The Cellulose System in the Cell Wall ofMicrasterias

Abstract

The cellulose system of the cell wall ofMicrasterias denticulataandMicrasterias rotatawas analyzed by diffraction contrast transmission electron microscopy, electron diffraction, and X-ray analysis. The studies, achieved on disencrusted cell ghosts, confirmed that the cellulose microfibrils occurred in crisscrossed bands consisting of a number of parallel ribbon-like microfibrils. The individual microfibrils had thicknesses of 5 nm for a width of around 20 nm, but in some instances, two or three microfibrils merged into one another to yield larger monocrystalline domains reaching up to 60 nm in lateral size. The orientation of the cellulose ofMicrasteriasis very unusual, as it was found that in the cell wall, the equatorial crystallographic planes of cellulose having ad-spacing of 0.60 nm [(110) in the Iβ cellulose unit cell defined by Sugiyamaet al.,1991,Macromolecules24, 4168–4175] were oriented perpendicular to the cell wall surface. Up to now, such orientation has been found only inSpirogyra,another member of the Zygnemataceae group. The unusual structure of the secondary wall cellulose ofMicrasteriasmay be tentatively correlated with the unique organization of the terminal complexes, which in this alga occur as hexagonal arrays of rosettes.