Auxin-induced changes in the molecular weight of hemicellulosic polysaccharides of the avena coleoptile cell wall

The average molecular weight of the water soluble hemicelluloses (hemicellulose B) of the Avena coleoptile cell wall was determined by gel permeation chromatography (GPC) and viscometry. Analysis of the neutral sugar composition of henucellulose B eluted from a GPC column (Sepharose 4B) indicated that it consists of β-glucan with a high molecular weight and arabinoxylan with a low molecular weight. A kinetic study of the effect of auxin on the molecular distribution of henucellulose B demonstrated that auxin decreased the β-glucan content of the hemicellulose as early as the first hour incubation, but not the arabinoxylan content, when it stimulated the extension of the coleoptile segments. Calculation of the weight-average molecular weight from the chromatograms suggested that auxin decreased the molecular weight of hemicellulose B; this was also confirmed by viscometry. Thus, auxin may cause cell wall loosening, leading to cell extension, through its effect on β-glucan degradation or through the decrease in the molecular weight of hemicellulose B.