PHENOTYPIC CHARACTERIZATION OF A TOBACCO MUTANT IMPAIRED IN AUXIN POLAR TRANSPORT

A mutation in tobacco (Nicotiana tabacum L. cv 'Xanthi') called lat (l ow auxin transport) that changes many morphogenic features throughout the lift. of tile plant has been isolated. Abnormalities were observed in seed development, embryogenesis, cotyledon formation. leaf initiat ion and development, leaf veination pattern, and flower development, S elfed R-2 lat mutant plants set between 60% and 90% fewer seeds than w ild-type tobacco, and about 10% of these seeds did not germinate. Non- germinating seeds contained either abnormal embryos or abnormal endosp erm tissues. There was no uniformity in the stage at which embryonic d evelopment ceased in the aberrant seeds, Seedlings often revealed abno rmal and highly varied phenotypes after germination. In some of these cases, cotyledons were heart-shaped, fused, cup-shaped, or cylindrical . Leaf morphology ranged from normal to cup-shaped, and some leaves oc casionally produced shoots from the leaf midvein. Flowers ranged from normal to compound with occasional fused floral parts or split petals. Stamens were sometimes petal-like. This unusual assortment of phenoty pic changes suggested that the mutation might affect a basic component of plant metabolism. We found that polar transport of indole-3-acetic acid (IAA) was reduced to about 9-19% of the wild-type level in the i nflorescence axis of selfed R-2 lat mutants. In addition, supplementat ion of 1-naphthaleneacetic acid (NAA) to sterile media suppressed some of the abnormalities of the Int mutation so long as the plants grew t here. Similarities in the phenotype of embryos, cotyledon and leaf sha pes, translocation of labeled IAA, and response to applied NAA indicat e that the lar locus of tobacco may be analogous to the pin locus of A rabidopsis, or produce a protein that functions in the same auxin-tran sport pathway.