Abstract
In the era of technology, nanotechnology has been introduced as a new window for agriculture. However, no attention has been paid to the effect of cerium dioxide nanoparticles (nCeO(2)) on the reproductive stage of plant development to evaluate their toxicity and safety. To address this important topic, bean plants (Phaseolus vulgaris L.) treated aerially with nCeO(2) suspension at 250-2000 mg L(-1) were cultivated until flowering and seed production in the greenhouse condition. Microscopy analysis was carried out on sectioned anthers and ovules at different developmental stages. The pollen's mother cell development in nCeO(2) treatments was normal at early stages, the same as control plants. However, the results indicated that pollen grains underwent serious structural damages, including chromosome separation abnormality at anaphase I, pollen wall defect, and pollen grain malformations in nCeO(2)-treated plants at the highest concentration, which resulted in pollen abortion and yield losses. On the ovule side, the progression of development only at the highest concentration was modified in the two-nucleated embryo sac stage, probably due to apoptosis in nuclei. Nevertheless, the findings confirmed the more pronounced vulnerability of male reproductive development under nCeO(2) exposure than female development. The higher concentration decreased seed productivity, including seed set in either pods or whole plant (13% and 18% compared to control, respectively). The data suggested the potential application of nCeO(2) at optimal dosages as a plant productivity ameliorative. However, a higher dosage is considered as an eco-environmental hazard. To our best knowledge, this is the first study analyzing reproductive plant response upon exposure to nCeO(2).