“…It appears that the sgfp expression was genotype-dependent in terms of differences in callus cell types they produced, which has been described by Bec et al (1998). Moreover, differences in the sgfp expression in calluses of the two cultivars bombarded using a Helios gene gun might be attributed to the difference in biological constraint such as the activity of endogenous nuclease (Barandiaran et al, 1998), local RNA silencing which blocks expression of transgene (Baulcombe, 2004;Miki et al, 2005) and physical constraint such as callus cell density, callus compactness or callus friability that might not be exactly identical in these cultivars.…”