Utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi (Lohmann) Kamptner

• Published in: The New phytologist Vol. 120; no. 1; pp. 153 - 158
• Main Authors: Nimer, N.A, Dixon, G.K, Merrett, M.J
• Format: Journal Article
• Language: English
• Published: Oxford, UK Cambridge University Press 1992; Blackwell Publishing Ltd; Blackwell
• Subjects: Algae; algae and seaweeds; Bicarbonates; Biological and medical sciences; carbon; Carbon dioxide; Centrifugation; Emiliania; Flux density; Fundamental and applied biological sciences. Psychology; gas exchange; Inorganic carbon utilization; inorganic compounds; Membrane potential; Metabolism; Microalgae; Oxygen; Photons; Photosynthesis; Photosynthesis, respiration. Anabolism, catabolism; photosynthetic oxygen evolution; Plant physiology and development; Enzymatic activity; Carbonic anhydrase; Enzyme; Membrane transport; Algae; Chrysophycophyta; Membrane potential; Metabolism; Photosynthesis; Carbon; Thallophyta; Hydrogencarbonates
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.1992.tb01068.x

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 Emiliania 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 O2evolution (K0.5[DIC]) was 2.86 mM; the rate of non-enzymic dehydration of HCO3 -greatly exceeding the rate of CO2fixation. 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.