Photosynthesis in the Aquatic MacrophyteEgevia densa. I. 14CO2 Fixation at Natural CO2 Concentrations

1977 ◽  
Vol 4 (2) ◽  
pp. 169 ◽  
Author(s):  
JA Browse ◽  
FI Dromgoole ◽  
JMA Brown
Keyword(s):  
Time Course ◽  
Calvin Cycle ◽  
High Rate ◽  
Previous Suggestion ◽  
Fixation Rate ◽  
14Co2 Fixation ◽  
Co2 Concentrations ◽  
Phosphoglyceric Acid ◽  
Sugar Phosphates ◽  
Inorganic Carbon Concentration

In *14C time-course and pulse-chase experiments, the photosynthetic fixation rate for Egeria densa Planch. was about 19 �mol C (g dry wt)-1 min-1 (13.7 mg C (g dry wt)-1 h-1) at a total inorganic carbon concentration of 1.0 x 10-3 M, pH 6.8 and 75-80% light saturation. At this high rate, under conditions closely approximating those of plants in the field, 14C distribution into 3-phosphoglyceric acid, sugar phosphates and sucrose indicates that the Calvin cycle is the primary carboxylation mechanism and responsible for over 90% of the 14C initially incorporated. Malate accounts for only 5 % of the initial 14CO2 fixation and is not actively further metabolized. Additional label from Calvin cycle intermediates enters malate during the cold chase treatment. It is suggested that the predominant 14C fixation into malic acid, noted in previous reports on Hydrocharitacean species, may be due to very low experimental CO2 concentrations and a consequent suppression of the Calvin cycle activity. Compounds of the glycollate pathway were detected in sufficient quantities to give some support to the previous suggestion of photorespiratory activity in Egeria.

14CO2 fixation in leaf discs of Phaseolus vulgaris

1970 ◽  
Vol 48 (6) ◽  
pp. 1259-1263 ◽  
Author(s):  
Imre A. Tamas ◽  
R. G. S. Bidwell
Keyword(s):  
Phaseolus Vulgaris ◽  
Calvin Cycle ◽  
Temporary Increase ◽  
Hexose Monophosphate ◽  
Phaseolus Vulgaris L ◽  
Leaf Discs ◽  
14Co2 Fixation ◽  
Transient Rise ◽  
Phosphoglyceric Acid ◽  
Rapid Drop

Leaf discs of Phaseolus vulgaris L. were exposed to 14CO2 in light, and transient changes in the radioactivity of photosynthetic intermediates were determined when illumination was interrupted or the CO2 concentration lowered. The responses of phosphoglyceric acid, hexose monophosphate, and ribulose diphosphate showed that the Calvin cycle operates in this tissue. Turning off the light caused a rapid drop in 14C-sucrose and in the total 14C-content of the tissue, with a simultaneous rise in radioactive alanine, glutamate, malate, and aspartate, suggesting the rapid entry of sucrose carbon into respiratory pathways. Lowering the CO2 concentration resulted in a transient rise in 14C-glycolate which was followed by a temporary increase in 14C-serine-glycine and in the ambient CO2 concentration. This supports the hypothesis that glycolate produced in photosynthesis is a substrate for glycine and serine synthesis as well as for CO2 evolution.

Stomatal Metabolism: CO2 Fixation and Respiration

1977 ◽  
Vol 4 (4) ◽  
pp. 611
Author(s):  
N Thorpe ◽  
F.L Milthorpe
Keyword(s):  
Flux Density ◽  
Co2 Fixation ◽  
Calvin Cycle ◽  
Co2 Concentration ◽  
High Rate ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Initial Fixation ◽  
Sugar Phosphates ◽  
Early Fixation

