Nitrite Reduction in Reconstituted and Whole Spinach Chloroplasts during Carbon Dioxide Reduction

Nitrite reduction in either whole, isolated spinach chloroplasts (Spinacia oleracea L.) or in reconstituted spinach chloroplasts is stimulated by a short period of photosynthetic CO₂ fixation in the light prior to nitrite addition. With reconstituted chloroplasts, a similar stimulation can be obtained in nitrite reduction without CO₂ fixation by the addition of dihydroxyacetone phosphate or fructose 6-phosphate. Specific intermediate metabolites of the photosynthetic carbon reduction cycle may have a regulatory role in nitrite reduction in chloroplasts in the light.     

Photophosphorylation and Carbon Dioxide Fixation by Chloroplasts Isolated from Populus deltoides

A system has been developed for the isolation of photosynthetically active chloroplasts from leaves of Populus deltoides. A high proportion of the chloroplasts appeared intact. The maximum rates of different photosynthetic processes were as follows: CO₂ fixation 3.5 micromoles per milligram chlorophyll per hour, noncyclic ATP synthesis 10 micromoles per milligram chlorophyll per hour, and cyclic ATP synthesis 300 micromoles per milligram chlorophyll per hour.     

Effect of Disalicylidenepropanediamine on the Light-dependent Reduction of Carbon Dioxide and Glycerate 3-Phosphate in Intact Spinach Chloroplasts

Disalicylidenepropanediamine (DSPD) at 0.1 to 1 mm levels inhibited light-dependent (14)CO(2) assimilation in intact spinach chloroplasts about 50 to 80%, and this inhibition was accompanied by an increased ratio of (14)C-glycerate 3-phosphate to (14)C-glyceraldehyde 3-phosphate. Enzymatic analysis established that DSPD also inhibited the light-dependent reduction of glycerate 3-phosphate in intact spinach chloroplasts. DSPD at 0.5 mm did not inhibit ribose 5-phosphate isomerase, ribulose 5-phosphate kinase, glycerate 3-phosphate kinase, NADP(+)-linked glyceraldehyde 3-phosphate dehydrogenase or ribulose 1,5-diphosphate carboxylase. The inhibition of chloroplast (14)CO(2) assimilation by DSPD appeared to be related to the inhibition of the photosynthetic electron transport chain. These observations are consistent with experimental results which demonstrated that DSPD inhibited directly the chloroplast lamellar membrane-mediated, light-dependent reduction of ferredoxin (Trebst, A. and M. Burba, 1967, Z. Pflanzenphysiol. 57: 419-433 and Ben-Amotz, A. and M. Avron, 1972, Plant Physiol. 49: 244-248).     

Effect of Adenosine Monophosphate, Adenosine Diphosphate, and Reduced Nicotinamide Adenine Dinucleotide on Adenosine Triphosphate-dependent Carbon Dioxide Fixation in the Autotroph Thiobacillus neapolitanus

The observation that adenosine triphosphate (ATP)-dependent CO(2) fixation in extracts of chemosynthetic and photosynthetic autotrophs may be regulated in part by adenosine monophosphate (AMP) was extended to the strict autotroph Thiobacillus neapolitanus (X). In addition, this report presents data which include adenosine diphosphate (ADP) in the regulatory role. When the primary CO(2) acceptor, ribose-5-phosphate, was replaced by ribulose-1,5-diphosphate, no inhibition of CO(2) fixation occurred unless the Mg(++) concentration was limiting. A molar ratio of 5:1 AMP or ADP to ATP reduced the specific activity (micromoles of CO(2) fixed per milligram of protein per minute) of the extracts from 0.22 to 0.12 and 0.11, respectively. The reported stimulation of the carboxylative phase of ATP-dependent CO(2) fixation by reduced nicotinamide adenine dinucleotide (NADH(2)) was investigated. Adding NADH(2) to the extracts did not stimulate CO(2) fixation, even at carbonate levels from 0.05 to 30 mumoles, except in the absence of ribose-5-phosphate. Slight increases in CO(2) fixation were noted when the assay system was incubated in air instead of the usual helium atmosphere.     

