Transient GUS expression from a TRV vector in hairy roots. (A) Hairy root cultures were initiated and incubated for 5 (gray bars) or 7 days (black bars) prior to co-culture with A. tumefaciens clones harboring pTRV1 and pTRV2-GUS. Values represent the mean ± SD of three co-cultures harvested six days after initiation. Four separate experiments were conducted over a period of 13 months. Means labeled with the same Greek letter are not different from each other at the 95% significance level. (B) Histochemical detection of transient GUS expression in representative samples collected from Experiments 1 (top) and 4 (bottom). Hairy roots were incubated with X-Gluc substrate in 1.5 mL microcentrifuge tubes for 60 minutes at room temperature. Areas stained blue are positive for GUS expression.