Study on the induction of cell apex and its developent

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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