Enhanced Hoechst 33258 fluorescence in plants.

The topological features of isolated Chinese hamster ovary metaphase chromosomes were studied with high resolution scanning electron microscopy (SEM) using the techniques of direct current sputtering for the deposition of metal on the specimens. Metaphase chromosome surfaces consist of numerous compact microconvules of an average diameter of 520 ± 78 Å when corrected for the thickness of the gold-palladium coating (80 ± 2 Å). These microconvules contain several orders of supercoiling. The superhelical structures were detected also in water-spread preparations. Most of the isolated chromosomes had membrane-like structures attached at the distal portions of the chromatids forming a terminal “plate”. Limited tryptic digests of such isolated chromosomes resulted in considerable stretching of the chromatids and revealed a series of interchromatidal fibers with diameters of 203 ± 38 Å (corrected for gold coating). Treatment of these chromosomes with EDTA revealed a longitudinal array of fibers within the chromatids. The diameters of these fibers decreased as the concentration of EDTA was increased. The technique of direct current sputtering for the preparation of chromosomes for scanning microscopy is satisfactory for detailed topological ultrastructural studies in the 70 Å range.