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The effects of light intensity and carbon dioxide (CO2) concentration on the growth of the highly CO2-tolerant green alga Chlorococcum littorale were studied in batch cultures. Four mathematical representations were compared for the specific growth rate-light response curve: a rectangular hyperbolic function, Steele's exponential function, a Poisson function and a hyperbolic tangent function. The hyperbolic tangent function, which is commonly used for representing the photosynthesis-light relationship, gave the best fit as evaluated by the extended information criterion (EIC). EIC proved to be applicable as a criterion to this kind of nonlinear model selection problem. Carbon dioxide, the sole carbon source for photoautotrophic growth of this alga, inhibited the growth rate at concentrations higher than pCO2 of 0.02. A substrate inhibition model was successfully used to simulate the relationship between the specific growth rate and CO2 response.

An extremely-high-CO2-tolerant alga, Chlorococcum littorale, showed high quantum efficiency of PSII (PhiII) in the light at 40% CO2, as well as at 5% CO2. However, PhiII decreased greatly when chloramphenicol (CAP) was added at 40% CO2, while no such decrease was observed at 5% CO2. Cycloheximide showed no effect on PhiII at either 5% or 40% CO2. The amount of a 76 kDa polypeptide (p76) on SDS-PAGE decreased markedly in the presence of CAP at 40% CO2 but not at 5% CO2. A partial amino acid sequence of p76 was 71-100% identical (10-14 identical residues out of 14 amino acids determined) to those of transketolases (TKLs) reported in higher plants and a cyanobacterium. In agreement with these observations, the TKL activity in C. littorale was decreased by CAP at 40% CO2, but not at 5% CO2. The transient decrease in TKL activity caused by CAP under 40% CO2 was well correlated with that in PhiII. These results indicate that the addition of CAP directly or indirectly influences the stability of TKL in C. littorale at 40% CO2, but not at 5% CO2, and that photosynthetic activity was reduced by a decrease in TKL activity.

Regulation of energy balance in photosystems in response to extremely-high-CO2 (40%) and low-CO2 (0.04%) stress was studied in extremely-high-CO2-tolerant green microalgae, Chlorococcum littorale and Chlorella sp. UK001. To investigate the energy input process, we assessed an F714/F685-ratio in a 77K fluorescence emission spectrum induced by 440-nm excitation in intact cells, which represents a ratio of fluorescence intensities derived from light-harvesting chlorophyll complexes in PSI and PSII. The F714/F685-ratio increased in several days after transferring C. littorale cells from air to 40% CO2, from 3% to 40% CO2 and from 3% to air. In all cases, the increase in the F714/F685-ratio was observed in high cell density culture, but no or a little increase was apparent in sparse cell density culture, when these cultures were illuminated at 250 micromol photon m-2 s-1. Even in the sparse culture, however, a similar increase in the F714/F685-ratio was observed when C. littorale cells were transferred from 3% to 40% CO2 at 20 micromol photon m-2 s-1. The cell density did not affect the F714/F685-ratio when CO2 concentration was kept at 3%. The activity of PSI electron (e-) transport was much higher in 40% CO2-grown cells than in 3% CO2-grown cells irrespective of the cell density during the culture, whereas the difference in PSII activity between them was small. The PSI activity at high cell density was higher also in air-grown cells than that in 3% CO2-grown cells. In both dense and sparse culture, 40% CO2-grown cells and air-grown cells showed higher relative quantum yield of PSI in the presence of DCMU than 3% CO2-grown cells, suggesting an increase in cyclic electron flow around PSI. Likewise, the increase in the F714/F685-ratio in response to the transfer to 40% CO2 was observed also in another extremely-high-CO2-tolerant alga, Chlorella sp. UK001. The possible role of the increases in the F714/F685-ratio, PSI/PSII activity ratio and cyclic e- transport activity in extremely-high-CO2 acclimation is discussed in comparison with low-CO2 acclimation.

Microalgal photosynthesis is efficient enough to fix CO2 in both atmosphere and industrially discharged gases, and is a possible future alternative for CO2 reduction. This paper describes physiological responses of microalgal cells to extremely high CO2 concentrations, capability of microalgal cells to fix CO2 at both indoor and outdoor culture experiments, and efforts to establish a culture collection of marine microalgae. Recent researches indicate that microalgae are likely to play a key role in worldwide issues of the coming century. [ABSTRACT FROM AUTHOR]

Effects of CO[SUB2] concentration during growth on intracellular structure were studied with five species of Chlorella and Scenedesmus obliquus. Cells grown under ordinary air conditions (low-CO: cells) had a well developed pyrenoid surrounded by starch, while those grouse under high CO[SUB2] conditions (high-CO[SUB2] cells) had a less developed pyrenoid or no detectable pyrenoid. Two mitochondria, one at each side of the neck of the projection of the chloroplast close to the pyrenoid, were found in low CO[SUB2] cells of C. vulgaris 11h. Usually, lamellar stacks extended in parallel in the chloroplast of low-CO[SUB2] cells of C. vulgaris 11h, while a grana-like structure was found in high.CO[SUB2] cells. However, in C. pyrenoidosa, granalike structures u,ere found more commonly in low-CO, cells than in high-CO[SUB2] cells. These results suggest that development of pyrenoid starch is generally correlated with growth under low CO[SUB2] conditions, whereas CO[SUB2] effects on lamellar stacking are sprats dependent. [ABSTRACT FROM AUTHOR]

Examines biosynthesis and intracellular processing of carbonic anhydrase in Chlamydomonas reinhardtii. Localization of the glycoprotein outside the plasma membrane; Carbon dioxide concentration during photoautotropic growth; Biosynthesis and intracellular processing of carbonic anhydrase.