desmotubule

Desmotubule is a slender tubule of the endoplasmic reticulum that runs through the plasmodesma, a membrane-lined channel that traverses the plant cell wall to connect the cytoplasm of neighboring plant cells. The desmotubule lumen is continuous with the endoplasmic reticulum of both adjoining cells, linking their ER networks and forming the central axis of the plasmodesmal channel. Surrounding the desmotubule is a cytoplasmic sleeve bounded by the plasma membrane, through which most intercellular movement is facilitated.

In function, the desmotubule is not the primary conduit for macromolecule transport. Transport and gating occur mainly through the cytoplasmic sleeve, whose size and permeability are regulated by mechanisms such as callose deposition at the plasmodesmatal neck. The desmotubule provides a structural core and may serve as a scaffold for plasmodesmal proteins and for lipid or signaling exchanges at ER–plasma membrane contact sites.

Desmotubules are characteristic of plant plasmodesmata and their properties can influence intercellular connectivity. During development, stress, or signaling, changes in nucleotide or lipid composition and in callose dynamics can modify the aperture of the plasmodesmata, thereby affecting symplastic transport. The term desmotubule reflects its origin as a desmotic, or binding-associated, tubule derived from the endoplasmic reticulum.