Shoot Apex

The delineation of the embryonic shoot apex is much more cryptic than that of root apex. The shoot apical meristem, the epiphysis, is determined in an early globular stage embryo before the cell cleavage that delineates the protoderm. The storage protein mRNA are not detected in epiphyseal cells but in cotyledonary cells at one embryonic stage, indicating a functional difference, and the "O" line is the lower boundary of the epiphysis. At the transition stage, the centrally localized epiphyseal cells divide more slowly than the cotyledon cell progenitors, resulting in the formation of a bilaterally symmetrical heart stage embryo.