Uptake of iron oxide nanoparticles inhibits the photosynthesis of the wheat after foliar exposure.

Iron oxide nanoparticles (nFeO)-filled materials have been widely employed in various products and their effects on plants have attracted considerable attention because of their potential release into the environment. Currently, numerous studies reporting the influences of iron-bearing nanoparticles on plants are focused on root or seed exposure. However, plants exposed to atmospheric iron-bearing nanoparticles through the leaves and their impacts on plants are still not well understood. This study focused on the uptake, translocation, and effects of foliar exposure of nFeO on wheat seedlings. Wheat seedlings were foliar applied to various concentrations of nFeO (0, 60 and 180 μg per plant) for 1, 7, 14 or 21 d. Our results demonstrated that after exposure for 21 d, the concentrations of Fe in leaves, stems, and roots were 1100, 280 and 160 μg kg, respectively. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), as well as the backscattered electron (BSE) images, revealed the stomatal opening was likely the pathway for nFeO uptake. Analysis of the transfer rate, translocation of Fe from leaves to stems and roots, suggested the involvement of plant Fe regulation processes. Particularly, the antioxidant enzymatic activities and malondialdehyde levels in leaves were modified, which was ascribed to the excessive hydroxyl radical (OH) generated via the Fenton-like reaction mediated by nFeO. Finally, the OH facilitated the degradation of chlorophyll, posting a negative impact on the photosynthesis, and thus inhibited the biomass production. These findings are meaningful to understand the fate and physiological effects of atmospheric nFeO in crops.