Plants photosynthetic phosphorylation

ATP is produced in the cell from ADP as a result of three types of phosphorylations - substrate-level phosphorylations, oxidative phosphorylation, and, in plants, photosynthetic phosphorylation. 

Z Gromet-Elhanan and Dl Arnon (1965) Effect of desaspidin on photosynthetic phosphorylation. Plant Physiol 40 1060-1065... 

Krogmann DW, Jagendore AT and Avron M (1959) Uncouplers of spinach chloroplast photosynthetic phosphorylation. Plant Physiol 34 272—277. 

Black, C.C., A. San Pietro, G. Norris, and D. Limbach Photosynthetic phosphorylation in the presence of spinach phosphodoxin Plant Physiol. 39 (1964) 279-283. 

Fig 1 shows the effect of pig adenodoxin in cyclic and pseudo cyclic photosynthetic phosphorylations. Although these reactions are specific of photosynthetic aganisms, the animal ferredoxin can replace plant ferredoxin vnth a rather good efficiency in the case of pseudocyclic photophosphorylation. On the otha hand, adkenodoxin is unable to donate electrons in the cydic pathway. These observations suggest that this animal ferredoxin can be photaeduced through PSI and the assodated bound iron sulfa centas. 

Nothing is known with certainty about metabolic pathways for the degradation of ascorbic acid or of its use in the plant. Although some biologists consider that it is a catalyst in photosynthetic phosphorylation, this is by no means certain, and until more positive evidence is advanced it is safer to consider that this acid fulfils some as yet imperfectly known metabolic function in the active plant cell. 

Another study of soybeans indicated that when plants were grown in media with an increasing lead concentration, respiration rates increased up to 60 mg/1 of lead in the culture media, with rates decreasing above this concentration [41]. Plants treated with lead had a reduced photosynthetic rate and a reduced photosynthetic phosphorylation rate. 

Ferredoxins are proteins containing equal numbers of iron and sulphur atoms in each active centre. They transfer electrons below the potential of the hydrogen electrode. The 8Fe-8S ferredoxins are associated with the most primitive organisms (obligate anaerobic fermenters and photosynthesizers) where they are used for electron-transfer in the pyruvate phosphoroclastic system the 4Fe-4S types probably came next in evolution and are found in sulphate- and nitrate-reducing bacteria. The later zFe-zS ferredoxins are found in plants and animals where they are essential for oxidative phosphorylation in mitochondria, for photosynthetic phosphorylation in chloroplasts, and for the synthesis of catecholamine hormones. The individual types are distinguished by e.s.r. and Mossbauer spectra. For a review, see Hall and Evans (1969). 

In a study designed to determine the mode of action of atrazine in higher plants, Shimabukuro and Swanson (1969) concluded that atrazine inhibits the Hill reaction and its noncyclic phosphorylation, while being ineffective against cyclic photophosphorylation. Atrazine readily penetrated the chloroplast of resistant as well as susceptible plants. In tolerant plants such as sorghum, the metabolism of atrazine was postulated to occur outside the chloroplasts to form water-soluble and insoluble residues that reduced the concentration of photosynthetic inhibitors in the chloroplasts. 

In Chapter 4 (Section 4.1D), we indicated that the radiation input of the sun to the earth s atmosphere averages 1366 W m-2 (the solar constant ). Some of the radiant energy is used to form ATP and NADPH in chloroplasts. In turn, these energy currencies lead to the reductive fixation of CO2 into a carbohydrate in photosynthesis (see Fig. 5-1). In the same photosynthetic cells, in other plant cells, and in animal cells, the carbohydrates formed during photosynthesis can serve as the energy source for mitochondrial respiration, which leads to the generation of ATP by oxidative phosphorylation. 

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