ON THE POLARITY OF CELLULOSE IN THE CELL-WALL OF VALONIA

The orientation of the triclinic phase of cellulose in the cell wall o f Valonia ventricosa J. Agardh was investigated by X-ray- and electron -diffraction analysis. In addition to the well-documented uniplanar-ax ial organization of the cell wall which requires that the a axis shou ld be always perpendicular to the wall surface, the direction of this axis was also found to be pointing outward from the plasma membrane si de of the wall. This unidirectionality was persistent throughout the v arious layers that constitute the cell wall and also for the three mic rofibrillar orientations that occur in Valonia cell walls. The unidire ctionality of the a axis indicates, in particular, that the Valonia c ellulose microfibrils are not twisted along their axis. These observat ions are consistent with a cellulose biosynthetic scheme where a close association exists between terminal-complex orientations and those of the cellulose microfibrils. In this context, the unidirectionality of the a axis of cellulose seems to be related to the restricted mobili ty of the terminal complexes which are able to slide in the plasma mem brane but not to rotate along their long axis.