Penetration, Development and Emigration of Juveniles of the Nematode Meloidogyne arenaria in Myrobalan Plum (Prunus cerasifera) Clones Bearing the Ma Resistance Genes

Penetration, development and emigration of M. arenaria in the roots of three Myrobalan plum (Prunus cerasifera) clones genetically characterized for their resistance to root-knot nematodes (RKN) were studied during the 10 (penetration) and 15 (emigration) days following the date of inoculation (D) of 2500 juveniles (J2s) per plant into the soil. Miniaturized tests were conducted on the two resistant clones P.2175 (Ma1 gene) and P.1079 (Ma2 gene) and the susceptible clone P.2032 (recessive for both genes), obtained from micropropagated plantlets and grown in mini-containers under controlled conditions at 25°C in a growth chamber. For penetration and development studies, nematodes in the roots were recovered by the acid fuchsin-lactophenol staining technique. Equivalent numbers of J2s were recovered in all the clones at D+1 and D+2. Subsequently, the numbers increased rapidly in P.2032 and were significantly different from those in P.1079 and P.2175 that remained at a low level. No swollen larvae were observed in the resistant clones. In P.2032, the first swollen larvae were observed at D+4, the first females were observed at D+12, whereas the first females with attached egg sacs and the first new-generation J2s were obtained between D+21 and D+28. Our data suggest that the resistance phenomenon does not act on the very early nematode penetration but acts later by preventing feeding-site induction and development into the third-stage. For emigration studies, plants in which J2s had been allowed to penetrate for two days (from D to D+2) were washed free of soil, repotted and then, after various periods of growth, soil-free roots were placed under a mistifier to evaluate the numbers of emigrating individuals. Emigration of J2s from the roots occured mainly from D+2 to D+4 in all the genotypes and was very limited from D+4 to D+10. There was no significant differences in the number of emigrated juveniles between the resistant and susceptible clones, indicating that emigration cannot explain the difference in the numbers of nematodes recovered in the roots.     

The evaluation of permethrin for wood preservation

The toxicity of the synthetic pyrethroid permethrin (NRDC 143) to a range of wood destroying insects has been investigated. In tests using Hylotrupes bajulus, Anobium punctatum, Lyctus brunneus and Reticulitermes santonensis permethrin showed a similar order of toxicity to that of gamma-BHC. Although the toxicity of permethrin to adult A. punctatum was of the same order as that of gamma-BHC, the toxicity to larvae was rather lower. The implications of these results are discussed and it is concluded that, subject to further field evaluation, permethrin could provide an alternative to gamma-BHC and dieldrin in wood preservatives.     

Docosahexaenoic Acid Is Naturally Concentrated at the sn-2 Position in Triacylglycerols of the Australian Thraustochytrid Aurantiochytrium sp. Strain TC 20

The Labyrinthulomycetes or Labyrinthulea are a class of protists that produce a network of filaments that enable the cells to glide along and absorb nutrients. One of the main two Labyrinthulea groups is the thraustochytrids, which are becoming an increasingly recognised and commercially used alternate source of long-chain (LC, ≥C₂₀) omega-3 containing oils. This study demonstrates, to our knowledge for the first time, the regiospecificity of the triacylglycerol (TAG) fraction derived from Australian thraustochytrid Aurantiochytrium sp. strain TC 20 obtained using ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) analysis. The DHA present in the TC 20 TAG fraction was determined to be concentrated in the sn-2 position, with TAG (16:0/22:6/16:0) identified as the main species present. The sn-2 preference is similar to that found in salmon and tuna oil, and differs to seal oil containing largely sn-1,3 LC-PUFA. A higher concentration of sn-2 DHA occurred in the thraustochytrid TC 20 oil compared to that of tuna oil.     

