Silver Nanoparticles Restore Root Growth of White Mustard Inhibited by Nitrate

Although the stimulatory effect of silver nanoparticles (Ag NPs) on root elongation has been studied, their effect in the presence of high nitrate levels remains unknown. In this study, we demonstrated that elongation of the primary root of white mustard ( Sinapis alba ) inhibited by nitrate was restored by the presence of Ag NPs. Ag NPs also increased root length under normal conditions in cultivation medium or water. RNA-seq of seedling roots revealed that the presence of Ag NPs affected the expression of glutamate receptors, genes involved in ethylene and auxin signaling, and in the ion homeostasis. Exposure to NO 3 − affected expression of nitrate transporters and genes involved in nitrate assimilation, borate transport, nicotianamine biosynthesis and cell wall processes. Despite significant differences in root growth in the presence of Ag NPs and NO 3 − , expression of genes involved in response to various stresses (e.g. pathogens, hypoxia, oxidative stress) and suberin and cutin biosynthesis increased under both treatments. Possible mechanisms responsible for the changes in root growth exposed to Ag NPs and NO 3 − were investigated in a series of the experiments. It revealed that the inhibitory effect of nitrate and the stimulatory effect of Ag NPs were related to the presence of ROS. The stimulatory effect was not specific to Ag NPs. Ionic Ag + had a similar effect.