Detection of Protein-Bound Amino Groups in Plant Tissue by Schiff Base Formation and Azo Coupling

This account pertains to the detection of protein-bound amino groups in fresh, freehand sections of bean cotyledons. Two separate reagents were used: (A) p-aminobenz-aldehyde and (B) p-dimethylaminobenzaldehyde. Both of these compounds, by virtue of their free aldehyde groups, condensed with native amino groups to form their respective Schiff bases. The free amino groups of the resultant Schiff base with reagent A were diaz-otized and coupled with an arylamine, whereas the Schiff base produced in the sections treated with reagent B was treated with nitrous acid to yield its nitroso derivative which was finally coupled with H acid to produce a purple-red dye.