RELATIONSHIP BETWEEN POLYSACCHARIDE SYNTHESIS AND CELL-WALL LOOSENING IN AUXIN-INDUCED ELONGATION OF RICE COLEOPTILE SEGMENTS

Polysaccharide synthesis inhibitors 2,6-dichlorobenzonitrile (DCB) at 10(-6) M, monensin at 10(-7) M and galactose at 3 x 10(-3) M and above suppressed elongation growth of intact rice coleoptiles submerged in water. Auxin (indoleacetic acid)-induced elongation of excised rice coleoptiles was suppressed by monensin and galactose, but not by DCB at these concentrations. Neither monensin nor galactose influenced the minimum stress-relaxation time and the relaxation rate of the cell wall of coleoptile segments. DCB inhibited the incorporation of [C-14]glucose into the cellulosic polysaccharides without affecting that into the matrix polysaccharides, while monensin and galactose inhibited the incorporation into both the matrix and the cellulosic polysaccharides. Thus, only the synthesis of matrix polysaccharides is required for auxin-induced elongation and the synthesis is not directly related to cell wall loosening in rice coleoptile segments. The synthesis of matrix polysaccharides may contribute to auxin-induced cell elongation by fixing or extending polymers already present in the cell wall.