Female Gametophyte Development And Reproductive Process In Hickory (Carya Cathayensis Sarg.)

Hickory (Carya cathayensis) is China's unique high-quality dry fruit tree and woody oil plant. It mainly distributes at Tianmu mountain system matched between Zhejiang province and Anhui province. In order to reveal reproduction secrets of hickory, verify the existence of apomixis phenomenon, explore the origin of polyembryony and the occurrence mechanism in hickory, guide the breeding work, female gametophyte development and reproductive process from pollination, germination and growth of pollen tubes, fertilization to embryonic development were studied on the view of controlled pollination and embryology by means of paraffin section, fluorescence staining and scanning electron microscopy. Main results are as follows:1. The ovule was unitegmic, orthotropous and crassinucellate in Hickory. Female gametophyte was polygonal embryo sac with 8 nucleis. There was corresponding relation between the developmental process of female gametophyte and the color status of stigmas. The whole developmental process of the female gametophyte was with very short time.2. Female flowers pollinated among the time nearly 10 days from light red to light dark purple of the stigma color had fruit setting. The fruit setting rate was highest when female flowers were pollinated in bright red stage, followed by that when the stigma of female flower was in purplish red, light red and light dark purple. Fruits also were harvested under the treatment of bagging and without pollination and smearing the stigma with 2,4-D could promote the fruit setting with the fruit setting rate at 4%. Harvest fruits and seeds of Carya cathayensis×Carya illinoensis enlarged obviously and the exocarp color was more green compared with the control which indicated that there was metaxenia phenomenon. Harvest fruits and seeds under the treatment of bagging and without pollination and smearing with 2,4-D were relatively small. The proportion of the polyembryonic seedling in hickory was 9.04%( statistic 586 seedlings) in natural conditions and polyembryonic seedlings could develop and grow well.3. There were no germinated pollens when pollen vigor testing was conducted using 13 different culture mediums. TTC and acetic red dyeing could be used to determine pollen viability inaccurately. Hickory pollen began germinating after pollinated 8 hours and the pollen tube grew normally through in situ germinating experiment. There were degradation signs of the egg apparatus and the endosperm developed normally at the mature embryo sac stage or after fertilization at the middle May. With the endosperm developing, the ovule enlarged and nucellar tissue were absorbed only remaining epidermis cells expect the nucellar beak region. Most nucellar cells in the nucellar beak region had increased volume with different degree of vacuolization. During the process of the disintegration of some nucellar cells near the embryo sac, some cells divided and formed nucellar embryo initials with small shaped cells and compact structure. One or more cell clusters formed at the micropylar end with the division of initials at the late June. Cell clusters developed and elongated and presented as rod-shape at first. The embryo experienced bulboid type embryo, heart embryo, torpedo embryo and cotyledon embryo in sequence. Endocarp began to shrink with the embryo 2~3mm at the late July, from then on endosperm was absorbed gradually and embryo developed rapidly. The growth and filling of the embryo depended on the development of meristem at the lower margin of the cotyledon lobes.The embryo in hickory origined from nucellar cells and it belonged to adventitious embryony reproduction one type of apomixis.