Evolution of cellular acidic ion accumulation in brown algae and its implication in the phylogeny of Dictyotales

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Cellular pH estimated from cell extract pH and the ion compositions of major inorganic ions(AnィイD1+ィエD1 NHィイD24ィエD2ィイD1+ィエD1, KィイD1+ィエD1, MgィイD12+ィエD1, CaィイD12+,ィエD1 ClィイD1-ィエD1, BrィイD1-ィエD1, NOィイD23ィエD2ィイD1-ィエD1, SOィイD24ィエD2ィイD12-ィエD1) were studied by ion chromatography in 60 species of 10 orders (Dictyotales, Desmarestiales, Ectocarpales, Chordariales, Scytosiphonales, Dictyosiphonales, Cutleriales, Sporochnales, Laminariales and Fucales) of Phaeophyceae. Two species in the order Dictyotales, Dictyopteris sp. and Zonaria stipitata Tanaka et K.Nozawa, were newly found to be highly acidic (pH 1.1 and 1.4 within cells), in addition to previously reported dictyotalean species, Dictyopteris latiuscula (Okamura) Okamura, D.prolifera (Okamura) Okamura, D.repens (Okamura) Bφrgesen and Spatoglossum crassum J.Tanaka. They all contained high concentrations of SOィイD24ィエD2ィイD12-ィエD1 perhaps within the vacuoles. Furthermore, Delamarea attanuata (Kjellman) Rosenvinge (Dictyosiphonales) and Talassiophyllum clathrus (Gmel.) P.et R. (Laminariales) were shown to contain relatively high concentrations of SOィイD24ィエD2ィイD12-ィエD1 balanced by relatively high concentrations of CaィイD12+ィエD1. Molecular phylogenetic study using rbcL gene sequences supported the notion that the accumulation of cellular acidic substances occurred independently in Desmarestiales and Dictyotales. In contrast to the case in Desmarestiales, highly acidic species did not form monophyletic group in Dictyotales.