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Angiosperm Flora of India

Both Plant and Bacterial Nitrate Reductases Contribute to Nitric Oxide Production in Medicago truncatula Nitrogen-Fixing Nodules

Publication Type:Journal Article
Year of Publication:2011
Authors:Horchani, F, Prévot, M, BOSCARI, ALEXANDRE, Evangelisti, E, Meilhoc, E, Bruand, C, Raymond, P, Boncompagni, E, Aschi-Smiti, S, Puppo, A, BROUQUISSE, RENAUD
Journal:Plant Physiology
Volume:155
Issue:2
Date Published:2011
ISBN Number:00320889
Keywords:Medicago
Abstract:

Nitric oxide (NO) is a signaling and defense molecule of major importance in living organisms. In the model legume Medicago truncatula, NO production has been detected in the nitrogen fixation zone of the nodule, but the systems responsible for its synthesis are yet unknown and its role in symbiosis is far from being elucidated. In this work, using pharmacological and genetic approaches, we explored the enzymatic source of NO production in M. truncatula-Sinorhizobium meliloti nodules under normoxic and hypoxic conditions. When transferred from normoxia to hypoxia, nodule NO production was rapidly increased, indicating that NO production capacity is present in functioning nodules and may be promptly up-regulated in response to decreased oxygen availability. Contrary to roots and leaves, nodule NO production was stimulated by nitrate and nitrite and inhibited by tungstate, a nitrate reductase inhibitor. Nodules obtained with either plant nitrate reductase RNA interference double knockdown (MtNR1/2) or bacterial nitrate reductase-deficient (napA) and nitrite reductase-deficient (nirK) mutants, or both, exhibited reduced nitrate or nitrite reducíase activities and NO production levels. Moreover, NO production in nodules was found to be inhibited by electron transfer chain inhibitors, and nodule energy state (ATP-ADP ratio) was significantly reduced when nodules were incubated in the presence of tungstate. Our data indicate that both plant and bacterial nitrate reductase and electron transfer chains are involved in NO synthesis. We propose the existence of a nitrate-NO respiration process in nodules that could play a role in the maintenance of the energy status required for nitrogen fixation under oxygenlimiting conditions.

URL:http://www.jstor.org/stable/41434174
Short Title:Plant Physiology
Taxonomic name: 
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Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith