Staining Plant Cells with Silver. III. The Mechanism

Silver does not stain all cytological structures with the same intensity. The chemical basis for differential silver staining is unclear, but differences in protein side groups available to react with silver are likely involved. These include amine, carboxyl, phosphate, sulfhydryl and hydroxyl moieties. Here we report an investigation of the chemical groups that could be involved in salt-nylon silver staining of onion root tip squashes. Based on the results, we conclude that SN silver staining primarily depends on the presence of tyrosine hydroxyl groups, and we propose a mechanism for staining.