Topic 17.2 Rice Embryogenesis
Rice illustrates a distinct pattern of embryogenesis that is typical of many monocots (Web Figure 17.2.A). Like many plants, the patterns of division associated with embryogenesis in rice are more variable than those in Arabidopsis. Nevertheless, it is possible to describe embryogenesis in rice in terms of five morphologically defined developmental stages (Itoh et al. 2005):
- Zygotic stage. This single-celled stage follows fusion of the haploid egg and sperm.
- Globular stage. This stage occurs 2–4 DAP (days after pollination). Following an initial horizontal division to create the apical and basal cells, a series of variable cell divisions create a multilayered, globular embryo (see Web Figure 17.2.A, part A).
- Coleoptile stage. At 5 DAP, the coleoptile (specialized tubular first leaf), shoot apical meristem , root apical meristem, and radicle (embryonic root) form (see Web Figure 17.2.A, part B).
- Juvenile vegetative stage. At 6–10 DAP, the shoot apical meristem initiates several vegetative leaves (see Web Figure 17.2.A, part C).
- Maturation stage. During 11–20 DAP, the expression of maturation-related genes precedes the onset of dormancy (see Web Figure 17.2.A, part D).
Web Figure 17.2.A Rice (a monocot in the grass [Poaceae] family) embryonic development illustrating the globular stage (A), coleoptile stage (B), juvenile embryo stage (C), and mature embryo stage (D). The scutellum is a modified cotyledon specialized to absorb sugars released from the endosperm during germination. (Courtesy of Y. Nagato.)