Study on the induction of cell apex and its developent

通过细胞离心法和偏振红光照射，在原丝体侧壁上诱导出一个新的细胞顶端。分析了原丝分裂的发育过程，描述了分枝形成过程中细胞骨架结构的变化。白光照射诱导细胞分裂7h后，原丝体细胞被基础离心法分离，使细胞核移位到原丝线基底部。在离心后立即或在黑暗中孵育两天后，将原丝体转移到连续偏振红光中。细胞分裂发生在红色或黑暗条件下。如果细胞分裂发生在距原丝体顶端平均250微米以下的地方，则新的原丝体顶端从非常靠近顶端和/或基细胞的细胞分裂壁的侧壁分支出来。然而，如果原丝体的一部分，无论细胞分裂壁，被微束偏振红光照射，一种新的…更多的分枝只在受照部位出现。研究了细胞核在新的分支发育过程中的行为，在细胞分裂后，无论是在红色还是在黑暗条件下，两个核都离开了分裂位置。在红光照射下，细胞在细胞分裂壁附近增厚，但细胞核定位于远离分叉部位。当一个新的顶端开始生长时，一个核回到分枝位置并爬行到新的分支中。另一方面，在微束照射下，当一个核移动到束流中时，会分化出一个新的尖端。值得注意的是，纺锤形的钩子可以从原来的顶端或底部进入分支，表明细胞核没有头部和尾巴。在此过程中，还观察到微管和微丝的变化。在细胞加厚之前，在未来的分枝部位暂时出现了类似前相带或亚顶端环状结构的微管带(Murata和Wada 1989)。有趣的微管图案从新的顶端展开。较少

A new cell apex was induced as a branch on a side wall of a protonema by cell centrifugation and polarized red light irradiation. A developmental process of the branch was analyzed and changes on cytoskeletal pattern during the branch formation were described.A protonemal cell was centrifuged basipetally to dislocate a nucleus to the protonemal basal part after an induction of cell division by irradiation with white light for 7 hr. The protonemata were transferred to the continuous polarized red light immediately after the centrifugation or after two days incubation in the dark. Cell division was taken place under the red or the dark condition. If the cell division occurred at more than 250 um below in average from the tip of protonemata, a new protonemal apex branched out from a side wall very close to the cell dividing wall of an apical and/or basal cell. However, if a part of protonema, irrespective of cell dividing wall, was irradiated with a microbeam of polarized red light, a new … More branch developed only at the irradiated site. Behavior of a nucleus during the process of new branch development were investigated.After the cell division, both nuclei moved away from the division site both in red and dark conditions. Under whole cell irradiation with red light, cell thicking occurred near the cell dividing wall but nuclei localized far from the branching site. When a new apex started to grow, a nucleus came back to the branching site and crawled into the new branch. On the other hand, under microbeam irradiation, a new apex was differentiated when a nucleus moved into the beam. It is note worthy that a spindle-shaped uncleus can get into a branch from their former tip or bottom, indicating that a nucleus has not head and tail.Changes of mictotubuled and microfilaments during the process were also observed. A microtubule band like a preprophase band or subapical ring structure (Murata and Wada 1989) appeared tentatively at the future branching site before cell thickning. Fun-like pattern of microtubuled spread out from the new apex. Less