Nitration of γ-tocopherol in plant tissues
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Nitration of γ-tocopherol has been suggested to be an important mechanism for the regulation and detoxification of reactive nitrogen oxide species in animal tissues. To investigate whether this reaction does also occur in plants, reversed phase high-performance liquid chromatography (HPLC) and mass spectrometry (LC-MS) were used for analysis of 5-nitro-γ-tocopherol (5-NγT) in leaves and seeds. 5-nitro-γ-tocopherol (5-NγT) could be detected in an in vitro system where it was most likely generated by the reaction of γ-tocopherol with a nitric oxide radical. In vivo 5-NγT was identified in leaves of the Arabidopsis mutant line (vte4), which has insertion in the gene encoding γ-tocopherol methyltransferase and consequently lacks α-tocopherol and accumulates high levels of γ-tocopherol. Quantification of NOx in leaves revealed that the vte4 mutant in comparison to wild type and the mutant vte1, which does not contain any tocopherol, has a reduced NOx concentration. The level of 5-NγT in leaves of the vte4 mutant was shown to depend on the developmental stage and on the duration of light exposure. 5-NγT was also detectable in germinating seeds of Brassica napus, Nicotiana tabacum and Arabidopsis thaliana. These seeds have in common high γ-tocopherol contents. The rate of germination at two days after imbibition inversely correlated with the γ-tocopherol content of the seeds. The result suggests that γ-tocopherol or its respective derivative, 5-NγT, may prolong early development by reducing the level of NOx.
KeywordsArabidopsis thaliana LC-MS Nitric oxide 5-NγT Plants Tocopherols
Liquid chromatography-mass spectroscopy
We thank Dean DellaPenna (East Lansing, Michigan,USA) for providing seeds of the transgenic lines tmt18 and tmt49. Siegfried Wolffram from the Institute of Animal Nutrition and Physiology (Kiel, Germany) is thanked for providing the electrochemical detector. The authors thank Jon Falk for helpful discussion and Kirsten Krause for critical reading of the manuscript. Thorsten Walter is thanked for technical support. This research was supported by the German Research Foundation (DFG, Graduiertenkolleg 820).
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