Cereal grain, rachis and pulse seed amino acid delta N-15 values as indicators of plant nitrogen metabolism

Natural abundance delta N-15 values of plant tissue amino acids (AAs) reflect the cycling of N into and within plants, providing an opportunity to better understand environmental and anthropogenic effects on plant metabolism. In this study, the AA delta N-15 values of barley (Hordeum vulgare) and bread wheat (Triticum aestivum) grains and rachis and broad bean (Vicia faba) and pea (Pisum sativum) seeds, grown at the experimental farm stations of Rothamsted, UK and Bad Lauchstadt, Germany, were determined by GC-C-IRMS. It was found that the delta N-15 values of cereal grain and rachis AAs could be largely attributed to metabolic pathways involved in their biosynthesis and catabolism. The relative N-15-enrichment of phenylalanine can be attributed to its involvement in the phenylpropanoid pathway and glutamate has a delta N-15 value which is an average of the other AAs due to its central role in AA-N cycling. The relative M delta N-15 values of broad bean and pea seeds were very different from one another, providing evidence for differences in the metabolic routing of AAs to the developing seeds in these leguminous plants. This study has shown that AA delta N-15 values relate to known AA biosynthetic pathways in plants and thus have the potential to aid understanding of how various external factors, such as source of assimilated N, influence metabolic cycling of N within plants. (C) 2013 The Authofs. Published by Elsevier Ltd. All rights reserved.