Plasmodesma
Microscopic channels enabling plant cell communication.
Plasmodesmata (singular: plasmodesma) are microscopic channels that traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. They evolved independently in several lineages, including members of the Charophyceae, Charales, Coleochaetales, Phaeophyceae, and all embryophytes (land plants). Unlike animal cells, plant cells are surrounded by a polysaccharide cell wall, and plasmodesmata provide direct, regulated, symplastic transport of substances between neighboring cells. There are two forms: primary plasmodesmata, formed during cell division, and secondary plasmodesmata, which can form between mature cells. Primary plasmodesmata arise when fractions of the endoplasmic reticulum become trapped across the middle lamella as new cell walls are synthesized between two newly divided cells. At these formation sites, the wall does not thicken further, and thin areas called pits develop, normally pairing up between adjacent cells. The desmotubule, a tube of appressed endoplasmic reticulum, runs between cells alongside the cortical ER, with no luminal space between them. A typical plant cell may have between 1,000 and 100,000 plasmodesmata, equating to 1 to 10 per square micrometer, each approximately 50–60 nanometers in diameter at the midpoint. They are constructed of three main layers: the plasma membrane, a fluid-filled cytoplasmic sleeve, and the desmotubule. Smaller molecules like sugars and amino acids diffuse through the cytoplasmic sleeve, while larger molecules such as proteins and RNA can also pass, sometimes facilitated by unknown mechanisms. Permeability is regulated by callose accumulation around the neck region, which reduces pore diameter, or by dilation and active gating to allow transport of macromolecules like signaling molecules and transcription factors. Electron-dense material, possibly composed of myosin and actin, appears around the desmotubule and plasma membrane, connected by spoke-like structures that may split the channel into smaller pathways. Plasmodesmata transport proteins, short interfering RNA, messenger RNA, viroids, and viral genomes between cells.
- type
- Cellular structure
- found_in
- Plant cells and some algal cells
- diameter
- Approximately 50–60 nm at midpoint
- density
- 1 to 10 per μm²
- forms
- Primary and secondary plasmodesmata
- key_function
- Intercellular transport and communication
Lore & Background
Primary plasmodesmata form during cell division when fractions of the endoplasmic reticulum become trapped across the middle lamella as new cell walls are synthesized. These eventually become cytoplasmic connections between cells. Secondary plasmodesmata can form between mature, non-dividing cells, though the process is not fully understood and may involve degrading enzymes and ER proteins. Structurally, a plasmodesma consists of three main layers: the plasma membrane (continuous with the cell membrane), the cytoplasmic sleeve (a fluid-filled space for molecular trafficking), and the desmotubule (a tube of appressed endoplasmic reticulum). The desmotubule is not thought to be the main route for transport. Electron-dense material, possibly composed of myosin and actin, may split the plasmodesma into smaller channels. Plasmodesmata transport proteins, short interfering RNA, messenger RNA, viroids, and viral genomes. Increasing calcium concentrations constrict the opening. Actin microfilaments and myosin proteins are involved in directing viral movement proteins to plasmodesmata.
Reader's Guide
Plasmodesmata are fundamental to plant physiology, enabling direct cell-to-cell communication that is essential for growth, development, and response to environmental stimuli. They allow the symplastic transport of nutrients, signaling molecules, and genetic material, coordinating activities across tissues. Their ability to regulate the size exclusion limit provides a mechanism for controlling which molecules pass, influencing processes such as flowering (via Flowering Locus T protein) and viral infection. Viruses exploit plasmodesmata by using movement proteins to increase pore size and travel through the plant. The presence of cytoskeletal components like actin and myosin suggests active, regulated transport rather than passive diffusion alone. Understanding plasmodesmata has implications for agriculture, particularly in developing virus-resistant crops and improving nutrient distribution. Their independent evolution in multiple algal lineages highlights their adaptive value in multicellular organisms with cell walls.
Did You Know?
- Primary plasmodesmata form during cell division when endoplasmic reticulum is trapped across the middle lamella.
- Increasing calcium concentrations in the cytoplasm constricts the opening of surrounding plasmodesmata.
More in Cell And Molecular Biology 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record