Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 64, Issue 11, Pages 3373-3383Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/ert175
Keywords
Ammonium uptake; Chlamydomonas; glutamine synthetase; nitrate and nitrite uptake; nitrate reductase; nitric oxide; nitrite reductase; post-translational regulation
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Funding
- MINECO (Ministerio de Economia y Competitividad, Spain) [BFU2011-29338]
- European FEDER programme
- Junta de Andalucia [P08-CVI-04157]
- Plan Propio de la Universidad de Cordoba
- MINECO
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Nitrate and ammonium are major inorganic nitrogen sources for plants and algae. These compounds are assimilated by means of finely regulated processes at transcriptional and post-translational levels. In Chlamydomonas, the expression of several genes involved in high-affinity ammonium (AMT1.1, AMT1.2) and nitrate transport (NRT2.1) as well as nitrate reduction (NIA1) are downregulated by ammonium through a nitric oxide (NO)-dependent mechanism. At the post-translational level, nitrate/nitrite uptake and nitrate reductase (NR) are also inhibited by ammonium, but the mechanisms implicated in this regulation are scarcely known. In this work, the effect of NO on nitrate assimilation and the high-affinity ammonium uptake was addressed. NO inhibited the high-affinity uptake of ammonium and nitrate/nitrite, as well as the NR activity, in a reversible form. In contrast, nitrite reductase and glutamine synthetase activities were not affected. The in vivo and in vitro studies suggested that NR enzyme is inhibited by NO in a mediated process that requires the cell integrity. These data highlight a role of NO in inorganic nitrogen assimilation and suggest that this signalling molecule is an important regulator for the first steps of the pathway.
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