title: Hydrotropism in abscisic acid, wavy, and gravitropic mutants of Arabidopsis thaliana.
abstract: We have developed experimental systems to study hydrotropism in seedling roots of Arabidopsis thaliana (L.) Heynh. Arabidopsis roots showed a strong curvature in response to a moisture gradient, established by applying 1% agar and a saturated solution of KCl or K(2)CO(3) in a closed chamber. In this system, the hydrotropic response overcame the gravitropic response. Hydrotropic curvature commenced within 30 min and reached 80-100 degrees within 24 h of hydrostimulation. When 1% agar and agar containing 1 MPa sorbitol were placed side-by-side in humid air, a water potential gradient formed at the border between the two media. Although the gradient changed with time, it still elicited a hydrotropic response in Arabidopsis roots. The roots curved away from 0.5-1.5 MPa of sorbitol agar. Various Arabidopsis mutants were tested for their hydrotropic response. Roots of aba1-1 and abi2-1 mutants were less sensitive to hydrotropic stimulation. Addition of abscisic acid restored the normal hydrotropic response in aba1-1 roots. In comparison, mutants that exhibit a reduced response to gravity and auxin, axr1-3 and axr2-1, showed a hydrotropic response greater than that of the wild type. Wavy mutants, wav2-1 and wav3-1, showed increased sensitivity to the induction of hydrotropism by the moisture gradient. These results suggest that auxin plays divergent roles in hydrotropism and gravitropism, and that abscisic acid plays a positive role in hydrotropism. Furthermore, hydrotropism and the wavy response may share part of a common molecular pathway controlling the directional growth of roots.
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Takahashi
authors.forename: Nobuharu
authors.initials: N
authors.lastname: Goto
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Okada
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics; D002254:Carbonates; D018522:Gravitropism / Q000502:physiology*; D006133:Growth Substances / Q000235:genetics; D007210:Indoleacetic Acids / Q000494:pharmacology; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics; D009997:Osmotic Pressure / Q000187:drug effects; D010749:Phosphoprotein Phosphatases / Q000235:genetics; D010937:Plant Growth Regulators / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D011188:Potassium / Q000502:physiology; D011189:Potassium Chloride / Q000494:pharmacology; D013012:Sorbitol / Q000494:pharmacology; D014157:Transcription Factors; D018523:Tropism / Q000502:physiology*; D014867:Water / Q000494:pharmacology / Q000502:physiology*
chemical_list: C081977:AXR1 protein, Arabidopsis; C110728:AXR3 protein, Arabidopsis; D029681:Arabidopsis Proteins; D002254:Carbonates; D006133:Growth Substances; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D010937:Plant Growth Regulators; D014157:Transcription Factors; D014867:Water; D013012:Sorbitol; D011189:Potassium Chloride; D000040:Abscisic Acid; C037593:potassium carbonate; C106443:ABI2 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases; D011188:Potassium