Toxicity of chromium to the marine planktonic copepodAcartia clausi,Giesbrecht

The toxicity of chromium to the marine planktonic copepodAcartia clausi, Giesbrecht was studied. The LC50 48 h values (concentration of chromium lethal to 50% of the test animals) vary with the experimental temperature, the form of chromium compound tested and the annual generation to which theAcartia specimens belong. The elevation of temperature resulted in a considerable increase ofAcartia's sensitivity to chromium. Cr⁶⁺ in the form of Na₂CrO₄ was more toxic toA. clausi than in the form of CrO₃ · Cr³⁺ in the form of Cr(NO₃)₃ 9 H₂O precipitated to the bottom and was not toxic toAcartia.Acartia specimens belonging to the summer generation were more sensitive to chromium than those belonging to the winter or autumn generation. The exposure ofAcartia to sublethal concentrations of chromium resulted in a reduction of its longevity proportional to the chromium concentrations used.Furthermore, whenA. clausi was exposed to sublethal chromium concentrations it showed a decrease of feeding capacity and increase of respiratory rates, which became more pronounced with increasing chromium concentrations.     

Pollution effects on the phytoplankton-zooplankton relationships in an inshore environment

The quantitative and qualitative relationships between the phytoplankton and zooplankton populations were examined for one year in an inshore environment (Elefsis Bay) of the Aegean Sea. It was found that quantitative relationships among these populations were influenced by the trophic level of the environment and their stocks were significantly correlated only in non-polluted conditions. The quantitative relationship between the principal grazers in the zooplankton population (Acartia clausi, Oithona nana) and the phytoplankton dominant species Exuviaella baltica, upon which these copepods were believed to graze preferentially, was tested and the results were discussed.     

Structure and development of the egg of the glossiphoniid leech Theromyzon rude: reorganization of the fertilized egg during completion of the first meiotic division

Reorganization of the fertilized egg during completion of the first meiotic division was studied in the glossiphoniid leech Theromyzon rude. Rotation of the meiotic spindle, presumably as a result of changes in the length and arrangement of astral fibers, allows one of its poles to approach the prospective animal pole (AP), which appears as a differentiated region of the ectoplasm. The peripheral spindle pole is greatly modified during its anchorage to the AP and is dismantled upon emission of the first pole cell. Meanwhile, the central spindle pole is less modified and is reused during the second meiotic division. Redistribution of microvilli, as well as rearrangement of the ectoplasmic actin lattice, lead to remodeling of the egg surface. Emission of the first pole cell is preceded by a contraction wave that seems to arise by condensation of subcortical actin filaments at the equator of the egg. Poleward displacement of this wave causes evagination of the AP and ooplasmic segregation. A cytokinetic contractile ring forms by assembly of cortical actin filaments at the base of the AP evagination. When this process is disturbed by colchicine or cytochalasin B treatment, abortive or ghost pole cells may be formed.     

Influence of short-chain fatty acids on the production of spiramycin by Streptomyces ambofaciens

Summary The addition of short-chain fatty acids stimulates the production of spiramycin by Streptomyces ambofaciens cultivated on dextrins and ammonium chloride. The fatty acids were activated by two enzymatic systems. The first system (acyl-CoA synthetases) was present only during the exponential phase. The second system (acylkinases coupled with acylphosphotransferases) was synthesized during the growth phase and during the stationary phase, in which spiramycin production started. Short-chain fatty acids induced the synthesis of acylkinases and acylphosphotransferases. Added at the beginning of cultures, they increased the specific activity of these enzymes during the exponential growth phase. Added at the early stationary phase, the specific activity of these enzymes and of the spiramycin production increased. Excess ammonium in the culture considerably lowered the specific activity of acylkinases synthesized in the stationary phase, when spiramycin productiin started. This ammonium effect can be reduced by the addition of short-chain fatty acids.Offprint requests to: A. Lebrihi     

Interspecific incompatibility in Populus: inhibition of tube growth and behaviour of the male germ unit inP. deltoides×P. alba cross

Summary In order to better understand the cellular events controlling interspecific incompatibility in the genus Populus, the incompatible cross betweenP. deltoides andP. alba has been investigated both at the light and electron microscopic levels. Stained in decolourized aniline blue and observed by epifluorescence microscopy, most incompatible pollen grains are seen to germinate at the stigma surface. Numerous incompatible pollen tubes reach the base of the style where they are arrested 19 h after pollination. Ultrastructural observations on in vivo growing incompatible pollen tubes confirm these data. Very few cytoplasmic modifications are seen within living pollen tubes reaching the lower end of the style or within arrested ones, except the presence of polymorphic plastids. In this predominantly tricellular system, the male germ unit (MGU) is apparently initiated at pollen maturity as an association between the vegetative nucleus and sperm cells. It is maintained during pollen tube growth within the style and persists within arrested incompatible pollen tubes. The unique observation of an association between a dividing generative cell at metaphase and the vegetative nucleus is also reported. Arrested pollen tubes are characterized by apical deformations and accumulation of callose within their thickened cell walls. These cytological data provide additional information on the cellular events associated with interspecific incompatibility in Populus.Abbreviations DAPI 4,6-diamino-2-phenylindole - FCR fluorochromatic reaction - MGU male germ unit     

