Root segments (5 mm) incubated on CIM were harvested and further incubated for 6 h in GUS staining solution [100 mM Tris/ NaCl buffer, pH 7, 2 mM ferricyanide, 2 mM X-gluc (5-bromo-4-chloro-3-indolyl-D-glucuronide), 2 mM ferrocyanide, 10 mM EDTA and 0.1% Triton X-100] at 37°C in the dark. The staining solution was removed, and the tissues were dehydrated in an ethanol series from 70% v/v to absolute ethanol. Samples were visualized under the light microscope.