The present study was conducted to investigate the cell wall properties in two wheat (Triticum aestivum L.) cultivars differing in their sensitivity to Al stress. Seedlings of Al-resistant, Inia66 and Al-sensitive, Kalyansona cultivars were grown in complete nutrient solutions for 4 days and then subjected to treatment solutions containing Al (0, 50 microM) in a 0.5 mM CaCl(2) solution at pH 4.5 for 24 h. Root elongation was inhibited greatly by the Al treatment in the Al-sensitive cultivar compared to the Al-resistant cultivar. The Al-resistant cultivar accumulated less amount of Al in the root apex than in the Al-sensitive cultivar. The contents of pectin and hemicellulose in roots were increased with Al stress, and this increase was more conspicuous in the Al-sensitive cultivar. The molecular mass of hemicellulosic polysaccharides was increased by the Al treatment in the Al-sensitive cultivar. The increase in the content of hemicellulose was attributed to increase in the contents of glucose, arabinose and xylose in neutral sugars. Aluminum treatment increased the contents of ferulic acid and p-coumaric acid especially in the Al-sensitive cultivar by increasing the activity of phenylalanine ammonia lyase (PAL, EC 4.3.1.5). Aluminum treatment markedly decreased the beta-glucanase activity in the Al-sensitive cultivar, but did not exert any effect in the Al-resistant cultivar. These results suggest that the modulation of the activity of beta-glucanase with Al stress may be involved in part in the alteration of the molecular mass of hemicellulosic polysaccharides in the Al-sensitive cultivar. The increase in the molecular mass of hemicellulosic polysaccharides and ferulic acid synthesis in the Al-sensitive cultivar with Al stress may induce the mechanical rigidity of the cell wall and inhibit the elongation of wheat roots.