水稻胚囊壁的形成与发育观察

FORMATION AND DEVELOPMENT OF EMBRYO SAC WALL IN RICE

通过透射电镜对水稻(Oryza sativa L.)功能大孢子形成开始至胚囊成熟期间胚囊壁的形成与发育进行观察,结果表明:水稻胚囊壁是在原有功能大孢子壁的基础上,通过与其周围退化珠心细胞留下的壁相叠合,使壁加厚。功能大孢子近合点端壁存在胞间连丝,其中个别胞间连丝可保留到八核胚囊。胚囊壁上内突最早于四核胚囊近珠孔端发生。八核胚囊形成后,内突的发育在胚囊不同的细胞中表现不同,其中以中央细胞最具特点,表现为先在中央细胞与珠心相接的近珠孔端和近合点端两个区域的胚囊壁上形成,以后近珠孔端胚囊壁上的内突大量增加,而近合点端的却增加不明显,中部胚囊壁上的内突出现的时间相对较晚。到胚囊成熟时,近珠孔端胚囊壁上内突的分布密度最大,中部次之,近合点端的最小,三个区域上内突的形态各异。反足细胞与珠心相接的胚囊壁上内突的形成时间较早,但以后的发育却相对缓慢,数量增加不明显。2个助细胞交界处胚囊壁上的丝状器在胚囊未明显膨大时已形成。卵细胞除在与助细胞交界处的壁外,其它部位不形成明显的内突结构。

The formation and development of the wall of embryo sac, from functional megaspore to mature embryo sac of rice (Oryza sativa L.), were studied with transmission electron microscopy. Results showed that the embryo sac wall was derived from the wall of the functional megaspore. Later , it became much thickened mainly due to the piling up of wall remains from the degenerated nu-cellar cells. Plasmodesmata were frequently observed in the wall near the chalazal pole of the functional megaspore. Some of these plasmodesmata persisted through the stage of eight-nucleate embryo sac formation. At the four-nucleate embryo sac stage, wall ingrowths began in the micropyle region. At the eight-nucleate embryo sac stage cells began to form in the embryo sac but the patterns of development of wall ingrowths in these cells were different. In the central cell, wall ingrowth appeared in the region of the embryo sac wall adjacent to the nucellar cells, especially in the region near the micropyle and the chalaza pole. Wall ingrowths were quite well developed in the wall near the micropyle region and much more well-developed in the mature cell. Ingrowths failed to develop in other parts of the cell wall. In the antipodals, ingrowths developed only in the region of the embryo sac wall adjacent to nucellar cells. Ingrowths were absent in other regions of the wall of the antipodals. In the synergids, only the common wall between the synergids developed wall ingrowths. These wall ingrowths later formed part of the filiform apparatus which could be observed clearly before the embryo sac was obviously enlarged. In the egg cell, ingrowths were limited only in the wall adjacent to the synergids. The reasons and the functional significance of the formation of wall ingrowths in various parts of the embryo sac were discussed.