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Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv. / Härtill 6 uppsatser.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2001. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2001. / Härtill 4 uppsatser.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 77-88). Also available on the World Wide Web.

Les modèles climatiques prédisent pour le futur une accentuation de la fréquence et de l’intensité des épisodes de sécheresse, ce qui affecterait sérieusement les écosystèmes forestiers. En conséquence, il y a une demande croissante pour du matériel végétal plus résistant à la sécheresse, et pour la compréhension des mécanismes génétiques et physiologiques de la tolérance des arbres à la sécheresse. Dans des conditions de sécheresse, la tension dans les vaisseaux du xylème augmente, et la cavitation peut se produire causant une embolie du vaisseau qui devient alors non fonctionnel. La vulnérabilité du xylème à la cavitation est corrélée à la tolérance à la sécheresse, indiquant l’importance de ce caractère pour la tolérance à la sécheresse. Cependant, peu était connu sur la variabilité de ce caractère au niveau intra-spécifique et ses bases génétiques étaient inconnues. Dans un premier temps, nous avons démontré que la vulnérabilité à la cavitation du xylème de peuplier (Populus tremula x Populus alba) s’acclimate à des conditions de sol plus sec et que ceci s’accompagne de changements dans la structure du xylème et d’expressions géniques. Ce processus d’acclimatation appuie l’hypothèse du rôle important joué par la vulnérabilité du xylème à la cavitation dans la tolérance à la sécheresse. Dans un second temps, nous avons étudié les bases structurales et génétiques de la vulnérabilité à la cavitation grâce à deux approches. La première a consisté à étudier les changements anatomiques et d’expressions géniques se produisant au cours de l’acclimatation de la vulnérabilité du xylème à la cavitation à des conditions plus sèches. Nous avons déterminé que l’augmentation de la vulnérabilité à la cavitation dans des conditions plus sèches est corrélée à une diminution du diamètre de la paroi de la ponctuation. Nous avons observé des changements d’expression géniques dans des conditions de sécheresse mais ceux ci n’ont pas pu être reliés à un changement de la vulnérabilité à la cavitation. Dans une seconde approche, nous avons utilisé dix lignées de peupliers dont l’expression de gènes impliqués dans le métabolisme de la lignine ont été modifiés et deux lignées surexprimant une pectine méthylestérase (PME) pour examiner le rôle de ces gènes dans la vulnérabilité à la cavitation. Chez les peupliers ayant un métabolisme des lignines modifié, nous avons également testé la relation entre les propriétés hydriques et mécaniques. Nous apportons des preuves que les lignines et les pectines (à travers les PME) sont impliquées dans la vulnérabilité à la cavitation et nos données sur les lignées transgéniques de peupliers ne soutiennent pas un lien exclusif entre les propriétés hydriques et mécaniques. / 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.

Thesis (M. Sc.)--University of Alberta, 2009. / Title from PDF file main screen (viewed on Oct. 19, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science, Department of Renewable Resources, University of Alberta." Includes bibliographical references.

The genus Populus consists of many ecologically and economically important forest tree species. Their rapid growth makes them one of the most productive hardwoods growing in temperate latitudes. Populus spp. frequently hybridize where their ranges overlap, and poplar hybrids are the most frequently planted genotypes for fiber production. To better understand the genomics of hybridization in Populus, we sampled and sequenced the genome of 574 poplar trees from six east-west transects across the hybrid zone between Populus trichocarpa and Populus balsamifera in western North America. I used these data to characterize population structure within and between transects, and hybridization between the species. There was a consistent transition from greater P. balsamifera ancestry in the north and east to greater P. trichocarpa ancestry in the south and west. Hybridization between the species was common across each of the six transects, though more common in colder climates. The results also showed that both latitude and longitude affect the genetic structure of this species complex, and that subtle introgression from P. balsamifera may facilitate adaptation of P. trichocarpa to colder climates. / Master of Science / The genus Populus has many ecologically and economically important forest tree species. Balsam poplar (Populus balsamifera) and black cottonwood (Populus trichocarpa) are two such species, both for fiber production and models for understanding tree biology and adaptation. Whereas black cottonwood is distributed close to the west coast of North America from California through Alaska, balsam poplar mostly occurs across the interior of Canada from Newfoundland through Alberta. Where their ranges overlap, the species often hybridize. In this study, we used genome sequencing of trees collected across six east-west transects from Washington state through British Columbia, Canada, and Alaska to understand genetic variation and the geography of hybridization. I found evidence of widespread hybridization across all transects. While the influence of P. balsamifera was extensive in northern populations, a large number of pure P. trichocarpa were found in southern populations. The transition from P. trichocarpa to P. balsamifera was also steeper in the south than the north, with a narrower hybrid zone in the south. Additionally, I found that gene flow among some populations was limited by temperature and geographical barriers. Taken together, my results suggest genetic structure and hybridization within and between these species is driven by climate variation, and that P. balsamifera ancestry may help northern P. trichocarpa populations adapt to their local environments.

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Thesis (Ph. D.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.