Arsenic transformations in the soil-rhizosphere-plant system: fundamentals and potential application to phytoremediation.

The buffering capacity values of several herbage species and of silage made from this herbage, and the contributions of plant constituents to this buffering, between pH 4 and 6, were determined, and found to vary with the herbage species; values in the silages were normally two to three times greater than those in the plant materials. The anion fraction of the plant materials accounted for 68–80% of the total buffering capacity, and for 73–88% in the silages. Buffering caused by plant proteins was estimated to be 10–20% of the total buffering capacity.



The buffering capacity of wilted red clover (Trifolium pratense) was 18% lower than that of fresh red clover, and the total organic acid content of wilted clover was also lower than that in fresh clover.



The organic acids were responsible for most of the buffering effect in herbages and silages. In Italian ryegrass (Lolium multiflorum), the main buffers were malate and citrate, but, in red clover, glycerate and malate were the main buffers. The clovers studied contained a high level of glycerate (4% of dry matter). During ensilage, malate, citrate and glycerate were extensively broken down. The increased buffering capacity during ensilage was caused mainly by the formation of lactates and acetates.

The buffering constituents of herbage and of silage

INTRODUCfION . MEASUREMENTS OF INTRACELLULAR pH . MECHANISMS FOR pH REGULATION .. Intracellular Buffers .

