DISTRIBUTION AND CHANGES OF RESERVE MATERIALS IN COTYLEDON CELLS OF PANAX-GINSENG RELATED TO DIRECT SOMATIC EMBRYOGENESIS AND GERMINATION

Cotyledon explants from zygotic embryos of Panax ginseng produced soma tic embryos on Murashige and Skoog basal medium without growth regulat ors. Somatic embryos developed directly from epidermal cells at the co tyledon base. Somatic embryos were always formed from the side of the cotyledon opposite to the one attached to the medium surface regardles s of cotyledon orientation. The frequency of somatic embryo formation from the abaxial epidermis (66%) was much higher than that from the ad axial epidermis (12%). Differences in embryogenic response were likely related to cell structure. Abaxial epidermal cells were filled with r eserve materials (lipid bodies), while adaxial epidermal cells were de void of any prominent reserves. During germination, the reserve materi als in the cells of the cotyledons disappeared rapidly. At the same ti me, the competency of somatic embryo formation from cotyledon explants declined rapidly to zero. Upon culture of the cotyledon explants (for somatic embryo induction), lipid bodies slowly disappeared, but starc h grains accumulated prominently. Reserve materials disappeared after commencement of embryogenic cell division. During germination, lipid b odies rapidly disappeared, and chloroplasts developed instead of starc h grains.