Chromatin affinity in interphase --Maillet, DS, Walden, DB Although it has been possible to examine nuclear organization in metaphase cells, interphase is the stage of the cell-cycle where genes are active and chromatin organization may be necessary for cell type expression. Horn (Ph. D. thesis, University of Western Ontario, London Ontario, 1973) observed that the K10 knob could be seen in Feulgen stained interphase nuclei; in the presence of two copies of the K10 chromosome, the knobs were close together. Entire tassels, collected in the morning (ambient temperature 25 C) from inbred Mo17 grown in our nursery, were kept at 27 C or 43 C with the cut end in water for 24 h. Utilizing the methods described in our previous contribution, we were able to examine the arrangement of chromatin in interphase binucleate tapetal cell preparations. By comparing the negatives of cells photographed after C-banding and after silver staining, the relative distance between the knobs on chromosomes 6 (present on both the C-banded and silver stained negatives) and 7 (present on only the silver stained negative) and between chromosomes 6 and 7 could be measured. Measurements were divided by the diameter of the nucleus and compared between 30 heat shocked and 30 control nuclei. From earlier work (Maillet et al. MNL 1999, 73: 67-68) we reasoned that heat shock would disrupt nuclear organization. The diameter of spread nuclei was higher in the heat shocked sample perhaps because less structure remained. The mean relative distance between the knobs on chromosome 7 was higher in the heat shocked cells than in the control. This change cannot be explained by the change in diameter of the nuclei as the mean relative distance between the knob on chromosome 6 and the distance between the knobs on 6 and 7 did not change (Table 1.). The data suggest that the knob on chromosome 7 and adjacent chromatin are close together during interphase and that heat shock causes a disruption of organization.

Table 1. Two sample t-test of Mo17 interphase affinities between heat shocked and control and the diameter of the nuclei sampled.
 
  chromosome affinities      
comparison HS mean SD Control mean SD df t
chromosomes        
7 to 7 4.08 +/- 1.97 2.44 +/-1.18 58 1.86*
6 to 6 3.86 +/- 2.03 2.94 +/- 1.43 58 0.20
6 to 7 4.34 +/- 2.01 3.12 +/- 1.45 118 0.21
nuclei diameter 8.97 +/- 1.05 6.68 +/- 0.97 58 8.63

* significant at t(1), 0.05, 58

significant at t (2), 0.05, 118
 
 


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