Search

The response of marine phytoplankton to the ongoing increase in atmospheric pCO reflects the consequences of both increased CO concentration and decreased pH in surface seawater. In the model diatom Thalassiosira weissflogii, we explored the effects of varying pCO and pH, independently and in concert, on photosynthesis and respiration by incubating samples in water enriched in H O. In long-term experiments (~6-h) at saturating light intensity, we observed no effects of pH or pCO on growth rate, photosynthesis or respiration. This absence of a measurable response reflects the very small change in energy used by the carbon concentrating mechanism (CCM) compared to the energy used in carbon fixation. In short-term experiments (~3 min), we also observed no effects of pCO or pH, even under limiting light intensity. We surmise that in T. weissflogii, it is the photosynthetic production of NADPH and ATP, rather than the CO-saturation of Rubisco that controls the rate of photosynthesis at low irradiance. In short-term experiments, we observed a slightly higher respiration rate at low pH at the onset of the dark period, possibly reflecting the energy used for exporting H and maintaining pH homeostasis. Based on what is known of the biochemistry of marine phytoplankton, our results are likely generalizable to other diatoms and a number of other eukaryotic species. The direct effects of ocean acidification on growth, photosynthesis and respiration in these organisms should be small over the range of atmospheric pCO predicted for the twenty-first century. [ABSTRACT FROM AUTHOR]

The photosynthetic, unicellular green alga, Chlamydomonas reinhardtii, lives in environments that often contain low concentrations of CO and HCO, the utilizable forms of inorganic carbon (C). C. reinhardtii possesses a carbon concentrating mechanism (CCM) which can provide suitable amounts of C for growth and development. This CCM is induced when the CO concentration is at air levels or lower and is comprised of a set of proteins that allow the efficient uptake of C into the cell as well as its directed transport to the site where Rubisco fixes CO into biomolecules. While several components of the CCM have been identified in recent years, the picture is still far from complete. To further improve our knowledge of the CCM, we undertook a mutagenesis project where an antibiotic resistance cassette was randomly inserted into the C. reinhardtii genome resulting in the generation of 22,000 mutants. The mutant collection was screened using both a published PCR-based approach (Gonzalez-Ballester et al. ) and a phenotypic growth screen. The PCR-based screen did not rely on a colony having an altered growth phenotype and was used to identify colonies with disruptions in genes previously identified as being associated with the CCM-related gene. Eleven independent insertional mutations were identified in eight different genes showing the usefulness of this approach in generating mutations in CCM-related genes of interest as well as identifying new CCM components. Further improvements of this method are also discussed. [ABSTRACT FROM AUTHOR]

The articles in this special issue of Photosynthesis Research arose from the presentations given at the Eighth International Symposium on Inorganic Carbon Uptake by Aquatic Photosynthetic Organisms held from May 27 to June 1, 2013 in New Orleans, Louisiana USA. The meeting covered all the aspects of CO concentrating mechanisms (CCMs) present in photosynthetic bacteria, microalgae and macrophytes, and spanned disciplines from the molecular biology of CCMs to the importance of CCMs in aquatic ecosystems. The publications in this special issue represent our current understanding of CCMs and highlight recent advances in the field. The influences of CCMs on algal biofuel production as well as recent efforts to use the CCM to improve crop plants are also explored. [ABSTRACT FROM AUTHOR]

This review presents an overview of the two ways that cyanobacteria, algae, and plants have adapted to high O and low CO concentrations in the environment. First, the process of photorespiration enables photosynthetic organisms to recycle phosphoglycolate formed by the oxygenase reaction catalyzed by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Second, there are a number of carbon concentrating mechanisms that increase the CO concentration around Rubisco which increases the carboxylase reaction enhancing CO fixation. This review also presents possibilities for the beneficial modification of these processes with the goal of improving future crop yields. [ABSTRACT FROM AUTHOR]

