Plant regeneration via direct embryo axis-like shoot and root formation from excised cotyledon explants of ginseng seedlings

Cotyledon explants of Panax ginseng at various developmental stages were cu ltured I,on Murashige and Skoog (MS) medium with 0.5 mu M indole butyric ac id and 8.8 mu M N-6-benzyladenine. Upon culturing of cotyledon explants fro m mature zygotic embryos, 34% of the explants formed somatic embryos, and 4 6% formed adventitious shoots. In the cotyledon explains from 1-wk old seed lings, embryos, and axis-like shoots and roots developed at a high frequenc y (79%) near the excised portion of the cotyledon base. The developmental p attern of embryo axis-like organ formation was structurally different from that of somatic embryos and adventitious shoots but similar to that of part s of the embryos axis of zygotic embryos . In the early stages of embryo ax is-like organ formation, epicotyl-like shoot primordia were developed direc tly from the cotyledon base after 2 wk of culture: subsequently roots devel oped near the base of the epicotyl-like shoots and eventually generated int o plantlets with both shoots and roots. The frequency of embryo asis-like o rgan formation rapidly declined as the growth of seedlings proceeded. In ad dition, the frequency of somatic embryo and adventitious bud formation rapi dly declined with the age of the cotyledons. Plant regeneration via embryo axis-like ol gan formation might Lr a new pattern of morphogenesis in P. gi nseng cotyledon culture.