scholarly journals The roles of carbonic anhydrases in сarbon concentrating mechanisms of aquatic photoautotrophs

Algologia ◽  
2021 ◽  
Vol 31 (4) ◽  
pp. 337-352
Author(s):  
O.V. Polishchuk ◽  
Keyword(s):  
Lipid Bilayers ◽  
Inorganic Carbon ◽  
Multiple Roles ◽  
Co2 Production ◽  
Aquatic Environments ◽  
Carbonic Anhydrases ◽  
Inner Surface ◽  
Carbon Concentrating Mechanisms ◽  
Co2 Concentrating Mechanisms ◽  
Aquatic Angiosperms

The article surveys multiple roles of carbonic anhydrases (CAs) in inorganic carbon (Ci) acquisition by cyanobacteria, microalgae, and macrophytes under Ci limiting conditions. Slow Ci diffusion in aquatic environments imposes the need for carbon concentrating mechanisms (also named CO2 concentrating mechanisms, CCMs) in aquatic photoautotrophs to transport Ci against the gradient and ensure CO2 supply to photosynthesis. There are common requirements for efficient CCM functioning in cyanobacteria, algae, and aquatic angiosperms, including active transport of HCO3- to the Ci-concentrating compartment and CO2 generation from the HCO3- pool in the Rubisco-enriched subcompartment. Facilitating Ci diffusion in aqueous solutions and across lipid bilayers, CAs play essential roles in CCMs that are best studied in cyanobacteria, green algae, and diatoms. Roles of CAs in CCMs depend on their localization and include facilitation of active transmembrane Ci uptake by its supplying at the outer surface (Role 1) and removal at the inner surface (Role 2), as well as the acceleration of CO2 production from HCO3- near Rubisco (Role 3) in a special CO2-tight compartment, carboxysome in cyanobacteria or pyrenoid in microalgae. The compartmentalization of CAs is also critical because, if activated in the HCO3- –concentrating compartment, they can easily eliminate the Ci gradient created by CCMs.

scholarly journals The carbonic anhydrase CAH1 is an essential component of the carbon-concentrating mechanism in Nannochloropsis oceanica

2017 ◽  
Vol 114 (17) ◽  
pp. 4537-4542 ◽  
Author(s):  
Christopher W. Gee ◽  
Krishna K. Niyogi
Keyword(s):  
Carbonic Anhydrase ◽  
Molecular Mechanisms ◽  
Inorganic Carbon ◽  
Carbonic Anhydrases ◽  
Nannochloropsis Oceanica ◽  
Essential Component ◽  
Protein Levels ◽  
Photosynthetic Organisms ◽  
Carbon Concentrating Mechanisms ◽  
Carbonic Anhydrase 1

Aquatic photosynthetic organisms cope with low environmental CO2 concentrations through the action of carbon-concentrating mechanisms (CCMs). Known eukaryotic CCMs consist of inorganic carbon transporters and carbonic anhydrases (and other supporting components) that culminate in elevated [CO2] inside a chloroplastic Rubisco-containing structure called a pyrenoid. We set out to determine the molecular mechanisms underlying the CCM in the emerging model photosynthetic stramenopile, Nannochloropsis oceanica, a unicellular picoplanktonic alga that lacks a pyrenoid. We characterized CARBONIC ANHYDRASE 1 (CAH1) as an essential component of the CCM in N. oceanica CCMP1779. We generated insertions in this gene by directed homologous recombination and found that the cah1 mutant has severe defects in growth and photosynthesis at ambient CO2. We identified CAH1 as an α-type carbonic anhydrase, providing a biochemical role in CCM function. CAH1 was found to localize to the lumen of the epiplastid endoplasmic reticulum, with its expression regulated by the external inorganic carbon concentration at both the transcript and protein levels. Taken together, these findings show that CAH1 is an indispensable component of what may be a simple but effective and dynamic CCM in N. oceanica.

