Nitro-oxidative stress correlates with Se tolerance of Astragalus species.

At high concentrations selenium (Se) exerts phytotoxic effects in non-tolerant plant species partly due to the induction of secondary nitro-oxidative stress; however, these processes are not fully understood. In order to get a more accurate view about the involvement of nitro-oxidative processes in plant Se sensitivity, this study aims to characterize and compare Se-triggered changes in reactive oxygen (ROS) and nitrogen species (RNS) metabolism and the consequent protein tyrosine nitration as a marker of nitrosative stress in non-accumulator Astragalus membranaceus and in Se hyperaccumulator Astragalus bisulcatus.The observed parameters (Se accumulation, microelement homeostasis, tissue-level changes in the roots, germination, biomass production, root growth, cell viability) supported that A. membranaceus is Se sensitive while the hyperaccumulator A. bisulcatus tolerates high Se doses. We first revealed that in A. membranaceus, Se sensitivity coincides with the Se-induced disturbance of superoxide metabolism leading to its accumulation. Furthermore, Se increased the production or disturbed the metabolism of RNS (nitric oxide, peroxynitrite, S-nitrosoglutathione) consequently resulting in intensified protein tyrosine nitration in sensitive A. membranaceus. In the (hyper)tolerant and hyperaccumulator A. bisulcatus, Se-induced ROS/RNS accumulation and tyrosine nitration proved to be negligible suggesting that this species is able to prevent Se-induced nitro-oxidative stress which can contribute to the Se tolerance of this species.