Morphological aspect and chemical composition of Skeletonema costatum (Bacillariophyceae) growing in natural nutritive media with the aid of a culture system of dialysing fibers

The growth of Skeletonema costatum, under natural nutriment conditions, was studied using a bulk culture fiber dialyzing apparatus. The diatom displayed normal development of chain length (average cell number per chain) which coincided with the culture growth stages; that is, the cell number per colony increased during the active division period and decreased thereafter with the beginning of the prestationary phase. This morphological behaviour showed that the alga cells were not affected by such physical shocks as collision or tension occurring during repeated cell transfers from growth chambers to the dialyzing apparatus or at the time of their passage through the fiber fascicles. Measured at different growth stages, the cell contents in carbon, nitrogen, and chlorophyll confirmed the above results and showed for S. costatum a biological productivity comparable with that obtained in smaller dialyzing containers (dialyzing bags). Through a comparison between the dialyzing culture and a static culture grown in an enriched medium, certain characteristics were determined.     

Activité migratoire des tétranyques: Mise en évidence d'un rythme

Résumé L'étude en différentes conditions de la migration verticale deTetranychus urticae dans de fortes infestations, a permis de mettre en éviduence un rythme circadien caractérisé par un mouvement alterné de montée et de descente, la population migrant vers le haut des plantes en début d'après-midi. Ce rythme est en partie endogène puisqu'il se maintient plusieurs jours dans des conditions constantes.      

Oxidative capacity and capillary density of diaphragm motor units

Motor units in the cat diaphragm (DIA) were isolated in situ by microdissection and stimulation of C5 ventral root filaments. Motor units were classified based on their isometric contractile force responses and fatigue indexes (FI). The muscle fibers belonging to individual units (i.e., the muscle unit) were identified using the glycogen-depletion method. Fibers were classified as type I or II based on histochemical staining for myofibrillar adenosine triphosphatase (ATPase) after alkaline preincubation. The rate of succinate dehydrogenase (SDH) activity of each fiber was determined using a microphotometric procedure. The location of capillaries was determined from muscle cross sections stained for ATPase after acid (pH = 4.2) preincubation. The capillarity of muscle unit fibers was determined by counting the number of capillaries surrounding fibers and by calculating the number of capillaries per fiber area. A significant correlation was found between the fatigue resistance of DIA units and the mean SDH activity of muscle unit fibers. A significant correlation was also observed between DIA unit fatigue resistance and both indexes of muscle unit fiber capillarity. The mean SDH activity and mean capillary density of muscle unit fibers were also correlated. We conclude that DIA motor unit fatigue resistance depends, at least in part, on the oxidative capacity and capillary density of muscle unit fibers.     

Physical mapping of the von Recklinghausen neurofibromatosis region on chromosome 17

The von Recklinghausen neurofibromatosis (NF1) locus has been linked to chromosome 17, and recent linkage analyses place the gene on the proximal long arm. NF1 probably resides in 17q11.2, since two unrelated NF1 patients have been identified who possess constitutional reciprocal translocations involving 17q11.2 with chromosomes 1 and 22. We have used a somatic-cell hybrid from the t(17;22) individual, along with other hybrid cell lines, to order probes around the NF1 locus. An additional probe, 17L1, has been isolated from a NotI linking library made from flow-sorted chromosome 17 material and has been mapped to a region immediately proximal to the translocation breakpoint. While neither NF1 translocation breakpoint has yet been identified by pulse-field gel analysis, an overlap between two probes, EW206 and EW207, has been detected. Furthermore, we have identified the breakpoint in a non-NF1 translocation, SP-3, on the proximal side of the NF1 locus. This breakpoint has been helpful in creating a 1,000-kb pulsed-field map, which includes the closely linked NF1 probes HHH202 and TH17.19. The combined somatic-cell hybrid and pulsed-field gel analysis we report here favors the probe order D17Z1-HHH202-TH17.19-CRYB1-17L1-NF1- (EW206, EW207, EW203, L581, L946)-(ERBB2, ERBA1). The agreement in probe ordering between linkage analysis and physical mapping is excellent, and the availability of translocation breakpoints in NF1 should now greatly assist the cloning of this locus.     

