Soluble and Cell Wall Peroxidases in Reed Canarygrass in Relation to Disease Resistance and Localized Lignin Formation

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Abstract
Reed canarygrass (Phalaris arundinacea L.) leaf discs were inoculated with Helminthosporium avenae Eidam and floated on water. In inoculated discs, the activity of soluble, ionic wall-bound and covalent wall-bound peroxidases was about twice the level of activity in noninoculated discs. The increase was attributable to increases in activity of 3 cathodic isoperoxidases and to the appearance of a new cathodic isoperoxidase. Peroxidase activity in cryostat microtome sections of inoculated discs was histochemically localized in the wall near the site of attempted penetration. When inoculated discs were floated on solutions of cycloheximide (25 .mu.g/ml), increases in peroxidase activity were inhibited, and the fungus penetrated the tissue. The inhibition of peroxidase activity was related to inhibition of cathodic isoperoxidase activity. Anodic isoperoxidase activity did not show changes in response to inoculation or cycloheximide treatment. The resistance mechanism in P. arundinacea probably involves an induction of cathodic isoperoxidases in challenged tissue. These peroxidases may function in the biosynthesis of lignin at the site of attempted penetration.