Effects of cerium oxide nanoparticles and cadmium on corn (Zea mays L.) seedlings physiology and root anatomy

Heavy metals and engineering nanoparticles (ENPs) are chemical compounds that, in the recent years, have attracted environmental concerns. Particularly, cadmium (Cd) and cerium oxide nanoparticles (CeO₂NPs) have attracted researchers' interest because of their chemical and biophysical properties. Most of the previous studies were conducted on C₃ plants, which produce three‑carbon compound via the Calvin cycle. This research observed and measured the effects of CeO₂NPs and Cd on a C₄ species, where photosynthesis makes an intermediate four‑carbon compound that later splits into a three‑carbon compound for the Calvin cycle. Twenty sweet corn seedlings were grown in plastic pots filled with sand under greenhouse conditions and then assigned to a completely randomized experimental design for one month. Four treatments were established: (a.) 0.5 mg kg⁻¹ Cd²⁺ dry sand, (b.) 500 mg kg⁻¹ CeO₂NPs dry sand, (c.) 0.5 mg kg⁻¹ Cd + 500 mg kg⁻¹ CeO₂NPs and (d.) 0 mg kg⁻¹ Cd and CeO₂NPs as the control. At termination, plant roots and shoots were separated and the concentrations of Cd and Ce in these tissues were determined. Significant differences were found in corn root and leaf biomass, where CeO₂NPs promoted the corn growth and development, while Cd hindered the leaf dry weight. No changes were found in chlorophyll contents, but differences were reported in stomatal conductance with higher values registered when CeO₂NPs and Cd were applied. Finally, root anatomical changes were analyzed and a clear set of apoplastic barriers closer to the root tip were detected under the exposure of CeO₂NPs and Cd. In conclusion CeO₂NPs and Cd, alone or in combination, significantly affected the physiology and the root anatomy of corn plants.