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301.
Magali Zbinden Bruce Shillito Constance de Villardi de Montlaur François Guyot Marie-Anne Cambon-Bonavita 《Journal of experimental marine biology and ecology》2008,359(2):131-140
The Rimicaris exoculata dominates the megafauna of some of the Mid Atlantic ridge hydrothermal vent sites. This species harbors a rich community of bacterial epibionts inside its gill chamber. Literature data indicate that a single 16S rRNA phylotype dominates this epibiotic community, and is assumed to be a sulfide-oxidizing bacteria. However attempts of cultivation were not successful and did not allow to confirm it. The aim of our study was to test the hypothesis of sulfide oxidation in the gill chamber, by a multidisciplinary approach, using in vivo experiments at in situ pressure in the presence of sulfide, microscopic observations and a molecular survey. Morphology of microorganisms, before and after treatment, was analyzed to test the effect of sulfide depletion and re-exposure. Our observations, as well as molecular data indicate a wider diversity than previously described for this shrimp's epibiotic community. We observed occurrence of bacterial intracellular sulfur- and iron-enriched granules and some methanotrophic-like bacteria cells for the first time. Genes that are characteristic of methane-oxidizing (pmoA) and sulfide-oxidizing (APS) bacteria were identified. These results suggest that three metabolic types (iron, sulfide and methane oxidation) may co-occur within the epibiont community associated with Rimicaris exoculata. As this shrimp colonizes chemically contrasted environments, the relative abundance of each metabolic type could vary according to the local availability of reduced compounds. 相似文献
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Exogenous abscisic acid fate during maturation of hybrid larch (Larix×leptoeuropaea) somatic embryos
The maturation of somatic embryogenesis of hybrid larch is an essential step for plantlet production. ABA controls not only synchronicity of maturation, but has important consequences on eventual viability of the plantlet. To gain understanding of the role of this plant growth regulator during the maturation process of hybrid larch somatic embryos, we studied the incorporation of [ 3 H]-(±)-abscisic acid [tritiated (±)-ABA] over 6 weeks of culture. Results showed a rapid incorporation of label into the tissues directly in contact with the culture medium. Accumulation of tritiated (±)-ABA occurred mainly in the maturing somatic embryos found at the periphery of the embryogenic mass but not in direct contact with the culture medium. Tritiated (±)-ABA was mainly conjugated as a glucose ester form. Rates of tritium incorporation indicated a significant build-up in tritiated (±)-ABA metabolization at the third week of culture. The weekly measurement of labelling in the culture medium over 6 weeks showed no localized exhaustion of tritiated (±)-ABA in positions where the embryogenic masses were placed in Petri dishes. The calculated ABA internal content of the maturing somatic embryos was similar to published ELISA measurements of ABA. This result suggests an absence of endogenous ABA synthesis by somatic embryos of hybrid larch during maturation. 相似文献
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A simple procedure for the preparation of soluble human succinate dehydrogenase is described. These preparations have proved suitable for analysis by zone electrophoresis, using a specific stain to detect activity after separation. In a survey of succinate dehydrogenase from various tissues and different individuals, no evidence for genetic heterogeneity due to the expression of either multiple loci or alternative alleles at the succinate dehydrogenase locus was found. However, epigenetic heterogeneity in both molecular size and charge was seen and various explanations for the occurrence of the isoenzymes are explored. Estimates of molecular size (93,300 ± 9100) suggest that the smallest active unit of succinate dehydrogenase accounts for the major part of the solubilized activity. Kinetic studies have shown that the apparent K
m
values for succinate (0.9mm) and PMS (0.4mm) are comparable to those previously described for the beef heart enzyme, and these parameters were not significantly altered when the enzyme was removed from the membrane milieu. However a marked non-succinate-dependent activation of the membrane-associated enzyme at 38C is apparently lost on solubilization, and this observation may have some bearing on earlier reports of an apparent decrease in V
max on solubilization of succinate dehydrogenase. 相似文献
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