Regulation mechanism of exogenous nitric oxide on phenanthrene uptake by ryegrass roots

Polycyclic aromatic hydrocarbons (PAHs) constitute a category of persistent organic contaminants that possess the potential to induce carcinogenic, teratogenic, and mutagenic consequences. Our previous findings have revealed that plant roots actively take up PAHs through co-transport with protons, and auxin can promote PAHs uptake by wheat roots. It remains unclear whether nitric oxide (NO), a signaling molecule involved in numerous physiological processes in plants and downstream of auxin, can affect PAHs uptake by plant roots. In our study, 50 μmol/L sodium nitroprusside (SNP) significantly enhanced phenanthrene uptake after 4 h of exposure. After the addition of SNP (50 μmol/L), the H⁺ flux on root surface increased, and H⁺-ATPase activity was activated, indicating that exogenous NO promotes phenanthrene uptake by plant roots via activating H⁺-ATPase. By studying the effects of 50 μmol/L cyclic guanosine monophosphate (cGMP), 5 mmol/L Ca²⁺, and 50 μmol/L adenosine monophosphate (AMP) on phenanthrene uptake by ryegrass roots and measuring root calcium-dependent protein kinases (CDPK) activity, we demonstrated that exogenous NO promotes phenanthrene uptake through the signaling pathway of NO, cGMP, Ca²⁺, CDPK, 14-3-3 protein and H⁺-ATPase. The results contribute significant insights into elucidating the underlying mechanisms of NO modulating PAHs absorption by plant roots, thereby offering crucial strategies for advancing food safety measures and enhancing the phytoremediation potential of soils and waters contaminated with PAHs.