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Diazonium Compounds Localize Grass Cell Wall Phenolics: Relation to Wall Digestibility

Richard B. Russell Agric. Res. Ctr., USDA-ARS, P.O. Box 5677, Athens, GA 30613

^* Corresponding author.

Phenolic compounds in plant cell walls limit forage digestibility. The objective of this work was to compare three diazonium salts with more widely used lignin stains for their ability to stain phenolic compounds in grass cell walls and to relate the results to cell wall digestibility. Acid phloroglucinol, chlorine-sulfite, azure B, diazotized sulfanilic acid, diazotized p-nitroaniline, or p-nitrobezenediazonium tetrafluoroborate was reacted with a series of low molecular weight phenolic compounds (acids, aldehydes, and esters), lignin extracts, and intact plant cell walls in leaf blades and stems of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.]. In vitro digestibility of individual plant cell walls was assessed by microscopy of sections incubated with rumen fluid. Diazonium salts were more effective than acid phloroglucinol, chlorine-sulfite, or azure B in forming colored compounds with phenolic acids, aldehydes, and esters. Lignin preparations from grasses gave positive reactions with all stains, and differences in color reactions occurred with some plants. Polysaccharides did not have positive histochemical reactions with the exception of larchwood xylan, which apparently contained phenolics that reacted with all stains except acid phloroglucinol and azure B. The diazonium salts and chlorine-sulfite tended to give positive reactions with the same cell wall types, but the salts gave more stable colors and no false negatives. Treatment of a series of warm-and cool-season grass leaf blades with diazotized sulfanilic acid indicated positive reactions with indigestible tissues of both grass types and with the slowly or partially digested cell walls of warm-season grasses. Diazonium compounds offer an improved method to characterize histochemically the phenolics of plant cell walls.

Received for publication November 20, 1989.