天竺葵雌性生殖单位的超微结构

应用透射电镜研究了临近受精时天竺葵(Pelargonium hortorum Bailey)胚囊中的卵细胞、助细胞和中央细胞的结构。证明了卵细胞与助细胞以及助细胞与助细胞之间从合点端至珠孔端有很大的面积以质膜分界,仅珠孔端少部分以壁分隔。卵细胞与中央细胞之间同样缺乏细胞壁。在卵细胞的合点端,两质膜不同程度地分离形成宽窄相间的间隙。在间隙的絮状基质中存在小泡,这些小泡的产生似与卵和中央细胞中周质内质网的活动有关。推测小泡为多糖性质,可能为合子新壁的建造提供物质。卵细胞质中含巨大线粒体,质体和内质网也较丰富。基于超微结构的特征,可认为卵细胞具高度的生理合成活动的潜能。中央细胞极核位于珠孔端与卵器细胞毗邻,有利于在双受精作用中同时发生精细胞与卵细胞和精细胞与中央细胞核的融合。中央细胞的侧壁在珠孔端形成内突,具传递细胞的特点,表明这是雌配子体向孢子体摄取营养的重要部位。助细胞的细胞质含丰富的细胞器,这与多数植物中的相似,但具几个明显的特征,即核中存在微核仁,内质网形成圆球体或脂体,线粒体富集在丝状器的附近。传粉后花粉管进入胚囊之前,两个助细胞中一个退化。

ULTRASTRUCTURAL ASPECTS OF THE FEMALE GERM UNIT IN PELARGONIUM HORTORUM

The constituent cells of the female germ unit in the embryo sac of Pelargonium hortorum Bailey just before fertilization were studied using transmission electron microscope. It was revealed that a large area between the egg and synergids and between the synergids were seperated by their plasma membranes at the chalazal portion of the egg apparatus.Only a small portion at the micropylar end of the cells had normal wall. Common wall was also lacking between the egg and the central cell at the chalazal end. Furthermore, the space between the two plasma membranes was alternatively narrow and wide. There were a large number of single or double membrane-bound vesicles in the wider space. These vesicles appeared to be originated from the cortical ER in the egg and central cell, and probably contained substances essential for the formation of the zygote wall. The egg had numerous giant mitochondria, starch-contained plastids and RER. Based on the ultrastructural observations,it is proposed that the egg cell is provided high potential of physiological synthetic activity but still being quiescentas compared to the synergid. In the central cell, the location of the polar nuclei (or secondary nucleus) toward the micropylar end is essential for the simultaneous fusion of the sperm and egg and sperm and central cell during double fertilization. At the micropylar end of the central cell, lateral wall ingrowths developed abutted against the nucellus which was characteristic as transfer cell and indicated important site for the megagametophyte to obtain nutrients from the sporophyte. A great number of mitochondria were located toward the filiform apparatus in the synergids, which was quite similar as occurred in many other plants with the exception of the following features,Lipid bodies were formed at the end of RER,The nucleus of the synergids contained micronucleolus. After pollination but before the entrance of the pollen tube in the embryo sac, one of the synergid cells began to degenerate.