Silver nanoparticles (AgNPs) are used for their antimicrobial properties in many commercially available products, including pesticides, but they can pose a risk to the environment due to their toxicity, reactivity and accumulation in plants. Due to their large surface area to volume ratio, AgNPs are highly reactive and susceptible to the release of silver ions, which potentially increases their toxicity. Plant hormones are largely responsible for the normal growth of plants, and auxin is one of the most important phytohormones that play a role in many metabolically important plant processes. The Arabidopsis thaliana is an established model organism in molecular and cellular biology. In this thesis, the effects of PVP-AgNPs and silver ions (AgNO3) on Arabidopsis seedlings after one, three, five, seven, nine, and eleven days of treatment were investigated. The seeds were germinated for four days on a solid MS medium and afterwards on a modified solid ½ MS medium supplemented with PVP-AgNPs or silver ions at final concentrations of 25, 50 and 100 μM. Control seedlings were transferred to silver-free solid medium. In AgNO3-supplemented solid medium, the formation of AgNPs was noticed which were stabilized on the third day. After the third day and until the eleventh day, the absorbance of the newly formed AgNPs in medium slowly decreased. In contrast, PVP-AgNPs were stabilized in the solid medium around the eighth day. PVP-AgNPs and newly formed AgNPs affected the root length and were localized in the root cap and in the intercellular space and cell wall of the root tip. No significant changes in root and cotyledon structures were observed, but changes in chloroplast ultrastructure were observed on treatment with 100 μM AgNO3 after the eleventh day. A change in the accumulation and transport of auxin was observed in all treatments, which depended on the concentration and length of treatment, indicating that the plant adjusted to the AgNPs stress.