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Plant physiologists set about comprehending the genesis of the C4 photosynthetic pathway after its discovery by Hatch and Slack. They discovered that a sophisticated combination of morphological and biochemical adaptations allowed the plant to concentrate CO2 around RuBisCO to achieve maximum efficiency. We categorize the evolutionary events leading to C4 photosynthesis, beginning with anoxygenic photosynthesis and the evolution of RuBisCO to the cooling of Earth by the Great Oxygenation Event that led to the oxygenic photosynthesis. The evolutionary descent of the C4 plants is a phenomenon that occurred around 30 million years ago. Due to industrialization and population growth, improved photosynthetic efficiency and carbon fixation of C4 plants could contest the current global scenario of rising CO2 concentration. C3 crops engineered with C4 traits, implemented on a large scale, could impact the climate globally. Here we discuss the various strategies used to introduce C4 traits in the C3 plants and the potential techniques to be considered for successful hybridization. [ABSTRACT FROM AUTHOR]

Rapid changes on nutrient supply and CO2 concentration that occurred in the northern South China Sea (SCS) during the Early Oligocene, provides an ideal natural laboratory, allowing us to peer into the coccolithophores' physiology in the geological records. In this study, we established a new nannofossil assemblage index, termed as E* ratio, which is calculated by the relative abundance of eutrophic taxa and meso-oligotrophic taxa ( E ∗ = e e + c × 100 , where e is eutrophic taxa, and c is meso-oligotrophic taxa). Eutrophic taxa include small Reticulofenestra, Reticulofenestra lockeri group, Reticulofenestra bisecta group and Coccolithus pelagicus group, while meso-oligotrophic taxa include Cyclicargolithus spp. The E* ratio is well correlated with nutrient proxy during the Early Oligocene, while with different covarying patterns under the higher and lower CO2 condition. By comparing the assemblage changes to the published data, we suggest that coccolithophores may change the way they use carbon source and nutrient with the decline of CO2. Furthermore, this implies a possible initiation of the carbon concentrating mechanism. [ABSTRACT FROM AUTHOR]

Carbon concentrating mechanism (CCM) and photorespiration (PR) are interlinked and co-regulated in Chlamydomonas reinhardtii, but conditions where co-regulation alters are not sufficiently explored. Here, we uncover that PR gene transcripts, like CCM transcripts, are induced even in the dark when both processes are not active. Such diurnal cycles show that transcript levels peak in the middle of 12 h day, decline by early part of 12-h dark followed by their onset again at mid-dark. Interestingly, the onset in the mid-dark phase is sensitive to high CO2, implying that the active carbon sensing mechanism operates even in the dark. The rhythmic alterations of both CCM and PR transcript levels are unlinked to circadian clock: the "free-running state" reveals no discernible rhythmicity in transcript changes. Only continuous light leads to high transcript levels but no detectable transcripts were observed in continuous dark. Asynchronous continuous light cultures, upon shifting to low from high CO2 exhibit only transient induction of PR transcripts/proteins while CCM transcript induction is stable, indicating the loss of co-regulation between PR and CCM gene transcription. Lastly, we also describe that both CCM and PR transcripts/proteins are induced in low CO2 even in mixotrophic cultures, but only in high light, the same being attenuated in high CO2, implying that high light is a mandatory "trigger" for CCM and PR induction in low CO2 mixotrophy. Our study provides comprehensive analyses of conditions where CCM and PR were differently regulated, setting a paradigm for a detailed mechanistic probing of these responses. [ABSTRACT FROM AUTHOR]

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]

Transgenic potato ( Solanum tuberosum L. cv. Desiree) plants expressing components of a novel cyanobacterial photorespiratory glycolate catabolism pathway were developed. Transgenic plant expressing glcD1 (glycolate dehydrogenase I) gene was referred to as synGDH and transgenic plants expressing gcl (glyoxylate carboligase) and tsr (tartronic semialdehyde reductase) genes simultaneously were designated as synGT. Both synGDH and synGT plants showed stable gene transformation, integration and expression. Enhanced glyoxylate contents in synGDH plants were detected as compared to synGT and non-transgenic (NT) plants. Phenotypic evaluation revealed that synGDH plants accumulated 11 % higher dry weight, while, tuber weight was 38 and 16 % higher than NT and synGT, respectively. Upon challenging the plants in high temperature and high light conditions synGDH plants maintained higher Fv/ Fm and showed less bleaching of chlorophyll as compared to synGT and NT plants. These results indicate that genetic transformation of complete pathway in one plant holds promising outcomes in terms of biomass accumulation to meet future needs for food and energy. [ABSTRACT FROM AUTHOR]

