Use of DNA fluorochromes for studying meiosis in the woody species Thryptomene calycina.

The fluorescent DNA probes DAPI and Hoechst 33258 produce superior images to the traditional acetocarmine stain of the small chromosomes of the woody shrub Thryptomene calycina at all stages of microsporocyte meiosis and microspore mitosis. Hoechst 33258 was slightly superior to DAPI because of reduced background fluorescence. Binding with the DNA-specific probes required a fixative containing chloroform to remove autofluorescent materials, a pretreatment with acetic acid and a pH of least 6 during treatment. The nucleoli did not fluoresce after treatment with DAPI or Hoechst 33258. Superior resolution of chromosomes after treatment with the fluorochromes enabled easy determination of the haploid number at metaphase I, metaphase II and at metaphase of the microspore mitosis.