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Levels of ammonia, nitrite, and nitrate in alfalfa root nodules supplied with nitrate

AuthorsBecana Ausejo, Manuel ; Aparicio-Tejo, Pedro María ; Sánchez-Díaz, Manuel
KeywordsMedicago sativa
nodule cytosol
proteolytic activity
Issue Date1985
CitationJournal of Plant Physiology 119 (4): 359–367 (1985)
AbstractProtein content, protease activity, and levels of NH4+, NO2- and NO3- were determined in the plant and bacteroid fractions of alfalfa (Medicago sativa L. cv. Aragon) nodules supplied with NO3- (0—200mM). Protein of the host cell cytosol represented approximately 70 % of the total nodule protein. The effect of NO3- on plant cytosolic protein closely paralleled that on bacteroid protein. Protein of both nodule fractions remained constant upon exposure to NO3- concentrations below 20 mM and was reduced by 30% above 20 mM NO3-. Patterns of proteolytic activity were inversely correlated to those of the corresponding protein for both bacteroids and cytosol. The nodule level of NH4+ was basically unaffected by increasing added NO3- whereas NO2- accumulated in both bacteroids and plant cytosol, although to a greater extent in the latter. Likewise, NO3- accumulated in the cytosol with much higher relative values than those of NO2-. Only trace or null amounts of NO3- were found in the corresponding bacteroids. Linear correlations either between bacteroidal and cytosolic NO2-, or between NO2- in both fractions and cytosolic NO3- levels were highly significant. The overall results indicate that the whole nodule capacity of NO2- reduction is not sufficient to avoid accumulation of NO2-, and support the view that NO2- plays a more important role than NH4+ or NO3- itself as inhibitor of nodule activity.
Description9 Pags.
Publisher version (URL)http://dx.doi.org/10.1016/S0176-1617(85)80103-6
Appears in Collections:(EEAD) Artículos
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