Plasmodesmen

Plasmodesmen, more commonly referred to in English as plasmodesmata, are microscopic channels that traverse the cell walls of plant cells, linking the cytoplasm of neighboring cells and enabling symplastic transport and signaling. Each plasmodesma consists of a plasma membrane–lined channel that contains a desmotubule, a narrow tube derived from the endoplasmic reticulum, with cytoplasmic space that can regulate passage. The desmotubule connects the endoplasmic reticulum of adjacent cells, forming a continuous cytoplasmic continuum through the cell wall. Primary plasmodesmata form during cytokinesis as cells divide; secondary plasmodesmata can develop later by deposition of ER-derived strands through existing walls.

Movement through plasmodesmata is size- and signal-dependent, allowing small metabolites, ions, hormones, RNAs, and some proteins to pass, often via plasmodesmata-localized movement proteins or through selective gating. The size exclusion limit can be modulated by callose deposition at the neck region; enzymes such as callose synthases and beta-1,3-glucanases regulate this dynamic permeability, in response to development or stress.

Plasmodesmata play a key role in development, coordinating patterning, differentiation, and responses to pathogens. They also facilitate viral movement, as many plant viruses encode movement proteins to widen the channel and move genome through the plasmodesmatal pore.

Although plasmodesmata are characteristic of land plants, similar intercellular channels exist in some algae; in animals, gap junctions serve a functionally analogous role but with different structure.