Mutants of Nicotiana plumbaginifolia with increased sensitivity to auxin

Two non-allelic, monogenic recessive mutations, aus1 and aus2, have been isolated which result in auxin hypersensitivity in mutant Nicotiana plumbaginifolia plants. At relatively low concentrations of indole-3-acetic acid or 1-naphthaleneacetic acid, the elongation growth of mutant seedling hypocotyls is more inhibited than in the case of the wild type; at high auxin concentrations, mutant seedlings are killed. The leaves of mature mutant plants degenerate after a spray treatment with auxin that has only a mild, transient effect on the wild type. Seedling hypocotyls of aus1 are more sensitive to L-tryptophan than those of the wild type but do not differ in their response to the D-isomer. The mutant is also more sensitive to ethylene and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, but not to either 6-benzyladenine or abscisic acid. Mutant seedlings display several distinct morphological characters: mild leaf epinasty, short primary root, increased root branching and no root hairs.