Gravitropism of inflorescence stems in starch-deficient mutants of Arabidopsis

Int J Plant Sci. 1999;160(3):521-7. doi: 10.1086/314142.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / ultrastructure
  • Gravitropism / physiology*
  • Gravity Sensing / physiology*
  • Hypocotyl / growth & development
  • Mutation
  • Plant Stems / growth & development*
  • Plant Stems / ultrastructure
  • Plastids / physiology*
  • Starch / deficiency
  • Starch / metabolism


  • Starch