Changes in the levels of peroxidase and phenylalanine ammonia-lyase inBrassica napus cultivars showing variable resistance toLeptosphaeria maculans
Peroxidase and phenylalanine ammonia-lyase activities (PAL) were determined in leaves of healthy and inoculatedBrassica napus cultivars, showing differential disease reaction towards a virulent and a weakly virulent strain ofLeptosphaeria 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 significant increase in both peroxidase and PAL activity was observed when the moderately resistant cultivar, Cresor, was challenged with the weakly virulent strain. Highest activity of the two enzymes was detected 2 d after inoculation. Very low peroxidase activity was detected in both strains ofL. maculans, while no PAL activity was detectable in either of the strains. Cytochemical tests revealed increased peroxidase activity following inoculation, mainly in the epidermal and guard cells.
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