Yu H S, Russell S D
Department of Botany and Microbiology, University of Oklahoma, Norman 73019.
Eur J Cell Biol. 1993 Aug;61(2):338-48.
Generative cell mitosis was examined in stylar-grown pollen tubes of Nicotiana tabacum using serial sectioning, transmission electron microscopy and computer-assisted reconstruction. Before mitosis, the generative cell has a cage-like organization of cytoplasmic microtubules. The mitotic spindle forms when the cytoplasmic microtubules reduce in frequency and kinetochore microtubules form in an area delimited by sheets of endoplasmic reticulum; no preprophase band of microtubules is observed. At metaphase, 21 pairs of kinetochores are distributed unevenly along the length and depth of the cell without the formation of a strictly planar metaphase plate. The metaphase spindle is highly oblique, with diffuse subpoles distributed along the sides of the cell, colocalized with endoplasmic reticulum lamellae. From these dispersed subpoles the kinetochore bundles emanate, closely associated with tubular endoplasmic reticulum. Anaphase consists of three principal processes: convergence of diffused mitotic poles, shortening of the kinetochore bundles, and the elongation of the spindle by an average of nearly 50%. At mid-anaphase, a phragmoplast begins to form, mainly by the assembly of new microtubules at the equatorial area, which form as a cluster of numerous short microtubules. Cytokinesis is essentially conventional, with centrifugal cell plate formation. Cytoplasmic microtubules are restored in the newly formed "brother" sperm cells in a distribution similar to that in the generative cell but fewer in number.
利用连续切片、透射电子显微镜和计算机辅助重建技术，对烟草花柱中生长的花粉管中的生殖细胞有丝分裂进行了研究。在有丝分裂之前，生殖细胞具有笼状的细胞质微管结构。当细胞质微管频率降低且着丝粒微管在内质网片层界定的区域形成时，有丝分裂纺锤体形成；未观察到微管的前期带。在中期，21对着丝粒沿细胞的长度和深度不均匀分布，未形成严格平面的中期板。中期纺锤体高度倾斜，分散的亚极沿细胞两侧分布，与内质网片层共定位。着丝粒束从这些分散的亚极发出，与管状内质网紧密相连。后期包括三个主要过程：分散的有丝分裂极汇聚、着丝粒束缩短以及纺锤体平均伸长近50%。在后期中期，成膜体开始形成，主要是通过在赤道区域组装新的微管，这些微管形成为许多短微管的簇。胞质分裂基本上是常规的，形成离心细胞板。新形成的“兄弟”精子细胞中的细胞质微管恢复，其分布与生殖细胞中的相似，但数量较少。
