The effects of phytic acid, iron, and genetic mutations on the phosphate responses of Arabidopsis thaliana

Phosphate deficiency is an important constraint to agricultural productivity. Attempts are underway to characterize the physiological and molecular responses to phosphate deficiency of the model plant, Arabidopsis thaliana. The hope is that this information will contribute to the breeding of phosphate efficient crops. As part of this effort, this thesis presents the extensive analysis of the role of phytic acid and iron in the root archiecture modifications of A. thaliana during phosphate deficiency, and the characterization of two mutants involved in A. thaliana\u27s maintenance of phosphate homeostasis. Phytic acid is an abundant but poorly available organic form of phosphate in soils. When it was added as as source of phosphate to the medium used in this study A. thaliana grew well. Extensive analysis revealed that this was not because the plants were breaking down phytic acid, but because phytic acid was chelating all the iron. These results and those from additional studies lead to the conclusion that the primary root growth inhibition of A. thaliana during phosphate deficiency is likely in response to an increase in iron avaibility. A screen for mutants with altered growth on medium containing phytic acid led to the identification of the JW32 mutant. JW32 has a defect in its root development that decreases its ability to acquire phosphate from the growth medium. The region containing the mutated gene in JW32 has now been narrowed to a region of chromosome 3 containing 192 predicted genes. In conjunction with the work on JW32, another mutant, 114:4S:38, that has elevated tissue levels of phosphate when grown on phosphate sufficient medium was similarly characterized