Afforestation and reforestation programs utilizing available fields for biofuel production, carbon sequestration, and other uses linked to climate change are looking to tree physiologists to identify species and genotypes best-suited to their purposes. The ideal poplar genotype for use in Canadian programs would be drought-resistant, cold-climate adapted, and fast-growing, thus requiring an understanding of links between a variety of physiological traits linked to growth and productivity. This study examined the basis for variations in water-use efficiency within four selected populations of Populus trichocarpa and Populus balsamifera (2 provenances each). Each species included both a northern and a southern provenance. Correlations between water-use efficiency, nitrogen-use efficiency, ¹³C/¹²C isotope ratio, stomatal conductance, and overall productivity were evaluated. Gas exchange variables measured included net photosynthesis, transpiration rate, stomatal conductance, and intercellular CO₂ content. Water-use efficiency and ¹³C content across all genotypes were highly correlated. Results suggested that variation in water-use efficiency was primarily related to variation in stomatal conductance across all genotypes. Whereas differences in net photosynthesis in this study were not significant between species, P. balsamifera did reveal a higher average stem volume overall. Although variation in stomatal conductance was the major determinant of differences in water-use efficiency, positive correlations were found between ¹³C isotope abundance and net photosynthesis in both P. balsamifera provenances. In this regard, results for the northern P. balsamifera provenance are the most consistent across all gas-exchange and growth trait correlations, in terms of meeting expectations for sink-driven water-use efficiency. The findings in this study suggest the possibility of identifying poplar genotypes with an absence of trade-off between water-use efficiency and nitrogen-use efficiency, notably among genotypes from the northern P. balsamifera provenance, near Gillam.

No description available.

Hundreds of proteins have been detected in phloem and xylem sap, even though the cells involved in long distance phloem and xylem transport are incapable of protein synthesis at maturity. We are now beginning to learn the identity and function of these proteins, but this knowledge is generally limited to annual plants. The first objective of this study was to identify phloem and xylem sap proteins in the perennial, poplar. Using LC-MS/MS, 48 proteins were identified in poplar phloem exudate and 98 proteins were identified in xylem sap. A large number of phloem exudate proteins are insect defense proteins that include protease inhibitors and polyphenol oxidase and also members of the pop3/SPI gene family, whereas a number of xylem sap proteins were pathogenesis-related proteins such as thaumatin-like proteins (TLPs) and chitinases that function in pathogen defense. The importance of xylem sap proteins in pathogen defense has been previously demonstrated, however, the role of phloem proteins in insect defense is currently unknown. A major question to be addressed in order to understand the function of phloem proteins is if they are differentially regulated in response to insect herbivory. The second objective of this study was to identify poplar phloem proteins differentially regulated in response to simulated insect feeding. Using two-dimensional gel electrophoresis, two proteins, PtTLP1 and pop3.1, were consistently upregulated 24 hours post-wounding. The third objective of this study was to produce antibodies against these proteins to use to further characterize their expression and localization patterns. Antibodies were also produced against another phloem exudate protein, pop3.4, which is 40% similar to pop3.1. The origin of all three proteins inside sieve elements was confirmed with immunolocalization. PtTLP 1, pop3.1 and pop3.4 antisera labelled organelle-like structures in sieve elements and also phloem parenchyma cells. For PtTLP1, these structures were identified as starch and starch containing plastids. All three antisera also labelled cell wall proteins in different cell types. Overall, this study represents the first large-scale analysis of phloem and xylem sap proteomes from a perennial and describes the first observation of wound-inducible phloem sap proteins.

Proanthocyanidins (PAs) are polymeric phenolic chemicals produced by many plant species that may contribute to protection of tissues against biotic and abiotic stress conditions. In poplar (Populus spp.) leaves, PA biosynthesis is rapidly activated by insect herbivore damage, indicating that PAs may be an inducible chemical defence. In this study, the expression of PA biosynthetic genes was monitored in poplar leaves exposed to several stress stimuli. The PA pathway was shown to be rapidly activated at the level of gene transcription by stresses such as elevated light, UV-B irradiation and infection of leaves by a biotrophic fungal parasite. A transcription factor gene of the R2R3 MYB type, MYB134, was found to be co-activated with PA biosynthetic genes under these stress conditions. When overexpressed in transgenic poplar, this gene induced a strong, specific activation of the PA pathway, indicating that it might function as a regulator of stress-induced PA metabolism in poplar. MYB134 was shown to bind to promoter fragments of PA biosynthetic genes which contained a conserved DNA cis-element found in the promoter regions of many other phenylpropanoid genes including putative MYB134-regulated genes. A global transcriptome analysis of leaves of the MYB134-overexpressing poplar plants confirmed that the PA pathway activation was complete and specific, and led to the identification of a number of putative novel PA biosynthetic and regulatory genes. These results indicate that stress-responsive PA and flavonoid metabolism in poplar may be regulated by a complex system involving both positive and negative regulation. Preliminary results are also presented related to analysis of PA functions in transgenic plants, and the use of MYB134 to engineer PA metabolism in plants other than poplar. This study provides insight into the regulatory mechanisms controlling stress-induced PA metabolism, and expands our understanding of roles that this biological response may play in poplar.

