Photosynthetic electron transport determines nitrate reductase gene expression and activity in higher plants.
The influence of photosynthetic electron flow in chloroplasts on the expression and enzyme activity of the cytosolic nitrate reductase (NR) was studied. Using light sources that predominantly excite either photosystem I (PSI) or photosystem II (PSII), we modulated photosynthetic electron transport in tobacco, Arabidopsis, and Lemna sprouts. In all instances, oxidation of components of photosynthetic electron flow by PSI light correlated with an increase in NR activity and/or transcription. This is confirmed by experiments with electron transport inhibitors 3-(3',4'-dichlorophenyl)-1,1'-dimethyl urea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone. In addition, a Lemna mutant deficient in the cytochrome b(6)/f complex failed to respond to the different light sources and exhibited a constitutively high level of NR activity. These data indicate that NR is activated by the oxidized state of an electron transport component located after the plastoquinone pool. An involvement of the cytoplasmic photoreceptor phytochrome A in this light regulation could be excluded, since an Arabidopsis phytochrome A mutant exhibited a wild-type like response. The observation that NR activity in the cytoplasm and the expression of its gene in the nucleus is controlled by signals from photosynthetic electron flow adds a new facet to the intracellular cross-talk between chloroplasts and the nucleus.
Sherameti
Irena
I
Institut für Allgemeine Botanik, Lehrstuhl für Pflanzenphysiologie, Dornburger Strasse 159, 07743 Jena, Germany.
Sopory
Sudhir K
SK
Trebicka
Artan
A
Pfannschmidt
Thomas
T
Oelmuller
Ralf
R
D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D019677:Artificial Gene Fusion; D001483:Base Sequence; D017931:DNA Primers; D004579:Electron Transport; D015971:Gene Expression Regulation, Enzymologic; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics*; D010084:Oxidation-Reduction; D010788:Photosynthesis; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics / Q000502:physiology*
D017931:DNA Primers; D012333:RNA, Messenger; D009565:Nitrate Reductases; D050901:Nitrate Reductase