Periodic Report Summary - CHROMELIM (Chromosome elimination in plant wide hybrids - ... from a model system in Hordeum to problems of speciation, gene introgression and breeding new crop plants.) Interspecific hybrids between the related wild barley species hordeum marinum and h. bulbosum were generated and tested regarding their chromosomal stability and chromatin properties. Unlike h. vulgare and h. bulbosum hybrid embryos, there was no effect of temperature on uniparental chromosome elimination or retention during hybrid seed development and seven chromosomes from each parent were detected according to genomic in situ hybridisation analyses. The centromere-specific histone H3 gene (CENH3) of both parental genomes was active in hybrid plants. Indirect immunostaining of flow-sorted 2C nuclei indicated that no major reorganisation of histone H3 methylation, namely K4, K9 and K27, H3K9 acetylation and histone H2A ubiquitination marks or location of active ribonucleic acid (RNA) polymerase II sites occurred after interspecific hybridisation.