A Short Ethylene Pretreatment Confers EIN3/EIL1-Dependent Tolerance to Silver Nanoparticles in Arabidopsis Roots

Silver nanoparticles (AgNPs) are widely used for their antimicrobial properties, and their release into the environment has raised concerns about their effects on plant growth. We previously showed that AgNP inhibits primary root elongation in Arabidopsis thaliana by disrupting polar auxin transport and local auxin biosynthesis. Because silver ions are classical inhibitors of ethylene perception, the contribution of ethylene to AgNP toxicity has been difficult to resolve. Here, we asked whether ethylene signaling mediates AgNP toxicity in Arabidopsis roots or limits it, combining ethylene biosynthesis and signaling mutants with a 3-h pretreatment with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) given before exposure rather than during it. AgNP inhibited primary root growth in acs higher-order mutants, aco1-1, aco2-1, ein2 and ein3-1/eil1-3, showing that canonical ethylene signaling is not required for inhibition. The pretreatment reduced the subsequent inhibition of root growth and the accumulation of propidium iodide (PI)-detectable cellular damage in the wild type but not in ein3-1/eil1-3, whereas roots of plants overexpressing EIN3 were already less sensitive and were not further protected. It also increased callose in the elongation zone of AgNP-treated wild-type roots, in an EIN3/EIL1-dependent manner, although whether callose contributes to the protection was not tested. Prolonged AgNP exposure suppressed ACC-induced root hair formation and markedly reduced EIN3-GFP accumulation. Together, these findings indicate that ethylene signaling is not required for AgNP-induced root growth inhibition but limits its severity through EIN3/EIL1.