title: Gravitropism of inflorescence stems in starch-deficient mutants of Arabidopsis.
abstract: Previous studies have assayed the gravitropic response of roots and hypocotyls of wild type Arabidopsis thaliana, two reduced-starch strains, and a starchless strain. Because there have been few reports on inflorescence gravitropism, in this article, we use microscopic analyses and time-course studies of these mutants and their wild type to study gravitropism in these stems. Sedimentation of plastids was observed in endodermal cells of the wild type and reduced-starch mutants but not in the starchless mutant. In all of these strains, the short inflorescence stems (1.0-2.9 cm) were less responsive to the gravistimulus compared with the long stems (3.0-6.0 cm). In both long and short inflorescence stems, the wild type initially had the greatest response; the starchless mutant had the least response; and the reduced starch mutants exhibited an intermediate response. Furthermore, growth rates among all four strains were approximately equal. At about 6 h after reorientation, inflorescences of all strains returned to a position parallel to the gravity vector. Thus, in inflorescence stems, sedimentation of plastids may act as an accelerator but is not required to elicit a gravitropic response. Furthermore, the site of perception appears to be diffuse throughout the inflorescence stem. These results are consistent with both a plastid-based statolith model and the protoplast pressure hypothesis, and it is possible that multiple systems for gravity perception occur in plant cells.
authors.affiliation: Department of Botany, Miami University, Oxford, Ohio 45056, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Weise
authors.forename: J Z
authors.initials: JZ
authors.lastname: Kiss
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000648:ultrastructure; D018522:Gravitropism / Q000502:physiology*; D018466:Gravity Sensing / Q000502:physiology*; D018546:Hypocotyl / Q000254:growth & development; D009154:Mutation; D018547:Plant Stems / Q000254:growth & development* / Q000648:ultrastructure; D018087:Plastids / Q000502:physiology*; D013213:Starch / Q000172:deficiency / Q000378:metabolism
chemical_list: D013213:Starch