The substrate preference and histochemical localization argue against the direct role of cucumber stress-related anionic peroxidase in lignification

The substrate preference and the localization of cucumber (Cucumis sativus L.) stress-related anionic peroxidase (srPRX) were investigated in order to assess whether this activity correlates with the lignification. The result s showed that none of the purified srPRX isoenzymes (PRX 1 - 3) could oxidi ze the lignin monomer analog syringaldazine. The srPRX immunospecific signa l was found to be highly abundant in both the extrafascicular and fascicula r phloem regions in cucumber stem and leaf petiole. In Nicotiana, Petunia a nd Dahlia, the srPRX homologs were specifically deposited in both outer and inner phloem elements of stem and in both abaxial and adaxial phloem of le af stems. The srPRX mRNA expression analysis showed similar pattern as for immunolocalization. The subcellular localization of immunospecific srPRX de monstrated that at least part of the peroxidase could be ionically-bound to phloem cell wall.