Effects of Silver Nanoparticle Exposure on Growth, Physiological and biochemical Parameters of Dracocephalum moldavica L. Zahra Haghighi Pak1, Naser Karimi*2, Hossein Abbaspour1

The increasing commercial production and the broad usage of engineered nanoparticles (ENPs) have led to concerns over the potential adverse impacts of these ENPs on biota in natural environments. Silver nanoparticles (AgNPs) are one of the most important and widely used ENPs which enter natural ecosystems. In this study we examined the effects of AgNPs on growth and some physiological parameters of Dracocephalum moldavica L. The experiment was conducted hydroponically in a AgNPs spiked solution. The AgNPs toxicity exhibited a decline in growth and chlorophyll content of D. moldavica at elevated concentrations (> 40 mg/L). AgNPs significantly induced oxidative stress by increasing H2O2 production in a concentration dependent manner. The phytotoxicity of AgNPs led to an increase in catalase and peroxidase activities and synthesis of antioxidant compounds such as carotenoids, proline and total soluble carbohydrate. The decline of chlorophyll content at highest AgNPs treatment (80 mg/L) was associated with disturbances in photosynthetic capacity which ultimately results in the reduction of D. moldavica growth. Increase carotenoids, proline and total soluble carbohydrate content suggest that compatible solutes may contribute to osmotic adjustment at the cellular level and enzyme protection stabilizing the structure of macromolecules and organelles. Our results indicate important new avenues of research for understanding the fate of AgNPs in hydroponic media, the interactions between AgNPs and D. moldavica.