甘薯珠心细胞的超微结构研究

本文叙述了甘薯珠心细胞在衰退前的发育过程中的超微结构变化.一般珠心表皮细胞和离胚囊较远的珠心细胞以及胚囊发育初期靠近胚囊的细胞有较大的核质比和清晰的核被膜;细胞质中线粒体、核糖体、高尔基体和内质网等细胞器十分丰富,功能也非常活跃;细胞中有较多的小液泡;细胞壁上具有较多的胞间连丝.随着胚囊的扩展和珠心细胞的发育,在离胚囊稍近的珠心细胞中,出现平行内质网槽库和同心内质网环,同心内质网包围的细胞质被消化后形成小液泡.通过新液泡的形成,原有液泡的扩大与合并,珠心细胞形成大的中央液泡,此时,珠心细胞由具有分生组织细胞特征转化为呈现薄壁组织细胞的典型特征,以后,胚囊的进一步扩展将导致珠心细胞的衰亡.

STUDIES ON THE ULTRASTRUCTURE OF NUCELLAR CELLS IN IPOMEOA BATATAS

The present paper reports the ultrastructural changes of nucellar cells in Ipomeoa bftiatas during their development before degeneration. In general, nucellar epidermis and nucellar cells situated at a distapce to the embryo sac and close to the embryo sac at the early stages of development have a high value of the nueleo-cytoplasmic ratio and a clear-cut nuclear envelope. They have abundant mitochondria, many starch grains. Mitochondria and starch grains vary in their shapes and interior structure. They have a large quantity of free ribpsomes, dictyosomes actively secreting vesicles, and some long or short cisternae of rough endopiasmic reticulum (RER). There are also more or less small yacuoles in the cytoplasm.Plenty of plasmodesmata are seen on their cell walls, through which neighbonring cells communicate with each other. Along with the enlargement of the embryo sac and development of those nucellar cells, RER of the nucellar cells close to the embryo sac increase rapidly. In their cytoplasm, parallel RER cisternae and concentric RER whorls are present. The latter probably functions as an autophagic device in certain conditions. A new small vavuole would form where the part of cytopiasm surrounded by concentric whorl was digested. Through formation of new vacuoles, the enlargement of original Yacuoles, and the fusion of vacuoles, the nutellar cells form a large central vacuole. Now, the meristematic nucellar cells have changed into typical parenchymatous cells. The further enlargement of the embryo sac cause the degeneration of nearby nucellar cells.