The CO acquisition was analyzed in Chlamydomonas acidophila at pH 2.4 in a range of medium P and Fe concentrations and at high and low CO condition. The inorganic carbon concentrating factor (CCF) was related to cellular P quota ( Q), maximum CO-uptake rate by photosynthesis ( $$ V_{{{ \max },{\text{O}}_{ 2} }} $$), half saturation constant for CO uptake ( K), and medium Fe concentration. There was no effect of the medium Fe concentration on the CCF. The CCF increased with increasing Q in both high and low CO grown algae, but maximum Q was 6-fold higher in the low CO cells. In high CO conditions, the CCF was low, ranging between 0.8 and 3.5. High CCF values up to 9.1 were only observed in CO-limited cells, but P- and CO-colimited cells had a low CCF. High CCF did not relate with a low K as all CO-limited cells had a low K (<4 μM CO). High C-pools in cells with high Q suggested the presence of an active CO-uptake mechanism. The CCF also increased with increasing $$ V_{{{ \max },{\text{O}}_{ 2} }} $$ which reflect an adaptation to the nutrient in highest demand (CO) under balanced growth conditions. It is proposed that the size of the CCF in C. acidophila is more strongly related to porter density for CO uptake (reflected in $$ V_{{{ \max },{\text{O}}_{ 2} }} $$) and less- to high-affinity CO uptake (low K) at balanced growth. In addition, high CCF can only be realized with high Q. [ABSTRACT FROM AUTHOR]

The fluxes of CO and oxygen during photosynthesis by cell suspensions of Tessellaria volvocina and Mallomonas papillosa were monitored mass spectrometrically. There was no rapid uptake of CO only a slow drawdown to compensation concentrations of 26 μM for T. volvocina and 18 μM for M. papillosa, when O evolution ceased, indicating a lack of active bicarbonate uptake by the cells. Darkening of the cells after a period of photosynthesis did not cause rapid release of CO, indicating the absence of an intracellular inorganic carbon pool. However, upon darkening a brief burst of CO was observed similar to the post-illumination burst characteristic of C higher plants. Treatment of the cells of both species with the membrane-permeable carbonic anhydrase inhibitor ethoxyzolamide had no adverse effect on photosynthetic rate, but stimulated the dark CO burst indicating the dark oxidation of a compound formed in the light. In the absence of any active accumulation of inorganic carbon photosynthesis in these species should be inhibited by O. This was investigated in four synurophyte species T. volvocina, M. papillosa, Synura petersenii, and Synura uvella: photosynthetic O evolution rates in all four algae, measured by O electrode, were significantly higher (40-50%) in media at low O (4%) than in air-equilibrated (21% O) media, indicating an O inhibition of photosynthesis (Warburg effect) and thus the occurrence of photorespiration in these species. [ABSTRACT FROM AUTHOR]

Cyanobacteria (as well as many chemoautotrophs) actively pump inorganic carbon (in the form of HCO) into the cytosol in order to enhance the overall efficiency of carbon fixation. The success of this approach is dependent upon the presence of carboxysomes-large, polyhedral, cytosolic bodies which sequester ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) and carbonic anhydrase. Carboxysomes seem to function by allowing ready passage of HCO into the body, but hindering the escape of evolved CO, promoting the accumulation of CO in the vicinity of RubisCO and, consequently, efficient carbon fixation. This selectivity is mediated by a thin shell of protein, which envelops the carboxysome's enzymatic core and uses narrow pores to control the passage of small molecules. In this review, we summarize recent advances in understanding the organization and functioning of these intriguing, and ecologically very important molecular machines. [ABSTRACT FROM AUTHOR]

The response of marine phytoplankton to the ongoing increase in atmospheric pCO 2 reflects the consequences of both increased CO 2 concentration and decreased pH in surface seawater. In the model diatom Thalassiosira weissflogii, we explored the effects of varying pCO 2 and pH, independently and in concert, on photosynthesis and respiration by incubating samples in water enriched in H 2 18 on growth rate, photosynthesis or respiration. This absence of a measurable response reflects the very small change in energy used by the carbon concentrating mechanism (CCM) compared to the energy used in carbon fixation. In short-term experiments (~3 min), we also observed no effects of pCO 2 on growth rate, photosynthesis or respiration. This absence of a measurable response reflects the very small change in energy used by the carbon concentrating mechanism (CCM) compared to the energy used in carbon fixation. In short-term experiments (~3 min), we also observed no effects of pCO 2 or pH, even under limiting light intensity. We surmise that in T. weissflogii, it is the photosynthetic production of NADPH and ATP, rather than the CO 2 -saturation of Rubisco that controls the rate of photosynthesis at low irradiance. In short-term experiments, we observed a slightly higher respiration rate at low pH at the onset of the dark period, possibly reflecting the energy used for exporting H + and maintaining pH homeostasis. Based on what is known of the biochemistry of marine phytoplankton, our results are likely generalizable to other diatoms and a number of other eukaryotic species. The direct effects of ocean acidification on growth, photosynthesis and respiration in these organisms should be small over the range of atmospheric pCO 2 predicted for the twenty-first century.