Chemical synthesis of a 7 kDa insect gonadotropic neurohormone

An original insect neurohormone of 65 residues was synthesized by the solid-phase methodology using t-Boc strategy and Boc-Val-PAM–resin. The purification, conducted by several steps of liquid chromatography having mass, polarity or charge as separative criteria, yielded the product with the correct molecular weight of 6922 Da determined by mass spectrometry. The synthetic peptide had both the same affinity for the antinative neurohormone serum and the same biological activity as the native neurohormone.     

Effects of T3 and rearing temperature on growth and skeletal myosin heavy chain isoform transition during early development in the salmonid Salvelinus alpinus (L.)

Rearing of 1-year-old Arctic charr (Salvelinus alpinus) at 12°C, as well as the administration of 50 or 75 mgT₃/kg feed, accelerated the neonatal to adult fast myosin heavy chain transition, but the effect of temperature was more dramatic than the effect of T₃ administration. The endogenous plasma levels of T₃ in charrs reared at 12°C were higher than those of analogous groups reared at natural temperature, which in the period under study was between 0.5 and 12°C. As in other species, T₃ seemed to play a role in the regulation of the neonatal to adult fast myosin isoform transition by down-regulating the levels of the neonatal and increasing the levels of an adult fast myosin heavy chain. Temperature seemed to accelerate this transition at least, but not only, by inducing an increase in the endogenous levels of T₃ in the Arctic charr.     

Partial Purification and Immunocytocharacterization of the Plasma Membrane ATPase of Jerusalem artichoke (Helianthus tuberosus L.) Tubers in Relation to Dormancy

Plasmalemma ATPase from Jerusalem artichoke tubers was studiedin relation to the dormancy of tubers. After partial purification,one peptide of 110 kDa appeared on SDS PAGE electrophoresisfrom dormant and non-dormant materials. ATPase specific activitywas twice higher on dormant material in the crude and solubilizedfractions, but was the same in both materials after partialpurification. Immunolabeling of this enzyme was made using aspecific antibody raised against the C terminal portion of theH⁺-ATPase from Arabidopsis thaliana. Immunolabeling was morepronounced in dormant material, in vitro and in situ. Severalworks had shown that the C terminal part of the enzyme couldbe involved in its regulation. The results presented are discussedin relation to the hypothesis according to which an internaleffector could modulated the plasmalemma ATPase activity, duringdormancy breaking. (Received October 25, 1993; Accepted September 6, 1994)     

Effect of exogeneous methyl oleate on the time course of some parameters of Streptomyces hygroscopicus NRRL B-1865 culture

Addition of methyl oleate to a Streptomyces hygroscopicus NRRL B-1865 culture modified the metabolic properties of this strain. This addition decreased the pH of the medium, increased the valine uptake of the cells and reduced their consumption of glucose until the beginning of antibiotic biosynthesis, which was delayed. At the same time, an increase in growth (× 1.8) and a marked improvement in antibiotic production (× 20) could be observed. The use of labelled methyl oleate showed that methyl oleate was not a precursor of antibiotics produced by S. hygroscopicus NRRL B-1865. It is suggested that methyl oleate addition may cause some alteration in membrane permeability, inducing an increase in H⁺ extrusion and stimulating the accumulation of branched amino acids, known to be direct precursors of polyether antibiotics. Correspondence to: L. David     

The loss of culturability by Escherichia coli cells in seawater depends on availability of phosphate ions and phosphate transport systems

Using strains with or without the PhoE porin or different components of the phosphate regulon, we determined that maintenance of the culturability of Escherichia coli in seawater depended significantly on the presence of structures allowing access of phosphate ions to the periplasm, then to the cytoplasm of cells. Cells totally deprived of the two main phosphate transport systems (Pit, Pst) exhibited the highest loss of culturability. Most of this effect resulted from the loss of the high-affinity Pst system, and more specifically that of the periplasmic phosphate-binding protein PhoS. Survival was enhanced in seawater supplemented with phosphate (0.5 mm), whether or not these structures were present. From an ecological point of view, it is assumed that the presence of phosphate ions, even at low concentrations, can influence the behavior of E. coli cells in seawater. Offprint requests to: M.J. Gauthier     

Volatile sensation: The chemical ecology of the earthy odorant geosmin

Geosmin may be the most familiar volatile compound, as it lends the earthy smell to soil. The compound is a member of the largest family of natural products, the terpenoids. The broad distribution of geosmin among bacteria in both terrestrial and aquatic environments suggests that this compound has an important ecological function, for example, as a signal (attractant or repellent) or as a protective specialized metabolite against biotic and abiotic stresses. While geosmin is part of our everyday life, scientists still do not understand the exact biological function of this omnipresent natural product. This minireview summarizes the current general observations regarding geosmin in prokaryotes and introduces new insights into its biosynthesis and regulation, as well as its biological roles in terrestrial and aquatic environments.     

