Hygroscopic movements in Geraniaceae: The structural variations that are responsible for coiling or bending

Yael Abraham, Rivka Elbaum

Research output: Contribution to journalArticlepeer-review


The family Geraniaceae is characterized by a beak-like fruit, consisting of five seeds appended by a tapering awn. The awns exhibit coiling or bending hygroscopic movement as part of the seed dispersal strategy. Here we explain the variation in the hygroscopic reaction based on structural principles. We examined five representative species from three genera: Erodium, Geranium, and Pelargonium. Using X-ray diffraction, and electron and polarized light microscopy, we measured the cellulose microfibril angles in relation to the cell and cellulose helix axes. The behavior of separated single cells during dehydration was also examined. A bi-layered structure characterizes all the representative genera studied, with a hygroscopically contracting inner layer, and a stiff outer layer. We found that the cellulose arrangement in the inner layer is responsible for the type of awn deformation (coiling or bending). In three of the five awns examined, we identified an additional coiling outer sublayer, which adds coiling deformation to the awn. We divide the movements into three types: bending, coiling, and coiled-bending. All movement types are found in the Geranium genus. These characteristics are of importance for understanding the evolution of seed dispersal mechanisms in the Geraniaceae family.

Original languageAmerican English
Pages (from-to)584-594
Number of pages11
Issue number2
StatePublished - Jul 2013


  • Cell wall structure
  • Coiling
  • Geraniaceae
  • Hygroscopic movement
  • Polarized light microscopy
  • Polscope
  • Seed dispersal
  • Small-angle X-ray scattering (SAXS)

All Science Journal Classification (ASJC) codes

  • Physiology
  • Plant Science


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