title: Acclimation of wild-type cells and CO2-insensitive mutants of the green alga Chlorella ellipsoidea to elevated [CO2].
abstract: CO(2)-insensitive mutants of the green alga Chlorella ellipsoidea were previously shown to be unable to repress an inorganic carbon-concentrating mechanism (CCM) when grown under 5% CO(2). When air-grown, wild-type (WT) cells were transferred to 5% CO(2), an abrupt drop of P(max) to 43% the original level of air-grown cells was observed within the initial 12 h. Photosynthetic affinities of WT cells to dissolved inorganic carbon (DIC) were maintained at high levels for the initial 4 d of acclimation, and then decreased gradually to lower levels over the next 6 d. In contrast to WT cells, the CO(2)-insensitive mutant, ENU16, exhibited a constant P(max) at maximum levels and a low K(1/2)[DIC] throughout the acclimation period. The rapid P(max) drop within 12 h of acclimation in WT cells was significantly reduced by treatment with 0.5 mm of 6-ethoxybenzothiazole-2-sulphonamide (EZA), a specific membrane-permeable inhibitor of carbonic anhydrase (CA), suggesting the participation of internal CAs in the temporary drop in P(max) in WT cells. WT and ENU16 cells were grown in controlled equilibrium [CO(2)], and the photosynthetic rate of each acclimated cell type was measured under equilibrated growth [DIC] conditions. In WT cells acclimated to 0.14-0.4% [CO(2)], K(1/2)[DIC] values increased as [CO(2)] increased, and the photosynthetic rates at growth DIC conditions were shown to decrease to about 70% the P(max) level in this intermediate [CO(2)] range. Such decreases in the net photosynthetic rates were not observed in ENU16. These results suggest that algal primary production could be depressed significantly under moderately enriched CO(2) conditions as a result of acquiring intermediate affinities for DIC because of their sensitive responses to changes in the ambient [CO(2)].
authors.affiliation: Department of Bioscience, Kwansei-Gakuin University, 2-1 Gakuen, Sanda, Hyogo, 669-1337, Japan.
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Ochiai
authors.forename: Brian
authors.initials: B
authors.lastname: Colman
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Matsuda
mesh_terms: D000064:Acclimatization / Q000187:drug effects; D052160:Benzothiazoles / Q000494:pharmacology; D002245:Carbon Dioxide / Q000378:metabolism*; D002708:Chlorella / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D016296:Mutagenesis; D009154:Mutation; D010788:Photosynthesis / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: C523270:6-ethoxybenzothiazole-2-sulfonamide; D052160:Benzothiazoles; D013449:Sulfonamides; D002245:Carbon Dioxide