Cytofluorometric DNA base determination for the investigation of heterochromatin and heterochromatin amplification.

The measurement of chromomycin A3/DAPI fluorescence ratios is shown to allow base content determinations in eu- and heterochromatic regions of interphase cell nuclei. The base content values obtained in chromocenters and euchromatin of Scilla sibirica agree with those measured earlier [12] on the band and non-band areas of the chromosomes of this species. In Sinapis alba three different heterochromatin types, with regard to base content, can be discerned. The heterochromatin amplification observed in the polyploid nuclei of Sinapis roots and hypocotyl involves either all three heterochromatin types, with little resulting change of the total nuclear base content, or only one or the other of them, with a measurable shift of the base content.

Selective excitation of mithramycin or DAPI fluorescence on double-stained cell nuclei and chromosomes.

Fluorescence spectra of leukocytes stained by both mithramycin and DAPI showed that the fluorescence of the two dyes can be separated efficiently by using different excitation wavelengths, for instance the 435 nm and the 365 nm mercury lines. In human chromosomes the complementary ("reverse") banding pattern produced by these dyes may thus be observed on double stained chromosome spreads. In plants, for instance in Anemone blanda, the two dyes may reveal two different banding patterns. The results of absorption and fluorescence measurements suggest the existence of at least two binding sites, or types, for each dye, with different fluorescent yields and binding strengths.