Tropane alkaloid production and shoot regeneration in hairy and adventitious root cultures of Duboisia myoporoides-D. leichhardtii hybrid

Co-culture conditions for Duboisia myoporoides-D. leichhardtii hybrid hairy root induction were investigated using leaf explants and Agrobacterium rhizogenes ATCC 15834. The bacteria density and duration of co-culture greatly affected the induction rate; the highest rate of 50% was obtained when the leaf explants were co-cultured for 2 d with 10⁶ bacteria. One hairy root clone that showed the fastest root growth was selected and used for comparison study with adventitious roots cultured with 0.5 mg/l indole-3-acetic acid (IAA). The hairy roots cultured in Murashige and Skoog (MS) liquid medium grew well and yielded much more tropane alkaloids (35 mg/l scopolamine and 17 mg/l hyoscyamine) than adventitious roots cultured in 0.5 mg/l IAA after 6 weeks of culture at 25°C in the dark. The hairy and adventitious roots (2.5 cm) grown in liquid media were divided into 5 parts (each 0.5 cm) along the root axis. Distribution of scopolamine and IAA was then determined by enzyme-linked immunosorbent assay (ELISA). Inverse relationship between contents of scopolamine and IAA was observed in the hairy roots; increase of scopolamine and decrease of IAA were proportional to the distance from the root meristem. In contrast, the contents of scopolamine and IAA were relatively constant in the adventitious roots. In shoot regeneration experiments, the hairy and adventitious root segments (1 cm) were placed onto 1/2 MS solid medium containing various concentrations of IAA and BA cultured at 25°C under 16 h light. In adventitious roots, the shoots regenerated on media containing 6-benzyladenine (BA) (0.5 to 5 mg/l), and 100% regeneration was observed in medium with 0.1 mg/l IAA and 2 mg/l BA. On the other hand, shoot regeneration was only observed in 33% of hairy roots cultured on medium containing 5 mg/l BA.