Uptake of HCO₃ and CO₂ in Cells and Chloroplasts from the Microalgae Chlamydomonas reinhardtii and Dunaliella tertiolecta¹

Gabi Amoroso, Dieter Sültemeyer^*, Christoph Thyssen, and Heinrich P. Fock

Fachbereich Biologie der Universität, Postfach 3049, D-67653 Kaiserslautern, Germany

Mass-spectrometric disequilibrium analysis was applied to investigate CO₂ uptake and HCO₃ transport in cells and chloroplasts of the microalgae Dunaliella tertiolecta and Chlamydomonas reinhardtii, which were grown in air enriched with 5% (v/v) CO₂ (high-Ci cells) or in ambient air (low-Ci cells). High- and low-Ci cells of both species had the capacity to transport CO₂ and HCO₃, with maximum rates being largely unaffected by the growth conditions. In high- and low-Ci cells of D. tertiolecta, HCO₃ was the dominant inorganic C species taken up, whereas HCO₃ and CO₂ were used at similar rates by C. reinhardtii. The apparent affinities of HCO₃ transport and CO₂ uptake increased 3- to 9-fold in both species upon acclimation to air. Photosynthetically active chloroplasts isolated from both species were able to transport CO₂ and HCO₃. For chloroplasts from C. reinhardtii, the concentrations of HCO₃ and CO₂ required for half-maximal activity declined from 446 to 33 µm and 6.8 to 0.6 µm, respectively, after acclimation of the parent cells to air; the corresponding values for chloroplasts from D. tertiolecta decreased from 203 to 58 µm and 5.8 to 0.5 µm, respectively. These results indicate the presence of inducible high-affinity HCO₃ and CO₂ transporters at the chloroplast envelope membrane.

Plant Physiol. (1998) 116: 193-201
Copyright Clearance Center:   0032-0889/98/116/0193/09
© 1998 American Society of Plant Physiologists

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