The rate of fixation of CO2 by epidermis attached to the leaf of Commelina cyanea was linear with photon flux density up to 1.08 mE m-� s-� and with CO2 concentration from 0 to 355 ppm. Detached epidermis, on the other hand, showed no response to photon flux density and had rates in the light which were only twice those in the dark. There was substantial leakage of all labelled methanol-soluble substances from isolated epidermis. Its apparent reduced functioning may well be associated with this leakage rather than reflecting transport from the mesophyll. The early fixation products in light and dark were similar in attached and detached epidermis. These were mainly aspartate and malate in contrast to the Calvin cycle intermediates formed in mesophyll in the light. It seems likely that phosphoenolpyruvate carboxylase is closely implicated in the initial fixation of CO2 by stomata and is responsible for the much higher rates of fixation per unit of chlorophyll by epidermis than by mesophyll. Although aspartate and malate are the major products detectable after 2 min feeding with 14CO2 and remain as a high proportion of labelled products during a subsequent 12CO2 chase, amino acids, sugars and sugar phosphates together with polysaccharides and other methanol-insoluble products are eventually labelled. Attempts to measure respiration rates of attached epidermis were unsuccessful due to fixation of mesophyll-respired CO2; the rate in detached epidermis was high, suggesting a high rate of turnover of carbon products by stomata, but we were unable to relate this to rates in attached epidermis. Rates were higher in CO2-free than in CO2-containing environments, indicating a possible explanation of the CO2 effect on stomata.

scholarly journals Design and in vitro realization of carbon-conserving photorespiration

2018 ◽  
Vol 115 (49) ◽  
pp. E11455-E11464 ◽  
Author(s):  
Devin L. Trudeau ◽  
Christian Edlich-Muth ◽  
Jan Zarzycki ◽  
Marieke Scheffen ◽  
Moshe Goldsmith ◽  
...  
Keyword(s):  
Carbon Fixation ◽  
Calvin Cycle ◽  
Computational Design ◽  
Carbon Loss ◽  
Fixation Rate ◽  
Bisphosphate Carboxylase ◽  
Stoichiometric Model ◽  
Synthetic Routes ◽  
Coa Reductase

Photorespiration recycles ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) oxygenation product, 2-phosphoglycolate, back into the Calvin Cycle. Natural photorespiration, however, limits agricultural productivity by dissipating energy and releasing CO2. Several photorespiration bypasses have been previously suggested but were limited to existing enzymes and pathways that release CO2. Here, we harness the power of enzyme and metabolic engineering to establish synthetic routes that bypass photorespiration without CO2 release. By defining specific reaction rules, we systematically identified promising routes that assimilate 2-phosphoglycolate into the Calvin Cycle without carbon loss. We further developed a kinetic–stoichiometric model that indicates that the identified synthetic shunts could potentially enhance carbon fixation rate across the physiological range of irradiation and CO2, even if most of their enzymes operate at a tenth of Rubisco’s maximal carboxylation activity. Glycolate reduction to glycolaldehyde is essential for several of the synthetic shunts but is not known to occur naturally. We, therefore, used computational design and directed evolution to establish this activity in two sequential reactions. An acetyl-CoA synthetase was engineered for higher stability and glycolyl-CoA synthesis. A propionyl-CoA reductase was engineered for higher selectivity for glycolyl-CoA and for use of NADPH over NAD+, thereby favoring reduction over oxidation. The engineered glycolate reduction module was then combined with downstream condensation and assimilation of glycolaldehyde to ribulose 1,5-bisphosphate, thus providing proof of principle for a carbon-conserving photorespiration pathway.

