Silica Nanoparticles Enhance Disease Resistance in Arabidopsis Plants

In plants, pathogen attack can induce an immune response known as systemic acquired resistance (SAR) that protects against a broad spectrum of pathogens. In the search for safer agrochemicals, silica nanoparticles (SiO(2)-NPs, food additive E551) have recently been proposed as a new tool. However, initial results are controversial, and the molecular mechanisms of SiO(2)-NP-induced disease resistance are unknown. Here, we show that SiO(2)-NPs, as well as soluble orthosilicic acid (Si(OH)(4)), can induce SAR in a dose-dependent manner, that involves the defence hormone salicylic acid. Nanoparticle uptake and action occurred exclusively through stomata (leaf pores facilitating gas exchange) and involved extracellular adsorption in leaf air spaces of the spongy mesophyll. In contrast to treatment with SiO(2)-NPs, induction of SAR by Si(OH)(4) was problematic, since high concentrations caused stress. We conclude that SiO(2)-NPs have the potential to serve as an inexpensive, highly efficient, safe, and sustainable alternative for plant disease protection.