Inferring landscape resistance to gene flow when genetic drift is spatially heterogeneous

In connectivity models, land cover types are assigned cost values characterizing their resistance to species movements. Landscape genetic methods infer these values from the relationship between genetic differentiation and cost distances. The spatial heterogeneity of population sizes, and consequently genetic drift, is rarely included in this inference although it influences genetic differentiation. Similarly, migration rates and population spatial distributions potentially influence this inference. Here, we assessed the reliability of cost value inference under several migration rates, population spatial patterns and degrees of population size heterogeneity. Additionally, we assessed whether considering intra-population variables, here using gravity models, improved the inference when drift is spatially heterogeneous. We simulated several gene flow intensities between populations with varying local sizes and spatial distributions. We then fit gravity models of genetic distances as a function of (i) the ‘true’ cost distances driving simulations or alternative cost distances, and (ii) intra-population variables (population sizes, patch areas). We determined the conditions making the identification of the ‘true’ costs possible and assessed the contribution of intra-population variables to this objective. Overall, the inference ranked cost scenarios reliably in terms of similarity with the ‘true’ scenario (cost distance Mantel correlations), but this ‘true’ scenario rarely provided the best model goodness of fit. Ranking inaccuracies and failures to identify the ‘true’ scenario were more pronounced when migration was very restricted (<4 dispersal events/generation), population sizes were most heterogeneous and some populations were spatially aggregated. In these situations, considering intra-population variables helps identify cost scenarios reliably, thereby improving cost value inference from genetic data.     

Recherches cytogénétiques sur les solanum,section tuberarium

Résumé Il ressort de divers essais de traitement de graines deS. Antipoviczii, par la colchicine, que la concentration optima est de l'ordre de 0,2%. La durée de l'immersion doit être d'environ 6 heures, s'il s'agit de graines prégermées; de 5 à 6 jours, s'il s'agit de graines sèches. Des observations analogues ont été faites, après traitements semblables, chezS. verrucosum etS. longipedicellatum.Le traitement, dans les conditions précitées, de graines deS. tuberosum, variétés Flava et Katahdin, a donné des plantes octoploïdes réduites, à feuilles coriaces, à pigmentation très foncée, terminalement ramifiées (Flava) ou non ramifiées (Katahdin); elles se sont montrées entièrement stériles pendant deux années consécutives, après avoir végété pendant 9 à 10 mois; leurs tubercules sont petits et peu nombreux.

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Summary Various colchicine treatments of seeds, inS. Antipoviczii, have shown that the optimum concentration of the solution is 0,2%. Pre-germinated seeds should be soaked for about 6 hours and dry seeds 5 or 6 days, as is indicated through cytological analysis at various steps of the treatment. The same result have been obtained withS. verrucosum andS. longipedicellatum.After such a treatment, octoploids plants ofS. tuberosum var. Flava and var. Katahdin have been produced, which remain small and form thick dark-green leaves; the stem is thick, but very flexible, with dense terminal ramification (Flava) or without ramification (Katahdin). They produce a few small tubers but are completely sterible; in 1953 and in 1954, no flower has appeared even after a vegetative period of 9–10 months each year.

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Samenvatting Een vergelijking van verschillende colchicine-concentraties, waarin zaden vanSolanum antipoviczii geweekt werden, heeft aangetoond dat de optimum-concentratie van de oplossing 0.2% bedraagt. Voorgekiemde zaden verlangen een onderdompeling van ongeveer zes uur, droge zaden vereisen vijf tot zes dagen, zoals bleek uit een cytologische analyse op verschillende tijdstippen tijdens de behandeling. Dezelfde resultaten werden verkregen metS. verrucosum en metS. longipedicellatum.Na zulk een behandeling werden octoploide planten vanS. tuberosum var. Flava en var. Katahdin verkregen, welke planten klein blijven en donkergroene, leerachtige bladeren vormen; de stengel is dik, maar goed buigbaar, met een dichte terminale vertakking (Flava) of onvertakt (Katahdin). Deze planten bleken twee jaar lang (1953 en 1954) volkomen steriel te zijn, in deze zin, dat ze na een vegetatieve groeitijd van 9–10 maanden niet tot bloei zijn gekomen. Wel produceerden ze talrijke kleine knolletjes.

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Recherches subsidiées par le Fonds National de la Recherche Scientifique (Crédits aux Chercheurs).