Comparison of Root Apical Cell Wall Response to Aluminum Stress between Polygonaceae Plants and Rape

In this study,3 polygonaceae plants (Polygonum lapathifolium,Polygonum perfoliatum,Polygonum hydropiper) and 2 genotypes of rape (Brassica campestris L.cv.Xiangyou NO.3 and cv.Ganyou NO.2) were used to investigate the relationship between the effects of aluminum (Al) on root elongation and the amount of root apical cell wall polysaccharides.The results showed that the root elongation was decreased with increase of Al concentrations applied,but the inhibition was more conspicuous for rape,indicating higher Al resistance in polygonaceae plants,with the highest Al resistance for Polygonum lapathifolium and Al sensitivity for Ganyou NO.2.In 5 plants,the Al content in 0～10 mm root segments was significantly higher than that in 10～20 mm,and the Al content of 0～10 mm root segments was evidently higher in rape than in polygonaceae plants.The amount of cell wall pectin,hemicellulose 1,hemicellulose 2 in 0～10 mm root segments increased under Al stress,especially in Al-sensitive genotype Ganyou NO.2.Whether the roots were exposed to Al or not,the amount of cell wall polysaccharides in 0～10 mm root segments was higher in 2 rape cultivars than in 3 polygonaceae plants especially for Polygonum lapathifolium.Reducing the methylation degree of pectin in cell walls with 1.0 mol/L NH3·H2O for 2 h,the accumulated amount of Al in cell wall was decreased,especially in 2 rape cultivars.These findings suggested that lower contents of cell wall pectin,hemicellulose 1,hemicellulose 2 and higher degree of pectin methylation in 0～10 mm root segments,which decreased root apical Al content and thereby improved root growth,were important reasons for the highest Al resistance in Polygonum lapathifolium.