Graphitic Carbon Nitride (CN) Reduces Cadmium and Arsenic Phytotoxicity and Accumulation in Rice ( L.).

The present study investigated the role of graphitic carbon nitride (CN) in alleviating cadmium (Cd)- and arsenic (As)-induced phytotoxicity to rice ( L.). A high-temperature pyrolysis was used to synthesize the CN, which was characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, and dynamic light scattering. Rice seedlings were exposed to CN at 50 and 250 mg/L in half-strength Hoagland's solution amended with or without 10 mg/L Cd or As for 14 days. Both Cd and As alone resulted in 26-38% and 49-56% decreases in rice root and shoot biomass, respectively. Exposure to 250 mg/L CN alone increased the root and shoot fresh biomass by 17.5% and 25.9%, respectively. Upon coexposure, Cd + CN and As + CN alleviated the heavy metal-induced phytotoxicity and increased the fresh weight by 26-38% and 49-56%, respectively. Further, the addition of CN decreased Cd and As accumulation in the roots by 32% and 25%, respectively, whereas the metal contents in the shoots were 30% lower in the presence of CN. Both As and Cd also significantly altered the macronutrient (K, P, Ca, S, and Mg) and micronutrient (Cu, Fe, Zn, and Mn) contents in rice, but these alterations were not evident in plants coexposed to CN. Random amplified polymorphic DNA analysis suggests that Cd significantly altered the genomic DNA of rice roots, while no difference was found in shoots. The presence of CN controlled Cd and As uptake in rice by regulating transport-related genes. For example, the relative expression of the Cd transporter in roots was upregulated by approximately threefold with metal exposure, but CN coamendment lowered the expression. Similar results were evident in the expression of the As transporter in roots. Overall, these findings facilitate the understanding of the underlying mechanisms by which carbon-based nanomaterials alleviate contaminant-induced phyto- and genotoxicity and may provide a new strategy for the reduction of heavy metal contamination in agriculture.