title: Effects of Ca and Mg on growth and calcification of the coccolithophorid Pleurochrysis haptonemofera: Ca requirement for cell division in coccolith-bearing cells and for normal coccolith formation with acidic polysaccharides.
abstract: The effects of Ca2+ and Mg2+ on cellular growth and calcification in Pleurochrysis haptonemofera were investigated. In the presence of a normal concentration of Mg2+, coccolith-bearing cells (C-cells) required more than 0.5 mM Ca2+ for growth, while naked cells could grow even with 0.5 mM Ca2+. The calcification rate of C-cells, which was determined using decalcified cells, was significantly repressed with less than or equal to 0.5 mM Ca2+. Although the calcification rate did not change so much with 5-30 mM Ca2+, it decreased with higher concentrations of Ca2+, as well as C-cell-specific growth repression. Under these conditions, Ca2+ affected the rate of coccolith formation, but neither the coccolith morphology nor total amounts and ratios of divalent cations and acidic polysaccharides (Ph-PS-1, -2, and -3) were included in coccoliths. These findings suggest that sufficient calcification is required for the division of C-cells. Under low Ca2+ and high Mg2+ conditions, coccoliths with an abnormal morphology, having immature shield elements, were synthesized. Composition analysis of the coccoliths revealed high Mg/Ca and low Ph-PS-2/(Ph-PS-1 and -3) ratios, as compared with those under low Ca2+ and normal Mg2+ conditions, suggesting that the abnormal morphology is due to a change in the crystal type and/or acidic polysaccharide composition.
authors.affiliation: School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Katagiri
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Takatsuka
authors.forename: Shoko
authors.initials: S
authors.lastname: Fujiwara
authors.forename: Mikio
authors.initials: M
authors.lastname: Tsuzuki
mesh_terms: D002118:Calcium / Q000008:administration & dosage* / Q000378:metabolism*; D002119:Calcium Carbonate / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D056890:Eukaryota / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000008:administration & dosage*; D011134:Polysaccharides / Q000737:chemistry*
chemical_list: D011134:Polysaccharides; D002119:Calcium Carbonate; D008274:Magnesium; D002118:Calcium