Changes in nuclear DNA content, cell and nuclear size, and frequency of cell division in the cotyledons of Brassica napus L. during embryogenesis
1990
Silcock, D.J. | Haas, Dorothy | Bryant, J.A. | Hughes, S.G.
Cellular behaviour was examined during embryogenesis in Brassica napus to test whether or not polyploidy occurs in the cotyledons during the phase of oil deposition. Nuclear DNA content, nuclear and cell size, and the mitotic index were measured in the cotyledons on various days post anthesis (dpa). In squashed monolayers from 15 dpa cotyledons, a polyploid (> 5C) population was detected together with a substantial number of cells in G2 (4C). Nuclear volume was measured on sectioned tissues and, at 15 dpa, the range of values from the cotyledons (40-500 micrometers3) contrasted with that in the vestigial suspensor and endosperm (50- > 600 micrometers3). At 15 dpa the nuclear volume data suggest that whilst cells in the cotyledons were in G1 and G2 many endosperm and suspensor cells were polyploid. Thus, polyploidy observed in the squashed monolayers was probably due to contaminating endosperm/suspensor cells. At 25 and 35 dpa, polyploidy was not detected; all cells were in G1 (2C) and cell area increased. The mitotic index peaked at 20 dpa before declining and given the narrower distribution of nuclear volumes at 25 and 35 dpa (50-300 micrometers3), these data are consistent with cell arrest in G1. Thus, polyploidy was not detected in the cotyledons of B. napus which differs from what is known about cellular development in legume cotyledons.
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