No description available.

In our study, the decrease of H2O2 levels in wounding-treated tissues of soybean ( Glycine Max ) hypocotyls is accompanied by the enhancement of the POD activity. The POD activity was significantly enhanced 0.5 d after wounding treatment. The laccase activity was significantly enhanced 1-2 d after wounding treatment. The enhancement of POD by mechanical wounding occurred a day earlier than laccase. The increase in activities of POD and laccase is correlated with a rise in lignin contents in wounding-treated tissues. We suggest that in control tissues, laccase might play major role on the lignin biosynthesis, hence, POD by utilizing H2O2 play the major role on the lignin biosynthesis during the wounding process.

Stress-induced changes in the emissions of volatiles from many economically-important plants have been demonstrated in studies over the past decade. Plants such as cotton and corn change both the composition and concentration of their emissions when subjected to wounding, herbivory and pathogen attack. Terpene-accumulating plants have been overlooked as potential objects of such studies although work on conifers has shown that species rich in constitutive defences can also exhibit induced responses. The aim of this study was to investigate whether terpene-accumulating plants respond to stress by altering their foliar emissions qualitatively and/or quantitatively. Species examined included Salvia officinalis (common sage), Melaleuca alternifolia (Australian tea tree) and Ocimum minimum (Bush basil). An experimental design was developed to eliminate factors such as leaf ontogeny that can affect the obtained results and complicate their interpretation. Small-scale solvent extraction and HS-SPME-based techniques were also developed; they enabled the quantitative determination of treatment-induced changes over periods ranging from 10 minutes to 6 months. Treatment of plants included mechanical wounding, herbivory, pathogen attack and chemical elicitation. Overall, statistically significant induced-changes were observed for both leaf-oil composition and concentration. The response of the different species used varied. O. minimum exhibited the greatest compositional changes whilst M. alternifolia was the only species for which oil-concentration changes were observed. The demonstrated changes were not as great as those reported in similar studies with non-terpene producing plants. The results indicate that the high metabolic costs associated with the production and storage of constitutive defences may be responsible for the limited induction of further defensive responses / Doctor of Philosophy (PhD)

Les plantes sont soumises durant leur vie à de nombreux stress environnementaux. Face à ces contraintes, les végétaux ont développé au cours de l'évolution différentes stratégies. La plus emblématique est la mise en place du métabolisme spécialisé, représenté par une grande diversité chimique et fonctionnelle. Bien que ce métabolisme soit de plus en plus étudié ces dernières années, de nombreuses lacunes persistes à son propos, liées notamment (i) à la complexité des modifications métabolomiques engendrées par la perception de stress, (ii) aux coûts et avantages que ces métabolites imputent à la plante les accumulant, et (iii) aux voies métaboliques menant à cette diversité de composés. Pour appréhender ces différentes problématiques, nous avons adopté une stratégie combinant des approches de phytochimie, de biologie moléculaire et de génétique. Dans un premier temps, nous avons étudié les changements métaboliques globaux engendrés par l’application de deux stress environnementaux, l’ozone et la blessure mécanique, sur une plante modèle au laboratoire, le panais, en fonction du temps. Les résultats de ces travaux nous ont permis d’identifier 40 métabolites différentiellement accumulés dans ces conditions, dont certaines furocoumarines. Par la suite, nous avons focalisé notre étude sur ces molécules en évaluant leurs profils d’accumulation, en condition de stress par blessures mécaniques, par la biais d’analyses différentielles. A partir de ces données, nous avons initié la recherche et l'identification de gènes candidats potentiellement impliqués dans cette voie à partir de plusieurs banques transcriptomiques et génomiques de panais. La fonction des gènes sélectionnés a été évalué par des approches d'expression hétérologue dans la levure. En parallèle de ces travaux, nous avons développé une stratégie destinée à mieux comprendre le coût métabolique de la synthèse de métabolites spécialisés. Pour ce faire, nous avons adapté aux furocoumarines une technique de clonage multigénique permettant de transférer dans une plante, et en une seule opération, plusieurs gènes impliqués dans la même voie de biosynthèse. Cette méthode nous a permis d'initier la génération de lignées stables ayant intégré les deux premiers gènes de la voie. Ces plantes seront comparées à des plantes sauvages et permettront ainsi d’étudier les coûts métaboliques et physiologiques de l’introduction de cette nouvelle voie de biosynthèse ainsi que ses bénéfices en termes de défense de la plante. / Plants are subjected to many environmental stresses during their life. Faced with these constraints, plants have developed different strategies during their evolution. The most emblematic is the establishment of a specialized metabolism, represented by a great chemical and functional diversity. Although this metabolism has been studied more and more in recent years, many gaps remain, related in particular (i) to the complexity of the metabolomic changes generated by the perception of stress, (ii) to the costs and benefits that these metabolites impute to the producing plant, and (iii) to the metabolic pathways leading to the diversity of compounds. To cope with these different issues, we adopted a strategy combining approaches of phytochemistry, molecular biology and genetics. First, we studied global metabolic changes caused by the application of two environmental stresses, ozone and mechanical wounding, on parsnip. The obtained results allowed us to identify 40 metabolites differentially accumulated under these conditions, including some furocoumarins. Subsequently, we focused our study on these molecules by evaluating their accumulation profiles under mechanical wounding stress condition, using differential analyzes. From this data, we initiated the search and identification of candidate genes potentially involved in this pathway based on transcriptomic and genomic parsnip libraries analyses. The function of the selected genes was evaluated by heterologous expression approach in yeast. In parallel to this work, we have developed a strategy to better understand the metabolic cost of specialized metabolites synthesis. To do this, we have adapted a multigene cloning method to furocoumarines, allowing to transfer several genes involved in the same pathway in a plant, in a single operation. This method allowed us to initiate the generation of stable lines having integrated the first two genes of the pathway. These plants will be compared to wild plants and will thus allow to study the metabolic and physiological costs of the introduction of this new biosynthetic pathway and its benefits in terms of plant defense.