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

Studies on Nitrogen-Fixing Blue-Green Algae. I. Growth and Nitrogen Fixation by Anabaena Cylindrica Lemm

Ferredoxins as Electron Carriers in Photosynthesis and in the Biological Production and Consumption of Hydrogen Gas

Ferredoxins as electron carriers in photosynthesis and in the biological production and consumption of hydrogen gas.

https://www.pnas.org/content/pnas/55/4/928.full.pdf

A new ferredoxin-dependent carbon reduction cycle in a photosynthetic bacterium.

A previous article (1) has described a reconstituted “catalytic” chloroplast system in which, as in the intact leaf, the dark reactions of photosynthetic COz assimilation depended on light for the generation of assimilatory power (2), i.e. reduced triphosphopyridine nucleotide and adenosine triphosphate. The companion paper (3) discusses the sitesof action of photochemically generated ATP and TPNHz in the reductive carbohydrate cycle which operates in isolated chloroplasts. This communication gives further evidence for the action of the photochemically generated assimilatory power on two phases of the reductive carbohydrate cycle in isolated chloroplasts: the carboxylative phase which includes the phosphorylation of ribulose monophosphate and the fixation of COZ, and the reductive phase, which includes the reduction of 3-phosphoglyceric acid and the formation of hexose phosphate. The evidence to be presented here is derived from experiments in which the availability of ATP and TPNHz for CO2 assimilation was decreased either by the use of inhibitors or by special arrangements of experimental conditions; certain of the inhibitors acted on single enzymatic reactions in CO2 assimilation.

Photosynthesis by isolated chloroplasts.

The recent discoveries of the importance of small amounts of boron, manganese, copper, and zinc (1, 2, 4, 7, 13) in the physiology of higher plants, and in a number of soil-plant problems of considerable agricultural importance, have added interest to studies on the role of these elements in plant nutrition. The mostobvious and important question is whether or not these elements are indispensable to the growth of plants. Recent investigations in this laboratory (12) on the importance of cer am metals in minute quantity in the economy of higher plants, have resulted in the development of an experimental technique which makes possible a consistent and reproducible demonstration of the essentiality of copper, manganese, and zinc for the growth of higher plants. Although the details of the procedures will be described elsewhere (12) it is desired to present at this time some considerations and conclusions which may be of general interest. It was deemed desirable to test experimentally the essentiality of each element according to the following criteria: an element is not considered essential unless (a) a deficiency of it makes it impossible for the plant to complete the vegetative or reproductive stage of its life cycle; (b) such deficiency is specific to the element in question, and can be prevented or corrected only by supplying this element; and (c) the element is directly involved in the nutrition of the plant quite apart from its possible effects in correctinug some unfavorable microbiological or chemical condition of the soil or other culture medium. From that standpoint a favorable response from adding a given element to the culture medium does not constitute conclusive evidence of its indispensability in plant nutrition. Conclusive proof of the indispensability of the so-called microelements, that is, elements required in minute amounts by plants, can be obtained by the use of artificial culture media (the water culture technique was used in this investigation), provided special procedures are employed to remove incidental impurities. The physiological importance of these contaminants is illustrated by the finding that young tomato plants grown in Pyrex glass containers with nutrient solutions deficient in zinc gave a measurable response to the addition of 1 gamma (0.001 mg.) of zinc to a plant (this gave a zinc concentration in the culture solution of 5 parts per billion). This response to a minute amount of zinc as well as similar responses to copper and manganese were consistently obtained only when redistilled water and purified chemicals were used. The metal content of ordinary distilled water was reduced by redistillation, using 371

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Daniel I. Arnon

Papers

Studies on Nitrogen-Fixing Blue-Green Algae. I. Growth and Nitrogen Fixation by Anabaena Cylindrica Lemm

Ferredoxins as electron carriers in photosynthesis and in the biological production and consumption of hydrogen gas.

A new ferredoxin-dependent carbon reduction cycle in a photosynthetic bacterium.

Photosynthesis by isolated chloroplasts.

The essentiality of certain elements in minute quantity for plants with special reference to copper.