Variations in dark respiration and mitochondrial numbers within needles of Pinus radiata grown in ambient or elevated CO2 partial pressure

Within-leaf variations in cell size, mitochondrial numbers and dark respiration rates were compared in the most recently expanded tip, the mid-section and base of needles of Pinus radiata D. Don trees grown for 4 years in open-top chambers at ambient (36 Pa) or elevated (65 Pa) carbon dioxide partial pressure (p(CO2)a). Mitochondrial numbers and respiratory activity varied along the length of the needle, with the highest number of mitochondria per unit cytoplasm and the highest rate of respiration per unit leaf area at the base of the needle. Regardless of the location of the cells (tip, middle or basal sections), needles collected from trees grown in elevated p(CO2)a had nearly twice the number of mitochondria per unit cytoplasm as those grown in ambient p(CO2)a. This stimulation of mitochondrial density by growth at elevated p(CO2)a was greater at the tip of the needle (2.7 times more mitochondria than in needles grown in ambient CO2) than at the base of the needle (1.7 times). The mean size of individual mitochondria was unaffected either by growth at elevated p(CO2)a or by position along the needle. Tree growth at elevated p(CO2)a had a variable effect on respiration per unit leaf area, significantly increasing respiration in the tip of the needles (+25%) and decreasing respiration at the mid-section and base of the needles (-14% and -25%, respectively). Although a simple relationship between respiration per unit leaf area and mitochondrial number per unit cytoplasm was found within each CO2 treatment, the variable effect of growth at elevated p(CO2)a on respiration along the length of the needles indicates that a more complex relationship must determine the association between structure and function in these needles.     

La chromatographie sur couche mince: Principes et possibilités

Résumé Après un bref rappel des avantages de la chromatographie de surface sur la chromatographie sur colonne, on compare les avantages et les inconvénients respectifs de la chromatographie sur couche mince et de la chromatographie sur papier. Les méthodes générales de la chromatographie sur couche mince (CCM) sont présentées (préparation des couches, types de couches, dépot des échantillons à analyser, CCM analytique, CCM préparative, moyens de développement des chromatogrammes). Les principes généraux des divers types de chromatographie (adsorption, partage direct, partage inversé, relargage, exclusion-diffusion, échange d'ions, spécifique) qui peuvent être mis en oeuvre sont rappelés et des exemples concrets sont donnés dans chaque cas. Les problèmes de l'électrophorése et de la chromato-electrophorése sur couche mince sont également évoqués. Bien que cette méthode analytique soit le plus simple et le puissant moyen de séparation des corps en mélange, il est nécessaire de rappeler que bien des erreurs de conception sont à la base de son manque de développement dans certains domaines (chromatographie des substances hydrosolubles par exemple). A titre d'exemple on rappelle que la première chromatographie de relargage et la première chromato-electrophorése basse tension n'ont été réalisées que tout récemment.

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Summary After a brief summary of the advantages of surface chromatography compared to column chromatography, the respective advantages and inconveniences of thin-layer and paper chromatography are compared. The general methods of thin-layer chromatography are presented (preparation of the layers, types of layers, deposition of the samples to be analyzed, analytical TLC, preparative TLC, methods for developing the chromatograms). The general principles of the various types of chromatography (adsorption, direct partition, reverse partition, salting out, exclusion-diffusion, ion-exchange, specific chromatography) that may be used are reminded of, and concrete examples given in each case. The problems of electrophoresis and thin layer chromato-electrophoresis are also treated. Though this analytical method be the simplest and most powerful means for the isolation of components in mixtures, it is necessary to remind that quite a number of errors in the conception are responsible for its lack of development in certain fields (water soluble substances chromatography, for instance). As an example one might remember that the first salting-out chromatography, and the first low-tension chromatoelectrophoresis have been developed only very recently.

