Silica nanoparticles enhance disease resistance in Arabidopsis plants

In plants, pathogen attack can induce an immune response known as systemic acquired resistance that protects against a broad spectrum of pathogens. In the search for safer agrochemicals, silica nanoparticles (SiO₂ NPs; food additive E551) have recently been proposed as a new tool. However, initial results are controversial, and the molecular mechanisms of SiO₂ NP-induced disease resistance are unknown. Here we show that SiO₂ NPs, as well as soluble Si(OH)₄, can induce systemic acquired resistance in a dose-dependent manner, which involves the defence hormone salicylic acid. Nanoparticle uptake and action occurred exclusively through the stomata (leaf pores facilitating gas exchange) and involved extracellular adsorption in the air spaces in the spongy mesophyll of the leaf. In contrast to the treatment with SiO₂ NPs, the induction of systemic acquired resistance by Si(OH)₄ was problematic since high Si(OH)₄ concentrations caused stress. We conclude that SiO₂ NPs have the potential to serve as an inexpensive, highly efficient, safe and sustainable alternative for plant disease protection.