"Paxillus involutus" forms ectomycorrhizal relationships with a number of coniferous and deciduous tree species. Because the fungus has somewhat unspecialized nutrient requirements and a relatively broad host specificity, it has been frequently used in research and seedling inoculation programs. There is evidence of the benefit to trees of this arrangement: in one experiment where "P. involutus" was cultivated on the root exudate of red pine ("Pinus resinosa"), the root showed markedly increased resistance to pathogenic strains of the ubiquitous soil fungus "Fusarium oxysporum". Seedlings inoculated with "P. involutus" also showed increased resistance to "Fusarium". Thus "P. involutus" may be producing antifungal compounds which protect the host plants from root rot. "Paxillus involutus" also decreases the uptake of certain toxic elements, acting as a buffer against heavy metal toxicity in the host plant. For example, the fungus decreased the toxicity of cadmium and zinc to Scots pine ("Pinus sylvestris") seedlings: even though cadmium itself inhibits ectomycorrhiza formation in seedlings, colonization with "P. involutus" decreases cadmium and zinc transport to the plant shoots and alters the ratio of zinc transported to the roots and shoots, causing more cadmium to be retained in the roots of the seedlings rather than distributed through its entire metabolism. Evidence suggests that the mechanism for this detoxification involves the cadmium binding to the fungal cell walls, as well as accumulating in the vacuolar compartments. Further, ectomycorrhizal hyphae exposed to copper or cadmium drastically increase production of a metallothionein—a low molecular weight protein that binds metals.