Morphogenesis and Embryogenesis in Long-term Cultures of Digitalis

Long-term cultures were established from hypocotyl of nine Digitalis species as well as from various explants of seedlings and adult plants of Digitalis lanata. The morphogenetic capacity of a total of 21 cell cultures was tested under selected hormonal conditions. Three types of strains could be distinguished: (1)strains exhibiting somatic embryogenesis, (2)strains capable of shoot and root formation and (3)strains with only root regeneration. In agreement with experimental experience in other plant systems the morphogenetic capac-ity of a given Digitalis cell culture is thoroughly dependent on genetic factors, on the plant tissue used as primary explant and on hormonal conditions in the induction medium. Embryogenic strains were obtained from hypocotyl of D. lutea and from D. lanata filaments, if cell cultures were initiated on media with 2,4-D (1-5 mgl-I ) and kinetin (0.02-3 mgl-I). Most of the embryogenic strains grew rapidly on 2,4-D-containing media retaining their morpho-genetic capacity undiminished over more than three years. About 20 embryogenic strains were investigated with respect to their morphogenetic response under different hormonal condi-tions. The possible application of embryogenic Digitalis cell cultures for clonal propagation of high quality inbred lines and for induced synthesis of cardenolides is discussed.