• Plasmodesmata are microscopic channels which transverse the cell wall of plant cell and some algal cell and enabling transport and communication between them
  • Neighboring plant cells are therefore separated by a pair of cell wall and the intervening middle lamella, forming an extra cellular domain known as the apoplast.
  • Cell wall are permeable to small soluble protein and other solute.
  • Plasmodesmata enable direct regulated symplastic intracellular transport of substance between cells.
  • There are two forms of plasmodesmata .

#Primary – It is formed during cell division

#Secondary – It is form between mature cell

  • The plasmodesmata are narrow channels that act as intercellular cytoplasmic bridge to facilitate communication and transport of material between plant cells.
  • The plasmodesmata serve to connect the symplastic space in the plant and are extremely specialize channel that allow for intracellular movement of water various nutrient and other molecules.
  • These are located in narrow areas of cell walls called primary pit fields and they are so dense in these area.
  • They make up one percent of the entire area of cell wall

Structure of Plasmodesmata

  • plasma membrane is continuous between cell
  • with in the plasmodesmal pore  a tightly wound cylinder of membrane termed the desmotubule runs the length of the plasmodesmata
  • This structure is studied by Tilney by using plasmolysis, Trion X detergent extraction and protease digestion.
  • Thus he suggests that desmotubule provide a rigid stability to plasmodesmata and confer a fixed diameter and pore size to plamodesmal canal.
  • Desmotuble is linked to E.R. in each of the adjacent cells forming a dynamic endomembrane continuum in the symplastic space
  • A typical plant cell may have between 103 and 105 plasmodesmata connecting it with adjacent cell to between 1-10µm²
  • Plasmodesmata are approximately 50-60 nm in diameter, at the midpoint are constructed of three main layers: the plasma membrane, cytoplasmic sleeve, and desmotubules.

1 – Plasmodesmatal Plasma membrane

  • This is continuous extension of the cell membrane or plasma lemma.

2-Cytoplasmic sleeve

  • It is fluid filled space enclosed by plasma membrane
  • The larger molecules including protein and RNA pass through the cytoplasmic sleeve diffusively.
  • The mechanism of regulation of plasmodesmatal transport is the accumulation of the polysaccharide callose that accumulates around the neck region of plasmodesmata to form a collar reducing their diameter and thereby controlling permeability to substance in the cytoplasm.

3- Desmotubules

  • These are tube of appressed endoplasmic reticulum that run between two adjacent cell.
  • some molecule are known to be transported through this channel
  • Around the desmotubule and P.M. area of and electron dense material have been seen often joined together by spoke -like structures that seem to split the plasmodesmata in to smaller channel.
  • These may be composed of myosin and actin which are part of the cyto-skeleton.


  • In vascular plants the basic plasmodesmal structure is a tube of plasma membrane surrounding a strand of modified ER, with particulate material between them. 
  • interprets the ultrastructure of vascular plants in a cross and longitudinal sections. 
  • Essential features of plasmodesmata is a cell to cell tubule of the plasma membrane that surrounds a cylindrical strand of tightly furled ER, the desmotubule. 
  • A thin darkly stained central rod occupies the center of the desmotubule. 
  • A cytoplasmic sleeve or the cytoplasmic annulus lying between the desmotubule and plasma membrane is considered as a possible pathway for the cell-to-cell water and solute movement. 
  • The desmotubule is essentially a solid strand of lipid, the central rod is composed of the lipid polar groups and a few proteins that can physically occupy the inner core of the tightly furled lipid bilayer. 
  • Much of the cytoplasmic annulus is occupied by proteinaceous material. 
  • These particles are associated with both the outer surface of the desmotubules and the inner surface of the plasma membrane. 
  • In the cross section, 7-to-9 gaps occur between the particles. 
  • The distance across the gaps is about 2-3nm as comparable with the 4nm channel diameter. 
  • These gaps are the physical basis of cell-to-cell transport.
  • A wide range of plasmodesmal morphologies have been observed, within the same plants. 
  • These include differences in length, branching and size of the central cavity. 
  • The functional significance of the variations is largely unknown.


  • It plays an important role in cell to cell communication. 
  • To investigate this function microelectrodes have been employed to monitor the flow of electric current from cell to cell in plant tissue (as in case of animal gap junctions.). 
  • Such studies reveal that electric current passes between plant cells linked by plasmodesmata more readily than it does between the cells that are not linked by plasmodesmata. 
  • The magnitude of the current flow is directly related to the number of plasmodesmata present.  
  • This suggests that it plays a role in cell-to-cell communication, comparable to that played by gap junctions in animals.
  • They serve to connect the symplastic space in the plant and are extremely specialized channels that allow for intercellular movement of water, various nutrients, and other molecules.
  • They allow the passage of molecules with molecular weights of less than 800 daltons.
  • Plasmodesmata have been shown to transport proteins (including transcription factors), short interfering RNA, messenger RNA, viroids, and viral genomes from cell to cell.
  • Plasmodesmata are also used by cells in the phloem, and symplastic transport is used to regulate the sieve-tube cells by the companion cells.
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