High-resolution scanning electron microscopy of chromatin bodies and replication bands of isolated macronuclei in the hypotrichous ciliate Euplotes aediculatus

We observed isolated and demembranated macronuclei of Euplotes aediculatus with a field emission scanning electron microscope (JEOL JSM-6401F) to exam ine three-dimensional surface structures of chromatin bodies and the replic ation band. Freezing and thawing in 0.25 M sucrose followed by treatment wi th 1% acetic acid demembranated the isolated macronuclei. Each macronucleus was composed of a large number of granular chromatin bodies of various siz es (0.2-1.0 mu m in diameter). Despite their size variation, each chromatin body was composed of small granules (uniform diameter of ca. 50 nm) with f requent filamentous bridge connections to neighboring chromatin bodies. On the replication band, the chromatin bodies were disintegrated into their co mponent 50 nm granules. In some areas, the surface was observed to be compo sed of smaller particles of ca. 10 nm in diameter.