IN-VITRO DEVELOPMENT OF MAIZE IMMATURE EMBRYOS - A TOOL FOR EMBRYOGENESIS ANALYSIS

During monocot embryo development, the zygote goes through a proembryo stage characterized by a radial symmetry and later becomes a true emb ryo with a bilateral symmetry, In order to determine culture condition s for immature embryonic stages, proembryos and embryos were isolated from controlled pollinated maize plants and developed in vitro. Precis e culture conditions were determined for each type of explant: a monol ayer system for embryos using NBM medium enriched with maltose (0.25 M ) but without hormones, and a bilayer system for proembryo stages usin g N6 medium supplemented with maltose (0.35 M) and zeatin (3 mM). Morp hological, cytological, and in situ hybridization analysis have shown that the resulting embryos (stages 1-2), developed in vitro, were simi lar to those formed in vivo and subsequently gave rise to fertile plan ts. This work demonstrates that successful embryo differentiation is d ependent on specific parameters including the genotype, the nature of the carbon source, the type and concentration of hormones used and ori entation of the embryos on the medium. The potential use of these resu lts for embryo rescue and mutant analysis are discussed.