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**Plasmodesmata Formation and Structure**:
– Primary plasmodesmata form during cellular division.
– Pits are formed in cell walls for plasmodesmata insertion.
– Plasmodesmata can be inserted between non-dividing cells.
– Secondary plasmodesmata increase density during cell wall growth.
– Enzymes and ER proteins stimulate secondary plasmodesmata formation.
– Plasmodesmata are 50-60nm in diameter.
– Consist of plasma membrane, cytoplasmic sleeve, and desmotubule.
– Allow diffusion of small molecules and ions.
– Permeability can be regulated by callose accumulation.
– Permeability can be increased through dilation or structural remodeling.

**Plasmodesmata Transport**:
– Transport proteins, RNA, viroids, and viral genomes.
– Size exclusion limit determines molecule passage.
– Calcium concentrations can constrict plasmodesmata opening.
– Active transport mechanisms may involve proteins on the desmotubule.
– Mathematical models exist for estimating transport across plasmodesmata.

**Cytoskeletal Components and Viral Interactions**:
– Actin microfilaments, microtubules, and myosin proteins are cytoskeletal components.
– Actin filaments transport viral movement proteins to plasmodesmata.
– Viruses use actin filaments to move through plasmodesmata.
– Myosin proteins play a crucial role in directing viral cargoes to plasmodesmata.
– Microtubules are essential for cell-to-cell transport of viral RNA.
– Various methods are used by viruses to transport themselves, with microtubules playing a significant role.

**Viral Interactions with Plasmodesmata**:
Cucumber mosaic virus and tobacco mosaic virus interactions.
– Actin filaments are used for viral movement through plasmodesmata.
– Myosin proteins are involved in viral protein targeting to plasmodesmata.
– Microtubules play a significant role in the transport of viral RNA.

**Regulation and Significance of Plasmodesmata**:
– Regulation of solute flux and symplasmic permeability.
– Intercellular communication facilitated by plasmodesmata.
– Callose homeostasis and its role in regulating plasmodesmata permeability.
– Essential for plant growth, development, responses to stimuli, and overall health.

Plasmodesma (Wikipedia)

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 species that have these structures include members of the Charophyceae, Charales, Coleochaetales and Phaeophyceae (which are all algae), as well as all embryophytes, better known as land plants. Unlike animal cells, almost every plant cell is surrounded by a polysaccharide cell wall. Neighbouring plant cells are therefore separated by a pair of cell walls and the intervening middle lamella, forming an extracellular domain known as the apoplast. Although cell walls are permeable to small soluble proteins and other solutes, plasmodesmata enable direct, regulated, symplastic transport of substances between cells. There are two forms of plasmodesmata: primary plasmodesmata, which are formed during cell division, and secondary plasmodesmata, which can form between mature cells.

The structure of a primary plasmodesma. CW=cell wall, CA=callose, PM=plasma membrane, ER=endoplasmic reticulum, DM=desmotubule, Red circles=actin, Purple circles and spokes=other unidentified proteins

Similar structures, called gap junctions and membrane nanotubes, interconnect animal cells and stromules form between plastids in plant cells.

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