We manipulated the enzyme activity levels of the alcohol fermentation pathway, pyruvate decarboxylase (PDC), and alcohol dehydrogenase (ADH) in Arabidopsis using sense and antisense overexpression of the corresponding genes (PDC1, PDC2, and ADH1). Transgenic plants were analyzed for levels of fermentation and evaluated for changes in hypoxic survival. Overexpression of either Arabidopsis PDC1 or PDC2 resulted in improved plant survival. In contrast, overexpression of Arabidopsis ADH1 had no effect on flooding survival. These results support the role of PDC as the control step in ethanol fermentation. Although ADH1 null mutants had decreased hypoxic survival, attempts to reduce the level of PDC activity enough to see an effect on plant survival met with limited success. The combination of flooding survival data and metabolite analysis allows identification of critical metabolic flux points. This information can be used to design transgenic strategies to improve hypoxic tolerance in plants.Plants are constantly challenged by environmental stresses that reduce crop yield (e.g. salinity, low temperature, drought, and flooding). Soils with excess water account for 15.7% of the arable land in the United States, and flooding accounted for 16.4% of the crop insurance claims, making it the second highest cause of crop loss in the United States (Boyer, 1982). Traditionally, plant breeders have selected directly for increased stress tolerance, however, selection for flooding tolerance has been performed only in rice (Oryza sativa), where a genetic mapping approach was used to identify major and minor genes involved in submergence tolerance (Sripongpangkul et al., 2000; Xu et al., 2000). Transgenic plants with increased tolerance to drought, salinity, low temperatures, or a combination of these stresses (Nelson et al., 1998; Huang et al., 2000) were obtained by introducing genes for the overaccumulation of benign compounds (e.g. Gly betaine, mannitol, and Pro) that are believed to act as osmolytes. Other groups have increased stress tolerance in Arabidopsis by overexpressing transcription factors (Jaglo-Ottosen et al., 1998; Kasuga et al., 1999; Yamaguchi-Shinozaki and Shinozaki, 2001) or signal transduction components (Piao et al., 2001; Tamminen et al., 2001).There is substantial variation among terrestrial crop species in their ability to tolerate waterlogging conditions. Even rice, which is adapted to life in a flooded environment, incurs damage if the shoots are completely submerged for periods of time (Drew, 1997; Quimio et al., 2000). Genetic variation in flooding tolerance has been found in rice, maize (Zea mays), barley (Hordeum vulgare), and Arabidopsis. In some cases, this variation results from specific mutants (Harberd and Edwards, 1982; Dolferus et al., 1985; Lemke-Keyes and Sachs, 1989; Ricard et al., 1998). Several studies have focused on the effect of overexpression of genes on flooding tolerance. Zhang et al. (2000) overexpressed a gene involved in cytokinin biosynthesis and demonstrated improve...

Nitrogen (N) is the most important factor limiting crop productivity worldwide. The ability of plants to acquire N from applied fertilizers is one of the critical steps limiting the efficient use of nitrogen. To improve N use efficiency, genetically modified plants that overexpress alanine aminotransferase (AlaAT) were engineered by introducing a barley AlaAT cDNA driven by a canola root specific promoter (btg26). Compared with wild-type canola, transgenic plants had increased biomass and seed yield both in the laboratory and field under low N conditions, whereas no differences were observed under high N. The transgenics also had increased nitrate influx. These changes resulted in a 40% decrease in the amount of applied nitrogen fertilizer required under field conditions to achieve yields equivalent to wild-type plants.