Carbon dark-fixation

Other sand-based systems using COi pulse-chase procedures have been used to produce carbon budgets for Festuca ovina and Plantago lanceolata seedlings (30) and white lupin (Lupimis albiis) (31). Significantly, CO2 pulse labeling of proteoid roots of white lupin under phosphate-deficient conditions showed that high levels of dark fixation of COi by the roots took place and that 66% of this root-fixed carbon was exuded from the roots (31). Clearly, dark fixation of CO2 by roots and subsequent rhizodeposition is an area that deserves further study in the future. 

Ozone causes both quantitative and qualitative changes in carbon dioxide fixation patterns. Wilkinson and Bames, using carbon dioxide-found a reduction in radioactivity in soluble sugars and increases in free amino acids and sugar phosphates in white pine after a 10-min exposure to ozone at 0.10 ppm. Miller observed a decrease in carbon dioxide-fixation in ponderosa pines that correlated with loss of chlorophyll, after exposure to ozone at 0.30-0.35 ppm. The Hill reaction rates of chloroplasts isolated from healthy and ozone-injured ponderosa pine indicated that both light and dark reactions of the chloroplasts from ozone-injured plants were depressed. Barnes found depressed photosynthesis and stimulated respiration in seedlings of four pine species of the southeastern United States after exposure to ozone at 0.15 ppm. 

The urea herbicides do not inhibit seed-germination to any extent, or the growth of nonphotosynthetic tissue, nor do they interfere with dark-fixation reactions. Monuron-treated bean-leaves which were fed 14C02 in the light, however, decreased in sucrose content (as percent of ethanol-soluble materials) from 70 to 2% in 72 hours.185 Most of the carbon-14 label... 

The photosynthetic block precedes sucrose synthesis, and sucrose partially reverses the inhibition caused by the lack of fixation of carbon dioxide. D-Fructose disappears first, after treatment, followed by sucrose, and then u-glucose.188 It is likely that other metabolic systems are involved as well, since the amino acid distributions were not identical to the I4C02 dark-fixation products.189 Uptake of sucrose-14C increased some acids (as-... 

Starvation. The early reports that Hill inhibitors limited photosynthesis and that starch disappeared from treated plants, prompted some investigators to refer to these compounds as photosynthesis inhibitors. Photosynthesis is inhibited because ATP and NADFH are not available for carbon dioxide fixation. However, there is little evidence that the plants starve to death. If this were the only process affected, phytotoxic symptoms should resemble those that appear on plants kept in total darkness. Deficiency of photosynthate does limit new growth, but does not account for the morphological alterations that occur within a few hours after treatment. The mechanisms that lead to phytotoxicity appear to be considerably more complex than would result from limiting carbohydrate synthesis by suppression of carbon dioxide fixation (2). ... 

Carbon dioxide is also fixed in the dark by photosynthetic organisms by the so-called Wood-Werkman reaction (Wood and Stjemholm, 1962). The CO2 assimilated, however, rarely exceeds that formed by dark respiration i.e. there is no net CO2 uptake. On the other hand, the amount of organic carbon derived from CO2 may be as high as 30% in heterotrophic bacteria and 90% in mixotrophic organisms. In the natural environment, non-photo-synthetic CO2 fixation by these organisms, together with the above-mentioned dark fixation by photosynthetic organisms, may under some condi-... 

The reactions of the Calvin cycle, which is the process of carbon dioxide fixation in plants (also known as the dark cycle), are listed below ... 

Even when the main source of cell carbon is not CO2 (heterotrophic growth), CO2 fixation reactions are still important as the dark fixation reactions, essential for the operation of many biosynthetic pathways. In both autotrophic and heterotrophic growth, CO2 can also play a catalytic role (Raven, 1974). 

Carbon dioxide fixation by flax cotyledons measured by an IRGA with illumination of 115 Wm , previously incubated with 10 % monuron in the dark or light of 5.25 or 30 Wm , from Pallett... 

Pfeffer s interpretation of CAM is an excellent example of scientific intuition. The biochemical mechanism of CAM, and in particular the occurrence of carbon dioxide fixation in darkness and the pathway of malic acid conversion to carbohydrates were unknown when Pfeffer wrote his Pflanzenphysiologie. 

