Uptake of Cd²⁺ by ectomycorrhizal fungus Paxillus involutus and the modulation of H₂O₂ in Cd²⁺ influx

ObjectiveThe uptake of Cd²⁺ by ectomycorrhizal fungus Paxillus involutus and the modulation of H₂O₂ in Cd²⁺ influx were investigated in this study.

Method Two Paxillus involutus strains, MAJ and NAU, were subjected to 50 μmol/L CdCl₂ for 24 hours, and then fluxes of Ca²⁺ and Cd²⁺ were examined by non-invasive micro-test technique.

Result The results showed that Cd²⁺ treatment caused the Cd²⁺ influx, and the Ca²⁺ influx was also significantly enhanced by Cd²⁺ in MAJ and NAU hyphae. However, the Cd²⁺-elicited influxes of Cd²⁺ and Ca²⁺ were both restricted by Ca²⁺ channel inhibitors including Verapamil, GdCl₃, TEA (Tetraethylammonium), indicating that Cd²⁺ and Ca²⁺ simultaneously entered the hyphal cell through plasma membrane (PM) Ca²⁺-permeable channels (CaPCs). The promotion of Ca²⁺ by Cd²⁺ implied that Cd²⁺ activated CaPCs, thus leading to an increased entry of Ca²⁺, in addition to Cd²⁺. Moreover competitive inhibition experiments were also conducted to verify whether Cd²⁺ and Ca²⁺ entered into the mycelium through CaPCs in the PM. The influx of Cd²⁺ in MAJ and NAU was lowered by increased concentration of Ca²⁺, and vice versa. Therefore, Cd²⁺ and Ca²⁺ competitively permeated the plasma membrane through Ca²⁺-permeable channels. Additionally, the influxes of Ca²⁺ and Cd²⁺ in mycelium were enhanced by 1 mmol/L H₂O₂ while suppressed by the ROS scavenger, DMTU (N, N′-Dimethylthiourea). This indicated that H₂O₂ could mediate the entry of Cd²⁺ through PM Ca²⁺-permeable channels in fungal hyphae.

Conclusion In conclusion, the ectomycorrhizal fungus Paxillus involutus has the ability of Cd²⁺ enrichment and the influx of Cd²⁺ can be facilitated through CaPCs activated by H₂O₂.