Plasmodesmata (Pds) traverse the cell wall to establish a symplastic continuum through most of the plant. Despite central roles in plant growth development and defence very little is know about their constituent parts or mechanisms of regulation. Rapid and reversible deposition of callose in the cell wall surrounding the Pd apertures is proposed to provide a regulatory process through physical constriction of the symplastic channel. From a proteomic analysis of Arabidopsis thaliana suspension cell walls, we identified a family of Pd callose-binding proteins (PDCBs) which target Pds in newly-divided and in differentiated cells. These proteins contain signal sequences for a glycosylphosphotidylinositol (GPI)-linkage. Since many well characterised GPI-anchor proteins are known to localise on the extracellular face of the plasma membrane, PDCB proteins may interact with callose in the cell wall providing a structural anchor between the plasma membrane component of Pds and the cell wall.