Photosynthetic CO2 fixation

An intriguing stress-induced alteration in gene expression occurs in a succulent plant, Mesembryanthemum crystallinum, which switches its primary photosynthetic CO2 fixation pathway from C3 type to CAM (Crassulacean acid metabolism) type upon salt or drought stress (Winter, 1974 Chapter 8). Ostrem et al. (1987) have shown that the pathway switching involves an increase in the level of mRNA encoding phosphoenol-pyruvate carboxylase, a key enzyme in CAM photosynthesis. 

Lieberei, R., Pock, H. and Biehl, B. (1992) Cyanogenesis inhibits active pathogen defence in plants inhibition by gaseous HCN of photosynthetic CO2 fixation and respiration in intact leaves. /. Appl. Bot., 70, 230-38. 

Figure 11.13 Effects of the addition of dissolved inorganic N (NELj and NOj , 5 pM each), N-containing rainfall (collected at Morehead City, NC), iron (as EDTA-chelated and non-chelated FeCla 0.2 pM each EDTA, and the combination of NOs and EDTA-chelated FeCls) on coastal Atlantic Ocean phytoplankton communities. In situ bioassays were conducted for 5 days on seawater collected approximately 25 km SE of Beaufort, NC in the summer of 1994. Phytoplankton growth responses are reported as photosynthetic CO2 fixation and chlorophyll a accumulation. Indicates treatments were significantly (p < 0.05) from controls, using Bonferroni a posteriori comparisons of the means. See Paerl etal. (1999) for details of the experimental procedures.

Calvin and Benson Discovered that phosphoglyceiic acid is an early intermediate in photosynthetic CO2 fixation. 

In another project in our laboratories, transformation of the tabacco plastid genome has been achieved [20]. Introduction of the gene for improved RuBisCO into the plant will be our next interest. If a Cs plant has Galdieria RuBisCO for its photosynthetic CO2 fixation, the CO2 compensation point of the transformant will decrease from 50 ppm to 20 ppm. The transformant can fix CO2 at a considerable rate photosynthetically at 50 ppm where the ordinary Ca plants cannot adsorb CO2. Thereby, the water-use efficiency of the transformant will be substantially improved. 

Photosynthetic CO2 fixation performance by a helical tubular photobioreactor incorporating Chlorella sp. under outdoor culture conditions... 

In general, calcification is governed by photosynthetic and non-photosynthetic CO2 fixation and, one may recognize an evolutionary sequence from simple chemical precipitation caused by the environmental effects of procaryotes to the highly organized membranous calcification systems found in eucaryotic algae and animals. 

The primary mode of action of bentazon is the inhibition of photosynthetic CO2-fixation by the plants (Mine and Matsunaka, 1973, 1975). A marked inhibition of C02-fixation develops rapidly both in resistant rice and in sensitive Cyperus serotinus after treatment with bentazon, but while tolerant rice recovers almost completely in 5 days, sensitive Cyperus serotinus does not recover. 

The initial step in the photosynthetic CO2 fixation consists of the addition of CO2 to ribulose-1,5 bisphosphate. The intermediate six-carbon compound is subsequently cleaved into two molecules of phospho-glycerate. The latter is then partly recycled in the Calvin cycle, where it is used to regenerate ribulose bisphosphate and partly converted to starch. 

Carbonic anhydrase (CA, EC4.2.1.1), which catalyzes the reversible reaction between HCOJ and dissolved CO2, is widely distributed throughout the plant as well as animal kingdoms. It has relation to photosynthetic CO2 fixation, which can be inferred from its intracellular distribution. There have been several reports indicating that CA is mainly localized in the chloroplasts of C3 plants and in the cytoplasm of C4 plants [1,2,3], which is in accordance with the localization of Rubisco in C3 plants and PEPCase in C4 plants. So far the role of CA in higher plants has been less studied than in algae. 

The Role of Carbonic Anhydrase in Regulating Photosynthetic CO2 Fixation in Higher... 

TCA cycle inhibitor, inhibit photosynthetic CO2 fixation in C thiosulphatum, and (iii) the finding tW C thiosulphalum possesses a-ketoglutarate synthase and pyruvate synthase, enzymes that are peculiar to R.C.C., but lacks ribulose bisphosphate carboxylase and phosphoribulokinase (EC 2.7.1.19), enzymes that are unique to the Calvin cycle. 

Ribulosa b/ phosphate carboxylase, ribulose bisphosphate carboxylase/oxygeiuise, Rubisco, car-boxydismutase, Fraetion-l protein (EC 4.1.1.39) the enzyme responsible for catalysing photosynthetic CO2 fixation in all photosynthetic organisms except green sulfur bacteria (Chlorobiaceae). In plants it occurs in the chloroplast stroma where it constitutes about 50% of the total protein it should be noted. 

Osmond and Bjorkman (1975) found that light-dependent CO2 fixation in K. daigremontiana was inhibited by O2 in the same manner as C3 plants, whereas dark CO2 fixation was independent of 4%, 26%, or 36% O2. Further, O2 inhibition of photosynthetic CO2 fixation is accompanied by a high CO2 compensation point (Allaway et al., 1974a). Unlike C3 plant photorespiration, however, the O2 inhibition of photosynthetic CO2 fixation is not eliminated by high CO2 tension, and the postillumination CO2 burst is present at low O2 (Osmond and Bjorkman, 1975 see Fig. 5.13). 

A further model (Beevers et al., 1966) is founded on the assumption that in CAM the PEP-C pathway of CO2 fixation (i.e., malic acid synthesis) and photosynthetic CO2 fixation compete for CO2 as a common substrate. Hence, during the day, malic acid synthesis should be retarded because, due to competition, the CO2 as the substrate of PEP-C will be in short supply. 

Laetsch,W.M. Chloroplast specialication on Dicotyledons possessing the C4-dicarboxylic acid pathway of photosynthetic CO2 fixation. Am. J. Bot. 55,875-883 (1968) Laetsch,W.M. The C4 syndrome a structural analysis. Ann. Rev. Plant Physiol. 25, 24-52 (1974)... 

Glyceric acid is formed as an intermediate of glycolate pathway. It is also obtained by dephosphorylation of 3-phosphoglyceric acid which is an intermediate of carbohydrate metabolism, the initial product of photosynthetic CO2 fixation via the Calvin cycle, or an oxygenation product of ribulose bis-phosphate in photorespiration. 

End-on (q -OCO) coordination mode has remained elusive for a long time. Nevertheless, this coordination mode may play an important role in biological systems. In photosynthetic CO2 fixation, an oxygen-bound CO2 ligand has been proposed to be enzymatically reduced by ilbulose-1,5-biphosphate carboxylase-oxygenase (RuBisCO) [47]. A crystallographic study on a deacetoxycephalosporin C synthase (DAOCS) mutant showed the presence of electron density close to the iron center of the active site, which was found to be consistent with the presence of a monodentate O-coordinated CO2 molecule [48]. 

The mono- and diphosphates of ribulose have been reported to be present among early products of photosynthetic CO2 fixation in algae, e.g., Scenedeamus. A pathway for the origin of this diphosphate has not yet been suggested, although Marmur and Schlenk have described the aldolase-catalyzed combination of dihydroxyacetone phosphate and glycolaldehyde phosphate to form what must have been a ketopentose diphosphate. ... 

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