Quantitative aspects of RNA synthesis and polyadenylation in 1-cell and 2-cell mouse embryos

Development ◽  
1983 ◽  
Vol 74 (1) ◽  
pp. 169-182
Author(s):  
Kerry B. Clegg ◽  
Lajos Pikó
Keyword(s):  
Time Course ◽  
Specific Activity ◽  
Average Length ◽  
State Level ◽  
Mouse Embryos ◽  
High Rate ◽  
Rna Sequences ◽  
Cell Stage ◽  
New Synthesis ◽  
Cell Embryo

Mouse embryos at the late 1-cell and late 2-cell stages were labelled with [3H]adenosine for periods of up to 320 min during which the specific activity of the ATP pool was constant. The time course of the molar accumulation of adenosine was calculated for tRNA, high-molecular-weight poly(A)− RNA and poly(A) tails versus internal regions of poly(A)+ RNA. Most of the adenosine incorporation into tRNA is due to turnover of the 3′-terminal AMP but some new synthesis of tRNA also appears to take place in both 1-cell and 2-cell embryos at a rate of about 0·2 pg/embryo/h. In the poly(A)- RNA fraction, an unstable component which is assumed to be heterogeneous nuclear RNA is synthesized at a high rate and accumulates at a steady-state level of about 1·5 pg/embryo in the 1-cell embryo and about 3·0 pg/embryo in the 2-cell embryo. Both 1-cell and 2-cell embryos synthesize relatively stable heterogeneous poly(A)− RNA, assumed to be mRNA, at a rate of about 0·3 pg/embryo/h; 2-cell embryos also synthesize mature ribosomal RNA at a rate of about 0·4 pg/embryo·h. Internally labelled poly(A)+ RNA is synthesized at a low rate in the 1-cell embryo, about 0·045 pg/embryo/h, but the rate increases to about 0·2 pg/embryo/h by the 2-cell stage. A striking feature of the 1-cell embryo is the high rate of synthesis of poly(A) tails, about 2·5 × 106 tails/embryo/h of an average length of (A)43, due almost entirely to cytoplasmic polyadenylation. This and other evidence suggests a turnover of the poly(A)+ RNA population in 1-cell embryos as a result of polyadenylation of new RNA sequences and degradation of some of the pre-existing poly(A)+ RNA. In the 2-cell embryo, the rate of synthesis of poly(A) tails (average length (A)93) is estimated at about 0·8 × 106tails/embryo/h and a significant fraction of poly(A) synthesis appears to be nuclear.

Effect of Salinity on Photosynthetic 14CO2 Fixation and Amino Acid Pools of Bellerochea yucatanensis (v. Stosch) and Thalassiosira rotula (Meunier)

1985 ◽  
Vol 40 (7-8) ◽  
pp. 527-530
Author(s):  
Günter Döhler ◽  
Joachim Zink
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Aspartic Acid ◽  
Marine Diatoms ◽  
14Co2 Fixation ◽  
Low Salt ◽  
Photosynthetic Products ◽  
Sugar Phosphates ◽  
Total Amino Acids

Abstract The marine diatoms Bellerochea yucatanensis and Thalassiosira rotula were grown at different salinities (20/25, 35, and 40/45‰ salinity (S), respectively) under normal air (0.035 vol.% CO2). No significant variations in the percentage of gross photosynthetic products (e.g. total amino acids, sugar phosphates) were found as a function of salinity during growth. The bulk of the soluble 14C-radioactivity was detected in amino acids. 14C-labelling of glutamine increased markedly with salinity. Low salt - grown algae are characterized by enhanced amino acid pools, mainly of aspartic acid, asparagine and glutamine. It was found that the tested amino acids are not involved in osmoregulation.

Effects of ozone on 14CO2 fixation patterns in pine

1973 ◽  
Vol 51 (9) ◽  
pp. 1573-1578 ◽  
Author(s):  
Thomas G. Wilkinson ◽  
Robert L. Barnes
Keyword(s):  
Amino Acids ◽  
Free Amino Acids ◽  
Free Amino ◽  
Soluble Sugars ◽  
Pinus Strobus ◽  
Relative Activity ◽  
Ozone Treatment ◽  
White Pine ◽  
14Co2 Fixation ◽  
Sugar Phosphates

