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First published online October 28, 2005; 10.1104/pp.105.067967 Plant Physiology 139:1460-1471 (2005) © 2005 American Society of Plant Biologists The rib1 Mutant of Arabidopsis Has Alterations in Indole-3-Butyric Acid Transport, Hypocotyl Elongation, and Root Architecture1Department of Biology, McGill University, Montreal, Quebec, Canada H3A 1B1 (J.P., C.S.W.); and Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 (A.M.R., G.K.M.)
Polar transport of the auxin indole-3-butyric acid (IBA) has recently been shown to occur in Arabidopsis (Arabidopis thaliana) seedlings, yet the physiological importance of this process has yet to be fully resolved. Here we describe the first demonstration of altered IBA transport in an Arabidopsis mutant, and show that the resistant to IBA (rib1) mutation results in alterations in growth, development, and response to exogenous auxin consistent with an important physiological role for IBA transport. Both hypocotyl and root IBA basipetal transport are decreased in rib1 and root acropetal IBA transport is increased. While indole-3-acetic acid (IAA) transport levels are not different in rib1 compared to wild type, root acropetal IAA transport is insensitive to the IAA efflux inhibitor naphthylphthalamic acid in rib1, as is the dependent physiological process of lateral root formation. These observed changes in IBA transport are accompanied by altered rib1 phenotypes. Previously, rib1 roots were shown to be less sensitive to growth inhibition by IBA, but to have a wild-type response to IAA in root elongation. rib1 is also less sensitive to IBA in stimulation of lateral root formation and in hypocotyl elongation under most, but not all, light and sucrose conditions. rib1 has wild-type responses to IAA, except under one set of conditions, low light and 1.5% sucrose, in which both hypocotyl elongation and lateral root formation show altered IAA response. Taken together, our results support a model in which endogenous IBA influences wild-type seedling morphology. Modifications in IBA distribution in seedlings affect hypocotyl and root elongation, as well as lateral root formation.
1 This work was supported by a grant from the Natural Sciences and Engineering Research Council of Canada (to C.S.W.), the J.W. McConnell McGill University Majors Fellowship (to J.P.), and grants from the National Aeronautics and Space Administration Specialized Center for Research and Training (North Carolina State University; to A.M.R. and G.K.M.) and the National Aeronautics and Space Administration (grant no. NAG2–1507 to G.K.M). 2 Present address: Department of Biology, University of North Carolina, Chapel Hill, NC 27599. 3 Present address: Department of Plant Cellular and Molecular Biology, Ohio State University, Columbus, OH 43210. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Gloria K. Muday (muday{at}wfu.edu). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.067967. * Corresponding author; e-mail muday{at}wfu.edu; fax 336–758–6008. Received July 5, 2005; returned for revision August 23, 2005; accepted August 24, 2005. Related articles in Plant Physiol.:
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