Figure 2.

Longitudinal thin sections (5 μm) showing Al-induced callose formation in wheat cv Scout 66. Confocal images of aniline blue fluorescence of control (A) and Al-induced (20 μm, 3 h) callose in the root apex (B), in control transition zone stele (C; natural occurrence at the sieve tubes, arrows), in similar region after Al treatments (D; arrows indicate natural sieve tube callose and asterisks indicate Al-induced callose), preferential localization of Al-induced callose at PD/pit-field regions (arrows) in the epidermal (E) and cortical cells (F). Asterisks in B and D indicate callose localization to pit fields. Background is black, and bright white fluorescence indicates callose occurrence. Al-induced patchy pattern of callose at pit-field regions are visible only in paradermal sections (see text for details) or portions of sections (E). Use of confocal microscopy coupled with thin sections revealed the original patchy appearance (from pit-fields) of callose, which is conspicuous mainly at rapidly expanding longitudinal walls compared with radial walls (F). Scale bar represents 25 μm.