The mechanisms of appearance of aposporous initial cell and apomictic embryo sac formation in Paspalum notatum

Abstract

To clarify the mechanisms of aposporous embryo sac initial cell (AIC) appearance and apomictic embryo sac formation, several apomictic and obligately sexual varieties of bahia grass (Paspalum notatum) were studied cytological and quantitatively. Over 300 young buds from every variety were treated by clearing fluid (Herr 1982) and observed with nomarski differential interference-contrast optics. The observations revealed that, there was no cytological difference between sexual and apomicts up to megasporogenesis. After megasporogenesis, however, the megaspore usually degenerated and in final, disappeared in the apomicts in contradistinction to that in sexual to form 8-nucleate embryo sac. At the same time, AIC, which is originated from nucellar tissue around the megaspore, appeared with a sharp knife shape, and inserted the space that the degenerated megaspore left. When the ovary length was measured and used as an index, it is understood that the ovules of facultative apomicts usually contain several AICs, and the numbers increased as the ovary grew before anthesis. AIC appearance was different event from obligate sexual one, so it could be considered as a related candidate with apomixis gene expression. Therefore, the results of this study will be used to provide the information on isolation of apomixis gene from apomictic varieties.