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.