31.6
Plasmodesmes
Dans un organisme multicellulaire, les cellules doivent communiquer pour travailler ensemble de manière coordonnée. Les cellules communiquent notammen…
Les cellules végétales ont des parois cellulaires rigides qui maintiennent la forme cellulaire mais entravent la communication cellulaire. Des canaux microscopiques dans les parois cellulaires appelés plasmodesmes relient directement le cytoplasme des cellules adjacentes, permettant l’échange moléculaire pour la communication.
Les plasmodesmes primaires sont créés lors de la division cellulaire, tandis que les plasmodesmes secondaires se forment entre les parois cellulaires existantes des cellules voisines.
Les plasmodesmes sont tapissés d’une membrane, contenant une structure centrale étroite en forme de tube appelée desmotubule. Le Desmotubule est formé par une extension du RE qui relie les cellules adjacentes.
Le cytosol circule librement entre les deux cellules, formant un réseau continu appelé le symplaste.
Les cellules contrôlent le passage des molécules en régulant le diamètre des plasmodesmes.
Lorsque la callose, un polysaccharide, s’accumule, le canal est rétréci, ne laissant passer que l’eau et les petites molécules.
Lorsque le callose se décompose, le canal est dilaté, ce qui permet aux molécules plus grosses de passer à travers.
En dégradant les plasmodesmes, les cellules perdent la connectivité symétrique avec leurs voisines.
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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.