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Zusammenfassung Die Vorzüge der Oberflächen-Chromatographie gegenüber der Säulen-Chromatographie wurden kurz aufgezählt und die Besonderheiten der Dünnschicht- und der Papier-Chromatographie verglichen. Die Grundlagen der DC werden erklärt (Vorbereitung der Schicht, Arten der Schicht, Auftragen der Proben, analytische DC, vorbereitende DC, Entwicklungsverfahren der Chromatogramme). Anschließend werden die grundsätzlichen Verfahren der verschiedenen Typen von Chromatographie erörtert (Adsorption, direkte Trennung, inversierte Trennung, Aussalzen, Diffusion, Ionenaustausch, spezifische Verfahren), die praktisch infrage kommen. Für jeden Typ werden Beispiele gegeben. Die Probleme der Elektrophorese und der Elektrophorese-DC werden ebenfalls behandelt. Obwohl diese Analysenmethode das einfachste und stärkste Trennverfahren für Stoffgemische ist, so muß daran erinnert werden, daß ihre Entwicklung in gewissen Gebieten durch Fehler in der Auffassung gehemmt worden ist, zum Beispiel ihre Anwendung für wasserlösliche Stoffe. Verfasser weist darauf hin, daß die erste Aussalz-DC und die erste Niederspannungs-Chromato-Elektrophorese erst ganz kürzlich realisiert wurden.

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Avec la collaboration technique de MademoiselleCh. Thommegay et de MademoiselleA.-M. Drapier.     

Response of Bluebunch Wheatgrass and Medusahead to Defoliation

Our objective was to determine the short-term response of bluebunch wheatgrass and medusahead to defoliation of wheatgrass designed to stimulate regrowth through tillering. We hypothesized that defoliating bluebunch wheatgrass by 20% at the 3 to 3.5 leaf stage followed by a 50% defoliation at peak standing crop would increase its tillering and biomass production. Consequently, we expected a reduction of the density and biomass of medusahead over that of bluebunch wheatgrass defoliated 50% at peak standing crop. Treatments included four initial medusahead densities (200, 333, 444, 600 plants · m^-2) created by hand-pulling and three defoliation regimes factorially arranged (12 treatment combinations) in a randomized complete-block design and replicated four times at two sites. In 2006 and 2007, defoliation was accomplished by hand-clipping bluebunch wheatgrass 1) by 50% once at peak standing crop (late June); 2) by 20% at the 3 to 3.5 leaf stage, then again to 50% at peak standing crop (mid May, late June); or 3) plants were not clipped. Density was sampled in 2006 and 2007, and biomass was harvested only at Star Mountain (near Riverside, Oregon) in 2007 because Warm Springs (near Drewsey, Oregon) was burned by a wildfire before final 2007 data could be collected. In 2006, no treatments applied at either site detectably altered the number of tillers produced by bluebunch wheatgrass nor did they affect bluebunch wheatgrass density or biomass in 2007 at Star Mountain. Changes in medusahead density were not detected in 2006, but this annual invasive grass increased in density and biomass in 2007 at Star Mountain in plots receiving two defoliations. The relatively short growing period caused by summer drought and the relative intolerance of bluebunch wheatgrass to grazing make the twice-over grazing an unlikely practice for arid rangelands in the western United States. In fact, it could possibly increase the risk of annual grass invasion.     

Kinetics of substrate oxidation and hydrogen peroxide production by Mycoplasma mycoides subsp. mycoides Large Colony (LC) type and Mycoplasma mycoides subsp. capri

Mycoplasma mycoides subsp. mycoides Large Colony (LC) type is a pathogen of goats causing contagious agalactia and respiratory disease, found on all continents where small ruminants are kept. It shares close genetic characteristics with M. mycoides subsp. capri. Substrate oxidation by 22 strains of M. mycoides subsp. mycoides LC from nine countries was compared with that of eight strains of M. mycoides subsp. capri from five countries. There was considerable similarity in the substrates used, but substrate saturation coefficients (K_s) varied for different substrates. Substrate utilization patterns and K_s values did not (1) significantly differentiate the LC strains from each other, (2) show any correlation with geographical origin, or (3) distinguish the LC strains from the capri strains. These results support previous studies justifying the reclassification of these subspecies as a single species.