kalanchoe (14, 15).
Like plant tissues transformed with the T-DNA of the Ti
plasmid, plant lines containing Ri T-DNA grow in the
absence of phytohormones (16). The T-DNA present in these
lines was found to originate from one segment of the Ri
plasmid (3, 4, 17, 18). Therefore, it was likely that this section
of Ri DNA contained genes responsible for the unlimited
proliferation of the transformed lines. Indeed, it was shown
that an insertional mutation in the middle of this T-region
leads to the loss of rhizogenicity on kalanchoe leaves (19).