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On the resilience of nitrogen assimilation by intact roots under starvation, as revealed by isotopic and metabolomic techniques
Author(s) -
Bathellier Camille,
Tcherkez Guillaume,
Mauve Caroline,
Bligny Richard,
Gout Elizabeth,
Ghashghaie Jaleh
Publication year - 2009
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4198
Subject(s) - chemistry , assimilation (phonology) , citric acid cycle , nitrogen assimilation , metabolism , respiration , biochemistry , photosynthesis , nitrogen cycle , nitrogen , botany , biology , enzyme , philosophy , organic chemistry , linguistics
The response of root metabolism to variations in carbon source availability is critical for whole‐plant nitrogen (N) assimilation and growth. However, the effect of changes in the carbohydrate input to intact roots is currently not well understood and, for example, both smaller and larger values of root:shoot ratios or root N uptake have been observed so far under elevated CO 2 . In addition, previous studies on sugar starvation mainly focused on senescent or excised organs while an increasing body of data suggests that intact roots may behave differently with, for example, little protein remobilization. Here, we investigated the carbon and nitrogen primary metabolism in intact roots of French bean ( Phaseolus vulgaris L.) plants maintained under continuous darkness for 4 days. We combined natural isotopic 15 N/ 14 N measurements, metabolomic and 13 C‐labeling data and show that intact roots continued nitrate assimilation to glutamate for at least 3 days while the respiration rate decreased. The activity of the tricarboxylic acid cycle diminished so that glutamate synthesis was sustained by the anaplerotic phospho enol pyruvate carboxylase fixation. Presumably, the pentose phosphate pathway contributed to provide reducing power for nitrate reduction. All the biosynthetic metabolic fluxes were nevertheless down‐regulated and, consequently, the concentration of all amino acids decreased. This is the case of asparagine, strongly suggesting that, as opposed to excised root tips, protein remobilization in intact roots remained very low for 3 days in spite of the restriction of respiratory substrates. Copyright © 2009 John Wiley & Sons, Ltd.