Effects of plant-derived naphthoquinones on the growth of Pleurotus sajor-caju and degradation of the compounds by fungal cultures

The growth of the white-rot basidiomycete Pleurotus sajor-caju in malt-agar plates was inhibited by three naturally occurring, plant-derived naphthoqu inones: juglone, lawsone, and plumbagin. The latter two compounds exerted t he most potent antifungal activity, and lawsone killed the mycelium at conc entrations higher than 200 ppm. Plates containing juglone and lawsone prese nted large decolorized areas extending from area of fungal growth, suggesti ng an extracellular enzymatic degradation of these quinones. Screening of c ulture plates for extracellular enzymatic activities revealed the presence of both laccase and veratryl alcohol oxidase in most plates, the diffusion of both enzymes matching the decolorized area. In agitated cultures, the pr esence of juglone was found to stimulate the production of veratryl alcohol oxidase in a significant manner. This is the first time degradation of pla nt derived naphthoquinones by a white-rot fun.-us is reported.