Plant roots release a large number of border cells into the rhizosphere,which act as a chemical,physical and biological interface between roots and their surrounding environment.Interactive effects of low pH and aluminum toxicity on root growth and border cell characteristics were studied.Buckwheat was grown in aeroponic culture for 12 h with Al supply varying from 0,50 to 100 μmol L^-1,and solution pH from 3.5,4.5 to 5.5.Root elongation,border cell viability and mucilage layer of the plant were measured.With Al concentration increasing to 50 μ mol L^-1 and 100 μmol L^-1 root elongation decreased by 18.6% and 31.9% at pH 3.5,by 18.9% and 26.8% at pH 4.5,and by 8.5% both at pH5.5.The effect remained almost the same whether the plant was treated for 12 or 24 hours.With pH value decreasing to 3.5,border cell viability decreased by as much as 28.6%,but the mucilage layer was not much affected.Al treatment at 100 μ mol L^-1 significantly induced a thicker mucilage layer around border cells,about 64.6% thicker.Decreasing pH exacerbated the effect of aluminum toxicity on root growth and border cell characteristics.Lowest activity of border cells and the thickest mucilage occurred under the treatment of pH 3.5 and 100 μ mol L^-1 Al³⁺,which indicated great significant interaction between pH and Al³⁺ 1 The results suggest that low pH and aluminum toxicity act jointly impaire border cells,and the resultant mucilage layer around border cells plays a role of shield against Al damage.