Localization of Xyloglucan in the Macromolecular Complex Composed of Xyloglucan and Cellulose in Pea Stems¹

A macromolecular complex composed of xyloglucan and cellulose was isolated from elongating regions of stems of etiolated pea (Pisum sativum L. var Alaska) seedlings and binding of a xyloglucan-specific antibody was examined after treatment of the complex with endo-1,4-β-glucanase or 24% KOH. The antibody bound to the complex but the extent of binding was reduced after treatment of the complex with endo-1,4-β-glucanase and was hardly detectable after treatment with 24% KOH. The molecular weight of the xyloglucan that remained (5%) in the β-glucanase-treated complexes was less than 9,200. Pea xyloglucan was allowed to bind to enzymeand alkali-treated complexes to generaly reconstituted complexes. The amount of the antibody that bound to each type of reconstituted complex was similar but was much lower than that bound to the native complex. Immunogold labeling indicated that most of the antigen was widely distributed between microfibrils in the native complex, whereas the antigen appeared to be confined to the microfibrils in the reconstituted complexes. These findings suggest that a part of each xyloglucan molecule is strongly associated with cellulose microfibrils while the rest is free of the microfibrils in the native complex.