title: Uptake of CO(2) and bicarbonate by intact cells and chloroplasts of Tetraedron minimum and Chlamydomonas noctigama.
abstract: Using a mass-spectrometric disequilibrium technique, net uptake of HCO(3)(-) and CO(2) during steady-state photosynthesis was studied in whole cells and chloroplasts from the green algae Tetraedron minimum and Chlamydomonas noctigama, grown in air enriched with 5% (v/v) CO(2) (high-CO(2) cells) or in air [0.035% (v/v) CO(2); low-CO(2) cells]. High- and low-CO(2) cells of both species were able to take up CO(2) and HCO(3)(-), with maximum rates being largely unaffected by the growth conditions. High- and low-CO(2) cells of T. minimum showed a pronounced preference for HCO(3)(-) while the rates of net HCO(3)(-) and CO(2) uptake were similar in C. noctigama. The most significant differences between high- and low-CO(2) cells of the two species were the 5- to 6-fold increase in the apparent affinities of net HCO(3)(-) uptake and CO(2) uptake after acclimation to air. The high-affinity uptake systems for inorganic carbon were almost completely induced within 4 h in both algae. Photosynthetically active chloroplasts isolated from both species were also able to take up CO(2) and HCO(3)(-). As in whole cells, HCO(3)(-) was the dominant carbon species taken up by chloroplasts from T. minimum while CO(2) and HCO(3)(-) were taken up at similar rates in plastids from C. noctigama. In addition, high-affinity uptake systems for CO(2) and HCO(3)(-) were detected in chloroplasts preparations after acclimation of the parent cells to air. Isolation of ribulose-1,5-bisphosphate carboxylase/oxygenase revealed K(m) values of 13 and 42 micro M CO(2) for the enzymes from T. minimum and C. noctigama, respectively. These results are consistent with the presence of inducible and energy-dependent high-affinity HCO(3)(-) and CO(2) uptake systems associated with chloroplasts, indicating that these organelles play an important role in the CO(2)-concentrating mechanism.
authors.affiliation: FB-Biologie, Postfach 3049, 67653 Kaiserslautern, Germany.
authors.forename: E
authors.initials: E
authors.lastname: van Hunnik
authors.forename: G
authors.initials: G
authors.lastname: Amoroso
authors.forename: D
authors.initials: D
authors.lastname: Sültemeyer
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism* / Q000494:pharmacology; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism* / Q000494:pharmacology; D002696:Chlamydomonas / Q000166:cytology / Q000378:metabolism; D000460:Chlorophyta / Q000166:cytology / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide; D002244:Carbon; D012273:Ribulose-Bisphosphate Carboxylase; D010100:Oxygen