THE DIAGEOTROPICA GENE DIFFERENTIALLY AFFECTS AUXIN AND CYTOKININ RESPONSES THROUGHOUT DEVELOPMENT IN TOMATO

The interactions between the plant hormones auxin and cytokinin throug hout plant development are complex, and genetic investigations of the interdependency of auxin and cytokinin signaling have been limited. We have characterized the cytokinin sensitivity of the auxin-resistant d iageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) in a range of auxin-and cytokinin-regulated responses. Intact, etiolated dgt seedlings showed cross-resistance to cytokinin with respect to ro ot elongation, but cytokinin effects on hypocotyl growth and ethylene synthesis in these seedlings were not impaired by the dgt mutation. Se ven-week-old, green wild-type and dgt plants were also equally sensiti ve to cytokinin with respect to shoot growth and hypocotyl and interno de elongation. The effects of cytokinin and the dgt mutation on these processes appeared additive. In tissue culture organ regeneration from dgt hypocotyl explants showed reduced sensitivity to auxin but normal sensitivity to cytokinin, and the effects of cytokinin and the mutati on were again additive. However, although callus induction from dgt hy pocotyl explants required auxin and cytokinin, dgt calli did not show the typical concentration-dependent stimulation of growth by either au xin or cytokinin observed in wild-type calli. Cross-resistance of the dgt mutant to cytokinin thus was found to be limited to a small subset of auxin- and cytokinin-regulated growth processes affected by the dg t mutation, indicating that auxin and cytokinin regulate plant growth through both shared and separate signaling pathways.