Anatomy of Somatic Embryos from Maize Embryo Cultures

Putative somatic embryos of maize (Zea mays L.) that developed directly from the scutellum of immature zygotic embryos in agar culture were investigated in thin sections and by scanning electron microscopy to confirm the mode of regeneration. After 4-6 days in culture, a row of similar-sized swellings appeared on each zygotic embryo just above the proximal end of the scutellum and not against the agar. The swellings had broad-based connections to the original scutellum and a region of meristem-like cells near the bases, evidence of organogenesis. The swellings were then traced through a series of developmental stages resembling those known for zygotic embryos in maize both in form and in order and time of appearance. Confirmed presence of a coleoptile, an associated radicle, and a suspensor was proof of embryogenesis. However, time intervals for early stages of somatic embryo development were shorter than in zygotic embryos, which indicated that the somatic embryos arose from a group of meristematic cells rather than from a single totipotent cell. If the somatic embryos were not induced to germinate precociously, they enlarged and fused to form a hard, white, wavy-surfaced callus.