Study on the induction of cell apex and its developent

通过细胞离心和偏振光照射，在原丝体的侧壁上诱导出一个新的细胞顶端作为分支。分析了分支的发育过程，并描述了分支形成过程中细胞骨架的变化。原丝体细胞经白色诱导分裂7 h后离心，使核移位到原丝体基部。离心后立即或在黑暗中培养2 d后，将原丝体转移到连续偏振红光下。细胞分裂在红色或黑暗条件下进行。如果细胞分裂发生在比原丝体顶端平均低250 μ m以上的位置，则新的原丝体顶端从非常靠近顶端和/或基部细胞的细胞分隔壁的侧壁分支出来。然而，如果原丝体的一部分，不管细胞分隔壁，用偏振红光的微束照射， ...更多信息 分支仅在照射部位形成。研究了细胞核在新分支发育过程中的行为，细胞分裂后，在红色和黑暗条件下，两个细胞核都远离分裂部位。在红光全细胞照射下，细胞增厚发生在细胞分隔壁附近，但细胞核位于远离分支部位。当一个新的顶端开始生长时，一个细胞核回到分支部位并爬进新的分支。另一方面，在微束照射下，当细胞核移动到束中时，分化出新的顶点。值得注意的是，纺锤形核可由原来的顶端或底部进入分支，表明核没有头尾，并观察到微管和微丝在此过程中的变化。在细胞变厚之前，在未来的分支部位暂时出现了类似于前期带或近顶端环结构的微管带（Murata和Wada 1989）。从新生的顶端开始，微管呈漏斗状排列。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