Nonphotosynthetic processes

Evans (194) and by Vernon and Avron (128). A review by Malkin and Rabinowitz (129) summarizes the properties of the iron-sulfur proteins, and in particular discusses the work on ferredoxins linked to nonphotosynthetic processes this involvement of ferredoxin was implied in the earliest researches by Mortenson, Valentine, and Carnahan (130) and by Tagawa and Arnon (131). 

In contrast, the respiratory, fermentative, and other nonphotosynthetic processes of organisms tend to restore equilibrium by catalyzing or mediating chemical reactions releasing free energy and thus increasing the mean pe level. 

Table 5. SCP Production Processes Based on Nonphotosynthetic Microorganisms...

Root products, as defined by Uren and Reisenauer (17), represent a wide range of compounds. Only secretions are deemed to have a direct and immediate functional role in the rhizosphere. Carbon dioxide, although labeled an excretion, may play a role in rhizosphere processes such as hyphal elongation of vesicular-arbuscular mycorrhiza (39). Also, root-derived CO2 may have an effect on nonphotosynthetic fixation of CO2 by roots subject to P deficiency and thus contribute to exudation of large amounts of citrate and malate, as observed in white lupins (40). The amounts utilized are very small and, in any case, are extremely difficult to distinguish from endogenous CO2 derived from soil and rhizosphere respiration. 

Plant mitochondria supply the cell with ATP during periods of low illumination or darkness by mechanisms entirely analogous to those used by nonphotosynthetic organisms. In the light, the principal source of mitochondrial NADH is a reaction in which glycine, produced by a process known as photorespiration, is converted to serine (see Fig. 20-21) ... 

Triose phosphates produced by the Calvin cycle in bright sunlight, as we have noted, may be stored temporarily in the chloroplast as starch, or converted to sucrose and exported to nonphotosynthetic parts of the plant, or both. The balance between the two processes is tightly regulated, and both must be coordinated with the rate of carbon fixation. Five-sixths of the triose... 

Nonphotosynthetic Even though almost all living organisms depend either directly (green plants) or Processes indirectly (saprophytes and animals) upon photosynthesis to capture the energy of the... 

If one takes the global view of the energy stored in biomass compared to the total solar energy incident on the Earth, then the estimated overall efficiency is about 0.05%.This includes losses due to reflection, absorption by nonphotosynthetic pigments, the fact that much of the solar output is in the near-infrared region, which is not efficiently used by abundant organisms, and various cellular processes. 

In animals, the free energy In sugars and other molecules derived from food is released in the process of respiration. All synthesis of ATP in animal cells and in nonphotosynthetic microorganisms results from the chemical transformation of energy-rich compounds in the diet (e.g., glucose, starch). We discuss the mechanisms of photosynthesis and cellular respiration in Chapter 8. 

In plants, algae, and photosynthetic bacteria, beta-carotene plays an important role in photosynthesis, the process by which plants convert water and carbon dioxide into carbohydrates and oxygen. In nonphotosynthetic bacteria and fungi, beta-carotene protects the organism against the harmful effects of light and oxygen. 

Since its demonstration in photosynthetic organisms, the carboxylation enzyme has been demonstrated in E, coli and Thiobacillus. The physiological significance of this enzyme in nonphotosynthetic organisms is not clear, but its occurrence emphasizes that the carbon metabolism of photosynthesis is an enzymatic process distinct from the photochemical reaction. 

During the development of oilseed rape embryos starch accumulates transiently during the early stages of oil accumulation (P. da Silva and A.M. Smith, pers. comm.). Both starch and fatty acids are synthesized in the plastids and these processes are dependent upon the import of cytosolic metabolites in non-photosynthetic cells. Plastids have been isolated from several nonphotosynthetic tissues and characterized with respect to their enzyme capacities and utilization of exogenous substrates to support starch and fatty acid synthesis in vivo. These studies have revealed that the glycolytic pathway is present although the activities of some of the enzymes in the lower half of the pathway can be low. Pyruvate dehydrogenase is also present in these plastids. 

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