Etude olfactométrique de l'action de diverses substances allélochimiques végétales dans la recherche de l'hote par Diadromus pulchellus (Hymenoptera,Ichneumonidae)

Résumé La recherche de l'habitat d'un hôte potentiel par D. pulchellus, endoparasite considéré comme spécialiste des nymphes d'A. assectella, est abordée chez les adultes femelles et mâles, en olfactométrie, par l'étude de leur comportement locomoteur. L'activité locomotrice et l'attraction sont ainsi analysées en présence de substances allélochimiques issues ou non de végétaux pouvant abriter un hôte. Que les composés soufrés testés soient stables ou non, ils ne déclenchent pas d'attraction chez les hyménoptères quel que soit leur sexe et le type d'olfactomètre utilisé, contrairement aux imagos du phytophage-hôte, A. assectella, attirés par les composés soufrés instables spécifiques du poireau. L'activité locomotrice des hyménoptères des deux sexes est stimulée par divers composés volatils soufrés de synthèse ou émis naturellement par les Crucifères et par les Allium consommés par les larves d'A. assectella. Les substances efficaces sont généralément stables et sont caractérisées par le groupement actif R-S-, à condition que R ne soit pas un allyle. Par ailleurs, des composés volatils non soufrés contenus dans des végétaux autres que les Allium et les Crucifères ne stimulent pas le comportement locomoteur des hyménoptères. Ces différentes observations permettent d'envisager que D. pulchellus est un spécialiste inféodé à des microlépidoptères s'alimentant sur des végétaux soufrés et non sur les seuls Allium.

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Summary Searching the host habitat by the endoparasite wasp Diadromus pulchellus, considered to be a specialist of Acrolepiopsis assectella nymphs, is studied in females and males by analysis of locomotory behaviour in olfactometers. Thus, locomotor activity and attraction are studied in the presence or absence of air-borne volatiles emitted by plants able to shelter a potential host-moth. Stable and unstable sulphur compounds used do not release attraction in female and male ichneumonids whatever the type of olfactometer used. By contrast, phytophagous host adults are attracted by unstable specific sulphur compounds of the leek. Locomotor activities of D. pulchellus females and males are stimulated by various volatile sulphur compounds of synthetic origin or naturally occurring in Allium eaten by A. assectella larvae and in Crucifera. The effective compounds generally are stable and characterized by the active group R-S — in which the alkyl moiety must not be an allyl one. On the other hand, volatiles without sulphur, emitted by plants which do not belong to Cruciferae or Allium, do not stimulate the hymenopteran locomotor activity. These observations suggest that D. pulchellus is oligophagous, attracted to microlepidoptera developing on plants containing sulphur compounds and not only on Allium.

     

Protein-free models for the proton-coupled reduction of haemoproteins

Reduction of the bis-pilocarpate-haemin complex at pH greater than or equal to 10 involves the simultaneous uptake of an electron by the Fe(III) ion and a proton by the pendant alkoxide group of an axial ligand. This provides a protein-free model for reactions such as the proton-coupled reduction of cytochromes which involve cooperative Coulombic interaction between two non-bonded sites.     

Physical reasons for secondary structure stability: alpha-helices in short peptides

It was recently found that some short peptides (including C- and S-peptide fragments of RNase A) can have considerable helicity in solution, ^1–12 which was considered to be surprising. Does the observed helicity require a new explanation, or is it consistent with previous understanding? In this work we show that this helicity is consistent with the physical theory of secondary structure^12–19 based on an extension of the conventional Zimm-Bragg model.²⁰ Without any special modifications, this theory explains reasonably well almost all the experimentally observed dependencies of helicity on pH, temperature, and amino acid replacements. We conclude that the observed “general level” of helicity of C- and S-peptides (5–30% at room temperature and 10–50% near 0°C) is “normal” for short peptides consisting mainly of helix-forming and helix-indifferent residues. The helicity is modified by a multitude of weak specific side chain interactions, many of which are taken into account by the present theory;^13–19 some discrepancies between the theory and experiment can be explained by weak side-chain-side chain interactions that were neglected. A reasonable coincidence of the theory with experiment suggests that it had been used to investigate the role of local interactions in the formation of α-helical “embryos” in unfolded protein chains.     

