Isolation and Characterization of Plasmodesmata

This chapter discusses the isolation and characterization of plasmodesmata. Plasmodesmata are dynamic membrane specializations that traverse plant cell walls forming aqueous channels linking adjacent cells. The plasmodesma—like its animal counterpart, the gap junction—functions in the cytoplasmic movement of metabolites and ions. There is strong evidence that plasmodesmata may function to provide a mechanism for intercellular signaling. In addition to their normal physiological function, plasmodesmata can be altered and exploited by viruses as conduits for viral spread from cell to cell. There are also some indications that plasmodesmata in companion cells may be specialized, allowing for the transport of proteins from the companion cells to sieve tube elements. The outer limit of a plasmodesma is formed by the plasmalemma, which is continuous from cell to cell. Within the interior of the plasmalemma tubular envelope runs a strand of modified endoplasmic reticulum that is apparently appressed as seen in static endoplasmic reticulum (ER) micrograph studies and has been termed by various workers as “desmotubule” or “appressed endoplasmic reticulum.”