Ultrastructural Studies of Gametophytic Apomicts in Guinea Grass (Panicum maximum) I. Differentiation of Aposporous Initial Cell

The ultrastructural features of the developing megasporocyte, especially the timing of degeneration of sexual cells during megosporogenesis, and differentiation of aposporous initial cell (AIC) in facultative apomictic guinea grass (Panicum maximum) has been studied. The first degeneration was observed in dyad stage. Accompanying the degeneration of sexual cell, the cell adjacent to the dyad in chalazal side, derived from nucellus began to increase its size of cell and change its organelles and shape, and thus, the cell become to the first AIC usually located in micropylar side. The AIC appeared in order continently adjacent to the first AIC in the chalazal side. However, all of the AICs could become to the mature embryo sac with 4-nucleates. The interdependent patterns of the nucellar cell and AIC, and their relationship are also discussed at subcellular level.