The PAS Reaction for Staining Cell Walls

Abstract

INTRODUCTIONThe periodic acid Schiff (PAS) reaction is useful for looking at cell walls, especially in meristematic tissues. Total carbohydrates of insoluble polysaccharides (e.g., starch and cellulose) stain magenta to purplish red. Toluidine blue O or fast green is routinely used as a counterstain to improve contrast. In the gynoecium of the Arabidopsis flower, the transmitting tract cells are made of acid proteoglycans and acid glycoproteins. The cell walls of these cells should be stained with Alcian Blue instead of using the PAS reaction. Alcian Blue, which stains the walls a dark blue, can be used alone or as a counterstain with the PAS reaction to highlight cell walls that do not react with Alcian Blue.