Light-independent Carbon Fixation Research Articles

Prediction of Genes That Function in Methanogenesis and CO2 Pathways in Extremophiles.

Gaet’ale (GAL) and Mud’ara (MUP) are two hypersaline ponds located in the Danakil Depression recharged by underground water from the surrounding highlands. These two ponds have different pH, salinity, and show variation in the concentration of many ionic components. Metagenomic analysis concludes that GAL is dominated by bacteria as in the case of the other hypersaline and acidic ponds in the Danakil Depression. However, Archaea dominated the ponds of MUP. In the current study, the application of SEED and KEGG helped to map the ordered steps of specific enzyme catalyzed reaction in converting CO2 into cell products. We predict that highly efficient and light-independent carbon fixation involving phosphoenolpyruvate carboxylase takes place in MUP. On the contrary, genes encoding enzymes involved in hydrogenotrophic and acetoclastic methanogenesis appeared solely in ponds of GAL, implying the biological source of the hazardous methane gas in that environment. Based on the investigation of the sources of the genes of interest, it is clear that cooperative interactions between members of the two communities and syntrophic metabolism is the main strategy adapted to utilize inorganic carbon as a carbon source in both MUP and GAL. This insight can be used to design biotechnological applications of microbial communities in production of methane biogas or to minimize CO2 emissions.

The dynamics and stoichiometry of dissolved organic carbon release by kelp.

Canopy-forming kelps are foundational species in coastal ecosystems, fixing tremendous amounts of carbon, yet we know little about the ecological and physiological determinants of dissolved organic carbon (DOC) release by kelps. We examined DOC release by the bull kelp, Nereocystis luetkeana, in relation to carbon fixation, nutrient uptake, tissue nitrogen content, and light availability. DOC release was approximately 3.5 times greater during the day than at night. During the day, N. luetkeana blades released an average of 16.2% of fixed carbon as DOC. Carbon fixation increased with light availability but DOC release did not, leading to a lower proportion of fixed carbon released as DOC at high light levels. We found no relationship between carbon fixation and DOC release rates measured concurrently. Rather, DOC release by N. luetkeana blades declined with marginal significance as blade tissue nitrogen content increased and with experimental nitrate addition, supporting the role of stoichiometric relationships in DOC release. Using a stable isotope (13 C) tracer method, we demonstrated that inorganic carbon is rapidly fixed and released by N. luetkeana blades as 13 DOC, within hours. However, recently fixed carbon (13 DOC) comprised less than 20% of the total DOC released, indicating that isotope studies that rely on tracer production alone may underestimate total DOC release, as it is decoupled from recent kelp productivity. Comparing carbon and nitrogen assimilation dynamics of the annual kelp N. luetkeana with the perennial kelp Macrocystis pyrifera revealed that N. luetkeana had significantly higher carbon fixation, DOC production and nitrogen uptake rates per unit dry mass. Both kelp species were able to perform light-independent carbon fixation at night. Carbon fixation by the annual kelp N. luetkeana is as high as 2.35kg C·m-2 ·yr-1 , but an average of 16% of this carbon (376g C·m-2 ·yr-1 ) is released as DOC. As kelp forests are increasingly viewed as vehicles for carbon sequestration, it is important to consider the fate of this substantial quantity of DOC released by canopy-forming kelps.

Arctic Coralline Algae Elevate Surface pH and Carbonate in the Dark.

Red coralline algae are projected to be sensitive to ocean acidification, particularly in polar oceans. As important ecosystem engineers, their potential sensitivity has broad implications, and understanding their carbon acquisition mechanisms is necessary for making reliable predictions. Therefore, we investigated the localized carbonate chemistry at the surface of Arctic coralline algae using microsensors. We report for the first time carbonate ion concentration and pH measurements ([CO32-]) at and above the algal surface in the microenvironment. We show that surface pH and [CO32-] are higher than the bulk seawater in the light, and even after hours of darkness. We further show that three species of Arctic coralline algae have efficient carbon concentrating mechanisms including direct bicarbonate uptake and indirect bicarbonate use via a carbonic anhydrase enzyme. Our results suggest that Arctic corallines have strong biological control over their surface chemistry, where active calcification occurs, and that net dissolution in the dark does not occur. We suggest that the elevated pH and [CO32-] in the dark could be explained by a high rate of light independent carbon fixation that reduces respiratory CO2 release. This mechanism could provide a potential adaptation to ocean acidification in Arctic coralline algae, which has important implications for future Arctic marine ecosystems.

Native architecture of the Chlamydomonas chloroplast revealed by in situ cryo-electron tomography.

