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Calcification in Chara corallina : CO 2 hydroxylation generates protons for bicarbonate assimilation
Author(s) -
McConnaughey Ted
Publication year - 1991
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1991.36.4.0619
Subject(s) - bicarbonate , calcification , calcareous , chemistry , photosynthesis , chara , carbonate , inorganic chemistry , iodide , divalent , botany , biochemistry , biology , medicine , organic chemistry , pathology
The alga Chara corallina (Charophyta, Charophyceae) apparently generates protons through the hydroxylation and precipitation of CO 2 , which leaks from the cell into highly alkaline pericellular regions. Under mildly alkaline conditions, the loss of CO 2 to calcification is compensated by the production of twice as much CO 2 from HCO 3 − , using the protons generated during calcification. Experiments capitalize on Chara ’ s large cells with their alternating alkaline (calcareous) and acidic (noncalcareous) pericellular zones. 14 C uptake into carbonate and organic phases is fastest when the isotope is applied to the acidic zones. The ratio of calcification to photosynthesis is ∼ 1 at pH 8 and increases with pH approximately as simulated by a model in which both calcification and photosynthesis use carbon assimilated in the acidic zones. PIPES buffer ( pKa = 6.8) inhibits calcification and photosynthesis equally, suggesting competition with bicarbonate as a proton acceptor in the acidic zones. CAPS buffer ( pKa = 10.4) has little effect, suggesting that exogenous bicarbonate is not very important for calcification. Divalent Sr and Mn added to the medium precipitate primarily between the cell and calcareous encrustations, but phosphate does not. This result is consistent with the use of cellular Ca and CO 2 in extracellular calcification.