濒危植物木根麦冬的胚胎学研究

EMBRYOLOGICAL STUDIES ON ENDANGERED OPHIOPOGON XYLORRHIZUS(LILIACEAE)

木根麦冬的花药壁分为４层，即：表皮、药室内壁、中层与绒毡层。绒毡层为腺质型。大孢子母细胞减数分裂过程中的胞质分裂为连续型。小孢子四分体排列为左右对称型与四面体型。雌蕊子房壁在授粉后４～５天破裂。胚珠倒生，双珠被，厚珠心。大孢子四分体线形排列，胚囊发育为蓼型。极核在受精前融合成一个大的次生核。胚胎发育为紫菀型。核型胚乳。木根麦冬居群中存在雄性不育植株，约占５５．８％。胚胎在其发育早期约有４３．３％败育。根据本研究的实验观察，（１）雄性不育和自花授粉以及低效率的传粉机制而导致的异花传粉的失败；（２）部分胚胎的败育；（３）子房壁破裂而导致胚珠裸露等是木根麦冬有性生殖过程中的薄弱环节。

The embryological studies on an endangered species Ophiopogon xylorrhizus are reported in this paper. The anther was four sporangiate, and its wall was composed of four layers: epidermis, fibrous endothelium, middle layer and glandular tapetum. Cytokinesis of microspore mother cell in meiosis was of the Successive type, and tetrads were tetrahedral or isobilateral. The mature pollen grains were 2 celled. Ovules were anatropous, bitegminous, and crassinucellate. Ovary wall ruptured 4～5 days after fertilization. The development of embryo sacs conformed to the Polygonum type. The two polar nuclei fused into a secondary nucleus before fertilization. The embryogeny was of the Asterad type, and endosperm development corresponded to the Nuclear type. About 55.8% individuals in the population of O. xylorrhizus were found male sterile, and 43.3% of embryos aborted at early development stage. As a conclusion, we consider that (1)the failure of the xenogamy resulted from male sterility, autogamy and inefficient pollination agents, (2)embryo abortion and (3)exposure of young seeds during their early development are the weak links in the sexual reproduction of O. xylorrhizus, which would contribute to the endangerment of this species.