High frequency callus induction and plantlet regeneration from different explants of Picrorhiza kurroa - a medicinal herb of Himalayas

Picrorhiza kurroa is a medicinal herb prevalent in the North-Western Himalayan region at an altitude of 3000 - 4300 m. It is a rich source of hepatoprotective picrosides; picroside-i and picroside-ii and other medicinal metabolites such as picroside-iii, picroside-iv, apocynin, androsin, catechol, kutkoside, etc. Being pharmacologically important and listed as an endangered herb, optimization of in vitro conditions for callusing and regeneration is of paramount importance not only for the selection of cell lines with enhanced content of phytopharmaceuticals or in the genetic transformation of P. kurroa. Moreover, the regeneration hold a great promise in the production of metabolites in cell cultures. Callus cultures were established from different explants such as leaf discs, nodal and root segments of P. kurroa. Callus induction was highest (70%) in root segments followed by leaf discs (56.3%) and nodal segments (38.3%) on MS medium supplemented with 2,4-D (2 mg/l) + IBA (0.5 mg/l) + sucrose 3% (w/v) + agar-agar 0.8% (w/v). The callus cultures derived from different explants were differentiated into multiple shoots on MS medium containing different concentrations and combinations of BA, KN and IBA. Regeneration was highest in the calli derived from root segments and leaf discs on MS + BA (2 mg/l) + KN (3 mg/l) + sucrose 3% (w/v) + agar-agar 0.8% (w/v) with 76.7 and 72.2% calli forming shoot primordia, respectively. Most of the nodal segment derived calli got differentiated into roots rather shoots. Comparative callusing and shoot regeneration from different explants revealed that root segments are the best explant for in vitro studies in P. kurroa. The rooted plantlets were acclimatized to the external environment through hardening and eventually transferred to pots.