Investigation of structural and ultrastructural changes of canola (Brassica napus L.) leaf under cobalt oxide nanoparticles treatment

Cobalt oxide nanoparticles (Co3O4 NPs) are one of the most widely used magnetic NPs in various industries and their interactions with the environment are predictable. The aim of this study was to investigate the impact of Co3O4 NPs on leaf structure and ultrastructure of canola. Seeds were sown in pots under greenhouse conditions and after two weeks, seedlings were treated with Co3O4 NPs (0 and 4000 μg/mL) by leaf spray for five weeks. Then, leaf morphological changes were measured. Also, sampling from control leaf and NPs treatment 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 reduction in the length, width and area of leaf of canola treated with Co3O4 NPs were observed. Also, ultrastructural changes of canola leaf mesophilic cells treated with Co3O4 NPs including reduction of chloroplasts number and their swelling, accumulation and deposition of NPs in vacuoles and cell walls, observation of protein bodies, increase in the size of plastoglobules and starch grains in chloroplasts were observed. In addition, the results of cobalt elemental assay 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 Co3O4 NPs in canola leaves. Ultrastructural damage in TEM results indicated the toxicity of high concentration of Co3O4 NPs at the cellular level. Therefore, potential of hazardous effects of Co3O4 NPs on other crops and environment should be considered.