CHANGES IN THE LEVELS OF PEROXIDASE AND PHENYLALANINE AMMONIA-LYASE IN BRASSICA-NAPUS CULTIVARS SHOWING VARIABLE RESISTANCE TO LEPTOSPHAERIA-MACULANS

Peroxidase and phenylalanine ammonia-lyase activities (PAL) were deter mined in leaves of healthy and inoculated Brassica napus cultivars, sh owing differential disease reaction towards a virulent and a weakly vi rulent strain of Leptosphaeria maculans, the black leg pathogen. Both enzymes showed increased activities as the result of inoculation, PAL activity increasing as early as 12 h after inoculation. The most signi ficant increase in both peroxidase and PAL activity was observed when the moderately resistant cultivar, Cresor, was challenged with the wea kly virulent strain. Highest activity of the two enzymes was detected 2 d after inoculation. Very low peroxidase activity was detected in bo th strains of L maculans, while no PAL activity was detectable in eith er of the strains. Cytochemical tests revealed increased peroxidase ac tivity following inoculation, mainly in the epidermal and guard cells.