Peroxidases in Tobacco Abscission Zone Tissue. VI. Ultrastructural localization in plasmodesmata during ethylene-induced abscission

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The ultrastructural localization of peroxidases, during ethylene-induced abscission, in flower pedicels of Nicotiana tabacum L. cv. ‘Little Turkish’, has been investigated. Peroxidase activity has been localized in the plasmodesmata of abscission zone tissue that had been fixed in glutaraldehyde and subsequently incubated in diaminobenzidine (DAB) medium with post-fixation in osmium tetroxide. Preincubation of tissue in potassium cyanide, prior to incubation in DAB medium containing the inhibitor, demonstrates a significant reduction in DAB staining. Incubation of tissue in aminotriazole (an inhibitor of catalase activity), prior to incubation in DAB medium containing the inhibitor, does not inhibit the peroxidase activity in plasmodesmata incubated in DAB medium; however, aminothiazole does inhibit catalase present in the microbodies of DAB incubated tissue. It is suggested that proliferating plasmodesmata, in response to ethylene treatment, exhibit enhanced peroxidase activity and allow for the increased mobilization of peroxidase to the middle lamellar areas of the cell walls of abscising cells.