Investigating the impact of cerium oxide (CeO2) nanoparticles on structural and ultrastructural changes of marigold (Calendula officinalis L.) leaves

Cerium oxide nanoparticles (CeO2 NPs) are one of the most widely used NPs in the world and their interaction with the ecosystem is unavoidable. The aim of this study was to investigate structural and ultrastructural changes in marigold leaves under CeO2 NPs. Seeds were sown in pots under greenhouse conditions and after two weeks, seedlings were exposed to CeO2 NPs (0 and 3200 μg/mL) by leaf spray for five weeks. Then, leaf morphological changes were measured. Also, sampling from the control and NPs treatment leaf were performed to investigate structural and ultrastructural changes. Tissue preparation was performed and samples were examined by light and transmission electron microscopy (TEM). Morphological changes including diminish in the length, width and area of marigold leaf under CeO2 NPs were observed. Also, ultrastructural changes of mesophilic cells of marigold leaf under CeO2 NPs including diminish of chloroplasts number and their swelling, incement of peroxisomes number, disintegration of cell membrane, and accumulation and deposition of NPs in the intercellular spaces, cell wall and membrane, vacuole, peroxisome and chloroplast stroma were observed. In addition, the results of cerium elemental assessment by methods of inductive coupled plasma emission spectrometry (ICP-OES) and energy dispersive X-ray spectroscopy (EDX), in line with TEM results, showed the uptake and accumulation of CeO2 NPs in marigold leaves. Ultrastructural damage in TEM results indicated the toxicity of high dosage of CeO2 NPs at the cellular level. Therefore, potential of hazardous impacts of CeO2 NPs on other medicinal plants and environment should be considered.