The gammaproteobacterium Thiomicrospira crunogena XCL-2 is an aerobic sulfur-oxidizing hydrothermal vent chemolithoautotroph that has a CO concentrating mechanism (CCM), which generates intracellular dissolved inorganic carbon (DIC) concentrations much higher than extracellular, thereby providing substrate for carbon fixation at sufficient rate. This CCM presumably requires at least one active DIC transporter to generate the elevated intracellular concentrations of DIC measured in this organism. In this study, the half-saturation constant ( K) for purified carboxysomal RubisCO was measured (276 ± 18 µM) which was much greater than the K of whole cells (1.03 µM), highlighting the degree to which the CCM facilitates CO fixation under low CO conditions. To clarify the bioenergetics powering active DIC uptake, cells were incubated in the presence of inhibitors targeting ATP synthesis (DCCD) or proton potential (CCCP). Incubations with each of these inhibitors resulted in diminished intracellular ATP, DIC, and fixed carbon, despite an absence of an inhibitory effect on proton potential in the DCCD-incubated cells. Electron transport complexes NADH dehydrogenase and the bc complex were found to be insensitive to DCCD, suggesting that ATP synthase was the primary target of DCCD. Given the correlation of DIC uptake to the intracellular ATP concentration, the ABC transporter genes were targeted by qRT-PCR, but were not upregulated under low-DIC conditions. As the T. crunogena genome does not include orthologs of any genes encoding known DIC uptake systems, these data suggest that a novel, yet to be identified, ATP- and proton potential-dependent DIC transporter is active in this bacterium. This transporter serves to facilitate growth by T. crunogena and other Thiomicrospiras in the many habitats where they are found. [ABSTRACT FROM AUTHOR]

Bicarbonate species in the aqueous phase is the primary source for CO for the growth of microalgae. The potential of carbon dioxide (CO) fixation by Chlorella pyrenoidosa in enriched bicarbonate medium was evaluated. In the present study, effects of parameters such as pH, sodium bicarbonate concentration and inoculum size were assessed for the removal of CO by C. pyrenoidosa under mixotrophic condition. Central composite design tool from response surface methodology was used to validate statistical methods in order to study the influence of these parameters. The obtained results reveal that the maximum removal of CO was attained at pH 8 with sodium bicarbonate concentration of 3.33 g/l, and inoculum size of 30 %. The experimental results were statistically significant with R value of 0.9527 and 0.960 for CO removal and accumulation of chlorophyll content, respectively. Among the various interactions, interactive effects between the parameters pH and inoculum size was statistically significant ( P < 0.05) for CO removal and chlorophyll accumulation. Based on the studies, the application of C. pyrenoidosa as a potential source for carbon dioxide removal at alkaline pH from bicarbonate source is highlighted. [ABSTRACT FROM AUTHOR]

Agricultural yields have kept pace with the rising demands in the recent past as a result of the breeding and improved farming practices, but these practices alone will not be able to meet the demands of the future. The focus is now on the enhancement of the photosynthetic machinery. In photosynthesis, the rate limiting step is the one catalyzed by RuBisCO- Ribulose-1,5-bisphosphate carboxylase/oxygenase (4.1.1.39), which, because of its loose specificity and low turnover rate, is the primary target of most research programs directed towards improved photosynthesis. The other avenues of photosynthetic machinery that are under investigation to enhance it include-improved stomatal regulation and membrane permeability, RuBisCO with high specificity for CO and higher catalytic turnover; bypass of photorespiration and introduction of carbon concentrating mechanism (CCM) into the C plants. Carbon concentrating mechanisms cause accumulation of carbon dioxide in vicinity of RuBisCO producing a high CO/O ratio and hence an environment more suitable for carboxylation reactions than oxygenation reactions. This article includes the basic details of the major naturally occurring CCMs in various photosynthetic organisms to identify the knowledge gaps in each which could help study the prospects of its possible introduction into a non-native system as C plants which are devoid of any CCM. [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]

