Functional and structural chromosome analyses in autotetraploid Silene latifolia

Recent immunocytological and molecular data show that heterochromatic nucle ar regions, both constitutive and facultative, are modified differently (cy tosine hypermethylation and histone hypoacetylation) and late replicating, when compared to euchromatin. Intrusive and/or additive (supernumerary) DNA sequences are often functionally silenced; this is accompanied by their he terochromatinization. In this work we present a number of karyological stud ies on autotetraploid female cells of Silene latifolia (syn. Melandrium alb um). Immunofluorescence analyses do not indicate any global differences in DNA methylation, histone H4 acetylation, and chromosome replication pattern s which could arise as a consequence of the duplication of the whole chromo some set of the original diploid genome. Similarly, the number of silver-po sitive nucleoli roughly correlates to the ploidy level. Early replication a nd H4 hyperacetylation have been detected at all subterminal chromosome reg ions. This, together with cDNA in situ hybridization patterns, indicates th e localization of gene-rich regions. DNA methylation and chromosome replica tion patterns, but not histone H4 acetylation, show differences among the f our X chromosomes present: one to three X chromosomes were observed as hype rmethylated and/or late replicating. Taken together, the data demonstrate t hat there is no overall silencing of the additional two sets of autosomes i n the tetraploid cells, but the X chromosomes could be subject to an irregu lar dosage compensation. (C) 1999 Annals of Botany Company.