Photosynthetic Carbon Dioxide Fixation Research Articles

Role of Microorganisms in the Digestion of Lignocellulose by Termites

Photosynthetic fixation of carbon dioxide in our biosphere yields approxi­ mately 136 X lOIS g of dry plant material annually, which represents Earth's most abundant form of biomass (88). Two major constituents of such biomass are cellulose and lignin, and hence this material is often referred to as . lignocellulosic biomass, or simply lignocellulose. Most of the synthesis (about 2/3) occurs in terrestrial ecosystems where it is balanced, or nearly so, by the decomposition/respiration side of the carbon cycle (63). Decom­ position of lignocellulose is carr ied out primarily by microorganisms, chiefly fungi and bacteria. However, augmenting the activities of microbes is an arr ay of soil macro-invertebrates, whose effects may range from simple comminution and dispersion of plant material to actual dissimilation of the structural polymers of lignocellulose (86, 90, 91). Among the most abundant and important of these invertebrates ' are termites, which, with their associated microbial symbionts, dissimilate a significant proportion of the cellulose

Effects of Phosphorus Limitation on Respiratory Metabolism in the Green Alga Selenastrum minutum

The effects of phosphorus nutrition on several physiological and biochemical parameters of the green alga, Selenastrum minutum, have been examined. Algal cells were cultured in chemostats under conditions of either Pi limitation or nutrient sufficiency. Pi limitation resulted in: (a) a 5-fold lower rate of respiration, (b) a 3-fold decline in rates of photosynthetic carbon dioxide fixation and oxygen evolution, (c) a 3-fold higher rate of dark carbon dioxide fixation, (d) significant increases in activities of phosphoenolpyruvate (PEP) carboxylase and PEP phosphatase (128% and 158% of nutrient sufficient activities, respectively), (e) significant reductions in activities of nonphosphorylating NADP-glyceraldehyde-3-phosphate dehydrogenase and NAD malic enzyme, and (f) no change in levels of ATP:fructose-6-phosphate 1-phosphotransferase, phosphorylating NAD-glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase, and pyruvate kinase. The intracellular concentrations of Pi, ATP, AMP, soluble protein, and chlorophyll were also significantly reduced in response to Pi limitation. As well, the level of ADP was about 11-fold lower in the Pi-limited cells as compared to the nutrient sufficient controls. It was predicted that because of this low level of ADP, pyruvate kinase catalyzed conversion of PEP to pyruvate may be restricted in Pi-limited cells. During Pi limitation, PEP carboxylase and PEP phosphatase may function to "bypass" the ADP dependent pyruvate kinase, as well as to recycle Pi for its reassimilation into cellular metabolism.

Control of photosynthetic carbon dioxide fixation by the boundary layer, stomata and ribulose 1,5‐biphosphate carboxylase/oxygenase

Abstract Coefficients describing the sensitivity of the rate of photosynthetic carbon dioxide fixation to small changes in the stomatal conductance and boundary layer conductance are derived. These sensitivity or ‘control’ coefficients, together with those for the carboxylase and oxygenase activities of ribulose 1,5‐bisphosphate carboxylase/oxygenase, are calculated from standard gas exchange data and apply under conditions where leaf temperature and water vapour concentration at the leaf surface remain largely constant. It is shown that the magnitude of the control coefficients depends on conditions such as photon flux density, ambient CO2 concentration and relative humidity at the leaf surface. The extension of this analysis to encompass the sensitivity of the photosynthetic fluxes to changes in enzyme concentrations and kinetic properties is also discussed.

Regulation of Expression of Carbon-Assimilating Enzymes by Nitrogen in Maize Leaf

We have utilized the cellular differentiation gradient of the developed, youngest leaf to examine the regulation by nitrogen of levels of phosphoenolpyruvate carboxylase (PEPCase), pyruvate orthophosphate dikinase (PPDK), and ribulose 1,5-bisphosphate carboxylase in maize (Zea mays L.). The protein whose level regulated most preferentially by N availability was PEPCase, followed by PPDK, and the changes in level occurred most conspicuously at the photosynthetically maturing cells. Pulse and pulse-chase experiments to analyze photosynthetic fixation of [(14)C]CO(2) indicate that maize leaf primarily exploited a C(4)-mode of photosynthetic fixation of carbon dioxide even under a selective reduction in levels of these proteins. The effects of N on the synthesis of these proteins and the accumulation of corresponding mRNAs during recovery from a deficiency were examined by pulse and pulse-chase labeling with [(35)S]Met and by hybridization, respectively. The rate of turnover of PPDK was substantially higher than that of the other proteins. Results also showed that the reduced accumulation of PEPCase, as well as PPDK, under N deficiency could largely be accounted for a reduced level of synthesis of protein with a concomitant reduction in level of their mRNAs. This indicates that the N-dependent selective accumulation of these enzymes is primarily a consequence of level of its mRNAs.

