PEROXIDASE AND LACCASE ACTIVITIES IN MYCORRHIZAL AND NONMYCORRHIZAL FINE ROOTS OF NORWAY SPRUCE (PICEA-ABIES) AND LARCH (LARIX-DECIDUA)

Peroxidase (EC 1.11.1.7) and laccase (EC 1.10.3.1) activities were det ermined in mycorrhizal and non-mycorrhizal main and lateral roots of P icea abies (L.) Karst. (Norway spruce) and Larix decidua Mill. (larch) and in mycelia of the ectomycorrhizal fungus Laccaria amethystea (Bul l.) Murr. grown under axenic conditions. Peroxidase isozyme patterns w ere identified after isoelectric focusing. in both tree species, mycor rhizae contained the lowest, and laterals of noninoculated plants the highest, peroxidase activities. Pure mycelia of Laccaria amethystea co ntained considerable laccase activity but no peroxidase activity. Lacc ase activity was barely detected in noninoculated laterals of spruce, but was present in noninoculated laterals of larch and in main roots o f Norway spruce and larch. Highest laccase activities were found in my corrhizae of both tree species, indicating that most of the activity w as derived from the fungus. Laterals of Norway spruce contained eight, and those of larch five, acidic peroxidase isozymes. In mycorrhizae o f Norway spruce and larch, specific peroxidase isozymes with pi values of 4.5 and 6.2 and 5.8 and 6.0, respectively, were almost completely suppressed. The specific suppression of peroxidase suggests that the f ungal symbiont is able to modify the host defence response in mature m ycorrhizae.