中国水仙的胚胎学研究

Embryological Studies on Narcissus tazetta var. chinensis

中国水仙(Narcissustazetta var.chinensis)只开花不结实,以鳞茎球营养繁殖.在花芽发育过程中,减数分裂前的小孢子母细胞发育未显示异常.但在减数分裂过程中,许多细胞中显示出了异常的落后染色体现象.小孢子四分体主要呈左右对称型,细胞质分裂为连续型.四分体时期后,大部分小孢子呈空瘪状态,少部分小孢子含有染色较深的细胞质.约27%的花粉可发育成比较正常的二胞花粉.离体萌发实验中,有极少数花粉可萌发出花粉管,但在授粉的花柱柱头上未观察到花粉管.雌蕊由三心皮构成3室子房,中轴胎座,其上着生了上60～90个胚珠.胚珠倒生,双珠被,薄珠心.胚囊发生属于单孢子型,但大多数胚囊发育中途失败,只有约4%的胚囊可发育成7胞8核的蓼型胚囊.中国水仙雌、雄配子体发育异常和花粉在柱头上不能萌发是它只开花不结实的两个根本原因.

Chinese Narcissus has been a favorite ornamental plant in China for several hundred years.Since the plant blooms but has no seeds,it only reproduces by vegetative propagation.Embryological studies of Chinese Narcissus (Narcissus tazetta var.chinensis) were conducted to discovery the causes of sterility.The anther wall is composed of four layers and its tapetum is of the secretory type.The cytokinesis in microspores mother cells is of the successive type and the arrangement of the microspores in tetrad is tetrahedral.During meiosis of microspore mother cells,some chromosomes lag behind and several micronuclei are found in tetrads.After meiosis,as most microspores abort and cytoplasms decrease,only 27.7% of pollen grains could develop with full cytoplasm.Among the normal pollen grains,only 1.3% of them could germinate pollen tubes in culture medium.No pollen grain, however,could germinate on the stigma and no pollen tube was found in the style.The ovary is trilocular with axile placentation and the ovules are bitegminous,tenuinucellatae and anatropous.After meiosis of the megaspore mother cell,the chalazal megaspore develops into a polygonum type embryo sac.Most embryo sacs,however,degenerate during their development and only about 4.5% of megaspore mother cells could produce normal embryo sacs, each of which has one egg cell,two synergids,three antipodal cells and a central cell containing two polar nuclei.Some of the abnormal embryo sacs were hollow and some of them had over four nuclei in the centre.One reason of the sterility of Chinese polyanthus is the abnormality of microsporogenesis and megasporogenesis,which lead to few functional pollen grains and embryo sacs developing.The other reason is that the pollen grains can not germinate on the stigma and no pollen tube could grow into the style.