Quantitative Analysis of Chromosome Polytenization in Synthetic Autopolyploids of Arabidopsis thaliana

The analysis of chromosome polytenization in the nuclei of autopolyploids may help to determine how polyploidy affects plant growth. We performed fluorescence in situ hybridization (FISH) analysis with a centromeric DNA probe on diploid and synthetic autopolyploid series (tetraploid, hexaploid, and octaploid) of Arabidopsis thaliana to observe and quantify chromosome polytenization in polyploid plants. Our FISH analysis revealed that the number of signals of centromeric sequence was smaller than the number of chromosomes in the nuclei of basic genomes in polyploid strains, which indicates the polytenization of chromosomes. In addition, the degree of chromosome polytenization increased as the degree of ploidy increased. This result suggests that the suppression of cell proliferation in polyploid plants may be related to chromosome polytenization. The FISH analysis confirmed that chromosome polytenization occurred in the nuclei of endoreduplicated cells in all strains. We also demonstrated that the degree of polytenization increased according to the endoreduplication level. In particular, chromosomes in the nuclei of endoreduplicated octaploid cells were highly polytenized, which is likely related to the severe growth suppression observed in these cells. This is the first report to explicitly show that chromosome polytenization occurs not only in the nuclei of endoreduplicated cells but also in those of non-endoreduplicated cells (cells with a basic genome) in autopolyploid plants.