Chloroplast function is orchestrated by the organelle's intricate architecture. By combining cryo-focused ion beam milling of vitreous Chlamydomonas cells with cryo-electron tomography, we acquired three-dimensional structures of the chloroplast in its native state within the cell. Chloroplast envelope inner membrane invaginations were frequently found in close association with thylakoid tips, and the tips of multiple thylakoid stacks converged at dynamic sites on the chloroplast envelope, implicating lipid transport in thylakoid biogenesis. Subtomogram averaging and nearest neighbor analysis revealed that RuBisCO complexes were hexagonally packed within the pyrenoid, with ~15 nm between their centers. Thylakoid stacks and the pyrenoid were connected by cylindrical pyrenoid tubules, physically bridging the sites of light-dependent photosynthesis and light-independent carbon fixation. Multiple parallel minitubules were bundled within each pyrenoid tubule, possibly serving as conduits for the targeted one-dimensional diffusion of small molecules such as ATP and sugars between the chloroplast stroma and the pyrenoid matrix.

Cadmium Stress Responses inBrassica juncea: Hints from Proteomics and Metabolomics

Among heavy metal stressors, cadmium (Cd) pollution is one leading threat to the environment. In this view, research efforts have been increasingly put forward to promote the individuation of phytoextractor plants that are capable of accumulating and withstanding the toxic metals, including Cd, in the aerial parts. We hereby adopted the hyperaccumulator B. juncea (Indian mustard) as a model to investigate plant responses to Cd stress at low (25 μM) and high (100 μM) doses. Analytical strategies included mass-spectrometry-based determination of Cd and the assessment of its effect on the leaf proteome and metabolome. Results were thus integrated with routine physiological data. Taken together, physiology results highlighted the deregulation of photosynthesis efficiency, ATP synthesis, reduced transpiration, and the impairment of light-independent carbon fixation reactions. These results were supported at the proteomics level by the observed Cd-dependent alteration of photosystem components and the alteration of metabolic enzymes, including ATP synthase subunits, carbonic anhydrase, and enzymes involved in antioxidant responses (especially glutathione and phytochelatin homeostasis) and the Calvin cycle. Metabolomics results confirmed the alterations of energy-generating metabolic pathways, sulfur-compound metabolism (GSH and PCs), and Calvin cycle. Besides, metabolomics results highlighted the up-regulation of phosphoglycolate, a byproduct of the photorespiration metabolism. This was suggestive of the likely increased photorespiration rate as a means to cope with Cd-induced unbalance in stomatal conductance and deregulation of CO2 homeostasis, which would, in turn, promote CO2 depletion and O2 (and thus oxidative stress) accumulation under prolonged photosynthesis in the leaves from plants exposed to high doses of CdCl2. Overall, it emerges that Cd-stressed B. juncea might rely on photorespiration, an adaptation that would prevent the over-reduction of the photosynthetic electron transport chain and photoinhibition.

Thaumarchaeotal Signature Gene Distribution in Sediments of the Northern South China Sea: an Indicator of the Metabolic Intersection of the Marine Carbon, Nitrogen, and Phosphorus Cycles?

Thaumarchaeota are abundant and active in marine waters, where they contribute to aerobic ammonia oxidation and light-independent carbon fixation. The ecological function of thaumarchaeota in marine sediments, however, has rarely been investigated, even though marine sediments constitute the majority of the Earth's surface. Thaumarchaeota in the upper layer of sediments may contribute significantly to the reservoir of nitrogen oxides in ocean waters and thus to productivity, including the assimilation of carbon. We tested this hypothesis in the northern South China Sea (nSCS), a section of a large oligotrophic marginal sea with limited influx of nutrients, including nitrogen, by investigating the diversity, abundance, community structure, and spatial distribution of thaumarchaeotal signatures in surface sediments. Quantitative real-time PCR using primers designed to detect 16S rRNA and amoA genes in sediment community DNA revealed a significantly higher abundance of pertinent thaumarchaeotal than betaproteobacterial genes. This finding correlates with high levels of hcd genes, a signature of thaumarchaeotal autotrophic carbon fixation. Thaumarchaeol, a signature lipid biomarker for thaumarchaeota, constituted the majority of archaeal lipids in marine sediments. Sediment temperature and organic P and silt contents were identified as key environmental factors shaping the community structure and distribution of the monitored thaumarchaeotal amoA genes. When the pore water PO4(3-) concentration was controlled for via partial-correlation analysis, thaumarchaeotal amoA gene abundance significantly correlated with the sediment pore water NO2(-) concentration, suggesting that the amoA-bearing thaumarchaeota contribute to nitrite production. Statistical analyses also suggest that thaumarchaeotal metabolism could serve as a pivotal intersection of the carbon, nitrogen, and phosphorus cycles in marine sediments.

