Fig. 8. Chromatin dynamics during protoplast culture. Schematic representation of an interphase chromosome before and after protoplast formation and in the ddm1 mutant, showing repeat regions (colors) and gene-rich regions (gray). The loop organization of gene-rich euchromatin is based on previous studies (Fransz et al., 2002). For simplicity only chromosome 4 is shown, which has all major tandem repeats (180 bp, 45S rDNA and 5S rDNA). Most repeat regions become decondensed in protoplasts. Only the 45S rDNA domain remains partly condensed. Cultured cells show various levels of chromatin condensation. The sequence of recondensation events is 45S rDNA, 180 bp, 5S rDNA and interspersed repeats, such as transposable elements. ^aThe total size of repeat sequences in chromocenters is based on the total genomic size of the repeats shown in Table S2 in supplementary material. ^bValues are normalized to the maximal value of dataset (=leaf). ^cThe total size of high copy transposons in Arabidopsis is unknown. In the ddm1 mutant all repeats, except the low copy repeats, are in chromocenters (Soppe et al., 2002). Hence, the fraction of repeats in chromocenters of ddm1 is higher compared with chromocenters of cultured cells and lower compared with chromocenters in leaf nuclei.