The path of carbon in photosynthesis—Back to the future

F ive to ten billion tons of carbon dioxide from fossil-fuel based energy production and from deforestation burnoff are entering the atmosphere annually. Suggested solutions to this massive accumulation include alternate energy sources, energy conservation, massive reforestation and, in the long term, increased use of natural carbon dioxide reservoirs such as the oceans. Relatively neglected in global planning efforts are the opportunities which may lie in the genetic engineering of the two key enzymes in photosynthetic carbon dioxide fixation, phosphoribulokinase (PRK) and ribulosebisphosphate carboxylase/oxygenase (Rubisco). Even the smallest increase in the efficiency of CO 2 fixation by Rubisco would remove significant amounts of CO 2 from the atmosphere. (A 1% increase on a worldwide basis would theoretically fix 1.5.109 additional tons of CO 2 per year. It is estimated that 1.5.1011 tons of CO 2 are sequestered annually by photosynthesis.) Present funding in this area is modest by any standards and it is surprising that a concerted research program to achieve both an understanding and enhancement of the Rubisco reaction has not been implemented nor, perhaps, even seriously considered at a national level. With this in mind, the purpose of this review is to detail the background and research which led to the first isolation and characterization

Crystallization and structure of a recombinant ribulose-1,5-bisphosphate carboxylase

Ribulose-1,5-bisphosphate carboxylase/oxygenase is the key enzyme in photosynthetic carbon dioxide fixation and photorespiration. The dimeric carboxylase from the photosynthetic bacterium Rhodospirillum rubrum has been cloned and expressed in E. coli. The recombinant enzyme has been crystallized in a number of different crystal forms. The three-dimensional structure of the enzyme has been determined by X-ray crystallographic methods to 2.9Åresolution.

Studies into the action of the diphenyl ether herbicides acifluorfen and oxyfluorfen. Part I: Activation by light and oxygen in leaf tissue

AbstractThe effect of acifluorfen and oxyfluorfen on chlorophyll bleaching, lipid peroxidation and photosynthesis in pea leaf discs was studied. Both her‐ bicides induced light‐dependent bleaching and lipid peroxidation, the level of damage being greater at higher light intensities. Photosynthetic carbon dioxide fixation was only partially inhibited in treated leaf discs incubated in darkness, thus indicating that these herbicides did not inhibit photo‐ synthesis as a primary mode of action. Leaf discs maintained in darkness showed no visible signs of injury, and light‐dependent herbicide‐induced damage was reduced by incubating discs under nitrogen, orpre‐incubating them with the electron‐transport inhibitor monuron. It is suggested that acifluorfen and oxyfluorfen are activated by a light‐dependent process, which requires photosynthetic electron transport.

Control of the rate of photosynthetic carbon dioxide fixation

A simplified model of the reductive pentose phosphate pathway of photosynthesis is analysed in order to quantify the degree to which each of the constituent reactions controls the rate of CO2 fixation (given by the control coefficient). The analysis focuses on the four largely irreversible reactions of the cycle together with the first irreversible reaction in the sucrose and starch synthetic pathways. The model assumes that the other reactions are at equilibrium. The photorespiratory and electron transport systems are not included in the model. The analysis demonstrates that: (1) an analytical approach can be used to investigate the distribution of flux control in autocatalytic and moiety-conserved cycles; (2) measurements of enzyme kinetic parameters and certain fluxes and substrate concentrations can be used to solve the equations defining the enzyme control coefficients; (3) the conservation of total stromal phosphate and the intricate regulatory mechanisms of the photosynthetic system result in a relationship between the control coefficients that is complex and may defy any intuitive assessment of ‘rate limitation’; (4) ribulose-1,5-bisphosphate carboxylase / oxygenase may, under certain conditions, be a major controller of the rate of CO2 fixation and, by regulating the concentration of ribulose 1,5-bisphosphate, may be important in governing the ratio of organic to inorganic phosphate in the stroma; (5) the other enzymes may also serve an important role in determining the distribution of phosphate between organic and inorganic species because they catalyze reactions at the branch points between starch and sucrose synthesis and ribulose 1,5-bisphosphate regeneration; (6) these enzymes that catalyze ‘branch-pint’ reactions may have negative control coefficients because of their ability to reduce the total concentration of cycle intermediates; (7) an approach combining the use of the equations presented in this paper and flux and substrate concentration measurements may be adequate for determining the control coefficients of several enzymes of the reductive pentose phosphate pathway.

