CELL-CYCLE ACTIVATION DURING IMBIBITION AND VISIBLE GERMINATION IN EMBRYOS AND MEGAGAMETOPHYTES OF JACK PINE (PINUS-BANKSIANA LAMB)

Flow cytometric determination of cell cycle activation during imbibiti on and visible germination in Five families of jack pine (Pinus banksi ana Lamb.) embryos and megagametophytes revealed that in seeds that ha d 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 augment ation in the nuclei active in the 2C-4C cycle as well as those with DN A levels higher than the 4C state occured gradually and preceeded radi cle emergence. In megagametophyte tissue examined at various stages of imbibition, cell cycle activity became apparent rapidly following imb ibition. In nuclei of green and white embryos examined separately the chi(2) frequency distributions were significantly different for all th ree 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 embryo s where no significant linear relation was noted. Cell cycle activity in the hypocotyl + cotyledons region and the emerging radicle were exa mined separately. Functional relations found in the hypocotyl + cotyle dons region were not evident in the radicle. As visible germination pr oceeded, cell cycle activity in the hypocotyl + cotyledons region for this period of germination showed a reversal of the activity noted dur ing imbibition: Fewer nuclei were active and once again a higher propo rtion were found in the 2C state. (C) 1996 Annals of Botany Company