论文部分内容阅读
银杏 (GinkgobilobaL .)的大孢子母细胞在减数分裂前变成近长圆形 ,细胞核移向珠孔端 ,造粉质体围绕细胞核分布。线粒体主要分布在细胞的偏向合点端。细胞的偏向珠孔端存在大量的粗面内质网 ,而线粒体和质体较少。到了减数分裂前期Ⅰ时 ,细胞中液泡增加 ,向珠孔端的内质网减少。减数分裂的第一次分裂形成二分体细胞后 ,更表现出明显的极性分化。偏向珠孔端的细胞 (A)相对较小 ,细胞中除环状内质网和少量线粒体外 ,几乎看不到质体 ,而偏向合点端的细胞 (B)体积增大 ,各种细胞器的含量也较丰富。减数分裂第二次分裂时 ,这两个二分体细胞 (A和B细胞 )的分裂时间也不相同。形成直立四分体大孢子细胞时 ,最向合点端的细胞 (B2 )最大 ,成为具功能大孢子。其余 3个大孢子细胞陆续退化 ,但是细胞间差别很大。偏向珠孔端的两个细胞 (A1和A2 )首先退化。后来B1和B2 细胞之间形成了厚壁。由于减数分裂时极性的变化也可能形成T字型四分体大孢子细胞或只产生 3个大孢子细胞 ,最后只有最下面的一个细胞 (B2 )成为具功能大孢子。
Ginkgo biloba (Ginkgobiloba L.) megaspore mother cells become nearly oblong before meiosis, the nucleus moves toward the end of the pore, and the amyloplast is distributed around the nucleus. Mitochondria are mainly distributed in the cell’s biased point. The cells tend to have a large number of rough endoplasmic reticulum, but less mitochondria and plastid. At the pre-meiotic stage I, the vacuoles in the cells increased and the endoplasmic reticulum at the ends of the beads decreased. After the first division of meiosis to form the dyadic cells, it showed obvious polarity differentiation. The cells (A) which are more toward the end of the micropyle are relatively smaller. The plastids are almost not seen in the cells except for the ring endoplasmic reticulum and a few mitochondria, while the cells (B) More rich. At the second division of meiosis, the timing of the division of the two dyadous cells (A and B cells) is also different. When forming erect meristematic megaspore cells, the cell closest to the junction point (B2) becomes the largest, becoming a functional megaspore. The remaining three megaspore cells gradually degenerate, but the cells vary greatly. Two cells (A1 and A2) that are biased toward the pore end degenerate first. Later, thicker walls formed between B1 and B2 cells. Due to the change in polarity at meiosis, it is also possible to form T-shaped meristematic cells or to produce only 3 megaspore cells. Finally, only the bottommost cell (B2) becomes a megaspore with function.