Evaluation of stabilised diazonium salts for the detection of phenolic constituents of plant cell walls

Sections from laminae of perennial ryegrass and internodes of the annual ryegrass, Lolium termulentum, and red clover were treated with 11 stabilised diazonium salts at pH values between 5 and 9. The walls of cell types which fluoresced blue in ultraviolet radiation in the presence of NH3, and which gave red colorations with phloroglucinol‐HCl and Cl2‐Na2SO3 suggesting the presence of lignin, also gave colours with the diazonium salts. After treatment with the salts, lignified walls of grasses gave colours that were of longer wavelength than similar walls of red clover. The most distinct and most intense red colorations were given by p‐nitrobenzenediazonium tetrafluoroborate. Lignified walls were either undigested or only partially digested by rumen liquor. In contrast, unlignified walls gave little or no colour with the diazonium salts and were readily digested by the liquor.