Interaction of phenanthrene and potassium uptake by wheat roots: a mechanistic model

Polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic, mutagenic and toxic to both human and non-human organisms. Dietary intake of PAHs is a dominant route of exposure for the general population where food crops are a major source of dietary PAHs. Over 20% of main food crops contain PAHs that exceed the control limits in China. However, the mechanisms on PAH accumulation in crops are not well understood.

Here we report the physiological mechanism of potassium (K+)-stimulated uptake of phenanthrene (PHE, a model PAH) in wheat. PHE uptake is stimulated by the external K+. The addition of blockers (tetraethlyammonium and barium) for K+ channels does not suppress the process, suggesting that K+ channels are not involved. The introduction of PHE and K+ elicits a much greater depolarization in root cell membrane potential than that of either PHE or K+. K+ activates the plasma membrane proton (H+)-ATPase in a K+-dependent manner. The pattern is quite similar to that in PHE uptake in the presence of K+. The external medium pH treated with PHE and K+ is higher than that with K+, and lower than that with PHE, indicating that H+ pump involves in the interaction between PHE and K+ uptake.

Therefore, it is concluded that a K+ influx/H+ efflux reaction is coupled with the transport of PHE into wheat root cells. Our results provide a novel insight into the PHE uptake by crop roots.