梨受精前后胚囊的变化

VARIATIONS OF EMBRYO SAC OF PEAR BEFORE AND AFTER FERTILIZATION

梨受精前,胚囊处于4～8核期,体积较小,胚囊内无淀粉粒出现。当发育为成熟胚囊时,体积增大,胚囊内卵细胞核和中央细胞核的周围有淀粉粒密集,细胞质中也有淀粉粒分布。中央细胞中的淀粉粒比卵细胞中的大,助细胞和反足细胞中无淀粉粒。受精后,胚囊体积进一步增大,合子的核和初生胚乳核周围仍有淀粉粒存在。合子二分裂为2细胞原胚时,细胞中淀粉粒有所减少。初生胚乳核分裂为2个游离核时,淀粉粒分布在游离核的周围。受精后,一个助细胞被花粉管破坏,另一个退化消失。反足细胞也逐渐退化消失。助细胞与反足细胞内无淀粉粒。

Before fertilization, the embryo sac of pear in 4～8 nucleate stage was smaller and had none starch grain in it. In mature embryo sec, the size of embryo sac enlarged and starchgrains distributed densely around the nucleus of its egg cell and central cell as well as in cytoplasm. The starch grain in a central cell was larger than that in an egg cell while there was none starch grain in synergids and antipodal cells. After fertilization, starch grains still existed around the nuclei of zygote and primary endosperm. In 2-celled proembryo, the quantity of starch grains decreased. The starch grains distributed around the free endospermnuclei when they come from the first division of primary endosperm nucleus. After fertilization, one of two synergids was destroyed by pollen tube while the other one and antipodalcells degenerated and disappeared gradually. The starch grain was discovered neither in a synergid nor in antipodal cells.