31.6
Plasmodesmi
In un organismo multicellulare, le cellule devono comunicare per lavorare insieme in modo coordinato. Un modo in cui le cellule comunicano è attravers…
Le cellule vegetali hanno pareti cellulari rigide che mantengono la forma cellulare ma ostacolano la comunicazione cellulare. Canali microscopici nelle pareti cellulari chiamati plasmodesmi collegano direttamente il citoplasma delle cellule adiacenti, consentendo lo scambio molecolare per la comunicazione.
I plasmodesmi primari si formano durante la divisione cellulare, mentre i plasmodesmi secondari si formano tra le pareti cellulari esistenti delle cellule vicine.
I plasmodesmi sono rivestiti di membrana, contenenti una struttura centrale stretta simile a un tubo chiamata desmotubulo. Il desmoturo è formato da un'estensione del reticolo endoplasmatico che collega le cellule adiacenti.
Il citosol scorre liberamente tra le due cellule formando una rete continua chiamata simplasto.
Le cellule controllano il passaggio delle molecole regolando il diametro dei plasmodesmi.
Quando il callosio, un polisaccaride, si accumula, il canale si restringe, permettendo solo il passaggio dell'acqua e delle piccole molecole.
Quando il callosio si rompe, il canale si dilata, consentendo il passaggio di molecole più grandi.
Degradando i plasmodesmi, le cellule perdono la connettività simplastica con i loro vicini.
View the full transcript and gain access to JoVE Core videos
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.