Exploration the homeostasis of signaling molecules in monocotyledonous crops with different CuO nanoparticle tolerance

Copper is an essential microelement that is indispensable for plant growth and development. The use of copper oxide nanoparticles (CuO NPs) in industry and agriculture has also increased because of their beneficial prop- erties. However, excess amounts of CuO NPs may negatively affect the growth of monocotyledonous plant species, primarily through the generation of reactive oxygen species, which results in oxidative stress. Despite their increasingly widespread use, little is known regarding the signaling processes responsible for the effects of CuO NPs on the growth of monocotyledonous crops, or their impact on the homeostasis of reactive nitrogen species, hydrogen sulfide, and protein tyrosine nitration. In this study, the concentration of CuO NP that inhibits 50% of root growth was determined using sorghum, wheat, rye, and triticale as model plant species, and the NP-induced stress response and the balance of reactive molecules were assessed. Based on the effective concentration of CuO NP, wheat, rye, and triticale were more tolerant compared with sorghum, and entirely different response mechanisms in the homeostasis of reactive oxygen, nitrogen and sulfur species were observed. For the sensitive sorghum roots, the amount of reactive molecules was not significantly altered, whereas a significant increase in protein tyrosine nitration indicated a severely stressful state caused by CuO NPs. In contrast, the amount of reactive molecules increased significantly in the roots of the relatively tolerant species, and while the appearance of lipid peroxidation indicated oxidative stress, different changes in protein tyrosine nitration was associated with tolerance. The significant CuO NP- induced rise of endogenous H2S content in the root tips may be partly responsible for the relative tolerance of wheat, rye, and triticale compared with sorghum. CuO NP stress induced distinct modifications in the root tip cell walls of the examined species, where lignification was observed in the relatively sensitive sorghum, while in the tolerant species only callose deposition was detected. Overall, our results demonstrate that while mono- cotyledonous species with different CuO NP sensitivities may exhibit similar growth responses, the underlying changes in the dynamics of reactive molecules influence their tolerance