Mise en place de la réticulation des parois de maïs au cours du développement et impact sur la variabilité de la dégradabilité des polysaccharides pariétaux

Abstract : Maize potential value, as well as animal feed or as bioenergetics resources, is limited by the lignification of the cell wall and by the cross-linking between cell wall components. Improvement of cell wall enzymatic degradability is an important goal. In the present work we focused on the study of cell wall lignification including its establishment and the biochemical or anatomical cell wall related factors in order to investigate the impact of all these characteristics on cell wall degradability. In the first part of my work, 8 maize recombinant inbred lines were selected on the basis of their comparable lignin content and their contrasted cell wall degradability in order to assess the impact of biochemical traits on both the cell wall degradability and the plant agronomic performances independently of the main “lignin content” factor. These recombinant inbred lines and their parents were analyzed for esterified and etherified p-hydroxycinnamic acid content, for lignin content, composition and structure and for in vitro cell wall degradability. Lignin structure and esterified p-coumaric acid content were highly and significantly correlated with in vitro cell wall degradability. A multiple regression analysis showed that more than 80 % of cell wall degradability variations were explained by a regression model including two main explanatory factors: the lignin content and the estimated proportion of S lignin units esterified by p-coumaric acid. The morphological study showed that the biochemical factors limiting cell wall degradability were on the contrary favorable for ensuring agronomic performances. In the second part of my work, we studied the cell wall developmental pattern during maize internode growth. We compared the developmental pattern of 3 maize lines which presented quite similar lignin content but very different cell wall degradability at silage stage. We first characterized biochemically internodes sampled throughout plant development. Subsequently, we developed a method to quantify the variation of lignin spatial distribution within the whole stem section. At last, we completed our study of cell wall establishment by an anatomical characterization. From a temporal point of view, the different wall components were incorporated gradually during the development and three major steps were identified. From a spatial point of view, in the internode, the development of cell wall is different according to the considered region. Clearly genetic variations were observed for developmental pattern in both the two axes and were found to be associated with the variation of cell wall degradability. The results of this work were discussed firstly in terms of contribution to the understanding of cell wall lignification and of relationships between biochemical and anatomical factors with cell wall degradability variations and secondly in terms of application to propose solutions to improve cell wall quality.
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Yu Zhang. Mise en place de la réticulation des parois de maïs au cours du développement et impact sur la variabilité de la dégradabilité des polysaccharides pariétaux. Sciences agricoles. AgroParisTech, 2012. Français. ⟨NNT : 2012AGPT0092⟩. ⟨pastel-00951436⟩

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