Ethylene mediates CuO NP-induced ultrastructural changes and oxidative stress in Arabidopsis thaliana leaves

Metallic oxide nanoparticles (NPs) have received great importance due to their unique properties and valuable applications in various fields. The release of nanoparticles into the environment at large scale has become serious threat to ecosystem specially the plants. Various reports have illustrated the toxicity of CuO NPs on plants, but the hypothesis underlying ethylene mediated CuO NPs toxicity is still unknown. The present study was conducted to investigate the response of ethylene insensitive mutants (ein2-1, ein4 and etr1-3) and WT under CuO NPs exposure. The results of present study showed that CuO NPs adversely affected the biomass, chlorophyll contents, guard cells, stomatal aperture and other cell organelles, with consequent decline in plant biomass. Moreover, CuO NPs significantly increased the ROS accumulation, and induced toxicity in leaves of all four genotypes. However, ethylene insensitive mutants markedly showed less sensitivity to this damage as compared to WT seedlings. More importantly, higher level of CuO NPs significantly increased the activity of ethylene reporter EBS::GUS lines and transcript level of ethylene signaling and biosynthesis genes. Furthermore, the expression levels of antioxidant enzymes related genes were slightly enhanced by exogenous application of ethylene biosynthesis and perception antagonist cobalt (Co2+) and silver (Ag+) respectively than the treatment with CuO NPs stress alone. In contrary, it is significantly suppressed by ethylene biosynthesis precursor (ACC), which further provided the evidence that ethylene participates in CuO NPs induced oxidative damage and growth reduction in Arabidopsis thaliana leaves.