Effect of indole-3-acetic acid on cell wall loosening: Changes in mechanical properties and noncellulosic glucose content of Avena coleoptile cell wall

The effect of indole-3-acetic acid on cell wall loosening and chemical modifications of noncellulosic components of the cell wall in Avena coleoptile segments was studied and the following results were obtained. (1) Auxin decreased both the minimum stress-relaxation time (To) and the noncellulosic glucose content of the cell wall. (2) Decreases were observed in the absence or presence of mannitol solution at concentrations lower than 0.20 m which osmotically suppressed auxin-induced extension, while at concentrations higher than 0.25 m, there was little auxin effect, indicating that it is turgor-dependent. (3) The decrease in To of the cell wall and that in the noncellulosic glucose content caused by auxin in the presence of mannitol solutions of various concentrations paralleled each other (the correlation coefficient was 0.897). (4) Both decreases in To and glucose content caused by auxin were inhibited by nojirimycin (5-amino-5-deoxy-d-glucopyranose) in the presence of mannitol. The results suggest that auxin-induced cell wall loosening is caused by the degradation of noncellulosic rβ-glucan in the cell wall.