Cadmium affects peroxynitrite generation and tyrosine nitration in seedling roots of soybean (Glycine max L.)

• Short-term Cd stress induces endogenous ONOO− generation in roots of soybean.
• Proteins undergoing tyrosine nitration are down-regulated during Cd exposure.
• Soybean 3-nitrotyrosine targets reveal proteins involved mainly in primary metabolism.
• Sequential treatment with ONOO− and Cd up-regulate peroxiredoxin gene expression.

The effect of short-term (48 h) moderate (85 μM CdCl2) and high (170 μM CdCl2) cadmium (Cd) stress on endogenous peroxynitrite (ONOO−) generation was investigated in the roots of 2-days old seedlings of soybean (Glycine max L.). The control roots showed a relatively high level of ONOO−, whereas Cd-mediated ONOO− formation was detected only at high Cd stress. The Cd-induced ONOO− accumulation was accompanied by enhanced levels of both nitric oxide (NO) and superoxide (O2−). The contrasting response appeared during moderate stress which provoked a huge NADPH-oxidase dependent O2− accumulation with slightly elevated reactive nitrogen species formation. The nitroproteome analysis revealed a proteins pool undergoing tyrosine nitration that were down-regulated during both moderate and high Cd stress conditions. The most pronounced changes within the pool of 3-nitrotyrosine targets in soybean roots revealed proteins involved mainly in primary metabolism that are not implicated in plant defense strategy. Moreover, sequential treatment with ONOO− and Cd was tuned with diminished Cd toxicity and up-regulation of gene coding for peroxiredoxin (PrxII F). Taken together, soybean seedlings mainly exposed to moderate Cd stress, showed enhanced Pxr gene expression correlated with temperate ONOO− formation what finally affected post-translational protein modification via tyrosine nitration.