Dow Elano Europe, Letcombe Laboratory, Letcombe Regis, Oxon, OX12 9JT
Utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi (Lohmann) Kamptner
Article first published online: 28 APR 2006
Volume 120, Issue 1, pages 153–158, January 1992
How to Cite
NIMER, N. A., DIXON, G. K. and MERRETT, M. J. (1992), Utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi (Lohmann) Kamptner. New Phytologist, 120: 153–158. doi: 10.1111/j.1469-8137.1992.tb01068.x
- Issue published online: 28 APR 2006
- Article first published online: 28 APR 2006
- (Received 13 May 1991; accepted 9 September 1991)
- Inorganic carbon utilization;
- photosynthetic oxygen evolution;
- membrane potential
Inorganic carbon-dependent photosynthetic oxygen evolution was saturated at a photon flux density of 100 μmol m−2s−1for air-grown cells of a low calcifying strain of Emittania huxleyi (Lohmann) Kamptner. Measurement of photosynthetic oxygen evolution at constant inorganic carbon concentration but varying pH showed that exogenous bicarbonate was not a major carbon source for photosynthesis. At pH 8.0 the concentration of dissolved inorganic carbon (DIC) required for the half-maximal rate of photosynthetic O2 evolution (K0.5[DIC]) was 2.86 mm; the rate of non-enzymic dehydration of HCO3 greatly exceeding the rate of CO2 fixation. Carbon dioxide uptake occurs by diffusive entry as shown by the K0.5 [DIC] of 12.5 μM at pH 5.0.
Bicarbonate uptake, measured by the silicone-oil-layer centrigual filtering technique, did not show Michaelis-Menten type kinetics. The electrical membrane potential difference was determined from the distribution of the lipophilic cation tetra[3H]phenylphosphonium (TPP+) between cells and the media. Cells grown at pH 8.0 exhibited a negative membrane potential (inside of cell relative to outside) of about −60 mV.