Threat of global warming due to carbon dioxide (CO) emissions has stimulated research into carbon sequestration and emissions reduction technologies. Alkaline scrubbing allows CO to be captured as bicarbonate, which can be photochemically fixed by microalgae. The carbon concentrating mechanism (CCM), of which external carbonic anhydrase is a key component, allows organisms to utilise this bicarbonate. In order to select a suitable strain for this application, a screening tool is required. The current method for determining carbonic anhydrase activity, the Wilbur and Anderson assay, was found to be unsuitable as a screening tool as the associated error was unacceptably large and tests on whole cells were inconclusive. This paper presents the development of a new, whole cell assay to measure inorganic carbon uptake and external carbonic anhydrase activity, based on classical pH drift experiments. Spirulina platensis was successfully used to develop a correlation between the specific carbon uptake (C) and the specific pH change (dpH). The relationship is described by the following: C[mmol C (g dry algae) h] = 0.064 × (dpH). Inhibitor and salt dissociation tests validated the activity and presence of external carbonic anhydrase and allowed correlation between the Wilbur and Anderson assay and the new whole cell assay. Screening tests were conducted on S. platensis, Scenedesmus sp., Chlorella vulgaris and Dunaliella salina that were found to have carbon uptake rates of 5.76, 5.86, 3.86 and 2.15 mmol C (g dry algae) h, respectively. These results corresponded to the species' known bicarbonate utilisation abilities and validated the use of the assay as a screening tool. [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 interactive effects of inorganic carbon status, temperature and light on chlorosis induced by nitrogen deficiency, and the roles of Clp proteases in this process were investigated. In wild-type cultures grown in high or ambient CO2, following transfer to media lacking combined nitrogen, phycocyanin per cell dropped primarily through dilution of the pigment through cell division, and also suffered variable degrees of net degradation. When grown at high CO2 (5%), chlorophyll (Chl) suffered net degradation to a greater extent than phycocyanin. In marked contrast, growth at ambient CO2 resulted in Chl per cell dropping through dilution. Conditions that drove net Chl degradation in the wild-type resulted in little or no net Chl degradation in aclpPIinactivation mutant, with Chl content dropping largely through growth dilution in the mutant. The chlorotic response of aclpPIIinactivation strain was nearly the same as that of wild-type, although phycocyanin degradation may have been slightly accelerated in the former. [ABSTRACT FROM AUTHOR]

We have assessed the effect of vanadate as an inhibitor of plasma-membrane ATPase on photosynthesis and the ATP/ADP ratio in Chlamydomonas reinhardtii CW-92 (a mutant strain lacking a cell wall). This effect was compared in low-CO-adapted cells grown in media bubbled with air containing 400 or 70 μL · L CO. Evidence is presented indicating that cells grown at 70 μL · L CO have a higher rate of photosynthetic O evolution than cells grown at 400 μL · L CO, at limiting carbon concentrations. Extracellular and intracellular carbonic-anhydrase activities were, however, similar in cells grown in both of the low-carbon conditions. Vanadate inhibited, to a different extent, the HCO-dependent O evolution in cells grown at 400 and 70 μL · L CO. At 400 μM vanadate, inhibition reached 70-75% in cells grown at 400 μL · L but only 50% in those grown at 70 μL · L CO. The ATP/ADP ratios determined with and without vanadate at limiting concentrations of dissolved inorganic carbon indicated that more ATP was hydrolysed in algae grown at 70 μL · L than in those grown at 400 μL · L CO. We conclude that the maximal capacity to accumulate dissolved inorganic carbon is inversely related to the CO concentration in the medium. Activation and - or synthesis of vanadate-sensitive ATPase may be the major explanation for the higher capacity for HCO-dependent O evolution in cells grown under limited CO concentrations. [ABSTRACT FROM AUTHOR]