Research On Rice And Wheat Endosperm Free Mitotic Cell Process

Pollen germination in rice, wheat and barley had a influence on the spermatization of polar nucleus. The division and development of fertilized polar nucleus will determine the quantity of endosperm and will affect the grain weight and quality in rice,wheat and barley seed. In order to exploreâ‘ the germination of pollen grain and the growth of pollen tube,â‘¡division process of free nuclei of endosperm and its influencing factors,â‘¢the process of endosperm cellularization , this experiment had observed with light microscope and electron microscopeâ‘ the seed setting rate by removing stigma,â‘¡the changes of polar nucleus in two days of rice, wheat and barley,â‘¢the formation of the initial cell wall (contains anticlinal and percilinal wall) , by resin embedding combined with semi-thin section technology and ultra-thin section technology. The main results were as follows:(1) Rice pollen grain started to germinate two minutes after it reached the stigma. Half an hour later, the pollen tube reached the embryo sac, and it grew in stigma less slowly than grew in style and ovary. The pollen grain of wheat and barley started to germinate in three minutes, and the growing process of pollen tube was similar to rice's. After the pollen tube arrived at the base of the embryo sac, it would enter into embryo sac from a degenerated synergid and release two sperm cells. It was found that the synergid had degenerated before pollination in rice and wheat, while barley's synergid degenerated after the embryo sac mutured but before pollen tube's arrival. After the sperm cells entered into embryo sac, they would move near the top of degenerated synergid where was of thin cell walls. So the two germ cells would enter into the egg cell and the central cell easily. Although the sperm nucleus came to the egg nucleus earlier, its nucleus fusion finished less slowly than that of the sperm nucleus and the polar nucleus. It was found that rice's polar nucleus fertilized in 2 - 4 hours after pollination, while the polar nucleus fertilization finished in 3 ~ 5 hours.(2) After fertilization, zygote would undergo a period of dormancy, while the primary endosperm nucleus began to divide into free endosperm nuclei soon. The free endosperm nucleus of rice, wheat and barley all was larger than other cell's nucleus, and its nucleolus could be deeply stained. The free endosperm nucleus had heavy cytoplasm containing abundant organelles in active condition. The free endosperm nucleus of rice was nearly round, while wheat and barley's was basically oval.(3) The division ways of free nuclei in rice endosperm have diversity, i.e. mitosis, amitosis, and the daughter nuclei from mitosis went into amitosis immediately without interphase. The division velocity of free nuclei of endosperm in rice varies with the distance between the adjacent free nuclei. The velocity is faster when these free nuclei were separated from each other than when they were closed. Proper higher temperature could enhance the velocity of proliferation and also shortened the time of dividing cycle. To a certain extent, the nitrogenous fertilizer used at the booting stage and proper drought treatment could accelerate the division of free nuclei.(4)The cellularization of the endosperm is initiated in the vicinity of the peripheral embryo sac and proceeds to the inner embryo sac where it remains syncytial until well after the remainder of the endosperm has cellularized. The cellularization occurs as waves originating in the micropylar chamber and moving through the central chamber toward the chalazal tip. Prior to cellularization, a lot of small vesicles was emerged in the cytoplasm which surrounded the free nucleus, then these small vesicles combined into each other and formed larger vesicles. At last the initial anticlinal cell wall was developed between the two adjacent endosperm nuclei. The origin of the initial anticlinal cell wall comes from the fusion of the phragmoplasts and the inward prominency of the embryo sac wall, while the initial percilinal cell wall comes from the phragmoplas resulting in the alveoli periclinal division.(5)There are vesicles around the free growing initial anticlinal cell wall. With the help of the microtube, these vesicles move to the distal tip then these vesicles fuse with the distal tip leading the initial anticlinal cell wall precede centripetally.(6)In the cytoplasm of rice, a special kind of large vacuoles was found, which contain numbers of small vesicles, we named it "cell wall formation vesicles". These vesicles come from the cytoplasm and move to the newly formed cell wall. Then they fused with the cell membrane and release the small vesicles inside to enrich the cell wall.