9423651 Lomax Plant responses to developmental and environmental signals are controlled by a complex set of interactions between plant hormones and other growth regulators. The occurrence and relative ratio of the plant hormones auxin and cytokinin coordinate plant growth and differentiation, as well as environmental responses. There is a long history of research in this area, however, questions remain as to how the ratio of the two hormones is detected by the plant, as well as the molecular mechanisms of action of the hormones, either singly or in combination. Mutants can provide a powerful toml for dissecting physiological, biochemical, and molecular responses. The diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) is a single gene, recessive mutant previously characterized as auxin- insensitive, as it neither grows nor produces ethylene in response to applied auxin. Although isolated on the basis of its reduced gravitropic response, the dgt lesion results in a complex pleiotropic phenotype involving many aspects of plant form and function. Many of these characteristics are better associated with plants overexpressing cytokinin and it has been shown that much of the dgt phenotype can be mimicked in wild type tomato plants with exogenously- supplied cytokinin. The studies proposed here are designed to test that hypothesis and to establish whether the apparent increase in cytokinin sensitivity in dgt plants is the result of auxin insensitivity, altered cytokinin homeostasis, or alteration of some signal transduction component which controls or integrates the response to both hormones. Results from these studies will shed light on the regulation of auxin sensitivity as well as on cytokinin responsiveness in plants. The information gained will aid in our understanding of hormonal regulation of plant function, as well as in the elucidation of the molecular and cellular mechanisms of action for cytokinin and auxin.
