Structure and function of plasmodesmata

Little is known about the molecular architecture of plasmodesmata. Electron micrographs of plasmodesmata, although showing remarkably consistent features, do not reveal the dynamic nature of plasmodesmata. In addition, the generally accepted size exclusion limit of plasmodesmata of 1 kDa as determined by the microinjection of fluorescent probes, is not an accurate measure of the size of molecules that can move from cell to cell. In some cases, plasmodesmata allow the non-selective movement of proteins up to 50 kDa, whereas others allow the selective transport of proteins such as transcription factors. Insights to the molecular architecture of plasmodesmata and the mechanism of cell-to-cell transport can be gained by the examination of the type of molecules and conditions under which selective and passive movement of molecules occurs.