Chlorophyll a fluorescence: can it shed light on fundamental questions in photosynthetic carbon dioxide fixation?

Abstract A close, immediate and precise relationship between chlorophyll a fluorescence and photosynthetic carbon assimilation in vivo is demonstrated. The examples discussed include kinetics displayed during dark to light transitions plus oscillations and transients observed during changes in the gas phase surrounding the leaf. Remaining uncertainties surrounding the relationship between chlorophyll fluorescence and photosynthesis are attributed to the underlying complexity of the regulatory mechanisms involved. Examples are also given that show how multiple simultaneous measurements of different aspects of the photosynthetic process may contribute to the resolution of these uncertainties. The practical relevance of these matters is also discussed, particularly in relation to the limitations of the photosynthetic process and to the use of chlorophyll fluorescence as a diagnostic probe of chemical and genetic manipulation and stress.

Regulatory interaction of photosynthetic nitrate utilization and carbon dioxide fixation in the cyanobacterium Anacystis nidulans

The rate of photosynthetic nitrate utilization in Anacystis nidulans is strongly influenced by the availability of carbon dioxide. This dependence can be relieved by inhibiting the metabolism of the ammonium derived from nitrate reduction. Nitrate uptake seems to be modulated through a sensitive regulatory system integrating the photosynthetic metabolism of carbon and nitrogen, with CO 2 fixation products antagonizing the inhibitory effect of ammonium derivatives.

Photoinhibition and P700 in the Marine Diatom Amphora sp.

The marine diatom Amphora sp. was grown at a light intensity of 7.0 x 10(15) quanta centimeter(-2) second(-1). Light saturation of photosynthesis for these cells was between 6.0 and 7.0 x 10(16) quanta centimeter(-2) second(-1). At light intensities greater than saturation, photosynthetic (14)CO(2) fixation was depressed, while P700 unit size (chlorophyll a concentration/P700 activity) increased and number of P700 units per cell decreased. After a 1-hour exposure of Amphora sp. to a photoinhibitory light intensity of 2.45 x 10(17) quanta centimeter(-2) second(-1), there was a 45 to 50% decrease in the rate of (14)CO(2) fixation relative to the rate at the culture light intensity. There also was a 25% increase in P700 unit size and a 30% reduction in the number of P700 units per cell but no change in total chlorophyll a concentration. Following this period of photoinhibition, the cells were returned to a light regime similar to that in the original culture conditions. Within 1 hour, both number of P700 units per cell and P700 unit size returned to levels similar to those of cells which were kept at the culture light intensity. The rates of photosynthesis did not recover as rapidly, requiring 2 to 3 hours to return to the rate for the nonphotoinhibited cells. Our results indicate that a decrease in P700 activity (with a resultant increase in P700 unit size) may be partially responsible for the photoinhibition of algal photosynthetic carbon dioxide fixation.

Studies on photosynthetic electron transport, photophosphorylation and CO2fixation in zinc deficient leaf cells ofZea mavs. L.

Abstract The effect of Zn deficiency on rate of photosynthesis of leaf discs, isolated mesophyll and bundle sheath cells and chloroplasts of maize (Zea mays. L) was studied. The yield of mesophyll and bundle sheath cells obtained by enzymic digestion of the leaf tissues from Zn deficient plants is lower than the identical tissues from normal plants which suggests that Zn deficiency brings about some structural changes in the leaf cell. Photosynthetic oxygen evolution measured in the leaf discs is low due to Zn deficiency. Photosystem‐II dependent Hill reaction and non cyclic photophosphorylation of chloroplasts were also affected by Zn deficiency. Rate of photosynthetic carbon dioxide fixation by both bundle sheath and mesophyll cells obtained from Zn deficient leaf‐tissue waslower than the cells free from Zn deficiency. Addition of various metabolites like NADPH, ATP and PEP to Zn deficient mesophyll cells whowed marked enhancement in 14‐CO2 fixation. However, addition of NADPH, ATP and RuBP to Zn defici...

