Detection of reversion using nonsense codon-introduced uidA genes. A, Design of reporter genes used for the detection of base substitutions. Two reporter genes, uidA112G-T and uidA166G-T, were generated by substituting thymine (T) for guanine (G) at positions 112 or 166 of the uidA gene (Kovalchuk et al., 2000). B, Visualization of a GUS reversion sector in Arabidopsis following histochemical staining with 5-bromo-4-chloro-3-indolyl-β-d-GlcUA cyclohexylammonium salt. The box indicates GUS-positive cells with reversion of the uidA gene. Left, whole leaf; right, higher magnification image of stained cells.