Lorences, E. P. and Zarra, I. 1987. Auxin-induced growth in hypocotyl segments of Pinus pinaster Aiton. Changes in molecular weight distribution of hemicellulosic polysaccharides.—J. exp. Bot. 38: 960–967. The changes in the molecular weight distribution of water-soluble hemicelluloses and xyloglucan during auxin-induced growth of Pinus pinaster Aiton hypocotyl sections were investigated. IAA induced an increase in the relative amount of a high molecular weight polysaccharide (MW ≥ 5 × 106) and a depolymerization of the xyloglucan present in the water-soluble hemicelluloses extracted with 4% KOH. Moreover, the increase in the mean molecular weight distribution of total polysaccharides and xyloglucan of the water-soluble hemicelluloses extracted with 24% KOH was suppressed by auxin. We suggest that the decrease in the mass-average molecular weight of cell wall xyloglucan plays a critical role in the process responsible for the auxin-induced cell wall extension in gymnosperm plants, as has been demonstrated for monocot and dicot plants.