Technique d'élevage deChelonus contractus Nees. parasite dePhthorimea ocellatella Boyd.

Summary The Braconid,Chelonus contractus Nees, egg endoparasite ofPhthorimea ocellatella Boyd, in S.E. of France, presents only females in his progeny. Its breeding is easy with the help of the small wax moth:Gnorimoschema operculella Zell. The mass breeding is inspired from method that we established for the production ofMacrocentrus ancylivorus Roh.      

Modelling the temperature dependent growth rates of planktic foraminifera

The temperature influence on foraminifera growth rate was analysed using a mechanistic formulation that take into account enzyme inactivation at extreme temperatures. Growth rates are calculated using available published and unpublished laboratory culture experiments for eight species, including Neogloboquadrina pachyderma (sinistral and dextral forms), Neogloboquadrina dutertrei, Globigerina bulloides, Globigerinoides ruber, Globigerinoides sacculifer, Globigerinella siphonifera and Orbulina universa. Modeled growth formulas readily reproduce the observed growth patterns for all species. Similar growth patterns are observed for the species that have the same symbiotic algae G. ruber, G. sacculifer, and O. universa. However, different growth patterns are observed for herbivorous species (Neogloboquadrina genus) compared to carnivorous species with or without symbionts. Our growth estimates correspond well to in situ observations from both plankton tows and sediment traps. These estimates will help to improve the quantification of the effects of environmental parameters on foraminifera species distribution and abundance.     

Efficient microprojectile bombardment-mediated transformation of rice using gene cassettes

This study was aimed at determining whether gene cassettes (promoter-coding sequence-terminator) can be efficiently used in microprojectile acceleration-mediated co-transformation of rice in the place of whole plasmids, and to what extent their use influences the integration and expression of the co-transferred gene of interest. Two non-linked marker genes (yfp and hph) were co-introduced by microprojectile bombardment into cells of embryogenic calli in three separate experiments. Three different DNA structures were compared for their ability to transiently and stably transform rice cells: supercoiled or linearized whole-plasmid DNA, gene cassette DNA and single-stranded gene cassette DNA coated with Escherichia coli single-stranded binding (SSB) proteins. Our results demonstrate that microprojectile bombardment-mediated transformation of rice using gene cassettes is possible without significantly reducing transformation efficiency in comparison to the use of whole-plasmid DNA. Furthermore, no obvious difference in transgene integration pattern and inheritance was observed among plants transformed with gene cassettes compared to those transformed with the whole plasmid, except that concatemerization of molecules prior to integration was rarely observed in gene cassette transformants. Received: 4 April 2001 / Accepted: 13 August 2001     

L-Lactate cytochrome c reductase: rapid kinetic studies of electron transfers within the flavocytochrome b2-cytochrome c assembly

This study is part of a series aimed at the characterization of individual steps of electron transfer taking place between prosthetic flavin, heme b2, heme c within active sites and complexes. After rapid mixing of ferricytochrome c with partially reduced flavocytochrome b2, the reaction is followed at the level of two reactants, cytochrome b2 and cytochrome c. In order to define the proper reactivity of flavosemiquinone, conditions under which this form is highly stabilized (presence of pyruvate) have been chosen. With the help of simulations, it has been possible to characterize a rapid step of electron transfer from cytochrome b2 to cytochrome c within a complex (at approx. 70% saturation) and a slow step k = 5 s-1 assigned to cytochrome b2 reduction by flavosemiquinone within the active site of the pyruvate-liganded enzyme.     

Etude de l'adaptation de Bruchus affinisàLathyrus sylvestris: analyse de la mortalité avant l'installation des larves dans les graines

