Can transposable element copy number distribution parameters be estimated from natural populations of Drosophila melanogaster?

The copy frequency distribution of a transposable element family in a Drosophila melanogaster natural population is generally characterised by the values of the Charlesworths' model parameters α and β (Charlesworth & Charlesworth, 1983). The estimation of these parameters is made using the observed distribution of the occupied sites in a population sample. Several results have been interpreted as due either to the influence of stochastic factors or to deterministic factors (transposition, excision, selection…). The accuracy of this method was tested by estimations performed on samples from simulated populations. The results show that with the sample size usually used for natural population studies, the confidence intervals are too large to reasonably deduce either the element copy number distribution or the values of transposition and excision rate and selective coefficients.     

Phase transition kinetics of phosphatidic acid bilayers A stopped-flow study of the electrostatically induced transition

The kinetics of the electrostatically induced phase transition of dimyristoyl phosphatidic acid bilayers was followed using the stopped-flow technique. The phase transition was triggered by a fast change in the pH or the magnesium ion concentration and followed by recording the time dependence of the absorbance. When the phase transition was induced by a pH jump the time course of the absorbance could be described by two exponentials, their time constants displaying the for cooperative processes characteristic maximum at the transition midpoint. The time constants are in the 10 and 100 ms range for the H⁺ triggered transition from the fluid to the ordered state. A third slower process shows no appreciable temperature dependence and is probably caused by vesicle aggregation. For the OH^--induced transition fron the ordered to the fluid state the time constants are in the 100 and 1000 ms range. The fluid-ordered transition could also be triggered by addition of magnesium ions. Of the several observed processes only the fastest in the 10–100 ms time range could definitely be assigned to the fluid-ordered transition while the others are due to aggregation phenomena. The experimental data were compared with results obtained from pressure jump experiments and could be interpreted on the basis of theories for non-equilibrium relaxation.     

Specificity of the interaction of furfural with DNA

Furfural or 2-furaldehyde is a dietary mutagen and is present in various frequently consumed food products. The alkaline unwinding assay and protection of cleavage sites from the action of various restriction enzymes was used to study the interaction of furfural with DNA. Alkaline unwinding experiments showed the formation of an increasing number of strand breaks in duplex DNA both with increasing furfural concentration and with time of reaction. Treatment of lambda phage DNA with furfural protected cleavage with restriction endonucleases DraI and SspI but not with ApaI, BssHII and SacII. These results indicate that under the conditions used furfural reacts exclusively with AT base pairs. A minimum of 3-4 consecutive AT base pairs are required for this reaction. This was determined by the use of several restriction enzymes whose hexanucleotide recognition sequences contain subsets of AT base pairs.     

Basal prostaglandin synthesis by the isolated perfused rat kidney

In order to assess the main characteristics of the prostaglandin (PG) biosynthesis by the isolated perfused rat kidney, the urinary and venous outputs of PGE2, PGF2alpha, 6-keto-PGF1alpha and of thromboxane (Tx)B2 were followed during 120 min after an equilibration period of 30 min. Single pass kidneys were perfused with a Krebs-Henseleit solution added with Polygeline at a constant flow rate providing a perfusion pressure about 90 mm Hg. From the beginning of the study, major differences could be observed in the renal biosynthetic rate of the 4 PG studied which were mainly excreted into the venous effluent. During the perfusion, urinary and venous outputs of PGE2, PGF2alpha and of TxB2 remained stable whereas those of 6-keto-PGF1alpha sharply increased and were found inversely related to the glomerular filtration rate (r = -0.95; p n 0.001). Finally, the urinary and venous outputs of each of the four PGs studied were found positively related. It is concluded that the isolated perfused rat kidney is a valuable preparation for studying the biosynthesis of PGs and that, at least in thi model, the urinary excretion of PGs is a good index of their renal synthesis.     

