An electron-microscopical study of the plasmodesmata in the roots of young barley seedlings

Many plasmodesmata can be found in the walls of the cells of the endodermis and the pericycle of the roots. A mutual symplasmatic contact is thus established between the cells of the pericycle, endodermis and the innermost layer of the cortex. The radial walls of the endodermal cells are very thin and tend to become folded as a result of the fixation and embedding procedure. Virtually no plasmodesmata could be observed in these walls nor any striking feature which could be related to the presence of a Casparian strip. The plasmodesmata are spindle-shaped and lined by a membrane, which is a continuation of the plasmalemma. They all possess a central osmophilic strand. The pores on either end of the plasmodesmata are closed by the contact between plasmalemma and this strand. The substructure of the strand and its relationship to the endoplasmatic reticulum is discussed. Some rough calculations with respect to the role these structures may play in the process of intercellular transport are given and the significance of the plasmalemma for this type of transport is emphasized.