Effect of blue light on early sporophyte development of Saccharina japonica (Phaeophyta)

Growth and photosynthesis in the blade of Saccharina sporophytes are strongly stimulated by blue light. However, little is known about the effect of blue light on the early development and longitudinal photosynthesis profile of Saccharina sporophytes. In this study, S. japonica sporelings were cultured under blue or red light for 8 weeks. Blue light affected longitudinal, tangential cell divisions and tissue differentiation early in sporophyte development. The number of latitudinal cells in the blade under blue light was over fivefold that under red light. In addition, the number of cell layers was higher in the growing point than in the blade under blue light, whereas sporelings grown under red light contained only a single cell layer. Under blue light, the photosynthetic capacities of the growing region, blade and stipe were similar, and the maximum relative electron transport rate was even lower in the growing point than in the blade. The longitudinal photosynthesis profile suggested that blue light stimulated the enzymes participating in light-independent carbon fixation in the growing point and accordingly was less dependent on high light irradiances. Collectively, the results indicated that blue light promotes the early development of S. japonica sporophytes, which was attributed to both photomorphogenetic responses and photosynthetic reactions.

Physiological responses of the green alga Dunaliella parva (Volvocales, Chlorophyta) to controlled incremental changes in the N source.

This work is aimed at obtaining information on the acclimation processes of the green flagellate Dunaliella parva Lerche to gradual changes in the N source from NO3- to NH4+, in continuous cultures. Photosynthesis, dark respiration, and light-independent carbon fixation (LICF) rates, chlorophyll a fluorescence, RUBISCO and phosphoenolpyruvate carboxylase (PEPc) activities, plasmalemma electrical potential difference, cell volume, and absolute or relative amounts of major cell constituents were measured. Two phases characterised the response to the transition from NO3- to NH4+: (1) an initial phase in which photosynthesis and anaplerosis were stimulated and protein increased; (2) a subsequent phase in which most parameters reached new values that were close to those at the beginning of the experiment (100% NO3-). The only exceptions were PEPc activity and LICF, whose rates remained at least 2-fold higher than at 100% NO3-, when NH4+ was the sole N source. The results are indicative of a tendency to re-establish homeostasis, after an initial perturbation of the intracellular composition. The roles of different metabolic processes during acclimation are discussed.

Expression of carboxylating enzymes in Laminaria setchellii (Phaeophyceae)

Ribulose 1,5-bisphosphate carboxylase–oxygenase (RUBISCO) and phosphoenolpyruvate carboxykinase (PEPCK) catalyse the bulk of the carboxylation reaction in marine algae; however, little is known about the expression of these enzymes in the brown algae. The objective of this study was to assess the photosynthetic and light-independent carbon fixation (LICF) capacities along the thallus of Laminaria setchellii (Laminariales, Phycophyceae) and to relate the carboxylation patterns to the activity and abundance of RUBISCO and PEPCK. The translocation of photosynthetic products and the synthesis of specific amino acids through photosynthetic and LICF processes were also evaluated. Photosynthetic rates and in vitro RUBISCO activity were correlated with the abundance of the RUBISCO enzyme, suggesting that differential photosynthetic capacity in different regions of the thallus is regulated by the abundance of RUBISCO. Maximum LICF and PEPCK activity values were observed in the meristematic region of L. setchellii and were positively correlated with the abundance of the enzyme in the thallus. This also indicates that LICF capacity is regulated by PEPCK abundance. Pigment levels increased from the stipe and meristem towards the laminar region of the kelp, which is consistent with the observed increase in maximum photosynthesis. Collectively, our results indicate that photosynthesis is limited in the meristematic region by low RUBISCO activity, enzyme abundance and reduced pigment levels. Translocation rates of photosynthetic products from the tip of the lamina to the meristem were 10-fold greater in plants incubated in the light than in those kept in darkness, and the bulk of the labelling was determined as aspartate, glutamate and alanine. The differences of in vivo and in vitro carboxylation along the thallus suggest the need for whole plant carboxylation measurements to achieve accurate estimates of primary productivity in L. setchellii and possibly other Laminariales.

