| DNA Synthesis and cell division in alloplasmic lines
of common wheat, Triticum aestivum cv. Chinese Spring Takaji IKUSHIMA Research Reactor Inst., Kyoto Univ., Kumatori, Ohsaka As the one way to elucidate the nuclear genome functions, especially for chromosomal DNA replication, in alien cytoplasms, the duration of the mitotic cycle and its component periods were measured in root meristem cells of alloplasmic lines of a common wheat, Triticum aestivum cv. Chinese Spring (2n=42, AABBDD). After the seeds were germinated in the dark at 25C for 36 hrs on wet filter papers in petri dishes, 20-min pulse labelling with 1microCi/ml of [3H-met] thymidine (40 Ci/mM) were performed. Rinsed seeds were further germinated and their root tips were collected at intervals of 2 h up to 48 h after the end of the 3H-thymidine labelling. Slides were prepared autoradigoraphy using Kodak NTB 2 emulsion and they were exposed in dark boxes for 3 weeks at 4C. Labelled mitotic cells were counted and the per cent was plotted against time after 3H-thymidine labelling. The duration of the mitotic cycle (CT), and its parts: the presynthetic (G1), DNA synthetic (S), postsynthetic (G2) and mitotic (M) periods were estimated from the curves of per cent of labelled mitotic cells vs. hrs after labelling. Any allocytoplasm tested in this study, Ae. squarrosa, Ae. comosa or Ae. speltoides, did not preferentially affect a given mitotic stage or the duration of the mitotic cycle of the original nuclear donor, T. aestivum cv. Chinese Spring. Their G1, S, G2+M/2 and CT were 0.8, 10.0, 2.6 and 14.0h, respectively. This work was supported in part by grants from the Ministry of Education, Science and Culture of Japan. The author is grateful to Dr. K. Tsunewaki for generous provision of alloplasmic lines of Chinese Spring. |