Systematic stress persistence and recovery patterns of rice (Oryza sativa L.) roots in response to molybdenum disulfide nanosheets.

The increasing application of engineered nanomaterials (ENMs) unavoidably leads to environmental release and biological exposure. Understanding the potential hazards of ENMs on crops is essential for appropriate utilization and management. Herein, rice seedlings were hydroponically exposed to molybdenum sulfide (MoS, a typical ENM) nanosheets at 5-20 mg/L for 7 days and then depurated for another 7 days in a fresh culture medium. Exposure to MoS triggered irreversible reductions in root length (by 26.3%-69.9%) and tip number (by 22.2%-66.0%). Integration of biochemical assays, transcriptomic and metabolomics found that oxidative stress induced by MoS in roots was persistent, whereas the activation of aquaporins, ionic transportation, and energy synthesis was normalized due to the recovery of nutrient uptake. The down-regulated levels of genes and metabolites associated with peroxidases, hemicellulose synthesis, expansins, and auxins caused persistent structural damages (sclerosis and rupture) of root cell walls. Approximately 64.5%-84.8% of internalized MoS nanosheets were degraded, and the successive up-regulation of genes encoding cytochrome P450s and glutathione S-transferases reflected the biotransformation and detoxification of MoS in the depuration period. These findings provide novel insights into the persistence and recovery of MoS phytotoxicity, which will help advance the risk assessment of MoS application on environment.