desmotubulus

The desmotubule is a narrow tubule derived from the endoplasmic reticulum that traverses the plasmodesma, the intercellular channel in plant cell walls that connects neighboring cells. It runs through the center of the plasmodesmal canal and is continuous with the endoplasmic reticulum of both connected cells, so its lumen is in contact with the ER lumen on either side.

Within each plasmodesma, the desmotubule is surrounded by a cytoplasmic sleeve, a space through which most intercellular exchange occurs. The presence and geometry of the desmotubule influence the cross-sectional area and thus a channel’s permeability. Although the ER lumen of adjacent cells is connected via the desmotubule, bulk transport typically happens around it through the cytoplasmic sleeve and through regulated pathways at the plasmodesmal pore.

Functionally, the desmotubule provides a structural link between the ER of neighboring cells and participates in ER–plasma membrane contact sites and lipid exchange. Its precise role in directing intercellular transport remains a subject of study; most small-molecule movement is thought to occur outside the desmotubule, while the desmotubule contributes to the organization and regulation of the plasmodesmal channel.

Nomenclature and variation: the structure is sometimes referred to as the desmotubulus in older literature. Observations via electron microscopy show that the desmotubule can vary in appearance and may rearrange under developmental cues or stress, reflecting its integration into the dynamic architecture of plasmodesmata.