Studies On Mechanism Of Development Of Ovule And Formation Of Endosperm Cell In Ginkgo Biloba L.

Ginkgo biloba L., a lonely surviving precious plant in the world, has an important value of research and development. It's seed stone has been used as a medicated alimentation and has been developed into an important industry in our country.'G. Fozhi', an important seed-purpose cultivar of Ginkgo, was used as a material to take the below treatments: pollination on ovules, unpollination and GA₃ treatment. The divisive method, distribution and the statistic of number of free nucleus of Ginkgo were accomplished by the method of total dissection. The mechanisms of ovule development and the formation of endosperm cells were systematically observed and analyzed by the techniques and methods of semi-thin section and paraffin section. On the one hand, it has great importance for the study of the position of Ginkgo biloba in the taxonomy of gymnosperms, on the other hand, it provides theory and technical support for the study of the regulation of ginkgo seed. The main results are briefly summarized as follows:1. Ovules of Ginkgo developed normally within 21 days after pollination. The diameter of ovule increased by 5.7282 mm, and its length increased by 6.5972 mm; But the unpollinated ones stopped growing and fell off by then, its diameter only increased by 0.1014 mm, the length of it increased by 0.1021 mm; The ovules which were treated by stopped growing and fell off by then either, the diameter of ovule increased by 0.1025 mm, its length increased by 0.3111 mm.2. After 25 days by pollination, the maximum thickness of the integuments of ovules reached 958.8622μm, the peak of nucellar tissue and spongy tissue degraded slowly. The integuments of ovules which were not pollinated or GA₃ treated began to disintegrate at 25 days after pollination, their respective maximum thickness is 375.3811μm and 381.2312μm. The peak of nucellar tissue and spongy tissue degraded and shriveled. The rates of degradation are: spongy tissue> peak of nucellar tissue > integument.3. After 5 days by pollination, the outer integument began to form secretory cavity; 15 days after pollination, the outer cells of the integument increased constantly, and the parenchyma cells inside the beads were growing; 20 days after the pollination, the secretory cavity was completely differentiated. 15 days after unpollination and GA₃ treatment, cells of the outer integument and inner integument began to shrink; And 20 days after the treatments, cells of the outer and inner integument began to dissolve, and the inner ones dissoved earlier than the outer ones.4. After 5 days by pollination, the peak of the nucellar tissue were made up of a large number of close parenchyma cells, the nucleus of the cell was small and it was located in one end; 10-15 days after pollination, the parenchyma cells elongated along the longitudinal axis of the nucleus, the nucleus of the cell became large and it was located in the center of the cell; 20 days after the pollination, the differentiation of the cells of the peak in nucellar tissue slowed down, the volume of the parenchyma cells no longer increased and the nucleus became smaller and smaller. After 10 days by unpollination and GA₃ treatment, the nucellar tissue began to degenerate, the cell wall shrinked and became irregular-shaped. The nucleus of the cell occurs disintegration. 10-15 days after the treatments, the remaining part of the nucellus shriveled and the inner integument formed large internal cavity.5. After 3-5 days by pollination, the spongy tissue was arranged in close by 5-6 layers, the inner cells stained shallowly, the cytoplasm of the outer cells was dense and stained deeply; 10 days after pollination, the array of the spongy tissue cells became loose and the shape was nearly square; 5 days later, the inner spongy tissue began to degenerate; 25 days after pollination, the spongy tissue degenerated to 1-2 layers. 3-6 days after unpollination and GA₃ treatment, the spongy tissue was arranged in close by 5-6 layers; 10 days after the treatments, the spongy tissue became loose; 15-17 days after the treatments, the spongy tissue degenerated to 1-2 layers; The spongy tissue degenerated to one layer of dead cell 20days after the treatments.6. The development of female gametophyte experienced free nucleus stages from 5 to 30 days after pollination. Free nucleus splitted mainly in mitosis, but also associated with the amitosis after pollination. The number of the free nucleus grew the fastest 5-20 days after pollination, later, the number of the free nucleus increased slowly. Meanwhile, with the constant division of free nucleus, membranous oval gradually changed from ball to spherical. 5-7 days after pollination, free nucleus became less; 9-13 days after pollination, the number of the free nucleus increased constantly, at the same time, the free nucleus distributed uniform on the membrane; 20 days after pollination, free nucleus were pushed around. 3-6 days after unpollination and GA₃ treatment, free nucleus were less and mostly distributed in the central of cytoplasm; 10 days after the treatments, the number of the free nucleus increased constantly; 5-7 days later, free nucleus stopped dividing and original divided free nucleus disintegrated and disappeared.7. When it had formed about 4,000-5,000 nucleus, it was cellularization period. This period was about 30-65 days after pollination. 30 days after pollination, one layer of opening cells was formed which had no cell wall at the side near central cavum in the periphery. 45 days after pollination, the endosperm cell layers gradually increased from 1 layer to 2-3 layers, most of the cells were in a hollow, the distribution of amyloid was rarely observed; After 55 days by pollination, endosperm cell layers increased to 6-7 layers quickly; Cells around grew centripetal and dissociative, till cavum was filled with endosperm cells and the cellularization was finished after 60 days by pollination.The results of the study provides theoretical basis and technical support for the guiding of the high-seed-quality production of Ginkgo biloba.