Histological comparison of single somatic embryos of maize from suspension culture with somatic embryos attached to callus cells.

An embryogenic suspension culture of Zea mays, genotype 4C1, was obtained from friable callus that was cultured on solid medium and had been obtained from zygotic embryos. The suspension contained non-dividing elongated cells, clusters of dividing isodiametric cells, and globular, ovoid, and polar stages of somatic embryos. The single somatic embryos were blocked in shoot meristem formation: when transferred to regeneration medium they developed a root and, at the shoot side, a green cap with meristematic cells, but a scutellum and leaf primordia were not formed. In medium containing 2,4-dichlorophenoxy acetic acid, somatic embryos formed embryogenic callus aggregates, consisting of globular stage somatic embryos attached to each other via undifferentiated callus cells. These somatic embryos developed into mature embryos with the zygotic histological characteristics, such as scutellum and leaf primordia, in maturation medium, and then regenerated into plants in regeneration medium. By omitting the maturation phase, regeneration occurred via organogenesis. Polyembryos, i. e. embryos attached to each other without callus tissue in between, behaved as single somatic embryos. It is concluded that the attached callus tissue provides a factor that stimulates scutellum and leaf primordia formation.