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Metabolic origin of δ 15 N values in nitrogenous compounds from Brassica napus L. leaves
Author(s) -
GAUTHIER PAUL P. G.,
LAMOTHE MARLENE,
MAHÉ ALINE,
MOLERO GEMMA,
NOGUÉS SALVADOR,
HODGES MICHAEL,
TCHERKEZ GUILLAUME
Publication year - 2013
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2012.02561.x
Subject(s) - nitrogen , fractionation , brassica , rapeseed , chemistry , metabolism , isotopes of nitrogen , isotope , amino acid , nitrate , metabolic pathway , nitrogen cycle , stable isotope ratio , isotope fractionation , composition (language) , botany , biochemistry , biology , food science , chromatography , organic chemistry , physics , linguistics , philosophy , quantum mechanics
Nitrogen isotope composition ( δ 15 N) in plant organic matter is currently used as a natural tracer of nitrogen acquisition efficiency. However, the δ 15 N value of whole leaf material does not properly reflect the way in which N is assimilated because isotope fractionations along metabolic reactions may cause substantial differences among leaf compounds. In other words, any change in metabolic composition or allocation pattern may cause undesirable variability in leaf δ 15 N. Here, we investigated the δ 15 N in different leaf fractions and individual metabolites from rapeseed ( Brassica napus ) leaves. We show that there were substantial differences in δ 15 N between nitrogenous compounds (up to 30‰) and the content in ( 15 N enriched) nitrate had a clear influence on leaf δ 15 N. Using a simple steady‐state model of day metabolism, we suggest that the δ 15 N value in major amino acids was mostly explained by isotope fractionation associated with isotope effects on enzyme‐catalysed reactions in primary nitrogen metabolism. δ 15 N values were further influenced by light versus dark conditions and the probable occurrence of alternative biosynthetic pathways. We conclude that both biochemical pathways (that fractionate between isotopes) and nitrogen sources (used for amino acid production) should be considered when interpreting the δ 15 N value of leaf nitrogenous compounds.