Comparisons of three dry application autoradiographic techniques

We compared three common dry application techniques applied for the first time to phytoplankton taking up water-soluble radioisotopically labeled substrates. Following incubation of live phytoplankton communities in oligotrophic, nitrogen-limited Mountain Lake, Virginia, with Carbon-14 labeled methylamine-hydrochloride, an ammomium analog, we concentrated cells on 0.8 um pore size Millipore filters, then preserved filters in liquid nitrogen, and freeze-dried. Differences in the techniques are application of stripping film, preparation of freshly prepared film by dipping loops into liquid emulsion, and dipping cover slips in liquid emulsion. Following dark-incubation and development, autoradiographs were evaluated microscopically for reproducibility, fine resolution of silver grains, background scatter, and eaes of technique