Cerium oxide nanoparticles alter the salt stress tolerance of Brassica napus L. by modifying the formation of root apoplastic barriers

Abstract

Rapidly growing global population adds significant strains on the fresh water resources. Consequently, saline water is increasingly tapped for crop irrigation. Meanwhile, rapid advancement of nanotechnology is introducing more and more engineered nanoparticles into the environment and in agricultural soils. While some negative effects of ENPs on plant health at very high concentrations have been reported, more beneficial effects of ENPs at relatively low concentrations are increasingly noticed, opening doors for potential applications of nanotechnology in agriculture. In particular, we found that cerium oxide nanoparticles (CeO₂NPs) improved plant photosynthesis in salt stressed plants. Due to the close connections between salt stress tolerance and the root anatomical structures, we postulated that CeO₂NPs could modify plant root anatomy and improve plant salt stress tolerance. This study aimed at testing the hypothesis with Brassica napus in the presence of CeO₂NPs (0, 500 mg kg^-1 dry sand) and/or NaCl (0, 50 mM) in a growth chamber. Free hand sections of fresh roots were taken every seven days for three weeks and the suberin lamellae development was examined under a fluorescence microscope. The results confirmed the hypothesis that CeO₂NPs modified the formation of the apoplastic barriers in Brassica roots. In salt stressed plants, CeO₂NPs shortened the root apoplastic barriers which allowed more Na⁺ transport to shoots and less accumulation of Na⁺ in plant roots. The altered Na⁺ fluxes and transport led to better physiological performance of Brassica and may lead to new applications of nanotechnology in agriculture.

Keywords: Brassica napus; Canola; Cerium oxide nanoparticles; Root barriers; Salt stress.