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In folio isotopic tracing demonstrates that nitrogen assimilation into glutamate is mostly independent from current CO 2 assimilation in illuminated leaves of Brassica napus
Author(s) -
Gauthier Paul P. G.,
Bligny Richard,
Gout Elizabeth,
Mahé Aline,
Nogués Salvador,
Hodges Michael,
Tcherkez Guillaume G. B.
Publication year - 2010
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.2009.03130.x
Subject(s) - photorespiration , glutamine , glutamate synthase , photosynthesis , ammonium , chemistry , phloem , respiration , glutamine synthetase , biology , botany , biochemistry , amino acid , organic chemistry
Summary• Nitrogen assimilation in leaves requires primary NH 2 acceptors that, in turn, originate from primary carbon metabolism. Respiratory metabolism is believed to provide such acceptors (such as 2‐oxoglutarate), so that day respiration is commonly seen as a cornerstone for nitrogen assimilation into glutamate in illuminated leaves. However, both glycolysis and day respiratory CO 2 evolution are known to be inhibited by light, thereby compromising the input of recent photosynthetic carbon for glutamate production. • In this study, we carried out isotopic labelling experiments with 13 CO 2 and 15 N‐ammonium nitrate on detached leaves of rapeseed ( Brassica napus ), and performed 13 C‐ and 15 N‐nuclear magnetic resonance analyses. • Our results indicated that the production of 13 C‐glutamate and 13 C‐glutamine under a 13 CO 2 atmosphere was very weak, whereas 13 C‐glutamate and 13 C‐glutamine appeared in both the subsequent dark period and the next light period under a 12 CO 2 atmosphere. Consistently, the analysis of heteronuclear ( 13 C– 15 N) interactions within molecules indicated that most 15 N‐glutamate and 15 N‐glutamine molecules were not 13 C labelled after 13 C/ 15 N double labelling. That is, recent carbon atoms (i.e. 13 C) were hardly incorporated into glutamate, but new glutamate molecules were synthesized, as evidenced by 15 N incorporation. • We conclude that the remobilization of night‐stored molecules plays a significant role in providing 2‐oxoglutarate for glutamate synthesis in illuminated rapeseed leaves, and therefore the natural day : night cycle seems critical for nitrogen assimilation.