Involvement of Photosynthetic Carbon Reduction Cycle Intermediates in CO(2) Fixation and O(2) Evolution by Isolated Chloroplasts

The photosynthetic carbon reduction cycle intermediates can be divided into three classes according to their effects on the rate of photosynthetic CO₂ evolution by whole spinach (Spinacia oleracea) chloroplasts and on their ability to affect reversal of certain inhibitors (nigericin, arsenate, arsenite, iodoacetate, antimycin A) of photosynthesis: class I (maximal): fructose 1, 6-diphosphate, dihydroxyacetone phosphate, glyceraldehyde-3-phosphate, ribose-5-phosphate; class 2 (slight): glucose 6-phosphate, fructose 6-phosphate, ribulose-1, 5-diphosphate; class 3 (variable): glycerate 3-phosphate. While class 1 compounds influence the photosynthetic rate, they do not lower the Michaelis constant of the chloroplast for bicarbonate or affect strongly other photosynthetic properties such as the isotopic distribution pattern. It was concluded that the class 1 compounds influence the chloroplast by not only supplying components to the carbon cycle but also by activating or stabilizing a structural component of the chloroplast.     

Electrochemical Reduction of Carbon Dioxide on Pyrite as a Pathway for Abiogenic Formation of Organic Molecules

A wide spectrum of electrode potentials of minerals that compose sulfide ores enables the latter, when in contact with hydrothermal solutions, to form galvanic pairs with cathode potentials sufficient for electrochemical reduction of CO2. The experiments performed demonstrated the increase of cathode current on the rotating pyrite disc electrode in a range of potentials more negative than -800 mV in presence of CO2. In high-pressure experiments performed in a specially designed electrochemical cell equipped with a pyrite cathode and placed into autoclave, accumulation of formate was demonstrated after 24 hr passing of CO2 (50 atm, room temperature) through electrolyte solution. The formation of this product started on increasing the cathode potential to -800 mV (with respect to saturated silver chloride electrode). The yield grew exponentially upon cathode potential increase up to -1200 mV. The maximum current efficiency (0.12%) was registered at cathode potentials of about -1000 mV. No formate production was registered under normal atmospheric pressure and in the absence of imposed cathode potential. Neither in experiments, nor in control was formaldehyde found. It is proposed that the electrochemical reduction of CO2 takes part in the formation of organic molecules in hydrothermal solutions accompanying sulfide ore deposits and in 'black smokers' on the ocean floor.     

Carbon Dioxide Fixation by Lupin Root Nodules: II. Studies with C-labeled Glucose, the Pathway of Glucose Catabolism, and the Effects of Some Treatments That Inhibit Nitrogen Fixation

Labeling studies using detached lupin (Lupinus angustifolius) nodules showed that over times of less than 3 minutes, label from [3,4-¹⁴C]glucose was incorporated into amino acids, predominantly aspartic acid, to a much greater extent than into organic acids. Only a slight preferential incorporation was observed with [1-¹⁴C]- and [6-¹⁴C]glucose, while with [U-¹⁴C]-glucose more label was incorporated into organic acids than into amino acids at all labeling times. These results are consistent with a scheme whereby the “carbon skeletons” for amino acid synthesis are provided by the phosphoenolpyruvate carboxylase reaction.     

Studies on Dark Fixation of Carbon Dioxide in Kalanchoe: I. Effect of Water Stress and Growth Retardants

Rooted cuttings of Kalanchoë blossfeldiana cv. Feuer Bluteand K. crenatum failed to show a net dark CO₂ fixation whenraised in dilute nutrient solution. Dark CO₂ fixation (CAM)in these plants was initiated either by increasing the soluteconcentration or lowering the water potential of the nutrientsolution by addition of mannitol (0.11 M and 0.25 M) and carbowax4000 (0.16 M and 0.3 M). Initiation was also brought about byspraying the leaves with B-9 (N,dimethylamino-succinamicacid,300mg1^–1) or by addition of CCC (2 chloroethyl trimethylammonium chloride, 300 or 750 mg1^–1) to the nutrient medium.Failure of CAM in dilute solution was suggested to be due tolack of accumulation of photosynthates in the leaves. Waterstress and growth retardants brought about reduction of monilizationand/or translocation thereby leading to accumulation of assimilatesin the leaves and to initiation of dark CO₂ fixation.     

