F-actin participates in the process of the “partition-bundle division”

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A special kind of mitosis in wheat (Triticum aestivum L.) seedlings was observed after their exposure to the enhanced ultraviolet B (UV-B) radiation and named as “partition-bundle division”. To explore the abnormal mitosis, we focused on the variation of the actin filaments (F-actin) during the somatic cell division. The results showed that there are cyclic changes of F-actin during the cell cycle. In the interphase, F-actin displayed as long filaments and the “F-actin ring” surrounding the nucleus. In prophase and metaphase, F-actin was depolymerized into small pieces, which process accompanied nucleus disappearance. In the anaphase, the “actindepleted zone” (ADZ) appeared and then a bright zone full of F-actin appeared, which was named as “actin re-appeared zone”, which designated the position of the cell plate. In the telophase, F-actin pieces were aggregated into filaments and the “F-actin ring” re-appeared. Thus, after being exposed to the enhanced UV-B radiation, F-actin was broken into small bright spots during the interphase. And there exist several kinds of chromosome aberrations, including lagging chromosomes, chromosome bridge, and partition-bundle division. Results suggested that in the normal wheat seedling root cells F-actin surrounded the chromosomes, acting as one of the components of the aster-like structure. When injured by the enhanced UV-B radiation, F-actin could not surround the chromosome fully or distribute unequally at the cell poles, thus leading to the “partition-bundle division”. This all indicates that F-actin participates in the process of the “partition-bundle division” in wheat seedlings when they suffer from enhanced UV-B radiation.