Plasmodesmata

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Plasmodesmata (singular, plasmodesma) are microscopic channels of plants traversing the cell walls and middle lamella between pairs of plant cells and facilitating transport and communication between them. Unlike animal cells, plant cells are protected by a cell wall that is impermeable to large molecules such as proteins and in these cells plasmodesmata enable regulated intercellular transport. Plant cells can use both passive and active transport to move molecules and ions through the passage[citation needed]. A plasmodesma is constructed of three main layers, the plasma membrane, the cytoplasmic sleeve, and the desmotubule[citation needed].

Structure

Plasmodesmal plasma membrane

The plasma membrane portion of the plasmodesma is a continuous extension of the cellular plasmalemma[citation needed]. It is similar in structure to most cellular phospholipid bilayers.

Cytoplasmic sleeve

The cytoplasmic sleeve is enclosed by the plasma membrane and is an extension of the cytosol. Trafficking through plasmodesmata is assumed to occur through this passage. Smaller molecules (e.g. monosaccharides) and ions can easily pass through plasmodesmata by diffusion without the need for additional chemical energy. It is unknown how the selective transport of larger molecules, such as proteins, occurs. One hypothesis is that the polysaccharide callose accumulates around the neck region of plasmodesmata reducing their diameter and thereby controlling permeability to substances in the cytoplasm[citation needed].

Desmotubule

The desmotubule is a tube of appressed endoplasmic reticulum that runs between two adjacent cells[citation needed]. Some molecules are known to be transported through this channel[citation needed], but it is not thought to be the main route for plasmodesmatal transport.

Around the desmotubule and the plasmamembrane areas of an electron dense material have been seen, often joined together by spoke-like structures that seem to split the plasmodesma into smaller channels[citation needed]. These structures may be composed of myosin and actin[citation needed], which are part of the cell's cystoskeleton. If this is the case these proteins could be used in the selective transport of large molecules between the two cells.

Transport

File:MP-30-GFP.jpg
Tobacco mosaic virus movement protein 30 localizes to plasmodesmata.

Plasmodesmata have been shown to transport proteins, messenger RNA and viral genomes from cell to cell[citation needed]. The best studied of these are viral movement proteins such as those of the tobacco mosaic virus MP-30[citation needed]. MP-30 is thought to bind to the virus's own genome and shuttle it from infected cells to uninfected cells through plasmodesmata[citation needed]. Flowering Locus T protein moves from leaves to the shoot apical meristem through plasmodesmata to initiate flowering[citation needed].

Links

Video showing vesicular transport through the plasmodesmata of a Water Lily petal cell. Kinesin and Dynein actively move the vesicles along microtubule highways, into and out of the cell. [1]

References

de:Plasmodesmos it:Plasmodesma nl:Plasmodesma th:พลาสโมเดสมาตา


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