<p> Thellungiella salsuginea (also known as T. halophila), is an emerging model species for studies of plant tolerance to osmotic stress. Currently, Thellungiella plants originating from two geographical locations are being developed for research. Yukon Thellungiella is native to the saline and alkaline soils of the Yukon Territory, Canada. The seeds in this study were collected at the Takhini Salt-Flats near Whitehorse, YT, a sub-arctic and semi-arid region. Plants from the Yukon have been proposed to be a suitable species to study plant tolerance to salinity, cold temperatures, and water deficits. Shandong Thellungiella is native to the saline coast of north-eastern China in Shandong Province where the climate is temperate and affected by summer monsoons. This plant has been proposed as an ideal model for the study of salt tolerance mechanisms but is reported to show little drought tolerance.</p> <p> An objective of this study was to compare Yukon and Shandong Thellungiella plants with respect to their ability to withstand water deficits. Plants were grown simultaneously in controlled environment chambers where watering was withheld until plants visibly wilted. Wilting occurred at a leaf relative water (RWC) content of about 50-60% and then turgor was restored by re-watering. In a second experiment plants allowed to wilt and recover once were then subjected to a second wilting and recovery cycle. The third experimental approach tested the survival capacity of plants after experiencing a wilting episode where leaf RWC dropped to about 30%.</p> <p> With the first drought simulation treatment, both Yukon and Shandong plants took about 6 days to wilt when watering was stopped. After re-watering and recovery, the Yukon plants subjected to a second drought episode took almost two days longer to wilt
while the similarly treated Shandong plants showed no change in the days taken to wilt. This indicates that Yukon plants show improved tolerance to stress after a single exposure to a water deficit. Yukon plants were also able to grow and complete their life cycle following exposure to severe water deficit treatment whereas Shandong plants died. Measurements of solute potential showed that the Yukon plants re-established turgor at a lower solute potential of -2.06 +/- 0.03 MPa following recovery from a second drought treatment suggesting that this plant can undergo osmotic adjustment. No evidence of osmotic adjustment was observed for Shandong Thellungiella.</p> <p> Gas chromatography/mass spectrometry (GC/MS) was used to identify the metabolites associated with Thellungiella leaves recovering from water deficits relative to those from unstressed, well-watered controls. For comparison, metabolite profiles were also prepared from leaves of plants harvested at a Yukon field site during a dry year (2003) and a year of higher than normal rainfall (2005). The data was analyzed to identify treatment/sample-specific patterns using ANOVA to test for significance among quantitative and qualitative changes for individual metabolites. Significant changes were
then subjected to hierarchical cluster analysis (HCA) and principal component analysis (PCA). Using ANOVA and HCA, we were able to identify the most likely metabolite candidates contributing to the superior tolerance of Thellungiella, and their linkages between broad spectrums of metabolites. Using PCA we were able to assign clusters to the individual plant treatments for each plant source, and identify the most important components contributing to these clusters. Of the ca 289 components detected, only a small subset of components underwent statistically significant changes in abundance. Most of the drought-stress related changes were attributed to sugars: hexoses and disaccharides. Sugars accumulating in the more drought-tolerant Yukon plants and in a dry field season included fructose, glucose and galactose. Of the sugar alcohols, only myo-inositol showed patterns of interest in view of its enrichment in tissues showing superior tolerance to low water conditions. Similar patterns were also shown by the organic acid, threonic acid.</p> <p> A complementary approach was used to characterize metabolic traits associated with exposure to cold temperatures. In this study, a higher content of proline and citrate distinguished plants exposed to cold temperatures irrespective of whether the plants were in cabinets or in the field. Proline content, however, did not show drought-responsive accumulation under any drought treatment tested. As such, by comparison with the drought-stress data we can identify possible stress-specific signatures among metabolites undergoing changes. The study of stress-responsive traits could help develop a better understanding of plant systems and their response to specific environmental conditions.</p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21650 |
| Date | 09 1900 |
| Creators | Dedrick, Jeff |
| Contributors | Weretilnyk, Elizabeth A., Biology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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