The marine red alga Erythrocladia subintegra synthesizes cellulose microfibrils as determined by CBH I-gold labeling, X-ray and electron diffraction analyses. The cellulose microfibrils are quite thin, ribbon-like structures, 1-1.5nm in thickness (constant), and 10-33 nm in width (variable). Several laterally associated minicrystal components contribute to the variation in microfibrillar width. Electron diffraction analysis suggested a uniplanar orientation of the microfibrils with their (101) lattice planes parallel to the plasma membrane surface of the cell. The linear particle arrays bound in the plasma membrane and associated with microfibril impressions recently demonstrated in Erythrocladia have been shown in this study to be the cellulose-synthesizing terminal complexes (TCs). The TCs appear to be organized by a repetition of transverse rows consisting of four TC subunits, rather than by four rows of longitudinally- arranged TC subunits. The number of transverse rows varied between 8-26, corresponding with variation in the length of the TCs and the width of the microfibrils. The spacings between the neighboring transverse rows are almost constant being 10.5-11.5 nm. Based on the knowledge that Acetobacter, Vaucheria, and Erythrocladia synthesize similar thin, ribbon-like cellulose microfibrils, the structural characteristics common to the organization of distinctive TCs occurring in these three organisms has been discussed, so that the mode of cellulose microfibril assembly patterns may be deciphered.
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