On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa)
Legumes such as alfalfa (Medicago sativa L.) are vital N2-fixing crops accounting for a global N2 fixation of ∼35MtNyear -1. Although enzymatic and molecular mechanisms of nodule N2 fixation are now well documented, some uncertainty remains as to whether N2 fixation is strictly coupled with photosynthetic carbon fixation. That is, the metabolic origin and redistribution of carbon skeletons used to incorporate nitrogen are still relatively undefined. Here, we conducted isotopic labelling with both 15N2 and 13C-depleted CO2 on alfalfa plants grown under controlled conditions and took advantage of isotope ratio mass spectrometry to investigate the relationship between carbon and nitrogen turn-over in respired CO2, total organic matter and amino acids. Our results indicate that CO2 evolved by respiration had an isotopic composition similar to that in organic matter regardless of the organ considered, suggesting that the turn-over of respiratory pools strictly followed photosynthetic input. However, carbon turn-over was nearly three times greater than N turn-over in total organic matter, suggesting that new organic material synthesised was less N-rich than pre-existing organic material (due to progressive nitrogen elemental dilution) or that N remobilisation occurred to sustain growth. This pattern was not consistent with the total commitment into free amino acids where the input of new C and N appeared to be stoichiometric. The labelling pattern in Asn was complex, with contrasted C and N commitments in different organs, suggesting that neosynthesis and redistribution of new Asn molecules required metabolic remobilisation. We conclude that the production of new organic material during alfalfa growth depends on both C and N remobilisation in different organs. At the plant level, this remobilisation is complicated by allocation and metabolism in the different organs.
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Commonwealth Scientific and Industrial Research Organization (Australia)
2014-06-21
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Subjects: | Respiration, Photosynthesis, Nitrogen 15 isotope, Nitrogen fixation, Carbon isotopes, Carbon exchange, |
Online Access: | http://hdl.handle.net/10261/97654 |
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dig-idab-es-10261-976542016-09-02T09:32:08Z On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa) Molero Milán, Gemma Tcherkez, Guillaume Araus, José Luis Nogués, Salvador Aranjuelo, Iker Respiration Photosynthesis Nitrogen 15 isotope Nitrogen fixation Carbon isotopes Carbon exchange Legumes such as alfalfa (Medicago sativa L.) are vital N2-fixing crops accounting for a global N2 fixation of ∼35MtNyear -1. Although enzymatic and molecular mechanisms of nodule N2 fixation are now well documented, some uncertainty remains as to whether N2 fixation is strictly coupled with photosynthetic carbon fixation. That is, the metabolic origin and redistribution of carbon skeletons used to incorporate nitrogen are still relatively undefined. Here, we conducted isotopic labelling with both 15N2 and 13C-depleted CO2 on alfalfa plants grown under controlled conditions and took advantage of isotope ratio mass spectrometry to investigate the relationship between carbon and nitrogen turn-over in respired CO2, total organic matter and amino acids. Our results indicate that CO2 evolved by respiration had an isotopic composition similar to that in organic matter regardless of the organ considered, suggesting that the turn-over of respiratory pools strictly followed photosynthetic input. However, carbon turn-over was nearly three times greater than N turn-over in total organic matter, suggesting that new organic material synthesised was less N-rich than pre-existing organic material (due to progressive nitrogen elemental dilution) or that N remobilisation occurred to sustain growth. This pattern was not consistent with the total commitment into free amino acids where the input of new C and N appeared to be stoichiometric. The labelling pattern in Asn was complex, with contrasted C and N commitments in different organs, suggesting that neosynthesis and redistribution of new Asn molecules required metabolic remobilisation. We conclude that the production of new organic material during alfalfa growth depends on both C and N remobilisation in different organs. At the plant level, this remobilisation is complicated by allocation and metabolism in the different organs. Peer Reviewed 2014-06-03T11:20:25Z 2014-06-03T11:20:25Z 2014-06-21 2014-06-03T11:20:25Z artículo http://purl.org/coar/resource_type/c_6501 doi: 10.1071/FP13189 issn: 1445-4408 Functional Plant Biology 41(4): 331-341 (2014) http://hdl.handle.net/10261/97654 10.1071/FP13189 none Commonwealth Scientific and Industrial Research Organization (Australia) |
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Respiration Photosynthesis Nitrogen 15 isotope Nitrogen fixation Carbon isotopes Carbon exchange Respiration Photosynthesis Nitrogen 15 isotope Nitrogen fixation Carbon isotopes Carbon exchange |
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Respiration Photosynthesis Nitrogen 15 isotope Nitrogen fixation Carbon isotopes Carbon exchange Respiration Photosynthesis Nitrogen 15 isotope Nitrogen fixation Carbon isotopes Carbon exchange Molero Milán, Gemma Tcherkez, Guillaume Araus, José Luis Nogués, Salvador Aranjuelo, Iker On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa) |
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Legumes such as alfalfa (Medicago sativa L.) are vital N2-fixing crops accounting for a global N2 fixation of ∼35MtNyear -1. Although enzymatic and molecular mechanisms of nodule N2 fixation are now well documented, some uncertainty remains as to whether N2 fixation is strictly coupled with photosynthetic carbon fixation. That is, the metabolic origin and redistribution of carbon skeletons used to incorporate nitrogen are still relatively undefined. Here, we conducted isotopic labelling with both 15N2 and 13C-depleted CO2 on alfalfa plants grown under controlled conditions and took advantage of isotope ratio mass spectrometry to investigate the relationship between carbon and nitrogen turn-over in respired CO2, total organic matter and amino acids. Our results indicate that CO2 evolved by respiration had an isotopic composition similar to that in organic matter regardless of the organ considered, suggesting that the turn-over of respiratory pools strictly followed photosynthetic input. However, carbon turn-over was nearly three times greater than N turn-over in total organic matter, suggesting that new organic material synthesised was less N-rich than pre-existing organic material (due to progressive nitrogen elemental dilution) or that N remobilisation occurred to sustain growth. This pattern was not consistent with the total commitment into free amino acids where the input of new C and N appeared to be stoichiometric. The labelling pattern in Asn was complex, with contrasted C and N commitments in different organs, suggesting that neosynthesis and redistribution of new Asn molecules required metabolic remobilisation. We conclude that the production of new organic material during alfalfa growth depends on both C and N remobilisation in different organs. At the plant level, this remobilisation is complicated by allocation and metabolism in the different organs. |
format |
artículo |
topic_facet |
Respiration Photosynthesis Nitrogen 15 isotope Nitrogen fixation Carbon isotopes Carbon exchange |
author |
Molero Milán, Gemma Tcherkez, Guillaume Araus, José Luis Nogués, Salvador Aranjuelo, Iker |
author_facet |
Molero Milán, Gemma Tcherkez, Guillaume Araus, José Luis Nogués, Salvador Aranjuelo, Iker |
author_sort |
Molero Milán, Gemma |
title |
On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa) |
title_short |
On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa) |
title_full |
On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa) |
title_fullStr |
On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa) |
title_full_unstemmed |
On the relationship between C and N fixation and amino acid synthesis in nodulated alfalfa (Medicago sativa) |
title_sort |
on the relationship between c and n fixation and amino acid synthesis in nodulated alfalfa (medicago sativa) |
publisher |
Commonwealth Scientific and Industrial Research Organization (Australia) |
publishDate |
2014-06-21 |
url |
http://hdl.handle.net/10261/97654 |
work_keys_str_mv |
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