The nuclear envelope

2019 ◽  
pp. 140-146
Author(s):  
John C. Lucchesi
Keyword(s):  
Nuclear Envelope ◽  
Lipid Bilayers ◽  
Nuclear Membrane ◽  
Substantial Portion ◽  
Inner Membrane ◽  
Double Membrane ◽  
Stochastic Nature ◽  
Inner Surface ◽  
Associated Proteins ◽  
Or Gene

The nuclear envelope is a double membrane sheath made up of two lipid bilayers—an outer and an inner membrane. The inner surface of the inner membrane is associated with a meshwork of filaments made up of lamins and of lamin-associated proteins that constitute the lamina. A substantial portion of the genome contacts the lamina through lamina-associated domains (LADs). LADs usually position silent or gene-poor regions of the genome near the lamina and nuclear membrane. The position of some LADs is different in some cells of the same tissue, reflecting the stochastic nature of gene activity; it can also change during differentiation, allowing the necessary activation of particular genes. Contact of transcription units with nuclear pores can result in activation or, sometimes, repression. Some of the proteins that contribute to the structure of the pores can activate transcription by associating with genes or with super-enhancers away from the nuclear membrane.

Variability in the benefits of ocean acidification to photosynthetic rates of macroalgae without CO2-concentrating mechanisms

2020 ◽  
Vol 71 (3) ◽  
pp. 275 ◽  
Author(s):  
C. E. Cornwall ◽  
C. L. Hurd
Keyword(s):  
Ocean Acidification ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Surface Seawater ◽  
Seaweed Species ◽  
Photosynthetic Rates ◽  
Uptake Rates ◽  
Carbon Dioxide Co2 ◽  
Co2 Concentrating Mechanisms ◽  
Emissions Scenario

Increasing concentrations of surface-seawater carbon dioxide (CO2) (ocean acidification) could favour seaweed species that currently are limited for dissolved inorganic carbon (DIC). Among them, those that are unable to use CO2-concentrating mechanisms (CCMs) to actively uptake bicarbonate (HCO3–) across the plasmalemma are most likely to benefit. Here, we assess how the DIC uptake and photosynthetic rates of three rhodophytes without CCMs respond to four seawater CO2 concentrations representing pre-industrial (280μatm), present-day (400μatm), representative concentration pathway (RCP) emissions scenario 8.52050 (650μatm) and RCP 8.52100 (1000μatm). We demonstrated that the photosynthetic rates of only one species increase between the preindustrial and end-of-century scenarios, but because of differing photosynthetic quotients (DIC taken up relative to O2 evolved), all three increase their DIC uptake rates from pre-industrial or present-day scenarios to the end-of-century scenario. These variable, but generally beneficial, responses highlight that not all species without CCMs will respond to ocean acidification uniformly. This supports past assessments that, on average, this group will likely benefit from the impacts of ocean acidification. However, more concerted efforts are now required to assess whether similar benefits to photosynthetic rates and DIC uptake are also observed in chlorophytes and ochrophytes without CCMs.

Acquisition of inorganic carbon by the marine diatom Thalassiosira weissflogii

2002 ◽  
Vol 29 (3) ◽  
pp. 301 ◽  
Author(s):  
François M. M. Morel ◽  
Elizabeth H. Cox ◽  
Anne M. L. Kraepiel ◽  
Todd W. Lane ◽  
Allen J. Milligan ◽  
...  
Keyword(s):  
Inorganic Carbon ◽  
Marine Diatom ◽  
Published Data ◽  
Carbonic Anhydrases ◽  
Thalassiosira Weissflogii ◽  
Metal Centre ◽  
Natural Conditions ◽  
Major Species ◽  
Ambient Co2 ◽  
Inorganic Carbon Acquisition

Recent data on the physiology of inorganic carbon acquisition by the model marine diatom Thalassiosira weissflogii (Grunow) demonstrate the importance of the catalytic equilibration of HCO3-and CO2by carbonic anhydrases located in the periplasm and in the cytoplasm. These enzymes can use Zn, Co or Cd as their metal centre, and their activity increases at low ambient CO2. The silica frustule provides buffering for extracellular CA activity, The transmembrane transport of CO2 may occur by passive diffusion. Under CO2 limitation, the cytoplasmic HCO3–is used to form malate and oxaloacetic acid via phosphoenolpyruvate carboxylase. It appears that subsequent decarboxylation of these compounds in the chloroplast regenerates CO2 near the site of Rubisco, and thus provides the organism with an effective unicellular C4 photosynthetic pathway. These results, together with other published data, bring up two major questions regarding inorganic carbon acquisition in diatoms: What is the major species of inorganic carbon (CO2 or HCO3–) transported across the membrane under natural conditions? And what is the form of carbon (inorganic or organic) accumulated by the cells?

scholarly journals Inorganic carbon fluxes across the vadose zone of planted and unplanted soil mesocosms

