期刊
JOURNAL OF EXPERIMENTAL BOTANY
卷 64, 期 10, 页码 2701-2712出版社
OXFORD UNIV PRESS
DOI: 10.1093/jxb/ert122
关键词
Asparagine; carbon and nitrogen metabolites; feedback; Medicago truncatula; nitrogen fixation; nitrogenase activity; nodulation; phloem; phosphorus availability; plant growth; symbiosis capacity; translocation
资金
- German Academic Exchange Service (DAAD)
- Japan Society for the Promotion of Science (JSPS)
- Grants-in-Aid for Scientific Research [12F02510] Funding Source: KAKEN
Medicago truncatula is an important model plant for characterization of P deficiency on leguminous plants at the physiological and molecular levels. Growth optimization of this plant with regard to P supply is the first essential step for elucidation of the role of P in regulation of nodulation. Hence, a study was carried out to address the growth pattern of M. truncatula hydroponically grown at different gradual increases in P levels. The findings revealed that M. truncatula had a narrow P regime, with an optimum P level (12 M P) which is relatively close to the concentration that induces P toxicity. The accumulated P concentration (2.7 mg g(1) dry matter), which is normal for other crops and legumes, adversely affected the growth of M. truncatula plants. Under P deficiency, M. truncatula showed a higher symbiotic efficiency with Sinorhizobium meliloti 2011 in comparison with S. meliloti 102F51, partially as a result of higher electron allocation to N-2 versus H. The total composition of free amino acids in the phloem was significantly affected by P deprivation. This pattern was found to be almost exclusively the result of the increase in the asparagine level, suggesting that asparagine might be the shoot-derived signal that translocates to the nodules and exerts the down-regulation of nitrogenase activity. Additionally, P deprivation was found to have a strong influence on the contents of the nodule carbon metabolites. While levels of sucrose and succinate tended to decrease, a higher accumulation of malate was observed. These findings have provided evidence that N-2 fixation of M. truncatula is mediated through an N feedback mechanism which is closely related to nodule carbon metabolism.
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