Cytochemical Detection of Cell Wall Bound Peroxidase in Rust Infected Broad Bean Leaves*

Cell wall bound peroxidase activity, cytochemically detected by 3,3‐diaminobenzidine (DAB), appears unevenly distributed in areolae of broad bean (cv. Aguadulce) leaves infected by the rust fungus Uromyces viciae‐fahae (Pers.) Schroet. DAB positivity is not significantly traceable at the periphery of the areola and close to the site of uredinium formation; heavy DAB deposits occur on walls of haustoria containing mesophyll cells. Induction of localized peroxidase activity appears strictly related to the haustorium mother cell differentiation, i.e. to the incipient parasitic phase; it does not, however, counteract the intracellular growth of the haustorium.