Auxin-Induced Changes in the Molecular Weight Distribution of Cell Wall Xyloglucans in Avena Coleoptiles

The effect of auxin on the molecular weight (Mw) distribution of cell wall xyloglucans was investigated by gel permeation chromatography using coleoptile segments of Avena sativa L. cv. Victory, and the following results were obtained. The water-insoluble hemicellulose (HC-A) mainly consisted of xyloglucans. Iodine staining method revealed that relatively large amounts of xyloglucans were present in the water-soluble hemicellulose (HC-B) and water-soluble polysaccharide (WS) fractions. IAA did not cause remarkable changes in xyloglucan contents in the hemicellulose, but significantly increased the xyloglucan content in the WS fraction. IAA substantially decreased the weight-average Mw of HC-A. This effect became apparent within 30 min of the incubation period, and was not affected by the 0.15 M mannitol or 2% sucrose applied. Hydrogen ions also caused a decrease in the weight-average Mw of HC-A; its effect being reversible. Neither IAA nor hydrogen ions caused any remarkable changes in the weightaverage Mw of water-soluble xyloglucans in the HC-B. These results suggest that cell wall xyloglucans have an important role in auxininduced cell wall loosening in oat coleoptile cells.