Forisomes are proteins occurring in the sieve tubes of
. 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
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
,
pH, or concentration of
Ca2+ ions. Unlike most other moving
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s, the change is not dependent on
ATP
ATP may refer to:
Companies and organizations
* Association of Tennis Professionals, men's professional tennis governing body
* American Technical Publishers, employee-owned publishing company
* ', a Danish pension
* Armenia Tree Project, non ...
.
Forisomes function as valves in
sieve tubes
Sieve elements are specialized cells that are important for the function of phloem, which is a highly organized tissue that transports organic compounds made during photosynthesis. Sieve elements are the major conducting cells in phloem. Conductin ...
of the
phloem system, by reversibly changing shape between low-volume ordered
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
loid spindles and high-volume disordered spherical
conformations. The change from ordered to disordered conformation involves tripling of the protein's volume, loss of
birefringence
Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefring ...
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
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
at
sieve plates
Sieve elements are specialized cells that are important for the function of phloem, which is a highly organized tissue that transports organic compounds made during photosynthesis. Sieve elements are the major conducting cells in phloem. Conductin ...
. There are evidences that the forisomes's behavior could depend on
Ca2+ changes provoked by Ca
2+-permeable
ion channels
Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...
, located on the
endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
and
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
of
sieve elements.
responsible for shape changes.
Forisomes have possible applications as
biomimetic smart materials (e.g. valves in microdevices) or smart
composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
s.
References
{{Reflist
External links
Forisome: A smart plant protein inside a phloem systemForisome based biomimetic smart materials
Motor proteins
Smart materials
Plant proteins