THE ULTRASTRUCTURE OF ZYGOTIC EMBRYO DEVELOPMENT IN PEARL-MILLET (PENNISETUM-GLAUCUM, POACEAE)

The ultrastructure, morphology, and histology of zygotic embryogenesis in pearl millet (Pennisetum glaucum) were examined using light and el ectron microscopic techniques. Embryogenesis was initially characteriz ed by the presence of a vacuolated egg cell and zygote. The increased presence of Golgi bodies in the zygote suggested it was metabolically more active than the egg cell. The first zygotic division resulted in a densely cytoplasmic apical cell and a highly vacuolated basal cell. The club-shaped proembryo displayed a large amount of endoplasmic reti culum (ER) and ribosomes, very few lipids, and a continuous gradient o f vacuoles from the highly vacuolated basal suspensor cells to the den sely cytoplasmic apical cells. The embryo had well-defined parts by 8 days after pollination, including shoot and root meristems, coleoptile , scutellum, provascular system, and the first leaf primordium. Large increases in ER, lipids, starch, and vacuoles occurred in the scutellu m during the maturation of the embryo, except in the provascular cells . Throughout zygotic embryogenesis, embryo cells were connected by pla smodesmata except where intercellular spaces occurred. Ultrastructural , morphological, and histological observations of zygotic embryogenesi s in pearl millet are in agreement with previous reports for other gra ss species.