Cellulose microfibril assembly and orientation in some bangiophyte red algae: relationship between synthesizing terminal complexes and microfibril structure, shape, and dimensions

Abstract As shown by freeze-fracture electron microscopy, the linear terminal complexes (TCs) in Erythrocladia subintegra Rosenvinge, Erythrotrichia carnea (Dillwyn) J. Agardh, Porphyra leucosticta Thuret, and Porphyra yezoensis Ueda typically have regularly spaced rows of particles aligned transverse to the longitudinal axis of the TCs. The spacing between neighboring transverse particle rows is almost constant and ranges from 10.5 to 13.5 nm among the four species. The TC subunits appear to be interconnected by filament-like structures in transverse as well as longitudinal directions along the long axis of the TC. In the investigated species, both linear TCs and microfibrils are randomly distributed and the microfibrils show a flat, ribbon-like morphology. Isolated cellulose microfibrils in negatively stained preparations from Erythrocladia and Porphyra appear as thin, ribbon-shaped structures, 1 to 1.5 nm thick (constant) and 5 to 70 nm wide (variable). It is proposed that each protein particle subunit...