Seedlings of white pine (Pinus strobus L.) and detached shoots of white and loblolly (P. taeda L.) pines were exposed to various concentrations of ozone either before or during photosynthetic fixation of 14CO2. The major changes in distribution of 14C as a result of ozone treatment were (1) a reduction of relative activity in soluble sugars; (2) an increase in activity in sugar phosphates; and (3) an increase in activity in free amino acids, especially alanine. Significant differences in 14C fixation patterns were observed at ozone concentrations as low as 10 pphm (parts per hundred million), and during 14CO2 fixation times as short as 10 min. However, other combinations of treatment levels and times did not always result in statistically significant effects.

scholarly journals Proteolytic processing of potyviral proteins and polyprotein processing intermediates in insect and plant cells

2002 ◽  
Vol 83 (5) ◽  
pp. 1211-1221 ◽  
Author(s):  
Andres Merits ◽  
Minna-Liisa Rajamäki ◽  
Päivi Lindholm ◽  
Pia Runeberg-Roos ◽  
Tuija Kekarainen ◽  
...  
Keyword(s):  
Virus Replication ◽  
Time Course ◽  
Infected Plant ◽  
Plant Cells ◽  
Proteolytic Processing ◽  
High Rate ◽  
Detectable Effect ◽  
Virus Infectivity ◽  
Polyprotein Processing ◽  
Baculovirus System

Processing of the polyprotein encoded by Potato virus A (PVA; genus Potyvirus) was studied using expression of the complete PVA polyprotein or its mutants from recombinant baculoviruses in insect cells. The time-course of polyprotein processing by the main viral proteinase (NIaPro) was examined with the pulse–chase method. The sites at the P3/6K1, CI-6K2 and VPg/NIaPro junctions were processed slowly, in contrast to other proteolytic cleavage sites which were processed at a high rate. The CI-6K2 polyprotein was observed in the baculovirus system and in infected plant cells. In both cell types the majority of CI-6K2 was found in the membrane fraction, in contrast to fully processed CI. Deletion of the genomic region encoding the 6K1 protein prevented proper proteolytic separation of P3 from CI, but did not affect processing of VPg, NIaPro, NIb or CP from the polyprotein. The 6K2-encoding sequence could be removed without any detectable effect on polyprotein processing. However, deletion of either the 6K1 or 6K2 protein-encoding regions rendered PVA non-infectious. Mutations at the 6K2/VPg cleavage site reduced virus infectivity in plants, but had a less pronounced, albeit detectable, effect on proteolytic processing in the baculovirus system. The results of this study indicate that NIaPro catalyses proteolytic cleavages preferentially in cis, and that the 6K1/CI and NIb/CP sites can also be processed in trans. Both 6K peptides are indispensable for virus replication, and proteolytic separation of the 6K2 protein from the adjacent proteins by NIaPro is important for the rate of virus replication and movement.

CO2 Fixation in Anabaena cylindrica

1982 ◽  
Vol 37 (3-4) ◽  
pp. 213-217 ◽  
Author(s):  
Günter Döhler
Keyword(s):  
Co2 Fixation ◽  
Calvin Cycle ◽  
Total Radioactivity ◽  
Nitrogen Atmosphere ◽  
Anabaena Cylindrica ◽  
Dark Light ◽  
Initial Fixation ◽  
Phosphoglyceric Acid ◽  
Cyanobacterium Anabaena ◽  
Glycolate Metabolism

Abstract The cyanobacterium Anabaena cylindrica grown in a nitrogen -free medium at + 25 °C was used for short-term 14C-kinetics experiments under different conditions. During the dark/light transients the initial fixation products were mainly sugar monophosphates and 3-phosphoglyceric acid (Calvin cycle intermediates), aspartate (10% of total radioactivity) and glycine/serine. Io­ doacetamide (0.01 м) caused an inhibition o f photosynthetic 14CO2 fixation and a 14C-in corpor­ation into aspartate, glutamate and 3-phosphoglyceric acid only. During dark 14CO2 assimilation labelling of these products could be measured, too. In a nitrogen atmosphere (N2 + 0.04 vol. % CO2) a strong labelling of sugar monophosphates mainly at the beginning o f photosynthetic period could be observed. In an oxygen atmosphere (100% O2) an enhanced label of aspartate and glycerate and a decreased radioactivity in sugar monophosphates were found. Our results were discussed with reference to the operating of a phosphoenolpyruvate carboxylation reaction be­ sides the Calvin cycle and to the glycolate metabolism.

