CHROMOSOME CONDENSATION AND HOECHST 33258 FLUORESCENCE IN MEIOTIC CHROMOSOMES OF THE GRASSHOPPER SPATHOSTERNUM-PRASINIFERUM (WALKER)

Patterns of Hoechst 33258 fluorescence have been studied in grasshopper chromosomes. At metaphase of mitotic as well as meiotic divisions - when chromosomes were maximally compact - all the chromosomes fluoresced brightly but no differentially fluorescing regions were detected. However, when all the chromosomes, except the X, were highly extended at pachytene and diplotene stages a distinct differential fluorescence was observed: only the centromeres of the autosomal bivalents fluoresced brightly whereas the entire X univalent showed bright fluorescence. Restriction of differentially bright fluorescence to the more condensed regions of chromosomes suggests a modulatory role for chromosome condensation in the production of Hoechst fluorescence. This suggestion was further strengthened by the substantial quenching of fluorescence caused by removal of chromosomal proteins following treatment with H2SO4. Similarly, post-C-band-treatment staining with Hoechst also led to quenching, though now the centromeres of the chromosomes, including the X, retained their differential fluorescence. It is proposed, therefore, that in grasshopper chromosomes, H-fluorescence is modulated by chromosome condensation brought about by differential ratios of DNA/protein at different chromosome regions and at different division stages. © 1979 Springer-Verlag.