Analysis of a new mutant from Euglena gracilis resistant to streptomycin

We analysed a new mutant resistant to streptomycin, Sm 2 rBNgL (Sm 2). This mutant was resistant to 5 mg of streptomycin (STR) per ml when grown on solid organotrophic medium. Chlorophyll synthesis, photosynthetic carbon dioxide fixation and oxygen evolution were normal when dark-grown resting mutant cultures, containing 0.3 mg of streptomycin per ml, were transferred to t he light. The 32S small chloroplast ribosomal suunits extracted from this mutant lost their affinity for dihydrostreptomycin. Finally, comparison between electrophoretograms obtained with chloroplast ribosomal proteins extracted from wild-type and mutant suggested that one acidic protein of the 32S small ribosomal subunit might be modified. Results presented here and those obtained with another Euglena mutant resistant to streptomycin, Sm 1 rBNgL (Sm 1), (Freyssinet, Plant Sci. Lett. 5 (1875) 305) suggest that the streptomycin binding site is located in the unstable region of the 32S small chloroplast ribosomal subunits of Euglena.

DIVERSITY IN THE MECHANISM OF CARBON DIOXIDE FIXATION INDUNALIELLA TERTIOLECTA(CHLOROPHYCEAE)1

ABSTRACTThe mechanism of photosynthetic carbon dioxide fixation in the green flagellateDunaliella tertiolectaButcher varies during growth in batch culture. Evidence for this change comes from three sources: i) algae from the stationary phase incorporated a greater proportion of the fixed carbon into amino arids and protein than did cells from the mid‐exponential phase; ii) the activity of phosphoenolpyruvate carboxylase relative to that of ribulose‐1, 5‐di‐phosphate carboxylase increased with age in batch culture; and, iii) cells from the stationary phase appeared to utilize the bicarbonate ion as the substrate for photosynthesis, whereas those from mid‐exponential phase appeared to utilize fire carbon dioxide. These data suggest that a change of photosynthetic mechanism can occur within a single species of alga, depending on its physiological state.

Photosynthesis and Carbon Metabolism in Marine and Freshwater Diatoms

Summary A variety of diatom species (Bacillariophyceae) has comparatively been investigated with special respect to photosynthetic and light-independent carbon dioxide fixation. Dark fixation generally does not exceed 4–5% of photosynthetic 14C-incorporation. The assimilate pattern of long-term photosynthesis in H14CO3 comprises a complex variety of soluble and insoluble assimilates: considerable amounts of 14C are recovered from several amino acids, preferably from glutamate. Relatively few 14C is confined to low-molecular weight carbohydrates such as glucose and fructose. Sucrose or any polyhydroxy alcohols (mannitol) are not found to be 14C-labelled photosynthates. Appreciable amounts are converted to polymeric constituents, mainly to polysaccharides and to various lipids which account for more than 60% of total radiocarbon found in the soluble assimilates after longer periods of photosynthetic 14C-fixation. Experiments on short-term photosynthetic 14C-incorporation (5, 10, and 15 s) resulted in predominant 14C-labelling of phosphorylated compounds such as 3-phosphoglycerate and some sugar phosphates showing the typical time dependent decrease in percentage of 14C-labelling, whereas C4-compounds including aspartate and malate exhibited very different kinetics of 14C-labelling. Ribulose-1.5-biphosphate carboxylase (EC 4.1.1.39) is the most important carboxylating system. Appreciable rates of carboxylation by phosphoenolpyruvate carboxykinase (EC 4.1.1.31) are detectable as well. Activity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) could not be found. These results suggest that photosynthetic carbon fixation in diatoms does not resemble the C4-pathway, but generally follows the well documented Calvin scheme. The results are summarized with regard to the biochemical taxonomy of the Bacillariophyceae.

