Successful both somatic embryogenesis and Agrobacterium tumefaciens-mediated genetic transformation systems have been developed in PB260 clone. Several transgenic callus lines and plants expressing two reporter genes (gusA and/or GFP) and CuZnSOD gene driven by the CAMV 35S promoter are respectively maintained by cryopreservation and in greenhouse. Functional genomic analysis requires homogenous population of plants for further characterization. However, the primary transformant plants are considered unstable leading to a variation in transgene expression. With regards to this epigenetic control, the variability of the beta-Dglucuronidase activity has been assessed by fluorimetric assays in primary transformant plants both self-rooting and budded state. Our preliminary results show a relative homogeneity of GUS activity in the population of self-rooting primary transformant plants obtained directly by somatic embryogenesis. After green budding, a decrease in GUS activity is recorded leading to a higher variability. The effects of budding, rootstock, rootstock/scion interaction, quality and position of the scion are discussed.