2014 ◽  
Vol 11 (24) ◽  
pp. 7179-7192 ◽  
Author(s):  
E. M. Thaysen ◽  
D. Jacques ◽  
S. Jessen ◽  
C. E. Andersen ◽  
E. Laloy ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Plant Growth ◽  
Vadose Zone ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Carbon Dioxide Partial Pressure ◽  
Co2 Production ◽  
Post Harvest ◽  
Unplanted Soil ◽  
Soil Mesocosms

Abstract. The efflux of carbon dioxide (CO2) from soils influences atmospheric CO2 concentrations and thereby climate change. The partitioning of inorganic carbon (C) fluxes in the vadose zone between emission to the atmosphere and to the groundwater was investigated to reveal controlling underlying mechanisms. Carbon dioxide partial pressure in the soil gas (pCO2), alkalinity, soil moisture and temperature were measured over depth and time in unplanted and planted (barley) mesocosms. The dissolved inorganic carbon (DIC) percolation flux was calculated from the pCO2, alkalinity and the water flux at the mesocosm bottom. Carbon dioxide exchange between the soil surface and the atmosphere was measured at regular intervals. The soil diffusivity was determined from soil radon-222 (222Rn) emanation rates and soil air Rn concentration profiles and was used in conjunction with measured pCO2 gradients to calculate the soil CO2 production. Carbon dioxide fluxes were modeled using the HP1 module of the Hydrus 1-D software. The average CO2 effluxes to the atmosphere from unplanted and planted mesocosm ecosystems during 78 days of experiment were 0.1 ± 0.07 and 4.9 ± 0.07 μmol C m−2 s−1, respectively, and grossly exceeded the corresponding DIC percolation fluxes of 0.01 ± 0.004 and 0.06 ± 0.03 μmol C m−2 s−1. Plant biomass was high in the mesocosms as compared to a standard field situation. Post-harvest soil respiration (Rs) was only 10% of the Rs during plant growth, while the post-harvest DIC percolation flux was more than one-third of the flux during growth. The Rs was controlled by production and diffusivity of CO2 in the soil. The DIC percolation flux was largely controlled by the pCO2 and the drainage flux due to low solution pH. Modeling suggested that increasing soil alkalinity during plant growth was due to nutrient buffering during root nitrate uptake.

scholarly journals Carbon concentrating mechanisms maintain bloom biomass and CO<sub>2</sub> depletion in eutrophic lake ecosystems

2016 ◽  
Author(s):  
Ana M. Morales-Williams ◽  
Alan D. Wanamaker Jr. ◽  
John A. Downing
Keyword(s):  
Inorganic Carbon ◽  
Phytoplankton Bloom ◽  
Dissolved Inorganic Carbon ◽  
Negative Relationship ◽  
Eutrophic Lake ◽  
Anthropogenic Pressure ◽  
Phytoplankton Blooms ◽  
Eutrophic Lakes ◽  
Lake Ecosystems ◽  
Carbon Concentrating Mechanisms

Abstract. Harmful phytoplankton blooms are increasing in frequency, intensity, and duration in aquatic ecosystems worldwide. In many eutrophic lakes, these high levels of primary productivity correspond to periods of CO2 depletion in surface waters. Cyanobacteria and other groups of phytoplankton have the ability to actively transport bicarbonate (HCO3−) across their cell membrane when CO2 concentrations are limiting, possibly giving them a competitive advantage over algae not using carbon concentrating mechanisms (CCMs). To investigate whether CCMs can maintain phytoplankton bloom biomass under CO2 depletion, we measured δ13C signatures of dissolved inorganic carbon (δ13CDIC) and phytoplankton particulate organic carbon (δ13Cphyto) in sixteen mesotrophic to hypereutrophic lakes during the ice-free season of 2012. We used mass balance relationships to determine the dominant inorganic carbon species used by phytoplankton under CO2 stress. We found a significant positive relationship between phytoplankton biomass and phytoplankton δ13C signatures, as well as a significant non-linear negative relationship between water column ρCO2 and isotopic composition of phytoplankton, indicating a shift from diffusive uptake to active uptake by phytoplankton of CO2 or HCO3− during blooms. Calculated photosynthetic fractionation factors indicated that this shift occurs specifically when surface water CO2 drops below atmospheric equilibrium. Our results indicate active HCO3− uptake via CCMs may be an important mechanism maintaining phytoplankton blooms when CO2 is depleted. Further increases in anthropogenic pressure, eutrophication, and harmful cyanobacteria blooms are therefore expected to contribute to increased bicarbonate uptake to sustain primary production.

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