Ethylene accelerates copper oxide nanoparticle-induced toxicity at physiological, biochemical, and ultrastructural levels in rice seedlings

The enormous use of metal-based nanoparticles (NPs) in different sectors may result in enhanced accumulation in agricultural soil, which could impose negative effects on crop productivity. Hence, strategies are needed to explore the mechanisms of copper oxide nanoparticle (CuO NP)-induced toxicity in crops. The present study aimed to investigate the involvement of ethylene in CuO NP-induced toxicity in rice seedlings. Here, our results indicate that 450 mg L^-1 of CuO NPs induced toxic effects in rice seedlings. Thus, it was evidenced by the reduced plant biomass accumulation, enhanced oxidative stress indicators, and cellular ultrastructural damages. More importantly, the exogenous supply of ethylene biosynthesis and signaling antagonists cobalt (Co) and silver (Ag) respectively provided tolerance and improved the defense system of rice seedlings against CuO NP toxicity. The ethylene antagonists could significantly reduce the extent of ultrastructural and stomatal damage by controlling the ROS accumulation in rice seedlings under CuO NP stress. Furthermore, Co and Ag augmented the antioxidant defense system against CuO NP-induced toxicity. Contrary to that, all oxidative damage attributes were further enhanced exogenous application of ethylene biosynthesis precursor [1-aminocyclopropane-1-carboxylic acid (ACC)] in the presence of CuO NPs. In addition, ACC could increase the CuO NP-induced stomatal and ultrastructural damages by reducing the ROS-scavenging ability in rice seedlings. Taken together, these results indicate the involvement of ethylene in CuO NP-induced toxicity in rice seedlings.