Risk Assessment of Gold Nanoparticles in a Stable Arabidopsis Exposition System

Engineered nanomaterials (ENMs), due to their unique chemical and physical properties, are widely used in a variety of medical, industrial and agricultural applications. The global economic success of man-made nanosized composites has led to higher production and disposal rates and a diversification of emission sources into the environment. In particular, the peculiar electronic and optical characteristics of gold nanoparticles (AuNPs) have been extensively explored and exploited in recently developed agronomic techniques, leading to the direct exposure of terrestrial environments to these nanometric materials. However, despite recent advancements in nanotoxicological research, little is still known about the effects of nanoparticles on plants and their mechanisms of action. For these reasons, novel nanosafety approaches to assess the environmental impact of ENMs are required. The aim of this work was the establishment of stable and reproducible NP-plant exposure systems to study the physiological and molecular plant responses to AuNPs after short- and long-term exposure. Initial and overtime physicochemical characterizations of the colloidal gold solutions were carried out to ensure the monodispersity and stability of the particles. Exposure of Arabidopsis thaliana plants to moderate concentrations of AuNPs (10 mg/L) resulted to positively influence the growth of the seedlings, exhibiting longer primary roots, more numerous and longer lateral roots and increased rosette diameter. Also, after treatment, the plants showed reduced oxidative stress responses elicited by the immune-stimulatory PAMP flg22. Transcriptomics and proteomics studies showed downregulation of stress and immune-responses and upregulation of growth promoting genes, supporting the scenario that the trade-off between growth and immune/stress responses is shifted to the growth side after AuNP exposure. These omics datasets after AuNP exposure can be exploited in future works to study the underlying molecular mechanisms of AuNP-induced growth promotion.