Figure 9.

MALDI-TOF Mass Spectra of Acidic Oligoxylan Products Generated by β-Endoxylanase Digestion of the 4 N KOH Fractions from Wild-Type and fra8 Stems.

(A) General structures of the oligoxylans.

(B) Oligosaccharides from wild-type plants.

(C) Oligosaccharides from fra8 plants.

(D) Oligosaccharides from fra8 plants complemented with the wild-type FRA8 gene.

Two series of ions showing a mass increment of 132 D (corresponding to one xylosyl residue) were observed in all the spectra. These series correspond to oligosaccharides composed of four to six Xyl residues bearing a 4-O-Me-GlcA residue (X₄M, X₅M, and X₆M) or a nonmethylated GlcA residue (X₄G, X₅G, and X₆G). The abundance of X_nG oligosaccharides with a nonmethylated glucuronic acid was reduced drastically in the oligosaccharides isolated from fra8 plants (C) compared with the wild type (B). Complementation of the fra8 mutant with the wild-type FRA8 gene (D) restored the production of X_nG oligosaccharides with a nonmethylated glucuronic acid residue.