Growth of Sister Nuclei in Binucleate Cells Induced by Treatment with Methylxanthines

Abstract

<p>The responses of primary root cells of Vicia faba to two methylxanthines, 8-ethoxycaffeine and 3-isobutyl-1 methylxanthine were compared. The object was to determine whether or not the binucleate condition, induced by treatment with methylxanthines, could be used to estimate cell cycle duration in a marked subpopulation of cells. Binucleate cells induced by EOC did not divide; about 75% of those induced by IBMX had a cell cycle duration of 15-16 hours, i.e. close to the duration estimated for fast cycling cells.</p> <p>Methylxanthines may also induce other effects, e.g. (1) chromatid stickiness and tetraploid nucleus formation, (2) depression of mitotic index EOC and IBMX differed in their ability to induce these changes.</p> <p>Using binucleate cells, nuclear growth was followed throughout interphase. Nuclei did not grow continuously throughout interphase; there was a period of little or no growth initially and then a period in which the nuclei contracted. In IBMX induced binucleate cells, nuclear growth occurred and was rapid in the 2 hours prior to the entry of nuclei into mitosis. The other aspect of nuclear growth that was studied concerned the relative growth of the two sister nuclei of a binucleate cell. Sister nuclei were rarely of identical volumes.</p> <p>In most cases, large differences were seen between sister nuclei; these differences were maintained throughout interphase and into prophase. Nuclear shape changed during interphase but sister nuclei in a binucleate cell tended to have the same shape. The change in nuclear shape and the volume differences between sister nuclei are discussed in terms of nucleo-cytoplasmic interactions and the origin of the differential behaviour of sister nuclei present in a common cytoplasm.</p>