Silver nanoparticles regulate Arabidopsis root growth by concentration-dependent modification of reactive oxygen species accumulation and cell division

Silver nanoparticles (AgNPs) are widely used in industry, increasing their potential level in the environment. Plant root, the key organ absorbing water and nutrients, are directly exposed to the soil. Little is known about AgNP-mediated effects on plant root growth. Here, we show that AgNPs are absorbed by root and mostly localized in cell wall and intercellular spaces, which affect root growth in a dose-dependent manner. Increased root elongation was observed when Arabidopsis was exposed to an AgNP concentration of 50 mg L-1, while decreased elongation was observed at concentrations of equal to or more than 100 mg L-1. Similarly, there was an increase in the number of cells in the root apical meristem and also in cell-cycle related gene expression (CYCB1;1) at 50 mg L-1 AgNP, while both cell number and gene expression declined at concentrations equal to or more than 100 mg L-1. This indicates that AgNPs regulate root growth by affecting cell division. Reactive oxygen species (ROS) related genes were deferentially expressed after 50 mg AgNP treatment. Further studies showed that AgNPs induce ROS accumulation in root tips in a dose-dependent manner. KI treatment, which scavenges H2O2, partially rescued AgNP-inhibited root growth. The application 50 mg L-1 AgNPs also rescued the root length phenotype of upb1-1, a mutant with slightly higher ROS levels and longer root length. Our results revealed that ROS mediate the dose-dependent effects of AgNPs on root growth. These findings provide new insights into mechanisms underlying how AgNPs regulate root growth in Arabidopsis.