Résumé Bruchus affinis Frölich (Coléoptère, Bruchidae), est une espèce univoltine attirée sélectivement par les fleurs de L. sylvestris, qui constitue l'une des trois plantes dont les larves consomment les graines. Il s'agit d'un insecte typiquement spécialisé à l'exploitation de plantes particulières. Cependant, les femelles distribuent leurs ufs sur les gousses jeunes de L. sylvestris sans tenir compte, ni de leur disponibilité en graines, ni du nombre d'ufs déjà présents, alors que le développement des larves est solitaire. Les larves néonates perforent la gousse et gagnent des ovules. Plusieurs larves peuvent atteindre le même ovule, mais une seule se développe dans la graine en formation. Le nombre d'ufs pondus sur les premières gousses dépasse largement le nombre de graines qui se développeront dans ces gousses. La surabondance d'ufs sur les premières gousses entraîne une forte mortalité.Les déplacements des larves dans les gousses et leur comportement de pénétration dans les graines en croissance ne suppriment pas la compétition intraspécifique larvaire.Aucune adaptation n'ajuste la distribution des ufs et la répartition des larves à l'utilisation optimale des disponibilités en graines. Aucune stratégie adaptative ne limite le gaspillage de progéniture; la spécialisation trophique n'a pas entraîné un comportement reproducteur optimisant l'utilisation des ressources et la survie de la descendance.Bien que la période étudiée corresponde à moins de 10% de la durée du cycle annuel de B. affinis, la très forte mortalité observée entre la ponte et l'installation dans les graines constitue vraisemblablement le facteur-clé des fluctuations annuelles de la population. Les causes de cette mortalité varient d'une station à l'autre, et il est impossible de les hiérarchiser.     

Molecular adaptation of Chrysochus leaf beetles to toxic compounds in their food plants

Herbivores that feed on toxic plants must overcome plant defenses and occasionally may even benefit from them. The current challenge is to understand how herbivores evolve the necessary physiological adaptations and which changes at the molecular level are involved. In this context we studied the leaf beetles genus Chrysochus (Coleoptera, Chrysomelidae). Two species of this genus, C. auratus and C. cobaltinus, feed on plants that contain toxic cardenolides. These beetles not only avoid poisoning by the toxin but also use it for their own defense against predators. All other Chrysochus species feed on plants that are devoid of cardenolides. The most important active principle of cardenolides is their capacity to bind to and thereby block the ubiquitous Na(+)/K(+)-ATPase responsible for maintaining cellular potentials. By analyzing the DNA sequence of the putative ouabain-binding site of the alpha-subunit of the Na(+)/K(+)-ATPase gene of Chrysochus and its close relatives feeding on plants with or without cardenolides, we here trace the evolution of cardenolide insensitivity in this group of beetles. The most interesting difference among the sequences involves the amino acid at position 122. Whereas all species that do not encounter cardenolides have an asparagine in this position, both Chrysochus species that feed on cardenolide plants have a histidine instead. This single amino acid substitution has already been shown to confer cardenolide insensitivity in the monarch butterfly. A mtDNA-based phylogeny corroborates the hypothesis that the asparagine at position 122 of the alpha-subunit of the Na(+)/K(+)-ATPase gene as observed in Drosophila and other insects is the plesiomorphic condition in this group of leaf beetles. The later host-plant switch to cardenolide-containing plants in the common ancestor of C. auratus and C. cobaltinus coincides with the exchange of the asparagine for a histidine in the ouabain binding site.     

Changes in the oceanic 13C/12C ratio during the last 140 000 years: High-latitude surface water records

Detailed records of the carbon and oxygen isotopic ratios of Neogloboquadrina pachyderma are compared between nine high-latitude sediment cores, from the Northern and Southern Hemispheres, covering the last 140 000 yrs. The strong analogies between the δ¹³C records permit to define a δ¹³C stratigraphic scale, with three clear cut transitions simultaneous with the oxygen isotopic transitions 6/5 (125 kyrs.), 5/4 (65 kyrs.), and 2/1 (13 kyrs.). The δ¹³C records of N. pachyderma in the high-latitude cores, which follow the changes in δ¹³C of the surface water TCO₂ near areas of deep water formation present trends similar to the benthic foraminifera δ¹³C records in cores V19–30 and M12-392, although amplitudes of the isotopic shifts are different. This implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean.The ¹³C/¹²C ratios of N. pachyderma in the North Atlantic cores display larger regional variations at 18 kyrs. B.P. than at present. To explain these differences, we have plotted the 18 kyrs. B.P. δ¹³C values of N. pachyderma from 17 cores distributed N of 40°N. Comparison with published surface water temperature distribution at 18 kyrs. B.P. indicates that a strong divergent cyclonic cell, centered approximatively 55°N and 15°W, was active during most of the last ice-age maximum This hydrology, analogous to the present Weddell Sea, explains the published evidences of bottom water formation, if located on the northern flank of the gyre, and the strong polar front on the southern flank, probable location of intermediate water formation.