Fucosylated high molecular mass but not non-fucosylated low molecular mass xyloglucans undergo an extensive depolymerization in cell walls of azuki bean epicotyls

摘要

Epicotyl cuttings of azuki bean were incubated with [C-14]-glucose (Glc) or [H-3]-fucose (Fuc), and the metabolism of radiolabeled polymers in the 24% KOH-extractable cell wall fraction was investigated. Applied C-14-Glc and H-3-Fuc were predominantly incorporated into the glucan backbone and Fuc residue of xyloglucan molecules, respectively. On gel permeation chromatography, C-14-polymers consisted of a main peak (0.7-1.0 MDa) and shoulder peak (30 kDa). The pattern was similar to that of iodine-reactive xyloglucans in the fraction. On the other hand, H-3-polymers consisted of a single peak eluted around 0.7-1.0 MDa. The elution patterns of C-14- and H-3-polymers were constant during the incubation period, although incorporated radioactivity increased with time. In the pulse-chase experiment, the high molecular mass peaks (0.7-1.0 MDa) of both C-14- and H-3-polymers showed an extensive molecular mass downshift, but not the shoulder peak of C-14-polymers. These results indicate that xyloglucans in the fraction consist of two types of molecules; fucosylated high molecular mass polymers and non-fucosylated low molecular mass polymers. Azuki bean epicotyls may synthesize both types of xyloglucans independently, but only fucosylated xyloglucans undergo an active depolymerization in the cell wall. (C) 2010 Published by Elsevier GmbH.