CHARACTERIZATION OF THE GROWTH AND AUXIN PHYSIOLOGY OF ROOTS OF THE TOMATO MUTANT, DIAGEOTROPICA

Roots of the tomato (Lycopersicon esculentum, Mill.) mutant diageotrop ica (dgt) exhibit an altered phenotype. These roots are agravitropic a nd lack lateral roots. Relative to wild-type (VFN8) roots, dgt roots a re less sensitive to growth inhibition by exogenously applied IAA and auxin transport inhibitors (phytotropins), and the roots exhibit a red uction in maximal growth inhibition in response to ethylene. However, IAA transport through roots, binding of the phytotropin, tritiated nap hthylphthalamic acid ([H-3]NPA), to root microsomal membranes, NPA-sen sitive IAA uptake by root segments, and uptake of [H-3]NPA into root s egments are all similar in mutant and wild-type roots. We speculate th at the reduced sensitivity of dgt root growth to auxin-transport inhib itors and ethylene is an indirect result of the reduction in sensitivi ty to auxin in this single gene, recessive mutant. We conclude that dg t- roots, like dgt shoots, exhibit abnormalities indicating they have a defect associated with or affecting a primary site of auxin percepti on or action.