Étude du déterminisme de la préséance des bourgeons le long du rameau d’un an chez le pommier (Malus domestica [L.] Borkh.): approches morphologique, biochimique et moléculaire

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Étude du déterminisme de la préséance des bourgeons le long du rameau d’un an chez le pommier (Malus domestica [L.] Borkh.): approches morphologique, biochimique et moléculaire

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Étude par électrophorèse 2-D des modifications du profil protéique d’entre-nœuds de tomate à la suite d’une stimulation mécanique.

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The involvement of a Wall Associated Kinase in the response to gravistimulation in poplar stems

PosterPlants are able to sense organ tilt and reorient their growth according to the gravity vector. In angiosperm woody species, the motor for the stem straightening in parts undergoing cambial growth is differential maturation between the two sides of the stem. The dynamics of the gravitropic response involved the sensing of the local inclination angle (gravisensing) as well as the sensing of the local curvature which progressively takes place in the straightening process (Bastien et al (2013). If one wants to specifically address the question of the gravisensing / graviresponse in plants undergoing secondary growth, the gravistimulation should not induce organ deformation. This is why we chose to tilt staked poplar trees in our experimental design. From this, one challenging research question is the identification of molecular actors specifically involved in gravisensing / graviresponse. Since it has been proposed that plant cells could sense gravity through the cytoskeleton-plasma membrane-cell wall continuum, wall associated kinases (WAK) with an extracellular part that can bind to pectins localized in the cell wall, appear as molecular candidates. Using in silico approaches, we showed that the WAK family in poplar is the largest characterized to date with 175 sequences. Gene expression was analyzed in various organs and tissues. Most WAKs were weakly expressed. Only 28 WAKs were expressed in the stem. One WAK is of particular interest showing differential expression after tilting of the stem. The protein was localized in young xylem and bark cells devoid of amyloplasts. These data suggest that a WAK could be involved in the sensing/response to gravistimulation in a manner independent of the displacement of amyloplats which is behind the starch-statolith hypothesis (Sack, 1997)

Study of a Wall Associated Kinase in the response to gravistimulation in poplar stem

PosterInteractions between cell wall, plasma membrane and cytoplasm are essential for plant cell functions. It has been suggested that molecular actors at the interface of this continuum could be involved in gravity sensing, as described in the gravitational pressure model (Baluška and Volkmann, 2011). A change in the gravity vector would modify plasma membrane-cell wall mechanical relations with a tension between this two cell compartments at the upper side of the cell and a compression at the lower side. At the interface of the continuum, Wall-Associated Kinases (WAKs) appears as good molecular candidates. WAKs are receptor-like kinases that are able to link the pectins of the wall and a cytoplasmic protein kinase domain. To highlight and understand the role of WAKs in woody plant graviresponse, we used in silico approaches and showed the most expanded WAK family never identified to date with 175 members (Tocquard et al., 2014). We analyzed gene expression of the WAK family members in various organs and tissues of poplar tree and showed that WAKs were weakly expressed. Only 28 PtWAKs were expressed in the stem. One WAK is of particular interest showing differential expression after tilting of the poplar stem. The protein was localized in young xylem and bark cells devoid of amyloplasts. These data suggest that a WAK could be involved in the sensing/response to gravistimulation in a manner independent of the displacement of amyloplasts which is behind the starch-statolith hypothesis

Immunolabelling of intervessel pits for polysaccharides and lignin helps in understanding their hydraulic properties in Populus tremula × alba

Background and Aims The efficiency and safety functions of xylem hydraulics are strongly dependent on the pits that connect the xylem vessels. However, little is known about their biochemical composition and thus about their hydraulic properties. In this study, the distribution of the epitopes of different wall components (cellulose, hemicelluloses, pectins and lignins) was analysed in intervessel pits of hybrid poplar (Populus tremula × alba).Methods Immunogold labelling with transmission electron microscopy was carried out with a set of antibodies raised against different epitopes for each wall polysaccharide type and for lignins. Analyses were performed on both immature and mature vessels. The effect of sap ionic strength on xylem conductance was also tested.Key Results In mature vessels, the pit membrane (PM) was composed of crystalline cellulose and lignins. None of the hemicellulose epitopes were found in the PM. Pectin epitopes in mature vessels were highly concentrated in the annulus, a restricted area of the PM, whereas they were initially found in the whole PM in immature vessels. The pit border also showed a specific labelling pattern, with higher cellulose labelling compared with the secondary wall of the vessel. Ion-mediated variation of 24 % was found for hydraulic conductance.Conclusions Cellulose microfibrils, lignins and annulus-restricted pectins have different physicochemical properties (rigidity, hydrophobicity, porosity) that have different effects on the hydraulic functions of the PM, and these influence both the hydraulic efficiency and vulnerability to cavitation of the pits, including ion-mediated control of hydraulic conductance. Impregnation of the cellulose microfibrils of the PM with lignins, which have low wettability, may result in lower cavitation pressure for a given pore size and thus help to explain the vulnerability of this species to cavitation

Debout les plantes ! Imagerie à la verticale

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Debout les plantes ! Imagerie en microscopie horizontale.

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Debout les plantes ! Imagerie à la verticale

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Debout les plantes ! Imagerie en microscopie horizontale.

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