An electron microscope study of effects of various fixatives and thin-section enzyme treatments on a nuclear polyhedrosis virus

A comparison of fixatives and embedding media used in thin sectioning of polyhedra and isolated virions of the Pseudoplusia includens nuclear polyhedrosis virus demonstrated that best results are obtained with glutaraldehyde-OsO₄ fixation and epoxy embedding. Fixation was obtained with formaldehyde, acrolein-formaldehyde, or OsO₄ alone but the crystalline array of the polyhedral protein was not preserved. Glycol methacrylate embedding medium resulted in images of poor quality. Treatment of thin sections of polyhedra and virions with enzymes showed that the polyhedral membrane is resistant to digestion with proteases but the interiors of polyhedra were removed with pepsin, pronase, subtilisin, and a mixture of deoxyribonuclease and trypsin. Enzyme treatment of thin sections of virions resulted in removal of the nucleocapsid by all proteases tested except trypsin. A mixture of deoxyribonuclease and trypsin digested the nucleocapsid. The envelope of the virion resisted enzyme treatment.