Fragile site (16) (q22)

Summary The rare autosomal fragile site, fra (16)(q22), is the most common of all rare autosomal fragile sites and has a heterozygote frequency of about 5%. Evidence for it was found following the segregation expected from a simple codominant trait with complete penetrance; this is in contrast to a variety of other rare autosomal fragile sites. Based on the analysis of 12 families in which fra (16)(q22) is segregating, we found that, whereas complete penetrance could be confirmed, the transmitting parent was significantly more likely to be of the female sex. On the other hand, there was no evidence for preferential transmission to offspring of either sex.     

Enzymes associated with metabolism of xylose and other pentoses by Prevotella (Bacteroides) ruminicola strains, Selenomonas ruminantium D, and Fibrobacter succinogenes S85.

Prevotella (Bacteroides) ruminicola strains B(1)4 and S23 and Selenomonas ruminantium strain D used xylose as the sole source of carbohydrate for growth, whereas Fibrobacter succinogenes was unable to metabolize xylose. Prevotella ruminicola strain B(1)4 exhibited transport activity for xylose. In contrast, F. succinogenes lacked typical xylose uptake activity but did exhibit low binding potential for the sugar. Prevotella ruminicola strains B(1)4 and S23 as well as S. ruminantium D showed low xylose isomerase activities but higher xylulokinase activities, using assays that gave high activities for these enzymes in Escherichia coli. Xylose isomerase appeared to be produced constitutively in these ruminal bacteria, but xylulokinase was induced to varying degrees with xylose as the source of carbohydrate. Fibrobacter succinogenes lacked xylose isomerase and xylulokinase. All three species of ruminal bacteria possessed transketolase, xylulose-5-phosphate epimerase, and ribose-5-phosphate isomerase activities. Neither P. ruminicola B(1)4 nor F. succinogenes S85 showed significant phosphoketolase activity. The data indicate that F. succinogenes is unable to either actively uptake or metabolize xylose as a result of the absence of functional xylose permease, xylose isomerase, and xylulokinase activities, although it and both P. ruminicola and S. ruminantium possess the essential enzymes of the nonoxidative branch of the pentose phosphate cycle.     

Isolation and chromosomal localization of a novel FMS-like tyrosine kinase gene

We have isolated and sequenced part of a new gene of the tyrosine kinase family. This gene, called FLT3, has strong sequence similarities with members of a group of genes encoding growth factor receptors: FMS, KIT, and PDGFR. We have localized the human FLT3 gene to chromosome 13, band q12, and its mouse homolog to chromosome 5, region G.     

Energetics of the growth of Methanobacterium thermoautotrophicum and Methanococcus thermolithotrophicus on ammonium chloride and dinitrogen

Methanobacterium thermoautotrophicum was grown in continuous culture in a fermenter gassed with H₂ and CO₂ as sole carbon and energy sources, and in a medium which contained either NH₄Cl or gaseous N₂ as nitrogen source. Growth was possible with N₂. Steady states were obtained at various gas flow rates with NH₄Cl and with and the maintenance coefficient varied with the gas input and with the nitrogen source. Growth of Methanococcus thermolithotrophicus in continuous culture in a fermenter gassed with H₂, CO₂ as nitrogen, carbon and energy sources was also examined.Abbreviations molecular growth yield (g dry weight of cells per mol of CH₄ evolved) - growth rate (h^-1) - D dilution rate (h^-1) - rate (h_-1); relation of Neijssel and Tempest and of Stouthamer and Bettenhaussen - energy     

Characterization and purification of thermostable beta-glucosidase from Clostridium thermocellum.

A β-glucosidase was isolated from $\text{Clostridium thermocellum}$; the enzyme was localized in the periplasmic space.It was purified in a five-step procedure including ion-exchange chromatography on DEAE-Cellulose, chromatography on HA-Ultrogel and DEAE-Sephadex, gel filtration on AcA 34 Ultrogel and isoelectric focusing.The final preparation was purified 944-fold with a recovery of about 5% of the initial enzyme activity.Polyacrylamide disc electrophoresis of the purified enzyme gave a single band at pH 8.3. The enzyme is active towards cellobiose and p-nitrophenyl-β-D-glucoside(PNPG) and developed maximum activities at pH 6.0 and 65°C. A molecular weight of 50,000 daltons was estimated by gel filtration and the enzyme was isoelectric at pH 4.68.