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Plant Physiol, November 2000, Vol. 124, pp. 1327-1334
Mechanism of Arsenate Resistance in the Ericoid Mycorrhizal
Fungus Hymenoscyphus ericae
Jade M.
Sharples,
Andrew A.
Meharg,1
Susan M.
Chambers, and
John W.G.
Cairney*
Mycorrhiza Research Group, School of Science, University of Western
Sydney, P.O. Box 10, Kingswood NSW 2747, Australia (J.M.S., S.M.C.,
J.W.G.C.); and Institute of Terrestrial Ecology, Monks Wood, Abbots
Ripton, Huntingdon, Cambridgeshire PE17 2LS, United Kingdom (J.M.S.,
A.A.M.)
Arsenate resistance is exhibited by the ericoid mycorrhizal fungus
Hymenoscyphus ericae collected from As-contaminated mine soils. To investigate the mechanism of arsenate resistance, uptake kinetics for arsenate (H2AsO4 ),
arsenite (H3AsO3), and phosphate
(H2PO4) were determined in both
arsenate-resistant and -non-resistant H. ericae. The
uptake kinetics of H2AsO4,
H3AsO3, and
H2PO4 in both resistant and
non-resistant isolates were similar. The presence of 5.0 µM H2PO4 repressed
uptake of H2AsO4 and exposure to
0.75 mM H2AsO4
repressed H2PO4 uptake in both
H. ericae. Mine site H. ericae
demonstrated an enhanced As efflux mechanism in comparison with
non-resistant H. ericae and lost approximately 90% of
preloaded cellular As (1-h uptake of 0.22 µmol g1 dry
weight h1 H2AsO4)
over a 5-h period in comparison with non-resistant H.
ericae, which lost 40% of their total absorbed
H2AsO4. As lost from the fungal
tissue was in the form of H3AsO3. The results
of the present study demonstrate an enhanced
H3AsO3 efflux system operating in mine site
H. ericae as a mechanism for
H2AsO4 resistance. The ecological
significance of this mechanism of arsenate resistance is discussed.
1
Present address: Department of Plant and Soil
Science, University of Aberdeen, Cruickshank Building, St. Machar
Drive, Aberdeen AB24 3UU, Scotland, United Kingdom.
*
Corresponding author; e-mail j.cairney{at}nepean.uws.edu.au; fax
61-2-9685-9915.
© 2000 American Society of Plant Physiologists
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