This publication contains the most important information acquired over the last twenty years in the area of nitrogen metabolism and envisages new strategies to improve plant species of agronomic value by devising new techniques for growing them.

Nitrate Assimilation: Historical ResumeASSIMILATION OF NITRATE AND AMMONIUM: Sources of Nitrogen, Nitrogen Cycle, Root Structure, and Nitrogen Assimilation; Transport of Nitrate by Roots; Nitrate Assimilation: Nitrate and Nitrite Reductases; Ammoniacal Nutrition of Plants; Ammonium Assimilation; Integration of Nitrate Uptake in the Whole PlantSYMBIOTIC ASSIMILATION OF NITROGEN: Symbiotic Nitrogen Fixation; Symbiotic Signals in Rhizobium; Nitrogenase: Biochemical, Molecular, and Genetic Aspects; Nitrogen Assimilation by Ectomycorrhizal Symbiosis; Plant Growth Enhancement by Rhizobacteria; Rice Field Cyanobacteria: Ecology Contribution to Soil Fertility and Practical UtilizationSYNTHESIS AND TRANSPORT OF AMINO ACIDS AND CARBON/NITROGEN RELATIONSHIPS: Synthesis of Amino Acids; Transport of Amino Acids in Plants; Co-ordination between Nitrogen Photosynthetic and Respiratory Metabolism; Nitrogen (NO3) Nutrition and Distribution of Carbon in the PlantDISTRIBUTION OF NITROGEN DURING PLANT GROWTH AND DEVELOPMENT: 15N Methodology; Mobilization of Nitrogen Reserve in the Herbaceous Plants; Management of Nitrogen in Ligneous Species; Protein Synthesis in Grains and Seeds; Proteolysis in Higher Plants: Nature, Function, and RegulationNITROGEN:ECOPHYSIOLOGY AND AGRONOMY: Nitrogen Nutrition and Growth of Cultivated Swards; Nitrogen: Crops Production and Environment; Nodular Diagnosis: Agronomic Basis for an Integrated Improvement of Symbiotic Nitrogen Fixation and the N2-dependent Yield of Grain-legumes; Nitrogen and Pollution