ARSENATE SENSITIVITY IN ERICOID AND ECTOMYCORRHIZAL FUNGI

Abstract

Isolates of the endomycorrhizal fungus Hymenoscyphus ericae and the ectomycorrhizal fungus Hebeloma crustuliniforme from soils uncontaminated with AsO3−4, were compared with regard to their sensitivity to AsO3−4 in solution culture. When grown 4 4 in liquid media amended with a range of AsO3−4 concentrations, H. ericae demonstrated reduced sensitivity to AsO3−4 compared to H. crustuliniforme. The concentrations causing 50% inhibition of growth (EC50) were 1.33 mol/m3 and 0.33 mol/m3, respectively, for H. ericae and H. crustuliniforme. The compound AsO3−4 is a PO3−4 analogue for the plasmalemma PO3−4 transporter. The presence of PO3−4 in the media at high concentrations ameliorated the toxic effects of AsO3−4 in both the ericoid and ectomycorrhizal fungi. This could be due to both suppression of the PO3−4 transporter under high phosporus status and competition of PO3−4 with AsO3−4 for the transport protein. The kinetics of AsO3−4 influx in H. ericae and H. crustuliniforme were also investigated. Hymenoscyphus ericae demonstrated a high Km value, 0.071 mol/m3, consistent with values obtained for AsO3−4 -tolerant plants. We suggest that the high Km value may be a mechanism used by H. ericae to express reduced AsO3−4 sensitivity. The ecological significance of this reduced sensitivity is also discussed.