Effect of water stress and growth retardants. Ann. Bot. 41,493-500 (1977 a) Chaturvedi,S.N., Zabka,G. Studies on dark fixation of carbon dioxide in Kalanchoe. II. Effect of interaction of photoperiodic induction with water stress and growth retardants. Ann. Bot. 41,501-505 (1977b)... 

Deleens,E., Garnier-Dardart, . Carbon isotope composition of biochemical fractions isolated from leaves of Bryophyllum daigremontianum Berger, a plant with Crassulacean Acid Metabolism Some physiological aspects related to CO2 dark fixation. Planta 139, 214-248 (1977)... 

Kaplan, A., Gale,J. Separation of respiration from dark fixation of carbon dioxide in CAM plants. Isr. J. Bot. 25,59 (1975)... 

Kaplan, A., Gale,J., Poljakoff-Mayber,A. Simultaneous measurement of oxygen, carbon dioxide, and water vapour exchange of intact plants. J. Exp. Bot. 97, 214-219 (1976 a) Kaplan, A., Gale,J., Poljakoff-Mayber,A. Resolution of net dark fixation of carbon dioxide into its respiration and gross fixation components in Bryophyllum daigremontianum. J. Exp. Bot. 97,220-230 (1976 b)... 

Zabka,G.G., Chaturvedi,S.N. Water conservation in Kalanchoe blossfeldiana in relation to carbon dioxide dark fixation. Plant Physiol. 55, 532-535 (1975)... 

Zabka,G.G., Edelman,J. Pre-illumination as a factor in the dark-fixation of carbon dioxide by leaf disks of Kalanchoe blossfeldiana var. Feuer Bliite. J. Exp. Bot. 13, 11-19 (1961b) Zabka,G.G., Gregory, F.G., Edelman, J. Dark fixation of carbon dioxide in Kalanchoe blossfeldiana in relation to photoperiodism. Nature (London) 813,1375 (1959)... 

Stewart (1965) showed that Calothrix sp. and Nostoc sp. were capable of some dark fixation of over a 24-hour period, but it was considerably less than in the light. He considered that nitrogen fixation was not critically light dependent as long as supplies of carbon skeletons, reducing power, and energy were available. 

Werdan, K., Heldt, H.W., and Milovancer, M., 1973, The role of pH in the regulation of carbon dioxide fixation in the chloropiast stroma. Studies on CO2 fixation in the light and dark, Biochem. Acta, 396 276. 

The isolation of chloroplasts capable of performing all of the reactions normally regarded as photosynthetic including the fixation of carbon dioxide, the evolution of oxygen and the synthesis of sugars and polysaccharides unequivocally demonstrates that the site of photosynthesis is the chloroplast. Experiments involving the fractionation of chloroplasts have further shown that the dark reactions associated with carbon dioxide fixation are located in the stroma of the chloroplast and the light reactions , electron transport and photophosphorylation, takes place in the lamellar systems. 

The best known case of a rhythm in metabolic activity is that of the dark fixation of carbon dioxide in the leaves of Crassulacean... 

The fixation of carbon dioxide to form hexose, the dark reactions of photosynthesis, requires considerable energy. The overall stoichiometry of this process (Eq. 22.3) involves 12 NADPH and 18 ATP. To generate 12 equivalents of NADPH necessitates the consumption of 48 Einsteins of light, minimally 170 kj each. However, if the preceding ratio of l ATP per NADPH were correct, insufficient ATP for COg fixation would be produced. Six additional Einsteins would provide the necessary two additional ATP. Prom 54 Einsteins, or 9180 kJ, one mole of hexose would be synthesized. The standard free energy change, AG°, for hexose formation from carbon dioxide and water (the exact reverse of cellular respiration) is +2870 kj/mol. 

The dark reaction involves the fixation of carbon dioxide to form carbohydrates. The ATP and the NADPH produced in the light reaction drive this carbon fixation. It might be thought that the interruption of the Calvin cycle would also produce effective herbicides but this is not the case. There are two reasons why. First, the reaction is not an energetic reaction whose interruption would lead to the destruction of cellular components and second, the enzymes involved in the process are present in very high amounts. If an enzyme is to be targeted as a key step in the metabolism of a plant, it is important that it is present in small amounts and that it is not turned over very quickly. If an enzyme is abundant,... 

---