Amino Acid Export in Plants: A Missing Link in Nitrogen Cycling

After synthesis in the vegetative parts of the plant, assimilates are translocated to fruits through xylem and phloem. Research on factors controlling nutrient transport into developing seeds via the phloem has been stimulated by the development of the empty seed coat technique.There is a consensus that as assimilates are transported from maternal tissues to filial tissues they are delivered to the extracellular space (the apoplast) separating the two generations, prior to uptake from the apoplast into the tissues of the embryo or endosperm. The empty seed coat technique has been used for the study of several aspects of nutrient transport into seeds, e.g. metabolic control and turgorsensitive transport. The osmotic environment of seed tissues has a strong effect on assimilate transport into empty seeds. Several lines of evidence suggest that one of the main ‘secrets’ of the high sink strength of developing seeds, at least in many taxonomic groups of dicotyledons, is that the sink end of the phloem pathway is ‘bathed’ in an apoplast solution with a high concentration of osmotically active solutes. Data on maize do not fit this pattern. A turgor homeostat mechanism may help to maintain high solute concentrations in the seed apoplast. The apoplast environment of seed tissues may also stimulate synthesis of storage proteins and be involved in the prevention of precocious germination. In addition to the osmotic environment, other factors influencing sink strength are discussed. Some aspects of solute transformation during transport through seed tissues are described.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S096025850000115X

Transport of nutrients into developing seeds: a review of physiological mechanisms

Contributors. Preface. 1. Evaluation of the Transcriptome and Genome to Inform the Study of Metabolic Control in Plants (Oliver Thimm, Oliver E. Blasing, Bjorn Usadel and Yves Gibon). 2. The Use of Proteomics in the Study of Metabolic Control (Lee J. Sweetlove). 3. Study of Metabolic Control in Plants by Metabolomics (Oliver Fiehn). 4. Metabolite Transporters in the Control of Plant Primary Metabolism (Mechthild Tegeder and Andreas P.M. Weber). 5. Role of Protein Kinases, Phosphatases and 14--3--3 Proteins in the Control of Primary Plant Metabolism (Greg B.G. Moorhead, George W. Templeton and Hue T. Tran). 6. Redox Signal Transduction in Plant Metabolism (Santiago Mora--Garcia, Fabiana G. Stolowicz and Ricardo A. Wolosiuk). 7. Control of Carbon Fixation in Chloroplasts (Brigitte Gontero, Luisana Avilan and Sandrine Lebreton). 8. Control of Phosphoenolpyruvate Carboxylase in Plants (Hugh G. Nimmo). 9. Control of Sucrose Biosynthesis (Elspeth Macrae and John Lunn). 10. Control of Starch Biosynthesis in Vascular Plants and Algae (Matthew K. Morrell, Zhongyi Li, Ahmed Regina, Sadiq Rahman, Christophe D'Hulst and Steven G. Ball). 11. The Organization and Control of Plant Mitochondrial Metabolism (Allison E. McDonald and Greg C. Vanlerberghe). 12. Photosynthetic Carbon--Nitrogen Interactions: Modelling Inter--Pathway Control and Signalling (Christine H. Foyer, Graham Noctor and Paul Verrier). 13. Control of Sulfur Uptake, Assimilation and Metabolism (Malcolm J. Hawkesford, Jonathan R. Howarth and Peter Buchner). Index.

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Control of primary metabolism in plants

Cereal grain, rachis and pulse seed amino acid δ15N values as indicators of plant nitrogen metabolism.

The seed is the harvested organ in grain crops and, consequently, the accumulation of dry matter by the seed is an important component of the yield production process. The growth of individual seeds, usually characterised by the rate and duration of growth, is, at least partially, controlled by the seed itself. It is this control that gives the seed a significant role in the yield production process. Genetic variation in seed growth rate, which is substantial, is not related to yield, but variation related to environmental conditions during seed filling often is. Genetic and environmental variation in seed-fill duration is usually directly related to yield. Much is now known about the regulation of seed growth and this knowledge, if applied, may help answer some of the important questions still facing crop scientists as they try to increase yields in the future.

H.A. de Ruiter

Papers

Amino Acid Release from the Seed Coat of Developing Seeds of Vicia faba and Pisum sativum

Development of Chrysanthemum Cuttings: The Influence of Age and Position of the Axillary Buds