Combined PI-DAPI staining (CPD) reveals NOR asymmetry and facilitates karyotyping of plant chromosomes

This paper presents a preparative and staining procedure for plant mitotic chromosomes that uses a combination of PI (propidium iodide) and DAPI (4',6-diamidino-2-phenylindol) and which reveals a pattern of high-affinity regions for these fluorochromes. Nucleolar organiser regions (NORs), telomeres and centromeric regions exhibit high PI affinity (red), whereas other chromosomal regions exhibit high affinity for either PI (red) or DAPI (blue). NOR-bearing and other chromosomes are readily distinguished, facilitating karyotyping. The dual staining pattern was observed in all the plants tested. Aspects of NOR size, number and occurrence are discussed. A karyotype of rice metaphase chromosomes is presented, based on their fluorescent banding patterns.