Estimation of the size of freshwater ciliate populations by a sub-sampling technique

A technique is described for the estimation of the size of ciliate populations based on replicated counts. Sample drops were taken by automatic pipettes of different volume from activated sludge and from a small oligotrophic stream. Specific aims were: 1) the estimation of the number of species; 2) the estimation of the number of individual in each species; 3) the selection of a suitable sub-sample size and number of replicates. For each volume the cumulative increase in species taken in successive sub-samples was determined. For each species the minimum permissible sub-sample volume and the number of replicates required for an allowable error of 10% and 25% were determined. Lastly, the relationship between the mean number of individuals counted for each species and the relative coefficient of variation was visualized.     

Cell lines from imaginal discs ofDrosophila melanogaster

Summary New cell lines, designated as ML-DmDl≈10, were established from dissociated imaginal discs ofDrosophila melanogaster. The culture medium was prepared by mixing in a 1:1 ratio Cross and Sang’s M3(BF) medium, supplemented with 10% heat inactivated fetal bovine serum (FBS), with the supernatant of a primary embryonic cell culture made in the M3(BF) medium and supplementing this mixture with insulin. One cell line was established in the medium containing larval hemolymph instead of the primary culture supernatan, and another was established in fresh M3(BF) medium supplemented with insulin and FBS. In these mediums, imaginal disc cells first formed aggregates and cellular vesicles within a few weeks followed by the proliferation of thin-layered cells around them after about 1 mo. Ten cell lines have so far been established from two kinds of imaginal discs and disc mixtures. The ploidy of these cell lines was predominantly diploid. Population doubling time was about 50 to 70 h at 3 to 10 mo. after initiation of the culture. When the cell aggregates formed in vitro were implanted in metamorphosing larvae, they differentiated at high frequency into adult cuticular strutures in the early phase of the primary culture. This differentiation of aggregates was also observed, though at low frequency, in a culture maintained by dilution-transfer for 6 to 15 mo. in vitro.     

大鼠非致瘤四倍体细胞系的建立及细胞遗传学和酶学特征

从大鼠自然诱发的肉瘤细胞中,我们建立了一个四倍体细胞系(4n=84),命名为RC(ratcell)。它具有典型的成纤维细胞外形,能在玻璃表面贴壁生长,但不能生长在琼脂半固体培养基中。该细胞在含15％小牛血清的RPMI 1640培养基中生长良好,至今已连续繁殖112世代,细胞群体倍增时间约为15小时。染色体G-带分析表明,RC为整四倍体细胞,它的1条X染色体在第32至34区为均染区。RC细胞核仁组织者(NORs)活性显然比大鼠二倍体细胞NORs活性的加倍还高(P<0.001)。这个具有非常高NORs活性的RC细胞系对于研究细胞18S+28S rRNA基因转录活性的调控、基因表达与基因剂量关系有一定的意义。RC细胞还有异常高的磷酸酯酶活性,而且它的同工酶谱也与大鼠肌肉细胞明显不同。体内接种实验和扫描电镜的观察表明,RC是非致瘤细胞。RC细胞各号染色体的C-带图样与大鼠二倍体细胞无明显的差异。     

Toxoplasma gondii: Microassay to differentiate toxoplasma inhibiting factor and interleukin 2

Using a sensitive, economical, and reproducible microassay, the relationship of toxoplasma inhibiting factor to interleukin 2 has been examined. The assay developed took advantage of the observation that (1) Toxoplasma gondii tachyzoites replicated efficiently in the murine monocytic cell line, RAW 264; (2) treatment of RAW 264 cells with toxoplasma inhibiting factor prevented intracellular replication of the parasite to an extent similar to that observed with identical treatment of freshly isolated murine peritoneal exudate cells; and (3) [³H]uracil incorporation was an efficacious means to quantify replication (or inhibition of replication) of tachyzoites within the cell line. Although toxoplasma inhibiting factor and interleukin 2 were both present in the same lectin -and antigen-stimulated splenocyte supernatant fluids, results from microassays strongly suggested that the molecules were two distinct entities.     

Analysis of variations of handling-time inTrichogramma maidis

Variation in handling-time is studied in the association betweenTrichogramma maidis Pintureau & Vœgelé [Hym.: Trichogrammatidae] and one of its factitious hosts: the eggs of the Mediterranean flour mothEphestia kuehniella Zeller [Lep.: Pyralidae]. It is shown that the duration of egg laying behaviour decreases exponentially from the first host egg encountered onwards. This decreasing kinetic, which corresponds to a learning ability, shows a high variability between females, but a mother-daughter regression analysis fails to demonstrate any genetic transmissibility of this learning ability over 2 successive generations. Once the learning is over, there remains a residual variability which is, in part, under genetic control. The possible consequences of these results on the stability of host-parasite associations are discussed.      

Assessment of genetic variability for N2 fixation between and within provenances of Leucaena leucocephala and Acacia albida estimated by 15N labelling techniques

Nitrogen fixed in 13 provenances of Acacia albida and 11 isolines of Leucaena leucocephala inoculated with effective Rhizobium strains was measured by ¹⁵N techniques and the total N difference method. In the test soil, on the average, L. leucocephala derived about 65% of its total N from atmospheric N₂ fixation compared to about 20% by A. albida. Significant differences in the percentage of N derived from atmospheric N₂ (% Ndfa) occurred, between provenances or isolines within species. The % Ndfa ranged from 37 to 74% within L. leucocephala and from 6 to 37 within A. albida; (equivalent to 20–50 mg N plant^–1 and 4–37 mg N plant^–1 for the two species over three months, respectively) and was correlated with the nodule mass (r=0.91). The time course of N₂ fixation of three selected provenances (low, intermediate and good fixers) was followed at 12 weekly intervals over a 36 week period. The % Ndfa of all provenances and isolines increased with time; and except for one of the L. leucocephala provenances, % Ndfa was similar within species at the 36 weeks harvest. There was a significant correlation between % Ndfa and the amount of N₂ fixed (r=0.96). Significant interactions occurred between provenances and N treatments and often growth of uninoculated but N fertilized plants was less variable than for inoculated unfertilized plants.     

Acetylcholinesterase in Mouse Neuroblastoma NB2A Cells: Analysis of Production, Secretion, and Molecular Forms

The mouse neuroblastoma cell line NB2A produces cellular and secreted acetylcholinesterase (AChE). After incubation of the cells for 4 days the ratio between AChE secreted into the medium and AChE in the cells was 1:1. The cell-associated enzyme could be subdivided into soluble AChE (25%) and detergent-soluble AChE (75%). Both extracts contained predominantly monomeric AChE (4.6S) and minor amounts of tetrameric AChE (10.6S), whereas the secreted AChE in the culture supernatant contained only the tetrameric form. All forms were partially purified by affinity chromatography. It could be demonstrated that the secretory and the intracellular soluble tetramers were hydrophilic, whereas the detergent-soluble tetramer was an amphiphilic protein. On the other hand the soluble and the detergent-soluble monomeric forms were amphiphilic and their activity depended on the presence of detergent. By digestion with proteinase K amphiphilic monomeric and tetrameric AChE could be converted to a hydrophilic form that no longer required detergent for catalytic activity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of [3H]diisopropylfluorophosphate-labelled AChE gave one band at 64 kilodaltons (kD) under reducing conditions and two additional bands at 120 kD and 140 kD under nonreducing conditions.