Phytotoxicity, accumulation and transport of silver nanoparticles by Arabidopsis thaliana

Abstract

The widespread availability of nano-enabled products in the global market may lead to the release of a substantial amount of engineered nanoparticles in the environment, which frequently display drastically different physiochemical properties than their bulk counterparts. The purpose of the study was to evaluate the impact of citrate-stabilised silver nanoparticles (AgNPs) on the plant Arabidopsis thaliana at three levels, physiological phytotoxicity, cellular accumulation and subcellular transport of AgNPs. The monodisperse AgNPs of three different sizes (20, 40 and 80 nm) aggregated into much larger sizes after mixing with quarter-strength Hoagland solution and became polydisperse. Immersion in AgNP suspension inhibited seedling root elongation and demonstrated a linear dose–response relationship within the tested concentration range. The phytotoxic effect of AgNPs could not be fully explained by the released silver ions. Plants exposed to AgNP suspensions bioaccumulated higher silver content than plants exposed to AgNO₃ solutions (Ag⁺ representative), indicating AgNP uptake by plants. AgNP toxicity was size and concentration dependent. AgNPs accumulated progressively in this sequence: border cells, root cap, columella and columella initials. AgNPs were apoplastically transported in the cell wall and found aggregated at plasmodesmata. In all the three levels studied, AgNP impacts differed from equivalent dosages of AgNO₃.

Keywords::

• Arabidopsis thaliana
• silver nanoparticles
• particle size
• phytotoxicity
• accumulation and transport
• silver ions

Acknowledgments

This work was funded through an SIUC Interdisciplinary Seed Grant to Ma, Kolmakov and Geisler-Lee, and an SIUC Startup fund to Geisler. The authors wish to thank Dr. John Bozzola at SIUC IMAGE center for assisting in TEM and STEM, and Dr. Howard Berg at the Donald Danforth Plant Science Center in St. Louis, MO, in confocal microscopy.