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Title

Short-term inhibition of legume N2 fixation by nitrate - II. Nitrate effects on nodule oxygen diffusion

AuthorsMinchin, Frank R.; Becana Ausejo, Manuel ; Sprent, Janet Irene
KeywordsVigna
Phaseolus (N2 fixation)
Oxygen limitation (root nodule)
Nodule respiration
Nitrogenase inhibition
Nitrate reductase
Issue Date1989
PublisherSpringer
CitationPlanta 180 (1): 46-52 (1989)
AbstractA comparison was made of changes in nitrogenase (N2ase; EC 1.18.6.1) activity, oxygen diffusion resistance and NO3 - metabolism in symbioses of Phaseolus vulgaris L. and Vigna radiata (L.) Wilczek during a 3-d exposure to 10 mM NO3 -. Bacteroids from Phaseolus nodules lacked nitrate reductase (NR;EC 1.7.99.4) but those from Vigna nodules had elevated amounts of the enzyme. The nodule cytosol of both species contained assimilatory NR (EC 1.6.6.1). Both symbioses showed a C2H2-induced decline in N2ase activity, the extent of which remained constant with NO3 - exposure for Phaseolus but became greater for Vigna. Nitrate application for 3 d reduced maximum (pre-decline) rates of C2H2-reduction activity by 83% and 36% in Phaseolus and Vigna, respectively. Nitrogenase-linked respiration (NLR) closely paralleled N2ase activity as the carbon costs of N2ase were not significantly altered by NO3 -. The relationship between NLR and increases in external O2 concentration from 21 to 60% was used to characterize the oxygen diffusion resistance (R) of nodules from both species. In absolute terms the minimum R of Phaseolus nodules increased with NO3 -, whereas the ability to adjust this R in response to O2 was lost after 2d. For Vigna nodules the increase in minimum R was much smaller and the adjustment ability was retained for the 3-d period of NO3 - exposure. Bacteroids of Vigna and the cytosol of both species contained NR prior to NO3 - exposure, and activities increased 1.5- to 2-fold during the treatment period. Despite this, NO2 - was not detected in nodules of Phaseolus, and showed only a very small accumulation in the cytosol of Vigna nodules. It is proposed that nodules have a two-stage response to applied NO3 -. In the first stage NO3 - is restricted to the nodule cortex and causes a reversible increase in R. In the second stage NO3 - may enter the infected region and toxic amounts of NO2 - can be generated in nodules having high bacteroid andor cytosol NR activities. This NO2 - can irreversibly damage the nodules and accelerate their senescence. © 1989 Springer-Verlag.
Publisher version (URL)http://dx.doi.org/10.1007/BF02411409
URIhttp://hdl.handle.net/10261/96332
DOIhttp://dx.doi.org/10.1007/BF02411409
Identifiersdoi: 10.1007/BF02411409
issn: 0032-0935
e-issn: 1432-2048
Appears in Collections:(EEAD) Artículos
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