Abstract: The response of root systems of Al-resistant(Xiaimai-1) and Al-sensitive(Fu-84) wheat(Triticum aestivum L.) genotypes to Al toxicity and the relation between root tip cell wall composition and Al adsorption/desorption by root apex cell walls were examined in this paper.Root elongation of both genotypes was markedly inhibited when wheat roots were exposed to 30 mol/L AlCl3 solutions for 24 h,but the inhibition was more conspicuous for Fu-84.Relative root elongation rate of wheat genotypes was markedly decreased with the increasing of the Al concentration,and the inhibitory rate of root elongation was 33.3% for Xiaimai-1 and 70.9% for Fu-84 after 24 h treatment of 30 mol/L AlCl3.In both genotypes,the content of accumulated Al,pectin uronic acid and the amount of Al adsorbed by the cell walls in 0-10 mm root segments was significantly higher than those in 10-20 mm,but the desorption rate was slightly lower in cell walls of 0-10 mm root segments than that of 10-20 mm in Fu-84,however desorption rate had no difference in Xiaimai-1 between different root segments.In 010 mm root segments,the cell wall pectin content of Fu-84 was significantly higher than that of Xiaimai-1.Al content in the root tips and the amount of Al adsorption by the root tip cell wall in Fu-84 were higher than those in Xiaimai-1.Decreasing the degree of methylation(DM) of pectin in cell walls with 1.0 mol/L NH3H2O for 2 h,the total amount Al absorbed was decreased about 17.1% in Xiaimai-1 and 20.9% in Fu-84,while the effect on desorption rate was negligible.The preliminary results showed that root tip was the primary site of Al toxicity,and differences in pectin content and DM of pectin in cell wall of root tips contributed to genotypic differences in Al accumulation in root tips and thus Al resistance of wheat.