Thèse (Ph. D.)--Université Laval, 2005. / Titre de l'écran-titre (visionné le 28 novembre 2005). Bibliogr.

Th. doct.--Department of plant ecology--Groningue--Rijksuniversiteit te Groningen, 1989. / Bibliogr. p. 379-397. Index.

Th. doct.-ing.--Sci. agron.--Toulouse--I.N.P., 1985. N°: 383.

Th. doct.-ing.--Nancy, I.N.P.L., 1979.

Texte remanié de: Diss.--Heidelberg, 1989. / Bibliogr. p. 423-497, index.

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Understanding the dynamical bases of the interaction between the plant mineral nutrition and the circadian clock could contribute to improve crop yield and resistance to adverse conditions, such as mineral element deficiencies. Magnesium is an essential element that catalyzes more than six hundred enzymatic reactions and occupies the center of the chlorophyll structure in plants. Physiological targets of magnesium deficiency are generally better described in aerial than in belowground organs. In this thesis, we first characterized the root morphology of the model species Arabidopsis thaliana (Columbia-0) in response to magnesium supply during in vitro culture. The length of primary root and the number and length of lateral roots decreased during magnesium depletion. A local magnesium-rich source does not enhance the root foraging capacity, unlike some other major nutrients. Auxin and abscisic acid emerged as two hormones shaping root morphology in response to magnesium deficiency. Second, we investigated the natural variation of the root morphology response to magnesium supply in Arabidopsis. Thirty-six accessions were screened in vitro. Compared to the reference Columbia-0, some accessions had higher number and length of lateral roots at low magnesium supply. Root or shoot magnesium concentrations did not implicitly correlate with the root morphological traits. However, shoot calcium and root phosphorus concentrations correlated positively with the lateral root number and length, while root iron negatively with the length of primary root. Third, we focused on the interaction between the plant magnesium nutrition and the circadian clock circuit. We tested for a possible involvement of PHYTOCHROME INTERACTING FACTOR 3-LIKE 1 (PIL1) - a clock-associated gene that is down-regulated during magnesium depletion - in morphological and physiological responses, and for a circadian connection of PIL1 in the context of magnesium deficiency. The phenotypes of loss-of-function and overexpression lines did not reveal a major role of PIL1 in the magnesium deficiency symptom manifestation but rather in the plant mineral profile. The expression of PIL1 was apparently not under any circadian control. However, PIL1 seemed to regulate the expressions of some core clock genes (CCA1, LHY and PRR9), which were also targets during magnesium deficiency. In conclusion, PIL1 has a link with the circadian rhythm machinery but it does not emerge as a pivotal regulator of magnesium stress responses. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The interest around hemp is currently renewed for the production of bio-based and renewable materials in the context of global warming. This fibre crop is able to produce large amounts of fibres with different features and industrial application. The most valuable fibres, found in the phloem tissue, are rich in cellulose while relatively poor in lignin, by contrast with the xylem tissue. This thesis aims at studying the events related to the biogenesis of these two types of fibre. Using two different systems, we will investigate the molecular mechanisms related toelongation, secondary growth, deposition and maturation of the cell wall and bast fibre development.Our first objective is to provide a comprehensive overview of the transcriptional factors and phytohormones involved in primary and secondary growth. To this end, the development of the hemp hypocotyl is investigated by a high throughput transcriptomic approach, in addition to proteomics, phytohormone and lignin analyses and microscopy. We show that elongation and secondary growth are characterised by specific patterns of gene expression. The consequences on the biogenesis and modification of the cell walls are widely discussed.The second objective is to decipher the molecular actors associated with the development of the bast fibres. We first show that the contrasting composition of xylem and bast fibres is regulated at the transcriptional level. Next, we highlight the evolution of the transcriptome during the development of the bast fibres, from intrusive growth to thickening. We put a special emphasis on the study of cell wall-related genes (cellulose synthase, fasciclin-like arabinogalactan, transcription factors) and phytohormones. We also formulate several hypotheses to explain the hypolignification of the bast fibres.Finally, this thesis ends with the perspectives raised by our results, notably concerning the deposition of cellulose, non-cellulosic polysaccharides and lignin in the bast fibres. / info:eu-repo/semantics/nonPublished

La direction principale des travaux de recherche de ce mémoire est de valoriser les composés phytochimiques se trouvant au cœur de la flore nordique. Cette dernière possède de nombreuses adaptations impressionnantes aux conditions climatiques extrêmes sur ces territoires. On y retrouve peu de végétation pouvant se développer dû à l'environnement particulier de ces régions. La flore nordique du Québec exploite des mécanismes de défense différents et particuliers des végétaux ne se trouvant pas dans ces conditions. Dans ce contexte, l'objectif des recherches de ce projet de maîtrise est de faire l'investigation phytochimique des métabolites secondaires de Racomitrium lanuginosum, une bryophyte très peu étudiée. Pour ce faire, nous avons utilisé un processus d'extraction par solvants de différentes polarités, suivi de différentes étapes de purification et de caractérisation. Racomitrium lanuginosum est une mousse présente dans des écosystèmes du Sud et du Nord. Les échantillons étudiés proviennent du Nunavik, plus précisément des alentours de Kuujjuarapik-Whapmagoostui. Il s'agit de la première investigation phytochimique sur cette bryophyte pour des spécimens nordiques. Notre investigation phytochimique a commencé par un processus d'extraction avec de l'hexanes, suivi du dichlorométhane, puis du méthanol. Les extraits bruts ont été soumis à la chromatographie gazeuse couplée à la spectrométrie de masse (GC-MS) afin de faire l'identification putative de composés volatils. Par la suite, les extraits bruts ont été fractionnés par chromatographie liquide à moyenne pression (MPLC). Subséquemment, certaines fractions ont été soumises à la chromatographie en phase liquide couplée à la spectrométrie de masse (LC-MS) afin de faire l'identification putative des composés. Des molécules n'ayant pas été identifiées putativement ont été ensuite purifiées par chromatographie liquide à haute performance (HPLC) semi-préparative. Cette étape a permis d'obtenir certains métabolites secondaires purs pour en faire l'élucidation de la structure par résonance magnétique nucléaire (RMN) et par spectrométrie de masse. / The main direction of the research work of this thesis is to valorize the phytochemicals found in the heart of the northern flora. The latter has many impressive adaptations to the extreme climatic conditions in these territories. There is little vegetation that can develop due to the particular environment of these regions. The northern flora of Quebec exploits different and particular defence mechanisms of the plants not being in these conditions. In this context, the research objective of this master's project is to investigate phytochemically the secondary metabolites of Racomitrium lanuginosum, a very little studied bryophyte. To do so, we used a solvent extraction process of different polarities, followed by distinct purification and characterization steps. Racomitrium lanuginosum is a moss present in southern and northern ecosystems. The samples studied come from Nunavik, more precisely from the vicinity of Kuujjuarapik-Whapmagoostui. This is the first phytochemical investigation of this bryophyte for northern specimens. Our phytochemical investigation started with an extraction process with hexanes, followed by dichloromethane, then methanol. The crude extracts were subjected to gas chromatography-mass spectrometry (GC-MS) for putative identification of volatile compounds. Subsequently, the crude extracts were fractionated by medium pressure liquid chromatography (MPLC). Subsequently, some fractions were subjected to liquid chromatography-mass spectrometry (LC-MS) for putative identification of compounds. Molecules that were not putatively identified were then purified by semi-preparative high-performance liquid chromatography (HPLC). This step allowed us to obtain some pure secondary metabolites for structure elucidation by nuclear magnetic resonance (NMR) and mass spectrometry.