Pseudo-lignin, which can be broadly defined as aromatic material that yields a positive acid-insoluble (Klason) lignin value, has been reported to generate from biomass polysaccharides during dilute acid pretreatment (DAP). To investigate the fundamental chemistry of pseudo-lignin, a series of state-to-art analytical techniques including GPC, FT-IR and ¹³C NMR were applied to characterize pseudo-lignin extracted from poplar α-cellulose and holocellulose after DAP. The results showed that pseudo-lignin is polymeric (Mn ~ 1000 g/mol; Mw ~ 5000 g/mol) and consists of carbonyl, carboxylic, aromatic, methoxy and aliphatic structures, which can be produced from both dilute acid-treated cellulose and hemicellulose. During DAP, the hydrolysis of polysaccharides, which leads to some release of monosaccharides, and their subsequent dehydration reactions to form furfural and 5-hydromethylfurfural (HMF) takes place. Further rearrangements of furfural and/or HMF can produce aromatic compounds, which undergo further polymerization and/or polycondensation reactions to form pseudo-lignin. More importantly, pseudo-lignin was revealed to bind with cellulase enzymes unproductively and significantly retard enzymatic conversion of cellulose. As compared to native lignin after DAP, the inhibition effect arise from pseudo-lignin is much stronger, which clearly indicates pseudo-lignin formation should be avoided during DAP. Process optimization study indicated that addition of dimethyl sulfoxide (DMSO) to the DAP reaction medium can effectively increase sugar recovery and reduce pseudo-lignin formation, even under high-severity pretreatment conditions. The pseudo-lignin suppression property of DMSO has been attributed to the preferential arrangement of DMSO in the vicinity of the C1 carbon of the HMF molecule, thereby protecting HMF from further reactions to form pseudo-lignin.

No description available.

No description available.

The sucrose-nonfermenting-1 related kinase 1 (SnRK1) protein complex is a heterotrimeric serine/threonine protein kinase complex conserved in eukaryotes that acts as a regulator of carbon metabolism and energy homeostasis. The objective of this study was to determine if the SnRK1 protein complex has a role in the nitrogen response and during dormancy acquisition in poplar. Gene expression profiling of the PtdSnRK1, PtdAKINbeta, and PtdAKINgamma gene family members was carried out using a robust qRT-PCR assay. A subset of these genes showed modified expression patterns under differential nitrogen availability and during dormancy acquisition, suggesting that SnRK1 complexes comprised of specific subunits may be involved in the regulation of the response to nitrogen and during dormancy acquisition. The regulatory subunits PtdAKINbeta1.1, PtdAKINgamma1.1 and PtdAKINgamma2.3 were often identified using principal component analysis as significantly responsible for distinguishing treatments from one another and therefore merit further study. / Plant Biology

Afforestation and reforestation programs utilizing available fields for biofuel production, carbon sequestration, and other uses linked to climate change are looking to tree physiologists to identify species and genotypes best-suited to their purposes. The ideal poplar genotype for use in Canadian programs would be drought-resistant, cold-climate adapted, and fast-growing, thus requiring an understanding of links between a variety of physiological traits linked to growth and productivity. This study examined the basis for variations in water-use efficiency within four selected populations of Populus trichocarpa and Populus balsamifera (2 provenances each). Each species included both a northern and a southern provenance. Correlations between water-use efficiency, nitrogen-use efficiency, ¹³C/¹²C isotope ratio, stomatal conductance, and overall productivity were evaluated. Gas exchange variables measured included net photosynthesis, transpiration rate, stomatal conductance, and intercellular CO₂ content. Water-use efficiency and ¹³C content across all genotypes were highly correlated. Results suggested that variation in water-use efficiency was primarily related to variation in stomatal conductance across all genotypes. Whereas differences in net photosynthesis in this study were not significant between species, P. balsamifera did reveal a higher average stem volume overall. Although variation in stomatal conductance was the major determinant of differences in water-use efficiency, positive correlations were found between ¹³C isotope abundance and net photosynthesis in both P. balsamifera provenances. In this regard, results for the northern P. balsamifera provenance are the most consistent across all gas-exchange and growth trait correlations, in terms of meeting expectations for sink-driven water-use efficiency. The findings in this study suggest the possibility of identifying poplar genotypes with an absence of trade-off between water-use efficiency and nitrogen-use efficiency, notably among genotypes from the northern P. balsamifera provenance, near Gillam.

Thesis (Ph. D.)--Auburn University, 2008. / Vita. Includes bibliographical references (p. 223-241).