title: Space-time analysis of gravitropism in etiolated Arabidopsis hypocotyls using bioluminescence imaging of the IAA19 promoter fusion with a destabilized luciferase reporter.
abstract: Imaging analysis was carried out during the gravitropic response of etiolated Arabidopsis hypocotyls, using an IAA19 promoter fusion of destabilized luciferase as a probe. From the bright-field images we obtained the local deflection angle to the vertical, A, local curvature, C, and the partial derivative of C with respect to time, [Formula: see text]. These were determined every 19.9 µm along the curvilinear length of the hypocotyl, at ~10 min intervals over a period of ~6 h after turning hypocotyls through 90° to the horizontal. Similarly from the luminescence images we measured the luminescence intensity of the convex and concave flanks of the hypocotyl as well as along the median of the hypocotyl, to determine differential expression of auxin-inducible IAA19. Comparison of these parameters as a function of time and curvilinear length shows that the gravitropic response is composed of three successive elements: the first and second curving responses and a decurving response (autostraightening). The maximum of the first curving response occurs when A is 76° along the entire length of the hypocotyl, suggesting that A is the sole determinant in this response; in contrast, the decurving response is a function of both A and C, as predicted by the newly-proposed graviproprioception model (Bastien et al., Proc Natl Acad Sci USA 110:755-760, 2013). Further, differential expression of IAA19, with higher expression in the convex flank, is observed at A = 44°, and follows the Sachs' sine law. This also suggests that IAA19 is not involved in the first curving response. In summary, the gravitropic response of Arabidopsis hypocotyls consists of multiple elements that are each determined by separate principles.
authors.affiliation: Division of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan. kty@sci.hokudai.ac.jp.|Biosystems Science Course, Graduate School of Life Science, Hokkaido University, Sapporo, 060-0810, Japan. kty@sci.hokudai.ac.jp.
authors.forename: Kotaro T
authors.initials: KT
authors.lastname: Yamamoto
authors.affiliation: Division of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan.|Biosystems Science Course, Graduate School of Life Science, Hokkaido University, Sapporo, 060-0810, Japan.
authors.forename: Masaaki K
authors.initials: MK
authors.lastname: Watahiki
authors.affiliation: Division of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan.|Center for Sustainable Resource Science, RIKEN, Tsurumi-ku, Yokohama, 230-0045, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Matsuzaki
authors.affiliation: Division of Biological Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan.|Graduate School of Life and Environmental Sciences, Kyoto Prefecture University, Sakyo-ku, Kyoto, 606-8522, Japan.
authors.forename: Soichirou
authors.initials: S
authors.lastname: Satoh
authors.affiliation: Biosystems Science Course, Graduate School of Life Science, Hokkaido University, Sapporo, 060-0810, Japan.
authors.forename: Hisayo
authors.initials: H
authors.lastname: Shimizu
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D064527:Etiolation; D018506:Gene Expression Regulation, Plant; D018522:Gravitropism; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D007210:Indoleacetic Acids / Q000378:metabolism*; D008027:Light; D008156:Luciferases; D009154:Mutation; D010937:Plant Growth Regulators / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D036226:Seedlings / Q000235:genetics / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; C483308:IAA19 protein, Arabidopsis; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D008156:Luciferases
keywords: Arabidopsis; Aux/IAA; Auxin; Bioluminescence imaging; Gravitropism; Hypocotyl