Étude morphologique de l'architecture fine du mycélium de champignons mycorhiziens arbusculaires du genre glomus

Les spores de Glomus intraradices nouvellement formées sont soumises à un processus de dormance intrinsèque, levé par un passage à 4°C d'un minimum de 14 jours. Des changements morphologiques apparaissent au cours de ce processus, tels que, sans les 14 jours minimaux au froid, les spores mises à germer meurent majoritairement ou forment des patrons de croissance particuliers, confinés autour de la spore, très ramifiés, et dépourvus d'hyphes principaux. En revanche, dès que les 14 jours de rigueur au froid sont respectés, le taux de mortalité des spores mises à germer diminue et des hyphes principaux s'individualisent et s'allongent sur plusieurs centimètres. L'examen des processus morphologiques dans la littérature a révélé que le principe dimorphique se rencontrait tout au long du cycle de croissance externe du champignon MA, les hyphes tantôt formant de fines ramifications, les ± FB ¿ (Fine-Branching), tantôt s'allongeant sous la forme d'hyphes principaux, les ± RH ¿ (Runner-Hyphae). En phase germinative, les FB semblent apparaître en situation de stress. En phase pré-symbiotique, les FB sont représentés essentiellement par des structures ± fan-like ¿, les RH apparaissant dans le cas des rares colonisations racinaires directes. En phase extraradicale, les RH caractérisent les gros hyphes structuraux à partir desquels se ramifient des FB. Une nouvelle approche quantitative a été développée pour évaluer la croissance des hyphes, basée sur la mesure des dimensions fractales (DF). Cette technique a été appliquée à quatre souches de champignons MA du genre Glomus cultivées in vitro, soumises à l'influence de différentes molécules stimulant ou inhibant la croissance. La technique s'avère particulièrement efficace pour mesurer les FB germinatifs et les hyphes extraradicaux. La méthode traditionnelle de Grid-Line intersect (GL) demeure utile pour mesurer la longueur des RH germinatifs

Metabolic processes sustaining the reviviscence of lichen Xanthoria elegans (Link) in high mountain environments.

International audienceTo survive in high mountain environments lichens must adapt themselves to alternating periods of desiccation and hydration. Respiration and photosynthesis of the foliaceous lichen, Xanthoria elegans, in the dehydrated state were below the threshold of CO2-detection by infrared gas analysis. Following hydration, respiration totally recovered within seconds and photosynthesis within minutes. In order to identify metabolic processes that may contribute to the quick and efficient reactivation of lichen physiological processes, we analysed the metabolite profile of lichen thalli step by step during hydration/dehydration cycles, using 31P- and 13C-NMR. It appeared that the recovery of respiration was prepared during dehydration by the accumulation of a reserve of gluconate 6-P (glcn-6-P) and by the preservation of nucleotide pools, whereas glycolytic and photosynthetic intermediates like glucose 6-P and ribulose 1,5-diphosphate were absent. The large pools of polyols present in both X. elegans photo- and mycobiont are likely to contribute to the protection of cell constituents like nucleotides, proteins, and membrane lipids, and to preserve the integrity of intracellular structures during desiccation. Our data indicate that glcn-6-P accumulated due to activation of the oxidative pentose phosphate pathway, in response to a need for reducing power (NADPH) during the dehydration-triggered down-regulation of cell metabolism. On the contrary, glcn-6-P was metabolised immediately after hydration, supplying respiration with substrates during the replenishment of pools of glycolytic and photosynthetic intermediates. Finally, the high net photosynthetic activity of wet X. elegans thalli at low temperature may help this alpine lichen to take advantage of brief hydration opportunities such as ice melting, thus favouring its growth in harsh high mountain climates

Efecto de la inoculación con bacterias rizosféricas en dos variedades de trigo. Fase I: condiciones controladas

