Study of the competition between Pi and Cr (VI) for the use of Pi-transporter at Vicia faba L. using molecular modeling.

Recent studies have shown that Cr uses other element transporters such as phosphate transporters to enter cells. The aim of this work is to explore the interaction between dichromate and inorganic phosphate (Pi) in the plant of Vicia faba L. To study this interaction, we used three concentrations of Dipotassium hydrogen phosphate (KHPO) 10 mM (Pi10), 50 mM (Pi50) and 100 mM (Pi100) added alone or in combination with potassium dichromate (KCrO) Cr + Pi10, Cr + Pi50 and Cr + Pi100. In order to investigate the impact of this interaction on morpho-physiological parameters, the biomass, chlorophyll content, proline level, HO level, Catalase and Ascorbate peroxidase activity and Cr-bioaccumulation has been determined. For the molecular scale, the theoretical chemistry was used via molecular docking to explore the various interactions between dichromate CrO/HPO/HOP and the phosphate-transporter. We have selected the eukaryotic phosphate transporter (PDB: 7SP5) as the module. The results showed that KCrO negatively affects morpho-physiological parameters and generates oxidative damage (+84% HO than the control), which involved the production of antioxidant enzymes (+147% Catalase and +176% Ascorbate-peroxidase) and Proline (+108%). The addition of Pi improved the growth of Vicia faba L. and induces the partial restoration of the parameters affected by Cr (VI) to the normal levels. Also, it decreased oxidative damage and reduce Cr (VI) bioaccumulation in shoots and roots. Molecular docking has shown that the dichromate structure is more compatible and establishes more bonds with the Pi-transporter which generates a very stable complex compared to HPO/HOP. Overall, these results confirmed that there is a strong relationship between dichromate uptake and the Pi-transporter.