31.6
Plasmodesmata
In a multicellular organism, cells must communicate to work together in a coordinated manner. One way that cells communicate is through direct contact…
Plant cells have rigid cell walls that maintain cell shape but hinder cellular communication. Microscopic channels in the cell walls called plasmodesmata directly connect the cytoplasm of adjacent cells, allowing molecular exchange for communication.
Primary plasmodesmata are created during cell division, while secondary plasmodesmata are formed between the existing cell walls of neighboring cells.
Plasmodesmata are membrane-lined, containing a narrow tube-like central structure called the desmotubule. The Desmotubule is formed by an extension of the ER that connects adjacent cells.
The cytosol flows freely between the two cells making a continuous network called the symplast.
Cells control the passage of molecules by regulating the diameter of the plasmodesmata.
When callose, a polysaccharide, accumulates, the channel is constricted, allowing only water and small molecules to pass.
When callose breaks down, the channel is dilated, allowing larger molecules to pass through.
By degrading plasmodesmata, cells lose symplastic connectivity with their neighbors.
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Q1: What are plasmodesmata and why do plant cells need them?
Plasmodesmata are microscopic channels that connect the cytoplasm of adjacent plant cells, enabling direct molecular exchange and communication. Because rigid cell walls maintain plant cell shape but hinder communication, plasmodesmata create a continuous cytoplasmic network called the symplast, allowing nutrients and signaling molecules to flow freely between cells throughout the plant.
Q2: How do primary and secondary plasmodesmata differ in their formation?
Primary plasmodesmata form during cell division, while secondary plasmodesmata develop later between existing cell walls of neighboring cells. Both types create passageways connecting adjacent cells, but secondary plasmodesmata allow cells to establish new communication links after division, enabling flexible network expansion as tissues develop.
Q3: What is the desmotubule and what role does it play in plasmodesmata?
The desmotubule is a narrow, tube-like central structure within plasmodesmata formed by an extension of the endoplasmic reticulum that connects adjacent cells. It divides the plasmodesma into compartments while allowing cytosol to flow freely around it, maintaining the continuous symplastic network essential for plant cell communication.
Q4: How do plants regulate which molecules pass through plasmodesmata?
Plants control plasmodesmata permeability by regulating callose, a polysaccharide that accumulates to constrict channels, restricting passage to water and small molecules. When callose breaks down, channels dilate, allowing larger molecules like proteins and RNA to pass. This dynamic regulation enables selective molecular transport based on cellular needs.
Q5: What macromolecules can be transported through plasmodesmata?
Plasmodesmata transport specific macromolecules including receptor-like protein kinases, signaling molecules, transcription factors, and RNA-protein complexes. Beyond water and small nutrients, these versatile channels enable long-distance communication by moving regulatory molecules that coordinate plant growth, development, and responses to environmental signals.
Q6: How does plasmodesmata density change as plant cells grow?
As plant cells grow, the density of plasmodesmata decreases unless cells produce secondary plasmodesmata to maintain communication networks. This dynamic adjustment ensures adequate cell-to-cell connectivity despite increasing cell size, preventing isolation of growing cells from the symplastic network and preserving coordinated cellular function.
Q7: What happens to plant cells when plasmodesmata are degraded?
When plasmodesmata are degraded, cells lose symplastic connectivity with their neighbors, severing the continuous cytoplasmic network that enables molecular exchange. This disruption prevents communication and isolates affected cells from the broader plant communication system, potentially affecting coordinated cellular functions and nutrient distribution throughout tissues.