The amounts of nuclear DNA and the duration of DNA synthetic period (S) in related diploid and autotetraploid species of oats

The relative amounts of nuclear DNA of root meristematic cells of two related diploid Avena species, A. strigosa 2x and A. pilosa, which have different karyotypes, and an autotetraploid of one, A. strigosa 4x, were measured by Feulgen microspectrophotometry. The durations of various periods of their mitotic cycles were studied by autoradiography of cells pulse-labeled with tritiated thymidine. The results show that the autotetraploid, with twice the amount of nuclear DNA of its diploid, has the same duration of S period as the diploid, while A. pilosa, with intermediate nuclear DNA content, has a longer S period. These results support the hypothesis that homologous chromosomes or genomes require similar duration for their DNA synthesis and suggest that the structures of chromosomes are involved in temporal control of the DNA synthesis in cells.