Structure and Function
The plasmodesmata (singular,plasmodesma) are small channels in the cell walls of plants. They are cylindrical shaped. Plasmodesmata form when parts of the endoplasmic reticulum of a parent cell (during cell division) get caught in the cell wall of the resulting daughter cells. Cytosol (intracellular fluid) traveling through the plasmodesmata connects the insides of the cells and creates a continuous membrane of the adjacent cells (synctium), making the entire plant essentially connected throughout its body. There are usually between 1000 and 100,000 of these channels connecting one cell to the next. Most of them also contain a tubular structure called a desmotubule.
The plasmodesmata act as bridges connecting the cytoplasm of cells together, and are important for communication among cells. The channels allow free movement of the contents within. The openings can contract or dilate to allow different sized molecules through or to regulate movement of some molecules such as sugars, RNA proteins, and water, but this is still under debate.
The plasmodesmata act as bridges connecting the cytoplasm of cells together, and are important for communication among cells. The channels allow free movement of the contents within. The openings can contract or dilate to allow different sized molecules through or to regulate movement of some molecules such as sugars, RNA proteins, and water, but this is still under debate.
Relationship To Other Organelles
The plasmodesmata are most closely related to the cell wall, as they are almost literally just holes in the side of the walls. Their function in the movement of molecules through the cell wall during apoplastic transport is important. They are also related to the endoplasmic reticulum because that is what causes them to form during the plant's cell division.
Location
They are located in the epidermal layer of a plant, within the cell walls, so they are along the entire length of the plant's surface.
Consequence of Malfunction
If the plasmodesmata were not formed, then the plant would not be able to transport some nutrients throughout its body due to the lack of openings. This would also obscure the communication between cells.
Evolutionary Relationships
The true origin of plasmodesmata is unknown, but scientists believe that it most likely originated from either the class Chlorophyceae or Charophyceae, based on molecular phylogeny. It is also possible that some other groups developed plasmodesmata independently of the main two classes.