Thidiazuron-induced de novo shoot organogenesis on seedlings, etiolated hypocotyls and stem segments of Huang-qin

Development of an efficient in vitro propagation system for Huang-qin (Scut ellaria baicalensis), a traditional Chinese medicinal plant used in the tre atment of a wide range of human ailments, is described. Thidiazuron [TDZ: N -phenyl-N'- (1,2,3-thidiazol-5-ylurea)] effectively induced regeneration on cultured intact seedlings, etiolated hypocotyl explants and sterile stem s egments of Huang-qin. Histological examinations of excised hypocotyl or nod al explants revealed that adventitious shoots formed through an intermediat e callus. Comparison of TDZ-induced regeneration in the three tissue types indicated that isolation of explants was not essential for optimal regenera tive efficiency. Significantly more regenerants formed along hypocotyls of intact seedlings (20 shoots/explant) than were observed on excised hypocoty ls (9.7 shoots/explant) indicating that endogenous metabolites produced in adjacent tissues provided resources for the shoot initiation. More than 95% of de novo regenerants formed roots and then intact plantlets under either sterile culture or greenhouse conditions. Regeneration protocols developed in this study may provide the basis for improvement of this crop through t he identification of medicinally active constituents and eventual developme nt optimized pharmaceutical products.