ALTERNATIVE MORPHOGENETIC EVENTS IN CELL SUSPENSIONS

Two distinct types of regeneration, rhizogenesis and embryogenesis, were observed as alternative morphogenetic events in wild carrot cell suspensions. Petiole‐derived callus, grown on high‐auxin media lacking reduced nitrogen, was dispersed, passed through sieves, and the 45–75‐μ fraction was used to inoculate low‐auxin liquid media. After 2–3 weeks adventitious roots developed from endogenous primordia within large cell clumps. In contrast, liquid cultures inoculated with the same fraction, or with the fraction that passed a 45 μ pore sieve, from callus grown on media containing reduced nitrogen yielded enormous numbers of embryos. Globular proembryos were recognizable within several days of inoculation as bud‐like outgrowths from relatively few‐celled proembryogenic masses. The ontogeny of embryos from cultured cells has been compared to the ontogeny of the carrot seed embryo. These new data are discussed in the light of previous regenerative work with carrot cell cultures, current theories of causal aspects of embryogenesis in vitro, and current concepts of the forces controlling embryo development.