Impact of biologically synthesized silver nanoparticles on the growth and physiological responses in Brassica rapa ssp. pekinensis.

Silver nanoparticles (AgNPs) were extensively used in various fields, particularly in medicine as an antimicrobial agent. The unavoidable and extensive usage of AgNPs in turn accumulates in the environment. Plants are the essential base of ecosystem and are ready to disturb by environmental pollutants. Therefore, in the present study, we have planned to evaluate the impact of biologically synthesized AgNPs on the essential food crop Chinese cabbage (Brassica rapa ssp. pekinensis). The effects of AgNP-induced plant morphological and physiological changes were investigated in different concentrations (100, 250, and 500 mg/L). The results of morphological features showed that AgNPs at lower concentrations (100 mg/L) exhibit growth-stimulating activity, whereas at higher concentrations (250 and 500 mg/L), particularly, 500 mg/L exhibited growth-suppressing activities which are in terms of reduced root, shoot growth, and fresh biomass. The increased reactive oxygen species (ROS) generation, malondialdehyde production, anthocyanin biosynthesis, and decreased chlorophyll content were also more obviously present at higher concentrations of AgNPs. The concentration-dependent DNA damage was observed in the AgNP-treated plants. The molecular responses of AgNPs indicate that most of the genes related to secondary metabolism (glucosinolates, anthocyanin) and antioxidant activities were induced at higher concentrations of AgNP treatment. The dose-dependent phytotoxicity effects of AgNPs were also observed. Taken together, the highest concentration of AgNPs (500 mg/L) could induce growth-suppressing activities via the induction of ROS generation and other molecular changes in B. rapa seedlings.