Plasmodesmata
Structure:
Plasmodesmata are cylinder type things that act like bridges connecting one cell wall to another. They consist of two tubes, one inside the other. The outer tube is called the plasmalemma. It protects the inner tube, the desmotubule. The desmotubule is made up of membrane and tightly wound cytoplasmic strands. It is also covered with plasma membrane. The desmotubule is the back bone of th plasmodesmata. The cytoplasmic sleeve is the gap between the plasmalemma and the demotubule. This gap is thought to be where molecules pass through to get from one cell wall to another.
Here are some pictures of the structure of plasmodesmata:
The semi-cylinder of the outer layer is the plasmalemma. The cylinder within the plasmalemma is the desmotubule. The green balls are plasma membrane covering the desmotubule.
http://www.csse.monash.edu.au/~cbetts/pd/pdpics.html
For more pictures of plasmodesmata you can go to: http://www.csse.monash.edu.au/~cbetts/pd/pdpage.html
Functions:
Plasmodesmata are responsible for the transportation of molecules from one cell wall to another cell wall, and the signaling and communication between cells. Plasmodesmata transports different kinds of molecules such as proteins, nutrients, and hormones. They can choose which kind of molecules can go through them. They also regulate how much of a molecule can pass through. I f the plasmodesmata feels too much pressure at one of its ends, it will close up and not let cells pass until there is less pressure. A lot of communication between molecules occur in plasmodesmata. The communication initiates several reactions in the plasmodesmata. Plasmodesmata is important in cell communication and the transportation of molecules.
http://www.kenyon.edu/depts/biology/edwards/project/greg/pd.htm#st
Bibliography:
http://www.kenyon.edu/depts/biology/edwards/project/greg/pd.htm#st
http://129.49.19.42/biochem/citovsky.html
http://www.er.doe.gov/production/bes/eb/31a.html
http://www.springer-ny.com/catalog/np/apr99np/3-540-65169-1.html