Multi-walled carbon nanotubes and silver nanoparticles differentially affect seed germination, chlorophyll content, and hydrogen peroxide accumulation in carrot (Daucus carota L.)

Nanomaterials readily penetrate into plant cells, causing various developmental and physicochemical changes. We examined the differential effects of multi-walled carbon nanotubes (MWCNTs) and silver nanoparticles (AgNPs) on the seed germination, chlorophyll level, and hydrogen peroxide (H2O2) accumulation in carrot (Daucus carota L.), an important agricultural crop. In seed germination, MWCNTs did not cause significant changes, but AgNPs reduced germination rate by 20% and seedling root growth by 70% at day 5, compared to controls. The two nanomaterials caused a decrease in levels of a seed protein, DcHsp17.7, during seed germination. Total chlorophyll content in carrot leaf tissue was increased by 25% in the presence of the two nanomaterials (500 mg/L for 48 h). The amount of H2O2, one of the reactive oxygen species, was reduced by MWCNTs (500 mg/L for 48 h) to trace levels, but dramatically increased by AgNPs by 3 folds, compared to controls, indicating oxidative stress. Our results showed that AgNPs cause more severe inhibitory effects on carrot, compared to MWCNTs, inhibiting seed germination and disturbing redox oxygen species (ROS) homeostasis.