【摘要】 1.通过小孢子有丝分裂而形成的生殖细胞,在发育过程中有一系列的包括位移和变形的变化。最后生殖细胞变为纺锤体,准备另一次有丝分裂。在此时期,生殖细胞是裸露的,它只有自己的质膜和被营养细胞的质膜包围。生殖细胞的大部分为明显的椭圆形的核所占据,具高度凝集的染色质。在生殖细胞薄层的细胞质中,除核糖体外,所有的细胞器比营养细胞质中的明显的少,而且小。微管也能在纺锤形的生殖细胞的细胞质中看到,它们的排列方向是和细胞的长轴平行的。在生殖细胞中没有造粉质体。2.当生殖细胞已移位并和营养细胞再次紧密靠近后,它开始分裂。由生殖细胞分裂所形成的精细胞及其发育包括下列主要的变化:精细胞的形状由圆球形变为椭圆形,最后变为具尾延长的细胞。与此同时,细胞质的分布逐渐集中到精细胞的一端,形成细胞质的延伸,构成所谓的精细胞的尾部。有更多的细胞器,特别是线粒体集中在尾部。从生殖细胞分裂刚形成的精细胞是裸露的,所包围的质膜是不连续的。除精细胞的质膜之外,为营养细胞的质膜所包围,在后来的发育时期此双质膜变为连续的,并在一个极短的时期有壁物质——胼胝质沉积在质膜之间的空间。但在此时期之后细胞壁变为不连续的,壁物质明显降低。对生殖细胞分裂前的位置及精细胞发育中形态变化的意义进行了讨论。更多还原

【Abstract】 Ultrastructural events in wheat sperm cell development were examined from the divi- sion of generative cell stage to the maturation of sperm cell in pollen grains.The results are summarized as follows: 1.The generative cell in forming microspore by mitosis goes through a series of changes including the displacement and transformation.It finally becomes a spindle- shaped cell getting ready for another mitosis.The generative cell at this stage is naked, it is only surrounded by both membranes of its own and vegetative cell.Most part of the generative cell is occupied by the conspicuous elliptical nucleus with highly con- densed chromatin.With the exception of ribosomes, the organelles in the thin layer of generative cell cytoplasm are obviously fewer and smaller than those in the vegetative cytoplasm.The microtubules may also be seen in the cytoplasm of spindle-shaped gene- rative cell parallel to the long axis of the cell.There is no amyloplast in generative cell. 2.When the generative cell has moved to the position close to the vegetative nucleus again, it begins to divide.The formation of sperm cells as the result of mitosis of genera- tive cell, and the development of sperm cell involves the following main changes.The shape of the sperm cell tranforms from spherical to elliptical, finally it forms an elongat- ed cell with a tail-like structure.At the sametime, the distribution of cytoplasm gra- dually concentrated at one end of the sperm cell to form the cytoplasmic extension, so that the so called“tail”of the sperm cell is formed.There are more organelles, especial- ly the mitochondria, assembling in this part.The sperm cell just formed after mitosis is naked and the enclosed plasma membrane is discontinuous.The sperm cell membrane is enclosed by vegetative cell membrane, and the double membranes may be completed at a later stage.It is considered that the period which follows is very short, the deposition of wall material, the callose, occurs to fill up continuously the space between two mem- branes, but soon after this period the cell wall becomes discontinuous and the wall ma- terial is obviously decreased. The significance of the position of the generative cell before its mitosis and the mor- phological changes during the development of the sperm cell are discussed in this paper.更多还原