Carbon Dioxide Fixation by Lupin Root Nodules: I. Characterization, Association with Phosphoenolpyruvate Carboxylase, and Correlation with Nitrogen Fixation during Nodule Development

In vivo CO₂ fixation and in vitro phosphoenolpyruvate (PEP) carboxylase levels have been measured in lupin (Lupinus angustifolius L.) root nodules of various ages. Both activities were greater in nodule tissue than in either primary or secondary root tissue, and increased about 3-fold with the onset of N₂ fixation. PEP carboxylase activity was predominantly located in the bacteroid-containing zone of mature nodules, but purified bacteroids contained no activity. Partially purified PEP carboxylases from nodules, roots, and leaves were identical in a number of kinetic parameters. Both in vivo CO₂ fixation activity and in vitro PEP carboxylase activity were significantly correlated with nodule acetylene reduction activity during nodule development. The maximum rate of in vivo CO₂ fixation in mature nodules was 7.9 nmol hour⁻¹ mg fresh weight⁻¹, similar to rates of N₂ fixation and reported values for amino acid translocation.     

Multiple Neurite Formation in Neuroblastoma Cell Lines by Griseolic Acid, a Potent Inhibitor of Cyclic Nucleotide Phosphodiesterases

The morphological change of several neuroblastoma cell lines induced by griseolic acid, a novel and potent inhibitor of cyclic nucleotide phosphodiesterase (PDE), was examined. In the cell lines tested, Neuro-2a (a murine neuroblastoma cell line) showed dose-dependent (1 microM-1 mM) neurite extension. Griseolic acid markedly increased the intracellular cyclic AMP level of Neuro-2a cells, suppressed DNA synthesis (82% at 1 mM), and induced multipolar (multiple-neurite-bearing)-type neuritogenesis. A similar type of neurite outgrowth was induced by 8-bromo-cyclic AMP, which also elevated the intracellular cyclic AMP concentration. In contrast, when Neuro-2a cells were treated with retinoic acid, neurite formation was of the monopolar (single-neurite-bearing) type. Papaverine and theophylline, which have been frequently used as PDE inhibitors, failed to induce these morphological changes up to 1 mM, probably owing to the lesser potency of these compounds as compared with griseolic acid on the inhibition of PDE. Retinoic acid, theophylline, and papaverine were ineffective at elevating the intracellular cyclic AMP level. These results suggest that multipolar-type cell shape change in Neuro-2a cells is correlated with the accumulation of intracellular cyclic AMP and that griseolic acid is a useful compound to induce neuroblastoma cells into terminal differentiation.     

Overcoming Incompatibility in Brassica campestris L. by Carbon Dioxide, and Dark Fixation of the Gas by Self- and Cross-pollinated Pistils

Supplementing pollen suspension cultures with CO₂ (3–5per cent) caused a marked increase in germination and tube growthin vitro in Brassica campestris L. cv. toria. A weakening ofself-incompatibility by increased CO₂ levels from 3–5per cent was observed. The percentage of pollen tubes whichpenetrated the cuticle layer of stigmatic papilla cells in self-pollinatedpistils was high when CO₂ level was 5 per cent. Phosphoenolpyruvate (PEP) carboxylase activity was greater in the pollengerminated in 4 per cent CO₂ as compared to air (0.03 per cent).A possible role of CO₂ for self-recognition and control of pollentube growth is proposed, proposed. Brassica campestris L., carbon dioxide, self-incompatibility, phosphoenol pyruvate carboxylase     

Studies on Effect of Certain Quinones: I. Electron Transport, Photophosphorylation, and CO(2) Fixation in Isolated Chloroplasts

The effect of quinone herbicides and fungicides on photosynthetic reactions in isolated spinach (Spinacia oleracea) chloroplasts was investigated. 2,3-Dichloro-1,4-naphthoquinone (dichlone), 2-amino-3-chloro-1,4-naphthoquinone (06K-quinone), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) inhibited ferricyanide reduction as well as ATP formation. Benzoquinone had little or no effect on these reactions. The two reactions showed a differential sensitivity to these inhibitors. Dichlone was a strong inhibitor of both photosystems I and II; photosystem I was more sensitive to 06K-quinone than was photosystem II, whereas the reverse was true of chloranil. Chloranil and 06K-quinone inhibited ferricyanide reduction and the coupled photophosphorylation to the same extent, whereas dichlone affected photophosphorylation to a greater extent than the ferricyanide reduction.