Fertilization And Embryogenesis In Ginkgo Biloba L.

This dissertation mainly studied the male gametophyte development, fertilization and embryogenesis in Ginkgo biloba (L). The main results were as follows:1. The morphology of the nucleus membrane changed from smoothness to waveness as the spherical shaped spermatogenous nucleus began to elongate. The protuberant nuclear envelope was closed to the vacuole-like structure and the closest distance was only 3 μ m between them. The morphology of nucleolus also changed during the development of the spermatogenous. At the first stage, the nucleolus consisted of an outer ringed-electron-dense granular and an inner electron-lucent fibrous core, than it became a homogenously dense stained round structure.2. The blepharoplast continued to enlarge as the spermatogenous cell further developed. The organelles around the initial blepharoplast were very abundant, and among the organelles, the plastids were prominent. After the blepharoplast matured, the organelles decreased sharply but the proportion of the mitochondria increased. The organelles around the vacuole-like structure were abundant and regularly arranged, the osmiophilic drop was constrained to the area between the nucleus and the vacuole-like structure, while the mitochondria and plastids were mainly distributed near the blepharoplast. The Fibrillogranular body had three forms including "dumbelled", "sphericity", "abnormity conglomeration" in the spermatogenous cell and the sperm.3. A darkly stained area of about 20-30 μ m in size could be observed occasionally in the 40 μ m sized sperm nucleus before fertilization. At the time of fertilization, the sperm with the flagellum entered into the archegonium, only the male matter 20 μ m in diameter fused with the egg cell, and the sperm cytoplasm and the flagellum were left outside the egg cell. This indicated that the genetic substance in the sperm condensed before the sperm nucleus undergoing condensation before fertilization. The dark area in the sperm nucleus was probably the middle form of the nuclear condensation.4. The first division of the zygote was anticline division in situ. At the metaphase ofthe division, two layer membrane-like-structure appeared outside the chromosome, indicating that the sperm cytoplasm entered into the egg cell. At the telophase of the division, the cell plate emerged between the two daughter nuclei, but it disappeared in the following division. During the time of cell wall formation, numerous fibers radiated from the nuclei were conspicuous.5. The comparative studies on the anatomical and morphological characters of Ginkgoacea and Cycadaceae showed that Ginkgoacea possess more evolutive characters in the structure of the vegetative organs, the male gametophyte and seeds; but possess more primitive characters in the female gametophyte. The Ginkgoacea had some special property: the chloroplast and the tent pole in the female gametophyte, vacuole-like structure and fibrillogranular body in the spermatogenous cell and sperm cell and so on. Those showed that Ginkgoacea adopted different strategies from Cycadaceae as environment changed, and they had not directly related in phylogeny and undergone parallel development in evolutionary.