Examining the uptake and bioaccumulation of molybdenum nanoparticles and their effect on antioxidant activities in growing rice seedlings.

The synthesized α-MoO and MoS 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 and MoS 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, more accumulation of MoS 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 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 or MoS NPs indicate oxidative imbalance. Between α-MoO and MoS 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 NPs. The BCF > 1 for both α-MoO and MoS 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 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.