretory activity consisting essentially of changes in the appearance of the Golgi complex. During active periods of secretion, polysomes and ergastoplasmic elements are very numerous; free ribosomes and vesiculated ergastoplasmic cisternae characterize the periods of inactivity. Other cytoplasmic organelles undergo few variations. The secretory cycle as determined by cytological criteria does not exactly match the molting cycle. The first ultrastructural signs of activity appear during premolt. Shortly after ecdysis, images suggesting the release of secretory material can be observed. The electron microscopic data on cyclic changes during intermolt substantiate the existence of activity cycles in the cerebral glands as determined by physiological experiments.

     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Comparaison des divers types d'adultoides chezLocusta migratoria L.

Conclusion on aurait pu s'attendre à ce que les adultoïdes (stades Vbis) se groupent sur la même droite que les stades V normaux et les adultes prématurés (V) sur celle des imagos (fig. 6). On voit qu'il n'en est rien et que cela tient à ce que la croissance des organes du vol à la fin du développement larvaire deLocusta migratoria n'est pas représentée par une droite d'allométrie unique, mais présente une discontinuité à chacune des dernières mues, de sorte que les adultoïdes ne sont pas des stades V géants mais un stade supplémentaire ajouté au développement normal, et les imagos prématurés ne sont pas des adultes nains mais des adultes privés d'une partie de leur évolution larvaire.     

Effects of Mercuric Chloride on the Hydraulic Conductivity of Tomato Root Systems (Evidence for a Channel-Mediated Water Pathway)

A pressure-flux approach was used to evaluate the effects of HgCl2 on water transport in tomato (Lycopersicon esculentum) roots. Addition of HgCl2 to a root-bathing solution caused a large and rapid reduction in pressure-induced root water flux; the inhibition was largely reversible upon addition of [beta]-mercaptoethanol. Root system hydraulic conductivity was reduced by 57%. There was no difference between treatments in the K+ concentration in xylem exudate. The results are consistent with the presence of a protein-mediated path for transmembrane water flow in tomato roots.