Abstract: In order to explore changes of cell wall components and boron distribution under low pH in trifoliate root，the different pHs（4，5，6）and boron concentrations（0 and 10 μmol ? L-1）were set up in experiment. The results showed that boron deficiency and low pH could significantly inhibit root growth and elongation. When the boron concentration was suitable，the root length of pH 4 decreased by 26% and 29% compared with that of pH 5 and pH 6. When boron was absent，root dry weight of pH 4 was significantly reduced. However，when adding boron，the dry matter increase of pH 4 was not significant. When boron was enough，the boron content in the underground part of pH 4 increased significantly；compared with pH 6，the proportion of boron in protoplast and free boron to root boron in pH 4 reduced. Compared with pH 6，the proportion of boron in protoplasts to root boron treated by pH 4 increased and the proportion of free boron to root boron was not significantly changed under boron deficiency. Compared with pH 6，the cell wall extraction rate of pH 4 decreased when boron deficiency. Regardless of boron adequate or boron deficiency，pH 4 significantly decreased the content of chelate pectin in the cell wall of the roots of trifoliate. In the suitable boron treatment，the content of alkali soluble pectin treated by pH 4 and pH 5 decreased by 26% and 18% respectively than that of pH 6. The content of alkali soluble pectin treated by pH 4 decreased by about 20% than that of pH 6 and pH 5 treatments under boron deficiency. In addition，when boron deficiency，low pH had little effect on cellulose content in the root of trifoliate. However，the content of cellulose decreased with the decrease of pH value in suitable boron. Compared with pH 6，the cellulose content of pH 4 decreased by 13.8%. Most of the boron was bound to pectin，and the proportion of boron（Alk-B）in alkali soluble pectin was greater than that of chelated pectin（Chel-B）. Obviously，low pH can inhibit the root elongation by affecting the content of boron and components of the root cell wall.

Key words: trifoliate, pH, cell wall, pectin, cellulose, boron content