• 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.
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