COMPARISON WITH GAP JUNCTION
- In plants junctions are termed as plasmodesmata, whereas in animals it is termed as cell junctions.
- In plants plasmodesmata are found in pit-fields where the primary cell wall is thin and secondary cell wall is absent. In animals 3-types of junctions are found-
(i) Tight junction- which creates the permeability barriers across the layers of the cell.
(ii) Plaque bearing junctions- which stabilizes the cells against the mechanical stress.
(iii) Gap junctions- which prevents the movement across the cells.
- Gap junctions in electron micrographs appear as regions in which the plasma membrane of the two adjacent cells are aligned in parallel and separated by a tiny gap of 3nm.
- Plasmodesmata electron micrograph reveals that these are narrow channels in the cell wall that are lined by plasma membrane and transverse by the tubules of ER.
- Connexin proteins are observed on the membrane surface of the gap junctions, which are clusters of 6 connexin molecules surrounded by aqueous channels. No such structures are seen in plasmodesmata.
- Permeability of the gap junctions can be altered (closed and opened) by the changes in the membrane potential, intracellular pH and cyclic AMP levels.
- Plasmodesmata permeability is subjected to regulation by the internal conc. of Ca ions, but its mechanism is not well understood.
- In addition to their role in electrical coupling, gap junctions may have developmental and metabolic functions. No such functions are performed by plasmodesmata.