Examining the Uptake and Bioaccumulation of Molybdenum Nanoparticles and Their Effect on Antioxidant Activities in Growing Rice Seedlings

The synthesized α-MoO 3 and MoS 2 NPs had nanosheet and nanoflower-like structures with crystallite size of 21.34 nm and 4.32 nm, respectively. The uptake, bioaccumulation, and impact of these two Mo-NPs were studied in rice ( Oryza sativa L) cv. HUR 3022 seedlings exposed to 100, 500, and 1000 ppm concentrations in hydroponics for 10 days in the growth medium. The uptake of α-MoO 3 and MoS 2 NPs by rice exposed to 100 ppm concentrations of NPs led to the accumulation of 7.32 ppm/4.55 ppm and 1.84 ppm/1.19 ppm in roots/shoots, respectively, as compared to controls. Unlike MoO 3 , more accumulation of MoS 2 in roots reflect less translocation of this NP from roots to shoots. Results suggest tissue-specific distribution of NPs in rice seedlings. The increased growth and elevated protein levels in rice seedlings at 100 ppm concentrations of nanoparticles imply a stimulation in the repair mechanism at low doses indicating hormesis. MoS 2 NPs treatments led to increased chlorophyll a levels suggesting it to be non-compromising with photosynthetic process in rice. The high malondialdehyde levels and altered activities of antioxidant enzymes GPX, APX, and CAT in rice seedlings exposed to α-MoO 3 or MoS 2 NPs indicate oxidative imbalance. Between α-MoO 3 and MoS 2 NPs, the former shows toxic effects as reflected from the decreased levels of photosynthetic pigments at all concentrations; however, an activation of chloroplast ROS detoxification is evident in the presence of MoS 2 NPs. The BCF > 1 for both α-MoO 3 and MoS 2 NPs and TF of 0.6–2.0 and 0.42–0.65 suggest the latter to be more environmentally safe. In conclusion, a100 ppm MoS 2 NPs concentration has low translocation and less accumulation with no significant impact on growth of rice cv. HUR 3022 seedlings and appears to be environmentally safe for future applications.