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

LESSONS FROM CROP PLANT EVOLUTION . IMPROVING PHOTOSYNTHETIC RATE . CARBON PARTITIONING BETWEEN ORGANS . CHARACTERISTICS OF ESTABLISHED SOURCE·PATH·SINK SYSTEMS . Photosynthesis in Relation to Sink Demand . Phloem Loading . �r,Io"::; a fJnr::d"!:.�:.:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: Sink Properties .

Photosynthesis, carbon partitioning, and yield

Interest in plant asparagine has rapidly taken off over the past 5 years following the report that acrylamide, a neurotoxin and potential carcinogen, is present in cooked foods, particularly carbohydrate-rich foods such as wheat and potatoes which are subjected to roasting, baking or frying at high temperatures. Subsequent studies showed that acrylamide could be formed in foods by the thermal degradation of free asparagine in the presence of sugars in the Maillard reaction. In this article, our current knowledge of asparagine in plants and in particular its occurrence in cereal seeds and potatoes is reviewed and discussed in relation to acrylamide formation. There is now clear evidence that soluble asparagine accumulates in most if not all plant organs during periods of low rates of protein synthesis and a plentiful supply of reduced nitrogen. The accumulation of asparagine occurs during normal physiological processes such as seed germination and nitrogen transport. However, in addition, stress-induced asparagine accumulation can be caused by mineral deficiencies, drought, salt, toxic metals and pathogen attack. The properties and gene regulation of the enzymes involved in asparagine synthesis and breakdown in plants are discussed in detail.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1744-7348.2006.00104.x

Asparagine in plants

INTRODUCfION Techniques for Studying the Identity of Transported Solutes of Nitrogen . Nitrogen in Phloem and Xylem Fluids . Uptake. Assimilation. and Transport of Nitrogen by Roots . Transport of Nitrogen from Nodulated Roots of Nr/ixing Plants .. Initial Distribution of Xylem-Borne Nitrogen in Shoots .. Export of Nitrogen from Leaves in Phloem . Export of Nitrogen from Stem Tissue in the Phloem . RelationshipS Between Transport and Storage of Nitrogen .. Transport of Nitrogen to Deve/oping Fruits and Seeds Loading of Nitrogenous Solutes onto Xylem and Phloem .. Relationships Between Nitrogen Transport and the Production and Partitioning of Photosynthate .. CONCLUSIONS ..

Transport and Partitioning of Nitrogenous Solutes

INTRODUCTION 539 THE EXCHANGE OF REDUCED CARBON AND NITROGEN: AN OVERVIEW. ... 540 MAJOR PRODUCTS OF RECENTLY FIXED N2 EXPORTED FROM NODULES.... 542 SYNTHESIS OF AMIDES AND UREIDES 546 Ammonium Assimilation .... 546 Asparagine Synthesis . 547 Synthesis of 4-Methyleneglutamine 548 Synthesis of Citrulline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549 Biogenesis of Allantoin and Allantoic Acid 551 METABOLISM OF AMIDES AND UREIDES . ......... . . ... . . ........ .... . . .. ..... . 558 ENERGETICS OF SYNTHESIS AND METABOLISM OF THE PRODUCTS OF Nz FIXATION 564 SUMMARy......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567

Products of Biological Nitrogen Fixation in Higher Plants: Synthesis, Transport, and Metabolism

Collections of xylem exudate of root stumps or detached nodules, and of phloem bleeding sap from stems, petioles, and fruits were made from variously aged plants of Lupinus albus L. relying on nodules for their N supply. Sucrose was the major organic solute of phloem, asparagine, glutamine, serine, aspartic acid, valine, lysine, isoleucine, and leucine, the principal N solutes of both xylem and phloem. Xylem sap exhibited higher relative proportions of asparagine, glutamine and aspartic acid than phloem sap, but lower proportions of other amino acids. Phloem sap of petioles was less concentrated in asparagine and glutamine but richer in sucrose than was phloem sap of stem and fruit, suggesting that sucrose was unloaded from phloem and amides added to phloem as translocate passed through stems to sinks of the plant. Evidence was obtained of loading of histidine, lysine, threonine, serine, leucine and valine onto phloem of stems but the amounts involved were small compared with amides. Analyses of petiole phloem sap from different age groups of leaves indicated ontogenetic changes and effects of position on a shoot on relative rates of export of sucrose and N solutes. Diurnal fluctuations were demonstrated in relative rates of loading of sucrose and N solutes onto phloem of leaves. Daily variations in the ability of stem tissue to load N onto phloem streams were of lesser amplitude than, or out of phase with fluctuations in translocation of N from leaves. Data were related to recent information on C and N transport in the species.

Kathy Hamel

Papers

Transport of organic solutes in Phloem and xylem of a nodulated legume.