A key mechanism utilized by plants to make iron (Fe) available for uptake is the reduction of Fe(III) to Fe(II) via an inducible, plasma membrane-bound Fe(III) reductase. Genes encoding such enzymes have not yet been isolated from plants; however, two Fe(III) reductases have been cloned from yeast. FRE1 and FRE2 account for the total membrane-associated Fe(III) reductase activity in Saccharomyces cerevisiae. If yeast reductase genes could be expressed in a plant system, root Fe(III) reduction may be enhanced, leading to a decrease in Fe chlorosis in transgenic plants. FRE1 and FRE2 were introduced into tobacco via Agrobacterium-mediated transformation. Fe(III) reductase activity was measured in homozygous transformants containing FRE1, FRE2, or both. The highest Fe(III) reduction levels were found in lines containing both FRE1 and FRE2. Liquid reductase assays showed three to four times more Fe(III) reduction in these transformants as compared to controls, and visual plate assays showed reduction along the entire length of the roots. One FRE1 containing line initially exhibited chlorosis on medium with low Fe at pH 7.5, but later recovered. Other transformants and the control remained chlorotic. Agrobacterium-mediated transformation often produces mutant phenotypes. A temperature-dependent morphological mutant was found among the progeny of tobacco transformed by Agrobacterium. The mutation is recessive and is expressed at low temperature (21��C). Mutant characteristics include formation of thick, narrow leaves with abnormal mesophyll cells and near absence of apical dominance. Also in the greenhouse (21-23��C), most plants remain vegetative, and the few flowers that are formed have petaloid stamens. High temperature (30��C) reverses the mutant phenotype, with formation of normal leaves and restoration of apical dominance. However, many flowers still have petaloid stamens. This mutant shares several phenotypic characteristics with transgenic tobacco plants overexpressing maize and Arabidopsis homeodomain proteins. / Graduation date: 1997