Inorganic Carbon Accumulation and Photosynthesis in a Blue-green Alga as a Function of External pH

SyecococcEs lkopoliensis was grown in HCO03-limited chemostats.Growth at 50% the maximum rate occurred when the inorganic carbon concentration was 10 to 15 micromolar (or 5.6 to 8. nanomolar C02). The 02 to CO2 ratios during growth were as high as 192,000 to 1. At growth rates below 80% the maximum rate, essentially all the supplied inorganic carbon was converted to organic carbon, and the cells were carbon limited. Carbon-limited cells used HCO3-rather than CO2 for growth. They also exhibited a very high photosynthetic affinity for inorgnic carbon in short-term experiments. Cells growing at greater than 80% maximum growth rate, in the presence of high dissolved inorganic carbon, were termed carbon sufficient. These cells had photosynthetic affinities that were about 1000-fold lower than HCO3-limited cells and also had a reduced capacity for HC03-transport. HCO3--limited cells are reminiscent of the air-grown cells of batch culture studies while the carbon sufficient cells are reminiscent of high-CO2 grown cells. However, the low affinity cells of the present study were growing at CO2 concentrations less than air saturation. This suggests that supranormal levels of CO2 not required to induce the physiological changes usually ascribed to high CO2 cells.

“…5). Such accumulations are fully consistent with those measured during short-term experiments (4,9,17,22,26). These calculations (Fig.…”

Section: Methodssupporting

confidence: 79%

mentioning

confidence: 99%

Growth and Photosynthesis of the Cyanobacterium Synechococcus leopoliensis in HCO₃⁻-Limited Chemostats

Miller

Turpin²,

Canvin³

1984

“…It is evident that many microalgae take up inorganic carbon in the form of HCO3 (1,8,11,12,16,19,20), causing an accumulation of inorganic carbon in the cells (1,8,16,21) which results in the maintenance of low CO2 compensation points. The drop in specific radioactivity of '4C-inorganic carbon external to algae which has been measured in the present study, appears to be inconsistent with the presence of an active uptake system.…”

Section: Discussionmentioning

confidence: 99%

“…All assays were performed at the temperatures used for growth of the algae. NaH 4CO3 (2)(3)(4)(5)(6)(7)(8)(9)(10)iCi) was added to the cells and a 3 to 5 ml sample withdrawn in a syringe to determine the initial total DIC and 4C activity. Following separation of the cells by membrane filtration(4), 0.5 ml cellfree medium was added to 0.5 ml ethanolamine in a scintillation vial, and 0.25 to 0.5 ml injected directly into a modified gas chromatograph to determine total DIC (4).…”

Section: Introductionmentioning

confidence: 99%

Measurement of Photorespiration in Algae

Birmingham¹,

Coleman²,

Colman³

1982

Self Cite

The rates of true and apparent photosynthesis of two unicellular green algae, one diatom and four blue-green algae were measured in buffer at pH 8.0 at subsaturating concentrations of dissolved inorganic carbon (13-27 micromolar). Initial rates of depletion from the medium of inorganic carbon and "C activity caused by the algae in a closed system were measured by gas chromatography and by liquid scintillation couating, respectively. The rate of photorespiration was calculated as the difference between the rates of apparent and true photosynthesis. The three eucaryotic algae and two blue-green algae had photorespiratory rates of 10 to 28% that of tre photosynthesis at air levels of 02. Reduction of the 02 level to 2% caused a 52 to 91% reduction in photorespiratory rate. Two other blue-green algae displayed low photorespiratory rates, 2.4 to 6.2% that oftrue photosynthesis at air levels of 02, and reduction of the 02 concentration had no effect on these rates. (668) were obtained from the culture collection ofalgae at the University of Texas, Austin (culture collection numbers in parentheses). Phormidium molle was a gift from Dr. S. R. Brown, Queen's University, Kingston, Ontario.Algae were grown in batch culture without the addition of supplementary CO2 as previously described (4). Cells were harvested by centrifugation at 3,000g for 10 min, and resuspended in 50 mM K-phosphate (pH 7.8-8.0) which had been previously flushed with either 'COrfree' N2 or air to establish low or airsaturated levels of dissolved 02. The algal suspension was contained in an illuminated, water-jacketed cylindrical glass vessel sealed from the air with a layer of mineral oil as previously described (7) and the algae maintained in suspension by stirring with a magnetic stirrer. Light intensity for photorespiration measurements was 4 x 105, w cm-2. All assays were performed at the temperatures used for growth of the algae. NaH 4CO3 (2)(3)(4)(5)(6)(7)(8)(9)(10)iCi) was added to the cells and a 3 to 5 ml sample withdrawn in a syringe to determine the initial total DIC and 4C activity. Following separation of the cells by membrane filtration(4), 0.5 ml cellfree medium was added to 0.5 ml ethanolamine in a scintillation vial, and 0.25 to 0.5 ml injected directly into a modified gas chromatograph to determine total DIC (4). The depletion of DIC and radioactivity in the medium was similarly determined at timed intervals, after the lights had been turned on. To monitor release of acid-stable "4C-labeled compounds during photosynthesis, 0.5 ml cell-free medium was added to 0.5 ml 50%o glacial acetic acid and gently flushed with CO2 gas for 20 to 30 min prior to addition of 10 ml Bray's cocktail for liquid scintillation counting.Rates of true photosynthesis, apparent photosynthesis and photorespiration were calculated from the rates of 14C uptake and DIC uptake in the light following the method of Hew et al. (15).The rate of TPS was calculated from the initial rate of depletion of 14C activity in the medium over the initial 2 to 4 min ...

“…Plants which photosynthesize by the C4 photosynthetic pathway have certain gas exchange characteristics similar to those of the air-adapted algae due to the ability of C4 plants to concentrate C02 in the bundle sheath cells, where RuBP carboxylase is located (9). A C02-concentrating system operating by a totally different mechanism than that of C4 photosynthesis appears to be responsible for the efficient photosynthetic characteristics of air-adapted Chlamydomonas (2) and other algae (3,5,12,18,23). Although not well characterized, this C02-concentrating mechanism may involve active bicarbonate transport into the algal cells, raising the internal inorganic carbon concentration several-fold higher than that of the surrounding medium (2,3,5,13,18,23).…”

mentioning

confidence: 99%

Carbonic Anhydrase-Deficient Mutant of Chlamydomonas reinhardii Requires Elevated Carbon Dioxide Concentration for Photoautotrophic Growth

Spalding¹,

Spreitzer²,

Ogren³

1983

162

163

A mendelian mutant of the unicellular green alp Chlamydomonas reinhardii has been isolated which is deficient in carbonic anhydrase (EC 4.2.1.1) activity. This mutant strain, designated ca-1-12-1C (gene locus ca-i), was selected on the basis of a high C02 requirement for photoautotrophic growth. Photosynthesis by the mutant at atmospheric C02 concentration was very much reduced compared to wild type and, unlike wild type, was strongly inhibited by 02. In contrast to a CO2 compensation concentration of near zero in wild type at all 02 concentrations examined, the mutant exhibited a high, 02-stimulated C02 compensation concentration. Evidence of photorespiratory activity in the mutant but not in wild type was obtained from the analysis of photosynthetic products in the presence of '4CO2. At