“…However, one of the problems associated with the use of the bacterial gus gene as a reporter is the presence of 'endogenous GUS' activity in some species. Endogenous GUS activity has been reported in various organisms including: 1 -bacterial species, such as the enterobacterium E. coli and Shigella, nonenterobacterial such as Bacteroides and Clostridium (Hawkesworth et al, 1971), Streptococcus, Staphylococcus, Corynebacterium (Levvy and Marsh, 1959), Alcaligenes (Jefferson, 1989) and many soil bacteria (Ritz et al, 1994); 2 -Some tissues of vertebrates such as kidney, liver and spleen (Kyle et al, 1992), human breast milk (Alonso et al, 1991;Ince et al, 1995); 3 -Invertebrates such as snails (Levvy and Marsh, 1959), nematodes (Jefferson, 1985;Sebastiano et al, 1986) and insects (Langley et al, 1983;Levvy and Marsh, 1959), housefly (Musca domestica) and various locusts (Levvy and Marsh, 1959) and 4 -Plant species. In plants, endogenous GUS activity was first described in Arabidopsis by Jefferson et al (1987).…”