title: Agravitropic mutant for the study of hydrotropism in seedling roots.
abstract: Roots have been shown to respond to a moisture gradient by positive hydrotropism. Agravitropic mutant plants are useful for the study of the hydrotropism in roots because on Earth hydrotropism is obviously altered by the gravity response in the roots of normally gravitropic plants. The roots are able to sense water potential gradient as small as 0.5 MPa mm(-1). The root cap includes the sensing apparatus that causes a differential growth at the elongation region of roots. A gradient in apoplastic calcium and calcium influx through plasmamembrane in the root cap is somehow involved in the signal transduction mechanism in hydrotropism, which may cause a differential change in cell wall extensibility at the elongation region. We have isolated an endoxy loglucan transferase (EXGT) gene that is strongly expressed in pea roots and appears to be involved in the differential growth in hydrotropically responding roots. Thus, it is now possible to study hydrotropism in roots by comparing with or separate from gravitropism. These results also imply that microgravity conditions in space are useful for the study of hydrotropism and its interaction with gravitropism.
authors.affiliation: Institute of Genetic Ecology, Tohoku University, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Takahashi
authors.forename: M
authors.initials: M
authors.lastname: Takano
authors.forename: N
authors.initials: N
authors.lastname: Fujii
authors.forename: A
authors.initials: A
authors.lastname: Higashitani
authors.forename: M
authors.initials: M
authors.lastname: Yamashita
authors.forename: T
authors.initials: T
authors.lastname: Hirasawa
authors.forename: K
authors.initials: K
authors.lastname: Nishitani
mesh_terms: D015220:Calcium Channels / Q000502:physiology; D005362:Ficoll / Q000494:pharmacology; D017343:Genes, Plant; D016695:Glycosyltransferases / Q000235:genetics; D018522:Gravitropism / Q000187:drug effects / Q000502:physiology*; D008353:Mannitol / Q000494:pharmacology; D009154:Mutation; D009997:Osmotic Pressure; D018532:Pisum sativum / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D011092:Polyethylene Glycols / Q000494:pharmacology; D012399:Rotation; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013012:Sorbitol / Q000494:pharmacology; D018523:Tropism / Q000187:drug effects / Q000502:physiology*; D014867:Water / Q000502:physiology*; D018474:Weightlessness Simulation
chemical_list: D015220:Calcium Channels; D014867:Water; D005362:Ficoll; D008353:Mannitol; D011092:Polyethylene Glycols; D013012:Sorbitol; D016695:Glycosyltransferases; C073693:xyloglucan endotransglycosylase