Intracellular PH and its Regulation

1. Forms of Selenium.- 1.1 Low Molecular-Weight Compounds.- 1.1.1 Selenocysteine.- 1.1.2 Selenocystine.- 1.1.3 Selenohomocystine.- 1.1.4 Se-methylselenocysteine.- 1.1.5 Selenocystathionine.- 1.1.6 Selenomethionine.- 1.1.7 Se-methylselenomethionine.- 1.1.8 Dimethyl Selenide.- 1.1.9 Dimethyl Diselenide.- 1.1.10 Trimethyl Selenonium.- 1.1.11 Elemental Selenium.- 1.1.12 Selenotaurine.- 1.1.13 Selenocoenzyme A.- 1.1.14 Other Compounds.- 1.2 Macromolecular Forms of Selenium.- 1.2.1 Formate Dehydrogenase.- 1.2.2 Glycine Reductase.- 1.2.3 Nicotinic Acid Hydroxylase.- 1.2.4 Xanthine Hydrogenase.- 1.2.5 Thiolase.- 1.2.6 Glutathione Peroxidase.- 1.2.7 Miscellaneous Selenoproteins.- 1.2.8 Seleno-tRNA's.- 11.11 References.- 2. Selenium Deficiency Diseases in Animals.- 2.1 Introduction.- 2.2 Dietary Liver Necrosis and Factor 3.- 2.2.1 Discovery.- 2.2.2 Pathology.- 2.2.3 Biochemical Defect.- 2.2.4 Hepatosis Dietetica.- 2.3 Nutritional Muscular Dystrophy.- 2.3.1 Pathology.- 2.3.2 Prevention of NMD.- 2.4 Exudative Diathesis.- 2.5 Pancreatic Degeneration.- 2.6 Mulberry Heart Disease.- 2.7 Reproductive Problems.- 2.8 Myopathy of the Gizzard.- 2.9 Growth.- 2.10 Selenium-Responsive Unthriftiness of Sheep and Cattle.- 2.11 Periodontal Disease of Ewes.- 2.12 Encephalomalacia.- 11.11 References.- 3. Metabolism of Selenium.- 3.1 Absorption.- 3.2 Placental Transfer.- 3.3 Mechanism of the Antioxidant Action of Selenium.- 3.4 Effect of Paraquat.- 3.5 Effect on Cytochrome P-450.- 3.6 Selenium and Hepatic Heme Metabolism.- 11.11 References.- 4. Comparative Metabolism and Biochemistry of Selenium and Sulphur.- 4.1 Introduction.- 4.2 Comparative Metabolism of Selenium and Sulphur.- 4.2.1 Microorganisms.- 4.2.2 Plants.- 4.2.3 Animals.- 4.3 Comparative Biochemistry of Selenium and Sulphur.- 4.3.1 Selenopersulfide as an Electron Transfer Catalyst.- 4.3.2 Iron-Sulphur Proteins.- 4.3.3 Sulphur Salts and Selenium Toxicity in Animals.- 4.3.4 Other Selenium-Sulphur Interactions.- 11.11 References.- 5. Biological Interactions of Selenium with Other Substances.- 5.1 Cadmium.- 5.1.1 Pathological Effects.- 5.1.2 Cadmium-Zinc Interactions.- 5.1.3 Cadmium-Selenium Interactions.- 5.1.4 Effect on Drug Response.- 5.2 Arsenic.- 5.3 Copper.- 5.4 Silver.- 5.5 Cobalt.- 5.6 Manganese.- 5.7 Lead.- 5.8 Mercury.- 5.8.1 Inorganic and Organic Mercury.- 5.8.2 Tissue Distribution.- 5.8.3 Properties of the Mercury-Selenium Complex.- 5.8.4 Teratogenicity.- 5.9 Thallium.- 5.10 Tellurium.- 5.11 Vanadium.- 5.12 Bismuth.- 5.13 Other Substances.- 11.11 References.- 6. Environmental Occurrence of Selenium.- 6.1 Geochemistry of Selenium.- 6.2 Soil Selenium.- 6.3 Uptake and Concentration of Trace Elements in the Roots, Stems, and Leaves of Plants.- 6.4 Forage Selenium.- 6.5 Selenium in Water.- 6.6 Selenium in Food.- 6.7 Intakes and Recommended Daily Allowance in Humans.- 6.8 Regulations in Regard to Animal Diets.- 11.11 References.- 7. Toxicity of Selenium.- 7.1 Introduction.- 7.1.1 Acute Toxicity.- 7.1.2 Blind Staggers.- 7.1.3 Alkalai Disease.- 7.1.4 Toxicity in Rabbits.- 7.1.5 Toxicity in Hamsters.- 7.1.6 Toxicity in Sheep.- 7.1.7 Toxicity in Rats.- 7.1.8 Effect of Diet on Toxicity.- 7.1.9 Biochemical Lesions.- 7.1.10 LD50 of Various Selenium Compounds.- 7.2 Industrial Medical Aspects.- 7.2.1 Occupational Hazards.- 7.2.2 Permissible Limits for Selenium Exposure.- 7.2.3 Toxicity in Humans.- 11.11 References.- 8. Selenium in Health and Disease.- 8.1 Selenium and Cancer.- 8.1.1 Skin Cancer.- 8.1.2 Liver Cancer.- 8.1.3 Colon Cancer.- 8.1.4 Breast Cancer.- 8.1.5 Tracheal Cancer.- 8.1.6 Chemotherapeutic Effect of Selenium.- 8.1.7 Epidemiological Relationship.- 8.1.8 Selenium Blood Levels in Cancer Patients.- 8.1.9 Selenium as a Carcinogen.- 8.2 Selenium and Mutagenesis.- 8.2.1 Antimutagenicity.- 8.2.2 Mutagenicity.- 8.3 Selenium and Immunity.- 8.3.1 Effect of Selenium on Humoral Immunity.- 8.3.2 Cell-Mediated Immunity.- 8.3.3 Nonspecific Immune Effects of Selenium.- 8.4 Selenium and Dental Caries.- 8.5 The Anti-Inflammatory Properties of Selenium.- 8.6 Selenium and Heart Disease.- 8.6.1 Animals.- 8.6.2 Humans.- 8.7 Selenium and Aging.- 8.8 Cystic Fibrosis.- 8.9 Multiple Sclerosis.- 8.10 Cataracts.- 8.11 Other Diseases.- 8.12 Radioselenium as a Diagnostic Agent.- 11.11 References.- 9. Synthetic Forms of Selenium and Their Chemotherapeutic Uses.- 9.1 Anti-Infective Agents.- 9.1.1 Antibacterial.- 9.1.2 Antiviral.- 9.2 Antifungal Agents.- 9.3 Antiparasitic Agents.- 9.4 Compounds Affecting the Central Nervous System.- 9.4.1 Hypnotics.- 9.4.2 Analgesics and Local Anesthetics.- 9.4.3 Tranquilizing Drugs.- 9.5 Compounds that Affect the Autonomic Nervous System.- 9.6 Compounds that Affect the Circulatory System.- 9.7 Anti-Inflammatory Compounds.- 9.8 Antihistamines.- 9.9 Anticancer Agents.- 9.10 Antiradiation Agents.- 9.11 Steroids.- 9.12 Selenocoenzyme A.- 9.13 Selenium-Containing Carbohydrates.- 9.14 Seleno-Amino Acids.- 11.11 References.- 10. Analytical Methods of Selenium Determination.- 10.1 Introduction.- 10.2 Sample Preparation and Storage.- 10.3 Destructive Analysis.- 10.3.1 Ashing.- 10.3.2 Closed-System Combustion.- 10.3.3 Wet Digestion.- 10.3.4 Measurement of Selenium.- 10.4 Nondestructive Analysis.- 10.4.1 Neutron Activation Analysis.- 10.4.2 X-Ray Fluorescence Analysis.- 10.4.3 Proton-Induced X-Ray Emission.- References.

