Ultrastructure and development of the megagametophyte in Eleusine tristachya (Lam.) Lam. (Poaceae)

Eleusine tristachya (Lam.) Lam. is native from subtropical South American climates. Widespread in Argentina and Uruguay, it is frequently found in landscape prairies of the province of Buenos Aires. Megasporogenesis and megagametogenesis in this species were studied using light and transmission microscopy. The ovule is hemitropous, bitegmic and tenuinucellate. The megaspore mother cell enlarges and undergoes meiosis division resulting in a T-shaped tetrad of megaspores. The three micropylar megaspores degenerate, and the chalazal one develops into the Polygonum-type megagametophyte. The synergid cells have the cytoplasm very electron dense because it has got a rich complement of organelles. The synergid wall is strongly thickened at the micropylar pole, developing the filiform apparatus. At maturity, the antipodals originate a wall with large projections into the cytoplasm, acquiring transfer cells characteristics. The antipodals cytoplasm, enriched with organelles shows a high metabolic activity, and it is suggested that these cells perform as an efficient system for metabolites transport.