以甜菜无融合生殖单体附加系M14(Beta vulgaris, 2n=18+1)为实验材料, 利用电子显微镜技术对成熟胚囊及其超微结构进行研究。结果表明: M14成熟胚囊包括1个卵细胞、2个退化的助细胞、1个具有次生核的中央细胞和3-6个反足细胞。其卵细胞具有3种不同的形态: (1)极性正常的卵细胞, 细胞核位于合点端, 细胞质含有大量核糖体、线粒体、内质网等细胞器;
(2)细胞核位于细胞中央; (3)细胞核位于珠孔端, 且后2种形态细胞器的种类与数量少。大多数胚囊中的2个助细胞在开花前已退化。中央细胞的次生核位于反足细胞附近; 未经受精自发分裂前的卵细胞与中央细胞的细胞核大、核仁明显, 细胞器的种类与数量多, 呈现旺盛代谢活动特征, 成为二倍体孢子无融合生殖过程中, 卵细胞与次生核自发分裂的细胞学标志。

We investigated by electron microscopy the ultrastructural character of the mature embryo sac in the chromosome-9 monosomic addition line of Beta corolliflora Zoss. in sugar beet, designated M14. The mature embryo sac of M14 consisted of an egg cell, two synergids, a central cell with a secondary nucleus, and 3-6 antipodal cells. The egg cells in different embryo sacs showed different polarity and metabolic activity. They were classified into three types according to the polarity of egg cells: (1) egg cell with regular polarity—the nucleus was located at the chalazal end, and its cytoplasm was rich in organelles such as ribosomes,
mitochondria and endoplasmic reticulum; (2) egg cell with a nucleus at the micropylar end, and (3) egg cell with a centrally located nucleus. The eggs of the third type contained fewer organelles in cytoplasm. The two synergids degenerated before anthesis in most mature embryo sacs. The secondary nucleus, which was close to the antipodals, showed strong metabolic activity. Both the egg cell and the central cell contained large nuclei with distinct nucleoli and numerous organelles. The egg and the central cell were suggested to be active in metabolism, which could be a label of the autonomous division of unfertilized egg cell and central cell in diplospory.