Novel Insights into the Promoted Accumulation of Nitro-Polycyclic Aromatic Hydrocarbons in the Roots of Legume Plants

Substituted polycyclic aromatic hydrocarbons (sub-PAHs) are receiving increased attention due to their high toxicity and ubiquitous presence. However, the accumulation behaviors of sub-PAHs in crop roots remain unclear. In this study, the accumulation mechanism of sub-PAHs in crop roots was systematically disclosed by hydroponic experiments from the perspectives of utilization, uptake, and elimination. The obtained results showed an interesting phenomenon that despite not having the strongest hydrophobicity among the five sub-PAHs, nitro-PAHs (including 9-nitroanthracene and 1-nitropyrene) displayed the strongest accumulation potential in the roots of legume plants, including mung bean and soybean. The nitrogen-deficient experiments, inhibitor experiments, and transcriptomics analysis reveal that nitro-PAHs could be utilized by legumes as a nitrogen source, thus being significantly absorbed by active transport, which relies on amino acid transporters driven by H⁺-ATPase. Molecular docking simulation further demonstrates that the nitro group is a significant determinant of interaction with an amino acid transporter. Moreover, the depuration experiments indicate that the nitro-PAHs may enter the root cells, further slowing their elimination rates and enhancing the accumulation potential in legume roots. Our results shed light on a previously unappreciated mechanism for root accumulation of sub-PAHs, which may affect their biogeochemical processes in soils.