The symplast of a

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

is the inner side of a

cell 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 ...

in which water and low-molecular-weight

solutes In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solven ...

can freely

diffuse Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

. Symplast cells have more than one nucleus. ''Symplast'' could also refer to the connection of the inner contents (

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

) of neighbouring cells made by the microscopic channels that traverse the cell walls. These channels, which are called

plasmodesmata Plasmodesmata (singular: plasmodesma) are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Plasmodesmata evolved independently in several lineages, and spec ...

, allow the direct flow of small molecules such as sugars, amino acids, and ions between cells (from the inner part of one cell to the inner partof the next cell). Larger molecules, including

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The f ...

s and

plant virus Plant viruses are viruses that affect plants. Like all other viruses, plant viruses are obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses can be pathogenic to higher plants. ...

es, can also be transported through with the help of

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ov ...

structures. This allows direct cytoplasm-to-cytoplasm flow of water and other nutrients along concentration gradients. 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 The endodermis is the central, innermost layer of cortex in land plants. It is a cylinder of compact living cells, the radial walls of which are impregnated with hydrophobic substances (Casparian strip) to restrict apoplastic flow of water to th ...

''. Once solutes reach the endodermal cells through apoplastic flow larification needed: from where do those solutes come?? they are forced into the symplastic pathway due to the presence of the Casparian strip. Once the solutes are passively filtered larification needed: by what are they filtered? they eventually reach the

pericycle The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outer most part of the stele of plants. Although it is composed of non-vascular parenchyma cells, it's still considered part of the va ...

, where they can be moved into the

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

for long-distance transport. It is contrasted with the apoplastic flow, which means not crossing from one side of a membrane to its other side, but a flow ''inside'' the membrane/wall itself.

History

The symplastic transport was first realized by Eduard Tangl in 1879, who also discovered the

, a term coined by

Eduard Strasburger Eduard Adolf Strasburger (1 February 1844 – 18 May 1912) was a Polish-German professor and one of the most famous botanists of the 19th century. He discovered mitosis in plants. Life Eduard Strasburger was born in Warsaw, Congress Poland, ...

, 1901. In 1880, Hanstein coined the term symplast. The contrasting terms apoplast and symplast were used together in 1930 by Münch.Pickard, W. F. (2003). The role of cytoplasmic streaming in symplastic transport. ''Plant, Cell & Environment'' 26: 1-15

History

References

See also