Fig. 1. Schematic representation of stages of embryo development in Arabidopsis. The zygote divides to from an embryo composed of a filamentous suspensor (S) that maintains contact with maternal tissues, and a terminal embryo proper (EP). The embryo becomes green at the heart stage of development when chlorophyll and chloroplasts first form. The suspensor degenerates during the torpedo stage. This diagram was adapted from more detailed descriptions of embryo development (Meinke, 1994; West and Harada, 1993) and simplified to highlight stages related to the study reported here. A, apical cell; B, basal cell; C, cotyledon; PE, protoderm; PV, provascular tissues; H, hypocotyl; R, radicle; SC, seed coat; En, endosperm.