Cell cycle activation during imbibition and visible germination in embryos and megagametophytes of jack pine (Pinus banksiana Lamb.). [Erratum: June 1997, v. 79 (6), p. 713-714.]

Flow cytometric determination of cell cycle activation during imbibition and visible germination in five families of jack pine (Pinus banksiana Lamb.) embryos and megagametophytes revealed that in seeds that had undergone no imbibition the majority of cells were in the 2C state. As the imbibition period increased, less of the nuclei were blocked in the G0/G1 state and more become active in the cell cycle. The augmentation in the nuclei active in the 2C-4C cycle as well as those with DNA levels higher than the 4C state occurred gradually and preceeded radicle emergence. In megagametophyte tissue examined at various stages of imbibition, cell cycle activity became apparent rapidly following imbibition. In nuclei of green and white embryos examined separately the chi squared frequency distributions were significantly different for all three families after 144 h. As imbibition period increased, fewer nuclei from the green embryos were blocked in the 2C state, and more became active in the 2C-4C cell cycle. This was not the case for white embryos where no significant linear relation was noted. Cell cycle activity in the hypocotyl + cotyledons region and the emerging radicle were examined separately. Functional relations found in the hypocotyl + cotyledons region were not evident in the radicle. As visible germination proceeded, cell cycle activity in the hypocotyl + cotyledons region for this period of germination showed a reversal of the activity noted during imbibition: fewer nuclei were active and once again a higher proportion were found in the 2C state.