Resistance of wheat aleurone cell walls to acid and xylanase action

Isolated wheal (Triticum aestivum var. Potam) aleurone layers have a high c apacity to acidify their environment, and secrete hydrolytic enzymes (endox ylanase, glucanase, alpha -amylase, proteases, etc.) under the control of G A(3). Acidic pH and xylanases are found to be essential for cell wall relax ation in growing tissues, but aleurone is a non-growing, non-dividing tissu e. In this tissue, we studied the effect of these loosening factors on aleu rone cell walls. Exposure to pH 3.0 caused the release of carbohydrates and calcium ions fro m the pericarp, and a small amount of carbohydrates, mainly polysaccharides , from aleurone layers from which pericarp tissue had been removed. 50% of the total sugars released into the incubation medium by these isolated aleu rone tissue was arabinose, but no xylose, calcium ions, or phenolic compoun ds were found. Acid preincubation decreased by 30% the susceptibility of al eurone cell walls to degradation by exogenously-applied endoxylanase, and a lso modified the architecture of cell wail as observed by autofluorescence of phenolic groups. These findings suggest that acid treatment and endoxyla nase action, rather than having a loosening effect on aleurone cell wall, c an have an opposite effect, increasing the resistance of aleurone cell wall s to loosening.