title: Halogenated auxins affect microtubules and root elongation in Lactuca sativa.
abstract: We studied the effect of 4,4,4-trifluoro-3-(indole-3-)butyric acid (TFIBA), a recently described root growth stimulator, and 5,6-dichloro-indole-3-acetic acid (DCIAA) on growth and microtubule (MT) organization in roots of Lactuca sativa L. DCIAA and indole-3-butyric acid (IBA) inhibited root elongation and depolymerized MTs in the cortex of the elongation zone, inhibited the elongation of stele cells, and promoted xylem maturation. Both auxins caused the plane of cell division to shift from anticlinal to periclinal. In contrast, TFIBA (100 micromolar) promoted elongation of primary roots by 40% and stimulated the elongation of lateral roots, even in the presence of IBA, the microtubular inhibitors oryzalin and taxol, or the auxin transport inhibitor naphthylphthalamic acid. However, TFIBA inhibited the formation of lateral root primordia. Immunostaining showed that TFIBA stabilized MTs orientation perpendicular to the root axis, doubled the cortical cell length, but delayed xylem maturation. The data indicate that the auxin-induced inhibition of elongation and swelling of roots results from reoriented phragmoplasts, the destabilization of MTs in elongating cells, and promotion of vessel formation. In contrast, TFIBA induced promotion of root elongation by enhancing cell length, prolonging transverse MT orientation, delaying cell and xylem maturation.
authors.affiliation: Department of Biology, University of Louisiana at Lafayette, Louisiana 70504-2451, USA.
authors.forename: N
authors.initials: N
authors.lastname: Zhang
authors.forename: K H
authors.initials: KH
authors.lastname: Hasenstein
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D004136:Dinitrobenzenes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006540:Herbicides / Q000494:pharmacology; D006846:Hydrocarbons, Halogenated / Q000494:pharmacology*; D007210:Indoleacetic Acids / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology; D018545:Lactuca / Q000187:drug effects* / Q000254:growth & development; D018613:Microscopy, Confocal; D008870:Microtubules / Q000187:drug effects*; D017239:Paclitaxel / Q000494:pharmacology; D010797:Phthalimides / Q000494:pharmacology; D010937:Plant Growth Regulators / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D013424:Sulfanilamides; D013997:Time Factors
chemical_list: D004136:Dinitrobenzenes; D006540:Herbicides; D006846:Hydrocarbons, Halogenated; D007210:Indoleacetic Acids; D007211:Indoles; D010797:Phthalimides; D010937:Plant Growth Regulators; D013424:Sulfanilamides; C014612:indolebutyric acid; C002687:alpha-naphthylphthalamic acid; C012465:oryzalin; C030737:indoleacetic acid; D017239:Paclitaxel