title: Disruption of the actin cytoskeleton results in the promotion of gravitropism in inflorescence stems and hypocotyls of Arabidopsis.
abstract: The actin cytoskeleton is hypothesized to play a major role in gravity perception and transduction mechanisms in roots of plants. To determine whether actin microfilaments (MFs) are involved in these processes in stem-like organs, we studied gravitropism in Arabidopsis inflorescence stems and hypocotyls. Localization studies using Alexa Fluor-phalloidin in conjugation with confocal microscopy demonstrated a longitudinally and transversely oriented actin MF network in endodermal cells of stems and hypocotyls. Latrunculin B (Lat-B) treatment of hypocotyls caused depolymerization of actin MFs in endodermal cells and a significant reduction of hypocotyl growth rates. Actin MFs in Lat-B-treated inflorescence stems also were disrupted, but growth rates were not affected. Despite disruption of the actin cytoskeleton in these two organs, Lat-B-treated stems and hypocotyls exhibited a promotion of gravitropic curvature in response to reorientation. In contrast, Lat-B reduced gravitropic curvature in roots but also reduced the growth rate. Thus, in contrast to prevailing hypotheses, our results suggest that actin MFs are not a necessary component of gravitropism in inflorescence stems and hypocotyls. Furthermore, this is the first study to demonstrate a prominent actin MF network in endodermal cells in the putative gravity-perceiving cells in stems.
authors.affiliation: Department of Botany, Miami University, Oxford, Ohio 45056.
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Yamamoto
authors.forename: John Z
authors.initials: JZ
authors.lastname: Kiss
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry / Q000502:physiology*; D000199:Actins / Q000737:chemistry / Q000502:physiology*; D017360:Arabidopsis / Q000502:physiology*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000737:chemistry; D018522:Gravitropism / Q000502:physiology*; D006834:Hydrazines / Q000737:chemistry; D018546:Hypocotyl / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D018613:Microscopy, Confocal; D010590:Phalloidine / Q000737:chemistry; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D018547:Plant Stems / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
chemical_list: D000199:Actins; C417561:Alexa 488 hydrazide; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005456:Fluorescent Dyes; D006834:Hydrazines; D013844:Thiazoles; D053778:Thiazolidines; D010590:Phalloidine; C037068:latrunculin B