3.1 Establishment of hairy root clones
Hairy roots induced by A. rhizogenes provide an alternative system for the production of valuable bioactive compounds because of their genetic and biochemical stability (Zhou et al., 2011). In the present study, hairy roots were successfully induced by infection of cotyledon segments of V.officinalis with A. rhizogenes strain ATCC15834. Hairy roots emerged from the infected sites within 12-15 days with 30% transformation frequency and maintained on hormone free ½ MS medium. Among the hairy root clo nes, clone No. 9 was selected on the basis of its growth rate. The selected transformed clone showed rapid growth rate and tendency for profuse branching and active elongation, whilst untransformed roots did not show similar growth, elongation or branching pattern (Figure 1).