Comparative analysis of heterochromatin distribution in wild and cultivated Abelmoschus species based on fluorescent staining methods.

A comparative analysis of fluorochrome-binding pattern in nine taxa of Abelmoschus had shown that the type, amount and distribution pattern of heterochromatin were characteristic for each taxa. The fluorescent chromosome-binding sites obtained by chromomycin A3 (CMA) and 4′,6-diamidino-2-phenylindole (DAPI) staining in all the nine species showed constitutive heterochromatin CMA+, DAPI+ and CMA+/DAPI+. Large amount of heterozygosity was observed with regard to heterochromatin distribution pattern in all the taxa studied. The CMA+-binding sites are comparatively less than DAPI+-binding sites which is clearly evident as AT-rich regions are more than GC-rich regions in all the nine taxa analysed in Abelmoschus. These CMA+ and DAPI+-binding sites apparently rise with the increased in chromosome numbers of the different species. This pattern of heterochromatin heterogeneity seems to be a general characteristic feature. Therefore, the differential pattern of distribution of GC- and AT-rich sequences might have played an important role in diversification of the genus Abelmoschus. Polyploidy is an important factor in the evolution of Abelmoschus and the sole reason for range in chromosome numbers in this genus. It may be noted that, though often, but not always, the increase of DNA is caused by an increase in the amount of heterochromatin, i.e. increase of non-coding sections indicating restructuring of the heterochromatin. Thus, cumulative small and direct numerical changes might have played a role in the speciation of Abelmoschus.