Engineered silver nanoparticles are sensed at the plasma membrane and dramatically modify the physiology of <i>Arabidopsis thaliana</i> plants

<jats:title>Summary</jats:title><jats:p>Silver nanoparticles (Ag <jats:styled-content style="fixed-case">NP</jats:styled-content>s) are the world's most important nanomaterial and nanotoxicant. The aim of this study was to determine the early stages of interactions between Ag <jats:styled-content style="fixed-case">NP</jats:styled-content>s and plant cells, and to investigate their physiological roles. We have shown that the addition of Ag <jats:styled-content style="fixed-case">NP</jats:styled-content>s to cultivation medium, at levels above 300 mg L<jats:sup>−1</jats:sup>, inhibited <jats:italic>Arabidopsis thaliana</jats:italic> root elongation and leaf expansion. This also resulted in decreased photosynthetic efficiency and the extreme accumulation of Ag in tissues. Acute application of Ag <jats:styled-content style="fixed-case">NP</jats:styled-content>s induced a transient elevation of [Ca<jats:sup>2+</jats:sup>]<jats:sub>cyt</jats:sub> and the accumulation of reactive oxygen species (<jats:styled-content style="fixed-case">ROS</jats:styled-content>; partially generated by <jats:styled-content style="fixed-case">NADPH</jats:styled-content> oxidase). Whole‐cell patch‐clamp measurements on root cell protoplasts demonstrated that Ag <jats:styled-content style="fixed-case">NP</jats:styled-content>s slightly inhibited plasma membrane K<jats:sup>+</jats:sup> efflux and Ca<jats:sup>2+</jats:sup> influx currents, or caused membrane breakdown; however, in excised outside‐out patches, Ag <jats:styled-content style="fixed-case">NP</jats:styled-content>s activated Gd<jats:sup>3+</jats:sup>‐sensitive Ca<jats:sup>2+</jats:sup> influx channels with unitary conductance of approximately 56 <jats:styled-content style="fixed-case">pS</jats:styled-content>. Bulk particles did not modify the plasma membrane currents. Tests with electron paramagnetic resonance spectroscopy showed that Ag <jats:styled-content style="fixed-case">NP</jats:styled-content>s were not able to catalyse hydroxyl radical generation, but that they directly oxidized the major plant antioxidant, <jats:sc>l</jats:sc>‐ascorbic acid. Overall, the data presented shed light on mechanisms of the impact of nanosilver on plant cells, and show that these include the induction of classical stress signalling reactions (mediated by [Ca<jats:sup>2+</jats:sup>]<jats:sub>cyt</jats:sub> and <jats:styled-content style="fixed-case">ROS</jats:styled-content>) and a specific effect on the plasma membrane conductance and the reduced ascorbate.</jats:p>