Arabidopsis peroxidase-catalyzed copolymerization of coniferyl and sinapyl alcohols: kinetics of an endwise process

In order to determine the mechanism of the earlier copolymerization steps of two main lignin precursors, sinapyl (S) alcohol and coniferyl (G) alcohol, microscale in vitro oxidations were carried out with a PRX34 Arabidopsis thaliana peroxidase in the presence of H(2)O(2). This plant peroxidase was found to have an in vitro polymerization activity similar to the commonly used horseradish peroxidase. The selected polymerization conditions lead to a bulk polymerization mechanism when G alcohol was the only phenolic substrate available. In the same conditions, the presence of S alcohol at a 50/50 S/G molar ratio turned this bulk mechanism into an endwise one. A kinetics monitoring (size-exclusion chromatography and liquid chromatography-mass spectrometry) of the different species formed during the first 24 h oxidation of the S/G mixture allowed sequencing the bondings responsible for oligomerization. Whereas G homodimers and GS heterodimers exhibit low reactivity, the SS pinoresinol structure act as a nucleating site of the polymerization through an endwise process. This study is particularly relevant to understand the impact of S units on lignin structure in plants and to identify the key step at which this structure is programmed

Oxidoreductases provide a more generic response to metallic stressors (Cu and Cd) than hydrolases in soil fungi: new ecotoxicological insights

The present study investigates the effect of metals on the secretion of enzymes from12 fungal strains maintained in liquid cultures. Hydrolases (acid phosphatase, β-glucosidase, β-galactosidase, and N-acetyl-β-glucosaminidase) and ligninolytic oxidoreductases (laccase, Mn, and lignin peroxidases) activities, as well as biomass production, were measured in culture fluids from fungi exposed to Cu or Cd. Our results showed that all fungi secreted most of the selected hydrolases and that about 50 % of them produced a partial oxidative system in the absence of metals. Then, exposure of fungi to metals led to the decrease in biomass production. At the enzymatic level, Cu and Cd modified the secretion profiles of soil fungi. The response of hydrolases to metals was contrasted and complex and depended on metal, enzyme, and fungal strain considered. By contrast, the metals always stimulated the activity of ligninolytic oxidoreductases in fungal strains. In some of them, oxidoreductases were specifically produced following metal exposure. Fungal oxidoreductases provide a more generic response than hydrolases, constituting thus a physiological basis for their use as biomarkers of metal exposure in soils

Exocellular oxidases: tools to assess the exposure of soil fungi to xenobiotics?

Exocellular oxidases: tools to assess the exposure of soil fungi to xenobiotics?. 4th International Symposium on Environmental Aspects of Pesticide Microbiology, SETA

Thigmomorphogenesis in Solanum lycopersicum: Morphological and biochemical responses in stem after mechanical stimulation

The activation of the phenylpropanoid pathway in plants by environmental stimuli is one of the most universal biochemical stress responses known. In tomato plant, rubbing applied to a young internode inhibit elongation of the rubbed internode and his neighboring one. These morphological changes were correlated with an increase in lignification enzyme activities, phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidases (POD), 24 hours after rubbing of the forth internode. Furthermore, a decrease in indole-3-acetic acid (IAA) content was detected in the rubbed internode and the upper one. Taken together, our results suggest that decrease in rubbed internode length is a consequence of IAA oxidation, increases in enzyme activities (PAL, CAD and POD), and cell wall rigidification associated with induction of lignification process

Impact of the absence of stem-specific β-glucosidases on lignin and monolignols

Monolignol glucosides are thought to be implicated in the lignin biosynthesis pathway as storage and/or transportation forms of cinnamyl alcohols between the cytosol and the lignifying cell walls. The hydrolysis of these monolignol glucosides would involve beta-glucosidase activities. In Arabidopsis (Arabidopsis thaliana), in vitro studies have shown the affinity of beta-GLUCOSIDASE45 (BGLU45) and BGLU46 for monolignol glucosides. BGLU45 and BGLU46 genes are expressed in stems. Immunolocalization experiments showed that BGLU45 and BGLU46 proteins are mainly located in the interfascicular fibers and in the protoxylem, respectively. Knockout mutants for BGLU45 or BGLU46 do not have a lignin-deficient phenotype. Coniferin and syringin could be detected by ultra-performance liquid chromatography-mass spectrometry in Arabidopsis stems. Stems from BGLU45 and BGLU46 mutant lines displayed a significant increase in coniferin content without any change in coniferyl alcohol, whereas no change in syringin content was observed. Other glucosylated compounds of the phenylpropanoid pathway were also deregulated in these mutants, but to a lower extent. By contrast, BGLU47, which is closely related to BGLU45 and BGLU46, is not implicated in either the general phenylpropanoid pathway or in the lignification of stems and roots. These results confirm that the major in vivo substrate of BGLU45 and BGLU46 is coniferin and suggest that monolignol glucosides are the storage form of monolignols in Arabidopsis, but not the direct precursors of lignin

PIEGEAge des Composés Halogénés Lipophiles Organiques Rémanents (PIEGEACHLOR)

Le projet Piegeachlor s’est donné pour objectif de réduire la disponibilité des plusieurs familles de contaminants organochlorés retrouvés dans les sols. Les contaminants étudiés sont les polychlorobiphényles, les polychloro-dibenzo-dioxines et furanes, ainsi que la chlordécone.L’hypothèse initiale du projet était que des matrices carbonées issues de pyrolyse de ligneux telles que des biochars pouvaient jouer un rôle de séquestration.Les propriétés de séquestration ont été testées en mobilisant plusieurs méthodologies. La première est basée sur une approche in vitro, qualifiant la disponibilité environnementale. Elle simule la capacité d’un milieu aqueux à désorber les polluants. Les autres utilisaient un biote cible (ver, radis, courgette, poule) pour déterminer la biodisponibilité relative de chacun des contaminants en fonction de la matrice carbonée utilisée. Ces approches ont été appliquées d’abord sur des sols artificiels de type OCDE avec de la tourbe comme matière organique endogène. Après une sélection des matrices carbonées les plus performantes en termes de séquestration, une partie des tests précédemment décrits a été appliquée sur des sols naturels prélevés en métropole (Saint-Cyprien) et en Martinique (Morne-Rouge, Trinité), respectivement contaminé en PCB+PCDD/F et en CLD. Des essais d’innocuité de l’amendement ont également été menés