Characterization of heterochromatic regions in 'Trovita' orange (Citrus sinensis Osbeck) chromosomes by the fluorescent staining and FISH methods.

CMA/DAPI double staining and FISH methods using rDNA and telomere specific repeated sequences as probes were applied to characterize the large amount of heterochromatin in the telomeric regions of 'Trovita' orange (Citrus sinensis Osbeck) chromosomes. As a result, all the heterochromatic regions were CMA+/DAPI-, and thus were GC rich. Three CMA+/DAPI- heterochromatic regions were positive to the 26S rDNA probe. Telomere arrays consisting of Tm(A)Gn were detected on the extreme ends of each chromosome and most of the CMA+/DAPI- heterochromatic regions were ordered close inside the telomere-specific repeated sequences. The data obtained in this study will be useful for karyotyping, systematics, and molecular analysis of orange chromosomes.