Les plantes adaptent leur croissance en fonction des facteurs environnementaux dont la gravité qui est un facteur constant. Une modification de l’orientation de la plante par rapport à l’axe de la gravité, i.e. une inclinaison induit une réponse de redressement : le gravitropisme. Pour les parties aériennes le gravitropisme est négatif, c’est-à-dire que les plantes vont adapter leur croissance dans la direction opposée à la gravité. Chez les arbres, le redressement est assuré par à la formation asymétrique d’un bois aux propriétés physico-chimiques particulières appelé le bois de réaction. Des récepteurs kinases pourraient participer à la perception et à la réponse précoce au stimulus gravitropique qu’est l’inclinaison. Parmi ces familles protéiques, les kinases associées à la paroi (WAK) sont des candidats intéressants. La liaison de ces protéines à la paroi permettrait de percevoir les déformations qui sont supposées se produire par l’inclinaison de la tige. Nous avons alors identifié et caractérisé pour la première fois la famille WAKs chez une espèce ligneuse, le peuplier, qui est composée de 175 membres. L’étude d’accumulation des transcrits WAKs a permis d’identifier les gènes WAKs qui s’expriment dans la tige puis l’expression de ces gènes a été suivie lors d’une cinétique après inclinaison. Il s’avère que les gènes WAKs sont faiblement exprimés et que 25% des gènes présentent une expression différentielle après inclinaison. Ces données transcriptomiques suggèrent que les WAKs participeraient aux événements cellulaires précoces après l’inclinaison de tiges chez le peuplier. Enfin, une étude plus approfondie a été initiée sur PtWAK70 qui est localisée dans le jeune xylème et le phloème secondaire. Nous avons également généré des outils moléculaires dont l’objectif est d’identifier les interacteurs potentiels de la partie apoplastique de PtWAK70. / Plants adapt their growth to environmental factors whose gravity is a continuous one. A modification of plant orientation by tilting leads to a straightening response: gravitropism. For aerial parts, plants will adapt their growth upward (negative gravitropism). In trees, straightening is accomplished through asymmetric formation of reaction wood which exhibits modifications in its physicochemical properties. Receptors-like kinases could play a role in both perception and early response to a gravitropic stimulus. Among them, Wall-Associated Kinases (WAKs) are interesting candidates because they are bind to the cell wall. They could detect wall deformations that are supposed to occur after tilting of the stem. We identified and characterized for the first time in a woody species (poplar) the largest WAKs family with 175 members. An extensive study of WAKs transcripts accumulation was carried out to identify genes expressed in woody stem. These genes expressions were analyzed during a kinetic after tilting. WAKs genes were overall weakly expressed but 25% of analyzed genes showed a modulation in their transcript accumulation after tilting. This suggests they could play a role in early events after tilting of poplar stems. Lastly, a deeper study was initiated on PtWAK70 which is localized in young xylem and secondary phloem. We generated molecular tools to identify potentials interactors of PtWAK70 apoplastic part.

Adhesion between the plasma membrane and the cell wall and the existence of the continuum of these two compartments is needed for signal transmission, e.g. under pathogen attack, during cell expansion and cell wall growth, or in response to environmental conditions. This adhesion is, in addition to the turgor, provided by physical connection of both compartments. One of the best-known examples of physical connection is found in the root system, in the Caspary strip region, where it is required to maintain apoplastic barriers of the root system, even under adverse conditions and consequent plasmolysis. There is little information about the physical interconnection and the participating macromolecules but there are candidates, which could participate in this interaction. The diploma thesis deals with arabinogalactan (AGP) proteins with fasciclin-like domain (namely FLA9 and FLA2). These proteins may play a role in the adhesion of plasma membrane and cell wall and may be involved in the growth regulation and development of the root system. Both genes are are relatively strongly expressed in the roots, especially in the elongation zone and in the cortex, including the endodermis (according to chip data). Also, to a smaller extent, the thesis deals with integrin-like At14A protein. The most interesting...

The following work presents a hypothesis which identifies the origins and meaning of an ancient Mesoamerican concept known as the three stones of creation. Previous interpretations have tended to apply astronomical, spatial, or geographical models, while many conclusions have been made on the basis of one Classic Maya monument, Stela C of Quirigua. This thesis builds an argument for the temporal nature of these “stones,” used to metaphorically represent a sequence of separate units of time, referred to as eras, ages, or creations. A primary goal is to demonstrate that Quirigua Stela C provides in brief, summary form a chronology which is better defined through inscriptions in the Cross Group at Palenque, and in a sequence of panels at Yaxchilan containing beliefs about the origins of the ballgame. In constructing an argument for the temporal nature of the three stones of creation, every available context from a set of hieroglyphs mentioned in the Quirigua Stela C “creation” text—including Na Ho Chan (“First 5-Sky”) and “6-Sky”—is discussed in Chapter 2. In Chapter 3, these glyphs are shown to aid in the organization of the deeper past within the Palenque and Yaxchilan mythologies. When compared chronologically and thematically, these sites seem to point to the 24th century B.C.E. as the important termination of a time period (i.e., the planting of a creation stone) related to a mythic complex involving the death and underworld journey of the Maize Lord, followed by his resurrection, emergence, and/or accession to power. Key questions addressed include the antiquity of these beliefs and where the metaphors used to arrange time observed among the Classic Maya originate. In Chapter 4, earlier expressions of this time ideology are interpreted through iconographic conventions, ritual deposits, and monumental architecture at the Olmec site of La Venta. Similarly, Chapter 5 proposes that the Humboldt Celt, the earliest known example of the three stones of creation, arranges units of time into a sequence. These and other interpretations suggest the existence of an ancestral, Mesoamerican era-based time model to which later Postclassic, colonial, and contemporary beliefs, such as those expressed in the K’iche’-Mayan Popol Vuh, are fundamentally related. / text