Changes in cell-wall properties of wheat (Triticum aestivum) roots during aluminum-induced growth inhibition

The effects of aluminum (Al) on root elongation, the mechanical extensibili ty of the cell wall, and the amount of cell-wall polysaccharides in the roo ts of Al-resistant (Atlas 66) and Al-sensitive (Scout 66) cultivars of whea t (Triticum aestivum L.) were examined. Exposure to 10 rhoM AlCl3 for 6 h i nhibited root elongation in Scout 66 but not in Atlas 66. It also decreased the mechanical extensibility of the cell wan in the roots of both cultivar s, but prominently only in the roots of Scout 66. The amount of hemicellulo se in the 10-mm region of root apex of Scout 66 was increased by the exposu re to Al, especially in the apical regions. Al did not influence the neutra l sugar composition of either pectin or hemicellulose in Scout 66 roots. Ho wever, Al increased the weight-average molecular mass of hemicellulosic pol ysaccharides and the amounts of wall-bound ferulic and diferulic acids in S cout 66 roots. These findings suggest that Al modifies the metabolism of ce ll-wall components and thus makes the cell wall thick and rigid, thereby in hibiting the growth of wheat roots.