Abstract:

The structural and histochemical changes of the egg apparatus in the polyembryonic rice (Oryza sativa L.), ApⅢ with the highest frequence of additional embryos among the polyembryonic rice investigated, before and after fertilization were studied and compared with those of normal and other polyembryonic rices in a similar developmental period. A total of 2 932 ovules were observed and each of them contained only asingle embryo sac with a set of egg apparatus. Among 1 655 embryo sacs, there were 1 643 embryo sacs (99.27%) with one normal egg apparatus in each embryo sac, and only 12 embryo sacs (0.73%) from the remainder with 4 celled egg apparatus, i.e. two eggs and two synergids. Neither the numerous poly egg apparatus and egg like cells, nor the double set of embryo sacs each containing one egg apparatus and other abnormal egg apparatus in single ovary, which were reported by earlier investigators to have high frequency of embryo production in SB 1 and ApⅣ, were observed. The egg cell was located at the subterminal site of the micropylar end of embryo sac. The cytoplasm of egg cell was rich in protein materials and poly saccharide grains, which did not disappear until the division of zygote. The prominent nucleus was closely surrounded by protein and polysaccharide grains, which did not disappear until the division of zygote. No cytological difference was found between egg cells from the normal and abnormal egg apparatus. The two synergids were fully developed and situated at the upper most part of the micropylar end of the mature embryo sac. In most embryo sacs, the synergids were flask shaped with longer necks, and a widened cap shaped top, in close contact with the micropyle. The synergids had a well developed filiform apparatus. The characteristic appearance of the filiform apparatus as well as the cap neck region of synergids before and after pollen tube penetration were easily distinguishable from the egg cell. The structure, the stainability with Coomassie Brilliant Blue and PAS reaction, the process of accumulation, distribution and disapperance of the cytoplasmic protein materials and polysaccharide grains of the two synergids, the persistent and rarely the receptive synergids before and after pollen tube penetration, were closely similar to those of egg cell of the same developmental stage. In comparison with normal and other polyembryonic rice reported, the size of nucleus and nucleolus and their stainability also strongly resembled those of egg cell. Based on the results observed, the main conclusions are summarized as follows: (1) the additional embryos very frequently developed in the young and mature seed of polyembryonic rice ApⅢ were produced by one or two synergids of normal egg apparatus, rarely by 4 celled egg apparatus; (2) during fertilization, the synergids, in addition to the natural specific function of introducing pollen tube and transferring sperms to egg cell and central cell, could be closely associated with the potentiality to breed one or two additional embryos; and (3) as compared with that of normal or other polyembryonic rice it is firstly disclosed that in a few embryo sacs of ApⅢ, the cytoplasmic and nuclear structure, the active anabolism and catabolism of protein and polysaccharide materials and the delayed disorganization at the mid basal region of the receptive and persistent synergid still remained unchanged before the division of zygote. Such salient features could be the predisposition for the origin of additional embryos in ApⅢ.

多胚水稻ApIII的胚胎发生：受精前后卵器的结构和组织化学研究
母锡金 朱至清 蔡 雪 孙德兰 林金星*

（中国科学院植物研究所，北京100093）

摘要： 对高频率多胚水稻（Oryza satixa L）ApIII受精前后卵器的细胞结构和组织化学变化进行了观察，并同已报道的正常水稻和多胚水稻大至相同发育时期的卵器进行了比较，结果表明：ApIII的23932 个幼嫩子房中，每个子房只有一个胚囊。没有看到含有一对胚囊和每个胚囊里有一套卵器的现象。除解体的和含胚的胚囊外，1655个胚囊中，含1 个卵细胞和2个助细胞组成的正常卵器为1643 个（99.27% ），含2个卵细胞和2 个助细胞的4细胞卵器为12 个（0.73%）。没有观察到大量4细胞卵器、5细胞卵器（即由3 个卵细胞和2 个助细胞组成）和卵状细胞，以及其他4卵、5 卵卵器的变异类型。卵细胞位于对着子房壁维管束一侧。细胞质含丰富的蛋白质和多糖颗粒；细胞核位于细胞中下部，少有偏远轴端的，直到合子分裂前由蛋白质物质和多糖颗粒聚成的环所包裹。成熟胚囊中常见2 个助细胞。助细胞位于珠孔端靠子房壁维管束一侧，多数为长颈烧瓶状，少有长形和星月形的。其珠孔端壁内侧丝状器发达，细胞质的结构，蛋白质物质和多糖颗粒的积累、分布及消长，细胞核的大小、组织化学反应和周围物质的动态与卵细胞的相同。此外，ApIII 的２个助细胞存留时间较长。当花粉管进入助细胞的早期，助细胞的丝状器和帽颈端被花粉管损伤，中下部细胞质和核所在区仍保持完好。由以上结果得出结论：多胚水ApIII高频率的额外胚（１ 或２ 个）主要来自3 细胞正常卵器，极少来源于4细胞卵器；ApIII 的助细胞除在受精和胚胎发生早期具特殊功能外，与卵细胞相似的细胞质结构、物质代谢过程以及崩溃较晚可能与胚胎发生有关；在ApIII  的少数胚囊中，接受助细胞可能有发生胚的潜能。
关键词： 多胚水稻；卵器；胚囊；无配子生殖；生殖

通讯作者。E-mail: linjx@ns.ibcas.ac.cn

Key words: polyembryonic rice, egg apparatus, embryo sac, apogamety, reproduction