Fine structure of hydrous chromosomes observed by low vacuum scanning electron microscopy.

Chinese hamster metaphase chromosomes were stained with platinum (Pt) blue and observed in the hydrous state with low vacuum scanning electron microscopes (LVSEM). The coiled structure of the chromatin fibers in the chromosomes was well recognized through the surrounding perichromosomal substances in the backscattered electron (BSE) mode at accelerating voltages of over 20 kV. Findings indicated that chromatin fibers in native chromosomes have a structure similar to the hierarchic coiled model. The present study also demonstrated that not only surface structures but also subsurface structures can be studied in the BSE mode of LVSEM, when the subsurface structures have been stained with heavy metal salts such as Pt blue.