The dynamics of silicon deposition in the sorghum root endodermis.

•  The dynamics of silica deposition and Si aggregates formation in inner tangential walls of root endodermal cells, which occurs as an additional stage of endodermal development in sorghum (Sorghum bicolor), were studied. •  An environmental scanning electron microscope (ESEM) and X-ray microanalyzer (EDAX) were used to study sorghum roots grown hydroponically with Si (+ Si medium) and without Si (- Si medium). •  Silica aggregates were absent in roots of plants cultivated in - Si medium. However, their additional formation on fully mature and thickened endodermal cell walls took place when plants grown in - Si medium were transferred to + Si medium. The beginning of Si aggregates formation was observed and Si deposition detected 2 h after transfer to + Si medium. •  By dipping the apical root half in + Si medium, the silica aggregates were formed in the endodermis at the basal part of the root. This supports the hypothesis of outward Si transport from the xylem to the endodermis rather than radial inward Si movement and its deposition at the point of the apoplastic barrier represented by the endodermis.