Response of uptake and translocation of phenanthrene to nitrogen form in lettuce and wheat seedlings.

Polycyclic aromatic hydrocarbons (PAHs) are widespread chemicals that are potentially carcinogenic and toxic to human due to dietary intake of food crops contaminated by PAHs. To date, the mechanisms underlying root uptake and acropetal translocation of PAHs in crops are poorly understood. Here we describe uptake and translocation of phenanthrene (a model PAH) in relation to nitrogen form and concentration in wheat and lettuce seedlings. At concentrations of 0-15 mM, phenanthrene uptake by roots is enhanced with an increase in ammonium and inhibited with an increment of nitrate. Phenanthrene concentration in shoots is much lower than in roots, suggesting that the direction of phenanthrene transport is acropetal. Ammonium reduces both phenanthrene accumulation and bioconcentration factor in shoots, as well as translocation factor, but nitrate elevates them. Phenanthrene uptake increases nutrient solution pH in the treatments with either nitrate or ammonium. Thus, it is concluded that the root uptake and acropetal translocation of phenanthrene in crops are associated with nitrogen form. Our results provide both a novel insight into the mechanism on PAH transport in higher plants and a promising agronomic strategy to minimize PAH contamination in crops or to improve phytoremediation of PAH-contaminated soils or water via nitrogen management.