Investigation on diversity in the structure of cellulose-synthesizing terminal complexes among algal groups possessing chlorophyll a and c.

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The structure of cellulose microfibrils (CMFs) and cellulose-synthesizing terminal complexes (TCs) in some species with chlorophyll a and c such as phaeophycean, xanthophycean and dinophycean algae was examined by freeze fracture electron microscopy. Both of Sphacelaria rigidula (Phaeophyceae) and Botridium sp. (Xanthophyceae) synthesized ribbon-like CMFs. However, Sphacelaria had TCs whose subunits are arranged in a single linear row, whereas TCs in Botridium consisted of several diagonal rows of subunits. It was found first that alginates are present in Xanthophyceae besides in Phaeophyceae, indicating a phylogenetically close relationship between Xanthophyceae and Phaeophyceae. These results suggest that the TCs in both or either of - Xanthophyceae and/or Phaeophyceae had been acquired at divergence of these two clades. It was evident in the dinophycean Scrippsiella hexapraecingra that the thecal plates contain CMFs which form bundles consisting of several fine components by electron diffraction methods. A new TC was found in this alga.