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The utilization of bicarbonate ions by the marine microalga Nannochloropsis oculata (Droop) Hibberd
Author(s) -
MERRETT M. J.,
NIMER N. A.,
DONG L. F.
Publication year - 1996
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1996.tb00340.x
Subject(s) - bicarbonate , dcmu , dids , alkalinity , photosynthesis , carbonic anhydrase , chemistry , total inorganic carbon , oxygen evolution , photosystem ii , chloride , carbon dioxide , nuclear chemistry , biophysics , biochemistry , membrane , biology , enzyme , organic chemistry , electrode , electrochemistry
HCO 3 − utilization by the marine microalga Nannochloropsis oculata was investigated using a pH drift technique in a closed system. Light‐dependent alkalization of the medium resulted in a final pH of 10.5, confirming substantial HCO 3 − use by this alga. Alkalinity remained constant throughout the pH drift. Measurement of dissolved inorganic carbon (DIC) or the uptake of H 14 CO 3 − showed that nearly 50% of the total DIC remained external to the plasma membrane on completion of a pH drift. The rate of light‐driven alkalization was inhibited by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) and thus was dependent on photosynthesis. Light‐driven alkalization was not inhibited by a membrane‐impermeable inhibitor of carbonic anhydrase (CA), dcxtran‐bound sulphonamide (DBS), indicating that external CA was not involved in HCO 3 − utilization. The anion‐cxchangc inhibitor 4′,4′‐diisothiocyanostilbene‐2,2‐disulphonic acid (DIDS) completely inhibited light‐driven alkalization of the medium and H 14 CO 3 − uptake, providing unequivocal support for a direct uptake of H 14 CO 3 − . Chloride ions were essential for DIC‐dependent photosynthetic oxygen evolution, suggesting that bicarbonate transport occurs by HCO 3 − /CI − exchange.