NOR-associated heterochromatin of pepper chromo- somes stained with acridine orange

Acridine orange is a non-specific fluorescent dye which binds to DNA mainly by intercalating between base pairs. In human and animal cytogenetics this dye has been extensively utilized to show reverse banding pattern (RFA). Considering the absence of Gand R-bands in plant chromosomes, the use of acridine orange after pretreatment in Cbanding protocols has been applied for detecting heterochromatic segments associated with the nucleolus organizing regions (NORs). Therefore, the RFA technique, as applied to higher vertebrates, was used in this work for pepper (Capsicum annuum L.) chromosomes to detect NOR-associated heterochromatic segments. For the Capsicum genus, other methods described in the literature have led to conflicting NOR positions results. Bands emitting yellowish-green fluorescence were located in the secondary constriction of chromosome 5 and flanking the NOR of chromosome 11 of pepper. The maize chromosome 6, used as a known NOR position standard, showed similar results. Additional information and the banding pattern obtained suggest that this method can be used to differentiate between the α and -heterochromatin.