ACTIVATION OF OSMIUM AMMINE BY SO2-GENERATING CHEMICALS FOR EM FEULGEN-TYPE STAINING OF DNA

We present herein an improved method for the use of osmium ammine in a Feulgen-type reaction for specific staining of DNA at EM level and an analysis of its Schiff-type reagent behaviour. The activation of osmi um ammine to a Schiff-type reagent (so far routinely performed by bubb ling with gaseous SO2) can be accomplished by adding SO2-generating ch emicals as for light microscopy. When used after HCl hydrolysis on epo n or acrylate sections, activated osmium ammine behaves like a Schiff- type reagent, and the DNA staining can be selectively and completely a bolished by aldehyde blocking agents. This preparation has the advanta ge of eliminating the use of gaseous SO2 thus rendering the technique more widely available to laboratories which cannot handle gas cylinder s containing SO2. We recommend the use of osmium ammine in 8N acetic a cid and 40mM sodium metabisulfite for 1 h at 37 degrees C for epon sec tions, and in 0.2N HCl and 0.2M metabisulfite for 30 min at room tempe rature for acrylate sections.