QUANTITATIVE-ANALYSIS OF ULTRASTRUCTURAL-CHANGES DURING ZYGOTIC AND SOMATIC EMBRYOGENESIS IN PEARL-MILLET (PENNISETUM-GLAUCUM [L] R BR)

Ultrastructural changes during zygotic and somatic embryogenesis in pe arl millet (Pennisetum glaucum [L.] R. Br.) were quantified using morp hometric techniques. The total area per cell profile and the cell volu me percentage of the whole cell, endoplasmic reticulum (ER), Golgi bod ies, mitochondria, nuclei, lipids, plastids, starch grains and vacuole s were measured and comparisons made between three zygotic and three s omatic embryo developmental stages. All measurements were taken from s cutellar or scutellar-derived cells, Zygotic embryogenesis was charact erized by increases in cell size, lipids, plastids, starch, Golgi bodi es, mitochondria and ER. Somatic embryogenesis was characterized by tw o phases of cell development: (1) the dedifferentiation of scutellar c ells involving a reduction in cell and vacuole size and an increase in cell activity during somatic proembryoid formation and (2) the develo pment of somatic embryos in which most cell organelle quantities retur ned to values found in late coleoptile or mature pre-desiccation zygot ic stages. In summary, although their developmental pathways differed, the scutella of somatic embryos displayed cellular variations which w ere within the ranges observed for later stages of zygotic embryogenes is.