Forisomes are proteins occurring in the sieve tubes of Fabaceae. Their molecules are about 1-3 µm wide and 10-30 µm long. They expand and contract anisotropically in response to changes of electric field, pH, or concentration of Ca2+ ions. Unlike most other moving proteins, the change is not dependent on ATP.
Forisomes function as valves in sieve tubes of the phloem system, by reversibly changing shape between low-volume ordered crystalloid spindles and high-volume disordered spherical conformations. The change from ordered to disordered conformation involves tripling of the protein's volume, loss of birefringence present in the crystalline phase, 120% radial expansion and 30% longitudinal shrinkage. In Vicia it was shown that forisomes are associated to the endoplasmic reticulum at sieve plates. There are evidences that the forisomes's behavior could depend on Ca2+ changes provoked by Ca2+-permeable ion channels, located on the endoplasmic reticulum and plasma membrane of sieve elements.[1] responsible for shape changes.
Forisomes have possible applications as biomimetic smart materials (e.g. valves in microdevices) or smart composite materials.
References
- ^ Alexandra C.U. Furch; Aart J.E. van Bel; Mark D. Fricker; Hubert H. Felle; Maike Fuchs; Jens Hafke (2009). "Sieve Element Ca2+ Channels as Relay Stations between Remote Stimuli and Sieve Tube Occlussion in Vicia faba". The Plant Cell. 21 (7): 2118–2132. doi:10.1105/tpc.108.063107. PMC 2729599. PMID 19602624.