Detection and Quantification of S-Nitrosoglutathione (GSNO) in Pepper (Capsicum annuum L.) Plant Organs by LC-ES/MS

Glutathione (GSH) is one of the major, soluble, low molecular weight antioxidants, as well as the major non-protein thiol in plant cells. However, the relevance of this molecule could be even greater considering that it can react with nitric oxide (NO) to generate S-nitrosoglutathione (GSNO) which is considered to function as a mobile reservoir of NO bioactivity in plants. Although this NO-derived molecule has an increased physiological and phytopathological relevance in plants cells, its identification and quantification in plant tissues have not be reported so far. Using liquid chromatography-electrospray/mass spectrometry (LC-ES/MS), a method was set up to detect and quantify simultaneously GSNO as well reduced and oxidized glutathione (GSH and GSSG, respectively) in different pepper plant organs including roots, stems and leaves, and in Arabidopsis leaves. The analysis of NO and GSNO reductase (GSNOR) activity in these pepper organs showed that the content of GSNO was directly related to the content of NO in each organ and oppositely related to the GSNOR activity. This approach opens up new analytical possibilities to understand the relevance of GSNO in plant cells under physiological and stress conditions.