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Comparative study on the effects of silver nanoparticle and silver ions on disturbance of antioxidant system in roots of tobacco plants

Antimicrobial properties of silver and enhanced reactivity when applied in the form of nanoparticles (AgNPs) led to increased utilization of AgNPs in consumer products. Their release into environment directly affects biological systems and indirectly human health, as AgNPs can be transported through plants into the food chain. AgNPs can impose detrimental effects on plants, mainly through excess generation of reactive oxygen species (ROS), leading to induction of oxidative stress. In this work, in vitro grown tobacco (Nicotiana tabacum, L.) plants were exposed to AgNPs stabilized with cetyltrimethylammonium bromide (CTAB) or polyvinylpyrrolidone (PVP) coating and to ionic silver (AgNO3), applied in the same concentrations (25, 50 and 100 μM). The aim was to compare AgNP and AgNO3 impact by investigating ROS generation and subsequently changes in the antioxidant system in roots of tobacco plants in correlation to Ag accumulation upon exposure to ionic- and nano- silver. Silver uptake, ROS content and activities of antioxidant enzymes catalase (CAT), ascorbate (APX) and pyrogallol peroxidase (PPX), and superoxide dismutase (SOD) and their isoform patterns were determined. Uptake of AgNPs (observed with electron microscopy) and Ag accumulation in roots were correlated to increased ROS levels, which were most prominent after exposure to AgNP-PVP. Among aforementioned enzymes, the most significant changes were observed in SOD activities after all types of treatments, compared to control. The form of applied silver seemed to affect the expression of different isoenzymes, with the most notable differences observed in APX and PPX isoform patterns when comparing effects of Ag+ ions and AgNPs. Finally, immunoblotting assay showed higher abundance of antioxidant enzymes in treated compared to control plants. Obtained results suggest that oxidative stress is associated with AgNPs toxicity in plants, and cannot be ascribed only to dissolution of Ag+.

antioxidant enzymes, oxidative stress, phytotoxicity, reactive oxygen species, silver nanoparticles

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