黄蝉花生殖细胞有丝分裂期间微管的动态

MICROTUBULE CYTOSKELETON DYNAMICS IN THE GENERATIVE CELLS OF ALLAMANDA NERIIFOLIA HOOK DURING MITOSIS

用微管免疫荧光方法观察了黄蝉花生殖细胞在花粉管中进行有丝分裂时的微管动态。微管在不同分裂期的分布情形很不一样。当生殖细胞由花粉进入花粉管后,细胞便立刻开始分裂进入早前期,在这阶段微管以一个紧密微管网笼子形式存在生殖细胞内。之后,细胞进入中前期,在此阶段细胞核扩大,染色体变粗,而存在细胞内的微管网逐渐变为疏松散漫状,跟着细胞进入晚前期,而微管笼子则由网状变为纵向排列状。分裂进入早中期微管变细并呈波浪状,微管由笼子结构过渡到纺锤体结构。进入中期,纺锤体全部形成,在纺锤体内可以清楚地看到两种不同类型的微管束,一种附着在染色体上,而另一种则从一极延伸至另一极。跟着细胞进入早后期,在这一阶段姊妹染色体分开并分别移向两极,在赤道板位置微管明显减少。之后,细胞进入晚后期,姊妹染色体集中在两极,极端有新微管出现。在两个染色体团之间又汇集了许多类似成膜体微管的微管。细胞进入分裂末期,存在赤道板位置的微管又再次减少,而在中央部位则新形成一“成膜体联接区”,把两个新形成的精子连接着。

Changes in the structural organization of the microtubule cytoskelcton in the generative cells of A. neriifolia was followed during pollen germinaion, The generative cell once in the pollen tube divided immediately mitotically giving rise to two sperms. The division cycle was complete within about 4.5 hours, During early propbase the generative cell possessed a tigltly woven reticulate microtubule-cage The cage became much loosened d(?)ing mid prophase. When cell entered late prophase the retieulate-microtubuie-cage was then replaccd by an axial mic otubule-cage. The microtubule bundles that made up the cage were thick and straight. But they became wavy and thin when the cell entered prometaphase and was uhimately replaced by a new array of more centrally placed spindle microtubules at metaphase. Later, at early anaphase (or anaplase A), microtubules present at the equatorial plate region disappeared. But at the polar regio as more microtubules appeared. A new array of microtubules (resembling phragmoplast microtubules) also appeared when the cell entered late anaphase (or anaphaseB). At this phase, microtubule concentration was very high in the region between the two newly formed sperm nuclei. When the cell entered telophase, a junction-like structure started to form at the phragmoplast region. This junction somehow kept the two sperms attached to each other. The two sperms did not separate from each other even after seventeen hours under in vitro conditions.