Rabl organization is a type of interphase chromosome arrangement with centromeres and telomeres clustering at opposite nuclear poles. Here, we analyzed nuclear morphology and chromosome organization in cycling and endoreduplicated nuclei isolated from embryo and endosperm tissues of developing barley seeds. We show that endoreduplicated nuclei have an irregular shape, less sister chromatid cohesion at 5S rDNA loci, and a reduced amount of centromeric histone CENH3. While the chromosomes of the embryo and endosperm nuclei are initially organized in Rabl configuration, the centromeres and telomeres are intermingled within the nuclear space in the endoreduplicated nuclei with an increasing endoreduplication level. Such a loss of chromosome organization suggests that Rabl configuration is introduced and further reinforced by mitotic divisions in barley cell nuclei in a tissue- and seed age-dependent manner.

Centre of Plant Structural and Functional Genomics Institute of Experimental Botany of the Czech Academy of Sciences Šlechtitelů 31 779 00 Olomouc Czech Republic

Department of Plant and Microbial Biology Zürich Basel Plant Science Center University of Zürich Zollikerstrasse 107 8008 Zürich Switzerland

Field Crops Research Institute Agricultural Research Centre 9 Gamma Street Giza Cairo 12619 Egypt

The Polish Academy of Sciences The Franciszek Górski Institute of Plant Physiology Niezapominajek 21 30 239 Krakow Poland

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