Fig. 4.

The deposition of Casparian band-like material in the primary root of A. thaliana scr-3 and shr mutants observed by TEM. (A–C) Cross-section of an scr-3 root with an incomplete endodermal layer; the cortex consists of a mosaic of typical endodermal cells, outer cortical cells and atypical cortical cells originating from the tangentially non-divided cortical initials. (B) Neighbouring endodermal cells develop Casparian bands (asterisk) in a typical position within radial cell walls. (C) Atypical cortical cells deposit Casparian band-like material (triangle) in the centripetal junctions of their anticlinal cell walls. (D–F) Cross-section of an shr root with non-developed endodermis. (E) The cortex consists of a single layer of atypical cortical cells without Casparian bands; however, Casparian band-like material (arrowheads) is deposited ectopically in the middle lamellae of vascular cylinder cells. (F) Atypical cortical cells form thicker cell walls in comparison with the wild-type Ler. ac, atypical cortical cell; cw, cell wall; en, endodermis; ep, epidermis; oc, outer cortex; pe, pericycle; x, xylem. Scale bars (A) = 5 µm; (B, C, E, F) = 2 µm; (D) = 10 µm.