Influence of aerobic metabolism on IMP accumulation in fast-twitch muscle

1985 ◽  
Vol 248 (1) ◽  
pp. C37-C42 ◽  
Author(s):  
G. A. Dudley ◽  
R. L. Terjung
Keyword(s):  
Blood Flow ◽  
Functional Capacity ◽  
Time Course ◽  
Metabolic Stress ◽  
Aerobic Metabolism ◽  
High Rate ◽  
Fast Twitch Muscle ◽  
Fast Twitch ◽  
Peak Blood

Significant activation of AMP deaminase in fast-twitch muscle leads to a loss of ATP and accumulation of NH4 and IMP. Although this occurs during severe metabolic stress caused by intense contraction conditions, the process is probably influenced by the muscle's capacity for aerobic metabolism. We evaluated this possibility during moderately intense (5 Hz) contraction conditions in situ by following the time course of NH4 and IMP accumulation in fast-twitch, low-oxidative white (FTW) and fast-twitch, high-oxidative red (FTR) muscle of the rat. A high rate of IMP formation, resulting in a 50% loss of ATP content, occurred in normal FTW, but not FTR muscle, during contractions when blood flow was intact. Eliminating blood flow prior to contractions, however, removed the distinction between the FTR and FTW muscle. The FTR fiber section now produced a high IMP content and a stoichiometric loss of ATP. Thus the ability of the FTR fiber to sustain this contraction effort without an ATP loss is due to its greater functional capacity for aerobic metabolism. The FTW muscle section of trained animals exhibited a reduced accumulation of IMP and a smaller loss of ATP during the same 5-Hz stimulation. The mitochondrial content and peak blood flow of this FTW fiber section is increased by training. Thus it is probable that the cellular conditions leading to a significant accumulation of IMP in fast-twitch muscle are determined by the metabolic stress established by the contraction effort, relative to the muscle fiber's functional capacity for aerobic metabolism.

Einfluß von Sauerstoff auf die photosynthetische CO2-Fixierung von Synechococcus / Effect of Oxygen on Photosynthetic CO2 Fixation of Synechococcus

1981 ◽  
Vol 36 (1-2) ◽  
pp. 93-97
Author(s):  
Günter Döhler
Keyword(s):  
Co2 Fixation ◽  
Calvin Cycle ◽  
Anacystis Nidulans ◽  
Nitrogen Atmosphere ◽  
Phosphoglyceric Acid ◽  
Glycolate Metabolism ◽  
Effect Of Oxygen ◽  
High Degree ◽  
Oxygen Enhancement ◽  
Oxygen Concentrations

Abstract The cyanobacterium Synechococcus (Anacystis nidulans strain L 1402-1) was grown at +35 °C in air and in air enriched with 2.2 vol.% CO2. The effect of different oxygen concentrations (0, 2, 20, 50, 75 and 99.97 or 97.8 vol.%) was studied in low (0.03 vol.%) and high (2.2 vol.%) CO2 concentrations at + 35 °C. After exposure to a nitrogen atmosphere and low CO2 content I4C-bicarbonate was mainly incorporated into aspartate and glycine/serine. During oxygenic photosynthetic CO2 fixation label in aspartate decreased and a high degree of radioactivity could be found in 3-phosphoglyceric acid and sugar monophosphates. The Calvin cycle was the main fixing pathway in 2.2 vol.% CO2 during anoxygenic and oxygenic conditions independent on the O2 concentrations during the experiments. No oxygen enhancement of photosynthetic CO2 fixation could be found. Possible mechanism involved in CO2 fixation pathways and glycolate metabolism underlying the effect of oxygen was discussed.

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