Dioxide Assimilation in Plants

Since the subject of photosynthesis has been fully reviewed else-where only the results obtained with isotopic tracers will be discussed in this report. 

Kamen and Hassid exposed plants to an atmosphere of radioactive C 02 and were subsequently able to separate a radioactive fraction containing alcoholic and carboxyl groups. In the presence of light, radioactive CO2 was incorporated primarily into the non-carboxylic 

The first step in the assimilation of COj is assumed by Ruben, Kamen and coworkers to involve a non-photochemical reaction, catalyzed enzymically and resulting in the addition of CO2 to a large molecule. The process is initiated rapidly in the dark and gradually decreases in rate. These results suggest that it is reversible. Since no correlation could be found between the concentration of chlorophyll in the leaves and the COj uptake, it is believed that chlorophyll is not concerned with this initial reaction. Chlorophyll is believed to catalyze a second reaction involving the reduction of the carboxylic compound to an alcohol or polyalcohol. This second reaction, believed to occur in the presence of light, is endothermic and irreversible. 

By analogy with a reversible CO2 assimilation reaction known to occur in certain bacteria, Lipmann and Tuttle have proposed a theory explaining how carbon chains may be progressively lengthened by a process involving phosphorylation, CO2 assimilation and photoreduction. 

The source of hydrogen is the photolytic cleavage of water with oxygen resulting as a by-product. 

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M. Calvin (Berkeley) research on the carbon dioxide assimilation in plants. 

Melvin Calvin For his research on the carbon dioxide assimilation in plants. 1972 of electronic structure and geometry of molecules, particularly free radicals. Christian Anfinsen... 

Photosynthetic earboxylation the enzymatic fixation of carbon dioxide in photosynthesis. In C-3 plants, the photosynthetic earboxylation enzyme is ri-bulose iirphosphate carboxylase (EC 4.1.1.39). In C-4 plants it is phosphoeno/pyruvate carboxylase (EC 41.1.31). P. c. is the first step of carbon dioxide assimilation in photosynthesis, and one of the dark reactions. 

Kanai,R.H., Black,C.C. Biochemical basis for net CO2 assimilation in C4 plants. In Net carbon dioxide assimilation in higher plants. Proc. Soc. Sect. Am. Soc. Plant Physiol. Black, C.C. (ed.), pp. 75-93. Releigh Cotton-Inc. 1972 Kapil, R.N., Pugh,T.D., Newcomb, E.H. Microbodies and anomalous microcylinder in the ultrastructure of plants with Crassulacean Acid Metabolism. Planta 124, 231-244 (1975)... 

Ting, I. P., Johnson, H.B., Szarek,S.R. Net CO2 fixation in crassulacean acid metabolism plants. In Net Carbon Dioxide Assimilation in Higher Plants. Black,C. C. (ed.), pp.26-53. Proc. Symp. S. Sect. Am. Soc. Plant Physiol. Cotton Inc. Raleigh 1972 Ting, I. P., Johnson, H.B., Szarek,S.R., Brum,G.D. Gas Exchange and Productivity for Opuntia ssp. Riverside Prog. Rep. 1971... 

Willmer,C.M., Johnston, W.R. Carbon dioxide assimilation in some aerial plant organs and tissues. Planta 130,33-37 (1976)... 

Morikawa H., Higaki A., Nohno M., Takahashi M., Kamada M., Nakata M., Toyohara G., Okamura Y., Matsui K., Kitani S., Fujita K., Irifune K., and Goshima N., 1999, More than a 600-fold variation in nitrogen dioxide assimilation among 217 plant taxa. Plant Cell Environ. 21 180-190. 

Essentiality and Toxicity for Plants It is generally accepted that various plant species, especially marine and shore plants and those adapted to saline soils (Australian Atriplex vesicaria), require small amounts of sodium for normal development. Sodium is important for plants, though definite beneficial effects on growth and development have been observed in only a few species. Na enhances the growth of some species if potassium is deficient. Sodium cannot generally perform the specific function of potassium in plants. It does so to a limited extent only, even in plants that respond to sodium fertilization (Saalbach 1973). Na is assumed to influence osmotic pressures in the vacuoles, and the water content of colloids in the plasma. In many species of plants it is reported to be involved in carbon dioxide assimilation. Salt fertilization always increases sodium yields of sugar beet, carrot and chard, even if potassium fertiliza-... 

Isotopic labeling of selected components of the system frequently provides an answer to such questions. The technique possesses many different aspects adapted to individual cases. As an example, let us cite the many investigations of Melvin Calvin and coUaborators over a period of twenty years. In these studies, systematic use was made of c u bon dioxide labeled with C to elucidate the early steps of photosynthesis and the network of reactions involved in the assimilation of carbon dioxide by green plants. An important variation of the technique consists in the use of tracers in a kinetic sense. Among the several possibilities of this kind proposed by Neiman, one deserves special attention. 

Carbon dioxide assimilation, carbon fixation the incorporation of COj into larger organic compounds. C.d.a. is sometimes used as a synonym for photosynthesis, but strictly speaking photosynthesis is a series of reactions that generate the ATP and NAD(P)H required to drive the reactions of Cd.a. By far the greatest amount of C. d. a. occurs in green plants and cyanobacteria. Most of this occurs in the... 

III. Translocation and metabolic changes of carbon- C dioxide assimilated products in tea plants during autumn. Nippon Dojo-Hiryogaku Zasshi 39, 444 (1968) (in Japanese). 

Besides water, plants and animals constitute man s principal food. Plants and animals need organic carbon compounds in order to develop their body substance and to meet their energy requirements. In contrast to the animals, plants can build these carbon compounds from the basic substances water and carbon dioxide (assimilation). For this purpose, suf-hcient energy must be made available, e.g., by sunlight and its utilization via chlorophyl (green leaf). 

By using the experimental setup shown in Fig. 4.13, it was found that the amount of carbon dioxide assimilated at equal light intensity falling on the same surface was the same for leaves of different plants [178, 179], but this value increased with temperature, more or less rapidly for different leaves. This fact was attributed to the intervening of some thermal activated process. In every case, an optimal value of assimilation was attained and was not overcome by a further increase either in light intensity or in CO2 concentration. 

Figure 6.8a. Quantitative aspects of carbon dioxide and nicotine metabolism in tobacco plants carbon dioxide assimilation by one tobacco plant per day. Courtesy of Robinson, 1974 copyright 1974 by the American Association for the Advancement of Science.

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