Genetic Engineering of Symbiotic Nitrogen Fixation and Conservation of Fixed Nitrogen

The present volume developed from a symposium entitled "Enhancing Biological Production of Ammonia From Atmospheric Nitrogen and Soil Nitrate" that was held at Lake Tahoe, California in June, 1980. The meeting was supported by the National Science Foundation, Division of Engineering and Applied Sciences and by the College of Agricultural and Environmental Sciences, University of California, Davis. A total of 99 scientists from 41 insti­ tutions participated. Plants capture solar energy in photosynthesis and use mineral nutrients to produce human food and fiber products. The extent to which such materials are removed from agricultural production sites represents a permanent drain of mineral nutrients. Some plants of agronomic importance such as alfalfa, soybean, and clover associate with soil bacteria and use photosynthetic energy to reduce N2 to NH3. Many other free-living bacteria and some symbioses involving procaryotes and eucaryotes also reduce N2. Such processes repre­ sent one natural mechanism by which Man can augment soil N for agronomic purposes without using fossil fuel to synthesize and distribute N fertilizer. Other metabolic conversions in the N cycle and physical leaching processes remove N made available through N2 fixation. Thus nitrification, denitrification, and utilization of soil N by plants are processes that must be con­ sidered if one is to conserve N captured by N2 fixation. The meeting at Lake Tahoe united scientists from many disci­ plines to review the literature and to discuss current research directed toward the goal stated in the symposium title.

I. Introduction.- Prefatory Chapter: Enhancing Biological Production of Ammonia From Atmospheric Nitrogen and Soil Nitrate.- Support of Problem Focused Nitrogen Fixation Research at the National Science Foundation.- Biological Nitrogen Fixation Research at the University of California, Davis.- II. Genetics and Regulation of Nitrogen Fixation.- A. Molecular Cloning of Nitrogen Fixation Genes.- Molecular Cloning of Nitrogen Fixation Genes from Rhizobium meliloti.- Cloning DNA from Rhizobium meliloti Using a New Broad Host Range, Binary Vehicle System.- Molecular Cloning of Rhizobium japonicum DNA in E. coli and Identification of Nitrogen Fixation (Nif) Genes.- B. Genetics and Regulation of Nitrogen Fixation Genes.- The Identification, Location and Manipulation of Genes in Rhizobium.- The Role of Rhizobium Plasmids in Host Specificity.- “Redox Control” of Nitrogen Fixation: An Overview.- A Mutant of Rhizobium japonicum 110 with Elevated Nif Activity in Free-Living Culture.- C. Hydrogen Uptake and Energetics.- Detrimental and Beneficial Effects of Oxygen Exerted on Hydrogen-Oxidizing Bacteria.- Hydrogen Uptake (Hup) Plasmids: Characterization of Mutants and Regulation of the Expression of Hydrogenase.- Detection of Plasmids in Rhizobium japonicum.- Chemolithotrophy in Rhizobium.- Hydrogen Uptake (Hydrogenase) Activity of Rhizobium japonicum Strains Forming Nodules in Soybean Production Areas of the U.S.A.- D. Genetic Regulation of Stress Tolerance.- Proline Over-Production Enhances Nitrogenase Activity Under Osmotic Stress in Klebsiella pneumoniae.- Selection of Naturally Occurring Stress Tolerant Rhizobium.- III. Plant Factors Impacting Nitrogen Assimilation.- A. Measurements and Efficiency of N2 Fixation.- Evaluating Potentially Superior Rhizobium Strains inSoybeans.- Physiological Interactions Between Alaska Peas and Strains of Rhizobium leguminosarum That Differ in Plasmid-Like Genes.- Evaluating Elite Alfalfa Lines for N2-Fixation Under Field Conditions.- Successes and Problems Encountered While Breeding for Enhanced N2 Fixation in Alfalfa.- B. Photosynthesis and Nitrogen Utilization.- Biochemical Genetics of Ribulose Bisphosphate Carboxylase/Oxygenase: High Frequency Transfer and Chromosome Mobilization by Broad Host-Range R-Factors in CO2?Fixing Bacteria.- Photosynthetic Enzyme Regulation by the Ferredoxin/ Thioredoxin and the Ferralterin Mechanisms.- Regulation of Photosynthetic CO2 Fixation.- Hydrolysis of Ribulose-1, 5-Bisphosphate Carboxylase by Partially Purified Endoproteinases of Senescing Primary Barley Leaves.- The Relationship Between Ribulose Bisphosphate Carboxylase Concentration and Photosynthesis.- IV. Nitrogen Fixation by Nonlegumes.- Nitrogen Fixation by Cyanobacterial Heterocysts.- Photosynthate Limitation of Nitrogen Fixation in the Blue-Green Alga, Anabaena variabilis.- Physiological Studies on N2-Fixing Azolla.- Application of Azolla in Crop Production.- A New Woody Plant Which Fixes Nitrogen: Chamaebatia foliolosa (Rosaceae).- Soil Factors Limiting Nodulation and Nitrogen Fixation in Purshia.- V. Conservation of Fixed Nitrogen.- A. Denitrification.- Overview of Denitrification.- The Physiological Genetics of Denitrification in Pseudomonas.- On Regulating the Synthesis of Nitrate Reductase.- The Conversion of NO3? to NH4+ in Klebsiellapneumoniae.- Denitrification by the Photosynthetic Bacterium, Rhodopseudomonas sphaeroides Forma Sp. Denitrificans; Mechanism of Electron Transport to Nitrate and Nitrite Reduction.- Production of Nitrous Oxide as a Product of Nitrite Metabolism by EntericBacteria.- Use of Nitrogen-13 and Nitrogen 15 in Studies on the Dissimilatory Fate of Nitrate.- Soil Denitrification.- B. Acquisition and Assimilation of Plant Nitrogen.- Nitrate Transport Processes and Compartmentation in Root Systems.- Reduction of Nitrate and Nitrite in Barley Leaves in Darkness.- Influence of Light and CO2 on Nitrate Assimilation by Barley Seedlings.- Light Interaction With Nitrate Reduction.- Interaction Between NO3?, NO2?, and NH4+ During Assimilation in Detached Barley Leaves.- Vacuolar Nitrate and the Isolation of Vacuoles for Localization and Transport Studies.- The Effect of pH, Temperature, and NO3? Concentration on NH4+ Absorption and N2 (C2H2)- Fixation by Soybeans.- Recurrent Divergent and Mass Selections in Maize With Physiological and Biochemical Traits: Preliminary and Projected Application.- Inheritance of Nitrate Reductase.- Modelling Dynamic Aspects of Nitrogen in Soils and Plants.- Integration of Nitrate and Ammonium Assimilation in Higher Plants.- A New Approach to the Analysis of Reductive and Dissipative Costs in Nitrogen Assimilation.- Strategies for Achieving Self Sufficiency in Nitrogen on a Mixed Farm in Eastern Canada Based on Use of the Faba Bean.- List of Participants.