Plasmodesmata: intercellular channels for macromolecular transport in plants.

Plasmodesmata are special intercellular organelles that establish cytoplasmic and endomembrane (endoplasmic reticulum and nuclear envelope) continuity throughout most of the plant body. Microinjection studies have provided direct proof that plasmodesmata facilitate the cell-to-cell trafficking of viral movement proteins and nucleic acids. Evidence is now accumulating that plant-encoded proteins, including transcription factors, also move from cell to cell on this endogenous macromolecular trafficking pathway. The picture that is emerging is that the programming of plant development may involve this supracellular network for the effective delivery of one form of information molecule.