Kinetic characteristics of naphthalene,phenanthrene and pyrene uptake by wheat roots

Understanding the kinetic characteristics of polycyclic aromatic hydrocarbon(PAH)uptake by plant roots is important in revealing the mechanism of PAH uptake,and further in taking agronomic measures to reduce PAH accumulation in crops for a better food safety.Hydroponic experiments were employed to investigate the uptake of naphthalene,phenanthrene and pyrene(three representatives of PAHs)by wheat roots.Wheat roots can take up the three PAHs from Hoagland nutrient solution and the three PAHs absorbed by roots increase with incubation time.The uptake process consists of two sequential phases,a fast accumulation process and a slow one.The ability of wheat roots to take up the three PAHs is in the order of pyrene phenanthrene naphthalene.Concentration-dependent uptake of the three PAHs by wheat roots can be described with Michaelis-Menten equation and the Km values for naphthalene,phenanthrene and pyrene are 759.30,12.89 and 3.59 μmol·L-1,respectively.The affinity of the three PAHs to wheat root carrier proteins is pyrene phenanthrene naphthalene.The order of the affinity for the three PAHs is consistent with that of the Kow.Solution pH increases due to naphthalene,phenanthrene and pyrene uptake,and the order of increase in pH per molecule of the three PAHs absorbed is pyrene phenanthrene naphthalene.The trend in pH increase is in good agreement with that in affinity.Therefore,it is concluded that the uptake of naphthalene and pyrene by wheat roots is similar to that of phenanthrene.