ORIGIN AND DEVELOPMENT OF EMBRYO AND BUD PRIMORDIA DURING MATURATION OF EMBRYOGENIC CALLI OF ZEA-MAYS

Maize genotype 4Cl calli under embryo maturation conditions give rise to somatic embryos that can be regenerated into plants. This scanning electron microscope study shows that the pattern formation is as in zy gotic embryos. A globular stage somatic embryo forms a starch-containi ng scutellum, a coleoptile, and leaf primordia in the same order and p attern as in zygotic embryos. There is no callus tissue between shoot and root meristems, as occurs in organogenesis. However, the study als o reveals a different order of events: shoot meristems with leaf primo rdia develop at the base of leafy structures, on the surface of the ca llus. Similar structures were often named somatic embryos in the plant tissue culture literature, but they are more comparable to axillary b uds. A coleoptile is not present. Both structures develop into plants on regeneration medium. Maturation of somatic embryos that are attache d to callus aggregates is impaired in liquid culture; fewer embryos ma ture and regenerate probably because their cells have less cell to cel l contact than those grown on solid medium. Somatic embryos unattached to callus tissue grow in suspension culture; they lack a scutellum or have only a rudimentary one, lack a coleoptile and leaf primordia. Th ey develop roots but do not develop into plants in the media used in t his study.