关键词: 黄花菜, 超微结构, 助细胞, 卵细胞, 合子, 初生胚乳核

Abstract: We used transmission electron microscopy to study the ultrastructural changes in embryo
sac before and after fertilization，including synergid，egg，central cell，zygote and primary endosperm
nucleus of Hemerocallis citrina，so as to provide information on the reproductive biology of angiosperms
and related research into day lily. Results were as follows：Both of the two synergids had highly developed
filiform apparatus，and one degenerated after pollen tube penetrated in，the other persisted until zygophase.
The chalazal end of egg and synergid cells lacked cell wall before fertilization. But after fertilization，
zygote had integrated cell wall. Ultrastructural characteristics suggested that the egg which was inactive
with low metabolism could be activated by fertilization，and both the central cell and primary endosperm
show high metabolism. Sperm nucleus with double membrane，highly condensated chromatin and a few
nuclear pores immersed in the cytoplasm of egg. The remarkable characteristic of mature embryo sac of
day lily was that there was no large central vacuole in synergids，egg and central cell.

Key words: Hemerocallis citrina, ultrastructure, synergid, egg, zygote, the primary endosperm nucleus