Osmoregulation in response to drought stress
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Humankind is undoubtedly dependent upon plants. Our interactions are ancient and have developed gradually through eons of sharing the earth. Without their ability to transfer sunlight radiation into stored chemical energy, it is unlikely life would have evolved at all. This relationship is most clearly exemplified in modern agriculture, which produces food for our growing populations. Grasslands in particular make a significant contribution to food security by providing feed for livestock used for meat and milk production (O’Mara, 2012). Energy captured by plants can also be converted into ethanol for energy use (Tilman, Hill, & Lehman, 2006). Furthermore our largest current energy source is fossil fuels, which is actually energy stored by plants who died millions of years ago. Given our great dependence on agriculture for food and energy, researchers have been interested in studying many species of plants in their native environments. This can inform scientists about how plants have adapted to live in their respective habitats. Another relevant consideration, in light of the shifting climate in the United States to a more arid environment, is how plants have evolved to manage drought stress. Water is very important to all plant species as it is the primary carrier of sugar and nutrients throughout plants, and itself is required for ongoing metabolic processes and growth. Therefore if a plant can survive in a very dry environment, it must have a mechanism to manage the stress and maintain metabolic processes. Osmoregulation in plants is an important component of drought tolerance. It encompasses concerted efforts within plant cells to maintain a high water pressure so the metabolism can continue and the plant may live. It also helps to maintain the cellular integrity and minimize damage to membranes and organelles. Osmotic adjustment is part of this effort, and the first chapter of this thesis outlines a more efficient measure of osmotic adjustment suitable for high throughput analyses. These investigations were conducted using a clonal population of the switchgrass Panicum virgatum, a biofuel candidate. A method similar in concept to that developed in chapter 1 was used to investigate the genetic architecture of osmoregulation in the model plant system Arabidopsis thaliana. In chapter 2, a powerful genetic mapping population of natural accessions of Arabidopsis thaliana was used to do quantitative trait loci (QTL) mapping of osmoregulation. While these two investigations were conducted in different species, the insights gained in each about osmoregulation give the scientific community a better knowledge base about basic plant function which will be invaluable in the future.