Somatic embryogenesis in maize (Zea mays L.).

Maize is an herbaceous monocot with an annual cycle. Its embryo lies embedded in the endosperm at one side, toward the base of the caryopsis, with the primary root directed toward the attached end. The scutellum is large, lies directly against the endosperm, and partially encloses the embryonic axis. The primary root is enclosed by a coleorhiza. The suspensor persists during the maturation of the grain. Abbe and Stein (1954) have described eight stages of zygotic embryo development in maize by shoot apex development and this order of events has been confirmed in more detail by Van Lammeren (1986) in a scanning electron microscope study. The first stage is called the transition stage, in which a club- shaped embryo differentiates into a suspensor and the embryo proper. During the coleoptilar stage, the scutellum develops, a shoot apex becomes recognizable, and the almost circular coleoptilar primordium arises as a roll of meristematic tissue. The further six stages are distinguished by the number of leaf primordia. The scutellum becomes large and fleshy and initially has a groove from which the shoot meristem protrudes; the coleoptile covers more and more the shoot meristem and the developing leaf primordia; the first leaf primordium is situated opposite to the insertion of the scutellum and each subsequent leaf primordium forms opposite to the preceding one.