Intact spinach chloroplasts scavenge hydrogen peroxide with a peroxidase that uses a photoreductant as the electron donor, but the activity of ruptured chloroplasts is very low [Nakano and Asada (1980) Plant & Cell Physiol. 21: 1295]. Ruptured spinach chloroplasts recovered their ability to photoreduce hydrogen peroxide with the concomitant evolution of oxygen after the addition of glutathione and dehydroascorbate (DHA). In ruptured chloroplasts, DHA was photoreduced to ascorbate and oxygen was evolved in the process in the presence of glutathione. DHA reductase (EC 1.8.5.1) and a peroxidase whose electron donor is specific to L-ascorbate are localized in chloroplast stroma. These observations confirm that the electron donor for the scavenging of hydrogen peroxide in chloroplasts is L-ascorbate and that the L-ascorbate is regenerated from DHA by the system: photosystem I-*ferredoxin-*NADP^>glutathione. A preliminary characterization of the chloroplast peroxidase is given.

Hydrogen Peroxide is Scavenged by Ascorbate-specific Peroxidase in Spinach Chloroplasts

One of the first of the specialized agencies of the United Nations to become active, the Food and Agriculture Organization has elicited interest beyond the specialized field of agricultural economists. Attempting as it does to solve one of the very basic problems of the world, that of an adequate food supply, the organization represents a significant and hopeful international attempt to create a world in which there may actually exist “freedom from want.” The objectives of FAO, as formally expressed in the preamble to the constitution, read as follows:“The nations accepting this constitution being determined to promote the common welfare by furthering separate and collective action on their part for the purpose of raising levels of nutrition and standards of living of the people under their jurisdiction, securing improvements in the efficiency of the production of all food and agricultural products, bettering the conditions of rural populations, and thus contributing toward an expanding world economy, hereby establish the Food and Agriculture Organization of the United Nations.”

The Food and Agriculture Organization of the United Nations

1. Plant Nutrients. 2. The Soil as a Plant Nutrient Medium. 3. Nutrient Uptake and Assimilation. 4. Plant Water Relationships. 5. Plant Growth and Crop Production. 6. Fertilizer Application. 7. Nitrogen. 8. Sulphur. 9. Phosphorus. 10. Potassium. 11. Calcium. 12. Magnesium. 13. Iron. 14. Manganese. 15. Zinc. 16. Copper. 17. Molybdenum. 18. Boron. 19. Further Elements of Importance. 20. Elements with More Toxic Effects. General Readings. References. Index.

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Principles of plant nutrition

Coupling of Phosphorylation to Electron and Hydrogen Transfer by a Chemi-Osmotic type of Mechanism

Publisher Summary This chapter discusses the chemistry of submerged soils. The chemical changes in the submerged materials influence: (a) the character of the sediment or soil that forms, (b) the suitability of wet soils for crops, (c) the distribution of plant species around lakes and streams and in estuaries, deltas, and marine flood plains, (d) the quality and quantity of aquatic life, and (e) the capacity of lakes and seas to serve as sinks for terrestrial wastes. The single electrochemical property that serves to distinguish a submerged soil from a well-drained soil is its redox potential. The redox potential of a soil or sediment provides a quick, useful, semiquantitative measure of its oxidation–reduction status. Two recent developments have stimulated interest in the chemistry of submerged soils: the breeding of lowland rice varieties, with a high yield potential, and the pollution of streams, lakes, and seas, by domestic, agricultural, and industrial wastes. The chemistry of submerged soils is valuable: (a) in understanding the soil problems, limiting the performance of high-yielding rice varieties, and (b) in assessing the role of lake, estuarine, and ocean sediments as reservoirs of nutrients for aquatic plants and as sinks for terrestrial wastes.

The Chemistry of Submerged Soils

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2880%2981060-X

Photoreduction of ferredoxin by chloroplasts with or without an accompanying photoreduction of the bound iron—sulfur centers: Contrasting effects of electron donors to photosystems I and II

Role of Ferredoxin in the Energy Conversion Process of Photosynthesis.

The photochemical reduction of TPN, and also of diphosphopyridine nucleotide (13), pera?its the linking of the photolysis of water by isolated chloroplasts (the Hill reaction) to the many enzymatic reactions which are dependent on these pyridine nucleotides (10). Among these reactions, those which can be shown to occur in photosynthetic tissues are of special interest to photosynthesis. In the previously reported study (2) in which chloroplasts and malic enzyme from green leaves were used, the course of the reaction was followed by manometric measurements of the evolved oxygen. This communication reports the identification, with the aid of radioactive carbon, paper chromatography, and radioautography, of the organic compound, 1-malate, formed in this photosynthetic reaction. Tracer carbon was previously used in the study of the reaction with malic enzymes from non-photosynthetic tissues (14, 11), and the identification of 1-malate as a product of the reaction with the pigeon liver enzyme was reported by Vishniac and Ochoa (14), who used both chromotographic techniques and specific enzymatic decarboxylation methods. Previously described procedures (1, 4) were used for the growing of sugar beet and spinach plants in nutrient solutions in a greenhouse and for the maceration of leaves and the separation of chloroplast fragments from the cytoplasmic fluid. In the early experiments, malic enzyme was prepared from the cytoplasmic fluid in which the activity of the enzyme was found to be localized (2). In later experiments, the enzyme was prepared from the green slurry of the entire leaf; the chloroplastic material was removed with the first ammonium sulphate precipitation. The malic enzyme and the chloroplasts were usually prepared from the same leaves, but in certain experiments spinach chloroplasts were combined with malic enzyme of sugar beet. The procedure used for the preparation of malic enzyme was based on that of Vennesland (13) for the preparation of oxalacetic car-

Extracellular photosynthetic reactions. ii. identification of radioactive malate

Other investigators have isolated soluble, low-potential, c-type cytochromes (cytochrome c3) from a few photosynthetic procaryotes, i.e., a cyanobacterium and two species of purple nonsulfur bacteria. However, such cytochromes appeared to be absent from other purple bacteria, including Rhodospirillum rubrum and Chromatium vinosum. We now report evidence for the presence of low-potential c-type cytochromes in these two species, in which they were found to be bound to the photosynthetic membranes. Evidence for a membrane-bound, low-potential c-type cytochrome was also found in Rhodopseudomonas sphaeoides. The low-potential c-type cytochrome of R. rubrum was solubilized by a Triton X-100 treatment of chromatophores and was partly purified. It was found to have a molecular weight of about 17,000, a midpoint oxidation-reduction potential of -192 mV, and an alpha-absorption peak at 552 nm. It appears that low-potential c-type cytochromes may be present in all purple photosynthetic bacteria, of both the sulfur and the nonsulfur types.

Isolation and characterization of a membrane-bound, low-potential c-type cytochrome from purple photosynthetic bacteria, with special reference to Rhodospirillum rubrum.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2889%2980970-6

Daniel I. Arnon

Papers

Photoreduction of ferredoxin by chloroplasts with or without an accompanying photoreduction of the bound iron—sulfur centers: Contrasting effects of electron donors to photosystems I and II

Role of Ferredoxin in the Energy Conversion Process of Photosynthesis.

Extracellular photosynthetic reactions. ii. identification of radioactive malate

Isolation and characterization of a membrane-bound, low-potential c-type cytochrome from purple photosynthetic bacteria, with special reference to Rhodospirillum rubrum.

Photoreduction of NADP+ by a chloroplast photosystem II preparation: effect of light intensity