Forisomes belong to the group of non-dispersive P protein-bodies (see P-proteins for definition). They occur in faboid legumes (bean plants) only. They undergo a rapid, reversible switch from an elongated low-volume conformation into a spherical high-volume conformation. The high-volume state is induced when Ca2+ enters the cytoplasm of disturbed or severed sieve elements. High volume-state forisomes impede flow in the sieve tube.
In vitro, their volume increases up to 9-fold in response to divalent cations without requirement for chemical energy sources such as ATP. Cycling between low- and high-volume states can be induced in isolated forisomes by repetitive exchange of bathing media containing either Ca2+ or chelators. Diffusional electrotitration allows electric control of forisome expansion. They can be isolated in large numbers and remain functional after prolonged periods of storage. This unique combination of useful properties renders forisomes a paradigmatic model for proteinaceous smart materials (see Knoblauch et al. 2003 in the literature list).