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Biochemistry of selenium.

Dual Pattern of Ion Absorption by Plant Cells and by Plants

Relation of sulphate to selenium absorption by plants

The hypothesis developed to explain the quantitative aspects of selenate-sulfate antagonism was based on the assumption of unselective absorption and utilization of the two ions by virtue of their chemical similarity. The idea subsequently received support from plant analyses showing that the amount of selenium taken into the tissues of certain plants parallels that of sulfur, as though selenium absorption were determined by the sulfur requirement of the species. Arsenate toxicity is a function of phosphate availability, rubidium toxicity of potassium availability, and strontium toxicity of calcium availability. In view of the small number of pairs that can be selected on such a basis, positive results with all three are highly suggestive of the validity of the basic assumption. The present paper presents the experimental evidence on which these relationships were based.

Antagonism of certain elements essential to plants toward chemically related toxic elements.

IT WAS reported in an earlier publication (HurdKarrer, 1935) that wheat plants supplied with sodium selenite were less injured and contained less selenium in. their leaves than when the selenium was added to the soil as sodium selenate. In view of the fact that the selenite is the more easily reduced by organisms (Levine, 1914, 1915, 1925b), it seemed possible that its lesser toxicity might be due to its reduction to elemental selenium.Experiments were therefore designed to compare the toxicity of selenites and selenates in water cultures. There are several reports to the effect that the selenites are the more toxic (Levine, 1925a; Stoklasa, 1922; Turina, 1922), and the contrary evidence from the single soil experiment referred to above did not seem sufficient to controvert them. and selenites was checked by Dr. Lucien Greathouse, formerly of the Bureau of Plant Industry. Results obtained with those compounds found to be impure (K2SeO4 and H2SeO4) are omitted from this report. The seedlings were germinated in pure quartz sand, or on blotters moistened with distilled water, and transferred after about a week to 600 cc. widemouthed flasks containing the nutrient solutions. Three seedlings were grown in each flask, supported in holes of paraffined corks with cotton plugs. The flasks were kept in boxes, partitioned into compartments the size of the flasks, which provided partial shading of the roots. Two different series of nutrient solutions were used, having the composition shown in table 1, plus 100 cc. M/60 iron citrate in each case. The concentrations

Annie M. Hurd-Karrer

Papers

Relation of sulphate to selenium absorption by plants

Antagonism of certain elements essential to plants toward chemically related toxic elements.

Comparative toxicity of selenates and selenites to wheat

Structures corresponding to appressoria and substomatal vesicles produced on nutrient-solution agar by cereal rusts

Hydrogen-ion concentration of leaf juice in relation to environment and plant species