A non-protein amino acid (NPAA) - meta-Tyrosine (m-Tyr) a structural analog of phenylalanine is a harmful compound produced by chewing fescue (Festuca rubra L. ssp. commutata) and donkey-tail spurge (Euphorbia myrsinites L.) roots. In animal cells m-Tyr is commonly considered as a marker of oxidative stress, due to its generation in the presence of reactive oxygen species. As a material we have used 3-4 days old tomato (Solanum lycopersicum L.) seedlings treated for 24-72 h with m-Tyr (50 or 250 µM), resulting in inhibition of root growth by 50 or 100%, without lethal effect. Fluorescence of DAF-FM and APF derivatives was determined to show reactive nitrogen species (RNS) level in roots of tomato plants. m-Tyr-induced restriction of root elongation growth was related to formation of nitrated proteins described as content of 3-nitro tyrosine. Supplementation of tomato seedlings with m-Tyr enhanced superoxide radicals generation in roots and stimulated protein nitration. It correlated well to increase of fluorescence of DAF-FM derivatives, and transiently stimulated fluorescence of APF derivatives corresponding respectively to NO and ONOO- formation. Modifications in RNS formation induced by m-Tyr were linked to metabolism of nitrosoglutathione (GSNO). Activity of nitrosoglutatione reductase (GSNOR), catalyzing degradation of GSNO was enhanced by long term supplementation of tomato seedlings with m-Tyr, similarly as protein abundance, while transcripts level were only slightly altered by tested NPAA. We conclude, that secondary mode of action of m-Tyr in roots of tomato plants involves perturbation in RNS formation, alteration in GSNO metabolism and modification of protein nitration level.

 Acknowledgments: The work was financed by National Science Centre grant 2014/13/B/NZ9/02074