Nitration of gamma-tocopherol in plant tissues

Nitration of gamma-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-gamma-tocopherol (5-NgammaT) in leaves and seeds. 5-nitro-gamma-tocopherol (5-NgammaT) could be detected in an in vitro system where it was most likely generated by the reaction of gamma-tocopherol with a nitric oxide radical. In vivo 5-NgammaT was identified in leaves of the Arabidopsis mutant line (vte4), which has insertion in the gene encoding gamma-tocopherol methyltransferase and consequently lacks alpha-tocopherol and accumulates high levels of gamma-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-NgammaT in leaves of the vte4 mutant was shown to depend on the developmental stage and on the duration of light exposure. 5-NgammaT was also detectable in germinating seeds of Brassica napus, Nicotiana tabacum and Arabidopsis thaliana. These seeds have in common high gamma-tocopherol contents. The rate of germination at two days after imbibition inversely correlated with the gamma-tocopherol content of the seeds. The result suggests that gamma-tocopherol or its respective derivative, 5-NgammaT, may prolong early development by reducing the level of NOx.