Symplast

The symplast of a plant is the name for the inner side of a cell membrane in which water and low-molecular-weight solutes can freely diffuse. Symplast cells have more than one nucleus.

Symplast can also refer to the connection of the inner contents (cytoplasm) of neighbouring cells made by the microscopic channels that traverse the cell walls. These channels, which are called plasmodesmata, allow direct flow of small molecules such as sugars, amino acids, and ions between cells (from the inner part of one cell to the inner part of the next cell). Larger molecules, including transcription factors and plant viruses, can also be transported through, with the help of actin structures.

This allows direct cytoplasm-to-cytoplasm flow of water and other nutrients along concentration gradients.[clarification needed]

In particular, symplastic flow is used in the root systems to bring in nutrients from soil. Nutrient solutes move in this way through three skin layers of the roots: from cells of the epidermis, the outermost layer, through the cortex into the endodermis.

Once those nutrient solutes so have reached the endodermal cells, they for further transport (for distribution to places where they are needed) are forced into the symplastic pathway[clarification needed: haven't they been in this mode before??] due to the presence of the Casparian strip.[clarification needed: how?]

After the solutes have been passively filtered[clarification needed: by what and for what are they filtered?], they eventually reach the pericycle, where they can be moved into the xylem for long-distance transport.

Symplastic flow is contrasted with apoplastic flow, the latter meaning not crossing from one side of a membrane to its other side (by means of passing through a pore or tunnel/ channel), but a flow inside the membrane/wall itself as well as free floatation in the spaces between plant cells. ^[1]

History

The symplastic transport was first realized by Eduard Tangl in 1879, who also discovered the plasmodesmata,^[2] a term coined by Eduard Strasburger, 1901.^[3]^[4] In 1880, Hanstein coined the term symplast.^[5] The contrasting terms apoplast and symplast were used together in 1930 by Münch.^[6]^[7]

References

^ Freeman, Scott (2014). Biological Science. Boston: Benjamin Cummings. ISBN 9780321743671.
^ Köhler, Piotr; Carr, Denis J. (2006). "Eduard Tangl (1848-1905) - discoverer of plasmodesmata". Huntia. 12 (2): 169–172.
^ Tangl, E. (1879). Ueber offene Communicationen zwischen den Zellen des Endosperms einiger Samen. Jahrbüecherfüer Wissenschaftliche Botanik 12: 170–190.
^ Strasburger, E. (1901). Über plasmaverbindungen pflanzlicher zellen. Jahrbücher für Wissenschaftliche Botanik 36: 493–610.
^ Hanstein, J. 1880. Das Protoplasma. Heidelberg.
^ Münch, E (1930). Die Stoffbewegungen in der Pflanze. Verlag von Gustav Fischer, Jena.
^ Pickard, W. F. (2003). The role of cytoplasmic streaming in symplastic transport. Plant, Cell & Environment 26: 1-15, [1].

History

References

See also