UBC Theses and Dissertations
Effects of drought stress on metabolite profiles of hybrid and pure lines of Populus spp. Barchet, Genoa L. H.
Drought stress is perhaps the most commonly encountered abiotic stress plants experience in the natural environment, and is one of the most important factors limiting plant productivity. In the studies described in this text, drought-stressed poplar trees (Populus spp.) were analyzed for their metabolite content using the technique of untargeted metabolite profiling by employing gas chromatography coupled to mass spectrometry (GC/MS). The purpose of these analyses was to characterize the metabolite profile of poplar trees under drought stress in order to assess relative drought resistance and to investigate what mechanisms might be employed in the ability to resist drought. To do this, three independent experiments were carried out, each employing different poplar tree species and drought application protocols. For all three experiments, metabolite profiling identified key metabolites that increased or decreased in relative abundance upon exposure to drought stress. Overall, amino acids, the antioxidant phenolic compounds, catechin and kaempferol, and the osmolytes raffinose and galactinol exhibited increased levels under drought stress, whereas metabolites involved in photorespiration, redox regulation, and carbon fixation showed decreased levels under drought stress. One clone in particular, Okanese, in common with Experiments #1 and #2 described in this thesis, displayed unique responses to the imposed drought conditions. This clone was found to have higher stomatal conductance, transpiration rate, and leaf water potential, and lower growth rate in Experiments #2 and #1, respectively. Okanese also had lower accumulation of osmolytes such as raffinose, galactinol and proline, but higher overall levels of antioxidants such as catechin and dehydroascorbic acid. As such, it was proposed that osmotic adjustment as a mechanism for drought resistance in this clone is not as well developed in comparison to other clones investigated in this thesis, and that a possible alternative mechanism for the enhanced drought resistance displayed by Okanese may be due to differential allocation of resources towards root growth rather than osmotic adjustment.
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