Changes in the C/N balance caused by increasing external ammonium concentrations are driven by carbon and energy availabilities during ammonium nutrition in pea plants: the key roles of asparagine synthetase and anaplerotic enzymes.
An understanding of the mechanisms underlying ammonium (NH(4)(+)) toxicity in plants requires prior knowledge of the metabolic uses for nitrogen (N) and carbon (C). We have recently shown that pea plants grown at high NH(4)(+) concentrations suffer an energy deficiency associated with a disruption of ionic homeostasis. Furthermore, these plants are unable to adequately regulate internal NH4(+) levels and the cell-charge balance associated with cation uptake. Herein we show a role for an extra-C application in the regulation of C-N metabolism in NH(4)(+) -fed plants. Thus, pea plants (Pisum sativum) were grown at a range of NH(4)(+) concentrations as sole N source, and two light intensities were applied to vary the C supply to the plants. Control plants grown at high NH(4)(+) concentration triggered a toxicity response with the characteristic pattern of C-starvation conditions. This toxicity response resulted in the redistribution of N from amino acids, mostly asparagine, and lower C/N ratios. The C/N imbalance at high NH(4)(+) concentration under control conditions induced a strong activation of root C metabolism and the upregulation of anaplerotic enzymes to provide C intermediates for the tricarboxylic acid cycle. A high light intensity partially reverted these C-starvation symptoms by providing higher C availability to the plants. The extra-C contributed to a lower C4/C5 amino acid ratio while maintaining the relative contents of some minor amino acids involved in key pathways regulating the C/N status of the plants unchanged. C availability can therefore be considered to be a determinant factor in the tolerance/sensitivity mechanisms to NH(4)(+) nutrition in plants.
Instituto de Agrobiotecnología, IdAB, CSIC - Universidad Pública de Navarra - Gobierno de Navarra, 31006, Pamplona, Navarra, Spain. idoia.ariz@unavarra.es
Idoia
I
Ariz
Aaron C
AC
Asensio
Angel M
AM
Zamarreño
Jose M
JM
García-Mina
Pedro M
PM
Aparicio-Tejo
Jose F
JF
Moran
D064751:Ammonium Compounds / Q000494:pharmacology*; D001216:Asparagine / Q000096:biosynthesis; D001217:Aspartate-Ammonia Ligase / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism*; D004734:Energy Metabolism / Q000187:drug effects* / Q000528:radiation effects; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D008027:Light; D009584:Nitrogen / Q000378:metabolism*; D018532:Pisum sativum / Q000187:drug effects / Q000201:enzymology* / Q000528:radiation effects; D011073:Polyamines / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D064751:Ammonium Compounds; D011073:Polyamines; D005973:Glutamine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D001216:Asparagine; D002244:Carbon; D001217:Aspartate-Ammonia Ligase; D009584:Nitrogen