INORGANIC CARBON TRANSPORT IN RELATION TO CULTURE AGE AND INORGANIC CARBON CONCENTRATION IN A HIGH-CALCIFYING STRAIN OF EMILIANIA-HUXLEYI (PRYMNESIOPHYCEAE)

The relationships among inorganic carbon transport, bicarbonate availa bility, intracellular pH, and culture age were investigated in high-ca lcifying cultures of Emiliania huxleyi (Lohmann) Hay & Mohler. Measure ment of inorganic carbon transport by the silicone-oil centrifugation technique demonstrated that gadolinium, a potential Ca2+ channel inhib itor, blocked intracellular inorganic carbon uptake and photosynthetic (CO2)-C-14 fixation in exponential-phase cells. In stationary-phase c ells, the intracellular inorganic carbon concentration teas unaffected by gadolinium. Gadolinium was also used to investigate the link betwe en bicarbonate and Ca2+ transport in high-calcifying cells of E. huxle yi. Bicarbonate availability had significant and rapid effects on pH(i ) in exponential- but not in stationary-phase cells. 4',4'-Diisothiocy anostilbene-2,2'-disulfonic acid did not block bicarbonate uptake from the external medium by exponential-phase cells. Inorganic carbon util ization by exponential- and stationary-phase cells of Emiliania huxley i was investigated using a pH drift technique in a closed system. Ligh t-dependent alkalization of the medium by stationary-phase cells resul ted in a final pH of 10.1 and was inhibited by dextran-bound sulphonam ide, an inhibitor of external carbonic anhydrase. Exponential-phase ce lls did not generate a pH drift. Overall, the results suggest that for high-calcifying cultures off, huxleyi the predominant pathway of inor ganic carbon utilization differs in exponential and stationary phase c ells of the same culture.