Use of Feulgen image analysis densitometry to study the effect of genome size on nuclear size in polyploid sturgeons

Summary Feulgen image analysis densitometry (FIA) and image cytometry were used to study the relationship between the DNA content (pgDNA nucleus−1) and nuclear area (μm2) in blood smears of evolutionary tetraploid (4n) sterlet (Acipenser ruthenus) and stellate sturgeon (A. stellatus); evolutionary octaploid (8n) Siberian sturgeon (A. baerii) and Russian sturgeon (A. gueldenstaedtii); hexaploid (6n) and decaploid (10n) fish found within A. baerii stock; and A. baerii and A. gueldenstaedtii exhibiting dodecaploidy (12n). Standards used for FIA were blood smears of chicken (Gallus gallus domesticus; 2.5 pgDNA nucleus−1) and diploid and induced triploid tench, Tinca tinca (2.04 and 3.1 pgDNA nucleus−1, respectively). All ploidy levels were first verified by means of flow cytometry. Species of the same ploidy level, however differing in their DNA content, exhibited a similar mean erythrocyte nuclear area, as could be demonstrated on A. ruthenus and A. stellatus (19.27 and 19.79 μm2, respectively) with a respective mean DNA content of 3.72 and 4.68 pgDNA nucleus−1 and the same relationship was found for evolutionary octaploid (8n) A. baerii and A. gueldenstaedtii (29.87 and 30.09 μm2, respectively) with respective mean DNA content 8.29 and 7.87 pgDNA nucleus−1. The 0.19–0.32 pgDNA increments in DNA content of erythrocytes thus had no effect on their nuclear area. With increasing ploidy level, the DNA concentration (pgDNA per μm2 of erythrocyte nuclear area) was found not to increase linearly. The DNA in erythrocyte nuclei appeared to be more and more densely packed with an increase of the ploidy level (r = 0.98; R2 = 0.95).