Anisotropic contraction in forisomes: Simple models won't fit

Winfried S. Peters, Michael Knoblauch, Stephen A. Warmann, William F. Pickard, Amy Q. Shen

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Forisomes are ATP-independent, Ca2+-driven contractile protein bodies acting as reversible valves in the phloem of plants of the legume family. Forisome contraction is anisotropic, as shrinkage in length is associated with radial expansion and vice versa. To test the hypothesis that changes in length and width are causally related, we monitored Ca2+- and pH-dependent deformations in the exceptionally large forisomes of Canavalia gladiata by high-speed photography, and computed time-courses of derived geometric parameters (including volume and surface area). Soybean forisomes, which in the resting state resemble those of Canavalia geometrically but have less than 2% of the volume, were also studied to identify size effects. Calcium induced sixfold volume increases in forisomes of both species; in soybean, responses were completed in 0.15 s, compared to about 0.5 s required for a rapid response in Canavalia followed by slow swelling for several minutes. This size-dependent behavior supports the idea that forisome contractility might rest on similar mechanisms as those of polyelectrolyte gels, a class of artificial "smart" materials. In both species, time-courses of forisome length and diameter were variable and lacked correlation, arguing against a simple causal relationship between changes in length and width. Moreover, changes in the geometry of soybean forisomes differed qualitatively between Ca 2+-and pH-responses, suggesting that divalent cations and protons target different sites on the forisome proteins.

Original languageEnglish (US)
Pages (from-to)368-378
Number of pages11
JournalCell Motility and the Cytoskeleton
Issue number5
StatePublished - May 2008


  • Ca-dependent contractility
  • Canavalia gladiata [Jacq.] DC
  • Contractile protein
  • Contraction kinetics
  • Glycine max L.
  • pH-dependent contractility

ASJC Scopus subject areas

  • Structural Biology
  • Cell Biology


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