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Etude des déterminants de la vulnérabilité à la cavitation du xylème chez les peupliers

Abstract : Climatic models predict greater frequency and intensity of drought episodes in the future that would seriously affected forest ecosystems. As a consequence, there has been a rising demand for more drought-resistant plant materials and for the understanding of the physiological and genetic bases of tree drought tolerance. Under drought conditions, the tension in the xylem conduits increases and cavitation can occur that causes embolism and makes the vessel non functional. Xylem vulnerability to cavitation is correlated with drought tolerance, pointing that it’s an important trait for drought tolerance of trees. However, few was known about the variability of this trait at the within species level and its genetic bases were unknown. In a first part, we demonstrated that the xylem vulnerability to cavitation of poplar (Populus tremula × Populus alba) acclimated to drier soil conditions, and was accompanied with changes in xylem structure and gene expressions. This acclimation process supports the role of vulnerability to cavitation in drought tolerance. In a second part, we investigated the structural and genetic bases for vulnerability to cavitation through two approaches. In a first one, we investigated the anatomical changes and the gene expressions that occur during the acclimation of vulnerability to cavitation to drier conditions. We found that the increase in vulnerability to cavitation in drier soil conditions was related to a decrease in pit wall diameter. We observed changes in gene expressions in drier conditions but these changes could not be related to change in vulnerability to cavitation. In a second approach, we used ten transgenic poplar lines modified for expression of genes involved in lignin metabolism and two transgenic lines overexpressing a pectin methylesterase (PME) to examine the role of the respective genes in the vulnerability to cavitation. In poplars modified in lignin metabolism, we also tested the relation between hydraulic and mechanical properties. We present evidence that lignins and pectins (through PME) are involved in the vulnerability to cavitation and our data on the transgenic poplar lines do not support the exclusive link between mechanical vs. hydraulic properties.
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  • HAL Id : tel-00678590, version 1



Hosam Awad. Etude des déterminants de la vulnérabilité à la cavitation du xylème chez les peupliers. Sciences agricoles. Université Blaise Pascal - Clermont-Ferrand II, 2011. Français. ⟨NNT : 2011CLF22163⟩. ⟨tel-00678590⟩



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