NDLI: Ammonium assimilation in root nodules of actinorhizal Discaria trinervis. Regulation of enzyme activities and protein levels by the availability of macronutrients (N, P and C)

Content Provider	Springer Nature Link
Author	Valverde, Claudio Wall, Luis Gabriel
Copyright Year	2003
Abstract	Asparagine was found to be the main N compound exported from Discaria trinervis nodules. Aspartate (Asp), glutamate (Glu), alanine (Ala) and serine (Ser) were also detected in root xylem sap, but at lower concentrations. A comparable picture is found in nodulated alfalfa. We hypothesized that a similar set of enzymes for Asn synthesis was present in D. trinervis nodules. We demonstrate the expression of most of the enzymes involved in the synthesis of Asn from NH$^{+}$ $_{4}$ and oxoacids, in nodules – but not in roots – of fully symbiotic D. trinervis. By complementation of enzyme assays ($^{A}$) and immunodetection ($^{I}$) we detected glutamane-synthetase (GS$^{A, I}$), Asp-aminotransferase (AAT$^{A}$), malate-dehydrogenase (MDH$^{A, I}$, at least two isoforms), Glu-dehydrogenase (GDH$^{A}$), Glu-synthase (GOGAT$^{I}$) and Asn-synthetase (AS$^{I}$). PEP-carboxylase (PEPC) activity was not detected. We previously shown that N acts as a negative regulator of nodulation and nodule growth, while P is a strong stimulator for nodule growth. We present data on the regulation of nodule N metabolism by altering, during 4 weeks, the availability of N, P and light in symbiotic D. trinervis. NH$_{4}$NO$_{3}$ (2 mM) induced inactivation and degradation of nodule GS, MDH and AS, but activation of GDH and AAT; the amount of nitrogenase components was not affected. A 10-fold increase in P supply did not greatly affect activity and amount of enzymes, suggesting that N metabolism is not P-limited in nodules. On the other hand, suppression of P supply induced an important reduction of nodule GS, GOGAT, MDH and AS protein levels, although nitrogenase was not affected. GDH was the only measured activity that was stimulated by limiting P supply. Shading plants did result in complete degradation of nitrogenase and partial degradation of GS, AS and nodule-specific MDH isoform, but GDH and AAT were activated. These results are discussed in connection with the regulation of nodulation and nodule growth in D. trinervis.
Starting Page	139
Ending Page	153
Page Count	15
File Format	PDF
ISSN	0032079X
Journal	Plant and Soil
Volume Number	254
Issue Number	1
e-ISSN	15735036
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	2003-01-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Ecology Plant Sciences Plant Physiology Soil Science & Conservation
Content Type	Text
Resource Type	Article
Subject	Soil Science Plant Science

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