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Rapid assimilation of recently fixed N 2 in root nodules of Myrica gale
Author(s) -
Baker Andrea,
Parsons Richard
Publication year - 1997
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1997.tb05367.x
Subject(s) - asparagine , glutamine , asparagine synthetase , biochemistry , glutamine synthetase , glutamate synthase , amino acid , alanine , nitrogen assimilation , biology , root nodule , ammonium , nitrogen fixation , chemistry , nitrogen , enzyme , organic chemistry
In Myrica gale L. plants the assimilation of ammonia released by symbiotic Frankia was observed by 15 N 2 labelling and subsequent analysis of the isotopic enrichment of nodule amino acids over time by single ion monitoring gas chromatography‐mass spectrometry. In detached nodules of Myrica , glutamine was the first amino acid labelled at 30 s and subsequently the amino acids glutamate, aspartate, alanine and γ‐amino butyric acid (GABA) became labelled. This pattern of labelling is consistent with the incorporation of ammonium via glutamine synthetase [GS; EC 6.3.1.2]. No evidence for the ammonium assimilation via glutamate dehydrogenase [GDH; EC 1.4.1.2] was observed as glutamate became labelled only after glutamine. Using attached nodules and pulse‐chase labelling, we observed synthesis of glutamine, glutamate, aspartate, alanine, GABA and asparagine, and followed the transport of fixed nitrogen in the xylem largely as glutamine and asparagine. Estimation of the cost of nitrogen fixation and asparagine synthesis in Myrica nodules suggests a minimum of one sucrose required per asparagine produced. Rapid translocation of recently fixed nitrogen was observed in Myrica gale nodules as 80% of the nitrogen fixed during a 1‐h period was translocated out of the nodules within 9 h. The large pool of asparagine that is present in nodules may buffer the transport of nitrogen and thus act to regulate nitrogen fixation via a feedback mechanism.