A form-function analysis of photon capture for seaweeds

A large material of planktonic and semiplanktonic micro-crustaceans from various type of waters in south and central Sweden was computerized. The more frequent species were listed according to pH-preference and relation to humic content measured as mg Pt/l. Species indicating oligotrophy have their optima just below the neutral point, eurytopic ones around this level, while the eutrophic species Daphnia cucullata and D. magna were closely correlated with higher pH-levels. No really extreme pH-preference was observed. There is no link between trophic indication and the ranking list for humic content. Most planktic species occur at lower humic contents and semiplankters at higher.     

Properties of the foot inhibitor from hydra

Summary A substance was isolated from crude extracts of hydra that inhibits foot regeneration. This substance, the foot inhibitor, has a molecular weight of 500 daltons. It is a hydrophilic molecule, slightly basic in character and it has no peptide bonds. The pruified substance acts specifically and at concentrations lower than 10^–7 M. At this low concentration only foot and not head regeneration is inhibited. Hydra are sensitive to purified foot inhibitor between the second and eight hour after initiation of foot regeneration by cutting. In normal animals the foot inhibitor is most likely produced by nerve cells. A substance with similar biological and physico-chemical properties is found in other coelenterates.     

The use of inorganic substances to stimulate gut evacuation in Daphnia magna

Observations were done on the effect of inorganic substances on the gut evacuation process in Daphnia magna. Procedures which accelerate this process are described.     

RUS家族对植物生长发育的调控作用

叶绿体基因组编码许多参与光合作用和其他代谢过程的关键蛋白质,在叶绿体中合成的代谢物对于植物正常的生长发育至关重要。根对紫外线-B辐射敏感[Root-UVB (ultraviolet radiation B)-sensitive, RUS]蛋白属于叶绿体蛋白,由高度保守的DUF647结构域组成,在参与植物形态发生、物质运输和能量代谢等多种生命活动的调控中发挥作用。本文就近年来关于RUS家族在植物的胚胎发育、光形态建成、维生素B6稳态、生长素转运和花药发育等生长发育过程中的相关研究进行回顾和总结,为深入研究其在植物生长发育中的分子调控机制提供了参考。     

Immune challenge mediates vocal communication in a passerine bird: an experiment

Secondary sexual characters may have evolved in part to signalresistance to parasites. Avian song has been hypothesized tobe involved in this process, but the role of parasites in modulatingacoustic communication systems in birds remains largely unknown,owing to lack of experiments. We studied the relationship betweenparasitism, testosterone, song performance, and mating successin male collared flycatchers (Ficedula albicollis) by experimentallychallenging their immune system with a novel antigen. We predictedthat a challenge of the immune system would reduce song performance,and that this reduction would be conditional on the size ofa visual sexual signal, the forehead patch that was previouslyfound to reflect resistance. An antagonistic linkage betweentestosterone and immune function would predict that a challengeof the immune system should suppress testosterone level. Animmunological treatment by sheep red blood cells (SRBCs) triggereda decrease in body mass, testosterone level, and song rate,but other song traits were not significantly affected by theantigen challenge. Initial testosterone level was associatedwith forehead patch size and all song traits except song rate.SRBC injection caused stronger reduction in song rate amongmales with smaller forehead patches, and the change in songrate was also predictable by song features such as strophe complexityand length. We show that song rate and other song characteristicsmay be important cues in male-male competition and female choice.These results suggest that parasite-mediated sexual selectionhas contributed in shaping a complex acoustic communicationsystem in the collared flycatcher, and that testosterone mayplay an important role in this process. Parasitism may drivea multiple signaling mechanism involving acoustic and visualtraits with different signal function.     

Fungal laccases - occurrence and properties

Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.     

A critique of the utility of the prediction of protein secondary structure

The Chou-Fasman predictive algorithm for determining the secondary structure of proteins from the primary sequence is reviewed. Many examples of its use are presented which illustrate its wide applicability, such as predicting (a) regions with the potential for conformational change, (b) sequences which are capable of assuming several conformations in different environments, (c) effects of single amino acid mutations, (d) amino acid replacements in synthesis of peptides to bring about a change in conformation, (e) guide to the synthesis of polypeptides with definitive secondary structure,e.g. signal sequences, (f) conformational homologues from varying sequences and (g) the amino acid requirements for amphiphilicα-helical peptides.