In vitro development of maize immature embryos: a tool for embryogenesis analysis

During monocot embryo development, the zygote goes through a proembryostage characterized by a radial symmetry and later becomes a true embryowith a bilateral symmetry. In order to determine culture conditions forimmature embryonic stages, proembryos and embryos were isolated fromcontrolled pollinated maize plants and developed invitro. Precise culture conditions were determined for each typeof explant: a monolayer system for embryos using NBM medium enriched withmaltose (0.25 M) but without hormones, and a bilayer system for proembryostages using N6 medium supplemented with maltose (0.35 M) and zeatin (3mM). Morphological, cytological, and in situhybridization analysis have shown that the resulting embryos (stages 1-2),developed in vitro, were similar to those formedin vivo and subsequently gave rise to fertile plants.This work demonstrates that successful embryo differentiation is dependenton specific parameters including the genotype, the nature of the carbonsource, the type and concentration of hormones used and orientation of theembryos on the medium. The potential use of these results for embryo rescueand mutant analysis are discussed.