科研之友
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摘要
The double fertilization process and the development of endosperm and embryo were observed by microscopy in Eustoma grandiflorum. The flowers were fixed at various times after hand-pollination during stages of pollen tube extension, entry of pollen tubes into ovule, double fertilization, and early development of the embryo. Pollen grains initiated germination and penetrated the style 4 hours after pollination (HAP). Pollen tubes grew toward the ovule through the intercellular spaces along the solid style at 8 HAP. During pollen tube extension at 24 HAP, the generative cell divided into two sperm cells. Pollen tubes reached the ovary at 48 HAP, extended directly into the degenerating synergid cell and released the two sperm cells. One of the two sperm cells arrived adjacent to the egg cell at 60 HAP. Four to 5 days after pollination, a zygote was formed. The sperm nucleus adhered to the nuclear membrane of the secondary nucleus at 60 HAP. The primary endosperm nucleus was formed at 72 HAP. The zygote underwent the first mitosis 20 days after pollination. After the first divisions of the zygote, the apical cell divided transversely initially, and continued to develop to form the embryo proper; hence, the embryogenesis was of Solanad type. The mature seeds have a heart-shaped embryo. Only one spindle formed during the first mitosis of the zygote, and the fusion of male and female nucleoli took place before mitosis. The karyogamy was therefore of premitotic type.
