Alleviation of nitrogen stress in rice (Oryza sativa) by ceria nanoparticles

Abstract

This study explored the potential of ceria nanoparticles (CeO₂ NPs) to alleviate stress in hydroponic rice caused by low N (LN) and high N (HN) stresses. The N content in plants was measured after 3 weeks of treatment with CeO₂ NPs. The impact of CeO₂ NPs on plants under medium N (MN, a normal condition) was studied as a comparison. LN resulted in N deficiency while HN led to N excess in plants while impairing plant growth. CeO₂ NPs (100 and 500 mg L⁻¹) increased the N levels in roots and shoots under LN by 6–12% and 22–30%, respectively. However, under HN stress, 500 mg L⁻¹ CeO₂ NPs reduced the N levels in roots and shoots by 9% and 6%, respectively. CeO₂ NP treatment enhanced the activities of key enzymes involved in N assimilation, glutamine synthetase (GS), glutamine oxoglutarate aminotransferase (GOGAT) and glutamate dehydrogenase (GDH), accounting for the increased N content in plants under LN. Under HN, 500 mg L⁻¹ CeO₂ NPs downregulated the GS and GDH activity by 42% and 36%, respectively. CeO₂ NPs reduced oxidative membrane and DNA damage and enhanced plant tolerance to N-stress by regulating the antioxidant enzyme system and the levels of proline and phytohormones including gibberellin 3, abscisic acid, zeatin riboside and indole-3-acetic acid. However, when N is supplied normally, CeO₂ NPs caused oxidative stress in plants thereby impairing plant growth. A change of N conditions altered the root exudate composition and led to different extents of transformation of CeO₂ NPs at the root interface and different Ce uptake and translocation in plants. This study for the first time reported that CeO₂ NPs could act as an alleviator of N stress in rice, while it might be a risk when the N supply is normal.