Xyloglucan: The Molecular Muscle of Trees.

Background: Tension wood evolved in woody angiosperms to allow stems with secondary thickening to bend and thus maintain an optimal orientation. Stem bending is the result of longitudinal tensile stress that develops in tension wood tissues. In many species, a specialized secondary cell wall layer, the so-called gelatinous (G)-layer, develops, containing longitudinally orientated crystalline cellulose fibrils; these have been recently shown to generate the tensile stress by an unknown mechanism. The cellulose fibrils cannot, however, work in isolation. Both coherence between the fibrils and adherence of the G-layer to the adjacent cell wall layers are required to transfer the tensile stresses of the cellulose fibrils to the tissue. Previous work had not identified hemicelluloses within the G-layer. [ABSTRACT FROM PUBLISHER]