Effects of cadmium on non-mycorrhizal and mycorrhizal Norway spruce seedlings [Picea abies (L.) Karst.] and its ectomycorrhizal fungus Laccaria laccata (Scop, ex Fr.) Bk. & Br.: Sulphate reduction, thiols and distribution of the heavy metal

The effect of cadmium on assimilatory sulphate reduction and thiol content was studied in non-mycorrhizal and mycorrhizal Norway spruce seedlings (Picea abies) and its ectomycorrhtzal fungus Laccaria laccata. The distribution of cadmium was also investigated. Isotope dilution experiments indicated that the fungus reduced sulphate via adenosine 3′-phosphate 5′-phosphosulphate sulphotransferase, whereas Norway spruce seedlings assimilated sulphate via adenosine 5′-phosphosulphate sulphotransferase in both roots and needles. In mycorrhizal roots only the plant sulphotransferase activity could be measured. Mycorrhizal and non-mycorrhizal roots and the mycelium of Laccaria laccata contained increased activities of sulphotransferase and more acid-soluble thiols when cultivated with cadmium. The increase in acid-soluble thiols was due to phytochelatins in roots and to glutathione in Laccaria laccata, where neither phytochelatins nor metallothioneins could be detected. Even though the cadmium content of mycorrhizal roots was slightly higher than that of non-mycorrhizal roots, concentrations of phytochelatin were only half as high as in non-mycorrhizal roots. Cadmium content of needles of mycorrhizal plants was significantly lower than that of non-mycorrhizal plants. Most of the cadmium in Laccaria laccata was associated with the cell walls and could be exchanged with Ni2+