【摘要】 以20年生白桦(Betula platyphylla)的雌花序为材料,研究了白桦的大孢子发生、雌配子体形成和胚胎发育过程。结果表明:1)大孢子母细胞经过减数分裂形成直线排列的4个大孢子,其中珠孔端的3个大孢子退化,合点端的大孢子进行3次有丝分裂,形成八核胚囊,8个核迅速细胞化,最终发育为成熟胚囊。胚囊发育类型为单孢子蓼型胚囊;2)胚的发育经过原胚、球形胚、心形胚和鱼雷胚等阶段发育为成熟胚;胚柄在球形胚时期最发达,但胚柄短小,只由3个扁平细胞组成,之后逐渐退化。本文同时对雌花的结构和发育特点在桦木科各属中的异同、白桦胚胎发生类型及胚胎发育进程的同步性进行了讨论。更多还原

【Abstract】 This paper describes megasporogenesis, megagametogenesis, and the process of embryonic development of the female inflorescence in 20-year-old Betula platyphylla. Megaspore mother cells undergo meiosis, which results in the formation of 4 megaspores in a row. The chalazal-most cell develops into an 8-nuclei embryo sac after 3 rounds of mitosis. A mature embryo sac is produced after cellularization and nuclear migration. The other cells of the tetrad undergo degeneration. The mature embryo sac consists of an egg apparatus, a central cell, and 3 antipodal cells. The embryo sac is a monosporic Polygonum type. The zygote develops into a mature embryo going through proembryo, globular, heart, and torpedo stages. The suspensor is developed fully at the stage of globular embryo and consists of 3 cells, which are degenerated later. The organization and development of the female flower and the type and synchrony of embryogenesis in Betulaceae are also discussed.更多还原