A cyclic AMP response element mediates repression of tyrosine aminotransferase gene transcription by the tissue-specific extinguisher locus Tse-1

Tyrosine aminotransferase (TAT) gene expression is liver specific and inducible by glucocorticoids and via the cAMP signaling pathway. In fibroblasts and other nonliver cells the gene is subject to negative control by the trans-dominant tissue-specific extinguisher locus Tse-1. We identified a hepatocyte-specific enhancer that is repressed by Tse-1. Two distinct sequence motifs are absolutely essential for function of this enhancer: a cAMP response element (CRE), which is the target for repression by Tse-1, and a hepatocyte-specific element. The specificity of the enhancer is generated by the combination of these two essential elements, which are fully interdependent. In vivo footprinting indicates that Tse-1 acts by affecting protein binding at the CRE. A direct antagonism between Tse-1 and the cAMP signaling pathway suggests that Tse-1 plays a role in control of developmental activation of the TAT gene.     

Drosophila acetylcholinesterase: Characterization of different mutants resistant to insecticides

Selection of field populations originating from several countries allowed us to isolate 13 strains ofDrosophila melanogaster resistant to parathion.In vitro studies of acetylcholinesterase inhibition by paraoxon have been carried out on purified enzymes: most of the resistant strains harbor an altered acetylcholinesterase. Enzymes with higher resistance levels have been characterized with respect to their cross-resistance toward several insecticides. The patterns obtained have permitted us to group them and to delineate four categories. The existence of four distinct types of protein suggests that several mutations of acetylcholinesterase are responsible for insecticide resistance inDrosophila.     

Micropropagation of Sterculia urens Roxb. — an endangered tree species

An in vitro procedure for large scale multiplication of Sterculia urens Roxb. (Gum Kadaya Tree) has been developed using cotyledonary node segments. An average of 4.0 shoots per node were obtained on Murashige and Skoog's (MS) medium containing 2.0 mgl^–1 6-benzyl amino-purine (BAP) within 21 days of initial culture. Upon subsequent subculture 16 shoots/node could be harvested every three weeks and upto three times. Sixty per cent of the shoots were successfully rooted. Rooted plantlets were transferred to plastic pots containing soil under mist house conditions before they were finally exposed to an external environment. Fifty seven per cent of the plantlets survived in nursery sheds.     

Degradation of acrylic acid by fungi from petrochemical activated sludge

Summary Geotrichum sp. and Trichoderma sp. isolated from petrochemical effluent treatment plant activated sludge completely degraded 2 g acrylic acid/l as sole carbon source in 4 d. However, after neutralization with Ca(OH)₂, concentration as high as 10 g/l was degraded in 6 d. During the degradation acetic acid and -hydroxy propionic acid transiently accumulated.     

Demonstration of pH control in a commercial immobilized glucose isomerase

The synthesis of a variety of important biochemicals involves multistep enzyme-catalyzed reactions. In many cases, the optimal operating pH is much different for the individual enzymatic steps of such synthesis reactions. Yet, it may be beneficial if such reaction steps are combined or paired, allowing them to occur simultaneously, in proximity to one another, and at their respective optimal pH. This can be achieved by separating the micro-environments of the two steps of a reaction pathway using a thin urease layer that catalyzes an ammonia-forming reaction. In this article, the pH control system in a commercial immobilized glucose (xylose) isomerase pellet, which has an optimal pH of 7.5, is demonstrated. This system allows the glucose isomerase to have near its optimal pH activity when immersed in a bulk solution of pH 4.6. A theoretical analysis is also given for the effective fraction of the immobilized glucose isomerase, which remains active when the bulk pH is at 4.6 in the presence of 20 mM urea versus when the bulk pH is at its optimal pH of 7.5. Both theoretical and experimental results show that this pH control system works well in this case. (c) 1996 John Wiley & Sons, Inc.     

Transfer of heavy metals from sediment to fish,and their biliary excretion

Uptake and biliary excretion of metals were studied in rainbow trout, Oncorhynchus mykiss, exposed through spiked sediment to a mixture of seven heavy metals. Metal concentrations and toxicity of bile and blood plasma were used as indicators of exposure. Among the seven metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) only three (Cu, Hg, and Pb) were concentrated in the bile (bile-plasma ratio >1). Bile-plasma ratios in the rainbow trout were similar to those found in rats for Cu and Hg. Daphnia magna bioassays were used to determine toxicity of bile and blood plasma in the same trout. Toxicity of bile and blood plasma increased after treatment with acid. An analysis of variance (ANOVA) showed that toxicity of bile and blood plasma to D. magna in metal-exposed trout was significantly correlated with (1) bile and blood plasma test concentration, (2) acid treatment of bile and blood plasma (hydrolysis of metal-plasma and metal-bile complexes) and (3) sediment concentration of metals during exposure of trout. In order to significantly detect the magnitude of the exposure to a xenobiotic the biomarker must respond in a dose- or time-dependent manner. Therefore, the potential use of bile toxicity as a biomarker of heavy metal exposure in fish is probably limited by the low bioconcentration of many of these toxicants in bile.