Study of the Toxicity and Translocation of Chromium (VI) in Vicia faba Plant

In soil, chromium can be found in two main valence forms: hexavalent Cr (VI) and trivalent Cr (III). In terms of toxicity, the most toxic form to plants is Cr (VI). In the present study, we investigated the impact of Cr (VI) (0, 25, 50, 75 and 100 ppm) on growth, physiological parameters and the translocation kinetics of Cr (VI) in the faba bean plant (Vicia faba L.). The results showed that Cr (VI) negatively affects growth parameters (- 15% to - 72%), tolerance index (- 34.05% to - 64.7%), and reduce the total chlorophyll content (until 40%) compared to control plants without Cr (VI). However, the increase of Cr (VI) concentration in the soil, stimulated the synthesis of sugars (max 6,97 mg/g FM), proteins (max 62.89 µg/mg FM) and proline (max 98.57 µg/mg FM) and increased the electrolyte leakage (+ 2.5% to + 9%) compared to control plants. Cr (VI) concentrations in shoots and roots increased significantly for all Cr (VI) doses applied. The translocation factor results showed that the majority of the Cr (VI) absorbed by the plant is stored in the roots, with a very low bioaccumulation factor, which does not exceed 0.4. The findings show that Cr (VI) negatively affects the morpho-physiological parameters of Vicia faba, the bioaccumulation of organic solutes and the low bioaccumulation factor of Cr (VI) can be considered as a strategy of tolerance to Cr(V).

Genotoxic effects and mitosis aberrations of chromium (VI) on root cells of Vicia faba and its molecular docking analysis

Like other heavy metals, Cr (VI) is a powerful carcinogen and mutagen agent. Its toxic effects on plants are well considered. In order to elucidate its adverse effects, the present work aims to study the mitosis aberrations of Cr (VI) on the Vicia faba root-cells and its molecular docking analysis to understand the genotoxicity mechanisms. In-vivo, Vicia faba plants were exposed to 50 and 100 μM Cr (VI) for 48 h. In-silico, molecular docking and molecular dynamics simulation were used to study the interactions between dichromate and tubulin tyrosine ligase T2R-TTL (PDBID: 5XIW) with reference to Colchicine (microtubule inhibitor). According to our results, Cr (VI) affects growth and cell division and also induces many mitosis aberrations such as chromosome sticking, anaphase/telophase bridges, lagging chromosomes and fragmentation during all phases of mitosis. On the one hand, Cr (VI) reduces mitotic index and promotes micronuclei induction. The in-silico results showed that dichromate establishes very strong bonds at the binding site of the tubulin tyrosine ligase T2R-TTL, with a binding affinity of -5.17 Kcal/Mol and an inhibition constant of 163.59 μM. These interactions are similar to those of colchicine with this protein, so dichromate could be a very potent inhibitor of this protein's activity. TTL plays a fundamental role in the tyrosination/detyrosination of tubulin, which is crucial to the regulation of the microtubule cytoskeleton. Its inhibition leads to the appearance of many morphogenic abnormalities such as mitosis aberrations. In conclusion, our data confirm the highest genotoxicity effects of Cr (VI) on Vicia faba root-cells.

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 (K₂HPO₄) 10 mM (Pi10), 50 mM (Pi50) and 100 mM (Pi100) added alone or in combination with potassium dichromate (K₂Cr₂O₇) 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, H₂O₂ 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 Cr₂O₇^2-/HPO₄^2-/H₂O₄P^- and the phosphate-transporter. We have selected the eukaryotic phosphate transporter (PDB: 7SP5) as the module. The results showed that K₂Cr₂O₇ negatively affects morpho-physiological parameters and generates oxidative damage (+84% H₂O₂ 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 HPO₄^2-/H₂O₄P^-. Overall, these results confirmed that there is a strong relationship between dichromate uptake and the Pi-transporter.