rat5 plants were inoculated with a tumefaciens gv3101 harboring the t dna binary vector pbisn1 pbisn1 contains a gusa intron gene under the control of a u201c super promoter u201d ni et al 1995 narasimhulu et al 1996 two days after cocultivation the root segments were transferred to callus inducing medium containing timentin 100 u03bcg ml to kill the bacteria three days after infection a few segments were stained for gus activity using the chromogenic dye x gluc both the wild type and the rat5 mutant showed high levels of gus expression approximately 90 of the root segments stained blue fig3 a the remaining root segments were allowed to form calli on callus inducing medium containing timentin to kill agrobacterium but lacking any antibiotic for selection of plant transformation after four weeks numerous calli derived from at least five different ws and rat5 plants were stained with x gluc of the ws calli sampled 92 u00b1 12 showed large blue staining areas whereas only 26 u00b1 10 of the rat5 calli showed gus activity and most of these blue staining regions were small fig3 a these data indicate that although the rat5 mutant can transiently express the gusa gene at high levels it fails to stabilize gusa expression suspension cell lines were generated from these ws and rat5 calli and after an additional month the amount of t dna was assayed using as a hybridization probe the gusa intron gene located within the t dna of pbisn1 integrated into high molecular weight plant dna from ws and rat5 calli nam et al 1997 mysore et al 1998 fig3 b shows that although t dna.