Abstract: The micropyle of Brassica napus includes anexostome and an endostome. The exostome is basically open, but the endostome is a closed structure with only narrow gaps between two cuticle layers of the inner integumental epidermis. The embryo sac is composed of two synergids, an egg cell and a central cell; the antipodal cells are degenerated before the embryo sac maturation. The synergid has a micropylar filiform apparatus, but not a chalazal vacuole, and its nucleus is centrally located. Therefore it has not a typical polarity as synergids of most other plant species. Before pollination, the synergids of some ovules already show symptom of degeneration. After pollination but before entry of pollen tube, two synergids of the same embryo sac degenerate simultaneously. The egg cell is a typical polarized cell, with a big micropylar vacuole and a chalazally located nucleus. Before fertilization, the arch-shaped gap between two plasma membranes of the egg cell and central cell is filled with electro-densed granular and amorphous substances. The central cell possessed several big chalazal vacuoles; the polar nuclei and most cytoplasm are micropylarly located. The plastids in the central cell is characterized by big volume and quite prominent lamellae. The micropylar portion of the embryo sac wall bear well-developed ingrowths, which gradually sooth down towards the chalazal end.

Key words: Brassica napus, Micropyle, Embryo sac, Ultrastructure