Increasing Photosynthesis by Inhibiting Photorespiration with Glyoxylate

Glyoxylate treatment doubles net photosynthetic carbon dioxide fixation by tobacco leaf disks because inhibition of glycolate synthesis by glyoxylate results in decreased photorespiration. These observations show that photorespiration can be metabolically regulated and suggest that genetic or chemical alteration of pool sizes of certain metabolites can produce plants with increased photosynthesis.

Barley mutants with defects in photosynthetic carbon dioxide fixation

Carbon dioxide fixation by leaf pieces from 12 different chloroplast mutants and wild type barley has been analysed. In the light leaf pieces from wild type seedlings fixed14CO2 at a rate of approximately 80 μmoles per gram fresh weight per hour, or 40 μmoles per mg chlorophyll per hour. Fixation of14CO2 in darkness occurred at one to four per cent of the rate in light. Five of the mutants investigated (vir-zb 63, vir-l27, vir-zd69, vir-c12 andxan-m 3) were completely blocked in light-dependent CO2 fixation. The mutantsvir-m 29, vir-u46, xan-d49, xan-c47, vir-t45, xan-t50 andvir-k 23 all yielded reduced photosynthetic rates on a gram fresh weight basis, but, with the exception ofvir-k 23, their photosynthetic rates on a chlorophyll basis differed by less than a factor of two from that of the wild type. On a chlorophyll basisvir-k 23 showed an enhanced rate of14CO2 fixation in comparison with the wild type. Barley mutants lacking light-dependent14CO2 incorporation fixed in darkness or in light similar small amounts of14CO2 into malate, aspartate, glutamate and citrate as did the wild type in darkness. Photosynthetic products in the mutants capable of light-dependent CO2 fixation were qualitatively the same as in the wild type, and the patterns of distribution of tracer carbon gave no evidence of any defects in reactions following the fixation of CO2. The gross correlation between chlorophyll contents and photosynthetic rates on a chlorophyll basis among these mutants with the exception ofvir-k 23 suggests that the reduced absorption of light by the lower amounts of chlorophyll in these mutants is the major or only factor responsible for their reduced photosynthetic rates on a gram fresh weight of leaf basis. The suggestion is made thatvir-k 23, which is characterized by a far higher photosynthetic rate in bright light than the wild type on a chlorophyll basis, contains several-fold lower amounts of light-harvesting chlorophyll per photosynthetic unit than wild type, whereas the other mutants that are capable of photosynthesis have photosynthetic units of the same size as the wild type but fewer of them.

Comparative studies of glycollic acid uptake by four marine algae

Two marine diatoms, Skeletonema costatum (Grev.) Cleve and Thalassiosira pseudonana 3H, and two marine flagellates Dunaliella primolecta Butcher and Chlamydomonas euryale Lewin were studied for glycollic acid uptake. Only Thalassiosira assimilated appreciable quantities of glycollic acid under optimal photosynthetic conditions, the carbon uptake being about 1% of that in photosynthetic fixation of carbon dioxide. The other algae showed no appreciable glycollic acid uptake under similar conditions. The ability of Thalassiosira pseudonana to take up exogenous glycollic acid was examined particularly with respect to the effects of light and external concentrations of bicarbonate and glycollic acid.

THE PHYSIOLOGY OF NEOSPONGIOCOCCUM OVATUM DEASON

SummaryBy enrichment culture and conventional microbiological techniques the dominant alga of sewage trickle filters was obtained in axenic culture and identified as Neospongiococcutn ovatum Deason. A wide range of carbon compounds failed to support heterotrophic growth or alter the mean generation time or final cell yield in the light. The rate of photosynthetic carbon dioxide fixation was also unaffected by the growth conditions. The enzymes of the tricarboxylic acid cycle were present at comparable specific activity in cell extracts, but significant uptake of [14C]‐acetate or [14C]‐glycollate was not detected. It is suggested that impermeability to exogenous compounds may be an advantage in a toxic environment.

Evidence for C 4 photosynthesis in barley pericarp tissue

The products of photosynthetic carbon dioxide fixation were determined in isolated pericarps of immature barley grains. Of the carbon dioxide fixed after 1 min photosynthesis 84% was in the C 4 acid malic acid. The remaining label was in hexose phosphates and sucrose. By 2 min sucrose was the major labelled product and at 6 min accounted for 94% of the total carbon dioxide fixed.