Multiple insights into the two-sided effects of foliar application of cerium oxide nanoparticles on the growth of alfalfa (Medicago sativa L.)

Nanotechnology has a wide range of applications, and the pollution and toxicity of their overuse must also be taken seriously. The dual effects of cerium oxide nanoparticles (CeO2 NPs) on alfalfa (Medicago sativa L.) through regulating programmed cell death (PCD) were investigated. Herein, foliar spray of CeO2 NPs on alfalfa revealed a dose-dependent effect of CeO2 NPs. CeO2 NPs at low concentrations had a positive effect but at high concentrations had a phytotoxicity. Specifically, 100 mg L-1 CeO2 NPs improved morphology, biomass, pigments, photosynthesis, stomatal opening, ultrastructure, osmotic and redox homeostasis, the antioxidant enzyme and the anti-PCD genes, and several hormones, accompanied by lower PCD-promoting gene expression and cellular features. Conversely, 1000 mg L-1 CeO2 NPs induced PCD by causing oxidative damage, along with negative morphology, reduced quality, high Ce accumulation, weak photosynthesis, stomatal closure, lipid peroxidation, apoptosis, impaired cellular ultrastructure, DNA fragmentation, osmotic and redox instability, gene alterations, and hormonal fluctuations. Overall, alfalfa responds to the duality of CeO2 NPs by controlling PCD, which is regulated by a complex network. It proposes a fresh outlook on the rational utilization of CeO2 NPs, the promotion of sustainable agriculture, and the prevention of environmental pollution caused by nanomaterials.