Poster: Integrative plant physiology
Abs #
34: A Novel Model for the Rapid Modulation of Nitrate Reduction in Leaves by Redox Coupling of Plastidic and Cytosolic Metabolism
|
|
Presenter: |
Weber, Andreas PM, aweber@msu.edu |
Authors | Weber, Andreas PM (A) Schneidereit, Jörg (A) (C) Fiene, Gabi (C) Kaiser, Werner M (B) | | Affiliations: |
(A): Michigan State University
(B): Julius-von-Sachs-Institut für Biowissenschaften
(C): Universität zu Köln
|
| Web Site: | http://plantbiology.msu.edu/weber.shtml | |
Nitrogen is a major limiting factor for land plant growth and nitrate is the major N-source for most land plants. Nitrate reduction and assimilation is an energetically demanding biochemical process that requires 10 electrons and one ATP for the assimilation of one N-equivalent into one molecule of glutamate. The first step of nitrate assimilation is the reduction of nitrate to nitrite by nitrate reductase (NR). NR is regulated at the transcriptional and posttranslational level. Posttranslational deactivation of NR involves phosphorylation and binding of a 14-3-3 protein. Deactivation of NR occurs for example upon transition form the light to the dark. However, posttranslational deactivation of nitrate reductase cannot account exclusively for the modulation of NR activity in plants. For instance, extracts from dark-adapted leaves contain between 10-30% on the NR activity found in light-adapted leaves. However, the in situ rate of nitrate reduction in the dark is negligible, indicating additional limiting factors of nitrate reduction that have not yet been elucidated. Based on results obtained with transgenic tobacco plants showing antisense repression of a plastidic dicarboxylate transporter, we have developed the hypothesis that nitrate reduction in the cytosol is coupled to both (i) metabolism of 2-oxoglutarate and (ii) the redox state in the plastid stroma by the exchange of dicarboxylates between stroma and cytosol. This mechanism would allow a very rapid modulation of the rate of nitrate reduction in response to changes in plastidic metabolism and could explain the observed discrepancies between the activity of NR in leaf extracts and the actual in situ rate of nitrate reduction.
