Histochemical localisation of GUS activity. Razorblade sections in roots, petioles and stems of transgenic tobacco plants transformed with constructs S1, S3, B1S3, 35S and WT. Transverse petiole and stem sections and from S1, S2, S3, 35S and WT were stained with X-Gluc in NaH2 P04, pH 7.0, overnight at 37°C. Vertical root sections from the above constructs were also stained overnight with X-Gluc as above. Positive and negative controls were 35S and WT, used separately.