Ozone-induced effects on Arabidopsis thaliana and Glycine max: Growth, physiology, foliar injury and gene expression assessed by DNA microarray technology, RT-PCR and Taq-Man

This dissertation investigated the differential gene expression patterns related to the physiological, anti-oxidative and morphological changes observed in Arabidopsis thaliana and Glycine max during ozone exposure.; In experiment 1, four week old Arabidopsis thaliana, were exposed to four levels of ozone, that is carbon filtered air (control); ambient air; 1.5x ambient ozone and 2x ambient ozone, for an additional 4 weeks. The plants were then observed for morphological changes, analyzed for the physiological impact and DNA microarray was conducted to determine gene expression. Arabidopsis exposed to elevated ozone showed a downward curling of the leaves, reduced leaf rosette growth and some necrosis. Ozone exposed plants showed a decrease in the wet mass significantly (p < 0.0001) from 1.38g to 1.01g, There was no statistical difference in effects on dry mass (p > 0.4). Genetic analysis demonstrated that genes of similar function tend to be hyper-expressed and clustered. This clustering fell in 2 major functional groups: (1) Unclassified/Function Unknown (e.g. glutamate-rich protein) and (2) Cell rescue (e.g. superoxide dismutase). The same clustering patterns were also seen in genes that are co-expressed, e.g. cell maintenance (e.g. ferritin). Genes involved in metabolism and cell growth also clustered together and were down-regulated (e.g. p-glycoprotein).; In experiment 2, ten cultivars of Glycine max were exposed to 4 weeks of elevated ozone. The plants were observed for morphological changes, analyzed for the physiological impact and RT-PCR and Taq-Man analysis was performed to determine gene expression profiles. Growth inhibitions in response to ozone exposure were also observed in all 10-Glycine max cultivars. There was also visible, though variable, symptoms of ozone-induced stress (e.g. a yellowing). Significant differences in chlorophyll-content and in biomass were detected among the ten cultivars (p < 0.001).; When comparing gene expression for 6 different genes, the response was variable between 5 different cultivars selected for analysis. In all cases, ascorbate peroxidase, superoxide dismutase, heat shock protein were all hyper-expressed but catalase was not. Gluthathione peroxidase and gluthathione s-transferase response was marginal among the 5 cultivars. The fact that superoxide dismutase was hyper-expressed, did not translate to any observed protection for those plants.