Plasmodesmata and cell-to-cell transport in plants

Plasmodesmata traverse the wall between adjacent plant cells and interconnect them by way of concentric cylinders of plasma membrane and endoplasmic reticulum. The endoplasmic reticulum component probably has no lumen, but the annulus between the two membranes is analogous to the gap junctions of animal tissues with respect to continuity with the cytosol compartment and molecular size cut-off for transport.