In vitro-grown roots: a superior explant for prolific shoot regeneration of St. John's wort (Hypericum perforatum L. cv 'New Stem') in a temporary immersion bioreactor

Hypericum perforatum L. (St. John's wort) is a traditional medicinal plant, which has been used for the treatment of neurological disorders and depression. In vitro regeneration of St. John's wort provides one approach for mass clonal propagation of this facultative apomictic species. The current study was designed (i) to compare the regeneration potential of several explant types and (ii) to investigate the potential use of St. John's wort root explants for large-scale production in bioreactors. Root explants responded better than the shoot tip, leaf, hypocotyl or stem explants in terms of thidiazuron-induced shoot organogenesis. The efficacy of different auxins (indoleacetic acid (IAA), indolebutyric acid and naphthaleneacetic acid) for induction of de novo root organogenesis from root explant and the biomass accumulation were evaluated. All auxins tested effectively induced new roots, 32 roots per explant, with an optimal response in medium containing 5 μM IAA. Three types of bioreactors, airlift bioreactor, temporary immersion bioreactor (TI bioreactor) and Erlenmeyer flask, were compared for efficiency of root explants for de novo shoot organogenesis. In the TI bioreactor, the shoots elongated faster in comparison with other treatments. Transplanting ex vitro and acclimatization for a period of 7 days were sufficient to promote establishment of plants in the greenhouse and more than 95% of the regenerated plants survived. The results show that St. John's wort can be efficiently regenerated from root explants in a variety of bioreactors for aseptic production of bioactive compounds.