To elucidate the developmental stage at which phenotypic abnormalities were first evident in mrl embryos, seeds at various stages after pollination were sampled from heterozygous plants for paraffin sectioning. All mr embryos at 5 days after pollination (5 DAP) were unusual. Most mr embryos remained globular and differentiated no organs at this stage (Fig. 2A). In a few advanced embryos, radicle was recognized in a large basal region and the first leaf primordium was initiated in shoot (Fig. 2B). The embryos at 7 DAP showed various phenotypes. Shoot was not developed (Fig. 2C) or was relatively normal (Fig. 2D). The phenotypes also varied widely at 15 DAP, but commonly observed were the enlargement of basal region and the reduction of apical region (Fig. 2E,F). It is obvious that the development of mr embryo is retarded considerably compared to that of the wild type, and the basal region is enlarged in mr embryos. In contrast, the apical region seems to be reduced (Fig. 2D,E), resulting in the underdevelopment of shoot. Thus, it is suggested that the multiple radicles in mr embryos are due to the enlargement of basal region during early embryogenesis.

In the vegetative phase, the growth of mr seedlings was abnormal. The mrl seedlings frequently produced two radicles. Thus, the multiple radicles function normally. In seedlings at 1 week after germination, many tillers and roots were produced. (Fig. 3A). At 2 months after germination, the plant height was only 6 to 8 cm, and 12 to 24 cm in 4- months-old plants with numerous tillers (Fig. 3B). The phyllotaxy of mr plants was normal, but the leaf sheath and blade were narrow and twisted. Thus, mrl functions not only in embryogenesis but also in vegetative phase.