Effect of alkylated and intercalated DNA on the generation of superoxide anion by riboflavin

Superoxide anion (O ₂ ^.– ) was photogenerated upon illumination of riboflavin in fluorescent light. The rate of O ₂ ^.– formation was stimulated by double stranded DNA but not by denatured DNA or RNA. Depurinated DNA, which was predominantly depleted in guanine residues, did not exhibit the stimulatory effect, indicating an interaction of riboflavin, or active oxygen species derived from it, with guanine bases. Also, the stimulation of O ₂ ^.– photogeneration was not observed with ethidium bromide but was seen with proflavin-intercalated DNA. Since ethidium bromide intercalates preferentially between purines and pyrimidines, and proflavin prefers dA-dT rich sites, these results were interpreted to suggest that the interaction of riboflavin with DNA is mainly with GC or CG base pairs.     

Enhancement of shoot regeneration potential by liquid medium culture from mature cotyledons of sunflower (Helianthus annuus L.)

We describe here a liquid culture system for the regeneration of shoots at high frequencies from mature cotyledon tissues of three genotypes of sunflower (Helianthus annuus L.) one of which had previously been found to be recalcitrant to regeneration when cotyledons were cultured on solid medium. Cotyledons were excised from 2-day-old seedlings and incubated in liquid Murashige and Skoog's modified medium supplemented with 5.4 M naphthaleneacetic acid (NAA) and 4.4 M benzylaminopurine (BAP). After two weeks in culture, the whole upper surface of regenerating explants was covered with green shootlets. The percentages of regenerating explants of three genotypes varied between 60 and 70%, and the number of shoots per regenerating explant was highly increased. The shootlets were transferred to solid Murashige and Skoog's medium allowing shoot development, then to rooting medium. Rooted plantlets were successfully acclimatized and gave fertile plants. The role of liquid medium culture in the induction of sunflower regeneration is discussed.Abbreviations BAP 6-benzylaminopurine - NAA 1-naphthaleneacetic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid     

Effect of anticancer drugs on the release of interferon γ in vitro

Summary Some conventional and experimental anticancer drugs were tested for their effect on concanavalin-A-induced interferon release from rat splenocytes in vitro. When 2.5 × 10⁶ rat splenocytes/ml, stimulated with 1 µg/ml concanavalin A, were incubated with various non-cytotoxic doses of the vinca alkaloid vincristine, there was an inhibition of the release of interferon in culture supernatants. The antitumour antibiotics bleomycin and Adriamycin, alkylating agents 4-hydroperoxycyclophosphamide and mafosfamide, and the immunoactive peptides FK 156 and FK565 did not affect the release of interferon under similar conditions. However, cyclosporin A, in similar experiments, markedly inhibited the release of interferon .     

Somaclonal variation as a tool to develop pest resistant plants of Torenia fournieri ‘Compacta Blue’

Callus cultures of Torenia fournieri Compacta Blue were initiated on a modified Murashige and Skoog salt medium (MS) with 2.26 M 2,4-dichlorophenoxyacetic acid. Shoots were regenerated from these cultures using MS medium amended with 2.46 M indolebutyric acid and 8.88 M benzyladenine. These shoot cultures were subjected to two-spotted spidermite (Tetranychus urticae Koch.) and the greenhouse whitefly [Trialeurodes vaporariorum (Westwood)]. Pests were allowed to feed until such time that their populations started to decrease due to lack of food. The remaining live tissue of the Torenia was placed on MS medium amended with 2.28 M zeatin to induce new adventitious shoots and plantlets. Newly regenerated plantlets were acclimated to greenhouse conditions and evaluated for resistance to the pest to which they were subjected in vitro. Highly significant differences in pest numbers were found in somaclones for both the two-spotted spidermite and greenhouse whitefly when compared to control plants. A wide range of variability was observed among the somaclonal population. There were significantly fewer mite eggs laid on plants regenerated from in vitro cultures screened with two-spotted spidermites than on seed sown controls. Regenerants from cultures screened with whiteflies in vitro had fewer eggs, immatures and live adults than controls.Abbreviations BA benzyladenine - IBA indolebutyric acid - 2,4-d 2,4-dichlorophenoxyacetic acid - MS Murashige and Skoog salt medium Storrs Agricultural Research Station Scientific Publication 1641.