Plasmodesmata are small channels that join the cytoplasm to other plant cells. Plasmodesmata are formed when fractions of the endoplasmic reticulum are trapped across the middle lamella as new cell walls are synthesized between two newly divided plant cells.
A plant cell may have between 1000 and 100000 plasmodesmata. They are approximately 50 -60 nm in diameter. Plasmodesmata transport some very large molecules by a mechanism that is still unknown.
The size of the molecule that can pass through plasmodesmata is determined by the size exclusion limit. A majority of the plasmodesmata also contain a narrow tube-like structure called Desmotubule. Plasmodesmata are also used in phloem, symplastic transport to regulate the sieve tube cells by the companion cells.
