Fig. 7.

Development of apoplasmic barriers in roots. (A) Cross-section of the root of young maize plant grown hydroponically for 10 d with developed Casparian bands (white arrows) in the endodermis 6 mm from the root tip; scale bar = 50 µm. (B) Cross-section of the basal part of young maize plants grown hydroponically for 10 d with developed lateral root and suberin lamellae in exo- and endodermis; scale bar = 200 µm. Abbreviations: epi, epidermis; ex, exodermis; en, endodermis. (C) Scheme of development of apoplasmic barriers (Casparian bands and suberin lamellae) in exo- and endodermis of young maize plants grown hydroponically for 10 d and treated with Cd, Si or both elements together. C, control; Cd5, 5 µm Cd; Cd5 + Si, 5 µm Cd with 5 mm Si; Cd50, 50 µm Cd; Cd50 + Si, 50 µm Cd with 5 mm Si; Si, 5 mm Si. Different regions of the root can be distinguished: a region in which Casparian bands in endodermis are developed (solid blue lines), a region in which endodermal suberin lamellae are fully developed (solid green lines), a region in which the suberin lamellae in endodermis are partially developed (broken green lines), and a region in which suberin lamellae are fully developed in exodermis (solid orange lines). Because the length of roots grown in the absence and presence of Cd and/or Si differed, the distance from the root apex was expressed as a percentage of the total root length.