Cytological Observation of Double Fertilization and Its Duration in Oryza sativa
水稻双受精过程的细胞形态学及时间进程的观察

The fusion of female with male gametes and duration of double fertilization in Oryza sativa were studied by paraffin sectioning and fluorescence microscopy, to determine the stage of zygotes and provide basic information about the implementation of pollen-tube transgenic technology. Pollen grains germinated soon after pollination. Pollen tubes grew first into the intercellular space of branched penniform stigma and then through the intercellular space of transmitting tissue into the top of the ovary, further penetrating the ovary wall and primine to the micropyle. Green fluorescence was found in both pollen and pollen tubes. A pollen tube growing through the micropyle and interspace of the nucellus epidermis releases two sperms into one synergid. Two polar nuclei move to the micropylar end before sperm is released in a gap between the egg cell and central cell and subsequently taking off cytoplasm one after another. The sperm nucleus moving to the egg nucleus runs faster than the one to the polar nuclei. It fuses with the polar nuclei that are moving towards the antipodal cells at the chalazal end. Images showed the fusion process of male and female nuclei and polyspermous fertilization. Here we determined the schedule of fertilization in Oryza sativa. Pollen grains germinate soon after pollination. It takes about 0.5 h for a pollen tube from germination to arrive at the micropyle. About 0.5 h after pollination, the pollen tube releases two sperms into one synergid. At 0.5-2.5 h after pollination, the egg cell fuses with one sperm to form a zygote. About 10.0 h after pollination, the division of the zygote begins . The duration of the zygote lasts about 2.5-10.0 h. However, one sperm nucleus fuses with two polar nuclei at 1.0-3.0 h after pollination, and 5.0 h after pollination the primary endosperm nucleus begins to divide.