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Metabolism of Ammonium Ion and Glutamate in Relation to Nitrogen Supply and Utilization during Grain Development in Barley ¹

Department of Agricultural Biochemistry, School of Agriculture, University of Edinburgh, West Mains Road, Edinburgh EH9 3JG, Scotland

Changes in the activity of a number of enzymes concerned with amino acid synthesis and metabolism were recorded for the endosperm, testa pericarp, and embryo of developing barley (Hordeum distichum L.) grains. Both glutamate-pyruvate transaminase and glutamate-oxaloacetate transaminase activities were present in all tissues and at all ages examined. Glutamate dehydrogenase activity was largely confined to endosperm while glutamine synthetase activity was mainly in the testa pericarp.

Ammonium ion concentration was maximal in endosperm by 20 days after anthesis. Glutamate concentration varied in endosperm and was in the range of 3.5 to 8.5 mM between 20 and 45 days after anthesis. Significant levels of ammonium ion and glutamate were also present in the testa pericarp over the major part of the developmental period.