The experiment was carried out in a greenhouse so that the inoculation, both simple and combined (with the rhizospheric bacteria- Sinorhizobium and Azospirllium), en two varieties of Wheat. Materials and methodologies were used in accordance with previously prescribed conventional methodologies for this study. The experimental design was completely randomized, with 4 replicas and 10 treatments. A statistical analysis using two-way variance was done. Fertilized treatment was applied with NH4NO3 (150 ppm/kg soil). The content of chlorophyll foliage was evaluated, dry air weight, dry root weight, length of stem, and germination. In the event that differences appeared, it was determined through use of the Duncan Test, and the differences between varieties with t-Student. It is concluded that combined inoculation with the strain A2 (Sinorhizobium meliloti) and the strain N7 (Azospirillum zeae) had the greatest positive influence on the chlorophyll content of the plants. On the other hand, there was a great difference between the two varieties of wheat in terms of length of stem, dry air weight, and dry root weight. The results of dry air weight and dry root weight, upon combining the two factors that were studied, highly depended on the varietal characteristics of the plant and on the native population of rhizobacteria. The germination of the plants was not linked to any of the applied factors in the experiment.Se llevo a cabo un experimento bajo condiciones controladas para determinar la respuesta de dos variedades de trigo a la inoculacion simple y combinada realizada con Sinorhizobium y Azospirillum. Se utilizo una cepa de A. zeae, y dos cepas pertenecientes a S. meliloti. Los materiales y metodos aplicados correspondieron a lo descrito en las metodologias prestablecidas en este campo de estudio. Diseno experimental: completamente aleatorizado, con 20 tratamientos y 4 replicas. No se utilizo tratamiento fertilizado. Se evaluaron diferentes variables agronomicas, relacionadas con la arquitectura radical y la biomasa aerea. Analisis de varianza bifactorial. En caso de aparecer diferencias, se aplico analisis de varianza de un factor a la interaccion en primera instancia, o a los factores probados. Diferencias entre medias por LSD de Fisher. Se transformaron datos de conteo de digitos por �ãx. Se calculo correlacion y regresion multiple entre variables. Se concluye que la inoculacion combinada de Sinorhizobium con Azospirillum, asi como la inoculacion simple con Sinorhizobium, resultaron de alta importancia en las alternativas de inoculacion que se realizaron en el experimento. Existio una alta diferenciacion entre las dos variedades de trigo en determinadas variables agronomicas, lo que indica una influencia marcada de las caracteristicas varietales de las plantas. Se observó una fuerte relación estadística entre las variables peso seco aéreo y variables de la raíz para los tratamientos inoculados con A2 y A2+N7, respectivamente

The first unpaired electron placed inside a C-3-symmetry P-chirogenic cluster

The Pd-3(dppm*)(3)(CO)(n+) enantiomers (n = 2 (2), 1 (3)) were prepared either from (R, R)-or (S, S)-P-chirogenic bis(phenyl-m-xylylphosphino) methane (dppm*; 1) and Pd(OAc) 2 in the presence of CF3CO2H, CO and water (n = 2), and then by reductive electrolysis (n = 1). The stable enantiomeric [Pd-3((S,S)-dppm*)(3)(CO)](+center dot) (3), is the first C-3-symmetry radical-cation M-M bonded cluster, therefore the odd electron is delocalized onto the Pd-3 frame within this symmetry. The novel chiral species have been characterized by circular dichroism (CD) of both enantiomers of the Pd-3(dppm*)(3)(CO)(2+) clusters (2) and by EPR spectroscopy for the Pd-3((S, S)-dppm*)(3)(CO)(+center dot) paramagnetic compounds (3, g = 2.041). Evidence for reduced symmetry with respect to the achiral cluster was also obvious from the hyperfine splittings of the EPR signal which display three different hyperfine coupling values: 3 A(31P) = 83.9 10(-4) cm(-1), 3 X A(P-31) = 69.7 10(-4) cm(-1), 3 A(Pd-105) = 12.5 10(-4) cm(-1). In the absence of an X-ray structure for the paramagnetic clusters, DFT computations were performed to address the geometry. The optimized geometry of the Pd-3((S, S)-dppm*)(3)(CO)(+center dot) radicals (3) exhibits three phosphorus atoms placed well above the Pd-3 plane, while the three others are located below the trimetallic frame within C-3-symmetry due to intramolecular steric hindrance. This makes them chemically different with respect to the carbonyl group and explains the experimental EPR spectrum well. Consequently this C-3-symmetry deformation also induces a change in the shape of the SOMO (semi-occupied molecular orbital) towards this same symmetry compared to the corresponding achiral C-3v species

Prenatal diagnosis of Niemann-Pick type C disease: Current strategy from an experience of 37 pregnancies at risk

Thirty-seven pregnancies at risk for Niemann-Pick type C disease were monitored by study of cultured amniotic fluid cells (8 cases) or chorionic villus cells (29 cases) in 23 couples over the period 1984–91. An early protocol combined determination of sphingomyelinase activity with electron microscopy. The current strategy, based on the demonstration of specific abnormalities in intracellular processing of exogenous cholesterol, combines the study of the early phase (first 6 h) of LDL-induced cholesteryl ester formation and the histochemical evaluation (filipin staining after 24 h of LDL uptake) of the LDL-induced accumulation of unesterified cholesterol. Thirteen fetuses were predicted to be affected. Confirmation of the diagnosis was made by study of cholesterol processing in fetal skin fibroblast cultures and/or by demonstration of a characteristic lipid storage in fetal liver, already present at 14 w gestation. Definition of the biochemical phenotype (classical, variant, or intermediate) of the index case, with regard to cholesterol-processing abnormalities, is an absolute prerequisite to adequate genetic counseling in a given family. Prenatal diagnosis has now proved a safe procedure in the predominant (approximately 85%) group of families with the classical phenotype

Binding of carbohydrates and protein inhibitors to the surface of alpha-amylases

International audiencexx