Accumulation of these two substrates, necessary for biosynthesis of ONOO−, leads to
the generation of main nitrating agent [32–34] and may cause
nitration of apoplastic proteins. Indeed, our microscopic
results indicate that in cell suspensions cell wall areas are
heavily enriched in nitrotyrosines (Figs. 1 and 2), certainly
present in the apoplast (Fig. 2).