The effect of infection by Lactarius rufus or Scleroderma flavidum on the uptake of 63Ni by paper birch

Abstract

Nickel tolerance of birch seedlings is increased by infection with one ectomycorrhizal fungus, Scleroderma flavidum, but not by another, Lactarius rufus. The possibility that this difference is related to differences in uptake and (or) translocation of Ni was investigated using 63Ni. Mycorrhizal and nonmycorrhizal seedlings were grown either with or without Ni for 22 weeks before the presentation of 63Ni to roots. Both control and pretreated seedlings were exposed to 63Ni, in 85 μM Ni, for periods of 2 min to 48 h. After Ni uptake, the roots were desorbed with 50 mM Ca at 5 °C for 30 min. Total nonexchangeable 63Ni uptake into roots was unaffected by inoculation treatment, either in the presence or absence of dinitrophenol, a general metabolic inhibitor. However, the amount of Ca-exchangeable Ni was significantly affected by infection, and was lowest in S. flavidum infected seedlings. Additionally, infection influenced the effect of dinitrophenol on Ni uptake into shoots. Application of dinitrophenol increased Ni uptake into the shoots of L. rufus infected and uninfected plants, but this increase did not occur in S. flavidum infected plants. All shoots absorbed similar amounts of Ni in the absence of dinitrophenol. Thus, the S. flavidum birch mycorrhizae do not require metabolic energy to reduce Ni translocation from roots to shoots, while the other seedlings do. This may contribute to the increased Ni tolerance of this mycorrhizal association.