Interactions between C and N metabolism in Dunaliella salina cells cultured at elevated CO 2 and high N concentrations

Summary The green alga Dunaliella salina UTEX 200 was cultured at high (5 percnt;) [CO 2 ] in a medium containing 10 mmol/L of either NO 3 − or NH 4 + as the sole N source. Specific growth rate was 50 percnt; higher for NH 4 + -grown cells than for their counterparts cultured in the presence of NO 3 − . Cell size, protein content, Rubisco protein, phosphoenolpyruvate carboxylase (PEPC) activity, and light independent carbon fixation were enhanced by growth in the presence of NH 4 + . On the other hand, maximal photosynthetic rate and cell glycerol concentration were lower when N was supplied as NH 4 + . The activity of glutamine synthetase was affected very little by the N-source. D. salina UTEX 200 showed some peculiarities in its mechanism of adaptation to high [N] in comparison to other strains previously used for similar studies. This allowed dissection of the underlying mechanism of the growth response to high [N], highlighting the potential role of PEPC, the main anaplerotic enzyme, as a pivotal player in the adaptation of cells to these conditions.

SEASONAL PATTERNS OF PHOTOSYNTHESIS AND LIGHT‐INDEPENDENT CARBON FIXATION IN MARINE MACROPHYTES1

ABSTRACTThe contribution of light‐independent carbon fixation (LICF) to the overall carbon gain and the seasonal patterns of maximum photosynthesis (Pmax and LICF were characterized in a broad taxonomic range of macrophytes from Monterey Bay, California. Pmax and LICF rates (nmol C.g filtered seawater−1.min−1) varied among species and taxonomic groups examined, and as a function of tissue type in the phaeophyte Laminaria setchellii Silva (Phaeophyceae). On average, Pmax values were higher in the Rhodophyta, whereas LICF rates were greater in the Phaeophyceae. LICF rates were generally less than 5% of Pmax in the marine macrophytes studied and, as a consequence, cannot fully compensate for respiratory carbon losses, which usually are greater than 10% of Pmax. All species studied possessed the highest Pmax and LICF rates when irradiance levels were highest and decreased during periods of low incident irradiance. Seasonal patterns of Pmax and LICF in most of the macrophytes from the stenothermal environment of Monterey Bay were strongly correlated with photosynthetic photon flux rather than seawater temperature. The concomitant decrease of LICF and Pmax rates in all species examined argues against LICF playing a major role in carbon acquisition under light‐limiting conditions as suggested previously. Rather, the strong positive correlation of Pmax and LICF indicates the direct coupling of photosynthate (e.g. 3‐phosphoglyceric acid) generation with production of substrates for LICF reactions. Our results also suggest that LICF might be a useful indicator of photosynthetic metabolism in marine macrophytes.

Longitudinal Profiles of Growth, Photosynthesis and Light Independent Carbon Fixation in the Antarctic Brown Alga Ascoseira mirabilis

Article Longitudinal Profiles of Growth, Photosynthesis and Light Independent Carbon Fixation in the Antarctic Brown Alga Ascoseira mirabilis was published on January 1, 1995 in the journal Botanica Marina (volume 38, issue 1-6).

Photosynthesis, dark respiration and light independent carbon fixation of endemic Antarctic macroalgae

The light saturated photosynthesis, dark respiration and light independent carbon fixation of macroalgal species endemic to the Antarctic were measured. Five brown algae. Ascoseira mirabilis, Desmarestia anceps, D. antarctica, Phaeurus antarcticus, Himantothallus grandifolius and the red alga Palmaria decipiens were included. Rates of these three parameters at 0°C were very similar to those measured in other studies on temperate algae at higher temperature. This indicates a high degree of physiological adaptation to the Antarctic environment within these species. A comparison was made of polarographic and chemical means of measuring oxygen flux during photosynthesis and dark respiration at low temperature. There was a good correlation between measurements of oxygen evolution and carbon fixation, although apparent photosynthetic quotient values were in most cases high.

Photosynthetic and light-independent carbon fixation in Macrocystis, Nereocystis, and some selected Pacific Laminariales

The large kelp Macrocystis integrifolia and Nereocystis luetkeana off the coast of British Columbia have light saturation points at about 200 foot candles (1 foot candle = 10.76391 lx); however, photosynthetic rates remain unimpeded through mugh higher light intensities, up to 7000 foot candles. Short-term labelling experiments indicate that the Calvin cycle is operational in these plants, but, in addition, and particularly in the young growing parts, relatively high activities of phosphoenolpyruvate carboxykinase (PEP-CK)and correspondingly high rates of 14C fixation in the dark are observed. In older, mature parts, the activity of PEP-CK as well as the ability for light-independent 14C assimilation are lower. These observations are supported by data from a variety of other Pacific Laminariales. Pulse–chase experiments in the light and in the dark reveal characteristic differences between young and mature parts of the fronds: apart from qualitative difference in the soluble fraction of assimilates, the young parts show a significantly large proportion of radiocarbon confined to the ethanol-insoluble fraction.